brw_fs_dead_code_eliminate.cpp revision 60d507c3c5c7caed57119df0ab4d824ad1ea85dc 
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
24#include "brw_fs.h"
25#include "brw_fs_live_variables.h"
26#include "brw_cfg.h"
27
28/** @file brw_fs_dead_code_eliminate.cpp
29 *
30 * Dataflow-aware dead code elimination.
31 *
32 * Walks the instruction list from the bottom, removing instructions that
33 * have results that both aren't used in later blocks and haven't been read
34 * yet in the tail end of this block.
35 */
36
37bool
38fs_visitor::dead_code_eliminate()
39{
40   bool progress = false;
41
42   calculate_live_intervals();
43
44   int num_vars = live_intervals->num_vars;
45   BITSET_WORD *live = ralloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
46   BITSET_WORD *flag_live = ralloc_array(NULL, BITSET_WORD, 1);
47
48   foreach_block (block, cfg) {
49      memcpy(live, live_intervals->block_data[block->num].liveout,
50             sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
51      memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout,
52             sizeof(BITSET_WORD));
53
54      foreach_inst_in_block_reverse(fs_inst, inst, block) {
55         if (inst->dst.file == GRF && !inst->has_side_effects()) {
56            bool result_live = false;
57
58            if (inst->regs_written == 1) {
59               int var = live_intervals->var_from_reg(&inst->dst);
60               result_live = BITSET_TEST(live, var);
61            } else {
62               int var = live_intervals->var_from_reg(&inst->dst);
63               for (int i = 0; i < inst->regs_written; i++) {
64                  result_live = result_live || BITSET_TEST(live, var + i);
65               }
66            }
67
68            if (!result_live) {
69               progress = true;
70
71               if (inst->writes_accumulator || inst->writes_flag()) {
72                  inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
73               } else {
74                  inst->opcode = BRW_OPCODE_NOP;
75                  continue;
76               }
77            }
78         }
79
80         if (inst->dst.is_null() && inst->writes_flag()) {
81            if (!BITSET_TEST(flag_live, inst->flag_subreg)) {
82               inst->opcode = BRW_OPCODE_NOP;
83               progress = true;
84               continue;
85            }
86         }
87
88         if (inst->dst.file == GRF) {
89            if (!inst->is_partial_write()) {
90               int var = live_intervals->var_from_reg(&inst->dst);
91               for (int i = 0; i < inst->regs_written; i++) {
92                  BITSET_CLEAR(live, var + i);
93               }
94            }
95         }
96
97         if (inst->writes_flag()) {
98            BITSET_CLEAR(flag_live, inst->flag_subreg);
99         }
100
101         for (int i = 0; i < inst->sources; i++) {
102            if (inst->src[i].file == GRF) {
103               int var = live_intervals->var_from_reg(&inst->src[i]);
104
105               for (int j = 0; j < inst->regs_read(this, i); j++) {
106                  BITSET_SET(live, var + j);
107               }
108            }
109         }
110
111         if (inst->reads_flag()) {
112            BITSET_SET(flag_live, inst->flag_subreg);
113         }
114      }
115   }
116
117   ralloc_free(live);
118   ralloc_free(flag_live);
119
120   if (progress) {
121      foreach_block_and_inst_safe (block, backend_instruction, inst, cfg) {
122         if (inst->opcode == BRW_OPCODE_NOP) {
123            inst->remove(block);
124         }
125      }
126
127      invalidate_live_intervals();
128   }
129
130   return progress;
131}
132