1 /*
2 * Copyright © 2016 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
24 #include "nir.h"
25
26 static bool
instr_is_continue(nir_instr * instr)27 instr_is_continue(nir_instr *instr)
28 {
29 if (instr->type != nir_instr_type_jump)
30 return false;
31
32 return nir_instr_as_jump(instr)->type == nir_jump_continue;
33 }
34
35 static bool
lower_trivial_continues_block(nir_block * block,nir_loop * loop)36 lower_trivial_continues_block(nir_block *block, nir_loop *loop)
37 {
38 bool progress = false;
39 nir_instr *first_instr = nir_block_first_instr(block);
40 if (!first_instr || instr_is_continue(first_instr)) {
41 /* The block contains only a continue if anything */
42 nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
43 if (prev_node && prev_node->type == nir_cf_node_if) {
44 nir_if *prev_if = nir_cf_node_as_if(prev_node);
45 progress |= lower_trivial_continues_block(
46 nir_if_last_then_block(prev_if), loop);
47 progress |= lower_trivial_continues_block(
48 nir_if_last_else_block(prev_if), loop);
49 }
50
51 /* The lower_phis_to_regs helper is smart enough to push phi sources as
52 * far up if-ladders as it possibly can. In other words, the recursive
53 * calls above shouldn't be adding instructions to this block since it
54 * follows an if statement.
55 */
56 first_instr = nir_block_first_instr(block);
57 assert(!first_instr || instr_is_continue(first_instr));
58 }
59
60 nir_instr *last_instr = nir_block_last_instr(block);
61 if (!last_instr || !instr_is_continue(last_instr))
62 return progress;
63
64 /* We're at the end of a block that goes straight through to the end of the
65 * loop and continues to the top. We can exit normally instead of jump.
66 */
67 nir_lower_phis_to_regs_block(nir_loop_first_block(loop));
68 nir_instr_remove(last_instr);
69 return true;
70 }
71
72 static bool
lower_trivial_continues_list(struct exec_list * cf_list,bool list_ends_at_loop_tail,nir_loop * loop)73 lower_trivial_continues_list(struct exec_list *cf_list,
74 bool list_ends_at_loop_tail,
75 nir_loop *loop)
76 {
77 bool progress = false;
78 foreach_list_typed(nir_cf_node, cf_node, node, cf_list) {
79 bool at_loop_tail = list_ends_at_loop_tail &&
80 &cf_node->node == exec_list_get_tail(cf_list);
81 switch (cf_node->type) {
82 case nir_cf_node_block:
83 break;
84
85 case nir_cf_node_if: {
86 nir_if *nif = nir_cf_node_as_if(cf_node);
87 if (lower_trivial_continues_list(&nif->then_list, at_loop_tail, loop))
88 progress = true;
89 if (lower_trivial_continues_list(&nif->else_list, at_loop_tail, loop))
90 progress = true;
91 break;
92 }
93
94 case nir_cf_node_loop: {
95 nir_loop *loop = nir_cf_node_as_loop(cf_node);
96 if (lower_trivial_continues_list(&loop->body, true, loop))
97 progress = true;
98 if (lower_trivial_continues_block(nir_loop_last_block(loop), loop))
99 progress = true;
100 break;
101 }
102
103 case nir_cf_node_function:
104 unreachable("Invalid cf type");
105 }
106 }
107
108 return progress;
109 }
110
111 /**
112 * This simple pass gets rid of any "trivial" continues, i.e. those that are
113 * at the tail of a loop where we can just delete the continue instruction and
114 * control-flow will naturally and harmlessly take us back to the top of the
115 * loop.
116 */
117 bool
nir_opt_trivial_continues(nir_shader * shader)118 nir_opt_trivial_continues(nir_shader *shader)
119 {
120 bool progress = false;
121
122 nir_foreach_function(function, shader) {
123 if (function->impl == NULL)
124 continue;
125
126 /* First we run the simple pass to get rid of pesky continues */
127 if (lower_trivial_continues_list(&function->impl->body, false, NULL)) {
128 nir_metadata_preserve(function->impl, nir_metadata_none);
129
130 /* If that made progress, we're no longer really in SSA form. */
131 nir_lower_regs_to_ssa_impl(function->impl);
132 progress = true;
133 } else {
134 nir_metadata_preserve(function->impl, nir_metadata_all);
135 }
136 }
137
138 return progress;
139 }
140