src/panfrost/midgard/nir_undef_to_zero.c

   1 /*
   2  * Copyright (C) 2019 Collabora, Ltd.
   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 (Collabora):
  24  *   Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
  25  */
  26
  27 /**
  28  * @file
  29  *
  30  * Flushes undefined SSA values to a zero vector fo the appropriate component
  31  * count, to avoid undefined behaviour in the resulting shader. Not required
  32  * for conformance as use of uninitialized variables is explicitly left
  33  * undefined by the spec.  Works around buggy apps, however.
  34  *
  35  * Call immediately after nir_opt_undef. If called before, larger optimization
  36  * opportunities from the former pass will be missed. If called outside of an
  37  * optimization loop, constant propagation and algebraic optimizations won't be
  38  * able to kick in to reduce stuff consuming the zero.
  39  */
  40
  41 #include "compiler/nir/nir.h"
  42 #include "compiler/nir/nir_builder.h"
  43
  44 bool nir_undef_to_zero(nir_shader *shader);
  45
  46 bool
  47 nir_undef_to_zero(nir_shader *shader)
  48 {
  49    bool progress = false;
  50
  51    nir_foreach_function(function, shader) {
  52       if (!function->impl) continue;
  53
  54       nir_builder b;
  55       nir_builder_init(&b, function->impl);
  56
  57       nir_foreach_block(block, function->impl) {
  58          nir_foreach_instr_safe(instr, block) {
  59             if (instr->type != nir_instr_type_ssa_undef) continue;
  60
  61             nir_ssa_undef_instr *und = nir_instr_as_ssa_undef(instr);
  62
  63             /* Get the required size */
  64             unsigned c = und->def.num_components;
  65             unsigned s = und->def.bit_size;
  66
  67             nir_const_value v[NIR_MAX_VEC_COMPONENTS];
  68             memset(v, 0, sizeof(v));
  69
  70             b.cursor = nir_before_instr(instr);
  71             nir_ssa_def *zero = nir_build_imm(&b, c, s, v);
  72             nir_src zerosrc = nir_src_for_ssa(zero);
  73
  74             nir_ssa_def_rewrite_uses(&und->def, zerosrc);
  75
  76             progress |= true;
  77          }
  78       }
  79
  80       nir_metadata_preserve(function->impl, nir_metadata_block_index | nir_metadata_dominance);
  81
  82    }
  83
  84    return progress;
  85 }
  86
  87