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 if (cond) discard to discard_if(cond).
30 */
31
32 static bool
nir_opt_conditional_discard_block(nir_builder * b,nir_block * block)33 nir_opt_conditional_discard_block(nir_builder *b, nir_block *block)
34 {
35 if (nir_cf_node_is_first(&block->cf_node))
36 return false;
37
38 nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
39 if (prev_node->type != nir_cf_node_if)
40 return false;
41
42 nir_if *if_stmt = nir_cf_node_as_if(prev_node);
43 nir_block *then_block = nir_if_first_then_block(if_stmt);
44 nir_block *else_block = nir_if_first_else_block(if_stmt);
45
46 /* check there is only one else block and it is empty */
47 if (nir_if_last_else_block(if_stmt) != else_block)
48 return false;
49 if (!exec_list_is_empty(&else_block->instr_list))
50 return false;
51
52 /* check there is only one then block and it has only one instruction in it */
53 if (nir_if_last_then_block(if_stmt) != then_block)
54 return false;
55 if (exec_list_is_empty(&then_block->instr_list))
56 return false;
57 if (exec_list_length(&then_block->instr_list) > 1)
58 return false;
59 /*
60 * make sure no subsequent phi nodes point at this if.
61 */
62 nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node));
63 nir_foreach_instr_safe(instr, after) {
64 if (instr->type != nir_instr_type_phi)
65 break;
66 nir_phi_instr *phi = nir_instr_as_phi(instr);
67
68 nir_foreach_phi_src(phi_src, phi) {
69 if (phi_src->pred == then_block ||
70 phi_src->pred == else_block)
71 return false;
72 }
73 }
74
75 /* Get the first instruction in the then block and confirm it is
76 * a discard or a discard_if
77 */
78 nir_instr *instr = nir_block_first_instr(then_block);
79 if (instr->type != nir_instr_type_intrinsic)
80 return false;
81
82 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
83 if (intrin->intrinsic != nir_intrinsic_discard &&
84 intrin->intrinsic != nir_intrinsic_discard_if)
85 return false;
86
87 nir_src cond;
88
89 b->cursor = nir_before_cf_node(prev_node);
90 if (intrin->intrinsic == nir_intrinsic_discard)
91 cond = if_stmt->condition;
92 else
93 cond = nir_src_for_ssa(nir_iand(b,
94 nir_ssa_for_src(b, if_stmt->condition, 1),
95 nir_ssa_for_src(b, intrin->src[0], 1)));
96
97 nir_intrinsic_instr *discard_if =
98 nir_intrinsic_instr_create(b->shader, nir_intrinsic_discard_if);
99 nir_src_copy(&discard_if->src[0], &cond, discard_if);
100
101 nir_instr_insert_before_cf(prev_node, &discard_if->instr);
102 nir_instr_remove(&intrin->instr);
103 nir_cf_node_remove(&if_stmt->cf_node);
104
105 return true;
106 }
107
108 bool
nir_opt_conditional_discard(nir_shader * shader)109 nir_opt_conditional_discard(nir_shader *shader)
110 {
111 bool progress = false;
112
113 nir_builder builder;
114
115 nir_foreach_function(function, shader) {
116 if (function->impl) {
117 nir_builder_init(&builder, function->impl);
118 nir_foreach_block_safe(block, function->impl) {
119 progress |= nir_opt_conditional_discard_block(&builder, block);
120 }
121 }
122 }
123 return progress;
124 }
125