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25 #include "brw_vec4_live_variables.h"
28 /** @file brw_vec4_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.
40 vec4_visitor::dead_code_eliminate()
42 bool progress
= false;
44 calculate_live_intervals();
46 int num_vars
= live_intervals
->num_vars
;
47 BITSET_WORD
*live
= rzalloc_array(NULL
, BITSET_WORD
, BITSET_WORDS(num_vars
));
48 BITSET_WORD
*flag_live
= rzalloc_array(NULL
, BITSET_WORD
, 1);
50 foreach_block_reverse_safe(block
, cfg
) {
51 memcpy(live
, live_intervals
->block_data
[block
->num
].liveout
,
52 sizeof(BITSET_WORD
) * BITSET_WORDS(num_vars
));
53 memcpy(flag_live
, live_intervals
->block_data
[block
->num
].flag_liveout
,
56 foreach_inst_in_block_reverse_safe(vec4_instruction
, inst
, block
) {
57 if ((inst
->dst
.file
== VGRF
&& !inst
->has_side_effects()) ||
58 (inst
->dst
.is_null() && inst
->writes_flag())){
59 bool result_live
[4] = { false };
60 if (inst
->dst
.file
== VGRF
) {
61 for (unsigned i
= 0; i
< DIV_ROUND_UP(inst
->size_written
, 16); i
++) {
62 for (int c
= 0; c
< 4; c
++) {
63 const unsigned v
= var_from_reg(alloc
, inst
->dst
, c
, i
);
64 result_live
[c
] |= BITSET_TEST(live
, v
);
68 for (unsigned c
= 0; c
< 4; c
++)
69 result_live
[c
] = BITSET_TEST(flag_live
, c
);
72 /* If the instruction can't do writemasking, then it's all or
75 if (!inst
->can_do_writemask(devinfo
)) {
76 bool result
= result_live
[0] | result_live
[1] |
77 result_live
[2] | result_live
[3];
78 result_live
[0] = result
;
79 result_live
[1] = result
;
80 result_live
[2] = result
;
81 result_live
[3] = result
;
84 for (int c
= 0; c
< 4; c
++) {
85 if (!result_live
[c
] && inst
->dst
.writemask
& (1 << c
)) {
86 inst
->dst
.writemask
&= ~(1 << c
);
89 if (inst
->dst
.writemask
== 0) {
90 if (inst
->writes_accumulator
|| inst
->writes_flag()) {
91 inst
->dst
= dst_reg(retype(brw_null_reg(), inst
->dst
.type
));
93 inst
->opcode
= BRW_OPCODE_NOP
;
101 if (inst
->dst
.is_null() && inst
->writes_flag()) {
102 bool combined_live
= false;
103 for (unsigned c
= 0; c
< 4; c
++)
104 combined_live
|= BITSET_TEST(flag_live
, c
);
106 if (!combined_live
) {
107 inst
->opcode
= BRW_OPCODE_NOP
;
112 if (inst
->dst
.file
== VGRF
&& !inst
->predicate
&&
113 !inst
->is_align1_partial_write()) {
114 for (unsigned i
= 0; i
< DIV_ROUND_UP(inst
->size_written
, 16); i
++) {
115 for (int c
= 0; c
< 4; c
++) {
116 if (inst
->dst
.writemask
& (1 << c
)) {
117 const unsigned v
= var_from_reg(alloc
, inst
->dst
, c
, i
);
118 BITSET_CLEAR(live
, v
);
124 if (inst
->writes_flag() && !inst
->predicate
) {
125 for (unsigned c
= 0; c
< 4; c
++)
126 BITSET_CLEAR(flag_live
, c
);
129 if (inst
->opcode
== BRW_OPCODE_NOP
) {
134 for (int i
= 0; i
< 3; i
++) {
135 if (inst
->src
[i
].file
== VGRF
) {
136 for (unsigned j
= 0; j
< DIV_ROUND_UP(inst
->size_read(i
), 16); j
++) {
137 for (int c
= 0; c
< 4; c
++) {
138 const unsigned v
= var_from_reg(alloc
, inst
->src
[i
], c
, j
);
145 for (unsigned c
= 0; c
< 4; c
++) {
146 if (inst
->reads_flag(c
)) {
147 BITSET_SET(flag_live
, c
);
154 ralloc_free(flag_live
);
157 invalidate_live_intervals();