1/*
2 * Copyright © 2015 Broadcom
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_undef.c
28 *
29 * Handles optimization of operations involving ssa_undef.
30 */
31
32/**
33 * Turn conditional selects between an undef and some other value into a move
34 * of that other value (on the assumption that the condition's going to be
35 * choosing the defined value).  This reduces work after if flattening when
36 * each side of the if is defining a variable.
37 */
38static bool
39opt_undef_csel(nir_alu_instr *instr)
40{
41   if (instr->op != nir_op_bcsel && instr->op != nir_op_fcsel)
42      return false;
43
44   assert(instr->dest.dest.is_ssa);
45
46   for (int i = 1; i <= 2; i++) {
47      if (!instr->src[i].src.is_ssa)
48         continue;
49
50      nir_instr *parent = instr->src[i].src.ssa->parent_instr;
51      if (parent->type != nir_instr_type_ssa_undef)
52         continue;
53
54      /* We can't just use nir_alu_src_copy, because we need the def/use
55       * updated.
56       */
57      nir_instr_rewrite_src(&instr->instr, &instr->src[0].src,
58                            instr->src[i == 1 ? 2 : 1].src);
59      nir_alu_src_copy(&instr->src[0], &instr->src[i == 1 ? 2 : 1],
60                       ralloc_parent(instr));
61
62      nir_src empty_src;
63      memset(&empty_src, 0, sizeof(empty_src));
64      nir_instr_rewrite_src(&instr->instr, &instr->src[1].src, empty_src);
65      nir_instr_rewrite_src(&instr->instr, &instr->src[2].src, empty_src);
66      instr->op = nir_op_imov;
67
68      return true;
69   }
70
71   return false;
72}
73
74/**
75 * Replace vecN(undef, undef, ...) with a single undef.
76 */
77static bool
78opt_undef_vecN(nir_builder *b, nir_alu_instr *alu)
79{
80   if (alu->op != nir_op_vec2 &&
81       alu->op != nir_op_vec3 &&
82       alu->op != nir_op_vec4 &&
83       alu->op != nir_op_fmov &&
84       alu->op != nir_op_imov)
85      return false;
86
87   assert(alu->dest.dest.is_ssa);
88
89   for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
90      if (!alu->src[i].src.is_ssa ||
91          alu->src[i].src.ssa->parent_instr->type != nir_instr_type_ssa_undef)
92         return false;
93   }
94
95   b->cursor = nir_before_instr(&alu->instr);
96   nir_ssa_def *undef = nir_ssa_undef(b, alu->dest.dest.ssa.num_components,
97                                      nir_dest_bit_size(alu->dest.dest));
98   nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(undef));
99
100   return true;
101}
102
103/**
104 * Remove any store intrinsics whose value is undefined (the existing
105 * value is a fine representation of "undefined").
106 */
107static bool
108opt_undef_store(nir_intrinsic_instr *intrin)
109{
110   int arg_index;
111   switch (intrin->intrinsic) {
112   case nir_intrinsic_store_deref:
113      arg_index = 1;
114      break;
115   case nir_intrinsic_store_output:
116   case nir_intrinsic_store_per_vertex_output:
117   case nir_intrinsic_store_ssbo:
118   case nir_intrinsic_store_shared:
119      arg_index =  0;
120      break;
121   default:
122      return false;
123   }
124
125   if (!intrin->src[arg_index].is_ssa ||
126       intrin->src[arg_index].ssa->parent_instr->type != nir_instr_type_ssa_undef)
127      return false;
128
129   nir_instr_remove(&intrin->instr);
130
131   return true;
132}
133
134bool
135nir_opt_undef(nir_shader *shader)
136{
137   nir_builder b;
138   bool progress = false;
139
140   nir_foreach_function(function, shader) {
141      if (function->impl) {
142         nir_builder_init(&b, function->impl);
143         nir_foreach_block(block, function->impl) {
144            nir_foreach_instr_safe(instr, block) {
145               if (instr->type == nir_instr_type_alu) {
146                  nir_alu_instr *alu = nir_instr_as_alu(instr);
147
148                  progress = opt_undef_csel(alu) || progress;
149                  progress = opt_undef_vecN(&b, alu) || progress;
150               } else if (instr->type == nir_instr_type_intrinsic) {
151                  nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
152                  progress = opt_undef_store(intrin) || progress;
153               }
154            }
155         }
156
157         if (progress) {
158            nir_metadata_preserve(function->impl,
159                                  nir_metadata_block_index |
160                                  nir_metadata_dominance);
161         } else {
162#ifndef NDEBUG
163            function->impl->valid_metadata &= ~nir_metadata_not_properly_reset;
164#endif
165         }
166      }
167   }
168
169   return progress;
170}
171