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    void *mem_ctx = ralloc_parent(block);
  51
  52    nir_foreach_instr_safe(block, instr) {
  53       if (instr->type != nir_instr_type_phi)
  54          break;
  55
  56       nir_phi_instr *phi = nir_instr_as_phi(instr);
  57
  58       nir_ssa_def *def = NULL;
  59       bool srcs_same = true;
  60
  61       nir_foreach_phi_src(phi, src) {
  62          assert(src->src.is_ssa);
  63
  64          if (def == NULL) {
  65             def  = src->src.ssa;
  66          } else {
  67             if (src->src.ssa != def) {
  68                srcs_same = false;
  69                break;
  70             }
  71          }
  72       }
  73
  74       if (!srcs_same)
  75          continue;
  76
  77       assert(phi->dest.is_ssa);
  78       nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def),
  79                                mem_ctx);
  80       nir_instr_remove(instr);
  81
  82       *progress = true;
  83    }
  84
  85    return true;
  86 }
  87
  88 static bool
  89 remove_phis_impl(nir_function_impl *impl)
  90 {
  91    bool progress = false;
  92
  93    nir_foreach_block(impl, remove_phis_block, &progress);
  94
  95    return progress;
  96 }
  97
  98 bool
  99 nir_opt_remove_phis(nir_shader *shader)
 100 {
 101    bool progress = false;
 102
 103    nir_foreach_overload(shader, overload)
 104       if (overload->impl)
 105          progress = remove_phis_impl(overload->impl) || progress;
 106
 107    return progress;
 108 }
 109