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11 * The above copyright notice and this permission notice (including the next
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16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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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 cfg_t
cfg(&instructions
);
44 calculate_live_intervals(&cfg
);
46 int num_vars
= live_intervals
->num_vars
;
47 BITSET_WORD
*live
= ralloc_array(NULL
, BITSET_WORD
, BITSET_WORDS(num_vars
));
49 for (int b
= 0; b
< cfg
.num_blocks
; b
++) {
50 bblock_t
*block
= cfg
.blocks
[b
];
51 memcpy(live
, live_intervals
->bd
[b
].liveout
,
52 sizeof(BITSET_WORD
) * BITSET_WORDS(num_vars
));
54 foreach_inst_in_block_reverse(fs_inst
, inst
, block
) {
55 if (inst
->dst
.file
== GRF
&&
56 !inst
->has_side_effects() &&
57 !inst
->writes_flag()) {
58 bool result_live
= false;
60 if (inst
->regs_written
== 1) {
61 int var
= live_intervals
->var_from_reg(&inst
->dst
);
62 result_live
= BITSET_TEST(live
, var
);
64 int var
= live_intervals
->var_from_vgrf
[inst
->dst
.reg
];
65 for (int i
= 0; i
< inst
->regs_written
; i
++) {
66 result_live
= result_live
|| BITSET_TEST(live
, var
+ i
);
73 if (inst
->writes_accumulator
) {
74 inst
->dst
= fs_reg(retype(brw_null_reg(), inst
->dst
.type
));
76 inst
->opcode
= BRW_OPCODE_NOP
;
82 if (inst
->dst
.file
== GRF
) {
83 if (!inst
->is_partial_write()) {
84 int var
= live_intervals
->var_from_vgrf
[inst
->dst
.reg
];
85 for (int i
= 0; i
< inst
->regs_written
; i
++) {
86 BITSET_CLEAR(live
, var
+ inst
->dst
.reg_offset
+ i
);
91 for (int i
= 0; i
< inst
->sources
; i
++) {
92 if (inst
->src
[i
].file
== GRF
) {
93 int var
= live_intervals
->var_from_vgrf
[inst
->src
[i
].reg
];
95 for (int j
= 0; j
< inst
->regs_read(this, i
); j
++) {
96 BITSET_SET(live
, var
+ inst
->src
[i
].reg_offset
+ j
);
106 foreach_in_list_safe(fs_inst
, inst
, &instructions
) {
107 if (inst
->opcode
== BRW_OPCODE_NOP
) {
112 invalidate_live_intervals();