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i965: Do dead-code elimination in a single pass.

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The first pass marked dead instructions as opcode = NOP, and a second
pass deleted those instructions so that the live ranges used in the
first pass wouldn't change.

But since we're walking the instructions in reverse order, we can just
do everything in one pass. The only thing we have to do is walk the
blocks in reverse as well.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
This commit is contained in:
Matt Turner
2015-11-30 09:25:19 -08:00
parent 5a6f0bf5b8
commit 7e6a6f3e61
3 changed files with 16 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/mesa/drivers/dri/i965/brw_cfg.h
+3
View File
@@ -314,6 +314,9 @@ struct cfg_t {
#define foreach_block_safe(__block, __cfg) \
foreach_list_typed_safe (bblock_t, __block, link, &(__cfg)->block_list)
#define foreach_block_reverse_safe(__block, __cfg) \
foreach_list_typed_reverse_safe (bblock_t, __block, link, &(__cfg)->block_list)
#define foreach_inst_in_block(__type, __inst, __block) \
foreach_in_list(__type, __inst, &(__block)->instructions)
src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
+6 -15
View File
@@ -45,13 +45,13 @@ fs_visitor::dead_code_eliminate()
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) {
foreach_block_reverse_safe(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) {
foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
if (inst->dst.file == VGRF && !inst->has_side_effects()) {
bool result_live = false;
@@ -72,7 +72,6 @@ fs_visitor::dead_code_eliminate()
inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
} else {
inst->opcode = BRW_OPCODE_NOP;
continue;
}
}
}
@@ -81,7 +80,6 @@ fs_visitor::dead_code_eliminate()
if (!BITSET_TEST(flag_live, inst->flag_subreg)) {
inst->opcode = BRW_OPCODE_NOP;
progress = true;
continue;
}
}
@@ -93,7 +91,6 @@ fs_visitor::dead_code_eliminate()
!inst->writes_accumulator) {
inst->opcode = BRW_OPCODE_NOP;
progress = true;
continue;
}
if (inst->dst.file == VGRF) {
@@ -109,9 +106,10 @@ fs_visitor::dead_code_eliminate()
BITSET_CLEAR(flag_live, inst->flag_subreg);
}
/* Don't mark dead instructions' sources as live */
if (inst->opcode == BRW_OPCODE_NOP)
if (inst->opcode == BRW_OPCODE_NOP) {
inst->remove(block);
continue;
}
for (int i = 0; i < inst->sources; i++) {
if (inst->src[i].file == VGRF) {
@@ -132,15 +130,8 @@ fs_visitor::dead_code_eliminate()
ralloc_free(live);
ralloc_free(flag_live);
if (progress) {
foreach_block_and_inst_safe (block, backend_instruction, inst, cfg) {
if (inst->opcode == BRW_OPCODE_NOP) {
inst->remove(block);
}
}
if (progress)
invalidate_live_intervals();
}
return progress;
}
src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
+7 -14
View File
@@ -71,13 +71,13 @@ vec4_visitor::dead_code_eliminate()
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) {
foreach_block_reverse_safe(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(vec4_instruction, inst, block) {
foreach_inst_in_block_reverse_safe(vec4_instruction, inst, block) {
if ((inst->dst.file == VGRF && !inst->has_side_effects()) ||
(inst->dst.is_null() && inst->writes_flag())){
bool result_live[4] = { false };
@@ -115,7 +115,7 @@ vec4_visitor::dead_code_eliminate()
inst->dst = dst_reg(retype(brw_null_reg(), inst->dst.type));
} else {
inst->opcode = BRW_OPCODE_NOP;
continue;
break;
}
}
}
@@ -130,7 +130,6 @@ vec4_visitor::dead_code_eliminate()
if (!combined_live) {
inst->opcode = BRW_OPCODE_NOP;
progress = true;
continue;
}
}
@@ -150,9 +149,10 @@ vec4_visitor::dead_code_eliminate()
BITSET_CLEAR(flag_live, c);
}
/* Don't mark dead instructions' sources as live */
if (inst->opcode == BRW_OPCODE_NOP)
if (inst->opcode == BRW_OPCODE_NOP) {
inst->remove(block);
continue;
}
for (int i = 0; i < 3; i++) {
if (inst->src[i].file == VGRF) {
@@ -176,15 +176,8 @@ vec4_visitor::dead_code_eliminate()
ralloc_free(live);
ralloc_free(flag_live);
if (progress) {
foreach_block_and_inst_safe(block, backend_instruction, inst, cfg) {
if (inst->opcode == BRW_OPCODE_NOP) {
inst->remove(block);
}
}
if (progress)
invalidate_live_intervals();
}
return progress;
}