nir_repair_ssa.c revision 01e04c3f 
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
27struct 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 */
37static struct nir_phi_builder *
38prep_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
57static nir_block *
58get_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
67static bool
68repair_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(src, def) {
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(src, def) {
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
104bool
105nir_repair_ssa_impl(nir_function_impl *impl)
106{
107   struct repair_ssa_state state;
108
109   state.impl = impl;
110   state.phi_builder = NULL;
111   state.progress = false;
112
113   nir_metadata_require(impl, nir_metadata_block_index |
114                              nir_metadata_dominance);
115
116   nir_foreach_block(block, impl) {
117      nir_foreach_instr_safe(instr, block) {
118         nir_foreach_ssa_def(instr, repair_ssa_def, &state);
119      }
120   }
121
122   if (state.progress)
123      nir_metadata_preserve(impl, nir_metadata_block_index |
124                                  nir_metadata_dominance);
125
126   if (state.phi_builder) {
127      nir_phi_builder_finish(state.phi_builder);
128      ralloc_free(state.def_set);
129   }
130
131   return state.progress;
132}
133
134/** This pass can be used to repair SSA form in a shader.
135 *
136 * Sometimes a transformation (such as return lowering) will have to make
137 * changes to a shader which, while still correct, break some of NIR's SSA
138 * invariants.  This pass will insert ssa_undefs and phi nodes as needed to
139 * get the shader back into SSA that the validator will like.
140 */
141bool
142nir_repair_ssa(nir_shader *shader)
143{
144   bool progress = false;
145
146   nir_foreach_function(function, shader) {
147      if (function->impl)
148         progress = nir_repair_ssa_impl(function->impl) || progress;
149   }
150
151   return progress;
152}
153