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i965/fs: Dead code eliminate instructions writing the flag.

Browse source 
Most prominently helps Natural Selection 2, which has a surprising
number shaders that do very complicated things before drawing black.

instructions in affected programs:     21052 -> 16978 (-19.35%)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
This commit is contained in:
Matt Turner 2014-10-28 20:12:21 -07:00
parent bf8deb5514
commit 60d507c3c5
1 changed files with 22 additions and 4 deletions
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26
src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
View file

@ -43,15 +43,16 @@ fs_visitor::dead_code_eliminate()
int num_vars = live_intervals->num_vars;
BITSET_WORD *live = ralloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
BITSET_WORD *flag_live = ralloc_array(NULL, BITSET_WORD, 1);
foreach_block (block, cfg) {
memcpy(live, live_intervals->block_data[block->num].liveout,
sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout,
sizeof(BITSET_WORD));
foreach_inst_in_block_reverse(fs_inst, inst, block) {
if (inst->dst.file == GRF &&
!inst->has_side_effects() &&
!inst->writes_flag()) {
if (inst->dst.file == GRF && !inst->has_side_effects()) {
bool result_live = false;
if (inst->regs_written == 1) {
@ -67,7 +68,7 @@ fs_visitor::dead_code_eliminate()
if (!result_live) {
progress = true;
if (inst->writes_accumulator) {
if (inst->writes_accumulator || inst->writes_flag()) {
inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
} else {
inst->opcode = BRW_OPCODE_NOP;
@ -76,6 +77,14 @@ fs_visitor::dead_code_eliminate()
}
}
if (inst->dst.is_null() && inst->writes_flag()) {
if (!BITSET_TEST(flag_live, inst->flag_subreg)) {
inst->opcode = BRW_OPCODE_NOP;
progress = true;
continue;
}
}
if (inst->dst.file == GRF) {
if (!inst->is_partial_write()) {
int var = live_intervals->var_from_reg(&inst->dst);
@ -85,6 +94,10 @@ fs_visitor::dead_code_eliminate()
}
}
if (inst->writes_flag()) {
BITSET_CLEAR(flag_live, inst->flag_subreg);
}
for (int i = 0; i < inst->sources; i++) {
if (inst->src[i].file == GRF) {
int var = live_intervals->var_from_reg(&inst->src[i]);
@ -94,10 +107,15 @@ fs_visitor::dead_code_eliminate()
}
}
}
if (inst->reads_flag()) {
BITSET_SET(flag_live, inst->flag_subreg);
}
}
}
ralloc_free(live);
ralloc_free(flag_live);
if (progress) {
foreach_block_and_inst_safe (block, backend_instruction, inst, cfg) {