src/compiler/glsl/lower_vec_index_to_swizzle.cpp

   1 /*
   2  * Copyright © 2010 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 /**
  25  * \file lower_vec_index_to_swizzle.cpp
  26  *
  27  * Turns constant indexing into vector types to swizzles.  This will
  28  * let other swizzle-aware optimization passes catch these constructs,
  29  * and codegen backends not have to worry about this case.
  30  */
  31
  32 #include "ir.h"
  33 #include "ir_rvalue_visitor.h"
  34 #include "ir_optimization.h"
  35 #include "compiler/glsl_types.h"
  36 #include "main/macros.h"
  37
  38 namespace {
  39
  40 class ir_vec_index_to_swizzle_visitor : public ir_rvalue_visitor {
  41 public:
  42    ir_vec_index_to_swizzle_visitor()
  43    {
  44       progress = false;
  45    }
  46
  47    ir_rvalue *convert_vector_extract_to_swizzle(ir_rvalue *val);
  48
  49    virtual void handle_rvalue(ir_rvalue **);
  50
  51    bool progress;
  52 };
  53
  54 } /* anonymous namespace */
  55
  56 void
  57 ir_vec_index_to_swizzle_visitor::handle_rvalue(ir_rvalue **rv)
  58 {
  59    if (*rv == NULL)
  60       return;
  61
  62    ir_expression *const expr = (*rv)->as_expression();
  63    if (expr == NULL || expr->operation != ir_binop_vector_extract)
  64       return;
  65
  66    void *mem_ctx = ralloc_parent(expr);
  67    ir_constant *const idx =
  68       expr->operands[1]->constant_expression_value(mem_ctx);
  69    if (idx == NULL)
  70       return;
  71
  72    this->progress = true;
  73
  74    /* Page 40 of the GLSL 1.20 spec says:
  75     *
  76     *     "When indexing with non-constant expressions, behavior is undefined
  77     *     if the index is negative, or greater than or equal to the size of
  78     *     the vector."
  79     *
  80     * The quoted spec text mentions non-constant expressions, but this code
  81     * operates on constants.  These constants are the result of non-constant
  82     * expressions that have been optimized to constants.  The common case here
  83     * is a loop counter from an unrolled loop that is used to index a vector.
  84     *
  85     * The ir_swizzle constructor gets angry if the index is negative or too
  86     * large.  For simplicity sake, just clamp the index to [0, size-1].
  87     */
  88    const int i = CLAMP(idx->value.i[0], 0,
  89                        (int) expr->operands[0]->type->vector_elements - 1);
  90
  91    *rv = new(mem_ctx) ir_swizzle(expr->operands[0], i, 0, 0, 0, 1);
  92 }
  93
  94 bool
  95 do_vec_index_to_swizzle(exec_list *instructions)
  96 {
  97    ir_vec_index_to_swizzle_visitor v;
  98
  99    v.run(instructions);
 100
 101    return v.progress;
 102 }