2 * Copyright © 2014 Intel Corporation
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:
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
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
25 #include "brw_fs_live_variables.h"
28 /** @file brw_fs_dead_code_eliminate.cpp
30 * Dataflow-aware dead code elimination.
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.
38 fs_visitor::dead_code_eliminate()
40 bool progress
= false;
42 calculate_live_intervals();
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);
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
,
54 foreach_inst_in_block_reverse(fs_inst
, inst
, block
) {
55 if (inst
->dst
.file
== VGRF
&& !inst
->has_side_effects()) {
56 bool result_live
= false;
58 if (inst
->regs_written
== 1) {
59 int var
= live_intervals
->var_from_reg(inst
->dst
);
60 result_live
= BITSET_TEST(live
, var
);
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
);
71 if (inst
->writes_accumulator
|| inst
->writes_flag()) {
72 inst
->dst
= fs_reg(retype(brw_null_reg(), inst
->dst
.type
));
74 inst
->opcode
= BRW_OPCODE_NOP
;
80 if (inst
->dst
.is_null() && inst
->writes_flag()) {
81 if (!BITSET_TEST(flag_live
, inst
->flag_subreg
)) {
82 inst
->opcode
= BRW_OPCODE_NOP
;
88 if ((inst
->opcode
!= BRW_OPCODE_IF
&&
89 inst
->opcode
!= BRW_OPCODE_WHILE
) &&
90 inst
->dst
.is_null() &&
91 !inst
->has_side_effects() &&
92 !inst
->writes_flag() &&
93 !inst
->writes_accumulator
) {
94 inst
->opcode
= BRW_OPCODE_NOP
;
99 if (inst
->dst
.file
== VGRF
) {
100 if (!inst
->is_partial_write()) {
101 int var
= live_intervals
->var_from_reg(inst
->dst
);
102 for (int i
= 0; i
< inst
->regs_written
; i
++) {
103 BITSET_CLEAR(live
, var
+ i
);
108 if (inst
->writes_flag() && !inst
->predicate
) {
109 BITSET_CLEAR(flag_live
, inst
->flag_subreg
);
112 for (int i
= 0; i
< inst
->sources
; i
++) {
113 if (inst
->src
[i
].file
== VGRF
) {
114 int var
= live_intervals
->var_from_reg(inst
->src
[i
]);
116 for (int j
= 0; j
< inst
->regs_read(i
); j
++) {
117 BITSET_SET(live
, var
+ j
);
122 if (inst
->reads_flag()) {
123 BITSET_SET(flag_live
, inst
->flag_subreg
);
129 ralloc_free(flag_live
);
132 foreach_block_and_inst_safe (block
, backend_instruction
, inst
, cfg
) {
133 if (inst
->opcode
== BRW_OPCODE_NOP
) {
138 invalidate_live_intervals();