src/compiler/nir/nir_lower_discard_to_demote.c

   1 /*
   2  * Copyright © 2020 Valve 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 DEALINGS
  21  * IN THE SOFTWARE.
  22  *
  23  */
  24
  25 #include "nir.h"
  26 #include "nir_builder.h"
  27
  28 static bool
  29 nir_lower_discard_to_demote_instr(nir_builder *b, nir_instr *instr, void *data)
  30 {
  31    if (instr->type != nir_instr_type_intrinsic)
  32       return false;
  33
  34    nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  35    switch (intrin->intrinsic) {
  36    case nir_intrinsic_discard:
  37       intrin->intrinsic = nir_intrinsic_demote;
  38       b->shader->info.fs.uses_demote = true;
  39       return true;
  40    case nir_intrinsic_discard_if:
  41       intrin->intrinsic = nir_intrinsic_demote_if;
  42       b->shader->info.fs.uses_demote = true;
  43       return true;
  44    case nir_intrinsic_load_helper_invocation:
  45       intrin->intrinsic = nir_intrinsic_is_helper_invocation;
  46       return true;
  47    default:
  48       return false;
  49    }
  50 }
  51
  52 /**
  53  * This pass is intended as workaround for game bugs to force correct
  54  * derivatives after kill. This lowering is not valid in the general case
  55  * as it might change the result of subgroup operations and loop behavior.
  56  *
  57  * discard() will be lowered as demote() and gl_HelperInvocation
  58  * will be lowered as helperInvocationEXT().
  59  */
  60 bool
  61 nir_lower_discard_to_demote(nir_shader *shader)
  62 {
  63    if (shader->info.stage != MESA_SHADER_FRAGMENT)
  64       return false;
  65
  66    return nir_shader_instructions_pass(shader,
  67                                        nir_lower_discard_to_demote_instr,
  68                                        nir_metadata_all,
  69                                        NULL);
  70 }