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_phi_safe(phi, after) {
67 nir_foreach_phi_src(phi_src, phi) {
68 if (phi_src->pred == then_block ||
69 phi_src->pred == else_block)
70 return false;
71 }
72 }
73
74 /* Get the first instruction in the then block and confirm it is
75 * a discard or a demote instruction.
76 */
77 nir_instr *instr = nir_block_first_instr(then_block);
78 if (instr->type != nir_instr_type_intrinsic)
79 return false;
80
81 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
82 nir_intrinsic_op op = intrin->intrinsic;
83 nir_def *cond = if_stmt->condition.ssa;
84 b->cursor = nir_before_cf_node(prev_node);
85
86 switch (intrin->intrinsic) {
87 case nir_intrinsic_demote:
88 op = nir_intrinsic_demote_if;
89 break;
90 case nir_intrinsic_terminate:
91 op = nir_intrinsic_terminate_if;
92 break;
93 case nir_intrinsic_demote_if:
94 case nir_intrinsic_terminate_if:
95 cond = nir_iand(b, cond, intrin->src[0].ssa);
96 break;
97 default:
98 return false;
99 }
100
101 nir_intrinsic_instr *discard_if =
102 nir_intrinsic_instr_create(b->shader, op);
103 discard_if->src[0] = nir_src_for_ssa(cond);
104
105 nir_instr_insert_before_cf(prev_node, &discard_if->instr);
106 nir_instr_remove(&intrin->instr);
107 nir_cf_node_remove(&if_stmt->cf_node);
108
109 return true;
110 }
111
112 bool
nir_opt_conditional_discard(nir_shader * shader)113 nir_opt_conditional_discard(nir_shader *shader)
114 {
115 bool progress = false;
116
117 nir_builder builder;
118
119 nir_foreach_function_impl(impl, shader) {
120 builder = nir_builder_create(impl);
121
122 bool impl_progress = false;
123 nir_foreach_block_safe(block, impl) {
124 if (nir_opt_conditional_discard_block(&builder, block))
125 impl_progress = true;
126 }
127
128 if (impl_progress) {
129 nir_metadata_preserve(impl, nir_metadata_none);
130 progress = true;
131 } else {
132 nir_metadata_preserve(impl, nir_metadata_all);
133 }
134 }
135 return progress;
136 }
137