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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 * Is it safe to eliminate the instruction?
41 can_eliminate(const fs_inst
*inst
, BITSET_WORD
*flag_live
)
43 return !inst
->is_control_flow() &&
44 !inst
->has_side_effects() &&
45 !(flag_live
[0] & inst
->flags_written()) &&
46 !inst
->writes_accumulator
;
50 * Is it safe to omit the write, making the destination ARF null?
53 can_omit_write(const fs_inst
*inst
)
55 switch (inst
->opcode
) {
56 case SHADER_OPCODE_UNTYPED_ATOMIC
:
57 case SHADER_OPCODE_UNTYPED_ATOMIC_LOGICAL
:
58 case SHADER_OPCODE_TYPED_ATOMIC
:
59 case SHADER_OPCODE_TYPED_ATOMIC_LOGICAL
:
62 /* We can eliminate the destination write for ordinary instructions,
65 if (inst
->opcode
< 128 && inst
->mlen
== 0)
68 /* It might not be safe for other virtual opcodes. */
74 fs_visitor::dead_code_eliminate()
76 bool progress
= false;
78 calculate_live_intervals();
80 int num_vars
= live_intervals
->num_vars
;
81 BITSET_WORD
*live
= rzalloc_array(NULL
, BITSET_WORD
, BITSET_WORDS(num_vars
));
82 BITSET_WORD
*flag_live
= rzalloc_array(NULL
, BITSET_WORD
, 1);
84 foreach_block_reverse_safe(block
, cfg
) {
85 memcpy(live
, live_intervals
->block_data
[block
->num
].liveout
,
86 sizeof(BITSET_WORD
) * BITSET_WORDS(num_vars
));
87 memcpy(flag_live
, live_intervals
->block_data
[block
->num
].flag_liveout
,
90 foreach_inst_in_block_reverse_safe(fs_inst
, inst
, block
) {
91 if (inst
->dst
.file
== VGRF
) {
92 const unsigned var
= live_intervals
->var_from_reg(inst
->dst
);
93 bool result_live
= false;
95 for (unsigned i
= 0; i
< regs_written(inst
); i
++)
96 result_live
|= BITSET_TEST(live
, var
+ i
);
99 (can_omit_write(inst
) || can_eliminate(inst
, flag_live
))) {
100 inst
->dst
= fs_reg(retype(brw_null_reg(), inst
->dst
.type
));
105 if (inst
->dst
.is_null() && can_eliminate(inst
, flag_live
)) {
106 inst
->opcode
= BRW_OPCODE_NOP
;
110 if (inst
->dst
.file
== VGRF
) {
111 if (!inst
->is_partial_write()) {
112 int var
= live_intervals
->var_from_reg(inst
->dst
);
113 for (unsigned i
= 0; i
< regs_written(inst
); i
++) {
114 BITSET_CLEAR(live
, var
+ i
);
119 if (!inst
->predicate
&& inst
->exec_size
>= 8)
120 flag_live
[0] &= ~inst
->flags_written();
122 if (inst
->opcode
== BRW_OPCODE_NOP
) {
127 for (int i
= 0; i
< inst
->sources
; i
++) {
128 if (inst
->src
[i
].file
== VGRF
) {
129 int var
= live_intervals
->var_from_reg(inst
->src
[i
]);
131 for (unsigned j
= 0; j
< regs_read(inst
, i
); j
++) {
132 BITSET_SET(live
, var
+ j
);
137 flag_live
[0] |= inst
->flags_read(devinfo
);
142 ralloc_free(flag_live
);
145 invalidate_live_intervals();