src/compiler/nir/nir_repair_ssa.c

   1 /*
   2  * Copyright © 2016 Intel 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 #include "nir.h"
  25 #include "nir_phi_builder.h"
  26
  27 struct repair_ssa_state {
  28    nir_function_impl *impl;
  29
  30    BITSET_WORD *def_set;
  31    struct nir_phi_builder *phi_builder;
  32
  33    bool progress;
  34 };
  35
  36 /* Get ready to build a phi and return the builder */
  37 static struct nir_phi_builder *
  38 prep_build_phi(struct repair_ssa_state *state)
  39 {
  40    const unsigned num_words = BITSET_WORDS(state->impl->num_blocks);
  41
  42    /* We create the phi builder on-demand. */
  43    if (state->phi_builder == NULL) {
  44       state->phi_builder = nir_phi_builder_create(state->impl);
  45       state->def_set = ralloc_array(NULL, BITSET_WORD, num_words);
  46    }
  47
  48    /* We're going to build a phi.  That's progress. */
  49    state->progress = true;
  50
  51    /* Set the defs set to empty */
  52    memset(state->def_set, 0, num_words * sizeof(*state->def_set));
  53
  54    return state->phi_builder;
  55 }
  56
  57 static nir_block *
  58 get_src_block(nir_src *src)
  59 {
  60    if (src->parent_instr->type == nir_instr_type_phi) {
  61       return exec_node_data(nir_phi_src, src, src)->pred;
  62    } else {
  63       return src->parent_instr->block;
  64    }
  65 }
  66
  67 static bool
  68 repair_ssa_def(nir_ssa_def *def, void *void_state)
  69 {
  70    struct repair_ssa_state *state = void_state;
  71
  72    bool is_valid = true;
  73    nir_foreach_use(def, src) {
  74       if (!nir_block_dominates(def->parent_instr->block, get_src_block(src))) {
  75          is_valid = false;
  76          break;
  77       }
  78    }
  79
  80    if (is_valid)
  81       return true;
  82
  83    struct nir_phi_builder *pb = prep_build_phi(state);
  84
  85    BITSET_SET(state->def_set, def->parent_instr->block->index);
  86
  87    struct nir_phi_builder_value *val =
  88       nir_phi_builder_add_value(pb, def->num_components, def->bit_size,
  89                                 state->def_set);
  90
  91    nir_phi_builder_value_set_block_def(val, def->parent_instr->block, def);
  92
  93    nir_foreach_use_safe(def, src) {
  94       nir_block *src_block = get_src_block(src);
  95       if (!nir_block_dominates(def->parent_instr->block, src_block)) {
  96          nir_instr_rewrite_src(src->parent_instr, src, nir_src_for_ssa(
  97             nir_phi_builder_value_get_block_def(val, src_block)));
  98       }
  99    }
 100
 101    return true;
 102 }
 103
 104 static bool
 105 repair_ssa_block(nir_block *block, void *state)
 106 {
 107    nir_foreach_instr_safe(block, instr) {
 108       nir_foreach_ssa_def(instr, repair_ssa_def, state);
 109    }
 110
 111    return true;
 112 }
 113
 114 bool
 115 nir_repair_ssa_impl(nir_function_impl *impl)
 116 {
 117    struct repair_ssa_state state;
 118
 119    state.impl = impl;
 120    state.phi_builder = NULL;
 121    state.progress = false;
 122
 123    nir_metadata_require(impl, nir_metadata_block_index |
 124                               nir_metadata_dominance);
 125
 126    nir_foreach_block(impl, repair_ssa_block, &state);
 127
 128    if (state.progress)
 129       nir_metadata_preserve(impl, nir_metadata_block_index |
 130                                   nir_metadata_dominance);
 131
 132    if (state.phi_builder) {
 133       nir_phi_builder_finish(state.phi_builder);
 134       ralloc_free(state.def_set);
 135    }
 136
 137    return state.progress;
 138 }
 139
 140 /** This pass can be used to repair SSA form in a shader.
 141  *
 142  * Sometimes a transformation (such as return lowering) will have to make
 143  * changes to a shader which, while still correct, break some of NIR's SSA
 144  * invariants.  This pass will insert ssa_undefs and phi nodes as needed to
 145  * get the shader back into SSA that the validator will like.
 146  */
 147 bool
 148 nir_repair_ssa(nir_shader *shader)
 149 {
 150    bool progress = false;
 151
 152    nir_foreach_function(shader, function) {
 153       if (function->impl)
 154          progress = nir_repair_ssa_impl(function->impl) || progress;
 155    }
 156
 157    return progress;
 158 }