1 /*
2 * Copyright © 2014 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 * Authors:
24 * Jason Ekstrand (jason@jlekstrand.net)
25 *
26 */
27
28 #include "nir.h"
29
30 /*
31 * Implements a pass that tries to move uses vecN sources to their
32 * destinations. This is kind of like an inverse copy-propagation pass.
33 * For instance, if you have
34 *
35 * ssa_1 = vec4(a, b, c, d)
36 * ssa_2 = fadd(a, b)
37 *
38 * This will be turned into
39 *
40 * ssa_1 = vec4(a, b, c, d)
41 * ssa_2 = fadd(ssa_1.x, ssa_1.y)
42 *
43 * While this is "worse" because it adds a bunch of unneeded dependencies, it
44 * actually makes it much easier for vec4-based backends to coalesce the MOVs
45 * that result from the vec4 operation because it doesn't have to worry about
46 * quite as many reads.
47 */
48
49 /* Returns true if the given SSA def dominates the instruction. An SSA def is
50 * considered to *not* dominate the instruction that defines it.
51 */
52 static bool
ssa_def_dominates_instr(nir_ssa_def * def,nir_instr * instr)53 ssa_def_dominates_instr(nir_ssa_def *def, nir_instr *instr)
54 {
55 if (instr->index <= def->parent_instr->index) {
56 return false;
57 } else if (def->parent_instr->block == instr->block) {
58 return def->parent_instr->index < instr->index;
59 } else {
60 return nir_block_dominates(def->parent_instr->block, instr->block);
61 }
62 }
63
64 static bool
move_vec_src_uses_to_dest_block(nir_block * block)65 move_vec_src_uses_to_dest_block(nir_block *block)
66 {
67 bool progress = false;
68
69 nir_foreach_instr(instr, block) {
70 if (instr->type != nir_instr_type_alu)
71 continue;
72
73 nir_alu_instr *vec = nir_instr_as_alu(instr);
74
75 switch (vec->op) {
76 case nir_op_vec2:
77 case nir_op_vec3:
78 case nir_op_vec4:
79 break;
80 default:
81 continue; /* The loop */
82 }
83
84 /* Can't handle non-SSA vec operations */
85 if (!vec->dest.dest.is_ssa)
86 continue;
87
88 /* Can't handle saturation */
89 if (vec->dest.saturate)
90 continue;
91
92 /* First, mark all of the sources we are going to consider for rewriting
93 * to the destination
94 */
95 int srcs_remaining = 0;
96 for (unsigned i = 0; i < nir_op_infos[vec->op].num_inputs; i++) {
97 /* We can't rewrite a source if it's not in SSA form */
98 if (!vec->src[i].src.is_ssa)
99 continue;
100
101 /* We can't rewrite a source if it has modifiers */
102 if (vec->src[i].abs || vec->src[i].negate)
103 continue;
104
105 srcs_remaining |= 1 << i;
106 }
107
108 /* We can't actually do anything with this instruction */
109 if (srcs_remaining == 0)
110 continue;
111
112 for (unsigned i; i = ffs(srcs_remaining) - 1, srcs_remaining;) {
113 int8_t swizzle[4] = { -1, -1, -1, -1 };
114
115 for (unsigned j = i; j < nir_op_infos[vec->op].num_inputs; j++) {
116 if (vec->src[j].src.ssa != vec->src[i].src.ssa)
117 continue;
118
119 /* Mark the given channel as having been handled */
120 srcs_remaining &= ~(1 << j);
121
122 /* Mark the appropriate channel as coming from src j */
123 swizzle[vec->src[j].swizzle[0]] = j;
124 }
125
126 nir_foreach_use_safe(use, vec->src[i].src.ssa) {
127 if (use->parent_instr == &vec->instr)
128 continue;
129
130 /* We need to dominate the use if we are going to rewrite it */
131 if (!ssa_def_dominates_instr(&vec->dest.dest.ssa, use->parent_instr))
132 continue;
133
134 /* For now, we'll just rewrite ALU instructions */
135 if (use->parent_instr->type != nir_instr_type_alu)
136 continue;
137
138 assert(use->is_ssa);
139
140 nir_alu_instr *use_alu = nir_instr_as_alu(use->parent_instr);
141
142 /* Figure out which source we're actually looking at */
143 nir_alu_src *use_alu_src = exec_node_data(nir_alu_src, use, src);
144 unsigned src_idx = use_alu_src - use_alu->src;
145 assert(src_idx < nir_op_infos[use_alu->op].num_inputs);
146
147 bool can_reswizzle = true;
148 for (unsigned j = 0; j < 4; j++) {
149 if (!nir_alu_instr_channel_used(use_alu, src_idx, j))
150 continue;
151
152 if (swizzle[use_alu_src->swizzle[j]] == -1) {
153 can_reswizzle = false;
154 break;
155 }
156 }
157
158 if (!can_reswizzle)
159 continue;
160
161 /* At this point, we have determined that the given use can be
162 * reswizzled to actually use the destination of the vecN operation.
163 * Go ahead and rewrite it as needed.
164 */
165 nir_instr_rewrite_src(use->parent_instr, use,
166 nir_src_for_ssa(&vec->dest.dest.ssa));
167 for (unsigned j = 0; j < 4; j++) {
168 if (!nir_alu_instr_channel_used(use_alu, src_idx, j))
169 continue;
170
171 use_alu_src->swizzle[j] = swizzle[use_alu_src->swizzle[j]];
172 progress = true;
173 }
174 }
175 }
176 }
177
178 return progress;
179 }
180
181 static bool
nir_move_vec_src_uses_to_dest_impl(nir_shader * shader,nir_function_impl * impl)182 nir_move_vec_src_uses_to_dest_impl(nir_shader *shader, nir_function_impl *impl)
183 {
184 bool progress = false;
185
186 nir_metadata_require(impl, nir_metadata_dominance);
187
188 nir_index_instrs(impl);
189
190 nir_foreach_block(block, impl) {
191 progress |= move_vec_src_uses_to_dest_block(block);
192 }
193
194 nir_metadata_preserve(impl, nir_metadata_block_index |
195 nir_metadata_dominance);
196
197 return progress;
198 }
199
200 bool
nir_move_vec_src_uses_to_dest(nir_shader * shader)201 nir_move_vec_src_uses_to_dest(nir_shader *shader)
202 {
203 bool progress = false;
204
205 nir_foreach_function(function, shader) {
206 if (function->impl)
207 progress |= nir_move_vec_src_uses_to_dest_impl(shader,
208 function->impl);
209 }
210
211 return progress;
212 }
213