1/*
2 * Copyright © 2014 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 * Authors:
24 *    Connor Abbott (cwabbott0@gmail.com)
25 *
26 */
27
28#include "nir.h"
29
30/* SSA-based mark-and-sweep dead code elimination */
31
32typedef struct {
33   struct exec_node node;
34   nir_instr *instr;
35} worklist_elem;
36
37static void
38worklist_push(struct exec_list *worklist, nir_instr *instr)
39{
40   worklist_elem *elem = ralloc(worklist, worklist_elem);
41   elem->instr = instr;
42   instr->pass_flags = 1;
43   exec_list_push_tail(worklist, &elem->node);
44}
45
46static nir_instr *
47worklist_pop(struct exec_list *worklist)
48{
49   struct exec_node *node = exec_list_pop_head(worklist);
50   worklist_elem *elem = exec_node_data(worklist_elem, node, node);
51   return elem->instr;
52}
53
54static bool
55mark_live_cb(nir_src *src, void *_state)
56{
57   struct exec_list *worklist = (struct exec_list *) _state;
58
59   if (src->is_ssa && !src->ssa->parent_instr->pass_flags) {
60      worklist_push(worklist, src->ssa->parent_instr);
61   }
62
63   return true;
64}
65
66static void
67init_instr(nir_instr *instr, struct exec_list *worklist)
68{
69   nir_alu_instr *alu_instr;
70   nir_intrinsic_instr *intrin_instr;
71   nir_tex_instr *tex_instr;
72
73   /* We use the pass_flags to store the live/dead information.  In DCE, we
74    * just treat it as a zero/non-zero boolean for whether or not the
75    * instruction is live.
76    */
77   instr->pass_flags = 0;
78
79   switch (instr->type) {
80   case nir_instr_type_call:
81   case nir_instr_type_jump:
82      worklist_push(worklist, instr);
83      break;
84
85   case nir_instr_type_alu:
86      alu_instr = nir_instr_as_alu(instr);
87      if (!alu_instr->dest.dest.is_ssa)
88         worklist_push(worklist, instr);
89      break;
90
91   case nir_instr_type_intrinsic:
92      intrin_instr = nir_instr_as_intrinsic(instr);
93      if (nir_intrinsic_infos[intrin_instr->intrinsic].flags &
94          NIR_INTRINSIC_CAN_ELIMINATE) {
95         if (nir_intrinsic_infos[intrin_instr->intrinsic].has_dest &&
96             !intrin_instr->dest.is_ssa) {
97            worklist_push(worklist, instr);
98         }
99      } else {
100         worklist_push(worklist, instr);
101      }
102      break;
103
104   case nir_instr_type_tex:
105      tex_instr = nir_instr_as_tex(instr);
106      if (!tex_instr->dest.is_ssa)
107         worklist_push(worklist, instr);
108      break;
109
110   default:
111      break;
112   }
113}
114
115static bool
116init_block(nir_block *block, struct exec_list *worklist)
117{
118   nir_foreach_instr(instr, block)
119      init_instr(instr, worklist);
120
121   nir_if *following_if = nir_block_get_following_if(block);
122   if (following_if) {
123      if (following_if->condition.is_ssa &&
124          !following_if->condition.ssa->parent_instr->pass_flags)
125         worklist_push(worklist, following_if->condition.ssa->parent_instr);
126   }
127
128   return true;
129}
130
131static bool
132nir_opt_dce_impl(nir_function_impl *impl)
133{
134   struct exec_list *worklist = rzalloc(NULL, struct exec_list);
135   exec_list_make_empty(worklist);
136
137   nir_foreach_block(block, impl) {
138      init_block(block, worklist);
139   }
140
141   while (!exec_list_is_empty(worklist)) {
142      nir_instr *instr = worklist_pop(worklist);
143      nir_foreach_src(instr, mark_live_cb, worklist);
144   }
145
146   ralloc_free(worklist);
147
148   bool progress = false;
149
150   nir_foreach_block(block, impl) {
151      nir_foreach_instr_safe(instr, block) {
152         if (!instr->pass_flags) {
153            nir_instr_remove(instr);
154            progress = true;
155         }
156      }
157   }
158
159   if (progress)
160      nir_metadata_preserve(impl, nir_metadata_block_index |
161                                  nir_metadata_dominance);
162
163   return progress;
164}
165
166bool
167nir_opt_dce(nir_shader *shader)
168{
169   bool progress = false;
170   nir_foreach_function(function, shader) {
171      if (function->impl && nir_opt_dce_impl(function->impl))
172         progress = true;
173   }
174
175   return progress;
176}
177