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 MOV's
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 nir_foreach_instr(instr, block) {
68 if (instr->type != nir_instr_type_alu)
69 continue;
70
71 nir_alu_instr *vec = nir_instr_as_alu(instr);
72
73 switch (vec->op) {
74 case nir_op_vec2:
75 case nir_op_vec3:
76 case nir_op_vec4:
77 break;
78 default:
79 continue; /* The loop */
80 }
81
82 /* Can't handle non-SSA vec operations */
83 if (!vec->dest.dest.is_ssa)
84 continue;
85
86 /* Can't handle saturation */
87 if (vec->dest.saturate)
88 continue;
89
90 /* First, mark all of the sources we are going to consider for rewriting
91 * to the destination
92 */
93 int srcs_remaining = 0;
94 for (unsigned i = 0; i < nir_op_infos[vec->op].num_inputs; i++) {
95 /* We can't rewrite a source if it's not in SSA form */
96 if (!vec->src[i].src.is_ssa)
97 continue;
98
99 /* We can't rewrite a source if it has modifiers */
100 if (vec->src[i].abs || vec->src[i].negate)
101 continue;
102
103 srcs_remaining |= 1 << i;
104 }
105
106 /* We can't actually do anything with this instruction */
107 if (srcs_remaining == 0)
108 continue;
109
110 for (unsigned i; i = ffs(srcs_remaining) - 1, srcs_remaining;) {
111 int8_t swizzle[4] = { -1, -1, -1, -1 };
112
113 for (unsigned j = i; j < nir_op_infos[vec->op].num_inputs; j++) {
114 if (vec->src[j].src.ssa != vec->src[i].src.ssa)
115 continue;
116
117 /* Mark the given chanle as having been handled */
118 srcs_remaining &= ~(1 << j);
119
120 /* Mark the appropreate channel as coming from src j */
121 swizzle[vec->src[j].swizzle[0]] = j;
122 }
123
124 nir_foreach_use_safe(use, vec->src[i].src.ssa) {
125 if (use->parent_instr == &vec->instr)
126 continue;
127
128 /* We need to dominate the use if we are going to rewrite it */
129 if (!ssa_def_dominates_instr(&vec->dest.dest.ssa, use->parent_instr))
130 continue;
131
132 /* For now, we'll just rewrite ALU instructions */
133 if (use->parent_instr->type != nir_instr_type_alu)
134 continue;
135
136 assert(use->is_ssa);
137
138 nir_alu_instr *use_alu = nir_instr_as_alu(use->parent_instr);
139
140 /* Figure out which source we're actually looking at */
141 nir_alu_src *use_alu_src = exec_node_data(nir_alu_src, use, src);
142 unsigned src_idx = use_alu_src - use_alu->src;
143 assert(src_idx < nir_op_infos[use_alu->op].num_inputs);
144
145 bool can_reswizzle = true;
146 for (unsigned j = 0; j < 4; j++) {
147 if (!nir_alu_instr_channel_used(use_alu, src_idx, j))
148 continue;
149
150 if (swizzle[use_alu_src->swizzle[j]] == -1) {
151 can_reswizzle = false;
152 break;
153 }
154 }
155
156 if (!can_reswizzle)
157 continue;
158
159 /* At this point, we have determined that the given use can be
160 * reswizzled to actually use the destination of the vecN operation.
161 * Go ahead and rewrite it as needed.
162 */
163 nir_instr_rewrite_src(use->parent_instr, use,
164 nir_src_for_ssa(&vec->dest.dest.ssa));
165 for (unsigned j = 0; j < 4; j++) {
166 if (!nir_alu_instr_channel_used(use_alu, src_idx, j))
167 continue;
168
169 use_alu_src->swizzle[j] = swizzle[use_alu_src->swizzle[j]];
170 }
171 }
172 }
173 }
174
175 return true;
176 }
177
178 static void
nir_move_vec_src_uses_to_dest_impl(nir_shader * shader,nir_function_impl * impl)179 nir_move_vec_src_uses_to_dest_impl(nir_shader *shader, nir_function_impl *impl)
180 {
181 nir_metadata_require(impl, nir_metadata_dominance);
182
183 nir_index_instrs(impl);
184
185 nir_foreach_block(block, impl) {
186 move_vec_src_uses_to_dest_block(block);
187 }
188
189 nir_metadata_preserve(impl, nir_metadata_block_index |
190 nir_metadata_dominance);
191 }
192
193 void
nir_move_vec_src_uses_to_dest(nir_shader * shader)194 nir_move_vec_src_uses_to_dest(nir_shader *shader)
195 {
196 nir_foreach_function(function, shader) {
197 if (function->impl)
198 nir_move_vec_src_uses_to_dest_impl(shader, function->impl);
199 }
200 }
201