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
61 nir_src empty_src;
62 memset(&empty_src, 0, sizeof(empty_src));
63 nir_instr_rewrite_src(&instr->instr, &instr->src[1].src, empty_src);
64 nir_instr_rewrite_src(&instr->instr, &instr->src[2].src, empty_src);
65 instr->op = nir_op_mov;
66
67 return true;
68 }
69
70 return false;
71 }
72
73 /**
74 * Replace vecN(undef, undef, ...) with a single undef.
75 */
76 static bool
opt_undef_vecN(nir_builder * b,nir_alu_instr * alu)77 opt_undef_vecN(nir_builder *b, nir_alu_instr *alu)
78 {
79 if (!nir_op_is_vec(alu->op))
80 return false;
81
82 assert(alu->dest.dest.is_ssa);
83
84 for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
85 if (!alu->src[i].src.is_ssa ||
86 alu->src[i].src.ssa->parent_instr->type != nir_instr_type_ssa_undef)
87 return false;
88 }
89
90 b->cursor = nir_before_instr(&alu->instr);
91 nir_ssa_def *undef = nir_ssa_undef(b, alu->dest.dest.ssa.num_components,
92 nir_dest_bit_size(alu->dest.dest));
93 nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, undef);
94
95 return true;
96 }
97
98 static uint32_t
nir_get_undef_mask(nir_ssa_def * def)99 nir_get_undef_mask(nir_ssa_def *def)
100 {
101 nir_instr *instr = def->parent_instr;
102
103 if (instr->type == nir_instr_type_ssa_undef)
104 return BITSET_MASK(def->num_components);
105
106 if (instr->type != nir_instr_type_alu)
107 return 0;
108
109 nir_alu_instr *alu = nir_instr_as_alu(instr);
110 unsigned undef = 0;
111
112 if (nir_op_is_vec(alu->op)) {
113 for (int i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
114 if (alu->src[i].src.is_ssa &&
115 alu->src[i].src.ssa->parent_instr->type ==
116 nir_instr_type_ssa_undef) {
117 undef |= BITSET_MASK(nir_ssa_alu_instr_src_components(alu, i)) << i;
118 }
119 }
120 }
121
122 return undef;
123 }
124
125 /**
126 * Remove any store intrinsic writemask channels whose value is undefined (the
127 * existing value is a fine representation of "undefined").
128 */
129 static bool
opt_undef_store(nir_intrinsic_instr * intrin)130 opt_undef_store(nir_intrinsic_instr *intrin)
131 {
132 int arg_index;
133 switch (intrin->intrinsic) {
134 case nir_intrinsic_store_deref:
135 arg_index = 1;
136 break;
137 case nir_intrinsic_store_output:
138 case nir_intrinsic_store_per_vertex_output:
139 case nir_intrinsic_store_per_primitive_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
nir_opt_undef_instr(nir_builder * b,nir_instr * instr,void * data)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
nir_opt_undef(nir_shader * shader)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 }
193