/*
 * Copyright © 2010 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

/**
 * \file ast_to_hir.c
 * Convert abstract syntax to to high-level intermediate reprensentation (HIR).
 *
 * During the conversion to HIR, the majority of the symantic checking is
 * preformed on the program.  This includes:
 *
 *    * Symbol table management
 *    * Type checking
 *    * Function binding
 *
 * The majority of this work could be done during parsing, and the parser could
 * probably generate HIR directly.  However, this results in frequent changes
 * to the parser code.  Since we do not assume that every system this complier
 * is built on will have Flex and Bison installed, we have to store the code
 * generated by these tools in our version control system.  In other parts of
 * the system we've seen problems where a parser was changed but the generated
 * code was not committed, merge conflicts where created because two developers
 * had slightly different versions of Bison installed, etc.
 *
 * I have also noticed that running Bison generated parsers in GDB is very
 * irritating.  When you get a segfault on '$$ = $1->foo', you can't very
 * well 'print $1' in GDB.
 *
 * As a result, my preference is to put as little C code as possible in the
 * parser (and lexer) sources.
 */

#include "glsl_symbol_table.h"
#include "glsl_parser_extras.h"
#include "ast.h"
#include "glsl_types.h"
#include "program/hash_table.h"
#include "ir.h"
#include "ir_builder.h"

using namespace ir_builder;

static void
detect_conflicting_assignments(struct _mesa_glsl_parse_state *state,
			       exec_list *instructions);
static void
remove_per_vertex_blocks(exec_list *instructions,
                         _mesa_glsl_parse_state *state, ir_variable_mode mode);


void
_mesa_ast_to_hir(exec_list *instructions, struct _mesa_glsl_parse_state *state)
{
   _mesa_glsl_initialize_variables(instructions, state);

   state->symbols->separate_function_namespace = state->language_version == 110;

   state->current_function = NULL;

   state->toplevel_ir = instructions;

   state->gs_input_prim_type_specified = false;
   state->cs_input_local_size_specified = false;

   /* Section 4.2 of the GLSL 1.20 specification states:
    * "The built-in functions are scoped in a scope outside the global scope
    *  users declare global variables in.  That is, a shader's global scope,
    *  available for user-defined functions and global variables, is nested
    *  inside the scope containing the built-in functions."
    *
    * Since built-in functions like ftransform() access built-in variables,
    * it follows that those must be in the outer scope as well.
    *
    * We push scope here to create this nesting effect...but don't pop.
    * This way, a shader's globals are still in the symbol table for use
    * by the linker.
    */
   state->symbols->push_scope();

   foreach_list_typed (ast_node, ast, link, & state->translation_unit)
      ast->hir(instructions, state);

   detect_recursion_unlinked(state, instructions);
   detect_conflicting_assignments(state, instructions);

   state->toplevel_ir = NULL;

   /* Move all of the variable declarations to the front of the IR list, and
    * reverse the order.  This has the (intended!) side effect that vertex
    * shader inputs and fragment shader outputs will appear in the IR in the
    * same order that they appeared in the shader code.  This results in the
    * locations being assigned in the declared order.  Many (arguably buggy)
    * applications depend on this behavior, and it matches what nearly all
    * other drivers do.
    */
   foreach_in_list_safe(ir_instruction, node, instructions) {
      ir_variable *const var = node->as_variable();

      if (var == NULL)
         continue;

      var->remove();
      instructions->push_head(var);
   }

   /* Figure out if gl_FragCoord is actually used in fragment shader */
   ir_variable *const var = state->symbols->get_variable("gl_FragCoord");
   if (var != NULL)
      state->fs_uses_gl_fragcoord = var->data.used;

   /* From section 7.1 (Built-In Language Variables) of the GLSL 4.10 spec:
    *
    *     If multiple shaders using members of a built-in block belonging to
    *     the same interface are linked together in the same program, they
    *     must all redeclare the built-in block in the same way, as described
    *     in section 4.3.7 "Interface Blocks" for interface block matching, or
    *     a link error will result.
    *
    * The phrase "using members of a built-in block" implies that if two
    * shaders are linked together and one of them *does not use* any members
    * of the built-in block, then that shader does not need to have a matching
    * redeclaration of the built-in block.
    *
    * This appears to be a clarification to the behaviour established for
    * gl_PerVertex by GLSL 1.50, therefore implement it regardless of GLSL
    * version.
    *
    * The definition of "interface" in section 4.3.7 that applies here is as
    * follows:
    *
    *     The boundary between adjacent programmable pipeline stages: This
    *     spans all the outputs in all compilation units of the first stage
    *     and all the inputs in all compilation units of the second stage.
    *
    * Therefore this rule applies to both inter- and intra-stage linking.
    *
    * The easiest way to implement this is to check whether the shader uses
    * gl_PerVertex right after ast-to-ir conversion, and if it doesn't, simply
    * remove all the relevant variable declaration from the IR, so that the
    * linker won't see them and complain about mismatches.
    */
   remove_per_vertex_blocks(instructions, state, ir_var_shader_in);
   remove_per_vertex_blocks(instructions, state, ir_var_shader_out);
}


static ir_expression_operation
get_conversion_operation(const glsl_type *to, const glsl_type *from,
                         struct _mesa_glsl_parse_state *state)
{
   switch (to->base_type) {
   case GLSL_TYPE_FLOAT:
      switch (from->base_type) {
      case GLSL_TYPE_INT: return ir_unop_i2f;
      case GLSL_TYPE_UINT: return ir_unop_u2f;
      default: return (ir_expression_operation)0;
      }

   case GLSL_TYPE_UINT:
      if (!state->is_version(400, 0) && !state->ARB_gpu_shader5_enable)
         return (ir_expression_operation)0;
      switch (from->base_type) {
         case GLSL_TYPE_INT: return ir_unop_i2u;
         default: return (ir_expression_operation)0;
      }

   default: return (ir_expression_operation)0;
   }
}


/**
 * If a conversion is available, convert one operand to a different type
 *
 * The \c from \c ir_rvalue is converted "in place".
 *
 * \param to     Type that the operand it to be converted to
 * \param from   Operand that is being converted
 * \param state  GLSL compiler state
 *
 * \return
 * If a conversion is possible (or unnecessary), \c true is returned.
 * Otherwise \c false is returned.
 */
bool
apply_implicit_conversion(const glsl_type *to, ir_rvalue * &from,
                          struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;
   if (to->base_type == from->type->base_type)
      return true;

   /* Prior to GLSL 1.20, there are no implicit conversions */
   if (!state->is_version(120, 0))
      return false;

   /* From page 27 (page 33 of the PDF) of the GLSL 1.50 spec:
    *
    *    "There are no implicit array or structure conversions. For
    *    example, an array of int cannot be implicitly converted to an
    *    array of float.
    */
   if (!to->is_numeric() || !from->type->is_numeric())
      return false;

   /* We don't actually want the specific type `to`, we want a type
    * with the same base type as `to`, but the same vector width as
    * `from`.
    */
   to = glsl_type::get_instance(to->base_type, from->type->vector_elements,
                                from->type->matrix_columns);

   ir_expression_operation op = get_conversion_operation(to, from->type, state);
   if (op) {
      from = new(ctx) ir_expression(op, to, from, NULL);
      return true;
   } else {
      return false;
   }
}


static const struct glsl_type *
arithmetic_result_type(ir_rvalue * &value_a, ir_rvalue * &value_b,
                       bool multiply,
                       struct _mesa_glsl_parse_state *state, YYLTYPE *loc)
{
   const glsl_type *type_a = value_a->type;
   const glsl_type *type_b = value_b->type;

   /* From GLSL 1.50 spec, page 56:
    *
    *    "The arithmetic binary operators add (+), subtract (-),
    *    multiply (*), and divide (/) operate on integer and
    *    floating-point scalars, vectors, and matrices."
    */
   if (!type_a->is_numeric() || !type_b->is_numeric()) {
      _mesa_glsl_error(loc, state,
                       "operands to arithmetic operators must be numeric");
      return glsl_type::error_type;
   }


   /*    "If one operand is floating-point based and the other is
    *    not, then the conversions from Section 4.1.10 "Implicit
    *    Conversions" are applied to the non-floating-point-based operand."
    */
   if (!apply_implicit_conversion(type_a, value_b, state)
       && !apply_implicit_conversion(type_b, value_a, state)) {
      _mesa_glsl_error(loc, state,
                       "could not implicitly convert operands to "
                       "arithmetic operator");
      return glsl_type::error_type;
   }
   type_a = value_a->type;
   type_b = value_b->type;

   /*    "If the operands are integer types, they must both be signed or
    *    both be unsigned."
    *
    * From this rule and the preceeding conversion it can be inferred that
    * both types must be GLSL_TYPE_FLOAT, or GLSL_TYPE_UINT, or GLSL_TYPE_INT.
    * The is_numeric check above already filtered out the case where either
    * type is not one of these, so now the base types need only be tested for
    * equality.
    */
   if (type_a->base_type != type_b->base_type) {
      _mesa_glsl_error(loc, state,
                       "base type mismatch for arithmetic operator");
      return glsl_type::error_type;
   }

   /*    "All arithmetic binary operators result in the same fundamental type
    *    (signed integer, unsigned integer, or floating-point) as the
    *    operands they operate on, after operand type conversion. After
    *    conversion, the following cases are valid
    *
    *    * The two operands are scalars. In this case the operation is
    *      applied, resulting in a scalar."
    */
   if (type_a->is_scalar() && type_b->is_scalar())
      return type_a;

   /*   "* One operand is a scalar, and the other is a vector or matrix.
    *      In this case, the scalar operation is applied independently to each
    *      component of the vector or matrix, resulting in the same size
    *      vector or matrix."
    */
   if (type_a->is_scalar()) {
      if (!type_b->is_scalar())
         return type_b;
   } else if (type_b->is_scalar()) {
      return type_a;
   }

   /* All of the combinations of <scalar, scalar>, <vector, scalar>,
    * <scalar, vector>, <scalar, matrix>, and <matrix, scalar> have been
    * handled.
    */
   assert(!type_a->is_scalar());
   assert(!type_b->is_scalar());

   /*   "* The two operands are vectors of the same size. In this case, the
    *      operation is done component-wise resulting in the same size
    *      vector."
    */
   if (type_a->is_vector() && type_b->is_vector()) {
      if (type_a == type_b) {
         return type_a;
      } else {
         _mesa_glsl_error(loc, state,
                          "vector size mismatch for arithmetic operator");
         return glsl_type::error_type;
      }
   }

   /* All of the combinations of <scalar, scalar>, <vector, scalar>,
    * <scalar, vector>, <scalar, matrix>, <matrix, scalar>, and
    * <vector, vector> have been handled.  At least one of the operands must
    * be matrix.  Further, since there are no integer matrix types, the base
    * type of both operands must be float.
    */
   assert(type_a->is_matrix() || type_b->is_matrix());
   assert(type_a->base_type == GLSL_TYPE_FLOAT);
   assert(type_b->base_type == GLSL_TYPE_FLOAT);

   /*   "* The operator is add (+), subtract (-), or divide (/), and the
    *      operands are matrices with the same number of rows and the same
    *      number of columns. In this case, the operation is done component-
    *      wise resulting in the same size matrix."
    *    * The operator is multiply (*), where both operands are matrices or
    *      one operand is a vector and the other a matrix. A right vector
    *      operand is treated as a column vector and a left vector operand as a
    *      row vector. In all these cases, it is required that the number of
    *      columns of the left operand is equal to the number of rows of the
    *      right operand. Then, the multiply (*) operation does a linear
    *      algebraic multiply, yielding an object that has the same number of
    *      rows as the left operand and the same number of columns as the right
    *      operand. Section 5.10 "Vector and Matrix Operations" explains in
    *      more detail how vectors and matrices are operated on."
    */
   if (! multiply) {
      if (type_a == type_b)
         return type_a;
   } else {
      if (type_a->is_matrix() && type_b->is_matrix()) {
         /* Matrix multiply.  The columns of A must match the rows of B.  Given
          * the other previously tested constraints, this means the vector type
          * of a row from A must be the same as the vector type of a column from
          * B.
          */
         if (type_a->row_type() == type_b->column_type()) {
            /* The resulting matrix has the number of columns of matrix B and
             * the number of rows of matrix A.  We get the row count of A by
             * looking at the size of a vector that makes up a column.  The
             * transpose (size of a row) is done for B.
             */
            const glsl_type *const type =
               glsl_type::get_instance(type_a->base_type,
                                       type_a->column_type()->vector_elements,
                                       type_b->row_type()->vector_elements);
            assert(type != glsl_type::error_type);

            return type;
         }
      } else if (type_a->is_matrix()) {
         /* A is a matrix and B is a column vector.  Columns of A must match
          * rows of B.  Given the other previously tested constraints, this
          * means the vector type of a row from A must be the same as the
          * vector the type of B.
          */
         if (type_a->row_type() == type_b) {
            /* The resulting vector has a number of elements equal to
             * the number of rows of matrix A. */
            const glsl_type *const type =
               glsl_type::get_instance(type_a->base_type,
                                       type_a->column_type()->vector_elements,
                                       1);
            assert(type != glsl_type::error_type);

            return type;
         }
      } else {
         assert(type_b->is_matrix());

         /* A is a row vector and B is a matrix.  Columns of A must match rows
          * of B.  Given the other previously tested constraints, this means
          * the type of A must be the same as the vector type of a column from
          * B.
          */
         if (type_a == type_b->column_type()) {
            /* The resulting vector has a number of elements equal to
             * the number of columns of matrix B. */
            const glsl_type *const type =
               glsl_type::get_instance(type_a->base_type,
                                       type_b->row_type()->vector_elements,
                                       1);
            assert(type != glsl_type::error_type);

            return type;
         }
      }

      _mesa_glsl_error(loc, state, "size mismatch for matrix multiplication");
      return glsl_type::error_type;
   }


   /*    "All other cases are illegal."
    */
   _mesa_glsl_error(loc, state, "type mismatch");
   return glsl_type::error_type;
}


static const struct glsl_type *
unary_arithmetic_result_type(const struct glsl_type *type,
                             struct _mesa_glsl_parse_state *state, YYLTYPE *loc)
{
   /* From GLSL 1.50 spec, page 57:
    *
    *    "The arithmetic unary operators negate (-), post- and pre-increment
    *     and decrement (-- and ++) operate on integer or floating-point
    *     values (including vectors and matrices). All unary operators work
    *     component-wise on their operands. These result with the same type
    *     they operated on."
    */
   if (!type->is_numeric()) {
      _mesa_glsl_error(loc, state,
                       "operands to arithmetic operators must be numeric");
      return glsl_type::error_type;
   }

   return type;
}

/**
 * \brief Return the result type of a bit-logic operation.
 *
 * If the given types to the bit-logic operator are invalid, return
 * glsl_type::error_type.
 *
 * \param type_a Type of LHS of bit-logic op
 * \param type_b Type of RHS of bit-logic op
 */
static const struct glsl_type *
bit_logic_result_type(const struct glsl_type *type_a,
                      const struct glsl_type *type_b,
                      ast_operators op,
                      struct _mesa_glsl_parse_state *state, YYLTYPE *loc)
{
    if (!state->check_bitwise_operations_allowed(loc)) {
       return glsl_type::error_type;
    }

    /* From page 50 (page 56 of PDF) of GLSL 1.30 spec:
     *
     *     "The bitwise operators and (&), exclusive-or (^), and inclusive-or
     *     (|). The operands must be of type signed or unsigned integers or
     *     integer vectors."
     */
    if (!type_a->is_integer()) {
       _mesa_glsl_error(loc, state, "LHS of `%s' must be an integer",
                         ast_expression::operator_string(op));
       return glsl_type::error_type;
    }
    if (!type_b->is_integer()) {
       _mesa_glsl_error(loc, state, "RHS of `%s' must be an integer",
                        ast_expression::operator_string(op));
       return glsl_type::error_type;
    }

    /*     "The fundamental types of the operands (signed or unsigned) must
     *     match,"
     */
    if (type_a->base_type != type_b->base_type) {
       _mesa_glsl_error(loc, state, "operands of `%s' must have the same "
                        "base type", ast_expression::operator_string(op));
       return glsl_type::error_type;
    }

    /*     "The operands cannot be vectors of differing size." */
    if (type_a->is_vector() &&
        type_b->is_vector() &&
        type_a->vector_elements != type_b->vector_elements) {
       _mesa_glsl_error(loc, state, "operands of `%s' cannot be vectors of "
                        "different sizes", ast_expression::operator_string(op));
       return glsl_type::error_type;
    }

    /*     "If one operand is a scalar and the other a vector, the scalar is
     *     applied component-wise to the vector, resulting in the same type as
     *     the vector. The fundamental types of the operands [...] will be the
     *     resulting fundamental type."
     */
    if (type_a->is_scalar())
        return type_b;
    else
        return type_a;
}

static const struct glsl_type *
modulus_result_type(const struct glsl_type *type_a,
                    const struct glsl_type *type_b,
                    struct _mesa_glsl_parse_state *state, YYLTYPE *loc)
{
   if (!state->check_version(130, 300, loc, "operator '%%' is reserved")) {
      return glsl_type::error_type;
   }

   /* From GLSL 1.50 spec, page 56:
    *    "The operator modulus (%) operates on signed or unsigned integers or
    *    integer vectors. The operand types must both be signed or both be
    *    unsigned."
    */
   if (!type_a->is_integer()) {
      _mesa_glsl_error(loc, state, "LHS of operator %% must be an integer");
      return glsl_type::error_type;
   }
   if (!type_b->is_integer()) {
      _mesa_glsl_error(loc, state, "RHS of operator %% must be an integer");
      return glsl_type::error_type;
   }
   if (type_a->base_type != type_b->base_type) {
      _mesa_glsl_error(loc, state,
                       "operands of %% must have the same base type");
      return glsl_type::error_type;
   }

   /*    "The operands cannot be vectors of differing size. If one operand is
    *    a scalar and the other vector, then the scalar is applied component-
    *    wise to the vector, resulting in the same type as the vector. If both
    *    are vectors of the same size, the result is computed component-wise."
    */
   if (type_a->is_vector()) {
      if (!type_b->is_vector()
          || (type_a->vector_elements == type_b->vector_elements))
      return type_a;
   } else
      return type_b;

   /*    "The operator modulus (%) is not defined for any other data types
    *    (non-integer types)."
    */
   _mesa_glsl_error(loc, state, "type mismatch");
   return glsl_type::error_type;
}


static const struct glsl_type *
relational_result_type(ir_rvalue * &value_a, ir_rvalue * &value_b,
                       struct _mesa_glsl_parse_state *state, YYLTYPE *loc)
{
   const glsl_type *type_a = value_a->type;
   const glsl_type *type_b = value_b->type;

   /* From GLSL 1.50 spec, page 56:
    *    "The relational operators greater than (>), less than (<), greater
    *    than or equal (>=), and less than or equal (<=) operate only on
    *    scalar integer and scalar floating-point expressions."
    */
   if (!type_a->is_numeric()
       || !type_b->is_numeric()
       || !type_a->is_scalar()
       || !type_b->is_scalar()) {
      _mesa_glsl_error(loc, state,
                       "operands to relational operators must be scalar and "
                       "numeric");
      return glsl_type::error_type;
   }

   /*    "Either the operands' types must match, or the conversions from
    *    Section 4.1.10 "Implicit Conversions" will be applied to the integer
    *    operand, after which the types must match."
    */
   if (!apply_implicit_conversion(type_a, value_b, state)
       && !apply_implicit_conversion(type_b, value_a, state)) {
      _mesa_glsl_error(loc, state,
                       "could not implicitly convert operands to "
                       "relational operator");
      return glsl_type::error_type;
   }
   type_a = value_a->type;
   type_b = value_b->type;

   if (type_a->base_type != type_b->base_type) {
      _mesa_glsl_error(loc, state, "base type mismatch");
      return glsl_type::error_type;
   }

   /*    "The result is scalar Boolean."
    */
   return glsl_type::bool_type;
}

/**
 * \brief Return the result type of a bit-shift operation.
 *
 * If the given types to the bit-shift operator are invalid, return
 * glsl_type::error_type.
 *
 * \param type_a Type of LHS of bit-shift op
 * \param type_b Type of RHS of bit-shift op
 */
static const struct glsl_type *
shift_result_type(const struct glsl_type *type_a,
                  const struct glsl_type *type_b,
                  ast_operators op,
                  struct _mesa_glsl_parse_state *state, YYLTYPE *loc)
{
   if (!state->check_bitwise_operations_allowed(loc)) {
      return glsl_type::error_type;
   }

   /* From page 50 (page 56 of the PDF) of the GLSL 1.30 spec:
    *
    *     "The shift operators (<<) and (>>). For both operators, the operands
    *     must be signed or unsigned integers or integer vectors. One operand
    *     can be signed while the other is unsigned."
    */
   if (!type_a->is_integer()) {
      _mesa_glsl_error(loc, state, "LHS of operator %s must be an integer or "
                       "integer vector", ast_expression::operator_string(op));
     return glsl_type::error_type;

   }
   if (!type_b->is_integer()) {
      _mesa_glsl_error(loc, state, "RHS of operator %s must be an integer or "
                       "integer vector", ast_expression::operator_string(op));
     return glsl_type::error_type;
   }

   /*     "If the first operand is a scalar, the second operand has to be
    *     a scalar as well."
    */
   if (type_a->is_scalar() && !type_b->is_scalar()) {
      _mesa_glsl_error(loc, state, "if the first operand of %s is scalar, the "
                       "second must be scalar as well",
                       ast_expression::operator_string(op));
     return glsl_type::error_type;
   }

   /* If both operands are vectors, check that they have same number of
    * elements.
    */
   if (type_a->is_vector() &&
      type_b->is_vector() &&
      type_a->vector_elements != type_b->vector_elements) {
      _mesa_glsl_error(loc, state, "vector operands to operator %s must "
                       "have same number of elements",
                       ast_expression::operator_string(op));
     return glsl_type::error_type;
   }

   /*     "In all cases, the resulting type will be the same type as the left
    *     operand."
    */
   return type_a;
}

/**
 * Validates that a value can be assigned to a location with a specified type
 *
 * Validates that \c rhs can be assigned to some location.  If the types are
 * not an exact match but an automatic conversion is possible, \c rhs will be
 * converted.
 *
 * \return
 * \c NULL if \c rhs cannot be assigned to a location with type \c lhs_type.
 * Otherwise the actual RHS to be assigned will be returned.  This may be
 * \c rhs, or it may be \c rhs after some type conversion.
 *
 * \note
 * In addition to being used for assignments, this function is used to
 * type-check return values.
 */
ir_rvalue *
validate_assignment(struct _mesa_glsl_parse_state *state,
                    YYLTYPE loc, const glsl_type *lhs_type,
                    ir_rvalue *rhs, bool is_initializer)
{
   /* If there is already some error in the RHS, just return it.  Anything
    * else will lead to an avalanche of error message back to the user.
    */
   if (rhs->type->is_error())
      return rhs;

   /* If the types are identical, the assignment can trivially proceed.
    */
   if (rhs->type == lhs_type)
      return rhs;

   /* If the array element types are the same and the LHS is unsized,
    * the assignment is okay for initializers embedded in variable
    * declarations.
    *
    * Note: Whole-array assignments are not permitted in GLSL 1.10, but this
    * is handled by ir_dereference::is_lvalue.
    */
   if (lhs_type->is_unsized_array() && rhs->type->is_array()
       && (lhs_type->element_type() == rhs->type->element_type())) {
      if (is_initializer) {
         return rhs;
      } else {
         _mesa_glsl_error(&loc, state,
                          "implicitly sized arrays cannot be assigned");
         return NULL;
      }
   }

   /* Check for implicit conversion in GLSL 1.20 */
   if (apply_implicit_conversion(lhs_type, rhs, state)) {
      if (rhs->type == lhs_type)
	 return rhs;
   }

   _mesa_glsl_error(&loc, state,
                    "%s of type %s cannot be assigned to "
                    "variable of type %s",
                    is_initializer ? "initializer" : "value",
                    rhs->type->name, lhs_type->name);

   return NULL;
}

static void
mark_whole_array_access(ir_rvalue *access)
{
   ir_dereference_variable *deref = access->as_dereference_variable();

   if (deref && deref->var) {
      deref->var->data.max_array_access = deref->type->length - 1;
   }
}

static bool
do_assignment(exec_list *instructions, struct _mesa_glsl_parse_state *state,
              const char *non_lvalue_description,
              ir_rvalue *lhs, ir_rvalue *rhs,
              ir_rvalue **out_rvalue, bool needs_rvalue,
              bool is_initializer,
              YYLTYPE lhs_loc)
{
   void *ctx = state;
   bool error_emitted = (lhs->type->is_error() || rhs->type->is_error());
   ir_rvalue *extract_channel = NULL;

   /* If the assignment LHS comes back as an ir_binop_vector_extract
    * expression, move it to the RHS as an ir_triop_vector_insert.
    */
   if (lhs->ir_type == ir_type_expression) {
      ir_expression *const lhs_expr = lhs->as_expression();

      if (unlikely(lhs_expr->operation == ir_binop_vector_extract)) {
         ir_rvalue *new_rhs =
            validate_assignment(state, lhs_loc, lhs->type,
                                rhs, is_initializer);

         if (new_rhs == NULL) {
            return lhs;
         } else {
            /* This converts:
             * - LHS: (expression float vector_extract <vec> <channel>)
             * - RHS: <scalar>
             * into:
             * - LHS: <vec>
             * - RHS: (expression vec2 vector_insert <vec> <channel> <scalar>)
             *
             * The LHS type is now a vector instead of a scalar.  Since GLSL
             * allows assignments to be used as rvalues, we need to re-extract
             * the channel from assignment_temp when returning the rvalue.
             */
            extract_channel = lhs_expr->operands[1];
            rhs = new(ctx) ir_expression(ir_triop_vector_insert,
                                         lhs_expr->operands[0]->type,
                                         lhs_expr->operands[0],
                                         new_rhs,
                                         extract_channel);
            lhs = lhs_expr->operands[0]->clone(ctx, NULL);
         }
      }
   }

   ir_variable *lhs_var = lhs->variable_referenced();
   if (lhs_var)
      lhs_var->data.assigned = true;

   if (!error_emitted) {
      if (non_lvalue_description != NULL) {
         _mesa_glsl_error(&lhs_loc, state,
                          "assignment to %s",
                          non_lvalue_description);
         error_emitted = true;
      } else if (lhs_var != NULL && lhs_var->data.read_only) {
         _mesa_glsl_error(&lhs_loc, state,
                          "assignment to read-only variable '%s'",
                          lhs_var->name);
         error_emitted = true;
      } else if (lhs->type->is_array() &&
                 !state->check_version(120, 300, &lhs_loc,
                                       "whole array assignment forbidden")) {
         /* From page 32 (page 38 of the PDF) of the GLSL 1.10 spec:
          *
          *    "Other binary or unary expressions, non-dereferenced
          *     arrays, function names, swizzles with repeated fields,
          *     and constants cannot be l-values."
          *
          * The restriction on arrays is lifted in GLSL 1.20 and GLSL ES 3.00.
          */
         error_emitted = true;
      } else if (!lhs->is_lvalue()) {
         _mesa_glsl_error(& lhs_loc, state, "non-lvalue in assignment");
         error_emitted = true;
      }
   }

   ir_rvalue *new_rhs =
      validate_assignment(state, lhs_loc, lhs->type, rhs, is_initializer);
   if (new_rhs != NULL) {
      rhs = new_rhs;

      /* If the LHS array was not declared with a size, it takes it size from
       * the RHS.  If the LHS is an l-value and a whole array, it must be a
       * dereference of a variable.  Any other case would require that the LHS
       * is either not an l-value or not a whole array.
       */
      if (lhs->type->is_unsized_array()) {
         ir_dereference *const d = lhs->as_dereference();

         assert(d != NULL);

         ir_variable *const var = d->variable_referenced();

         assert(var != NULL);

         if (var->data.max_array_access >= unsigned(rhs->type->array_size())) {
            /* FINISHME: This should actually log the location of the RHS. */
            _mesa_glsl_error(& lhs_loc, state, "array size must be > %u due to "
                             "previous access",
                             var->data.max_array_access);
         }

         var->type = glsl_type::get_array_instance(lhs->type->element_type(),
                                                   rhs->type->array_size());
         d->type = var->type;
      }
      if (lhs->type->is_array()) {
         mark_whole_array_access(rhs);
         mark_whole_array_access(lhs);
      }
   }

   /* Most callers of do_assignment (assign, add_assign, pre_inc/dec,
    * but not post_inc) need the converted assigned value as an rvalue
    * to handle things like:
    *
    * i = j += 1;
    */
   if (needs_rvalue) {
      ir_variable *var = new(ctx) ir_variable(rhs->type, "assignment_tmp",
                                              ir_var_temporary);
      instructions->push_tail(var);
      instructions->push_tail(assign(var, rhs));

      if (!error_emitted) {
         ir_dereference_variable *deref_var = new(ctx) ir_dereference_variable(var);
         instructions->push_tail(new(ctx) ir_assignment(lhs, deref_var));
      }
      ir_rvalue *rvalue = new(ctx) ir_dereference_variable(var);

      if (extract_channel) {
         rvalue = new(ctx) ir_expression(ir_binop_vector_extract,
                                         rvalue,
                                         extract_channel->clone(ctx, NULL));
      }

      *out_rvalue = rvalue;
   } else {
      if (!error_emitted)
         instructions->push_tail(new(ctx) ir_assignment(lhs, rhs));
      *out_rvalue = NULL;
   }

   return error_emitted;
}

static ir_rvalue *
get_lvalue_copy(exec_list *instructions, ir_rvalue *lvalue)
{
   void *ctx = ralloc_parent(lvalue);
   ir_variable *var;

   var = new(ctx) ir_variable(lvalue->type, "_post_incdec_tmp",
			      ir_var_temporary);
   instructions->push_tail(var);
   var->data.mode = ir_var_auto;

   instructions->push_tail(new(ctx) ir_assignment(new(ctx) ir_dereference_variable(var),
						  lvalue));

   return new(ctx) ir_dereference_variable(var);
}


ir_rvalue *
ast_node::hir(exec_list *instructions, struct _mesa_glsl_parse_state *state)
{
   (void) instructions;
   (void) state;

   return NULL;
}

void
ast_function_expression::hir_no_rvalue(exec_list *instructions,
                                       struct _mesa_glsl_parse_state *state)
{
   (void)hir(instructions, state);
}

void
ast_aggregate_initializer::hir_no_rvalue(exec_list *instructions,
                                         struct _mesa_glsl_parse_state *state)
{
   (void)hir(instructions, state);
}

static ir_rvalue *
do_comparison(void *mem_ctx, int operation, ir_rvalue *op0, ir_rvalue *op1)
{
   int join_op;
   ir_rvalue *cmp = NULL;

   if (operation == ir_binop_all_equal)
      join_op = ir_binop_logic_and;
   else
      join_op = ir_binop_logic_or;

   switch (op0->type->base_type) {
   case GLSL_TYPE_FLOAT:
   case GLSL_TYPE_UINT:
   case GLSL_TYPE_INT:
   case GLSL_TYPE_BOOL:
      return new(mem_ctx) ir_expression(operation, op0, op1);

   case GLSL_TYPE_ARRAY: {
      for (unsigned int i = 0; i < op0->type->length; i++) {
         ir_rvalue *e0, *e1, *result;

         e0 = new(mem_ctx) ir_dereference_array(op0->clone(mem_ctx, NULL),
                                                new(mem_ctx) ir_constant(i));
         e1 = new(mem_ctx) ir_dereference_array(op1->clone(mem_ctx, NULL),
                                                new(mem_ctx) ir_constant(i));
         result = do_comparison(mem_ctx, operation, e0, e1);

         if (cmp) {
            cmp = new(mem_ctx) ir_expression(join_op, cmp, result);
         } else {
            cmp = result;
         }
      }

      mark_whole_array_access(op0);
      mark_whole_array_access(op1);
      break;
   }

   case GLSL_TYPE_STRUCT: {
      for (unsigned int i = 0; i < op0->type->length; i++) {
         ir_rvalue *e0, *e1, *result;
         const char *field_name = op0->type->fields.structure[i].name;

         e0 = new(mem_ctx) ir_dereference_record(op0->clone(mem_ctx, NULL),
                                                 field_name);
         e1 = new(mem_ctx) ir_dereference_record(op1->clone(mem_ctx, NULL),
                                                 field_name);
         result = do_comparison(mem_ctx, operation, e0, e1);

         if (cmp) {
            cmp = new(mem_ctx) ir_expression(join_op, cmp, result);
         } else {
            cmp = result;
         }
      }
      break;
   }

   case GLSL_TYPE_ERROR:
   case GLSL_TYPE_VOID:
   case GLSL_TYPE_SAMPLER:
   case GLSL_TYPE_IMAGE:
   case GLSL_TYPE_INTERFACE:
   case GLSL_TYPE_ATOMIC_UINT:
      /* I assume a comparison of a struct containing a sampler just
       * ignores the sampler present in the type.
       */
      break;
   }

   if (cmp == NULL)
      cmp = new(mem_ctx) ir_constant(true);

   return cmp;
}

/* For logical operations, we want to ensure that the operands are
 * scalar booleans.  If it isn't, emit an error and return a constant
 * boolean to avoid triggering cascading error messages.
 */
ir_rvalue *
get_scalar_boolean_operand(exec_list *instructions,
			   struct _mesa_glsl_parse_state *state,
			   ast_expression *parent_expr,
			   int operand,
			   const char *operand_name,
			   bool *error_emitted)
{
   ast_expression *expr = parent_expr->subexpressions[operand];
   void *ctx = state;
   ir_rvalue *val = expr->hir(instructions, state);

   if (val->type->is_boolean() && val->type->is_scalar())
      return val;

   if (!*error_emitted) {
      YYLTYPE loc = expr->get_location();
      _mesa_glsl_error(&loc, state, "%s of `%s' must be scalar boolean",
                       operand_name,
                       parent_expr->operator_string(parent_expr->oper));
      *error_emitted = true;
   }

   return new(ctx) ir_constant(true);
}

/**
 * If name refers to a builtin array whose maximum allowed size is less than
 * size, report an error and return true.  Otherwise return false.
 */
void
check_builtin_array_max_size(const char *name, unsigned size,
                             YYLTYPE loc, struct _mesa_glsl_parse_state *state)
{
   if ((strcmp("gl_TexCoord", name) == 0)
       && (size > state->Const.MaxTextureCoords)) {
      /* From page 54 (page 60 of the PDF) of the GLSL 1.20 spec:
       *
       *     "The size [of gl_TexCoord] can be at most
       *     gl_MaxTextureCoords."
       */
      _mesa_glsl_error(&loc, state, "`gl_TexCoord' array size cannot "
                       "be larger than gl_MaxTextureCoords (%u)",
                       state->Const.MaxTextureCoords);
   } else if (strcmp("gl_ClipDistance", name) == 0
              && size > state->Const.MaxClipPlanes) {
      /* From section 7.1 (Vertex Shader Special Variables) of the
       * GLSL 1.30 spec:
       *
       *   "The gl_ClipDistance array is predeclared as unsized and
       *   must be sized by the shader either redeclaring it with a
       *   size or indexing it only with integral constant
       *   expressions. ... The size can be at most
       *   gl_MaxClipDistances."
       */
      _mesa_glsl_error(&loc, state, "`gl_ClipDistance' array size cannot "
                       "be larger than gl_MaxClipDistances (%u)",
                       state->Const.MaxClipPlanes);
   }
}

/**
 * Create the constant 1, of a which is appropriate for incrementing and
 * decrementing values of the given GLSL type.  For example, if type is vec4,
 * this creates a constant value of 1.0 having type float.
 *
 * If the given type is invalid for increment and decrement operators, return
 * a floating point 1--the error will be detected later.
 */
static ir_rvalue *
constant_one_for_inc_dec(void *ctx, const glsl_type *type)
{
   switch (type->base_type) {
   case GLSL_TYPE_UINT:
      return new(ctx) ir_constant((unsigned) 1);
   case GLSL_TYPE_INT:
      return new(ctx) ir_constant(1);
   default:
   case GLSL_TYPE_FLOAT:
      return new(ctx) ir_constant(1.0f);
   }
}

ir_rvalue *
ast_expression::hir(exec_list *instructions,
                    struct _mesa_glsl_parse_state *state)
{
   return do_hir(instructions, state, true);
}

void
ast_expression::hir_no_rvalue(exec_list *instructions,
                              struct _mesa_glsl_parse_state *state)
{
   do_hir(instructions, state, false);
}

ir_rvalue *
ast_expression::do_hir(exec_list *instructions,
                       struct _mesa_glsl_parse_state *state,
                       bool needs_rvalue)
{
   void *ctx = state;
   static const int operations[AST_NUM_OPERATORS] = {
      -1,               /* ast_assign doesn't convert to ir_expression. */
      -1,               /* ast_plus doesn't convert to ir_expression. */
      ir_unop_neg,
      ir_binop_add,
      ir_binop_sub,
      ir_binop_mul,
      ir_binop_div,
      ir_binop_mod,
      ir_binop_lshift,
      ir_binop_rshift,
      ir_binop_less,
      ir_binop_greater,
      ir_binop_lequal,
      ir_binop_gequal,
      ir_binop_all_equal,
      ir_binop_any_nequal,
      ir_binop_bit_and,
      ir_binop_bit_xor,
      ir_binop_bit_or,
      ir_unop_bit_not,
      ir_binop_logic_and,
      ir_binop_logic_xor,
      ir_binop_logic_or,
      ir_unop_logic_not,

      /* Note: The following block of expression types actually convert
       * to multiple IR instructions.
       */
      ir_binop_mul,     /* ast_mul_assign */
      ir_binop_div,     /* ast_div_assign */
      ir_binop_mod,     /* ast_mod_assign */
      ir_binop_add,     /* ast_add_assign */
      ir_binop_sub,     /* ast_sub_assign */
      ir_binop_lshift,  /* ast_ls_assign */
      ir_binop_rshift,  /* ast_rs_assign */
      ir_binop_bit_and, /* ast_and_assign */
      ir_binop_bit_xor, /* ast_xor_assign */
      ir_binop_bit_or,  /* ast_or_assign */

      -1,               /* ast_conditional doesn't convert to ir_expression. */
      ir_binop_add,     /* ast_pre_inc. */
      ir_binop_sub,     /* ast_pre_dec. */
      ir_binop_add,     /* ast_post_inc. */
      ir_binop_sub,     /* ast_post_dec. */
      -1,               /* ast_field_selection doesn't conv to ir_expression. */
      -1,               /* ast_array_index doesn't convert to ir_expression. */
      -1,               /* ast_function_call doesn't conv to ir_expression. */
      -1,               /* ast_identifier doesn't convert to ir_expression. */
      -1,               /* ast_int_constant doesn't convert to ir_expression. */
      -1,               /* ast_uint_constant doesn't conv to ir_expression. */
      -1,               /* ast_float_constant doesn't conv to ir_expression. */
      -1,               /* ast_bool_constant doesn't conv to ir_expression. */
      -1,               /* ast_sequence doesn't convert to ir_expression. */
   };
   ir_rvalue *result = NULL;
   ir_rvalue *op[3];
   const struct glsl_type *type; /* a temporary variable for switch cases */
   bool error_emitted = false;
   YYLTYPE loc;

   loc = this->get_location();

   switch (this->oper) {
   case ast_aggregate:
      assert(!"ast_aggregate: Should never get here.");
      break;

   case ast_assign: {
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);

      error_emitted =
         do_assignment(instructions, state,
                       this->subexpressions[0]->non_lvalue_description,
                       op[0], op[1], &result, needs_rvalue, false,
                       this->subexpressions[0]->get_location());
      break;
   }

   case ast_plus:
      op[0] = this->subexpressions[0]->hir(instructions, state);

      type = unary_arithmetic_result_type(op[0]->type, state, & loc);

      error_emitted = type->is_error();

      result = op[0];
      break;

   case ast_neg:
      op[0] = this->subexpressions[0]->hir(instructions, state);

      type = unary_arithmetic_result_type(op[0]->type, state, & loc);

      error_emitted = type->is_error();

      result = new(ctx) ir_expression(operations[this->oper], type,
                                      op[0], NULL);
      break;

   case ast_add:
   case ast_sub:
   case ast_mul:
   case ast_div:
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);

      type = arithmetic_result_type(op[0], op[1],
                                    (this->oper == ast_mul),
                                    state, & loc);
      error_emitted = type->is_error();

      result = new(ctx) ir_expression(operations[this->oper], type,
                                      op[0], op[1]);
      break;

   case ast_mod:
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);

      type = modulus_result_type(op[0]->type, op[1]->type, state, & loc);

      assert(operations[this->oper] == ir_binop_mod);

      result = new(ctx) ir_expression(operations[this->oper], type,
                                      op[0], op[1]);
      error_emitted = type->is_error();
      break;

   case ast_lshift:
   case ast_rshift:
       if (!state->check_bitwise_operations_allowed(&loc)) {
          error_emitted = true;
       }

       op[0] = this->subexpressions[0]->hir(instructions, state);
       op[1] = this->subexpressions[1]->hir(instructions, state);
       type = shift_result_type(op[0]->type, op[1]->type, this->oper, state,
                                &loc);
       result = new(ctx) ir_expression(operations[this->oper], type,
                                       op[0], op[1]);
       error_emitted = op[0]->type->is_error() || op[1]->type->is_error();
       break;

   case ast_less:
   case ast_greater:
   case ast_lequal:
   case ast_gequal:
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);

      type = relational_result_type(op[0], op[1], state, & loc);

      /* The relational operators must either generate an error or result
       * in a scalar boolean.  See page 57 of the GLSL 1.50 spec.
       */
      assert(type->is_error()
	     || ((type->base_type == GLSL_TYPE_BOOL)
		 && type->is_scalar()));

      result = new(ctx) ir_expression(operations[this->oper], type,
                                      op[0], op[1]);
      error_emitted = type->is_error();
      break;

   case ast_nequal:
   case ast_equal:
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);

      /* From page 58 (page 64 of the PDF) of the GLSL 1.50 spec:
       *
       *    "The equality operators equal (==), and not equal (!=)
       *    operate on all types. They result in a scalar Boolean. If
       *    the operand types do not match, then there must be a
       *    conversion from Section 4.1.10 "Implicit Conversions"
       *    applied to one operand that can make them match, in which
       *    case this conversion is done."
       */
      if ((!apply_implicit_conversion(op[0]->type, op[1], state)
           && !apply_implicit_conversion(op[1]->type, op[0], state))
          || (op[0]->type != op[1]->type)) {
         _mesa_glsl_error(& loc, state, "operands of `%s' must have the same "
                          "type", (this->oper == ast_equal) ? "==" : "!=");
         error_emitted = true;
      } else if ((op[0]->type->is_array() || op[1]->type->is_array()) &&
                 !state->check_version(120, 300, &loc,
                                       "array comparisons forbidden")) {
         error_emitted = true;
      } else if ((op[0]->type->contains_opaque() ||
                  op[1]->type->contains_opaque())) {
         _mesa_glsl_error(&loc, state, "opaque type comparisons forbidden");
         error_emitted = true;
      }

      if (error_emitted) {
         result = new(ctx) ir_constant(false);
      } else {
         result = do_comparison(ctx, operations[this->oper], op[0], op[1]);
         assert(result->type == glsl_type::bool_type);
      }
      break;

   case ast_bit_and:
   case ast_bit_xor:
   case ast_bit_or:
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);
      type = bit_logic_result_type(op[0]->type, op[1]->type, this->oper,
                                   state, &loc);
      result = new(ctx) ir_expression(operations[this->oper], type,
                                      op[0], op[1]);
      error_emitted = op[0]->type->is_error() || op[1]->type->is_error();
      break;

   case ast_bit_not:
      op[0] = this->subexpressions[0]->hir(instructions, state);

      if (!state->check_bitwise_operations_allowed(&loc)) {
         error_emitted = true;
      }

      if (!op[0]->type->is_integer()) {
         _mesa_glsl_error(&loc, state, "operand of `~' must be an integer");
         error_emitted = true;
      }

      type = error_emitted ? glsl_type::error_type : op[0]->type;
      result = new(ctx) ir_expression(ir_unop_bit_not, type, op[0], NULL);
      break;

   case ast_logic_and: {
      exec_list rhs_instructions;
      op[0] = get_scalar_boolean_operand(instructions, state, this, 0,
                                         "LHS", &error_emitted);
      op[1] = get_scalar_boolean_operand(&rhs_instructions, state, this, 1,
                                         "RHS", &error_emitted);

      if (rhs_instructions.is_empty()) {
         result = new(ctx) ir_expression(ir_binop_logic_and, op[0], op[1]);
         type = result->type;
      } else {
         ir_variable *const tmp = new(ctx) ir_variable(glsl_type::bool_type,
                                                       "and_tmp",
                                                       ir_var_temporary);
         instructions->push_tail(tmp);

         ir_if *const stmt = new(ctx) ir_if(op[0]);
         instructions->push_tail(stmt);

         stmt->then_instructions.append_list(&rhs_instructions);
         ir_dereference *const then_deref = new(ctx) ir_dereference_variable(tmp);
         ir_assignment *const then_assign =
            new(ctx) ir_assignment(then_deref, op[1]);
         stmt->then_instructions.push_tail(then_assign);

         ir_dereference *const else_deref = new(ctx) ir_dereference_variable(tmp);
         ir_assignment *const else_assign =
            new(ctx) ir_assignment(else_deref, new(ctx) ir_constant(false));
         stmt->else_instructions.push_tail(else_assign);

         result = new(ctx) ir_dereference_variable(tmp);
         type = tmp->type;
      }
      break;
   }

   case ast_logic_or: {
      exec_list rhs_instructions;
      op[0] = get_scalar_boolean_operand(instructions, state, this, 0,
                                         "LHS", &error_emitted);
      op[1] = get_scalar_boolean_operand(&rhs_instructions, state, this, 1,
                                         "RHS", &error_emitted);

      if (rhs_instructions.is_empty()) {
         result = new(ctx) ir_expression(ir_binop_logic_or, op[0], op[1]);
         type = result->type;
      } else {
         ir_variable *const tmp = new(ctx) ir_variable(glsl_type::bool_type,
                                                       "or_tmp",
                                                       ir_var_temporary);
         instructions->push_tail(tmp);

         ir_if *const stmt = new(ctx) ir_if(op[0]);
         instructions->push_tail(stmt);

         ir_dereference *const then_deref = new(ctx) ir_dereference_variable(tmp);
         ir_assignment *const then_assign =
            new(ctx) ir_assignment(then_deref, new(ctx) ir_constant(true));
         stmt->then_instructions.push_tail(then_assign);

         stmt->else_instructions.append_list(&rhs_instructions);
         ir_dereference *const else_deref = new(ctx) ir_dereference_variable(tmp);
         ir_assignment *const else_assign =
            new(ctx) ir_assignment(else_deref, op[1]);
         stmt->else_instructions.push_tail(else_assign);

         result = new(ctx) ir_dereference_variable(tmp);
         type = tmp->type;
      }
      break;
   }

   case ast_logic_xor:
      /* From page 33 (page 39 of the PDF) of the GLSL 1.10 spec:
       *
       *    "The logical binary operators and (&&), or ( | | ), and
       *     exclusive or (^^). They operate only on two Boolean
       *     expressions and result in a Boolean expression."
       */
      op[0] = get_scalar_boolean_operand(instructions, state, this, 0, "LHS",
                                         &error_emitted);
      op[1] = get_scalar_boolean_operand(instructions, state, this, 1, "RHS",
                                         &error_emitted);

      result = new(ctx) ir_expression(operations[this->oper], glsl_type::bool_type,
                                      op[0], op[1]);
      break;

   case ast_logic_not:
      op[0] = get_scalar_boolean_operand(instructions, state, this, 0,
                                         "operand", &error_emitted);

      result = new(ctx) ir_expression(operations[this->oper], glsl_type::bool_type,
                                      op[0], NULL);
      break;

   case ast_mul_assign:
   case ast_div_assign:
   case ast_add_assign:
   case ast_sub_assign: {
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);

      type = arithmetic_result_type(op[0], op[1],
                                    (this->oper == ast_mul_assign),
                                    state, & loc);

      ir_rvalue *temp_rhs = new(ctx) ir_expression(operations[this->oper], type,
                                                   op[0], op[1]);

      error_emitted =
         do_assignment(instructions, state,
                       this->subexpressions[0]->non_lvalue_description,
                       op[0]->clone(ctx, NULL), temp_rhs,
                       &result, needs_rvalue, false,
                       this->subexpressions[0]->get_location());

      /* GLSL 1.10 does not allow array assignment.  However, we don't have to
       * explicitly test for this because none of the binary expression
       * operators allow array operands either.
       */

      break;
   }

   case ast_mod_assign: {
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);

      type = modulus_result_type(op[0]->type, op[1]->type, state, & loc);

      assert(operations[this->oper] == ir_binop_mod);

      ir_rvalue *temp_rhs;
      temp_rhs = new(ctx) ir_expression(operations[this->oper], type,
                                        op[0], op[1]);

      error_emitted =
         do_assignment(instructions, state,
                       this->subexpressions[0]->non_lvalue_description,
                       op[0]->clone(ctx, NULL), temp_rhs,
                       &result, needs_rvalue, false,
                       this->subexpressions[0]->get_location());
      break;
   }

   case ast_ls_assign:
   case ast_rs_assign: {
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);
      type = shift_result_type(op[0]->type, op[1]->type, this->oper, state,
                               &loc);
      ir_rvalue *temp_rhs = new(ctx) ir_expression(operations[this->oper],
                                                   type, op[0], op[1]);
      error_emitted =
         do_assignment(instructions, state,
                       this->subexpressions[0]->non_lvalue_description,
                       op[0]->clone(ctx, NULL), temp_rhs,
                       &result, needs_rvalue, false,
                       this->subexpressions[0]->get_location());
      break;
   }

   case ast_and_assign:
   case ast_xor_assign:
   case ast_or_assign: {
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = this->subexpressions[1]->hir(instructions, state);
      type = bit_logic_result_type(op[0]->type, op[1]->type, this->oper,
                                   state, &loc);
      ir_rvalue *temp_rhs = new(ctx) ir_expression(operations[this->oper],
                                                   type, op[0], op[1]);
      error_emitted =
         do_assignment(instructions, state,
                       this->subexpressions[0]->non_lvalue_description,
                       op[0]->clone(ctx, NULL), temp_rhs,
                       &result, needs_rvalue, false,
                       this->subexpressions[0]->get_location());
      break;
   }

   case ast_conditional: {
      /* From page 59 (page 65 of the PDF) of the GLSL 1.50 spec:
       *
       *    "The ternary selection operator (?:). It operates on three
       *    expressions (exp1 ? exp2 : exp3). This operator evaluates the
       *    first expression, which must result in a scalar Boolean."
       */
      op[0] = get_scalar_boolean_operand(instructions, state, this, 0,
                                         "condition", &error_emitted);

      /* The :? operator is implemented by generating an anonymous temporary
       * followed by an if-statement.  The last instruction in each branch of
       * the if-statement assigns a value to the anonymous temporary.  This
       * temporary is the r-value of the expression.
       */
      exec_list then_instructions;
      exec_list else_instructions;

      op[1] = this->subexpressions[1]->hir(&then_instructions, state);
      op[2] = this->subexpressions[2]->hir(&else_instructions, state);

      /* From page 59 (page 65 of the PDF) of the GLSL 1.50 spec:
       *
       *     "The second and third expressions can be any type, as
       *     long their types match, or there is a conversion in
       *     Section 4.1.10 "Implicit Conversions" that can be applied
       *     to one of the expressions to make their types match. This
       *     resulting matching type is the type of the entire
       *     expression."
       */
      if ((!apply_implicit_conversion(op[1]->type, op[2], state)
          && !apply_implicit_conversion(op[2]->type, op[1], state))
          || (op[1]->type != op[2]->type)) {
         YYLTYPE loc = this->subexpressions[1]->get_location();

         _mesa_glsl_error(& loc, state, "second and third operands of ?: "
                          "operator must have matching types");
         error_emitted = true;
         type = glsl_type::error_type;
      } else {
         type = op[1]->type;
      }

      /* From page 33 (page 39 of the PDF) of the GLSL 1.10 spec:
       *
       *    "The second and third expressions must be the same type, but can
       *    be of any type other than an array."
       */
      if (type->is_array() &&
          !state->check_version(120, 300, &loc,
                                "second and third operands of ?: operator "
                                "cannot be arrays")) {
         error_emitted = true;
      }

      ir_constant *cond_val = op[0]->constant_expression_value();
      ir_constant *then_val = op[1]->constant_expression_value();
      ir_constant *else_val = op[2]->constant_expression_value();

      if (then_instructions.is_empty()
          && else_instructions.is_empty()
          && (cond_val != NULL) && (then_val != NULL) && (else_val != NULL)) {
         result = (cond_val->value.b[0]) ? then_val : else_val;
      } else {
         ir_variable *const tmp =
            new(ctx) ir_variable(type, "conditional_tmp", ir_var_temporary);
         instructions->push_tail(tmp);

         ir_if *const stmt = new(ctx) ir_if(op[0]);
         instructions->push_tail(stmt);

         then_instructions.move_nodes_to(& stmt->then_instructions);
         ir_dereference *const then_deref =
            new(ctx) ir_dereference_variable(tmp);
         ir_assignment *const then_assign =
            new(ctx) ir_assignment(then_deref, op[1]);
         stmt->then_instructions.push_tail(then_assign);

         else_instructions.move_nodes_to(& stmt->else_instructions);
         ir_dereference *const else_deref =
            new(ctx) ir_dereference_variable(tmp);
         ir_assignment *const else_assign =
            new(ctx) ir_assignment(else_deref, op[2]);
         stmt->else_instructions.push_tail(else_assign);

         result = new(ctx) ir_dereference_variable(tmp);
      }
      break;
   }

   case ast_pre_inc:
   case ast_pre_dec: {
      this->non_lvalue_description = (this->oper == ast_pre_inc)
         ? "pre-increment operation" : "pre-decrement operation";

      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = constant_one_for_inc_dec(ctx, op[0]->type);

      type = arithmetic_result_type(op[0], op[1], false, state, & loc);

      ir_rvalue *temp_rhs;
      temp_rhs = new(ctx) ir_expression(operations[this->oper], type,
                                        op[0], op[1]);

      error_emitted =
         do_assignment(instructions, state,
                       this->subexpressions[0]->non_lvalue_description,
                       op[0]->clone(ctx, NULL), temp_rhs,
                       &result, needs_rvalue, false,
                       this->subexpressions[0]->get_location());
      break;
   }

   case ast_post_inc:
   case ast_post_dec: {
      this->non_lvalue_description = (this->oper == ast_post_inc)
         ? "post-increment operation" : "post-decrement operation";
      op[0] = this->subexpressions[0]->hir(instructions, state);
      op[1] = constant_one_for_inc_dec(ctx, op[0]->type);

      error_emitted = op[0]->type->is_error() || op[1]->type->is_error();

      type = arithmetic_result_type(op[0], op[1], false, state, & loc);

      ir_rvalue *temp_rhs;
      temp_rhs = new(ctx) ir_expression(operations[this->oper], type,
                                        op[0], op[1]);

      /* Get a temporary of a copy of the lvalue before it's modified.
       * This may get thrown away later.
       */
      result = get_lvalue_copy(instructions, op[0]->clone(ctx, NULL));

      ir_rvalue *junk_rvalue;
      error_emitted =
         do_assignment(instructions, state,
                       this->subexpressions[0]->non_lvalue_description,
                       op[0]->clone(ctx, NULL), temp_rhs,
                       &junk_rvalue, false, false,
                       this->subexpressions[0]->get_location());

      break;
   }

   case ast_field_selection:
      result = _mesa_ast_field_selection_to_hir(this, instructions, state);
      break;

   case ast_array_index: {
      YYLTYPE index_loc = subexpressions[1]->get_location();

      op[0] = subexpressions[0]->hir(instructions, state);
      op[1] = subexpressions[1]->hir(instructions, state);

      result = _mesa_ast_array_index_to_hir(ctx, state, op[0], op[1],
                                            loc, index_loc);

      if (result->type->is_error())
         error_emitted = true;

      break;
   }

   case ast_function_call:
      /* Should *NEVER* get here.  ast_function_call should always be handled
       * by ast_function_expression::hir.
       */
      assert(0);
      break;

   case ast_identifier: {
      /* ast_identifier can appear several places in a full abstract syntax
       * tree.  This particular use must be at location specified in the grammar
       * as 'variable_identifier'.
       */
      ir_variable *var = 
         state->symbols->get_variable(this->primary_expression.identifier);

      if (var != NULL) {
         var->data.used = true;
         result = new(ctx) ir_dereference_variable(var);
      } else {
         _mesa_glsl_error(& loc, state, "`%s' undeclared",
                          this->primary_expression.identifier);

         result = ir_rvalue::error_value(ctx);
         error_emitted = true;
      }
      break;
   }

   case ast_int_constant:
      result = new(ctx) ir_constant(this->primary_expression.int_constant);
      break;

   case ast_uint_constant:
      result = new(ctx) ir_constant(this->primary_expression.uint_constant);
      break;

   case ast_float_constant:
      result = new(ctx) ir_constant(this->primary_expression.float_constant);
      break;

   case ast_bool_constant:
      result = new(ctx) ir_constant(bool(this->primary_expression.bool_constant));
      break;

   case ast_sequence: {
      /* It should not be possible to generate a sequence in the AST without
       * any expressions in it.
       */
      assert(!this->expressions.is_empty());

      /* The r-value of a sequence is the last expression in the sequence.  If
       * the other expressions in the sequence do not have side-effects (and
       * therefore add instructions to the instruction list), they get dropped
       * on the floor.
       */
      exec_node *previous_tail_pred = NULL;
      YYLTYPE previous_operand_loc = loc;

      foreach_list_typed (ast_node, ast, link, &this->expressions) {
         /* If one of the operands of comma operator does not generate any
          * code, we want to emit a warning.  At each pass through the loop
          * previous_tail_pred will point to the last instruction in the
          * stream *before* processing the previous operand.  Naturally,
          * instructions->tail_pred will point to the last instruction in the
          * stream *after* processing the previous operand.  If the two
          * pointers match, then the previous operand had no effect.
          *
          * The warning behavior here differs slightly from GCC.  GCC will
          * only emit a warning if none of the left-hand operands have an
          * effect.  However, it will emit a warning for each.  I believe that
          * there are some cases in C (especially with GCC extensions) where
          * it is useful to have an intermediate step in a sequence have no
          * effect, but I don't think these cases exist in GLSL.  Either way,
          * it would be a giant hassle to replicate that behavior.
          */
         if (previous_tail_pred == instructions->tail_pred) {
            _mesa_glsl_warning(&previous_operand_loc, state,
                               "left-hand operand of comma expression has "
                               "no effect");
         }

         /* tail_pred is directly accessed instead of using the get_tail()
          * method for performance reasons.  get_tail() has extra code to
          * return NULL when the list is empty.  We don't care about that
          * here, so using tail_pred directly is fine.
          */
         previous_tail_pred = instructions->tail_pred;
         previous_operand_loc = ast->get_location();

         result = ast->hir(instructions, state);
      }

      /* Any errors should have already been emitted in the loop above.
       */
      error_emitted = true;
      break;
   }
   }
   type = NULL; /* use result->type, not type. */
   assert(result != NULL || !needs_rvalue);

   if (result && result->type->is_error() && !error_emitted)
      _mesa_glsl_error(& loc, state, "type mismatch");

   return result;
}


ir_rvalue *
ast_expression_statement::hir(exec_list *instructions,
                              struct _mesa_glsl_parse_state *state)
{
   /* It is possible to have expression statements that don't have an
    * expression.  This is the solitary semicolon:
    *
    * for (i = 0; i < 5; i++)
    *     ;
    *
    * In this case the expression will be NULL.  Test for NULL and don't do
    * anything in that case.
    */
   if (expression != NULL)
      expression->hir_no_rvalue(instructions, state);

   /* Statements do not have r-values.
    */
   return NULL;
}


ir_rvalue *
ast_compound_statement::hir(exec_list *instructions,
                            struct _mesa_glsl_parse_state *state)
{
   if (new_scope)
      state->symbols->push_scope();

   foreach_list_typed (ast_node, ast, link, &this->statements)
      ast->hir(instructions, state);

   if (new_scope)
      state->symbols->pop_scope();

   /* Compound statements do not have r-values.
    */
   return NULL;
}

/**
 * Evaluate the given exec_node (which should be an ast_node representing
 * a single array dimension) and return its integer value.
 */
static unsigned
process_array_size(exec_node *node,
                   struct _mesa_glsl_parse_state *state)
{
   exec_list dummy_instructions;

   ast_node *array_size = exec_node_data(ast_node, node, link);
   ir_rvalue *const ir = array_size->hir(& dummy_instructions, state);
   YYLTYPE loc = array_size->get_location();

   if (ir == NULL) {
      _mesa_glsl_error(& loc, state,
                       "array size could not be resolved");
      return 0;
   }

   if (!ir->type->is_integer()) {
      _mesa_glsl_error(& loc, state,
                       "array size must be integer type");
      return 0;
   }

   if (!ir->type->is_scalar()) {
      _mesa_glsl_error(& loc, state,
                       "array size must be scalar type");
      return 0;
   }

   ir_constant *const size = ir->constant_expression_value();
   if (size == NULL) {
      _mesa_glsl_error(& loc, state, "array size must be a "
                       "constant valued expression");
      return 0;
   }

   if (size->value.i[0] <= 0) {
      _mesa_glsl_error(& loc, state, "array size must be > 0");
      return 0;
   }

   assert(size->type == ir->type);

   /* If the array size is const (and we've verified that
    * it is) then no instructions should have been emitted
    * when we converted it to HIR. If they were emitted,
    * then either the array size isn't const after all, or
    * we are emitting unnecessary instructions.
    */
   assert(dummy_instructions.is_empty());

   return size->value.u[0];
}

static const glsl_type *
process_array_type(YYLTYPE *loc, const glsl_type *base,
                   ast_array_specifier *array_specifier,
                   struct _mesa_glsl_parse_state *state)
{
   const glsl_type *array_type = base;

   if (array_specifier != NULL) {
      if (base->is_array()) {

         /* From page 19 (page 25) of the GLSL 1.20 spec:
          *
          * "Only one-dimensional arrays may be declared."
          */
         if (!state->ARB_arrays_of_arrays_enable) {
            _mesa_glsl_error(loc, state,
                             "invalid array of `%s'"
                             "GL_ARB_arrays_of_arrays "
                             "required for defining arrays of arrays",
                             base->name);
            return glsl_type::error_type;
         }

         if (base->length == 0) {
            _mesa_glsl_error(loc, state,
                             "only the outermost array dimension can "
                             "be unsized",
                             base->name);
            return glsl_type::error_type;
         }
      }

      for (exec_node *node = array_specifier->array_dimensions.tail_pred;
           !node->is_head_sentinel(); node = node->prev) {
         unsigned array_size = process_array_size(node, state);
         array_type = glsl_type::get_array_instance(array_type, array_size);
      }

      if (array_specifier->is_unsized_array)
         array_type = glsl_type::get_array_instance(array_type, 0);
   }

   return array_type;
}


const glsl_type *
ast_type_specifier::glsl_type(const char **name,
                              struct _mesa_glsl_parse_state *state) const
{
   const struct glsl_type *type;

   type = state->symbols->get_type(this->type_name);
   *name = this->type_name;

   YYLTYPE loc = this->get_location();
   type = process_array_type(&loc, type, this->array_specifier, state);

   return type;
}

const glsl_type *
ast_fully_specified_type::glsl_type(const char **name,
                                    struct _mesa_glsl_parse_state *state) const
{
   const struct glsl_type *type = this->specifier->glsl_type(name, state);

   if (type == NULL)
      return NULL;

   if (type->base_type == GLSL_TYPE_FLOAT
       && state->es_shader
       && state->stage == MESA_SHADER_FRAGMENT
       && this->qualifier.precision == ast_precision_none
       && state->symbols->get_variable("#default precision") == NULL) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(&loc, state,
                       "no precision specified this scope for type `%s'",
                       type->name);
   }

   return type;
}

/**
 * Determine whether a toplevel variable declaration declares a varying.  This
 * function operates by examining the variable's mode and the shader target,
 * so it correctly identifies linkage variables regardless of whether they are
 * declared using the deprecated "varying" syntax or the new "in/out" syntax.
 *
 * Passing a non-toplevel variable declaration (e.g. a function parameter) to
 * this function will produce undefined results.
 */
static bool
is_varying_var(ir_variable *var, gl_shader_stage target)
{
   switch (target) {
   case MESA_SHADER_VERTEX:
      return var->data.mode == ir_var_shader_out;
   case MESA_SHADER_FRAGMENT:
      return var->data.mode == ir_var_shader_in;
   default:
      return var->data.mode == ir_var_shader_out || var->data.mode == ir_var_shader_in;
   }
}


/**
 * Matrix layout qualifiers are only allowed on certain types
 */
static void
validate_matrix_layout_for_type(struct _mesa_glsl_parse_state *state,
                                YYLTYPE *loc,
                                const glsl_type *type,
                                ir_variable *var)
{
   if (var && !var->is_in_uniform_block()) {
      /* Layout qualifiers may only apply to interface blocks and fields in
       * them.
       */
      _mesa_glsl_error(loc, state,
                       "uniform block layout qualifiers row_major and "
                       "column_major may not be applied to variables "
                       "outside of uniform blocks");
   } else if (!type->is_matrix()) {
      /* The OpenGL ES 3.0 conformance tests did not originally allow
       * matrix layout qualifiers on non-matrices.  However, the OpenGL
       * 4.4 and OpenGL ES 3.0 (revision TBD) specifications were
       * amended to specifically allow these layouts on all types.  Emit
       * a warning so that people know their code may not be portable.
       */
      _mesa_glsl_warning(loc, state,
                         "uniform block layout qualifiers row_major and "
                         "column_major applied to non-matrix types may "
                         "be rejected by older compilers");
   } else if (type->is_record()) {
      /* We allow 'layout(row_major)' on structure types because it's the only
       * way to get row-major layouts on matrices contained in structures.
       */
      _mesa_glsl_warning(loc, state,
                         "uniform block layout qualifiers row_major and "
                         "column_major applied to structure types is not "
                         "strictly conformant and may be rejected by other "
                         "compilers");
   }
}

static bool
validate_binding_qualifier(struct _mesa_glsl_parse_state *state,
                           YYLTYPE *loc,
                           ir_variable *var,
                           const ast_type_qualifier *qual)
{
   if (var->data.mode != ir_var_uniform) {
      _mesa_glsl_error(loc, state,
                       "the \"binding\" qualifier only applies to uniforms");
      return false;
   }

   if (qual->binding < 0) {
      _mesa_glsl_error(loc, state, "binding values must be >= 0");
      return false;
   }

   const struct gl_context *const ctx = state->ctx;
   unsigned elements = var->type->is_array() ? var->type->length : 1;
   unsigned max_index = qual->binding + elements - 1;

   if (var->type->is_interface()) {
      /* UBOs.  From page 60 of the GLSL 4.20 specification:
       * "If the binding point for any uniform block instance is less than zero,
       *  or greater than or equal to the implementation-dependent maximum
       *  number of uniform buffer bindings, a compilation error will occur.
       *  When the binding identifier is used with a uniform block instanced as
       *  an array of size N, all elements of the array from binding through
       *  binding + N – 1 must be within this range."
       *
       * The implementation-dependent maximum is GL_MAX_UNIFORM_BUFFER_BINDINGS.
       */
      if (max_index >= ctx->Const.MaxUniformBufferBindings) {
         _mesa_glsl_error(loc, state, "layout(binding = %d) for %d UBOs exceeds "
                          "the maximum number of UBO binding points (%d)",
                          qual->binding, elements,
                          ctx->Const.MaxUniformBufferBindings);
         return false;
      }
   } else if (var->type->is_sampler() ||
              (var->type->is_array() && var->type->fields.array->is_sampler())) {
      /* Samplers.  From page 63 of the GLSL 4.20 specification:
       * "If the binding is less than zero, or greater than or equal to the
       *  implementation-dependent maximum supported number of units, a
       *  compilation error will occur. When the binding identifier is used
       *  with an array of size N, all elements of the array from binding
       *  through binding + N - 1 must be within this range."
       */
      unsigned limit = ctx->Const.Program[state->stage].MaxTextureImageUnits;

      if (max_index >= limit) {
         _mesa_glsl_error(loc, state, "layout(binding = %d) for %d samplers "
                          "exceeds the maximum number of texture image units "
                          "(%d)", qual->binding, elements, limit);

         return false;
      }
   } else if (var->type->contains_atomic()) {
      assert(ctx->Const.MaxAtomicBufferBindings <= MAX_COMBINED_ATOMIC_BUFFERS);
      if (unsigned(qual->binding) >= ctx->Const.MaxAtomicBufferBindings) {
         _mesa_glsl_error(loc, state, "layout(binding = %d) exceeds the "
                          " maximum number of atomic counter buffer bindings"
                          "(%d)", qual->binding,
                          ctx->Const.MaxAtomicBufferBindings);

         return false;
      }
   } else {
      _mesa_glsl_error(loc, state,
                       "the \"binding\" qualifier only applies to uniform "
                       "blocks, samplers, atomic counters, or arrays thereof");
      return false;
   }

   return true;
}


static glsl_interp_qualifier
interpret_interpolation_qualifier(const struct ast_type_qualifier *qual,
                                  ir_variable_mode mode,
                                  struct _mesa_glsl_parse_state *state,
                                  YYLTYPE *loc)
{
   glsl_interp_qualifier interpolation;
   if (qual->flags.q.flat)
      interpolation = INTERP_QUALIFIER_FLAT;
   else if (qual->flags.q.noperspective)
      interpolation = INTERP_QUALIFIER_NOPERSPECTIVE;
   else if (qual->flags.q.smooth)
      interpolation = INTERP_QUALIFIER_SMOOTH;
   else
      interpolation = INTERP_QUALIFIER_NONE;

   if (interpolation != INTERP_QUALIFIER_NONE) {
      if (mode != ir_var_shader_in && mode != ir_var_shader_out) {
         _mesa_glsl_error(loc, state,
                          "interpolation qualifier `%s' can only be applied to "
                          "shader inputs or outputs.",
                          interpolation_string(interpolation));

      }

      if ((state->stage == MESA_SHADER_VERTEX && mode == ir_var_shader_in) ||
          (state->stage == MESA_SHADER_FRAGMENT && mode == ir_var_shader_out)) {
         _mesa_glsl_error(loc, state,
                          "interpolation qualifier `%s' cannot be applied to "
                          "vertex shader inputs or fragment shader outputs",
                          interpolation_string(interpolation));
      }
   }

   return interpolation;
}


static void
validate_explicit_location(const struct ast_type_qualifier *qual,
                           ir_variable *var,
                           struct _mesa_glsl_parse_state *state,
                           YYLTYPE *loc)
{
   bool fail = false;

   /* Checks for GL_ARB_explicit_uniform_location. */
   if (qual->flags.q.uniform) {
      if (!state->check_explicit_uniform_location_allowed(loc, var))
         return;

      const struct gl_context *const ctx = state->ctx;
      unsigned max_loc = qual->location + var->type->uniform_locations() - 1;

      /* ARB_explicit_uniform_location specification states:
       *
       *     "The explicitly defined locations and the generated locations
       *     must be in the range of 0 to MAX_UNIFORM_LOCATIONS minus one."
       *
       *     "Valid locations for default-block uniform variable locations
       *     are in the range of 0 to the implementation-defined maximum
       *     number of uniform locations."
       */
      if (qual->location < 0) {
         _mesa_glsl_error(loc, state,
                          "explicit location < 0 for uniform %s", var->name);
         return;
      }

      if (max_loc >= ctx->Const.MaxUserAssignableUniformLocations) {
         _mesa_glsl_error(loc, state, "location(s) consumed by uniform %s "
                          ">= MAX_UNIFORM_LOCATIONS (%u)", var->name,
                          ctx->Const.MaxUserAssignableUniformLocations);
         return;
      }

      var->data.explicit_location = true;
      var->data.location = qual->location;
      return;
   }

   /* Between GL_ARB_explicit_attrib_location an
    * GL_ARB_separate_shader_objects, the inputs and outputs of any shader
    * stage can be assigned explicit locations.  The checking here associates
    * the correct extension with the correct stage's input / output:
    *
    *                     input            output
    *                     -----            ------
    * vertex              explicit_loc     sso
    * geometry            sso              sso
    * fragment            sso              explicit_loc
    */
   switch (state->stage) {
   case MESA_SHADER_VERTEX:
      if (var->data.mode == ir_var_shader_in) {
         if (!state->check_explicit_attrib_location_allowed(loc, var))
            return;

         break;
      }

      if (var->data.mode == ir_var_shader_out) {
         if (!state->check_separate_shader_objects_allowed(loc, var))
            return;

         break;
      }

      fail = true;
      break;

   case MESA_SHADER_GEOMETRY:
      if (var->data.mode == ir_var_shader_in || var->data.mode == ir_var_shader_out) {
         if (!state->check_separate_shader_objects_allowed(loc, var))
            return;

         break;
      }

      fail = true;
      break;

   case MESA_SHADER_FRAGMENT:
      if (var->data.mode == ir_var_shader_in) {
         if (!state->check_separate_shader_objects_allowed(loc, var))
            return;

         break;
      }

      if (var->data.mode == ir_var_shader_out) {
         if (!state->check_explicit_attrib_location_allowed(loc, var))
            return;

         break;
      }

      fail = true;
      break;

   case MESA_SHADER_COMPUTE:
      _mesa_glsl_error(loc, state,
                       "compute shader variables cannot be given "
                       "explicit locations");
      return;
   };

   if (fail) {
      _mesa_glsl_error(loc, state,
                       "%s cannot be given an explicit location in %s shader",
                       mode_string(var),
      _mesa_shader_stage_to_string(state->stage));
   } else {
      var->data.explicit_location = true;

      /* This bit of silliness is needed because invalid explicit locations
       * are supposed to be flagged during linking.  Small negative values
       * biased by VERT_ATTRIB_GENERIC0 or FRAG_RESULT_DATA0 could alias
       * built-in values (e.g., -16+VERT_ATTRIB_GENERIC0 = VERT_ATTRIB_POS).
       * The linker needs to be able to differentiate these cases.  This
       * ensures that negative values stay negative.
       */
      if (qual->location >= 0) {
         switch (state->stage) {
         case MESA_SHADER_VERTEX:
            var->data.location = (var->data.mode == ir_var_shader_in)
               ? (qual->location + VERT_ATTRIB_GENERIC0)
               : (qual->location + VARYING_SLOT_VAR0);
            break;

         case MESA_SHADER_GEOMETRY:
            var->data.location = qual->location + VARYING_SLOT_VAR0;
            break;

         case MESA_SHADER_FRAGMENT:
            var->data.location = (var->data.mode == ir_var_shader_out)
               ? (qual->location + FRAG_RESULT_DATA0)
               : (qual->location + VARYING_SLOT_VAR0);
            break;
         case MESA_SHADER_COMPUTE:
            assert(!"Unexpected shader type");
            break;
         }
      } else {
         var->data.location = qual->location;
      }

      if (qual->flags.q.explicit_index) {
         /* From the GLSL 4.30 specification, section 4.4.2 (Output
          * Layout Qualifiers):
          *
          * "It is also a compile-time error if a fragment shader
          *  sets a layout index to less than 0 or greater than 1."
          *
          * Older specifications don't mandate a behavior; we take
          * this as a clarification and always generate the error.
          */
         if (qual->index < 0 || qual->index > 1) {
            _mesa_glsl_error(loc, state,
                             "explicit index may only be 0 or 1");
         } else {
            var->data.explicit_index = true;
            var->data.index = qual->index;
         }
      }
   }
}

static void
apply_image_qualifier_to_variable(const struct ast_type_qualifier *qual,
                                  ir_variable *var,
                                  struct _mesa_glsl_parse_state *state,
                                  YYLTYPE *loc)
{
   const glsl_type *base_type =
      (var->type->is_array() ? var->type->element_type() : var->type);

   if (base_type->is_image()) {
      if (var->data.mode != ir_var_uniform &&
          var->data.mode != ir_var_function_in) {
         _mesa_glsl_error(loc, state, "image variables may only be declared as "
                          "function parameters or uniform-qualified "
                          "global variables");
      }

      var->data.image.read_only |= qual->flags.q.read_only;
      var->data.image.write_only |= qual->flags.q.write_only;
      var->data.image.coherent |= qual->flags.q.coherent;
      var->data.image._volatile |= qual->flags.q._volatile;
      var->data.image.restrict_flag |= qual->flags.q.restrict_flag;
      var->data.read_only = true;

      if (qual->flags.q.explicit_image_format) {
         if (var->data.mode == ir_var_function_in) {
            _mesa_glsl_error(loc, state, "format qualifiers cannot be "
                             "used on image function parameters");
         }

         if (qual->image_base_type != base_type->sampler_type) {
            _mesa_glsl_error(loc, state, "format qualifier doesn't match the "
                             "base data type of the image");
         }

         var->data.image.format = qual->image_format;
      } else {
         if (var->data.mode == ir_var_uniform && !qual->flags.q.write_only) {
            _mesa_glsl_error(loc, state, "uniforms not qualified with "
                             "`writeonly' must have a format layout "
                             "qualifier");
         }

         var->data.image.format = GL_NONE;
      }
   }
}

static inline const char*
get_layout_qualifier_string(bool origin_upper_left, bool pixel_center_integer)
{
   if (origin_upper_left && pixel_center_integer)
      return "origin_upper_left, pixel_center_integer";
   else if (origin_upper_left)
      return "origin_upper_left";
   else if (pixel_center_integer)
      return "pixel_center_integer";
   else
      return " ";
}

static inline bool
is_conflicting_fragcoord_redeclaration(struct _mesa_glsl_parse_state *state,
                                       const struct ast_type_qualifier *qual)
{
   /* If gl_FragCoord was previously declared, and the qualifiers were
    * different in any way, return true.
    */
   if (state->fs_redeclares_gl_fragcoord) {
      return (state->fs_pixel_center_integer != qual->flags.q.pixel_center_integer
         || state->fs_origin_upper_left != qual->flags.q.origin_upper_left);
   }

   return false;
}

static void
apply_type_qualifier_to_variable(const struct ast_type_qualifier *qual,
                                 ir_variable *var,
                                 struct _mesa_glsl_parse_state *state,
                                 YYLTYPE *loc,
                                 bool is_parameter)
{
   STATIC_ASSERT(sizeof(qual->flags.q) <= sizeof(qual->flags.i));

   if (qual->flags.q.invariant) {
      if (var->data.used) {
         _mesa_glsl_error(loc, state,
                          "variable `%s' may not be redeclared "
                          "`invariant' after being used",
                          var->name);
      } else {
         var->data.invariant = 1;
      }
   }

   if (qual->flags.q.precise) {
      if (var->data.used) {
         _mesa_glsl_error(loc, state,
                          "variable `%s' may not be redeclared "
                          "`precise' after being used",
                          var->name);
      } else {
         var->data.precise = 1;
      }
   }

   if (qual->flags.q.constant || qual->flags.q.attribute
       || qual->flags.q.uniform
       || (qual->flags.q.varying && (state->stage == MESA_SHADER_FRAGMENT)))
      var->data.read_only = 1;

   if (qual->flags.q.centroid)
      var->data.centroid = 1;

   if (qual->flags.q.sample)
      var->data.sample = 1;

   if (state->stage == MESA_SHADER_GEOMETRY &&
       qual->flags.q.out && qual->flags.q.stream) {
      var->data.stream = qual->stream;
   }

   if (qual->flags.q.attribute && state->stage != MESA_SHADER_VERTEX) {
      var->type = glsl_type::error_type;
      _mesa_glsl_error(loc, state,
                       "`attribute' variables may not be declared in the "
                       "%s shader",
                       _mesa_shader_stage_to_string(state->stage));
   }

   /* Disallow layout qualifiers which may only appear on layout declarations. */
   if (qual->flags.q.prim_type) {
      _mesa_glsl_error(loc, state,
                       "Primitive type may only be specified on GS input or output "
                       "layout declaration, not on variables.");
   }

   /* Section 6.1.1 (Function Calling Conventions) of the GLSL 1.10 spec says:
    *
    *     "However, the const qualifier cannot be used with out or inout."
    *
    * The same section of the GLSL 4.40 spec further clarifies this saying:
    *
    *     "The const qualifier cannot be used with out or inout, or a
    *     compile-time error results."
    */
   if (is_parameter && qual->flags.q.constant && qual->flags.q.out) {
      _mesa_glsl_error(loc, state,
                       "`const' may not be applied to `out' or `inout' "
                       "function parameters");
   }

   /* If there is no qualifier that changes the mode of the variable, leave
    * the setting alone.
    */
   if (qual->flags.q.in && qual->flags.q.out)
      var->data.mode = ir_var_function_inout;
   else if (qual->flags.q.in)
      var->data.mode = is_parameter ? ir_var_function_in : ir_var_shader_in;
   else if (qual->flags.q.attribute
	    || (qual->flags.q.varying && (state->stage == MESA_SHADER_FRAGMENT)))
      var->data.mode = ir_var_shader_in;
   else if (qual->flags.q.out)
      var->data.mode = is_parameter ? ir_var_function_out : ir_var_shader_out;
   else if (qual->flags.q.varying && (state->stage == MESA_SHADER_VERTEX))
      var->data.mode = ir_var_shader_out;
   else if (qual->flags.q.uniform)
      var->data.mode = ir_var_uniform;

   if (!is_parameter && is_varying_var(var, state->stage)) {
      /* User-defined ins/outs are not permitted in compute shaders. */
      if (state->stage == MESA_SHADER_COMPUTE) {
         _mesa_glsl_error(loc, state,
                          "user-defined input and output variables are not "
                          "permitted in compute shaders");
      }

      /* This variable is being used to link data between shader stages (in
       * pre-glsl-1.30 parlance, it's a "varying").  Check that it has a type
       * that is allowed for such purposes.
       *
       * From page 25 (page 31 of the PDF) of the GLSL 1.10 spec:
       *
       *     "The varying qualifier can be used only with the data types
       *     float, vec2, vec3, vec4, mat2, mat3, and mat4, or arrays of
       *     these."
       *
       * This was relaxed in GLSL version 1.30 and GLSL ES version 3.00.  From
       * page 31 (page 37 of the PDF) of the GLSL 1.30 spec:
       *
       *     "Fragment inputs can only be signed and unsigned integers and
       *     integer vectors, float, floating-point vectors, matrices, or
       *     arrays of these. Structures cannot be input.
       *
       * Similar text exists in the section on vertex shader outputs.
       *
       * Similar text exists in the GLSL ES 3.00 spec, except that the GLSL ES
       * 3.00 spec allows structs as well.  Varying structs are also allowed
       * in GLSL 1.50.
       */
      switch (var->type->get_scalar_type()->base_type) {
      case GLSL_TYPE_FLOAT:
         /* Ok in all GLSL versions */
         break;
      case GLSL_TYPE_UINT:
      case GLSL_TYPE_INT:
         if (state->is_version(130, 300))
            break;
         _mesa_glsl_error(loc, state,
                          "varying variables must be of base type float in %s",
                          state->get_version_string());
         break;
      case GLSL_TYPE_STRUCT:
         if (state->is_version(150, 300))
            break;
         _mesa_glsl_error(loc, state,
                          "varying variables may not be of type struct");
         break;
      default:
         _mesa_glsl_error(loc, state, "illegal type for a varying variable");
         break;
      }
   }

   if (state->all_invariant && (state->current_function == NULL)) {
      switch (state->stage) {
      case MESA_SHADER_VERTEX:
         if (var->data.mode == ir_var_shader_out)
            var->data.invariant = true;
	      break;
      case MESA_SHADER_GEOMETRY:
         if ((var->data.mode == ir_var_shader_in)
             || (var->data.mode == ir_var_shader_out))
            var->data.invariant = true;
         break;
      case MESA_SHADER_FRAGMENT:
         if (var->data.mode == ir_var_shader_in)
            var->data.invariant = true;
         break;
      case MESA_SHADER_COMPUTE:
         /* Invariance isn't meaningful in compute shaders. */
         break;
      }
   }

   var->data.interpolation =
      interpret_interpolation_qualifier(qual, (ir_variable_mode) var->data.mode,
                                        state, loc);

   var->data.pixel_center_integer = qual->flags.q.pixel_center_integer;
   var->data.origin_upper_left = qual->flags.q.origin_upper_left;
   if ((qual->flags.q.origin_upper_left || qual->flags.q.pixel_center_integer)
       && (strcmp(var->name, "gl_FragCoord") != 0)) {
      const char *const qual_string = (qual->flags.q.origin_upper_left)
         ? "origin_upper_left" : "pixel_center_integer";

      _mesa_glsl_error(loc, state,
		       "layout qualifier `%s' can only be applied to "
		       "fragment shader input `gl_FragCoord'",
		       qual_string);
   }

   if (var->name != NULL && strcmp(var->name, "gl_FragCoord") == 0) {

      /* Section 4.3.8.1, page 39 of GLSL 1.50 spec says:
       *
       *    "Within any shader, the first redeclarations of gl_FragCoord
       *     must appear before any use of gl_FragCoord."
       *
       * Generate a compiler error if above condition is not met by the
       * fragment shader.
       */
      ir_variable *earlier = state->symbols->get_variable("gl_FragCoord");
      if (earlier != NULL &&
          earlier->data.used &&
          !state->fs_redeclares_gl_fragcoord) {
         _mesa_glsl_error(loc, state,
                          "gl_FragCoord used before its first redeclaration "
                          "in fragment shader");
      }

      /* Make sure all gl_FragCoord redeclarations specify the same layout
       * qualifiers.
       */
      if (is_conflicting_fragcoord_redeclaration(state, qual)) {
         const char *const qual_string =
            get_layout_qualifier_string(qual->flags.q.origin_upper_left,
                                        qual->flags.q.pixel_center_integer);

         const char *const state_string =
            get_layout_qualifier_string(state->fs_origin_upper_left,
                                        state->fs_pixel_center_integer);

         _mesa_glsl_error(loc, state,
                          "gl_FragCoord redeclared with different layout "
                          "qualifiers (%s) and (%s) ",
                          state_string,
                          qual_string);
      }
      state->fs_origin_upper_left = qual->flags.q.origin_upper_left;
      state->fs_pixel_center_integer = qual->flags.q.pixel_center_integer;
      state->fs_redeclares_gl_fragcoord_with_no_layout_qualifiers =
         !qual->flags.q.origin_upper_left && !qual->flags.q.pixel_center_integer;
      state->fs_redeclares_gl_fragcoord =
         state->fs_origin_upper_left ||
         state->fs_pixel_center_integer ||
         state->fs_redeclares_gl_fragcoord_with_no_layout_qualifiers;
   }

   if (qual->flags.q.explicit_location) {
      validate_explicit_location(qual, var, state, loc);
   } else if (qual->flags.q.explicit_index) {
      _mesa_glsl_error(loc, state, "explicit index requires explicit location");
   }

   if (qual->flags.q.explicit_binding &&
       validate_binding_qualifier(state, loc, var, qual)) {
      var->data.explicit_binding = true;
      var->data.binding = qual->binding;
   }

   if (var->type->contains_atomic()) {
      if (var->data.mode == ir_var_uniform) {
         if (var->data.explicit_binding) {
            unsigned *offset =
               &state->atomic_counter_offsets[var->data.binding];

            if (*offset % ATOMIC_COUNTER_SIZE)
               _mesa_glsl_error(loc, state,
                                "misaligned atomic counter offset");

            var->data.atomic.offset = *offset;
            *offset += var->type->atomic_size();

         } else {
            _mesa_glsl_error(loc, state,
                             "atomic counters require explicit binding point");
         }
      } else if (var->data.mode != ir_var_function_in) {
         _mesa_glsl_error(loc, state, "atomic counters may only be declared as "
                          "function parameters or uniform-qualified "
                          "global variables");
      }
   }

   /* Does the declaration use the deprecated 'attribute' or 'varying'
    * keywords?
    */
   const bool uses_deprecated_qualifier = qual->flags.q.attribute
      || qual->flags.q.varying;


   /* Validate auxiliary storage qualifiers */

   /* From section 4.3.4 of the GLSL 1.30 spec:
    *    "It is an error to use centroid in in a vertex shader."
    *
    * From section 4.3.4 of the GLSL ES 3.00 spec:
    *    "It is an error to use centroid in or interpolation qualifiers in
    *    a vertex shader input."
    */

   /* Section 4.3.6 of the GLSL 1.30 specification states:
    * "It is an error to use centroid out in a fragment shader."
    *
    * The GL_ARB_shading_language_420pack extension specification states:
    * "It is an error to use auxiliary storage qualifiers or interpolation
    *  qualifiers on an output in a fragment shader."
    */
   if (qual->flags.q.sample && (!is_varying_var(var, state->stage) || uses_deprecated_qualifier)) {
      _mesa_glsl_error(loc, state,
                       "sample qualifier may only be used on `in` or `out` "
                       "variables between shader stages");
   }
   if (qual->flags.q.centroid && !is_varying_var(var, state->stage)) {
      _mesa_glsl_error(loc, state,
                       "centroid qualifier may only be used with `in', "
                       "`out' or `varying' variables between shader stages");
   }


   /* Is the 'layout' keyword used with parameters that allow relaxed checking.
    * Many implementations of GL_ARB_fragment_coord_conventions_enable and some
    * implementations (only Mesa?) GL_ARB_explicit_attrib_location_enable
    * allowed the layout qualifier to be used with 'varying' and 'attribute'.
    * These extensions and all following extensions that add the 'layout'
    * keyword have been modified to require the use of 'in' or 'out'.
    *
    * The following extension do not allow the deprecated keywords:
    *
    *    GL_AMD_conservative_depth
    *    GL_ARB_conservative_depth
    *    GL_ARB_gpu_shader5
    *    GL_ARB_separate_shader_objects
    *    GL_ARB_tesselation_shader
    *    GL_ARB_transform_feedback3
    *    GL_ARB_uniform_buffer_object
    *
    * It is unknown whether GL_EXT_shader_image_load_store or GL_NV_gpu_shader5
    * allow layout with the deprecated keywords.
    */
   const bool relaxed_layout_qualifier_checking =
      state->ARB_fragment_coord_conventions_enable;

   if (qual->has_layout() && uses_deprecated_qualifier) {
      if (relaxed_layout_qualifier_checking) {
         _mesa_glsl_warning(loc, state,
                            "`layout' qualifier may not be used with "
                            "`attribute' or `varying'");
      } else {
         _mesa_glsl_error(loc, state,
                          "`layout' qualifier may not be used with "
                          "`attribute' or `varying'");
      }
   }

   /* Layout qualifiers for gl_FragDepth, which are enabled by extension
    * AMD_conservative_depth.
    */
   int depth_layout_count = qual->flags.q.depth_any
      + qual->flags.q.depth_greater
      + qual->flags.q.depth_less
      + qual->flags.q.depth_unchanged;
   if (depth_layout_count > 0
       && !state->AMD_conservative_depth_enable
       && !state->ARB_conservative_depth_enable) {
       _mesa_glsl_error(loc, state,
                        "extension GL_AMD_conservative_depth or "
                        "GL_ARB_conservative_depth must be enabled "
                        "to use depth layout qualifiers");
   } else if (depth_layout_count > 0
              && strcmp(var->name, "gl_FragDepth") != 0) {
       _mesa_glsl_error(loc, state,
                        "depth layout qualifiers can be applied only to "
                        "gl_FragDepth");
   } else if (depth_layout_count > 1
              && strcmp(var->name, "gl_FragDepth") == 0) {
      _mesa_glsl_error(loc, state,
                       "at most one depth layout qualifier can be applied to "
                       "gl_FragDepth");
   }
   if (qual->flags.q.depth_any)
      var->data.depth_layout = ir_depth_layout_any;
   else if (qual->flags.q.depth_greater)
      var->data.depth_layout = ir_depth_layout_greater;
   else if (qual->flags.q.depth_less)
      var->data.depth_layout = ir_depth_layout_less;
   else if (qual->flags.q.depth_unchanged)
       var->data.depth_layout = ir_depth_layout_unchanged;
   else
       var->data.depth_layout = ir_depth_layout_none;

   if (qual->flags.q.std140 ||
       qual->flags.q.packed ||
       qual->flags.q.shared) {
      _mesa_glsl_error(loc, state,
                       "uniform block layout qualifiers std140, packed, and "
                       "shared can only be applied to uniform blocks, not "
                       "members");
   }

   if (qual->flags.q.row_major || qual->flags.q.column_major) {
      validate_matrix_layout_for_type(state, loc, var->type, var);
   }

   if (var->type->contains_image())
      apply_image_qualifier_to_variable(qual, var, state, loc);
}

/**
 * Get the variable that is being redeclared by this declaration
 *
 * Semantic checks to verify the validity of the redeclaration are also
 * performed.  If semantic checks fail, compilation error will be emitted via
 * \c _mesa_glsl_error, but a non-\c NULL pointer will still be returned.
 *
 * \returns
 * A pointer to an existing variable in the current scope if the declaration
 * is a redeclaration, \c NULL otherwise.
 */
static ir_variable *
get_variable_being_redeclared(ir_variable *var, YYLTYPE loc,
                              struct _mesa_glsl_parse_state *state,
                              bool allow_all_redeclarations)
{
   /* Check if this declaration is actually a re-declaration, either to
    * resize an array or add qualifiers to an existing variable.
    *
    * This is allowed for variables in the current scope, or when at
    * global scope (for built-ins in the implicit outer scope).
    */
   ir_variable *earlier = state->symbols->get_variable(var->name);
   if (earlier == NULL ||
       (state->current_function != NULL &&
       !state->symbols->name_declared_this_scope(var->name))) {
      return NULL;
   }


   /* From page 24 (page 30 of the PDF) of the GLSL 1.50 spec,
    *
    * "It is legal to declare an array without a size and then
    *  later re-declare the same name as an array of the same
    *  type and specify a size."
    */
   if (earlier->type->is_unsized_array() && var->type->is_array()
       && (var->type->element_type() == earlier->type->element_type())) {
      /* FINISHME: This doesn't match the qualifiers on the two
       * FINISHME: declarations.  It's not 100% clear whether this is
       * FINISHME: required or not.
       */

      const unsigned size = unsigned(var->type->array_size());
      check_builtin_array_max_size(var->name, size, loc, state);
      if ((size > 0) && (size <= earlier->data.max_array_access)) {
         _mesa_glsl_error(& loc, state, "array size must be > %u due to "
                          "previous access",
                          earlier->data.max_array_access);
      }

      earlier->type = var->type;
      delete var;
      var = NULL;
   } else if ((state->ARB_fragment_coord_conventions_enable ||
              state->is_version(150, 0))
              && strcmp(var->name, "gl_FragCoord") == 0
              && earlier->type == var->type
              && earlier->data.mode == var->data.mode) {
      /* Allow redeclaration of gl_FragCoord for ARB_fcc layout
       * qualifiers.
       */
      earlier->data.origin_upper_left = var->data.origin_upper_left;
      earlier->data.pixel_center_integer = var->data.pixel_center_integer;

      /* According to section 4.3.7 of the GLSL 1.30 spec,
       * the following built-in varaibles can be redeclared with an
       * interpolation qualifier:
       *    * gl_FrontColor
       *    * gl_BackColor
       *    * gl_FrontSecondaryColor
       *    * gl_BackSecondaryColor
       *    * gl_Color
       *    * gl_SecondaryColor
       */
   } else if (state->is_version(130, 0)
              && (strcmp(var->name, "gl_FrontColor") == 0
                  || strcmp(var->name, "gl_BackColor") == 0
                  || strcmp(var->name, "gl_FrontSecondaryColor") == 0
                  || strcmp(var->name, "gl_BackSecondaryColor") == 0
                  || strcmp(var->name, "gl_Color") == 0
                  || strcmp(var->name, "gl_SecondaryColor") == 0)
              && earlier->type == var->type
              && earlier->data.mode == var->data.mode) {
      earlier->data.interpolation = var->data.interpolation;

      /* Layout qualifiers for gl_FragDepth. */
   } else if ((state->AMD_conservative_depth_enable ||
               state->ARB_conservative_depth_enable)
              && strcmp(var->name, "gl_FragDepth") == 0
              && earlier->type == var->type
              && earlier->data.mode == var->data.mode) {

      /** From the AMD_conservative_depth spec:
       *     Within any shader, the first redeclarations of gl_FragDepth
       *     must appear before any use of gl_FragDepth.
       */
      if (earlier->data.used) {
         _mesa_glsl_error(&loc, state,
                          "the first redeclaration of gl_FragDepth "
                          "must appear before any use of gl_FragDepth");
      }

      /* Prevent inconsistent redeclaration of depth layout qualifier. */
      if (earlier->data.depth_layout != ir_depth_layout_none
          && earlier->data.depth_layout != var->data.depth_layout) {
            _mesa_glsl_error(&loc, state,
                             "gl_FragDepth: depth layout is declared here "
                             "as '%s, but it was previously declared as "
                             "'%s'",
                             depth_layout_string(var->data.depth_layout),
                             depth_layout_string(earlier->data.depth_layout));
      }

      earlier->data.depth_layout = var->data.depth_layout;

   } else if (allow_all_redeclarations) {
      if (earlier->data.mode != var->data.mode) {
         _mesa_glsl_error(&loc, state,
                          "redeclaration of `%s' with incorrect qualifiers",
                          var->name);
      } else if (earlier->type != var->type) {
         _mesa_glsl_error(&loc, state,
                          "redeclaration of `%s' has incorrect type",
                          var->name);
      }
   } else {
      _mesa_glsl_error(&loc, state, "`%s' redeclared", var->name);
   }

   return earlier;
}

/**
 * Generate the IR for an initializer in a variable declaration
 */
ir_rvalue *
process_initializer(ir_variable *var, ast_declaration *decl,
		    ast_fully_specified_type *type,
		    exec_list *initializer_instructions,
		    struct _mesa_glsl_parse_state *state)
{
   ir_rvalue *result = NULL;

   YYLTYPE initializer_loc = decl->initializer->get_location();

   /* From page 24 (page 30 of the PDF) of the GLSL 1.10 spec:
    *
    *    "All uniform variables are read-only and are initialized either
    *    directly by an application via API commands, or indirectly by
    *    OpenGL."
    */
   if (var->data.mode == ir_var_uniform) {
      state->check_version(120, 0, &initializer_loc,
                           "cannot initialize uniforms");
   }

   /* From section 4.1.7 of the GLSL 4.40 spec:
    *
    *    "Opaque variables [...] are initialized only through the
    *     OpenGL API; they cannot be declared with an initializer in a
    *     shader."
    */
   if (var->type->contains_opaque()) {
      _mesa_glsl_error(& initializer_loc, state,
                       "cannot initialize opaque variable");
   }

   if ((var->data.mode == ir_var_shader_in) && (state->current_function == NULL)) {
      _mesa_glsl_error(& initializer_loc, state,
		       "cannot initialize %s shader input / %s",
		       _mesa_shader_stage_to_string(state->stage),
		       (state->stage == MESA_SHADER_VERTEX)
		       ? "attribute" : "varying");
   }

   /* If the initializer is an ast_aggregate_initializer, recursively store
    * type information from the LHS into it, so that its hir() function can do
    * type checking.
    */
   if (decl->initializer->oper == ast_aggregate)
      _mesa_ast_set_aggregate_type(var->type, decl->initializer);

   ir_dereference *const lhs = new(state) ir_dereference_variable(var);
   ir_rvalue *rhs = decl->initializer->hir(initializer_instructions, state);

   /* Calculate the constant value if this is a const or uniform
    * declaration.
    */
   if (type->qualifier.flags.q.constant
       || type->qualifier.flags.q.uniform) {
      ir_rvalue *new_rhs = validate_assignment(state, initializer_loc,
                                               var->type, rhs, true);
      if (new_rhs != NULL) {
         rhs = new_rhs;

         ir_constant *constant_value = rhs->constant_expression_value();
         if (!constant_value) {
            /* If ARB_shading_language_420pack is enabled, initializers of
             * const-qualified local variables do not have to be constant
             * expressions. Const-qualified global variables must still be
             * initialized with constant expressions.
             */
            if (!state->ARB_shading_language_420pack_enable
                || state->current_function == NULL) {
               _mesa_glsl_error(& initializer_loc, state,
                                "initializer of %s variable `%s' must be a "
                                "constant expression",
                                (type->qualifier.flags.q.constant)
                                ? "const" : "uniform",
                                decl->identifier);
               if (var->type->is_numeric()) {
                  /* Reduce cascading errors. */
                  var->constant_value = ir_constant::zero(state, var->type);
               }
            }
         } else {
            rhs = constant_value;
            var->constant_value = constant_value;
         }
      } else {
         if (var->type->is_numeric()) {
            /* Reduce cascading errors. */
            var->constant_value = ir_constant::zero(state, var->type);
         }
      }
   }

   if (rhs && !rhs->type->is_error()) {
      bool temp = var->data.read_only;
      if (type->qualifier.flags.q.constant)
         var->data.read_only = false;

      /* Never emit code to initialize a uniform.
       */
      const glsl_type *initializer_type;
      if (!type->qualifier.flags.q.uniform) {
         do_assignment(initializer_instructions, state,
                       NULL,
                       lhs, rhs,
                       &result, true,
                       true,
                       type->get_location());
         initializer_type = result->type;
      } else
         initializer_type = rhs->type;

      var->constant_initializer = rhs->constant_expression_value();
      var->data.has_initializer = true;

      /* If the declared variable is an unsized array, it must inherrit
       * its full type from the initializer.  A declaration such as
       *
       *     uniform float a[] = float[](1.0, 2.0, 3.0, 3.0);
       *
       * becomes
       *
       *     uniform float a[4] = float[](1.0, 2.0, 3.0, 3.0);
       *
       * The assignment generated in the if-statement (below) will also
       * automatically handle this case for non-uniforms.
       *
       * If the declared variable is not an array, the types must
       * already match exactly.  As a result, the type assignment
       * here can be done unconditionally.  For non-uniforms the call
       * to do_assignment can change the type of the initializer (via
       * the implicit conversion rules).  For uniforms the initializer
       * must be a constant expression, and the type of that expression
       * was validated above.
       */
      var->type = initializer_type;

      var->data.read_only = temp;
   }

   return result;
}


/**
 * Do additional processing necessary for geometry shader input declarations
 * (this covers both interface blocks arrays and bare input variables).
 */
static void
handle_geometry_shader_input_decl(struct _mesa_glsl_parse_state *state,
                                  YYLTYPE loc, ir_variable *var)
{
   unsigned num_vertices = 0;
   if (state->gs_input_prim_type_specified) {
      num_vertices = vertices_per_prim(state->in_qualifier->prim_type);
   }

   /* Geometry shader input variables must be arrays.  Caller should have
    * reported an error for this.
    */
   if (!var->type->is_array()) {
      assert(state->error);

      /* To avoid cascading failures, short circuit the checks below. */
      return;
   }

   if (var->type->is_unsized_array()) {
      /* Section 4.3.8.1 (Input Layout Qualifiers) of the GLSL 1.50 spec says:
       *
       *   All geometry shader input unsized array declarations will be
       *   sized by an earlier input layout qualifier, when present, as per
       *   the following table.
       *
       * Followed by a table mapping each allowed input layout qualifier to
       * the corresponding input length.
       */
      if (num_vertices != 0)
         var->type = glsl_type::get_array_instance(var->type->fields.array,
                                                   num_vertices);
   } else {
      /* Section 4.3.8.1 (Input Layout Qualifiers) of the GLSL 1.50 spec
       * includes the following examples of compile-time errors:
       *
       *   // code sequence within one shader...
       *   in vec4 Color1[];    // size unknown
       *   ...Color1.length()...// illegal, length() unknown
       *   in vec4 Color2[2];   // size is 2
       *   ...Color1.length()...// illegal, Color1 still has no size
       *   in vec4 Color3[3];   // illegal, input sizes are inconsistent
       *   layout(lines) in;    // legal, input size is 2, matching
       *   in vec4 Color4[3];   // illegal, contradicts layout
       *   ...
       *
       * To detect the case illustrated by Color3, we verify that the size of
       * an explicitly-sized array matches the size of any previously declared
       * explicitly-sized array.  To detect the case illustrated by Color4, we
       * verify that the size of an explicitly-sized array is consistent with
       * any previously declared input layout.
       */
      if (num_vertices != 0 && var->type->length != num_vertices) {
         _mesa_glsl_error(&loc, state,
                          "geometry shader input size contradicts previously"
                          " declared layout (size is %u, but layout requires a"
                          " size of %u)", var->type->length, num_vertices);
      } else if (state->gs_input_size != 0 &&
                 var->type->length != state->gs_input_size) {
         _mesa_glsl_error(&loc, state,
                          "geometry shader input sizes are "
                          "inconsistent (size is %u, but a previous "
                          "declaration has size %u)",
                          var->type->length, state->gs_input_size);
      } else {
         state->gs_input_size = var->type->length;
      }
   }
}


void
validate_identifier(const char *identifier, YYLTYPE loc,
                    struct _mesa_glsl_parse_state *state)
{
   /* From page 15 (page 21 of the PDF) of the GLSL 1.10 spec,
    *
    *   "Identifiers starting with "gl_" are reserved for use by
    *   OpenGL, and may not be declared in a shader as either a
    *   variable or a function."
    */
   if (is_gl_identifier(identifier)) {
      _mesa_glsl_error(&loc, state,
                       "identifier `%s' uses reserved `gl_' prefix",
                       identifier);
   } else if (strstr(identifier, "__")) {
      /* From page 14 (page 20 of the PDF) of the GLSL 1.10
       * spec:
       *
       *     "In addition, all identifiers containing two
       *      consecutive underscores (__) are reserved as
       *      possible future keywords."
       *
       * The intention is that names containing __ are reserved for internal
       * use by the implementation, and names prefixed with GL_ are reserved
       * for use by Khronos.  Names simply containing __ are dangerous to use,
       * but should be allowed.
       *
       * A future version of the GLSL specification will clarify this.
       */
      _mesa_glsl_warning(&loc, state,
                         "identifier `%s' uses reserved `__' string",
                         identifier);
   }
}


ir_rvalue *
ast_declarator_list::hir(exec_list *instructions,
                         struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;
   const struct glsl_type *decl_type;
   const char *type_name = NULL;
   ir_rvalue *result = NULL;
   YYLTYPE loc = this->get_location();

   /* From page 46 (page 52 of the PDF) of the GLSL 1.50 spec:
    *
    *     "To ensure that a particular output variable is invariant, it is
    *     necessary to use the invariant qualifier. It can either be used to
    *     qualify a previously declared variable as being invariant
    *
    *         invariant gl_Position; // make existing gl_Position be invariant"
    *
    * In these cases the parser will set the 'invariant' flag in the declarator
    * list, and the type will be NULL.
    */
   if (this->invariant) {
      assert(this->type == NULL);

      if (state->current_function != NULL) {
         _mesa_glsl_error(& loc, state,
                          "all uses of `invariant' keyword must be at global "
                          "scope");
      }

      foreach_list_typed (ast_declaration, decl, link, &this->declarations) {
         assert(decl->array_specifier == NULL);
         assert(decl->initializer == NULL);

         ir_variable *const earlier =
            state->symbols->get_variable(decl->identifier);
         if (earlier == NULL) {
            _mesa_glsl_error(& loc, state,
                             "undeclared variable `%s' cannot be marked "
                             "invariant", decl->identifier);
         } else if (!is_varying_var(earlier, state->stage)) {
            _mesa_glsl_error(&loc, state,
                             "`%s' cannot be marked invariant; interfaces between "
                             "shader stages only.", decl->identifier);
         } else if (earlier->data.used) {
            _mesa_glsl_error(& loc, state,
                            "variable `%s' may not be redeclared "
                            "`invariant' after being used",
                            earlier->name);
         } else {
            earlier->data.invariant = true;
         }
      }

      /* Invariant redeclarations do not have r-values.
       */
      return NULL;
   }

   if (this->precise) {
      assert(this->type == NULL);

      foreach_list_typed (ast_declaration, decl, link, &this->declarations) {
         assert(decl->array_specifier == NULL);
         assert(decl->initializer == NULL);

         ir_variable *const earlier =
            state->symbols->get_variable(decl->identifier);
         if (earlier == NULL) {
            _mesa_glsl_error(& loc, state,
                             "undeclared variable `%s' cannot be marked "
                             "precise", decl->identifier);
         } else if (state->current_function != NULL &&
                    !state->symbols->name_declared_this_scope(decl->identifier)) {
            /* Note: we have to check if we're in a function, since
             * builtins are treated as having come from another scope.
             */
            _mesa_glsl_error(& loc, state,
                             "variable `%s' from an outer scope may not be "
                             "redeclared `precise' in this scope",
                             earlier->name);
         } else if (earlier->data.used) {
            _mesa_glsl_error(& loc, state,
                             "variable `%s' may not be redeclared "
                             "`precise' after being used",
                             earlier->name);
         } else {
            earlier->data.precise = true;
         }
      }

      /* Precise redeclarations do not have r-values either. */
      return NULL;
   }

   assert(this->type != NULL);
   assert(!this->invariant);
   assert(!this->precise);

   /* The type specifier may contain a structure definition.  Process that
    * before any of the variable declarations.
    */
   (void) this->type->specifier->hir(instructions, state);

   decl_type = this->type->glsl_type(& type_name, state);

   /* An offset-qualified atomic counter declaration sets the default
    * offset for the next declaration within the same atomic counter
    * buffer.
    */
   if (decl_type && decl_type->contains_atomic()) {
      if (type->qualifier.flags.q.explicit_binding &&
          type->qualifier.flags.q.explicit_offset)
         state->atomic_counter_offsets[type->qualifier.binding] =
            type->qualifier.offset;
   }

   if (this->declarations.is_empty()) {
      /* If there is no structure involved in the program text, there are two
       * possible scenarios:
       *
       * - The program text contained something like 'vec4;'.  This is an
       *   empty declaration.  It is valid but weird.  Emit a warning.
       *
       * - The program text contained something like 'S;' and 'S' is not the
       *   name of a known structure type.  This is both invalid and weird.
       *   Emit an error.
       *
       * - The program text contained something like 'mediump float;'
       *   when the programmer probably meant 'precision mediump
       *   float;' Emit a warning with a description of what they
       *   probably meant to do.
       *
       * Note that if decl_type is NULL and there is a structure involved,
       * there must have been some sort of error with the structure.  In this
       * case we assume that an error was already generated on this line of
       * code for the structure.  There is no need to generate an additional,
       * confusing error.
       */
      assert(this->type->specifier->structure == NULL || decl_type != NULL
	     || state->error);

      if (decl_type == NULL) {
         _mesa_glsl_error(&loc, state,
                          "invalid type `%s' in empty declaration",
                          type_name);
      } else if (decl_type->base_type == GLSL_TYPE_ATOMIC_UINT) {
         /* Empty atomic counter declarations are allowed and useful
          * to set the default offset qualifier.
          */
         return NULL;
      } else if (this->type->qualifier.precision != ast_precision_none) {
         if (this->type->specifier->structure != NULL) {
            _mesa_glsl_error(&loc, state,
                             "precision qualifiers can't be applied "
                             "to structures");
         } else {
            static const char *const precision_names[] = {
               "highp",
               "highp",
               "mediump",
               "lowp"
            };

            _mesa_glsl_warning(&loc, state,
                               "empty declaration with precision qualifier, "
                               "to set the default precision, use "
                               "`precision %s %s;'",
                               precision_names[this->type->qualifier.precision],
                               type_name);
         }
      } else if (this->type->specifier->structure == NULL) {
         _mesa_glsl_warning(&loc, state, "empty declaration");
      }
   }

   foreach_list_typed (ast_declaration, decl, link, &this->declarations) {
      const struct glsl_type *var_type;
      ir_variable *var;

      /* FINISHME: Emit a warning if a variable declaration shadows a
       * FINISHME: declaration at a higher scope.
       */

      if ((decl_type == NULL) || decl_type->is_void()) {
         if (type_name != NULL) {
            _mesa_glsl_error(& loc, state,
                             "invalid type `%s' in declaration of `%s'",
                             type_name, decl->identifier);
         } else {
            _mesa_glsl_error(& loc, state,
                             "invalid type in declaration of `%s'",
                             decl->identifier);
         }
         continue;
      }

      var_type = process_array_type(&loc, decl_type, decl->array_specifier,
                                    state);

      var = new(ctx) ir_variable(var_type, decl->identifier, ir_var_auto);

      /* The 'varying in' and 'varying out' qualifiers can only be used with
       * ARB_geometry_shader4 and EXT_geometry_shader4, which we don't support
       * yet.
       */
      if (this->type->qualifier.flags.q.varying) {
         if (this->type->qualifier.flags.q.in) {
            _mesa_glsl_error(& loc, state,
                             "`varying in' qualifier in declaration of "
                             "`%s' only valid for geometry shaders using "
                             "ARB_geometry_shader4 or EXT_geometry_shader4",
                             decl->identifier);
         } else if (this->type->qualifier.flags.q.out) {
            _mesa_glsl_error(& loc, state,
                             "`varying out' qualifier in declaration of "
                             "`%s' only valid for geometry shaders using "
                             "ARB_geometry_shader4 or EXT_geometry_shader4",
                             decl->identifier);
         }
      }

      /* From page 22 (page 28 of the PDF) of the GLSL 1.10 specification;
       *
       *     "Global variables can only use the qualifiers const,
       *     attribute, uniform, or varying. Only one may be
       *     specified.
       *
       *     Local variables can only use the qualifier const."
       *
       * This is relaxed in GLSL 1.30 and GLSL ES 3.00.  It is also relaxed by
       * any extension that adds the 'layout' keyword.
       */
      if (!state->is_version(130, 300)
          && !state->has_explicit_attrib_location()
          && !state->has_separate_shader_objects()
          && !state->ARB_fragment_coord_conventions_enable) {
         if (this->type->qualifier.flags.q.out) {
            _mesa_glsl_error(& loc, state,
                             "`out' qualifier in declaration of `%s' "
                             "only valid for function parameters in %s",
                             decl->identifier, state->get_version_string());
         }
         if (this->type->qualifier.flags.q.in) {
            _mesa_glsl_error(& loc, state,
                             "`in' qualifier in declaration of `%s' "
                             "only valid for function parameters in %s",
                             decl->identifier, state->get_version_string());
         }
         /* FINISHME: Test for other invalid qualifiers. */
      }

      apply_type_qualifier_to_variable(& this->type->qualifier, var, state,
				       & loc, false);

      if (this->type->qualifier.flags.q.invariant) {
         if (!is_varying_var(var, state->stage)) {
            _mesa_glsl_error(&loc, state,
                             "`%s' cannot be marked invariant; interfaces between "
                             "shader stages only", var->name);
         }
      }

      if (state->current_function != NULL) {
         const char *mode = NULL;
         const char *extra = "";

         /* There is no need to check for 'inout' here because the parser will
          * only allow that in function parameter lists.
          */
         if (this->type->qualifier.flags.q.attribute) {
            mode = "attribute";
         } else if (this->type->qualifier.flags.q.uniform) {
            mode = "uniform";
         } else if (this->type->qualifier.flags.q.varying) {
            mode = "varying";
         } else if (this->type->qualifier.flags.q.in) {
            mode = "in";
            extra = " or in function parameter list";
         } else if (this->type->qualifier.flags.q.out) {
            mode = "out";
            extra = " or in function parameter list";
         }

         if (mode) {
            _mesa_glsl_error(& loc, state,
                             "%s variable `%s' must be declared at "
                             "global scope%s",
                             mode, var->name, extra);
         }
      } else if (var->data.mode == ir_var_shader_in) {
         var->data.read_only = true;

         if (state->stage == MESA_SHADER_VERTEX) {
            bool error_emitted = false;

            /* From page 31 (page 37 of the PDF) of the GLSL 1.50 spec:
             *
             *    "Vertex shader inputs can only be float, floating-point
             *    vectors, matrices, signed and unsigned integers and integer
             *    vectors. Vertex shader inputs can also form arrays of these
             *    types, but not structures."
             *
             * From page 31 (page 27 of the PDF) of the GLSL 1.30 spec:
             *
             *    "Vertex shader inputs can only be float, floating-point
             *    vectors, matrices, signed and unsigned integers and integer
             *    vectors. They cannot be arrays or structures."
             *
             * From page 23 (page 29 of the PDF) of the GLSL 1.20 spec:
             *
             *    "The attribute qualifier can be used only with float,
             *    floating-point vectors, and matrices. Attribute variables
             *    cannot be declared as arrays or structures."
             *
             * From page 33 (page 39 of the PDF) of the GLSL ES 3.00 spec:
             *
             *    "Vertex shader inputs can only be float, floating-point
             *    vectors, matrices, signed and unsigned integers and integer
             *    vectors. Vertex shader inputs cannot be arrays or
             *    structures."
             */
            const glsl_type *check_type = var->type;
            while (check_type->is_array())
               check_type = check_type->element_type();

            switch (check_type->base_type) {
            case GLSL_TYPE_FLOAT:
            break;
            case GLSL_TYPE_UINT:
            case GLSL_TYPE_INT:
               if (state->is_version(120, 300))
                  break;
            /* FALLTHROUGH */
            default:
               _mesa_glsl_error(& loc, state,
                                "vertex shader input / attribute cannot have "
                                "type %s`%s'",
                                var->type->is_array() ? "array of " : "",
                                check_type->name);
               error_emitted = true;
            }

            if (!error_emitted && var->type->is_array() &&
                !state->check_version(150, 0, &loc,
                                      "vertex shader input / attribute "
                                      "cannot have array type")) {
               error_emitted = true;
            }
         } else if (state->stage == MESA_SHADER_GEOMETRY) {
            /* From section 4.3.4 (Inputs) of the GLSL 1.50 spec:
             *
             *     Geometry shader input variables get the per-vertex values
             *     written out by vertex shader output variables of the same
             *     names. Since a geometry shader operates on a set of
             *     vertices, each input varying variable (or input block, see
             *     interface blocks below) needs to be declared as an array.
             */
            if (!var->type->is_array()) {
               _mesa_glsl_error(&loc, state,
                                "geometry shader inputs must be arrays");
            }

            handle_geometry_shader_input_decl(state, loc, var);
         }
      }

      /* Integer fragment inputs must be qualified with 'flat'.  In GLSL ES,
       * so must integer vertex outputs.
       *
       * From section 4.3.4 ("Inputs") of the GLSL 1.50 spec:
       *    "Fragment shader inputs that are signed or unsigned integers or
       *    integer vectors must be qualified with the interpolation qualifier
       *    flat."
       *
       * From section 4.3.4 ("Input Variables") of the GLSL 3.00 ES spec:
       *    "Fragment shader inputs that are, or contain, signed or unsigned
       *    integers or integer vectors must be qualified with the
       *    interpolation qualifier flat."
       *
       * From section 4.3.6 ("Output Variables") of the GLSL 3.00 ES spec:
       *    "Vertex shader outputs that are, or contain, signed or unsigned
       *    integers or integer vectors must be qualified with the
       *    interpolation qualifier flat."
       *
       * Note that prior to GLSL 1.50, this requirement applied to vertex
       * outputs rather than fragment inputs.  That creates problems in the
       * presence of geometry shaders, so we adopt the GLSL 1.50 rule for all
       * desktop GL shaders.  For GLSL ES shaders, we follow the spec and
       * apply the restriction to both vertex outputs and fragment inputs.
       *
       * Note also that the desktop GLSL specs are missing the text "or
       * contain"; this is presumably an oversight, since there is no
       * reasonable way to interpolate a fragment shader input that contains
       * an integer.
       */
      if (state->is_version(130, 300) &&
          var->type->contains_integer() &&
          var->data.interpolation != INTERP_QUALIFIER_FLAT &&
          ((state->stage == MESA_SHADER_FRAGMENT && var->data.mode == ir_var_shader_in)
           || (state->stage == MESA_SHADER_VERTEX && var->data.mode == ir_var_shader_out
               && state->es_shader))) {
         const char *var_type = (state->stage == MESA_SHADER_VERTEX) ?
            "vertex output" : "fragment input";
         _mesa_glsl_error(&loc, state, "if a %s is (or contains) "
                          "an integer, then it must be qualified with 'flat'",
                          var_type);
      }


      /* Interpolation qualifiers cannot be applied to 'centroid' and
       * 'centroid varying'.
       *
       * From page 29 (page 35 of the PDF) of the GLSL 1.30 spec:
       *    "interpolation qualifiers may only precede the qualifiers in,
       *    centroid in, out, or centroid out in a declaration. They do not apply
       *    to the deprecated storage qualifiers varying or centroid varying."
       *
       * These deprecated storage qualifiers do not exist in GLSL ES 3.00.
       */
      if (state->is_version(130, 0)
          && this->type->qualifier.has_interpolation()
          && this->type->qualifier.flags.q.varying) {

         const char *i = this->type->qualifier.interpolation_string();
         assert(i != NULL);
         const char *s;
         if (this->type->qualifier.flags.q.centroid)
            s = "centroid varying";
         else
            s = "varying";

         _mesa_glsl_error(&loc, state,
                          "qualifier '%s' cannot be applied to the "
                          "deprecated storage qualifier '%s'", i, s);
      }


      /* Interpolation qualifiers can only apply to vertex shader outputs and
       * fragment shader inputs.
       *
       * From page 29 (page 35 of the PDF) of the GLSL 1.30 spec:
       *    "Outputs from a vertex shader (out) and inputs to a fragment
       *    shader (in) can be further qualified with one or more of these
       *    interpolation qualifiers"
       *
       * From page 31 (page 37 of the PDF) of the GLSL ES 3.00 spec:
       *    "These interpolation qualifiers may only precede the qualifiers
       *    in, centroid in, out, or centroid out in a declaration. They do
       *    not apply to inputs into a vertex shader or outputs from a
       *    fragment shader."
       */
      if (state->is_version(130, 300)
          && this->type->qualifier.has_interpolation()) {

         const char *i = this->type->qualifier.interpolation_string();
         assert(i != NULL);

         switch (state->stage) {
         case MESA_SHADER_VERTEX:
            if (this->type->qualifier.flags.q.in) {
               _mesa_glsl_error(&loc, state,
                                "qualifier '%s' cannot be applied to vertex "
                                "shader inputs", i);
            }
            break;
         case MESA_SHADER_FRAGMENT:
            if (this->type->qualifier.flags.q.out) {
               _mesa_glsl_error(&loc, state,
                                "qualifier '%s' cannot be applied to fragment "
                                "shader outputs", i);
            }
            break;
         default:
            break;
         }
      }


      /* Precision qualifiers exists only in GLSL versions 1.00 and >= 1.30.
       */
      if (this->type->qualifier.precision != ast_precision_none) {
         state->check_precision_qualifiers_allowed(&loc);
      }


      /* Precision qualifiers apply to floating point, integer and sampler
       * types.
       *
       * Section 4.5.2 (Precision Qualifiers) of the GLSL 1.30 spec says:
       *    "Any floating point or any integer declaration can have the type
       *    preceded by one of these precision qualifiers [...] Literal
       *    constants do not have precision qualifiers. Neither do Boolean
       *    variables.
       *
       * Section 4.5 (Precision and Precision Qualifiers) of the GLSL 1.30
       * spec also says:
       *
       *     "Precision qualifiers are added for code portability with OpenGL
       *     ES, not for functionality. They have the same syntax as in OpenGL
       *     ES."
       *
       * Section 8 (Built-In Functions) of the GLSL ES 1.00 spec says:
       *
       *     "uniform lowp sampler2D sampler;
       *     highp vec2 coord;
       *     ...
       *     lowp vec4 col = texture2D (sampler, coord);
       *                                            // texture2D returns lowp"
       *
       * From this, we infer that GLSL 1.30 (and later) should allow precision
       * qualifiers on sampler types just like float and integer types.
       */
      if (this->type->qualifier.precision != ast_precision_none
          && !var->type->is_float()
          && !var->type->is_integer()
          && !var->type->is_record()
          && !var->type->is_sampler()
          && !(var->type->is_array()
               && (var->type->fields.array->is_float()
                   || var->type->fields.array->is_integer()))) {

         _mesa_glsl_error(&loc, state,
                          "precision qualifiers apply only to floating point"
                          ", integer and sampler types");
      }

      /* From section 4.1.7 of the GLSL 4.40 spec:
       *
       *    "[Opaque types] can only be declared as function
       *     parameters or uniform-qualified variables."
       */
      if (var_type->contains_opaque() &&
          !this->type->qualifier.flags.q.uniform) {
         _mesa_glsl_error(&loc, state,
                          "opaque variables must be declared uniform");
      }

      /* Process the initializer and add its instructions to a temporary
       * list.  This list will be added to the instruction stream (below) after
       * the declaration is added.  This is done because in some cases (such as
       * redeclarations) the declaration may not actually be added to the
       * instruction stream.
       */
      exec_list initializer_instructions;

      /* Examine var name here since var may get deleted in the next call */
      bool var_is_gl_id = is_gl_identifier(var->name);

      ir_variable *earlier =
         get_variable_being_redeclared(var, decl->get_location(), state,
                                       false /* allow_all_redeclarations */);
      if (earlier != NULL) {
         if (var_is_gl_id &&
             earlier->data.how_declared == ir_var_declared_in_block) {
            _mesa_glsl_error(&loc, state,
                             "`%s' has already been redeclared using "
                             "gl_PerVertex", var->name);
         }
         earlier->data.how_declared = ir_var_declared_normally;
      }

      if (decl->initializer != NULL) {
         result = process_initializer((earlier == NULL) ? var : earlier,
                                      decl, this->type,
                                      &initializer_instructions, state);
      }

      /* From page 23 (page 29 of the PDF) of the GLSL 1.10 spec:
       *
       *     "It is an error to write to a const variable outside of
       *      its declaration, so they must be initialized when
       *      declared."
       */
      if (this->type->qualifier.flags.q.constant && decl->initializer == NULL) {
         _mesa_glsl_error(& loc, state,
                          "const declaration of `%s' must be initialized",
                          decl->identifier);
      }

      if (state->es_shader) {
         const glsl_type *const t = (earlier == NULL)
            ? var->type : earlier->type;

         if (t->is_unsized_array())
            /* Section 10.17 of the GLSL ES 1.00 specification states that
             * unsized array declarations have been removed from the language.
             * Arrays that are sized using an initializer are still explicitly
             * sized.  However, GLSL ES 1.00 does not allow array
             * initializers.  That is only allowed in GLSL ES 3.00.
             *
             * Section 4.1.9 (Arrays) of the GLSL ES 3.00 spec says:
             *
             *     "An array type can also be formed without specifying a size
             *     if the definition includes an initializer:
             *
             *         float x[] = float[2] (1.0, 2.0);     // declares an array of size 2
             *         float y[] = float[] (1.0, 2.0, 3.0); // declares an array of size 3
             *
             *         float a[5];
             *         float b[] = a;"
             */
            _mesa_glsl_error(& loc, state,
                             "unsized array declarations are not allowed in "
                             "GLSL ES");
      }

      /* If the declaration is not a redeclaration, there are a few additional
       * semantic checks that must be applied.  In addition, variable that was
       * created for the declaration should be added to the IR stream.
       */
      if (earlier == NULL) {
         validate_identifier(decl->identifier, loc, state);

         /* Add the variable to the symbol table.  Note that the initializer's
          * IR was already processed earlier (though it hasn't been emitted
          * yet), without the variable in scope.
          *
          * This differs from most C-like languages, but it follows the GLSL
          * specification.  From page 28 (page 34 of the PDF) of the GLSL 1.50
          * spec:
          *
          *     "Within a declaration, the scope of a name starts immediately
          *     after the initializer if present or immediately after the name
          *     being declared if not."
          */
         if (!state->symbols->add_variable(var)) {
            YYLTYPE loc = this->get_location();
            _mesa_glsl_error(&loc, state, "name `%s' already taken in the "
                             "current scope", decl->identifier);
            continue;
         }

         /* Push the variable declaration to the top.  It means that all the
          * variable declarations will appear in a funny last-to-first order,
          * but otherwise we run into trouble if a function is prototyped, a
          * global var is decled, then the function is defined with usage of
          * the global var.  See glslparsertest's CorrectModule.frag.
          */
         instructions->push_head(var);
      }

      instructions->append_list(&initializer_instructions);
   }


   /* Generally, variable declarations do not have r-values.  However,
    * one is used for the declaration in
    *
    * while (bool b = some_condition()) {
    *   ...
    * }
    *
    * so we return the rvalue from the last seen declaration here.
    */
   return result;
}


ir_rvalue *
ast_parameter_declarator::hir(exec_list *instructions,
                              struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;
   const struct glsl_type *type;
   const char *name = NULL;
   YYLTYPE loc = this->get_location();

   type = this->type->glsl_type(& name, state);

   if (type == NULL) {
      if (name != NULL) {
         _mesa_glsl_error(& loc, state,
                          "invalid type `%s' in declaration of `%s'",
                          name, this->identifier);
      } else {
         _mesa_glsl_error(& loc, state,
                          "invalid type in declaration of `%s'",
                          this->identifier);
      }

      type = glsl_type::error_type;
   }

   /* From page 62 (page 68 of the PDF) of the GLSL 1.50 spec:
    *
    *    "Functions that accept no input arguments need not use void in the
    *    argument list because prototypes (or definitions) are required and
    *    therefore there is no ambiguity when an empty argument list "( )" is
    *    declared. The idiom "(void)" as a parameter list is provided for
    *    convenience."
    *
    * Placing this check here prevents a void parameter being set up
    * for a function, which avoids tripping up checks for main taking
    * parameters and lookups of an unnamed symbol.
    */
   if (type->is_void()) {
      if (this->identifier != NULL)
         _mesa_glsl_error(& loc, state,
                          "named parameter cannot have type `void'");

      is_void = true;
      return NULL;
   }

   if (formal_parameter && (this->identifier == NULL)) {
      _mesa_glsl_error(& loc, state, "formal parameter lacks a name");
      return NULL;
   }

   /* This only handles "vec4 foo[..]".  The earlier specifier->glsl_type(...)
    * call already handled the "vec4[..] foo" case.
    */
   type = process_array_type(&loc, type, this->array_specifier, state);

   if (!type->is_error() && type->is_unsized_array()) {
      _mesa_glsl_error(&loc, state, "arrays passed as parameters must have "
                       "a declared size");
      type = glsl_type::error_type;
   }

   is_void = false;
   ir_variable *var = new(ctx)
      ir_variable(type, this->identifier, ir_var_function_in);

   /* Apply any specified qualifiers to the parameter declaration.  Note that
    * for function parameters the default mode is 'in'.
    */
   apply_type_qualifier_to_variable(& this->type->qualifier, var, state, & loc,
                                    true);

   /* From section 4.1.7 of the GLSL 4.40 spec:
    *
    *   "Opaque variables cannot be treated as l-values; hence cannot
    *    be used as out or inout function parameters, nor can they be
    *    assigned into."
    */
   if ((var->data.mode == ir_var_function_inout || var->data.mode == ir_var_function_out)
       && type->contains_opaque()) {
      _mesa_glsl_error(&loc, state, "out and inout parameters cannot "
                       "contain opaque variables");
      type = glsl_type::error_type;
   }

   /* From page 39 (page 45 of the PDF) of the GLSL 1.10 spec:
    *
    *    "When calling a function, expressions that do not evaluate to
    *     l-values cannot be passed to parameters declared as out or inout."
    *
    * From page 32 (page 38 of the PDF) of the GLSL 1.10 spec:
    *
    *    "Other binary or unary expressions, non-dereferenced arrays,
    *     function names, swizzles with repeated fields, and constants
    *     cannot be l-values."
    *
    * So for GLSL 1.10, passing an array as an out or inout parameter is not
    * allowed.  This restriction is removed in GLSL 1.20, and in GLSL ES.
    */
   if ((var->data.mode == ir_var_function_inout || var->data.mode == ir_var_function_out)
       && type->is_array()
       && !state->check_version(120, 100, &loc,
                                "arrays cannot be out or inout parameters")) {
      type = glsl_type::error_type;
   }

   instructions->push_tail(var);

   /* Parameter declarations do not have r-values.
    */
   return NULL;
}


void
ast_parameter_declarator::parameters_to_hir(exec_list *ast_parameters,
                                            bool formal,
                                            exec_list *ir_parameters,
                                            _mesa_glsl_parse_state *state)
{
   ast_parameter_declarator *void_param = NULL;
   unsigned count = 0;

   foreach_list_typed (ast_parameter_declarator, param, link, ast_parameters) {
      param->formal_parameter = formal;
      param->hir(ir_parameters, state);

      if (param->is_void)
         void_param = param;

      count++;
   }

   if ((void_param != NULL) && (count > 1)) {
      YYLTYPE loc = void_param->get_location();

      _mesa_glsl_error(& loc, state,
                       "`void' parameter must be only parameter");
   }
}


void
emit_function(_mesa_glsl_parse_state *state, ir_function *f)
{
   /* IR invariants disallow function declarations or definitions
    * nested within other function definitions.  But there is no
    * requirement about the relative order of function declarations
    * and definitions with respect to one another.  So simply insert
    * the new ir_function block at the end of the toplevel instruction
    * list.
    */
   state->toplevel_ir->push_tail(f);
}


ir_rvalue *
ast_function::hir(exec_list *instructions,
                  struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;
   ir_function *f = NULL;
   ir_function_signature *sig = NULL;
   exec_list hir_parameters;

   const char *const name = identifier;

   /* New functions are always added to the top-level IR instruction stream,
    * so this instruction list pointer is ignored.  See also emit_function
    * (called below).
    */
   (void) instructions;

   /* From page 21 (page 27 of the PDF) of the GLSL 1.20 spec,
    *
    *   "Function declarations (prototypes) cannot occur inside of functions;
    *   they must be at global scope, or for the built-in functions, outside
    *   the global scope."
    *
    * From page 27 (page 33 of the PDF) of the GLSL ES 1.00.16 spec,
    *
    *   "User defined functions may only be defined within the global scope."
    *
    * Note that this language does not appear in GLSL 1.10.
    */
   if ((state->current_function != NULL) &&
       state->is_version(120, 100)) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(&loc, state,
		       "declaration of function `%s' not allowed within "
		       "function body", name);
   }

   validate_identifier(name, this->get_location(), state);

   /* Convert the list of function parameters to HIR now so that they can be
    * used below to compare this function's signature with previously seen
    * signatures for functions with the same name.
    */
   ast_parameter_declarator::parameters_to_hir(& this->parameters,
                                               is_definition,
                                               & hir_parameters, state);

   const char *return_type_name;
   const glsl_type *return_type =
      this->return_type->glsl_type(& return_type_name, state);

   if (!return_type) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(&loc, state,
                       "function `%s' has undeclared return type `%s'",
                       name, return_type_name);
      return_type = glsl_type::error_type;
   }

   /* From page 56 (page 62 of the PDF) of the GLSL 1.30 spec:
    * "No qualifier is allowed on the return type of a function."
    */
   if (this->return_type->has_qualifiers()) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(& loc, state,
                       "function `%s' return type has qualifiers", name);
   }

   /* Section 6.1 (Function Definitions) of the GLSL 1.20 spec says:
    *
    *     "Arrays are allowed as arguments and as the return type. In both
    *     cases, the array must be explicitly sized."
    */
   if (return_type->is_unsized_array()) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(& loc, state,
                       "function `%s' return type array must be explicitly "
                       "sized", name);
   }

   /* From section 4.1.7 of the GLSL 4.40 spec:
    *
    *    "[Opaque types] can only be declared as function parameters
    *     or uniform-qualified variables."
    */
   if (return_type->contains_opaque()) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(&loc, state,
                       "function `%s' return type can't contain an opaque type",
                       name);
   }

   /* Create an ir_function if one doesn't already exist. */
   f = state->symbols->get_function(name);
   if (f == NULL) {
      f = new(ctx) ir_function(name);
      if (!state->symbols->add_function(f)) {
         /* This function name shadows a non-function use of the same name. */
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(&loc, state, "function name `%s' conflicts with "
                          "non-function", name);
         return NULL;
      }

      emit_function(state, f);
   }

   /* Verify that this function's signature either doesn't match a previously
    * seen signature for a function with the same name, or, if a match is found,
    * that the previously seen signature does not have an associated definition.
    */
   if (state->es_shader || f->has_user_signature()) {
      sig = f->exact_matching_signature(state, &hir_parameters);
      if (sig != NULL) {
         const char *badvar = sig->qualifiers_match(&hir_parameters);
         if (badvar != NULL) {
            YYLTYPE loc = this->get_location();

            _mesa_glsl_error(&loc, state, "function `%s' parameter `%s' "
                             "qualifiers don't match prototype", name, badvar);
         }

         if (sig->return_type != return_type) {
            YYLTYPE loc = this->get_location();

            _mesa_glsl_error(&loc, state, "function `%s' return type doesn't "
                             "match prototype", name);
         }

         if (sig->is_defined) {
            if (is_definition) {
               YYLTYPE loc = this->get_location();
               _mesa_glsl_error(& loc, state, "function `%s' redefined", name);
            } else {
               /* We just encountered a prototype that exactly matches a
                * function that's already been defined.  This is redundant,
                * and we should ignore it.
                */
               return NULL;
            }
         }
      }
   }

   /* Verify the return type of main() */
   if (strcmp(name, "main") == 0) {
      if (! return_type->is_void()) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state, "main() must return void");
      }

      if (!hir_parameters.is_empty()) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state, "main() must not take any parameters");
      }
   }

   /* Finish storing the information about this new function in its signature.
    */
   if (sig == NULL) {
      sig = new(ctx) ir_function_signature(return_type);
      f->add_signature(sig);
   }

   sig->replace_parameters(&hir_parameters);
   signature = sig;

   /* Function declarations (prototypes) do not have r-values.
    */
   return NULL;
}


ir_rvalue *
ast_function_definition::hir(exec_list *instructions,
                             struct _mesa_glsl_parse_state *state)
{
   prototype->is_definition = true;
   prototype->hir(instructions, state);

   ir_function_signature *signature = prototype->signature;
   if (signature == NULL)
      return NULL;

   assert(state->current_function == NULL);
   state->current_function = signature;
   state->found_return = false;

   /* Duplicate parameters declared in the prototype as concrete variables.
    * Add these to the symbol table.
    */
   state->symbols->push_scope();
   foreach_in_list(ir_variable, var, &signature->parameters) {
      assert(var->as_variable() != NULL);

      /* The only way a parameter would "exist" is if two parameters have
       * the same name.
       */
      if (state->symbols->name_declared_this_scope(var->name)) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state, "parameter `%s' redeclared", var->name);
      } else {
         state->symbols->add_variable(var);
      }
   }

   /* Convert the body of the function to HIR. */
   this->body->hir(&signature->body, state);
   signature->is_defined = true;

   state->symbols->pop_scope();

   assert(state->current_function == signature);
   state->current_function = NULL;

   if (!signature->return_type->is_void() && !state->found_return) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(& loc, state, "function `%s' has non-void return type "
                       "%s, but no return statement",
                       signature->function_name(),
                       signature->return_type->name);
   }

   /* Function definitions do not have r-values.
    */
   return NULL;
}


ir_rvalue *
ast_jump_statement::hir(exec_list *instructions,
                        struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;

   switch (mode) {
   case ast_return: {
      ir_return *inst;
      assert(state->current_function);

      if (opt_return_value) {
         ir_rvalue *ret = opt_return_value->hir(instructions, state);

         /* The value of the return type can be NULL if the shader says
          * 'return foo();' and foo() is a function that returns void.
          *
          * NOTE: The GLSL spec doesn't say that this is an error.  The type
          * of the return value is void.  If the return type of the function is
          * also void, then this should compile without error.  Seriously.
          */
         const glsl_type *const ret_type =
            (ret == NULL) ? glsl_type::void_type : ret->type;

         /* Implicit conversions are not allowed for return values prior to
          * ARB_shading_language_420pack.
          */
         if (state->current_function->return_type != ret_type) {
            YYLTYPE loc = this->get_location();

            if (state->ARB_shading_language_420pack_enable) {
               if (!apply_implicit_conversion(state->current_function->return_type,
                                              ret, state)) {
                  _mesa_glsl_error(& loc, state,
                                   "could not implicitly convert return value "
                                   "to %s, in function `%s'",
                                   state->current_function->return_type->name,
                                   state->current_function->function_name());
               }
            } else {
               _mesa_glsl_error(& loc, state,
                                "`return' with wrong type %s, in function `%s' "
                                "returning %s",
                                ret_type->name,
                                state->current_function->function_name(),
                                state->current_function->return_type->name);
            }
         } else if (state->current_function->return_type->base_type ==
                    GLSL_TYPE_VOID) {
            YYLTYPE loc = this->get_location();

            /* The ARB_shading_language_420pack, GLSL ES 3.0, and GLSL 4.20
             * specs add a clarification:
             *
             *    "A void function can only use return without a return argument, even if
             *     the return argument has void type. Return statements only accept values:
             *
             *         void func1() { }
             *         void func2() { return func1(); } // illegal return statement"
             */
            _mesa_glsl_error(& loc, state,
                             "void functions can only use `return' without a "
                             "return argument");
         }

         inst = new(ctx) ir_return(ret);
      } else {
         if (state->current_function->return_type->base_type !=
             GLSL_TYPE_VOID) {
            YYLTYPE loc = this->get_location();

            _mesa_glsl_error(& loc, state,
                             "`return' with no value, in function %s returning "
                             "non-void",
            state->current_function->function_name());
         }
         inst = new(ctx) ir_return;
      }

      state->found_return = true;
      instructions->push_tail(inst);
      break;
   }

   case ast_discard:
      if (state->stage != MESA_SHADER_FRAGMENT) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state,
                          "`discard' may only appear in a fragment shader");
      }
      instructions->push_tail(new(ctx) ir_discard);
      break;

   case ast_break:
   case ast_continue:
      if (mode == ast_continue &&
          state->loop_nesting_ast == NULL) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state, "continue may only appear in a loop");
      } else if (mode == ast_break &&
         state->loop_nesting_ast == NULL &&
         state->switch_state.switch_nesting_ast == NULL) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state,
                          "break may only appear in a loop or a switch");
      } else {
         /* For a loop, inline the for loop expression again, since we don't
          * know where near the end of the loop body the normal copy of it is
          * going to be placed.  Same goes for the condition for a do-while
          * loop.
          */
         if (state->loop_nesting_ast != NULL &&
             mode == ast_continue) {
            if (state->loop_nesting_ast->rest_expression) {
               state->loop_nesting_ast->rest_expression->hir(instructions,
                                                             state);
            }
            if (state->loop_nesting_ast->mode ==
                ast_iteration_statement::ast_do_while) {
               state->loop_nesting_ast->condition_to_hir(instructions, state);
            }
         }

         if (state->switch_state.is_switch_innermost &&
             mode == ast_break) {
            /* Force break out of switch by setting is_break switch state.
             */
            ir_variable *const is_break_var = state->switch_state.is_break_var;
            ir_dereference_variable *const deref_is_break_var =
               new(ctx) ir_dereference_variable(is_break_var);
            ir_constant *const true_val = new(ctx) ir_constant(true);
            ir_assignment *const set_break_var =
               new(ctx) ir_assignment(deref_is_break_var, true_val);
	    
            instructions->push_tail(set_break_var);
         }
         else {
            ir_loop_jump *const jump =
               new(ctx) ir_loop_jump((mode == ast_break)
                  ? ir_loop_jump::jump_break
                  : ir_loop_jump::jump_continue);
            instructions->push_tail(jump);
         }
      }

      break;
   }

   /* Jump instructions do not have r-values.
    */
   return NULL;
}


ir_rvalue *
ast_selection_statement::hir(exec_list *instructions,
                             struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;

   ir_rvalue *const condition = this->condition->hir(instructions, state);

   /* From page 66 (page 72 of the PDF) of the GLSL 1.50 spec:
    *
    *    "Any expression whose type evaluates to a Boolean can be used as the
    *    conditional expression bool-expression. Vector types are not accepted
    *    as the expression to if."
    *
    * The checks are separated so that higher quality diagnostics can be
    * generated for cases where both rules are violated.
    */
   if (!condition->type->is_boolean() || !condition->type->is_scalar()) {
      YYLTYPE loc = this->condition->get_location();

      _mesa_glsl_error(& loc, state, "if-statement condition must be scalar "
                       "boolean");
   }

   ir_if *const stmt = new(ctx) ir_if(condition);

   if (then_statement != NULL) {
      state->symbols->push_scope();
      then_statement->hir(& stmt->then_instructions, state);
      state->symbols->pop_scope();
   }

   if (else_statement != NULL) {
      state->symbols->push_scope();
      else_statement->hir(& stmt->else_instructions, state);
      state->symbols->pop_scope();
   }

   instructions->push_tail(stmt);

   /* if-statements do not have r-values.
    */
   return NULL;
}


ir_rvalue *
ast_switch_statement::hir(exec_list *instructions,
                          struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;

   ir_rvalue *const test_expression =
      this->test_expression->hir(instructions, state);

   /* From page 66 (page 55 of the PDF) of the GLSL 1.50 spec:
    *
    *    "The type of init-expression in a switch statement must be a 
    *     scalar integer." 
    */
   if (!test_expression->type->is_scalar() ||
       !test_expression->type->is_integer()) {
      YYLTYPE loc = this->test_expression->get_location();

      _mesa_glsl_error(& loc,
                       state,
                       "switch-statement expression must be scalar "
                       "integer");
   }

   /* Track the switch-statement nesting in a stack-like manner.
    */
   struct glsl_switch_state saved = state->switch_state;

   state->switch_state.is_switch_innermost = true;
   state->switch_state.switch_nesting_ast = this;
   state->switch_state.labels_ht = hash_table_ctor(0, hash_table_pointer_hash,
						   hash_table_pointer_compare);
   state->switch_state.previous_default = NULL;

   /* Initalize is_fallthru state to false.
    */
   ir_rvalue *const is_fallthru_val = new (ctx) ir_constant(false);
   state->switch_state.is_fallthru_var =
      new(ctx) ir_variable(glsl_type::bool_type,
                           "switch_is_fallthru_tmp",
                           ir_var_temporary);
   instructions->push_tail(state->switch_state.is_fallthru_var);

   ir_dereference_variable *deref_is_fallthru_var =
      new(ctx) ir_dereference_variable(state->switch_state.is_fallthru_var);
   instructions->push_tail(new(ctx) ir_assignment(deref_is_fallthru_var,
                                                  is_fallthru_val));

   /* Initalize is_break state to false.
    */
   ir_rvalue *const is_break_val = new (ctx) ir_constant(false);
   state->switch_state.is_break_var =
      new(ctx) ir_variable(glsl_type::bool_type,
                           "switch_is_break_tmp",
                           ir_var_temporary);
   instructions->push_tail(state->switch_state.is_break_var);

   ir_dereference_variable *deref_is_break_var =
      new(ctx) ir_dereference_variable(state->switch_state.is_break_var);
   instructions->push_tail(new(ctx) ir_assignment(deref_is_break_var,
                                                  is_break_val));

   state->switch_state.run_default =
      new(ctx) ir_variable(glsl_type::bool_type,
                             "run_default_tmp",
                             ir_var_temporary);
   instructions->push_tail(state->switch_state.run_default);

   /* Cache test expression.
    */
   test_to_hir(instructions, state);

   /* Emit code for body of switch stmt.
    */
   body->hir(instructions, state);

   hash_table_dtor(state->switch_state.labels_ht);

   state->switch_state = saved;

   /* Switch statements do not have r-values. */
   return NULL;
}


void
ast_switch_statement::test_to_hir(exec_list *instructions,
                                  struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;

   /* Cache value of test expression. */
   ir_rvalue *const test_val =
      test_expression->hir(instructions,
			   state);

   state->switch_state.test_var = new(ctx) ir_variable(test_val->type,
                                                       "switch_test_tmp",
                                                       ir_var_temporary);
   ir_dereference_variable *deref_test_var =
      new(ctx) ir_dereference_variable(state->switch_state.test_var);

   instructions->push_tail(state->switch_state.test_var);
   instructions->push_tail(new(ctx) ir_assignment(deref_test_var, test_val));
}


ir_rvalue *
ast_switch_body::hir(exec_list *instructions,
                     struct _mesa_glsl_parse_state *state)
{
   if (stmts != NULL)
      stmts->hir(instructions, state);

   /* Switch bodies do not have r-values. */
   return NULL;
}

ir_rvalue *
ast_case_statement_list::hir(exec_list *instructions,
                             struct _mesa_glsl_parse_state *state)
{
   exec_list default_case, after_default, tmp;

   foreach_list_typed (ast_case_statement, case_stmt, link, & this->cases) {
      case_stmt->hir(&tmp, state);

      /* Default case. */
      if (state->switch_state.previous_default && default_case.is_empty()) {
         default_case.append_list(&tmp);
         continue;
      }

      /* If default case found, append 'after_default' list. */
      if (!default_case.is_empty())
         after_default.append_list(&tmp);
      else
         instructions->append_list(&tmp);
   }

   /* Handle the default case. This is done here because default might not be
    * the last case. We need to add checks against following cases first to see
    * if default should be chosen or not.
    */
   if (!default_case.is_empty()) {

      ir_rvalue *const true_val = new (state) ir_constant(true);
      ir_dereference_variable *deref_run_default_var =
         new(state) ir_dereference_variable(state->switch_state.run_default);

      /* Choose to run default case initially, following conditional
       * assignments might change this.
       */
      ir_assignment *const init_var =
         new(state) ir_assignment(deref_run_default_var, true_val);
      instructions->push_tail(init_var);

      /* Default case was the last one, no checks required. */
      if (after_default.is_empty()) {
         instructions->append_list(&default_case);
         return NULL;
      }

      foreach_in_list(ir_instruction, ir, &after_default) {
         ir_assignment *assign = ir->as_assignment();

         if (!assign)
            continue;

         /* Clone the check between case label and init expression. */
         ir_expression *exp = (ir_expression*) assign->condition;
         ir_expression *clone = exp->clone(state, NULL);

         ir_dereference_variable *deref_var =
            new(state) ir_dereference_variable(state->switch_state.run_default);
         ir_rvalue *const false_val = new (state) ir_constant(false);

         ir_assignment *const set_false =
            new(state) ir_assignment(deref_var, false_val, clone);

         instructions->push_tail(set_false);
      }

      /* Append default case and all cases after it. */
      instructions->append_list(&default_case);
      instructions->append_list(&after_default);
   }

   /* Case statements do not have r-values. */
   return NULL;
}

ir_rvalue *
ast_case_statement::hir(exec_list *instructions,
                        struct _mesa_glsl_parse_state *state)
{
   labels->hir(instructions, state);

   /* Conditionally set fallthru state based on break state. */
   ir_constant *const false_val = new(state) ir_constant(false);
   ir_dereference_variable *const deref_is_fallthru_var =
      new(state) ir_dereference_variable(state->switch_state.is_fallthru_var);
   ir_dereference_variable *const deref_is_break_var =
      new(state) ir_dereference_variable(state->switch_state.is_break_var);
   ir_assignment *const reset_fallthru_on_break =
      new(state) ir_assignment(deref_is_fallthru_var,
                               false_val,
                               deref_is_break_var);
   instructions->push_tail(reset_fallthru_on_break);

   /* Guard case statements depending on fallthru state. */
   ir_dereference_variable *const deref_fallthru_guard =
      new(state) ir_dereference_variable(state->switch_state.is_fallthru_var);
   ir_if *const test_fallthru = new(state) ir_if(deref_fallthru_guard);

   foreach_list_typed (ast_node, stmt, link, & this->stmts)
      stmt->hir(& test_fallthru->then_instructions, state);

   instructions->push_tail(test_fallthru);

   /* Case statements do not have r-values. */
   return NULL;
}


ir_rvalue *
ast_case_label_list::hir(exec_list *instructions,
                         struct _mesa_glsl_parse_state *state)
{
   foreach_list_typed (ast_case_label, label, link, & this->labels)
      label->hir(instructions, state);

   /* Case labels do not have r-values. */
   return NULL;
}

ir_rvalue *
ast_case_label::hir(exec_list *instructions,
                    struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;

   ir_dereference_variable *deref_fallthru_var =
      new(ctx) ir_dereference_variable(state->switch_state.is_fallthru_var);

   ir_rvalue *const true_val = new(ctx) ir_constant(true);

   /* If not default case, ... */
   if (this->test_value != NULL) {
      /* Conditionally set fallthru state based on
       * comparison of cached test expression value to case label.
       */
      ir_rvalue *const label_rval = this->test_value->hir(instructions, state);
      ir_constant *label_const = label_rval->constant_expression_value();

      if (!label_const) {
         YYLTYPE loc = this->test_value->get_location();

         _mesa_glsl_error(& loc, state,
                          "switch statement case label must be a "
                          "constant expression");

         /* Stuff a dummy value in to allow processing to continue. */
         label_const = new(ctx) ir_constant(0);
      } else {
         ast_expression *previous_label = (ast_expression *)
         hash_table_find(state->switch_state.labels_ht,
                         (void *)(uintptr_t)label_const->value.u[0]);

         if (previous_label) {
            YYLTYPE loc = this->test_value->get_location();
            _mesa_glsl_error(& loc, state, "duplicate case value");

            loc = previous_label->get_location();
            _mesa_glsl_error(& loc, state, "this is the previous case label");
         } else {
            hash_table_insert(state->switch_state.labels_ht,
                              this->test_value,
                              (void *)(uintptr_t)label_const->value.u[0]);
         }
      }

      ir_dereference_variable *deref_test_var =
         new(ctx) ir_dereference_variable(state->switch_state.test_var);

      ir_expression *test_cond = new(ctx) ir_expression(ir_binop_all_equal,
                                                        label_const,
                                                        deref_test_var);

      /*
       * From GLSL 4.40 specification section 6.2 ("Selection"):
       *
       *     "The type of the init-expression value in a switch statement must
       *     be a scalar int or uint. The type of the constant-expression value
       *     in a case label also must be a scalar int or uint. When any pair
       *     of these values is tested for "equal value" and the types do not
       *     match, an implicit conversion will be done to convert the int to a
       *     uint (see section 4.1.10 “Implicit Conversions”) before the compare
       *     is done."
       */
      if (label_const->type != state->switch_state.test_var->type) {
         YYLTYPE loc = this->test_value->get_location();

         const glsl_type *type_a = label_const->type;
         const glsl_type *type_b = state->switch_state.test_var->type;

         /* Check if int->uint implicit conversion is supported. */
         bool integer_conversion_supported =
            glsl_type::int_type->can_implicitly_convert_to(glsl_type::uint_type,
                                                           state);

         if ((!type_a->is_integer() || !type_b->is_integer()) ||
              !integer_conversion_supported) {
            _mesa_glsl_error(&loc, state, "type mismatch with switch "
                             "init-expression and case label (%s != %s)",
                             type_a->name, type_b->name);
         } else {
            /* Conversion of the case label. */
            if (type_a->base_type == GLSL_TYPE_INT) {
               if (!apply_implicit_conversion(glsl_type::uint_type,
                                              test_cond->operands[0], state))
                  _mesa_glsl_error(&loc, state, "implicit type conversion error");
            } else {
               /* Conversion of the init-expression value. */
               if (!apply_implicit_conversion(glsl_type::uint_type,
                                              test_cond->operands[1], state))
                  _mesa_glsl_error(&loc, state, "implicit type conversion error");
            }
         }
      }

      ir_assignment *set_fallthru_on_test =
         new(ctx) ir_assignment(deref_fallthru_var, true_val, test_cond);

      instructions->push_tail(set_fallthru_on_test);
   } else { /* default case */
      if (state->switch_state.previous_default) {
         YYLTYPE loc = this->get_location();
         _mesa_glsl_error(& loc, state,
                          "multiple default labels in one switch");

         loc = state->switch_state.previous_default->get_location();
         _mesa_glsl_error(& loc, state, "this is the first default label");
      }
      state->switch_state.previous_default = this;

      /* Set fallthru condition on 'run_default' bool. */
      ir_dereference_variable *deref_run_default =
         new(ctx) ir_dereference_variable(state->switch_state.run_default);
      ir_rvalue *const cond_true = new(ctx) ir_constant(true);
      ir_expression *test_cond = new(ctx) ir_expression(ir_binop_all_equal,
                                                        cond_true,
                                                        deref_run_default);

      /* Set falltrhu state. */
      ir_assignment *set_fallthru =
         new(ctx) ir_assignment(deref_fallthru_var, true_val, test_cond);

      instructions->push_tail(set_fallthru);
   }

   /* Case statements do not have r-values. */
   return NULL;
}

void
ast_iteration_statement::condition_to_hir(exec_list *instructions,
                                          struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;

   if (condition != NULL) {
      ir_rvalue *const cond =
         condition->hir(instructions, state);

      if ((cond == NULL)
          || !cond->type->is_boolean() || !cond->type->is_scalar()) {
         YYLTYPE loc = condition->get_location();

         _mesa_glsl_error(& loc, state,
                          "loop condition must be scalar boolean");
      } else {
         /* As the first code in the loop body, generate a block that looks
          * like 'if (!condition) break;' as the loop termination condition.
          */
         ir_rvalue *const not_cond =
            new(ctx) ir_expression(ir_unop_logic_not, cond);

         ir_if *const if_stmt = new(ctx) ir_if(not_cond);

         ir_jump *const break_stmt =
            new(ctx) ir_loop_jump(ir_loop_jump::jump_break);

         if_stmt->then_instructions.push_tail(break_stmt);
         instructions->push_tail(if_stmt);
      }
   }
}


ir_rvalue *
ast_iteration_statement::hir(exec_list *instructions,
                             struct _mesa_glsl_parse_state *state)
{
   void *ctx = state;

   /* For-loops and while-loops start a new scope, but do-while loops do not.
    */
   if (mode != ast_do_while)
      state->symbols->push_scope();

   if (init_statement != NULL)
      init_statement->hir(instructions, state);

   ir_loop *const stmt = new(ctx) ir_loop();
   instructions->push_tail(stmt);

   /* Track the current loop nesting. */
   ast_iteration_statement *nesting_ast = state->loop_nesting_ast;

   state->loop_nesting_ast = this;

   /* Likewise, indicate that following code is closest to a loop,
    * NOT closest to a switch.
    */
   bool saved_is_switch_innermost = state->switch_state.is_switch_innermost;
   state->switch_state.is_switch_innermost = false;

   if (mode != ast_do_while)
      condition_to_hir(&stmt->body_instructions, state);

   if (body != NULL)
      body->hir(& stmt->body_instructions, state);

   if (rest_expression != NULL)
      rest_expression->hir(& stmt->body_instructions, state);

   if (mode == ast_do_while)
      condition_to_hir(&stmt->body_instructions, state);

   if (mode != ast_do_while)
      state->symbols->pop_scope();

   /* Restore previous nesting before returning. */
   state->loop_nesting_ast = nesting_ast;
   state->switch_state.is_switch_innermost = saved_is_switch_innermost;

   /* Loops do not have r-values.
    */
   return NULL;
}


/**
 * Determine if the given type is valid for establishing a default precision
 * qualifier.
 *
 * From GLSL ES 3.00 section 4.5.4 ("Default Precision Qualifiers"):
 *
 *     "The precision statement
 *
 *         precision precision-qualifier type;
 *
 *     can be used to establish a default precision qualifier. The type field
 *     can be either int or float or any of the sampler types, and the
 *     precision-qualifier can be lowp, mediump, or highp."
 *
 * GLSL ES 1.00 has similar language.  GLSL 1.30 doesn't allow precision
 * qualifiers on sampler types, but this seems like an oversight (since the
 * intention of including these in GLSL 1.30 is to allow compatibility with ES
 * shaders).  So we allow int, float, and all sampler types regardless of GLSL
 * version.
 */
static bool
is_valid_default_precision_type(const struct glsl_type *const type)
{
   if (type == NULL)
      return false;

   switch (type->base_type) {
   case GLSL_TYPE_INT:
   case GLSL_TYPE_FLOAT:
      /* "int" and "float" are valid, but vectors and matrices are not. */
      return type->vector_elements == 1 && type->matrix_columns == 1;
   case GLSL_TYPE_SAMPLER:
      return true;
   default:
      return false;
   }
}


ir_rvalue *
ast_type_specifier::hir(exec_list *instructions,
                        struct _mesa_glsl_parse_state *state)
{
   if (this->default_precision == ast_precision_none && this->structure == NULL)
      return NULL;

   YYLTYPE loc = this->get_location();

   /* If this is a precision statement, check that the type to which it is
    * applied is either float or int.
    *
    * From section 4.5.3 of the GLSL 1.30 spec:
    *    "The precision statement
    *       precision precision-qualifier type;
    *    can be used to establish a default precision qualifier. The type
    *    field can be either int or float [...].  Any other types or
    *    qualifiers will result in an error.
    */
   if (this->default_precision != ast_precision_none) {
      if (!state->check_precision_qualifiers_allowed(&loc))
         return NULL;

      if (this->structure != NULL) {
         _mesa_glsl_error(&loc, state,
                          "precision qualifiers do not apply to structures");
         return NULL;
      }

      if (this->array_specifier != NULL) {
         _mesa_glsl_error(&loc, state,
                          "default precision statements do not apply to "
                          "arrays");
         return NULL;
      }

      const struct glsl_type *const type =
         state->symbols->get_type(this->type_name);
      if (!is_valid_default_precision_type(type)) {
         _mesa_glsl_error(&loc, state,
                          "default precision statements apply only to "
                          "float, int, and sampler types");
         return NULL;
      }

      if (type->base_type == GLSL_TYPE_FLOAT
          && state->es_shader
          && state->stage == MESA_SHADER_FRAGMENT) {
         /* Section 4.5.3 (Default Precision Qualifiers) of the GLSL ES 1.00
          * spec says:
          *
          *     "The fragment language has no default precision qualifier for
          *     floating point types."
          *
          * As a result, we have to track whether or not default precision has
          * been specified for float in GLSL ES fragment shaders.
          *
          * Earlier in that same section, the spec says:
          *
          *     "Non-precision qualified declarations will use the precision
          *     qualifier specified in the most recent precision statement
          *     that is still in scope. The precision statement has the same
          *     scoping rules as variable declarations. If it is declared
          *     inside a compound statement, its effect stops at the end of
          *     the innermost statement it was declared in. Precision
          *     statements in nested scopes override precision statements in
          *     outer scopes. Multiple precision statements for the same basic
          *     type can appear inside the same scope, with later statements
          *     overriding earlier statements within that scope."
          *
          * Default precision specifications follow the same scope rules as
          * variables.  So, we can track the state of the default float
          * precision in the symbol table, and the rules will just work.  This
          * is a slight abuse of the symbol table, but it has the semantics
          * that we want.
          */
         ir_variable *const junk =
            new(state) ir_variable(type, "#default precision",
                                   ir_var_temporary);

         state->symbols->add_variable(junk);
      }

      /* FINISHME: Translate precision statements into IR. */
      return NULL;
   }

   /* _mesa_ast_set_aggregate_type() sets the <structure> field so that
    * process_record_constructor() can do type-checking on C-style initializer
    * expressions of structs, but ast_struct_specifier should only be translated
    * to HIR if it is declaring the type of a structure.
    *
    * The ->is_declaration field is false for initializers of variables
    * declared separately from the struct's type definition.
    *
    *    struct S { ... };              (is_declaration = true)
    *    struct T { ... } t = { ... };  (is_declaration = true)
    *    S s = { ... };                 (is_declaration = false)
    */
   if (this->structure != NULL && this->structure->is_declaration)
      return this->structure->hir(instructions, state);

   return NULL;
}


/**
 * Process a structure or interface block tree into an array of structure fields
 *
 * After parsing, where there are some syntax differnces, structures and
 * interface blocks are almost identical.  They are similar enough that the
 * AST for each can be processed the same way into a set of
 * \c glsl_struct_field to describe the members.
 *
 * If we're processing an interface block, var_mode should be the type of the
 * interface block (ir_var_shader_in, ir_var_shader_out, or ir_var_uniform).
 * If we're processing a structure, var_mode should be ir_var_auto.
 *
 * \return
 * The number of fields processed.  A pointer to the array structure fields is
 * stored in \c *fields_ret.
 */
unsigned
ast_process_structure_or_interface_block(exec_list *instructions,
                                         struct _mesa_glsl_parse_state *state,
                                         exec_list *declarations,
                                         YYLTYPE &loc,
                                         glsl_struct_field **fields_ret,
                                         bool is_interface,
                                         enum glsl_matrix_layout matrix_layout,
                                         bool allow_reserved_names,
                                         ir_variable_mode var_mode)
{
   unsigned decl_count = 0;

   /* Make an initial pass over the list of fields to determine how
    * many there are.  Each element in this list is an ast_declarator_list.
    * This means that we actually need to count the number of elements in the
    * 'declarations' list in each of the elements.
    */
   foreach_list_typed (ast_declarator_list, decl_list, link, declarations) {
      decl_count += decl_list->declarations.length();
   }

   /* Allocate storage for the fields and process the field
    * declarations.  As the declarations are processed, try to also convert
    * the types to HIR.  This ensures that structure definitions embedded in
    * other structure definitions or in interface blocks are processed.
    */
   glsl_struct_field *const fields = ralloc_array(state, glsl_struct_field,
                                                  decl_count);

   unsigned i = 0;
   foreach_list_typed (ast_declarator_list, decl_list, link, declarations) {
      const char *type_name;

      decl_list->type->specifier->hir(instructions, state);

      /* Section 10.9 of the GLSL ES 1.00 specification states that
       * embedded structure definitions have been removed from the language.
       */
      if (state->es_shader && decl_list->type->specifier->structure != NULL) {
         _mesa_glsl_error(&loc, state, "embedded structure definitions are "
                          "not allowed in GLSL ES 1.00");
      }

      const glsl_type *decl_type =
         decl_list->type->glsl_type(& type_name, state);

      foreach_list_typed (ast_declaration, decl, link,
                          &decl_list->declarations) {
         if (!allow_reserved_names)
            validate_identifier(decl->identifier, loc, state);

         /* From section 4.3.9 of the GLSL 4.40 spec:
          *
          *    "[In interface blocks] opaque types are not allowed."
          *
          * It should be impossible for decl_type to be NULL here.  Cases that
          * might naturally lead to decl_type being NULL, especially for the
          * is_interface case, will have resulted in compilation having
          * already halted due to a syntax error.
          */
         const struct glsl_type *field_type =
            decl_type != NULL ? decl_type : glsl_type::error_type;

         if (is_interface && field_type->contains_opaque()) {
            YYLTYPE loc = decl_list->get_location();
            _mesa_glsl_error(&loc, state,
                             "uniform in non-default uniform block contains "
                             "opaque variable");
         }

         if (field_type->contains_atomic()) {
            /* FINISHME: Add a spec quotation here once updated spec
             * FINISHME: language is available.  See Khronos bug #10903
             * FINISHME: on whether atomic counters are allowed in
             * FINISHME: structures.
             */
            YYLTYPE loc = decl_list->get_location();
            _mesa_glsl_error(&loc, state, "atomic counter in structure or "
                             "uniform block");
         }

         if (field_type->contains_image()) {
            /* FINISHME: Same problem as with atomic counters.
             * FINISHME: Request clarification from Khronos and add
             * FINISHME: spec quotation here.
             */
            YYLTYPE loc = decl_list->get_location();
            _mesa_glsl_error(&loc, state,
                             "image in structure or uniform block");
         }

         const struct ast_type_qualifier *const qual =
            & decl_list->type->qualifier;
         if (qual->flags.q.std140 ||
             qual->flags.q.packed ||
             qual->flags.q.shared) {
            _mesa_glsl_error(&loc, state,
                             "uniform block layout qualifiers std140, packed, and "
                             "shared can only be applied to uniform blocks, not "
                             "members");
         }

         field_type = process_array_type(&loc, decl_type,
                                         decl->array_specifier, state);
         fields[i].type = field_type;
         fields[i].name = decl->identifier;
         fields[i].location = -1;
         fields[i].interpolation =
            interpret_interpolation_qualifier(qual, var_mode, state, &loc);
         fields[i].centroid = qual->flags.q.centroid ? 1 : 0;
         fields[i].sample = qual->flags.q.sample ? 1 : 0;

         /* Only save explicitly defined streams in block's field */
         fields[i].stream = qual->flags.q.explicit_stream ? qual->stream : -1;

         if (qual->flags.q.row_major || qual->flags.q.column_major) {
            if (!qual->flags.q.uniform) {
               _mesa_glsl_error(&loc, state,
                                "row_major and column_major can only be "
                                "applied to uniform interface blocks");
            } else
               validate_matrix_layout_for_type(state, &loc, field_type, NULL);
         }

         if (qual->flags.q.uniform && qual->has_interpolation()) {
            _mesa_glsl_error(&loc, state,
                             "interpolation qualifiers cannot be used "
                             "with uniform interface blocks");
         }

         if ((qual->flags.q.uniform || !is_interface) &&
             qual->has_auxiliary_storage()) {
            _mesa_glsl_error(&loc, state,
                             "auxiliary storage qualifiers cannot be used "
                             "in uniform blocks or structures.");
         }

         /* Propogate row- / column-major information down the fields of the
          * structure or interface block.  Structures need this data because
          * the structure may contain a structure that contains ... a matrix
          * that need the proper layout.
          */
         if (field_type->without_array()->is_matrix()
             || field_type->without_array()->is_record()) {
            /* If no layout is specified for the field, inherit the layout
             * from the block.
             */
            fields[i].matrix_layout = matrix_layout;

            if (qual->flags.q.row_major)
               fields[i].matrix_layout = GLSL_MATRIX_LAYOUT_ROW_MAJOR;
            else if (qual->flags.q.column_major)
               fields[i].matrix_layout = GLSL_MATRIX_LAYOUT_COLUMN_MAJOR;

            /* If we're processing an interface block, the matrix layout must
             * be decided by this point.
             */
            assert(!is_interface
                   || fields[i].matrix_layout == GLSL_MATRIX_LAYOUT_ROW_MAJOR
                   || fields[i].matrix_layout == GLSL_MATRIX_LAYOUT_COLUMN_MAJOR);
         }

         i++;
      }
   }

   assert(i == decl_count);

   *fields_ret = fields;
   return decl_count;
}


ir_rvalue *
ast_struct_specifier::hir(exec_list *instructions,
                          struct _mesa_glsl_parse_state *state)
{
   YYLTYPE loc = this->get_location();

   /* Section 4.1.8 (Structures) of the GLSL 1.10 spec says:
    *
    *     "Anonymous structures are not supported; so embedded structures must
    *     have a declarator. A name given to an embedded struct is scoped at
    *     the same level as the struct it is embedded in."
    *
    * The same section of the  GLSL 1.20 spec says:
    *
    *     "Anonymous structures are not supported. Embedded structures are not
    *     supported.
    *
    *         struct S { float f; };
    *         struct T {
    *             S;              // Error: anonymous structures disallowed
    *             struct { ... }; // Error: embedded structures disallowed
    *             S s;            // Okay: nested structures with name are allowed
    *         };"
    *
    * The GLSL ES 1.00 and 3.00 specs have similar langauge and examples.  So,
    * we allow embedded structures in 1.10 only.
    */
   if (state->language_version != 110 && state->struct_specifier_depth != 0)
      _mesa_glsl_error(&loc, state,
		       "embedded structure declarations are not allowed");

   state->struct_specifier_depth++;

   glsl_struct_field *fields;
   unsigned decl_count =
      ast_process_structure_or_interface_block(instructions,
                                               state,
                                               &this->declarations,
                                               loc,
                                               &fields,
                                               false,
                                               GLSL_MATRIX_LAYOUT_INHERITED,
                                               false /* allow_reserved_names */,
                                               ir_var_auto);

   validate_identifier(this->name, loc, state);

   const glsl_type *t =
      glsl_type::get_record_instance(fields, decl_count, this->name);

   if (!state->symbols->add_type(name, t)) {
      _mesa_glsl_error(& loc, state, "struct `%s' previously defined", name);
   } else {
      const glsl_type **s = reralloc(state, state->user_structures,
                                     const glsl_type *,
                                     state->num_user_structures + 1);
      if (s != NULL) {
         s[state->num_user_structures] = t;
         state->user_structures = s;
         state->num_user_structures++;
      }
   }

   state->struct_specifier_depth--;

   /* Structure type definitions do not have r-values.
    */
   return NULL;
}


/**
 * Visitor class which detects whether a given interface block has been used.
 */
class interface_block_usage_visitor : public ir_hierarchical_visitor
{
public:
   interface_block_usage_visitor(ir_variable_mode mode, const glsl_type *block)
      : mode(mode), block(block), found(false)
   {
   }

   virtual ir_visitor_status visit(ir_dereference_variable *ir)
   {
      if (ir->var->data.mode == mode && ir->var->get_interface_type() == block) {
         found = true;
         return visit_stop;
      }
      return visit_continue;
   }

   bool usage_found() const
   {
      return this->found;
   }

private:
   ir_variable_mode mode;
   const glsl_type *block;
   bool found;
};


ir_rvalue *
ast_interface_block::hir(exec_list *instructions,
                         struct _mesa_glsl_parse_state *state)
{
   YYLTYPE loc = this->get_location();

   /* The ast_interface_block has a list of ast_declarator_lists.  We
    * need to turn those into ir_variables with an association
    * with this uniform block.
    */
   enum glsl_interface_packing packing;
   if (this->layout.flags.q.shared) {
      packing = GLSL_INTERFACE_PACKING_SHARED;
   } else if (this->layout.flags.q.packed) {
      packing = GLSL_INTERFACE_PACKING_PACKED;
   } else {
      /* The default layout is std140.
       */
      packing = GLSL_INTERFACE_PACKING_STD140;
   }

   ir_variable_mode var_mode;
   const char *iface_type_name;
   if (this->layout.flags.q.in) {
      var_mode = ir_var_shader_in;
      iface_type_name = "in";
   } else if (this->layout.flags.q.out) {
      var_mode = ir_var_shader_out;
      iface_type_name = "out";
   } else if (this->layout.flags.q.uniform) {
      var_mode = ir_var_uniform;
      iface_type_name = "uniform";
   } else {
      var_mode = ir_var_auto;
      iface_type_name = "UNKNOWN";
      assert(!"interface block layout qualifier not found!");
   }

   enum glsl_matrix_layout matrix_layout = GLSL_MATRIX_LAYOUT_INHERITED;
   if (this->layout.flags.q.row_major)
      matrix_layout = GLSL_MATRIX_LAYOUT_ROW_MAJOR;
   else if (this->layout.flags.q.column_major)
      matrix_layout = GLSL_MATRIX_LAYOUT_COLUMN_MAJOR;

   bool redeclaring_per_vertex = strcmp(this->block_name, "gl_PerVertex") == 0;
   exec_list declared_variables;
   glsl_struct_field *fields;

   /* Treat an interface block as one level of nesting, so that embedded struct
    * specifiers will be disallowed.
    */
   state->struct_specifier_depth++;

   unsigned int num_variables =
      ast_process_structure_or_interface_block(&declared_variables,
                                               state,
                                               &this->declarations,
                                               loc,
                                               &fields,
                                               true,
                                               matrix_layout,
                                               redeclaring_per_vertex,
                                               var_mode);

   state->struct_specifier_depth--;

   if (!redeclaring_per_vertex)
      validate_identifier(this->block_name, loc, state);

   const glsl_type *earlier_per_vertex = NULL;
   if (redeclaring_per_vertex) {
      /* Find the previous declaration of gl_PerVertex.  If we're redeclaring
       * the named interface block gl_in, we can find it by looking at the
       * previous declaration of gl_in.  Otherwise we can find it by looking
       * at the previous decalartion of any of the built-in outputs,
       * e.g. gl_Position.
       *
       * Also check that the instance name and array-ness of the redeclaration
       * are correct.
       */
      switch (var_mode) {
      case ir_var_shader_in:
         if (ir_variable *earlier_gl_in =
             state->symbols->get_variable("gl_in")) {
            earlier_per_vertex = earlier_gl_in->get_interface_type();
         } else {
            _mesa_glsl_error(&loc, state,
                             "redeclaration of gl_PerVertex input not allowed "
                             "in the %s shader",
                             _mesa_shader_stage_to_string(state->stage));
         }
         if (this->instance_name == NULL ||
             strcmp(this->instance_name, "gl_in") != 0 || this->array_specifier == NULL) {
            _mesa_glsl_error(&loc, state,
                             "gl_PerVertex input must be redeclared as "
                             "gl_in[]");
         }
         break;
      case ir_var_shader_out:
         if (ir_variable *earlier_gl_Position =
             state->symbols->get_variable("gl_Position")) {
            earlier_per_vertex = earlier_gl_Position->get_interface_type();
         } else {
            _mesa_glsl_error(&loc, state,
                             "redeclaration of gl_PerVertex output not "
                             "allowed in the %s shader",
                             _mesa_shader_stage_to_string(state->stage));
         }
         if (this->instance_name != NULL) {
            _mesa_glsl_error(&loc, state,
                             "gl_PerVertex input may not be redeclared with "
                             "an instance name");
         }
         break;
      default:
         _mesa_glsl_error(&loc, state,
                          "gl_PerVertex must be declared as an input or an "
                          "output");
         break;
      }

      if (earlier_per_vertex == NULL) {
         /* An error has already been reported.  Bail out to avoid null
          * dereferences later in this function.
          */
         return NULL;
      }

      /* Copy locations from the old gl_PerVertex interface block. */
      for (unsigned i = 0; i < num_variables; i++) {
         int j = earlier_per_vertex->field_index(fields[i].name);
         if (j == -1) {
            _mesa_glsl_error(&loc, state,
                             "redeclaration of gl_PerVertex must be a subset "
                             "of the built-in members of gl_PerVertex");
         } else {
            fields[i].location =
               earlier_per_vertex->fields.structure[j].location;
            fields[i].interpolation =
               earlier_per_vertex->fields.structure[j].interpolation;
            fields[i].centroid =
               earlier_per_vertex->fields.structure[j].centroid;
            fields[i].sample =
               earlier_per_vertex->fields.structure[j].sample;
         }
      }

      /* From section 7.1 ("Built-in Language Variables") of the GLSL 4.10
       * spec:
       *
       *     If a built-in interface block is redeclared, it must appear in
       *     the shader before any use of any member included in the built-in
       *     declaration, or a compilation error will result.
       *
       * This appears to be a clarification to the behaviour established for
       * gl_PerVertex by GLSL 1.50, therefore we implement this behaviour
       * regardless of GLSL version.
       */
      interface_block_usage_visitor v(var_mode, earlier_per_vertex);
      v.run(instructions);
      if (v.usage_found()) {
         _mesa_glsl_error(&loc, state,
                          "redeclaration of a built-in interface block must "
                          "appear before any use of any member of the "
                          "interface block");
      }
   }

   const glsl_type *block_type =
      glsl_type::get_interface_instance(fields,
                                        num_variables,
                                        packing,
                                        this->block_name);

   if (!state->symbols->add_interface(block_type->name, block_type, var_mode)) {
      YYLTYPE loc = this->get_location();
      _mesa_glsl_error(&loc, state, "interface block `%s' with type `%s' "
                       "already taken in the current scope",
                       this->block_name, iface_type_name);
   }

   /* Since interface blocks cannot contain statements, it should be
    * impossible for the block to generate any instructions.
    */
   assert(declared_variables.is_empty());

   /* From section 4.3.4 (Inputs) of the GLSL 1.50 spec:
    *
    *     Geometry shader input variables get the per-vertex values written
    *     out by vertex shader output variables of the same names. Since a
    *     geometry shader operates on a set of vertices, each input varying
    *     variable (or input block, see interface blocks below) needs to be
    *     declared as an array.
    */
   if (state->stage == MESA_SHADER_GEOMETRY && this->array_specifier == NULL &&
       var_mode == ir_var_shader_in) {
      _mesa_glsl_error(&loc, state, "geometry shader inputs must be arrays");
   }

   /* Page 39 (page 45 of the PDF) of section 4.3.7 in the GLSL ES 3.00 spec
    * says:
    *
    *     "If an instance name (instance-name) is used, then it puts all the
    *     members inside a scope within its own name space, accessed with the
    *     field selector ( . ) operator (analogously to structures)."
    */
   if (this->instance_name) {
      if (redeclaring_per_vertex) {
         /* When a built-in in an unnamed interface block is redeclared,
          * get_variable_being_redeclared() calls
          * check_builtin_array_max_size() to make sure that built-in array
          * variables aren't redeclared to illegal sizes.  But we're looking
          * at a redeclaration of a named built-in interface block.  So we
          * have to manually call check_builtin_array_max_size() for all parts
          * of the interface that are arrays.
          */
         for (unsigned i = 0; i < num_variables; i++) {
            if (fields[i].type->is_array()) {
               const unsigned size = fields[i].type->array_size();
               check_builtin_array_max_size(fields[i].name, size, loc, state);
            }
         }
      } else {
         validate_identifier(this->instance_name, loc, state);
      }

      ir_variable *var;

      if (this->array_specifier != NULL) {
         /* Section 4.3.7 (Interface Blocks) of the GLSL 1.50 spec says:
          *
          *     For uniform blocks declared an array, each individual array
          *     element corresponds to a separate buffer object backing one
          *     instance of the block. As the array size indicates the number
          *     of buffer objects needed, uniform block array declarations
          *     must specify an array size.
          *
          * And a few paragraphs later:
          *
          *     Geometry shader input blocks must be declared as arrays and
          *     follow the array declaration and linking rules for all
          *     geometry shader inputs. All other input and output block
          *     arrays must specify an array size.
          *
          * The upshot of this is that the only circumstance where an
          * interface array size *doesn't* need to be specified is on a
          * geometry shader input.
          */
         if (this->array_specifier->is_unsized_array &&
             (state->stage != MESA_SHADER_GEOMETRY || !this->layout.flags.q.in)) {
            _mesa_glsl_error(&loc, state,
                             "only geometry shader inputs may be unsized "
                             "instance block arrays");

         }

         const glsl_type *block_array_type =
            process_array_type(&loc, block_type, this->array_specifier, state);

         var = new(state) ir_variable(block_array_type,
                                      this->instance_name,
                                      var_mode);
      } else {
         var = new(state) ir_variable(block_type,
                                      this->instance_name,
                                      var_mode);
      }

      var->data.matrix_layout = matrix_layout == GLSL_MATRIX_LAYOUT_INHERITED
         ? GLSL_MATRIX_LAYOUT_COLUMN_MAJOR : matrix_layout;

      if (state->stage == MESA_SHADER_GEOMETRY && var_mode == ir_var_shader_in)
         handle_geometry_shader_input_decl(state, loc, var);

      if (ir_variable *earlier =
          state->symbols->get_variable(this->instance_name)) {
         if (!redeclaring_per_vertex) {
            _mesa_glsl_error(&loc, state, "`%s' redeclared",
                             this->instance_name);
         }
         earlier->data.how_declared = ir_var_declared_normally;
         earlier->type = var->type;
         earlier->reinit_interface_type(block_type);
         delete var;
      } else {
         /* Propagate the "binding" keyword into this UBO's fields;
          * the UBO declaration itself doesn't get an ir_variable unless it
          * has an instance name.  This is ugly.
          */
         var->data.explicit_binding = this->layout.flags.q.explicit_binding;
         var->data.binding = this->layout.binding;

         state->symbols->add_variable(var);
         instructions->push_tail(var);
      }
   } else {
      /* In order to have an array size, the block must also be declared with
       * an instance name.
       */
      assert(this->array_specifier == NULL);

      for (unsigned i = 0; i < num_variables; i++) {
         ir_variable *var =
            new(state) ir_variable(fields[i].type,
                                   ralloc_strdup(state, fields[i].name),
                                   var_mode);
         var->data.interpolation = fields[i].interpolation;
         var->data.centroid = fields[i].centroid;
         var->data.sample = fields[i].sample;
         var->init_interface_type(block_type);

         if (fields[i].matrix_layout == GLSL_MATRIX_LAYOUT_INHERITED) {
            var->data.matrix_layout = matrix_layout == GLSL_MATRIX_LAYOUT_INHERITED
               ? GLSL_MATRIX_LAYOUT_COLUMN_MAJOR : matrix_layout;
         } else {
            var->data.matrix_layout = fields[i].matrix_layout;
         }

         if (fields[i].stream != -1 &&
             ((unsigned)fields[i].stream) != this->layout.stream) {
            _mesa_glsl_error(&loc, state,
                             "stream layout qualifier on "
                             "interface block member `%s' does not match "
                             "the interface block (%d vs %d)",
                             var->name, fields[i].stream, this->layout.stream);
         }

         var->data.stream = this->layout.stream;

         if (redeclaring_per_vertex) {
            ir_variable *earlier =
               get_variable_being_redeclared(var, loc, state,
                                             true /* allow_all_redeclarations */);
            if (!is_gl_identifier(var->name) || earlier == NULL) {
               _mesa_glsl_error(&loc, state,
                                "redeclaration of gl_PerVertex can only "
                                "include built-in variables");
            } else if (earlier->data.how_declared == ir_var_declared_normally) {
               _mesa_glsl_error(&loc, state,
                                "`%s' has already been redeclared", var->name);
            } else {
               earlier->data.how_declared = ir_var_declared_in_block;
               earlier->reinit_interface_type(block_type);
            }
            continue;
         }

         if (state->symbols->get_variable(var->name) != NULL)
            _mesa_glsl_error(&loc, state, "`%s' redeclared", var->name);

         /* Propagate the "binding" keyword into this UBO's fields;
          * the UBO declaration itself doesn't get an ir_variable unless it
          * has an instance name.  This is ugly.
          */
         var->data.explicit_binding = this->layout.flags.q.explicit_binding;
         var->data.binding = this->layout.binding;

         state->symbols->add_variable(var);
         instructions->push_tail(var);
      }

      if (redeclaring_per_vertex && block_type != earlier_per_vertex) {
         /* From section 7.1 ("Built-in Language Variables") of the GLSL 4.10 spec:
          *
          *     It is also a compilation error ... to redeclare a built-in
          *     block and then use a member from that built-in block that was
          *     not included in the redeclaration.
          *
          * This appears to be a clarification to the behaviour established
          * for gl_PerVertex by GLSL 1.50, therefore we implement this
          * behaviour regardless of GLSL version.
          *
          * To prevent the shader from using a member that was not included in
          * the redeclaration, we disable any ir_variables that are still
          * associated with the old declaration of gl_PerVertex (since we've
          * already updated all of the variables contained in the new
          * gl_PerVertex to point to it).
          *
          * As a side effect this will prevent
          * validate_intrastage_interface_blocks() from getting confused and
          * thinking there are conflicting definitions of gl_PerVertex in the
          * shader.
          */
         foreach_in_list_safe(ir_instruction, node, instructions) {
            ir_variable *const var = node->as_variable();
            if (var != NULL &&
                var->get_interface_type() == earlier_per_vertex &&
                var->data.mode == var_mode) {
               if (var->data.how_declared == ir_var_declared_normally) {
                  _mesa_glsl_error(&loc, state,
                                   "redeclaration of gl_PerVertex cannot "
                                   "follow a redeclaration of `%s'",
                                   var->name);
               }
               state->symbols->disable_variable(var->name);
               var->remove();
            }
         }
      }
   }

   return NULL;
}


ir_rvalue *
ast_gs_input_layout::hir(exec_list *instructions,
                         struct _mesa_glsl_parse_state *state)
{
   YYLTYPE loc = this->get_location();

   /* If any geometry input layout declaration preceded this one, make sure it
    * was consistent with this one.
    */
   if (state->gs_input_prim_type_specified &&
       state->in_qualifier->prim_type != this->prim_type) {
      _mesa_glsl_error(&loc, state,
                       "geometry shader input layout does not match"
                       " previous declaration");
      return NULL;
   }

   /* If any shader inputs occurred before this declaration and specified an
    * array size, make sure the size they specified is consistent with the
    * primitive type.
    */
   unsigned num_vertices = vertices_per_prim(this->prim_type);
   if (state->gs_input_size != 0 && state->gs_input_size != num_vertices) {
      _mesa_glsl_error(&loc, state,
                       "this geometry shader input layout implies %u vertices"
                       " per primitive, but a previous input is declared"
                       " with size %u", num_vertices, state->gs_input_size);
      return NULL;
   }

   state->gs_input_prim_type_specified = true;

   /* If any shader inputs occurred before this declaration and did not
    * specify an array size, their size is determined now.
    */
   foreach_in_list(ir_instruction, node, instructions) {
      ir_variable *var = node->as_variable();
      if (var == NULL || var->data.mode != ir_var_shader_in)
         continue;

      /* Note: gl_PrimitiveIDIn has mode ir_var_shader_in, but it's not an
       * array; skip it.
       */

      if (var->type->is_unsized_array()) {
         if (var->data.max_array_access >= num_vertices) {
            _mesa_glsl_error(&loc, state,
                             "this geometry shader input layout implies %u"
                             " vertices, but an access to element %u of input"
                             " `%s' already exists", num_vertices,
                             var->data.max_array_access, var->name);
         } else {
            var->type = glsl_type::get_array_instance(var->type->fields.array,
                                                      num_vertices);
         }
      }
   }

   return NULL;
}


ir_rvalue *
ast_cs_input_layout::hir(exec_list *instructions,
                         struct _mesa_glsl_parse_state *state)
{
   YYLTYPE loc = this->get_location();

   /* If any compute input layout declaration preceded this one, make sure it
    * was consistent with this one.
    */
   if (state->cs_input_local_size_specified) {
      for (int i = 0; i < 3; i++) {
         if (state->cs_input_local_size[i] != this->local_size[i]) {
            _mesa_glsl_error(&loc, state,
                             "compute shader input layout does not match"
                             " previous declaration");
            return NULL;
         }
      }
   }

   /* From the ARB_compute_shader specification:
    *
    *     If the local size of the shader in any dimension is greater
    *     than the maximum size supported by the implementation for that
    *     dimension, a compile-time error results.
    *
    * It is not clear from the spec how the error should be reported if
    * the total size of the work group exceeds
    * MAX_COMPUTE_WORK_GROUP_INVOCATIONS, but it seems reasonable to
    * report it at compile time as well.
    */
   GLuint64 total_invocations = 1;
   for (int i = 0; i < 3; i++) {
      if (this->local_size[i] > state->ctx->Const.MaxComputeWorkGroupSize[i]) {
         _mesa_glsl_error(&loc, state,
                          "local_size_%c exceeds MAX_COMPUTE_WORK_GROUP_SIZE"
                          " (%d)", 'x' + i,
                          state->ctx->Const.MaxComputeWorkGroupSize[i]);
         break;
      }
      total_invocations *= this->local_size[i];
      if (total_invocations >
          state->ctx->Const.MaxComputeWorkGroupInvocations) {
         _mesa_glsl_error(&loc, state,
                          "product of local_sizes exceeds "
                          "MAX_COMPUTE_WORK_GROUP_INVOCATIONS (%d)",
                          state->ctx->Const.MaxComputeWorkGroupInvocations);
         break;
      }
   }

   state->cs_input_local_size_specified = true;
   for (int i = 0; i < 3; i++)
      state->cs_input_local_size[i] = this->local_size[i];

   /* We may now declare the built-in constant gl_WorkGroupSize (see
    * builtin_variable_generator::generate_constants() for why we didn't
    * declare it earlier).
    */
   ir_variable *var = new(state->symbols)
      ir_variable(glsl_type::ivec3_type, "gl_WorkGroupSize", ir_var_auto);
   var->data.how_declared = ir_var_declared_implicitly;
   var->data.read_only = true;
   instructions->push_tail(var);
   state->symbols->add_variable(var);
   ir_constant_data data;
   memset(&data, 0, sizeof(data));
   for (int i = 0; i < 3; i++)
      data.i[i] = this->local_size[i];
   var->constant_value = new(var) ir_constant(glsl_type::ivec3_type, &data);
   var->constant_initializer =
      new(var) ir_constant(glsl_type::ivec3_type, &data);
   var->data.has_initializer = true;

   return NULL;
}


static void
detect_conflicting_assignments(struct _mesa_glsl_parse_state *state,
                               exec_list *instructions)
{
   bool gl_FragColor_assigned = false;
   bool gl_FragData_assigned = false;
   bool user_defined_fs_output_assigned = false;
   ir_variable *user_defined_fs_output = NULL;

   /* It would be nice to have proper location information. */
   YYLTYPE loc;
   memset(&loc, 0, sizeof(loc));

   foreach_in_list(ir_instruction, node, instructions) {
      ir_variable *var = node->as_variable();

      if (!var || !var->data.assigned)
         continue;

      if (strcmp(var->name, "gl_FragColor") == 0)
         gl_FragColor_assigned = true;
      else if (strcmp(var->name, "gl_FragData") == 0)
         gl_FragData_assigned = true;
      else if (!is_gl_identifier(var->name)) {
         if (state->stage == MESA_SHADER_FRAGMENT &&
             var->data.mode == ir_var_shader_out) {
            user_defined_fs_output_assigned = true;
            user_defined_fs_output = var;
         }
      }
   }

   /* From the GLSL 1.30 spec:
    *
    *     "If a shader statically assigns a value to gl_FragColor, it
    *      may not assign a value to any element of gl_FragData. If a
    *      shader statically writes a value to any element of
    *      gl_FragData, it may not assign a value to
    *      gl_FragColor. That is, a shader may assign values to either
    *      gl_FragColor or gl_FragData, but not both. Multiple shaders
    *      linked together must also consistently write just one of
    *      these variables.  Similarly, if user declared output
    *      variables are in use (statically assigned to), then the
    *      built-in variables gl_FragColor and gl_FragData may not be
    *      assigned to. These incorrect usages all generate compile
    *      time errors."
    */
   if (gl_FragColor_assigned && gl_FragData_assigned) {
      _mesa_glsl_error(&loc, state, "fragment shader writes to both "
                       "`gl_FragColor' and `gl_FragData'");
   } else if (gl_FragColor_assigned && user_defined_fs_output_assigned) {
      _mesa_glsl_error(&loc, state, "fragment shader writes to both "
                       "`gl_FragColor' and `%s'",
                       user_defined_fs_output->name);
   } else if (gl_FragData_assigned && user_defined_fs_output_assigned) {
      _mesa_glsl_error(&loc, state, "fragment shader writes to both "
                       "`gl_FragData' and `%s'",
                       user_defined_fs_output->name);
   }
}


static void
remove_per_vertex_blocks(exec_list *instructions,
                         _mesa_glsl_parse_state *state, ir_variable_mode mode)
{
   /* Find the gl_PerVertex interface block of the appropriate (in/out) mode,
    * if it exists in this shader type.
    */
   const glsl_type *per_vertex = NULL;
   switch (mode) {
   case ir_var_shader_in:
      if (ir_variable *gl_in = state->symbols->get_variable("gl_in"))
         per_vertex = gl_in->get_interface_type();
      break;
   case ir_var_shader_out:
      if (ir_variable *gl_Position =
          state->symbols->get_variable("gl_Position")) {
         per_vertex = gl_Position->get_interface_type();
      }
      break;
   default:
      assert(!"Unexpected mode");
      break;
   }

   /* If we didn't find a built-in gl_PerVertex interface block, then we don't
    * need to do anything.
    */
   if (per_vertex == NULL)
      return;

   /* If the interface block is used by the shader, then we don't need to do
    * anything.
    */
   interface_block_usage_visitor v(mode, per_vertex);
   v.run(instructions);
   if (v.usage_found())
      return;

   /* Remove any ir_variable declarations that refer to the interface block
    * we're removing.
    */
   foreach_in_list_safe(ir_instruction, node, instructions) {
      ir_variable *const var = node->as_variable();
      if (var != NULL && var->get_interface_type() == per_vertex &&
          var->data.mode == mode) {
         state->symbols->disable_variable(var->name);
         var->remove();
      }
   }
}
