src/glsl/lower_vec_index_to_swizzle.cpp

/*
 * Copyright © 2010 Intel Corporation
 *
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 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
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 * 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.
 *
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
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/**
 * \file lower_vec_index_to_swizzle.cpp
 *
 * Turns constant indexing into vector types to swizzles.  This will
 * let other swizzle-aware optimization passes catch these constructs,
 * and codegen backends not have to worry about this case.
 */

#include "ir.h"
#include "ir_visitor.h"
#include "ir_optimization.h"
#include "glsl_types.h"
#include "main/macros.h"

/**
 * Visitor class for replacing expressions with ir_constant values.
 */

class ir_vec_index_to_swizzle_visitor : public ir_hierarchical_visitor {
public:
   ir_vec_index_to_swizzle_visitor()
   {
      progress = false;
   }

   ir_rvalue *convert_vec_index_to_swizzle(ir_rvalue *val);

   virtual ir_visitor_status visit_enter(ir_expression *);
   virtual ir_visitor_status visit_enter(ir_swizzle *);
   virtual ir_visitor_status visit_enter(ir_assignment *);
   virtual ir_visitor_status visit_enter(ir_return *);
   virtual ir_visitor_status visit_enter(ir_call *);
   virtual ir_visitor_status visit_enter(ir_if *);

   bool progress;
};

ir_rvalue *
ir_vec_index_to_swizzle_visitor::convert_vec_index_to_swizzle(ir_rvalue *ir)
{
   ir_dereference_array *deref = ir->as_dereference_array();
   ir_constant *ir_constant;

   if (!deref)
      return ir;

   if (deref->array->type->is_matrix() || deref->array->type->is_array())
      return ir;

   assert(deref->array_index->type->base_type == GLSL_TYPE_INT);
   ir_constant = deref->array_index->constant_expression_value();
   if (!ir_constant)
      return ir;

   void *ctx = ralloc_parent(ir);
   this->progress = true;

   /* Page 40 of the GLSL 1.20 spec says:
    *
    *     "When indexing with non-constant expressions, behavior is undefined
    *     if the index is negative, or greater than or equal to the size of
    *     the vector."
    *
    * The quoted spec text mentions non-constant expressions, but this code
    * operates on constants.  These constants are the result of non-constant
    * expressions that have been optimized to constants.  The common case here
    * is a loop counter from an unrolled loop that is used to index a vector.
    *
    * The ir_swizzle constructor gets angry if the index is negative or too
    * large.  For simplicity sake, just clamp the index to [0, size-1].
    */
   const int i = MIN2(MAX2(ir_constant->value.i[0], 0),
		      (deref->array->type->vector_elements - 1));

   return new(ctx) ir_swizzle(deref->array, i, 0, 0, 0, 1);
}

ir_visitor_status
ir_vec_index_to_swizzle_visitor::visit_enter(ir_expression *ir)
{
   unsigned int i;

   for (i = 0; i < ir->get_num_operands(); i++) {
      ir->operands[i] = convert_vec_index_to_swizzle(ir->operands[i]);
   }

   return visit_continue;
}

ir_visitor_status
ir_vec_index_to_swizzle_visitor::visit_enter(ir_swizzle *ir)
{
   /* Can't be hit from normal GLSL, since you can't swizzle a scalar (which
    * the result of indexing a vector is.  But maybe at some point we'll end up
    * using swizzling of scalars for vector construction.
    */
   ir->val = convert_vec_index_to_swizzle(ir->val);

   return visit_continue;
}

ir_visitor_status
ir_vec_index_to_swizzle_visitor::visit_enter(ir_assignment *ir)
{
   ir->set_lhs(convert_vec_index_to_swizzle(ir->lhs));
   ir->rhs = convert_vec_index_to_swizzle(ir->rhs);

   return visit_continue;
}

ir_visitor_status
ir_vec_index_to_swizzle_visitor::visit_enter(ir_call *ir)
{
   foreach_iter(exec_list_iterator, iter, *ir) {
      ir_rvalue *param = (ir_rvalue *)iter.get();
      ir_rvalue *new_param = convert_vec_index_to_swizzle(param);

      if (new_param != param) {
	 param->replace_with(new_param);
      }
   }

   return visit_continue;
}

ir_visitor_status
ir_vec_index_to_swizzle_visitor::visit_enter(ir_return *ir)
{
   if (ir->value) {
      ir->value = convert_vec_index_to_swizzle(ir->value);
   }

   return visit_continue;
}

ir_visitor_status
ir_vec_index_to_swizzle_visitor::visit_enter(ir_if *ir)
{
   ir->condition = convert_vec_index_to_swizzle(ir->condition);

   return visit_continue;
}

bool
do_vec_index_to_swizzle(exec_list *instructions)
{
   ir_vec_index_to_swizzle_visitor v;

   v.run(instructions);

   return v.progress;
}