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 #include "nir_builder.h"
  26
  27 /** @file nir_opt_undef.c
  28  *
  29  * Handles optimization of operations involving ssa_undef.
  30  */
  31
  32 /**
  33  * Turn conditional selects between an undef and some other value into a move
  34  * of that other value (on the assumption that the condition's going to be
  35  * choosing the defined value).  This reduces work after if flattening when
  36  * each side of the if is defining a variable.
  37  */
  38 static bool
  39 opt_undef_csel(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_mov;
  67
  68       return true;
  69    }
  70
  71    return false;
  72 }
  73
  74 /**
  75  * Replace vecN(undef, undef, ...) with a single undef.
  76  */
  77 static bool
  78 opt_undef_vecN(nir_builder *b, nir_alu_instr *alu)
  79 {
  80    if (!nir_op_is_vec(alu->op))
  81       return false;
  82
  83    assert(alu->dest.dest.is_ssa);
  84
  85    for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
  86       if (!alu->src[i].src.is_ssa ||
  87           alu->src[i].src.ssa->parent_instr->type != nir_instr_type_ssa_undef)
  88          return false;
  89    }
  90
  91    b->cursor = nir_before_instr(&alu->instr);
  92    nir_ssa_def *undef = nir_ssa_undef(b, alu->dest.dest.ssa.num_components,
  93                                       nir_dest_bit_size(alu->dest.dest));
  94    nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(undef));
  95
  96    return true;
  97 }
  98
  99 static uint32_t
 100 nir_get_undef_mask(nir_ssa_def *def)
 101 {
 102    nir_instr *instr = def->parent_instr;
 103
 104    if (instr->type == nir_instr_type_ssa_undef)
 105       return BITSET_MASK(def->num_components);
 106
 107    if (instr->type != nir_instr_type_alu)
 108       return 0;
 109
 110    nir_alu_instr *alu = nir_instr_as_alu(instr);
 111    unsigned undef = 0;
 112
 113    if (nir_op_is_vec(alu->op)) {
 114       for (int i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
 115          if (alu->src[i].src.is_ssa &&
 116              alu->src[i].src.ssa->parent_instr->type ==
 117              nir_instr_type_ssa_undef) {
 118             undef |= BITSET_MASK(nir_ssa_alu_instr_src_components(alu, i)) << i;
 119          }
 120       }
 121    }
 122
 123    return undef;
 124 }
 125
 126 /**
 127  * Remove any store intrinsic writemask channels whose value is undefined (the
 128  * existing value is a fine representation of "undefined").
 129  */
 130 static bool
 131 opt_undef_store(nir_intrinsic_instr *intrin)
 132 {
 133    int arg_index;
 134    switch (intrin->intrinsic) {
 135    case nir_intrinsic_store_deref:
 136       arg_index = 1;
 137       break;
 138    case nir_intrinsic_store_output:
 139    case nir_intrinsic_store_per_vertex_output:
 140    case nir_intrinsic_store_ssbo:
 141    case nir_intrinsic_store_shared:
 142    case nir_intrinsic_store_global:
 143    case nir_intrinsic_store_scratch:
 144       arg_index =  0;
 145       break;
 146    default:
 147       return false;
 148    }
 149
 150    if (!intrin->src[arg_index].is_ssa)
 151       return false;
 152
 153    nir_ssa_def *def = intrin->src[arg_index].ssa;
 154
 155    unsigned write_mask = nir_intrinsic_write_mask(intrin);
 156    unsigned undef_mask = nir_get_undef_mask(def);
 157
 158    if (!(write_mask & undef_mask))
 159       return false;
 160
 161    write_mask &= ~undef_mask;
 162    if (!write_mask)
 163       nir_instr_remove(&intrin->instr);
 164    else
 165       nir_intrinsic_set_write_mask(intrin, write_mask);
 166
 167    return true;
 168 }
 169
 170 static bool
 171 nir_opt_undef_instr(nir_builder *b, nir_instr *instr, void *data)
 172 {
 173    if (instr->type == nir_instr_type_alu) {
 174       nir_alu_instr *alu = nir_instr_as_alu(instr);
 175       return opt_undef_csel(alu) || opt_undef_vecN(b, alu);
 176    } else if (instr->type == nir_instr_type_intrinsic) {
 177       nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 178       return opt_undef_store(intrin);
 179    }
 180
 181    return false;
 182 }
 183
 184 bool
 185 nir_opt_undef(nir_shader *shader)
 186 {
 187    return nir_shader_instructions_pass(shader,
 188                                        nir_opt_undef_instr,
 189                                        nir_metadata_block_index |
 190                                        nir_metadata_dominance,
 191                                        NULL);
 192 }