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11 * The above copyright notice and this permission notice (including the next
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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_reverse_safe(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_safe(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
->flags_written()) {
72 inst
->dst
= fs_reg(retype(brw_null_reg(), inst
->dst
.type
));
74 inst
->opcode
= BRW_OPCODE_NOP
;
79 if (inst
->dst
.is_null() && inst
->flags_written()) {
80 if (!(flag_live
[0] & inst
->flags_written())) {
81 inst
->opcode
= BRW_OPCODE_NOP
;
86 if ((inst
->opcode
!= BRW_OPCODE_IF
&&
87 inst
->opcode
!= BRW_OPCODE_WHILE
) &&
88 inst
->dst
.is_null() &&
89 !inst
->has_side_effects() &&
90 !inst
->flags_written() &&
91 !inst
->writes_accumulator
) {
92 inst
->opcode
= BRW_OPCODE_NOP
;
96 if (inst
->dst
.file
== VGRF
) {
97 if (!inst
->is_partial_write()) {
98 int var
= live_intervals
->var_from_reg(inst
->dst
);
99 for (int i
= 0; i
< inst
->regs_written
; i
++) {
100 BITSET_CLEAR(live
, var
+ i
);
105 if (!inst
->predicate
&& inst
->exec_size
>= 8)
106 flag_live
[0] &= ~inst
->flags_written();
108 if (inst
->opcode
== BRW_OPCODE_NOP
) {
113 for (int i
= 0; i
< inst
->sources
; i
++) {
114 if (inst
->src
[i
].file
== VGRF
) {
115 int var
= live_intervals
->var_from_reg(inst
->src
[i
]);
117 for (int j
= 0; j
< inst
->regs_read(i
); j
++) {
118 BITSET_SET(live
, var
+ j
);
123 flag_live
[0] |= inst
->flags_read(devinfo
);
128 ralloc_free(flag_live
);
131 invalidate_live_intervals();