1 /*
2 * Copyright 2018 Collabora Ltd.
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 * on the rights to use, copy, modify, merge, publish, distribute, sub
8 * license, and/or sell copies of the Software, and to permit persons to whom
9 * the 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 NON-INFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHOR(S) AND/OR THEIR SUPPLIERS BE LIABLE FOR ANY CLAIM,
19 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
20 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
21 * USE OR OTHER DEALINGS IN THE SOFTWARE.
22 */
23
24 #include "nir.h"
25 #include "compiler/nir/nir_builder.h"
26
27 static bool
lower_discard_if_instr(nir_builder * b,nir_instr * instr_,UNUSED void * cb_data)28 lower_discard_if_instr(nir_builder *b, nir_instr *instr_, UNUSED void *cb_data)
29 {
30 if (instr_->type != nir_instr_type_intrinsic)
31 return false;
32
33 nir_intrinsic_instr *instr = nir_instr_as_intrinsic(instr_);
34
35 if (instr->intrinsic == nir_intrinsic_discard_if) {
36 b->cursor = nir_before_instr(&instr->instr);
37
38 nir_if *if_stmt = nir_push_if(b, nir_ssa_for_src(b, instr->src[0], 1));
39 nir_discard(b);
40 nir_pop_if(b, if_stmt);
41 nir_instr_remove(&instr->instr);
42 return true;
43 } else if (instr->intrinsic == nir_intrinsic_terminate_if ||
44 instr->intrinsic == nir_intrinsic_demote_if) {
45 unreachable("todo: handle terminates and demotes for Vulkan");
46 }
47
48 /* a shader like this (shaders@glsl-fs-discard-04):
49
50 uniform int j, k;
51
52 void main()
53 {
54 for (int i = 0; i < j; i++) {
55 if (i > k)
56 continue;
57 discard;
58 }
59 gl_FragColor = vec4(0.0, 1.0, 0.0, 0.0);
60 }
61
62
63
64 will generate nir like:
65
66 loop {
67 //snip
68 if ssa_11 {
69 block block_5:
70 / preds: block_4 /
71 vec1 32 ssa_17 = iadd ssa_50, ssa_31
72 / succs: block_7 /
73 } else {
74 block block_6:
75 / preds: block_4 /
76 intrinsic discard () () <-- not last instruction
77 vec1 32 ssa_23 = iadd ssa_50, ssa_31 <-- dead code loop itr increment
78 / succs: block_7 /
79 }
80 //snip
81 }
82
83 which means that we can't assert like this:
84
85 assert(instr->intrinsic != nir_intrinsic_discard ||
86 nir_block_last_instr(instr->instr.block) == &instr->instr);
87
88
89 and it's unnecessary anyway since later optimizations will dce the
90 instructions following the discard
91 */
92
93 return false;
94 }
95
96 bool
nir_lower_discard_if(nir_shader * shader)97 nir_lower_discard_if(nir_shader *shader)
98 {
99 return nir_shader_instructions_pass(shader,
100 lower_discard_if_instr,
101 nir_metadata_none,
102 NULL);
103 }
104