Use yy_scan_string and stop caring about shader->SourceLen.

[mesa.git] / ast_to_hir.cpp

/*
 * 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 <stdio.h>
#include "main/imports.h"
#include "glsl_symbol_table.h"
#include "glsl_parser_extras.h"
#include "ast.h"
#include "glsl_types.h"
#include "ir.h"

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

   state->current_function = NULL;

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


/**
 * 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.
 */
static bool
apply_implicit_conversion(const glsl_type *to, ir_rvalue * &from,
                          struct _mesa_glsl_parse_state *state)
{
   if (to->base_type == from->type->base_type)
      return true;

   /* This conversion was added in GLSL 1.20.  If the compilation mode is
    * GLSL 1.10, the conversion is skipped.
    */
   if (state->language_version < 120)
      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. There are no implicit conversions between
    *    signed and unsigned integers."
    */
   /* FINISHME: The above comment is partially a lie.  There is int/uint
    * FINISHME: conversion for immediate constants.
    */
   if (!to->is_float() || !from->type->is_numeric())
      return false;

   switch (from->type->base_type) {
   case GLSL_TYPE_INT:
      from = new ir_expression(ir_unop_i2f, to, from, NULL);
      break;
   case GLSL_TYPE_UINT:
      from = new ir_expression(ir_unop_u2f, to, from, NULL);
      break;
   case GLSL_TYPE_BOOL:
      from = new ir_expression(ir_unop_b2f, to, from, NULL);
      break;
   default:
      assert(0);
   }

   return true;
}


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)
            return type_b;
      } 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())
            return type_a;
      }

      _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;
}


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)
{
   /* 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() || !type_b->is_integer()
       || (type_a->base_type != type_b->base_type)) {
      _mesa_glsl_error(loc, state, "type mismatch");
      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;
}


/**
 * 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,
                    const glsl_type *lhs_type, ir_rvalue *rhs)
{
   const glsl_type *rhs_type = rhs->type;

   /* 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 size of the LHS is zero,
    * the assignment is okay.
    *
    * Note: Whole-array assignments are not permitted in GLSL 1.10, but this
    * is handled by ir_dereference::is_lvalue.
    */
   if (lhs_type->is_array() && rhs->type->is_array()
       && (lhs_type->element_type() == rhs->type->element_type())
       && (lhs_type->array_size() == 0)) {
      return rhs;
   }

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

   return NULL;
}

ir_rvalue *
do_assignment(exec_list *instructions, struct _mesa_glsl_parse_state *state,
              ir_rvalue *lhs, ir_rvalue *rhs,
              YYLTYPE lhs_loc)
{
   bool error_emitted = (lhs->type->is_error() || rhs->type->is_error());

   if (!error_emitted) {
      /* FINISHME: This does not handle 'foo.bar.a.b.c[5].d = 5' */
      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->type, rhs);
   if (new_rhs == NULL) {
      _mesa_glsl_error(& lhs_loc, state, "type mismatch");
   } else {
      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->array_size() == 0) {
         ir_dereference *const d = lhs->as_dereference();

         assert(d != NULL);

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

         assert(var != NULL);

         if (var->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->max_array_access);
         }

         var->type = glsl_type::get_array_instance(lhs->type->element_type(),
                                                   rhs->type->array_size());
      }
   }

   ir_instruction *tmp = new ir_assignment(lhs, rhs, NULL);
   instructions->push_tail(tmp);

   return rhs;
}


/**
 * Generate a new temporary and add its declaration to the instruction stream
 */
static ir_variable *
generate_temporary(const glsl_type *type, exec_list *instructions,
                   struct _mesa_glsl_parse_state *state)
{
   char *name = (char *) malloc(sizeof(char) * 13);

   snprintf(name, 13, "tmp_%08X", state->temp_index);
   state->temp_index++;

   ir_variable *const var = new ir_variable(type, name);
   instructions->push_tail(var);

   return var;
}


static ir_rvalue *
get_lvalue_copy(exec_list *instructions, struct _mesa_glsl_parse_state *state,
                ir_rvalue *lvalue, YYLTYPE loc)
{
   ir_variable *var;
   ir_rvalue *var_deref;

   /* FINISHME: Give unique names to the temporaries. */
   var = new ir_variable(lvalue->type, "_internal_tmp");
   var->mode = ir_var_auto;

   var_deref = new ir_dereference_variable(var);
   do_assignment(instructions, state, var_deref, lvalue, loc);

   /* Once we've created this temporary, mark it read only so it's no
    * longer considered an lvalue.
    */
   var->read_only = true;

   return var_deref;
}


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

   return NULL;
}


ir_rvalue *
ast_expression::hir(exec_list *instructions,
                    struct _mesa_glsl_parse_state *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_equal,
      ir_binop_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[2];
   const struct glsl_type *type = glsl_type::error_type;
   bool error_emitted = false;
   YYLTYPE loc;

   loc = this->get_location();

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

      result = do_assignment(instructions, state, op[0], op[1],
                             this->subexpressions[0]->get_location());
      error_emitted = result->type->is_error();
      type = result->type;
      break;
   }

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

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

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

   case ast_lshift:
   case ast_rshift:
      _mesa_glsl_error(& loc, state, "FINISHME: implement bit-shift operators");
      error_emitted = true;
      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 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 ((state->language_version <= 110)
                 && (op[0]->type->is_array() || op[1]->type->is_array())) {
         _mesa_glsl_error(& loc, state, "array comparisons forbidden in "
                          "GLSL 1.10");
         error_emitted = true;
      }

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

      assert(result->type == glsl_type::bool_type);
      break;

   case ast_bit_and:
   case ast_bit_xor:
   case ast_bit_or:
   case ast_bit_not:
      _mesa_glsl_error(& loc, state, "FINISHME: implement bit-wise operators");
      error_emitted = true;
      break;

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

      if (!op[0]->type->is_boolean() || !op[0]->type->is_scalar()) {
         YYLTYPE loc = this->subexpressions[0]->get_location();

         _mesa_glsl_error(& loc, state, "LHS of `%s' must be scalar boolean",
                          operator_string(this->oper));
         error_emitted = true;
      }

      ir_constant *op0_const = op[0]->constant_expression_value();
      if (op0_const) {
         if (op0_const->value.b[0]) {
            op[1] = this->subexpressions[1]->hir(instructions, state);

            if (!op[1]->type->is_boolean() || !op[1]->type->is_scalar()) {
               YYLTYPE loc = this->subexpressions[1]->get_location();

               _mesa_glsl_error(& loc, state,
                                "RHS of `%s' must be scalar boolean",
                                operator_string(this->oper));
               error_emitted = true;
            }
            result = op[1];
         } else {
            result = op0_const;
         }
         type = glsl_type::bool_type;
      } else {
         ir_if *const stmt = new ir_if(op[0]);
         instructions->push_tail(stmt);

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

         if (!op[1]->type->is_boolean() || !op[1]->type->is_scalar()) {
            YYLTYPE loc = this->subexpressions[1]->get_location();

            _mesa_glsl_error(& loc, state,
                             "RHS of `%s' must be scalar boolean",
                             operator_string(this->oper));
            error_emitted = true;
         }

         ir_variable *const tmp = generate_temporary(glsl_type::bool_type,
                                                     instructions, state);

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

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

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

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

      if (!op[0]->type->is_boolean() || !op[0]->type->is_scalar()) {
         YYLTYPE loc = this->subexpressions[0]->get_location();

         _mesa_glsl_error(& loc, state, "LHS of `%s' must be scalar boolean",
                          operator_string(this->oper));
         error_emitted = true;
      }

      ir_constant *op0_const = op[0]->constant_expression_value();
      if (op0_const) {
         if (op0_const->value.b[0]) {
            result = op0_const;
         } else {
            op[1] = this->subexpressions[1]->hir(instructions, state);

            if (!op[1]->type->is_boolean() || !op[1]->type->is_scalar()) {
               YYLTYPE loc = this->subexpressions[1]->get_location();

               _mesa_glsl_error(& loc, state,
                                "RHS of `%s' must be scalar boolean",
                                operator_string(this->oper));
               error_emitted = true;
            }
            result = op[1];
         }
         type = glsl_type::bool_type;
      } else {
         ir_if *const stmt = new ir_if(op[0]);
         instructions->push_tail(stmt);

         ir_variable *const tmp = generate_temporary(glsl_type::bool_type,
                                                     instructions, state);

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

         if (!op[1]->type->is_boolean() || !op[1]->type->is_scalar()) {
            YYLTYPE loc = this->subexpressions[1]->get_location();

            _mesa_glsl_error(& loc, state, "RHS of `%s' must be scalar boolean",
                             operator_string(this->oper));
            error_emitted = true;
         }

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

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

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

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


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

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

      if (!op[0]->type->is_boolean() || !op[0]->type->is_scalar()) {
         YYLTYPE loc = this->subexpressions[0]->get_location();

         _mesa_glsl_error(& loc, state,
                          "operand of `!' must be scalar boolean");
         error_emitted = true;
      }

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

      result = do_assignment(instructions, state, op[0], temp_rhs,
                             this->subexpressions[0]->get_location());
      type = result->type;
      error_emitted = (op[0]->type->is_error());

      /* 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);

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

      result = do_assignment(instructions, state, op[0], temp_rhs,
                             this->subexpressions[0]->get_location());
      type = result->type;
      error_emitted = type->is_error();
      break;
   }

   case ast_ls_assign:
   case ast_rs_assign:
      _mesa_glsl_error(& loc, state,
                       "FINISHME: implement bit-shift assignment operators");
      error_emitted = true;
      break;

   case ast_and_assign:
   case ast_xor_assign:
   case ast_or_assign:
      _mesa_glsl_error(& loc, state,
                       "FINISHME: implement logic assignment operators");
      error_emitted = true;
      break;

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

      /* 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."
       */
      if (!op[0]->type->is_boolean() || !op[0]->type->is_scalar()) {
         YYLTYPE loc = this->subexpressions[0]->get_location();

         _mesa_glsl_error(& loc, state, "?: condition must be scalar boolean");
         error_emitted = true;
      }

      /* 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;
      }

      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 = generate_temporary(type,
                                                     instructions, state);

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

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

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

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

   case ast_pre_inc:
   case ast_pre_dec: {
      op[0] = this->subexpressions[0]->hir(instructions, state);
      if (op[0]->type->base_type == GLSL_TYPE_FLOAT)
         op[1] = new ir_constant(1.0f);
      else
         op[1] = new ir_constant(1);

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

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

      result = do_assignment(instructions, state, op[0], temp_rhs,
                             this->subexpressions[0]->get_location());
      type = result->type;
      error_emitted = op[0]->type->is_error();
      break;
   }

   case ast_post_inc:
   case ast_post_dec: {
      op[0] = this->subexpressions[0]->hir(instructions, state);
      if (op[0]->type->base_type == GLSL_TYPE_FLOAT)
         op[1] = new ir_constant(1.0f);
      else
         op[1] = new ir_constant(1);

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

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

      struct ir_rvalue *temp_rhs;
      temp_rhs = new 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, state, op[0],
                               this->subexpressions[0]->get_location());

      (void)do_assignment(instructions, state, op[0], temp_rhs,
                          this->subexpressions[0]->get_location());

      type = result->type;
      error_emitted = op[0]->type->is_error();
      break;
   }

   case ast_field_selection:
      result = _mesa_ast_field_selection_to_hir(this, instructions, state);
      type = result->type;
      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);

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

      ir_rvalue *const array = op[0];

      result = new ir_dereference_array(op[0], op[1]);

      /* Do not use op[0] after this point.  Use array.
       */
      op[0] = NULL;


      if (error_emitted)
         break;

      if (!array->type->is_array()
          && !array->type->is_matrix()
          && !array->type->is_vector()) {
         _mesa_glsl_error(& index_loc, state,
                          "cannot dereference non-array / non-matrix / "
                          "non-vector");
         error_emitted = true;
      }

      if (!op[1]->type->is_integer()) {
         _mesa_glsl_error(& index_loc, state,
                          "array index must be integer type");
         error_emitted = true;
      } else if (!op[1]->type->is_scalar()) {
         _mesa_glsl_error(& index_loc, state,
                          "array index must be scalar");
         error_emitted = true;
      }

      /* If the array index is a constant expression and the array has a
       * declared size, ensure that the access is in-bounds.  If the array
       * index is not a constant expression, ensure that the array has a
       * declared size.
       */
      ir_constant *const const_index = op[1]->constant_expression_value();
      if (const_index != NULL) {
         const int idx = const_index->value.i[0];
         const char *type_name;
         unsigned bound = 0;

         if (array->type->is_matrix()) {
            type_name = "matrix";
         } else if (array->type->is_vector()) {
            type_name = "vector";
         } else {
            type_name = "array";
         }

         /* From page 24 (page 30 of the PDF) of the GLSL 1.50 spec:
          *
          *    "It is illegal to declare an array with a size, and then
          *    later (in the same shader) index the same array with an
          *    integral constant expression greater than or equal to the
          *    declared size. It is also illegal to index an array with a
          *    negative constant expression."
          */
         if (array->type->is_matrix()) {
            if (array->type->row_type()->vector_elements <= idx) {
               bound = array->type->row_type()->vector_elements;
            }
         } else if (array->type->is_vector()) {
            if (array->type->vector_elements <= idx) {
               bound = array->type->vector_elements;
            }
         } else {
            if ((array->type->array_size() > 0)
                && (array->type->array_size() <= idx)) {
               bound = array->type->array_size();
            }
         }

         if (bound > 0) {
            _mesa_glsl_error(& loc, state, "%s index must be < %u",
                             type_name, bound);
            error_emitted = true;
         } else if (idx < 0) {
            _mesa_glsl_error(& loc, state, "%s index must be >= 0",
                             type_name);
            error_emitted = true;
         }

         if (array->type->is_array()) {
            /* If the array is a variable dereference, it dereferences the
             * whole array, by definition.  Use this to get the variable.
             *
             * FINISHME: Should some methods for getting / setting / testing
             * FINISHME: array access limits be added to ir_dereference?
             */
            ir_variable *const v = array->whole_variable_referenced();
            if ((v != NULL) && (unsigned(idx) > v->max_array_access))
               v->max_array_access = idx;
         }
      }

      if (error_emitted)
         result->type = glsl_type::error_type;

      type = result->type;
      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);

      result = new ir_dereference_variable(var);

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

         error_emitted = true;
      }
      break;
   }

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

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

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

   case ast_bool_constant:
      type = glsl_type::bool_type;
      result = new 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.
       */
      foreach_list_typed (ast_node, ast, link, &this->expressions)
         result = ast->hir(instructions, state);

      type = result->type;

      /* Any errors should have already been emitted in the loop above.
       */
      error_emitted = true;
      break;
   }
   }

   if (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(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;
}


static const glsl_type *
process_array_type(const glsl_type *base, ast_node *array_size,
                   struct _mesa_glsl_parse_state *state)
{
   unsigned length = 0;

   /* FINISHME: Reject delcarations of multidimensional arrays. */

   if (array_size != NULL) {
      exec_list dummy_instructions;
      ir_rvalue *const ir = array_size->hir(& dummy_instructions, state);
      YYLTYPE loc = array_size->get_location();

      /* FINISHME: Verify that the grammar forbids side-effects in array
       * FINISHME: sizes.   i.e., 'vec4 [x = 12] data'
       */
      assert(dummy_instructions.is_empty());

      if (ir != NULL) {
         if (!ir->type->is_integer()) {
            _mesa_glsl_error(& loc, state, "array size must be integer type");
         } else if (!ir->type->is_scalar()) {
            _mesa_glsl_error(& loc, state, "array size must be scalar type");
         } else {
            ir_constant *const size = ir->constant_expression_value();

            if (size == NULL) {
               _mesa_glsl_error(& loc, state, "array size must be a "
                                "constant valued expression");
            } else if (size->value.i[0] <= 0) {
               _mesa_glsl_error(& loc, state, "array size must be > 0");
            } else {
               assert(size->type == ir->type);
               length = size->value.u[0];
            }
         }
      }
   }

   return glsl_type::get_array_instance(base, length);
}


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

   if ((this->type_specifier == ast_struct) && (this->type_name == NULL)) {
      /* FINISHME: Handle annonymous structures. */
      type = NULL;
   } else {
      type = state->symbols->get_type(this->type_name);
      *name = this->type_name;

      if (this->is_array) {
         type = process_array_type(type, this->array_size, state);
      }
   }

   return type;
}


static void
apply_type_qualifier_to_variable(const struct ast_type_qualifier *qual,
                                 struct ir_variable *var,
                                 struct _mesa_glsl_parse_state *state,
                                 YYLTYPE *loc)
{
   if (qual->invariant)
      var->invariant = 1;

   /* FINISHME: Mark 'in' variables at global scope as read-only. */
   if (qual->constant || qual->attribute || qual->uniform
       || (qual->varying && (state->target == fragment_shader)))
      var->read_only = 1;

   if (qual->centroid)
      var->centroid = 1;

   if (qual->attribute && state->target != vertex_shader) {
      var->type = glsl_type::error_type;
      _mesa_glsl_error(loc, state,
                       "`attribute' variables may not be declared in the "
                       "%s shader",
                       _mesa_glsl_shader_target_name(state->target));
   }

   /* 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."
    */
   if (qual->varying) {
      const glsl_type *non_array_type;

      if (var->type && var->type->is_array())
         non_array_type = var->type->fields.array;
      else
         non_array_type = var->type;

      if (non_array_type && non_array_type->base_type != GLSL_TYPE_FLOAT) {
         var->type = glsl_type::error_type;
         _mesa_glsl_error(loc, state,
                          "varying variables must be of base type float");
      }
   }

   if (qual->in && qual->out)
      var->mode = ir_var_inout;
   else if (qual->attribute || qual->in
            || (qual->varying && (state->target == fragment_shader)))
      var->mode = ir_var_in;
   else if (qual->out || (qual->varying && (state->target == vertex_shader)))
      var->mode = ir_var_out;
   else if (qual->uniform)
      var->mode = ir_var_uniform;
   else
      var->mode = ir_var_auto;

   if (qual->uniform)
      var->shader_in = true;

   /* Any 'in' or 'inout' variables at global scope must be marked as being
    * shader inputs.  Likewise, any 'out' or 'inout' variables at global scope
    * must be marked as being shader outputs.
    */
   if (state->current_function == NULL) {
      switch (var->mode) {
      case ir_var_in:
      case ir_var_uniform:
         var->shader_in = true;
         break;
      case ir_var_out:
         var->shader_out = true;
         break;
      case ir_var_inout:
         var->shader_in = true;
         var->shader_out = true;
         break;
      default:
         break;
      }
   }

   if (qual->flat)
      var->interpolation = ir_var_flat;
   else if (qual->noperspective)
      var->interpolation = ir_var_noperspective;
   else
      var->interpolation = ir_var_smooth;

   if (var->type->is_array() && (state->language_version >= 120)) {
      var->array_lvalue = true;
   }
}


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

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

   /* FINISHME: Handle vertex shader "invariant" declarations that do not
    * FINISHME: include a type.  These re-declare built-in variables to be
    * FINISHME: invariant.
    */

   decl_type = this->type->specifier->glsl_type(& type_name, state);
   if (this->declarations.is_empty()) {
      /* There are only two valid cases where the declaration list can be
       * empty.
       *
       * 1. The declaration is setting the default precision of a built-in
       *    type (e.g., 'precision highp vec4;').
       *
       * 2. Adding 'invariant' to an existing vertex shader output.
       */

      if (this->type->qualifier.invariant) {
      } else if (decl_type != NULL) {
      } else {
            _mesa_glsl_error(& loc, state, "incomplete declaration");
      }
   }

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

      if (decl->is_array) {
         var_type = process_array_type(decl_type, decl->array_size, state);
      } else {
         var_type = decl_type;
      }

      var = new ir_variable(var_type, 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, uni form, or varying. Only one may be
       *     specified.
       *
       *     Local variables can only use the qualifier const."
       *
       * This is relaxed in GLSL 1.30.
       */
      if (state->language_version < 120) {
         if (this->type->qualifier.out) {
            _mesa_glsl_error(& loc, state,
                             "`out' qualifier in declaration of `%s' "
                             "only valid for function parameters in GLSL 1.10.",
                             decl->identifier);
         }
         if (this->type->qualifier.in) {
            _mesa_glsl_error(& loc, state,
                             "`in' qualifier in declaration of `%s' "
                             "only valid for function parameters in GLSL 1.10.",
                             decl->identifier);
         }
         /* FINISHME: Test for other invalid qualifiers. */
      }

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

      /* Attempt to add the variable to the symbol table.  If this fails, it
       * means the variable has already been declared at this scope.  Arrays
       * fudge this rule a little bit.
       *
       * 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 (state->symbols->name_declared_this_scope(decl->identifier)) {
         ir_variable *const earlier =
            state->symbols->get_variable(decl->identifier);

         if ((earlier != NULL)
             && (earlier->type->array_size() == 0)
             && 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.
             */

            if (var->type->array_size() <= (int)earlier->max_array_access) {
               YYLTYPE loc = this->get_location();

               _mesa_glsl_error(& loc, state, "array size must be > %u due to "
                                "previous access",
                                earlier->max_array_access);
            }

            earlier->type = var->type;
            delete var;
            var = NULL;
         } else {
            YYLTYPE loc = this->get_location();

            _mesa_glsl_error(& loc, state, "`%s' redeclared",
                             decl->identifier);
         }

         continue;
      }

      /* 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 (strncmp(decl->identifier, "gl_", 3) == 0) {
         /* FINISHME: This should only trigger if we're not redefining
          * FINISHME: a builtin (to add a qualifier, for example).
          */
         _mesa_glsl_error(& loc, state,
                          "identifier `%s' uses reserved `gl_' prefix",
                          decl->identifier);
      }

      instructions->push_tail(var);

      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.attribute) {
            mode = "attribute";
         } else if (this->type->qualifier.uniform) {
            mode = "uniform";
         } else if (this->type->qualifier.varying) {
            mode = "varying";
         } else if (this->type->qualifier.in) {
            mode = "in";
            extra = " or in function parameter list";
         } else if (this->type->qualifier.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->mode == ir_var_in) {
         if (state->target == vertex_shader) {
            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."
             */
            const glsl_type *check_type = var->type->is_array()
               ? var->type->fields.array : var->type;

            switch (check_type->base_type) {
            case GLSL_TYPE_FLOAT:
               break;
            case GLSL_TYPE_UINT:
            case GLSL_TYPE_INT:
               if (state->language_version > 120)
                  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 && (state->language_version <= 130)
                && var->type->is_array()) {
               _mesa_glsl_error(& loc, state,
                                "vertex shader input / attribute cannot have "
                                "array type");
               error_emitted = true;
            }
         }
      }

      if (decl->initializer != 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 ((state->language_version <= 110)
             && (var->mode == ir_var_uniform)) {
            _mesa_glsl_error(& initializer_loc, state,
                             "cannot initialize uniforms in GLSL 1.10");
         }

         if (var->type->is_sampler()) {
            _mesa_glsl_error(& initializer_loc, state,
                             "cannot initialize samplers");
         }

         if ((var->mode == ir_var_in) && (state->current_function == NULL)) {
            _mesa_glsl_error(& initializer_loc, state,
                             "cannot initialize %s shader input / %s",
                             _mesa_glsl_shader_target_name(state->target),
                             (state->target == vertex_shader)
                             ? "attribute" : "varying");
         }

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

         /* Calculate the constant value if this is a const or uniform
          * declaration.
          */
         if (this->type->qualifier.constant || this->type->qualifier.uniform) {
            ir_constant *constant_value = rhs->constant_expression_value();
            if (!constant_value) {
               _mesa_glsl_error(& initializer_loc, state,
                                "initializer of %s variable `%s' must be a "
                                "constant expression",
                                (this->type->qualifier.constant)
                                ? "const" : "uniform",
                                decl->identifier);
            } else {
               rhs = constant_value;
               var->constant_value = constant_value;
            }
         }

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

            /* Never emit code to initialize a uniform.
             */
            if (!this->type->qualifier.uniform)
               result = do_assignment(instructions, state, lhs, rhs,
                                      this->get_location());
            var->read_only = temp;
         }
      }

      /* 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.constant && decl->initializer == NULL) {
         _mesa_glsl_error(& loc, state,
                          "const declaration of `%s' must be initialized");
      }

      /* Add the vairable to the symbol table after processing the initializer.
       * 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."
       */
      const bool added_variable =
         state->symbols->add_variable(decl->identifier, var);
      assert(added_variable);
   }


   /* 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)
{
   const struct glsl_type *type;
   const char *name = NULL;
   YYLTYPE loc = this->get_location();

   type = this->type->specifier->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;
   }

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

   /* FINISHME: Handle array declarations.  Note that this requires
    * FINISHME: complete handling of constant expressions.
    */

   /* 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);
   if (var->mode == ir_var_auto)
      var->mode = ir_var_in;

   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");
   }
}


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


   /* 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->specifier->glsl_type(& return_type_name, state);

   assert(return_type != NULL);

   /* 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.
    */
   const char *const name = identifier;
   f = state->symbols->get_function(name);
   if (f != NULL) {
      ir_function_signature *sig = f->exact_matching_signature(&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 (is_definition && sig->is_defined) {
            YYLTYPE loc = this->get_location();

            _mesa_glsl_error(& loc, state, "function `%s' redefined", name);
            sig = NULL;
         }
      }
   } else if (state->symbols->name_declared_this_scope(name)) {
      /* 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);
      sig = NULL;
   } else {
      f = new ir_function(name);
      state->symbols->add_function(f->name, f);

      /* Emit the new function header */
      instructions->push_tail(f);
   }

   /* 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 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;

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

   /* Duplicate parameters declared in the prototype as concrete variables.
    * Add these to the symbol table.
    */
   state->symbols->push_scope();
   foreach_iter(exec_list_iterator, iter, signature->parameters) {
      ir_variable *const var = ((ir_instruction *) iter.get())->as_variable();

      assert(var != 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->name, 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;

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


ir_rvalue *
ast_jump_statement::hir(exec_list *instructions,
                        struct _mesa_glsl_parse_state *state)
{

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

      if (opt_return_value) {
         if (state->current_function->return_type->base_type ==
             GLSL_TYPE_VOID) {
            YYLTYPE loc = this->get_location();

            _mesa_glsl_error(& loc, state,
                             "`return` with a value, in function `%s' "
                             "returning void",
                             state->current_function->function_name());
         }

         ir_expression *const ret = (ir_expression *)
            opt_return_value->hir(instructions, state);
         assert(ret != NULL);

         /* FINISHME: Make sure the type of the return value matches the return
          * FINISHME: type of the enclosing function.
          */

         inst = new 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 ir_return;
      }

      instructions->push_tail(inst);
      break;
   }

   case ast_discard:
      /* FINISHME: discard support */
      if (state->target != fragment_shader) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state,
                          "`discard' may only appear in a fragment shader");
      }
      break;

   case ast_break:
   case ast_continue:
      /* FINISHME: Handle switch-statements.  They cannot contain 'continue',
       * FINISHME: and they use a different IR instruction for 'break'.
       */
      /* FINISHME: Correctly handle the nesting.  If a switch-statement is
       * FINISHME: inside a loop, a 'continue' is valid and will bind to the
       * FINISHME: loop.
       */
      if (state->loop_or_switch_nesting == NULL) {
         YYLTYPE loc = this->get_location();

         _mesa_glsl_error(& loc, state,
                          "`%s' may only appear in a loop",
                          (mode == ast_break) ? "break" : "continue");
      } else {
         ir_loop *const loop = state->loop_or_switch_nesting->as_loop();

         if (loop != NULL) {
            ir_loop_jump *const jump =
               new ir_loop_jump(loop,
                                (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)
{
   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 ir_if(condition);

   if (then_statement != NULL)
      then_statement->hir(& stmt->then_instructions, state);

   if (else_statement != NULL)
      else_statement->hir(& stmt->else_instructions, state);

   instructions->push_tail(stmt);

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


void
ast_iteration_statement::condition_to_hir(ir_loop *stmt,
                                          struct _mesa_glsl_parse_state *state)
{
   if (condition != NULL) {
      ir_rvalue *const cond =
         condition->hir(& stmt->body_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 ir_expression(ir_unop_logic_not, glsl_type::bool_type, cond,
                              NULL);

         ir_if *const if_stmt = new ir_if(not_cond);

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

         if_stmt->then_instructions.push_tail(break_stmt);
         stmt->body_instructions.push_tail(if_stmt);
      }
   }
}


ir_rvalue *
ast_iteration_statement::hir(exec_list *instructions,
                             struct _mesa_glsl_parse_state *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 ir_loop();
   instructions->push_tail(stmt);

   /* Track the current loop and / or switch-statement nesting.
    */
   ir_instruction *const nesting = state->loop_or_switch_nesting;
   state->loop_or_switch_nesting = stmt;

   if (mode != ast_do_while)
      condition_to_hir(stmt, 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, state);

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

   /* Restore previous nesting before returning.
    */
   state->loop_or_switch_nesting = nesting;

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


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

   return NULL;
}


ir_rvalue *
ast_struct_specifier::hir(exec_list *instructions,
                          struct _mesa_glsl_parse_state *state)
{
   unsigned decl_count = 0;

   /* Make an initial pass over the list of structure 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,
                       &this->declarations) {
      foreach_list_const (decl_ptr, & decl_list->declarations) {
         decl_count++;
      }
   }


   /* Allocate storage for the structure 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 are processed.
    */
   glsl_struct_field *const fields = (glsl_struct_field *)
      malloc(sizeof(*fields) * decl_count);

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

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

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

      foreach_list_typed (ast_declaration, decl, link,
                          &decl_list->declarations) {
         const struct glsl_type *const field_type =
            (decl->is_array)
            ? process_array_type(decl_type, decl->array_size, state)
            : decl_type;

         fields[i].type = (field_type != NULL)
            ? field_type : glsl_type::error_type;
         fields[i].name = decl->identifier;
         i++;
      }
   }

   assert(i == decl_count);

   const char *name;
   if (this->name == NULL) {
      static unsigned anon_count = 1;
      char buf[32];

      snprintf(buf, sizeof(buf), "#anon_struct_%04x", anon_count);
      anon_count++;

      name = strdup(buf);
   } else {
      name = this->name;
   }

   glsl_type *t = new glsl_type(fields, decl_count, name);

   YYLTYPE loc = this->get_location();
   if (!state->symbols->add_type(name, t)) {
      _mesa_glsl_error(& loc, state, "struct `%s' previously defined", name);
   } else {
      /* This logic is a bit tricky.  It is an error to declare a structure at
       * global scope if there is also a function with the same name.
       */
      if ((state->current_function == NULL)
          && (state->symbols->get_function(name) != NULL)) {
         _mesa_glsl_error(& loc, state, "name `%s' previously defined", name);
      } else {
         t->generate_constructor(state->symbols);
      }

      const glsl_type **s = (const glsl_type **)
         realloc(state->user_structures,
                 sizeof(state->user_structures[0]) *
                 (state->num_user_structures + 1));
      if (s != NULL) {
         s[state->num_user_structures] = t;
         state->user_structures = s;
         state->num_user_structures++;
      }
   }

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