1 /*
2 * Copyright © 2016 Red Hat
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_conditional_discard.c
28 *
29 * Handles optimization of lowering of
30 * - if (cond) discard to discard_if(cond) and
31 * - if (cond) demote to demote_if(cond)
32 * - if (cond) terminate to terminate_if(cond)
33 */
34
35 static bool
nir_opt_conditional_discard_block(nir_builder * b,nir_block * block)36 nir_opt_conditional_discard_block(nir_builder *b, nir_block *block)
37 {
38 if (nir_cf_node_is_first(&block->cf_node))
39 return false;
40
41 nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
42 if (prev_node->type != nir_cf_node_if)
43 return false;
44
45 nir_if *if_stmt = nir_cf_node_as_if(prev_node);
46 nir_block *then_block = nir_if_first_then_block(if_stmt);
47 nir_block *else_block = nir_if_first_else_block(if_stmt);
48
49 /* check there is only one else block and it is empty */
50 if (nir_if_last_else_block(if_stmt) != else_block)
51 return false;
52 if (!exec_list_is_empty(&else_block->instr_list))
53 return false;
54
55 /* check there is only one then block and it has only one instruction in it */
56 if (nir_if_last_then_block(if_stmt) != then_block)
57 return false;
58 if (exec_list_is_empty(&then_block->instr_list))
59 return false;
60 if (exec_list_length(&then_block->instr_list) > 1)
61 return false;
62 /*
63 * make sure no subsequent phi nodes point at this if.
64 */
65 nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node));
66 nir_foreach_instr_safe(instr, after) {
67 if (instr->type != nir_instr_type_phi)
68 break;
69 nir_phi_instr *phi = nir_instr_as_phi(instr);
70
71 nir_foreach_phi_src(phi_src, phi) {
72 if (phi_src->pred == then_block ||
73 phi_src->pred == else_block)
74 return false;
75 }
76 }
77
78 /* Get the first instruction in the then block and confirm it is
79 * a discard or a demote instruction.
80 */
81 nir_instr *instr = nir_block_first_instr(then_block);
82 if (instr->type != nir_instr_type_intrinsic)
83 return false;
84
85 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
86 nir_intrinsic_op op = intrin->intrinsic;
87 assert(if_stmt->condition.is_ssa);
88 nir_ssa_def *cond = if_stmt->condition.ssa;
89 b->cursor = nir_before_cf_node(prev_node);
90
91 switch (intrin->intrinsic) {
92 case nir_intrinsic_discard:
93 op = nir_intrinsic_discard_if;
94 break;
95 case nir_intrinsic_demote:
96 op = nir_intrinsic_demote_if;
97 break;
98 case nir_intrinsic_terminate:
99 op = nir_intrinsic_terminate_if;
100 break;
101 case nir_intrinsic_discard_if:
102 case nir_intrinsic_demote_if:
103 case nir_intrinsic_terminate_if:
104 assert(intrin->src[0].is_ssa);
105 cond = nir_iand(b, cond, intrin->src[0].ssa);
106 break;
107 default:
108 return false;
109 }
110
111 nir_intrinsic_instr *discard_if =
112 nir_intrinsic_instr_create(b->shader, op);
113 discard_if->src[0] = nir_src_for_ssa(cond);
114
115 nir_instr_insert_before_cf(prev_node, &discard_if->instr);
116 nir_instr_remove(&intrin->instr);
117 nir_cf_node_remove(&if_stmt->cf_node);
118
119 return true;
120 }
121
122 bool
nir_opt_conditional_discard(nir_shader * shader)123 nir_opt_conditional_discard(nir_shader *shader)
124 {
125 bool progress = false;
126
127 nir_builder builder;
128
129 nir_foreach_function(function, shader) {
130 if (function->impl) {
131 nir_builder_init(&builder, function->impl);
132
133 bool impl_progress = false;
134 nir_foreach_block_safe(block, function->impl) {
135 if (nir_opt_conditional_discard_block(&builder, block))
136 impl_progress = true;
137 }
138
139 if (impl_progress) {
140 nir_metadata_preserve(function->impl, nir_metadata_none);
141 progress = true;
142 } else {
143 nir_metadata_preserve(function->impl, nir_metadata_all);
144 }
145 }
146 }
147 return progress;
148 }
149