1 /*
2 * Copyright © 2021 Advanced Micro Devices, Inc.
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 /**
28 * This pass removes no-op assignment to gl_FragDepth.
29 *
30 * gl_FragDepth implicit value is gl_FragCoord.z, so if a shader only assign
31 * this value to gl_FragDepth, the store instruction is removed.
32 */
33
34 static bool
ssa_def_is_source_depth(nir_def * def)35 ssa_def_is_source_depth(nir_def *def)
36 {
37 nir_scalar scalar = nir_scalar_resolved(def, 0);
38 nir_instr *instr = scalar.def->parent_instr;
39 if (instr->type != nir_instr_type_intrinsic)
40 return false;
41
42 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
43 if (intrin->intrinsic != nir_intrinsic_load_frag_coord)
44 return false;
45
46 /* Depth is gl_FragCoord.z */
47 return scalar.comp == 2;
48 }
49
50 bool
nir_opt_fragdepth(nir_shader * shader)51 nir_opt_fragdepth(nir_shader *shader)
52 {
53 bool progress = false;
54 nir_intrinsic_instr *store_intrin = NULL;
55
56 if (shader->info.stage != MESA_SHADER_FRAGMENT)
57 goto end;
58
59 nir_function_impl *impl = nir_shader_get_entrypoint(shader);
60 nir_foreach_block(block, impl) {
61 nir_foreach_instr(instr, block) {
62 if (instr->type != nir_instr_type_intrinsic)
63 continue;
64
65 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
66 if (intrin->intrinsic != nir_intrinsic_store_deref &&
67 intrin->intrinsic != nir_intrinsic_store_output)
68 continue;
69
70 unsigned data_src;
71
72 if (intrin->intrinsic == nir_intrinsic_store_deref) {
73 nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
74 if (!nir_deref_mode_is(deref, nir_var_shader_out))
75 continue;
76
77 nir_variable *var = nir_deref_instr_get_variable(deref);
78 if (var->data.location != FRAG_RESULT_DEPTH)
79 continue;
80
81 data_src = 1;
82 } else {
83 nir_io_semantics sem = nir_intrinsic_io_semantics(intrin);
84
85 if (sem.location != FRAG_RESULT_DEPTH)
86 continue;
87
88 data_src = 0;
89 }
90
91 /* We found a write to gl_FragDepth */
92 if (store_intrin) {
93 /* This isn't the only write: give up on this optimization */
94 goto end;
95 } else {
96 if (ssa_def_is_source_depth(intrin->src[data_src].ssa)) {
97 /* We're writing gl_FragCoord.z in gl_FragDepth: remember
98 * intrin so we can try to remove it later. */
99 store_intrin = intrin;
100 } else {
101 /* We're writing something else: give up. */
102 goto end;
103 }
104 }
105 }
106 }
107
108 if (store_intrin) {
109 /* Found a single store to gl_FragDepth, and it writes gl_FragCoord.z to it.
110 * Remove it since that's the implicit value of gl_FragDepth.
111 */
112 nir_instr_remove(&store_intrin->instr);
113
114 nir_metadata_preserve(impl, nir_metadata_control_flow |
115 nir_metadata_loop_analysis |
116 nir_metadata_instr_index);
117 progress = true;
118 }
119
120 end:
121 if (!progress)
122 nir_shader_preserve_all_metadata(shader);
123 return progress;
124 }
125