src/compiler/nir/nir_opt_undef.c

   1 /*
   2  * Copyright © 2015 Broadcom
   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 DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "nir.h"
  25
  26 /** @file nir_opt_undef.c
  27  *
  28  * Handles optimization of operations involving ssa_undef.  For now, we just
  29  * make sure that csels between undef and some other value just give the other
  30  * value (on the assumption that the condition's going to be choosing the
  31  * defined value).  This reduces work after if flattening when each side of
  32  * the if is defining a variable.
  33  *
  34  * Some day, we may find some use for making other operations consuming an
  35  * undef arg output undef, but I don't know of any cases currently.
  36  */
  37
  38 static bool
  39 opt_undef_alu(nir_alu_instr *instr)
  40 {
  41    if (instr->op != nir_op_bcsel && instr->op != nir_op_fcsel)
  42       return false;
  43
  44    assert(instr->dest.dest.is_ssa);
  45
  46    for (int i = 1; i <= 2; i++) {
  47       if (!instr->src[i].src.is_ssa)
  48          continue;
  49
  50       nir_instr *parent = instr->src[i].src.ssa->parent_instr;
  51       if (parent->type != nir_instr_type_ssa_undef)
  52          continue;
  53
  54       /* We can't just use nir_alu_src_copy, because we need the def/use
  55        * updated.
  56        */
  57       nir_instr_rewrite_src(&instr->instr, &instr->src[0].src,
  58                             instr->src[i == 1 ? 2 : 1].src);
  59       nir_alu_src_copy(&instr->src[0], &instr->src[i == 1 ? 2 : 1],
  60                        ralloc_parent(instr));
  61
  62       nir_src empty_src;
  63       memset(&empty_src, 0, sizeof(empty_src));
  64       nir_instr_rewrite_src(&instr->instr, &instr->src[1].src, empty_src);
  65       nir_instr_rewrite_src(&instr->instr, &instr->src[2].src, empty_src);
  66       instr->op = nir_op_imov;
  67
  68       return true;
  69    }
  70
  71    return false;
  72 }
  73
  74 static bool
  75 opt_undef_block(nir_block *block, void *data)
  76 {
  77    bool *progress = data;
  78
  79    nir_foreach_instr_safe(block, instr) {
  80       if (instr->type == nir_instr_type_alu)
  81          if (opt_undef_alu(nir_instr_as_alu(instr)))
  82              (*progress) = true;
  83    }
  84
  85    return true;
  86 }
  87
  88 bool
  89 nir_opt_undef(nir_shader *shader)
  90 {
  91    bool progress = false;
  92
  93    nir_foreach_function(shader, function) {
  94       if (function->impl) {
  95          nir_foreach_block(function->impl, opt_undef_block, &progress);
  96          if (progress)
  97             nir_metadata_preserve(function->impl,
  98                                   nir_metadata_block_index |
  99                                   nir_metadata_dominance);
 100       }
 101    }
 102
 103    return progress;
 104 }