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
opt_undef_csel(nir_alu_instr * instr)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_imov;
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
opt_undef_vecN(nir_builder * b,nir_alu_instr * alu)78 opt_undef_vecN(nir_builder *b, nir_alu_instr *alu)
79 {
80 if (alu->op != nir_op_vec2 &&
81 alu->op != nir_op_vec3 &&
82 alu->op != nir_op_vec4 &&
83 alu->op != nir_op_fmov &&
84 alu->op != nir_op_imov)
85 return false;
86
87 assert(alu->dest.dest.is_ssa);
88
89 for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
90 if (!alu->src[i].src.is_ssa ||
91 alu->src[i].src.ssa->parent_instr->type != nir_instr_type_ssa_undef)
92 return false;
93 }
94
95 b->cursor = nir_before_instr(&alu->instr);
96 nir_ssa_def *undef = nir_ssa_undef(b, alu->dest.dest.ssa.num_components,
97 nir_dest_bit_size(alu->dest.dest));
98 nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(undef));
99
100 return true;
101 }
102
103 /**
104 * Remove any store intrinsics whose value is undefined (the existing
105 * value is a fine representation of "undefined").
106 */
107 static bool
opt_undef_store(nir_intrinsic_instr * intrin)108 opt_undef_store(nir_intrinsic_instr *intrin)
109 {
110 switch (intrin->intrinsic) {
111 case nir_intrinsic_store_var:
112 case nir_intrinsic_store_output:
113 case nir_intrinsic_store_per_vertex_output:
114 case nir_intrinsic_store_ssbo:
115 case nir_intrinsic_store_shared:
116 break;
117 default:
118 return false;
119 }
120
121 if (!intrin->src[0].is_ssa ||
122 intrin->src[0].ssa->parent_instr->type != nir_instr_type_ssa_undef)
123 return false;
124
125 nir_instr_remove(&intrin->instr);
126
127 return true;
128 }
129
130 bool
nir_opt_undef(nir_shader * shader)131 nir_opt_undef(nir_shader *shader)
132 {
133 nir_builder b;
134 bool progress = false;
135
136 nir_foreach_function(function, shader) {
137 if (function->impl) {
138 nir_builder_init(&b, function->impl);
139 nir_foreach_block(block, function->impl) {
140 nir_foreach_instr_safe(instr, block) {
141 if (instr->type == nir_instr_type_alu) {
142 nir_alu_instr *alu = nir_instr_as_alu(instr);
143
144 progress = opt_undef_csel(alu) || progress;
145 progress = opt_undef_vecN(&b, alu) || progress;
146 } else if (instr->type == nir_instr_type_intrinsic) {
147 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
148 progress = opt_undef_store(intrin) || progress;
149 }
150 }
151 }
152
153 if (progress)
154 nir_metadata_preserve(function->impl,
155 nir_metadata_block_index |
156 nir_metadata_dominance);
157 }
158 }
159
160 return progress;
161 }
162