src/glsl/nir/nir_opt_remove_phis.c

   1 /*
   2  * Copyright © 2015 Connor Abbott
   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  * Authors:
  24  *    Connor Abbott (cwabbott0@gmail.com)
  25  *
  26  */
  27
  28 #include "nir.h"
  29
  30 /*
  31  * This is a pass for removing phi nodes that look like:
  32  * a = phi(b, b, b, ...)
  33  *
  34  * Note that we can't ignore undef sources here, or else we may create a
  35  * situation where the definition of b isn't dominated by its uses. We're
  36  * allowed to do this since the definition of b must dominate all of the
  37  * phi node's predecessors, which means it must dominate the phi node as well
  38  * as all of the phi node's uses. In essence, the phi node acts as a copy
  39  * instruction. b can't be another phi node in the same block, since the only
  40  * time when phi nodes can source other phi nodes defined in the same block is
  41  * at the loop header, and in that case one of the sources of the phi has to
  42  * be from before the loop and that source can't be b.
  43  */
  44
  45 static bool
  46 remove_phis_block(nir_block *block, void *state)
  47 {
  48    bool *progress = state;
  49
  50    nir_foreach_instr_safe(block, instr) {
  51       if (instr->type != nir_instr_type_phi)
  52          break;
  53
  54       nir_phi_instr *phi = nir_instr_as_phi(instr);
  55
  56       nir_ssa_def *def = NULL;
  57       bool srcs_same = true;
  58
  59       nir_foreach_phi_src(phi, src) {
  60          assert(src->src.is_ssa);
  61
  62          if (def == NULL) {
  63             def  = src->src.ssa;
  64          } else {
  65             if (src->src.ssa != def) {
  66                srcs_same = false;
  67                break;
  68             }
  69          }
  70       }
  71
  72       if (!srcs_same)
  73          continue;
  74
  75       assert(phi->dest.is_ssa);
  76       nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def));
  77       nir_instr_remove(instr);
  78
  79       *progress = true;
  80    }
  81
  82    return true;
  83 }
  84
  85 static bool
  86 remove_phis_impl(nir_function_impl *impl)
  87 {
  88    bool progress = false;
  89
  90    nir_foreach_block(impl, remove_phis_block, &progress);
  91
  92    return progress;
  93 }
  94
  95 bool
  96 nir_opt_remove_phis(nir_shader *shader)
  97 {
  98    bool progress = false;
  99
 100    nir_foreach_overload(shader, overload)
 101       if (overload->impl)
 102          progress = remove_phis_impl(overload->impl) || progress;
 103
 104    return progress;
 105 }
 106