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ir3/array_to_ssa: remove trivial all-undef phis

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remove_trivial_phi erroneously skipped phis containing an undef src
because the remaining srcs may not dominate the phi. However, it's fine
to replace a phi whose srcs are all undef with undef. Fix this by simply
checking if all srcs are equal, whether undef or not.

Note that in practice, this often caused phis with undef srcs to be
inserted all the way up to the entry block, keeping their defs alive for
much longer than necessary.

Fixes unnecessary spilling in God Of War and Neon Noir traces.

Totals:
MaxWaves: 2381774 -> 2384954 (+0.13%)
Instrs: 49052269 -> 49052865 (+0.00%); split: -0.03%, +0.04%
CodeSize: 102493810 -> 102514296 (+0.02%); split: -0.02%, +0.04%
NOPs: 8391570 -> 8385296 (-0.07%); split: -0.14%, +0.07%
MOVs: 1448918 -> 1455153 (+0.43%); split: -0.43%, +0.86%
COVs: 824835 -> 824846 (+0.00%)
Full: 1714015 -> 1707987 (-0.35%)
(ss): 1125974 -> 1126692 (+0.06%); split: -0.14%, +0.21%
(sy): 553893 -> 553561 (-0.06%); split: -0.23%, +0.17%
(ss)-stall: 4011440 -> 4006144 (-0.13%); split: -0.21%, +0.08%
(sy)-stall: 16707741 -> 16664838 (-0.26%); split: -0.48%, +0.23%
STPs: 18953 -> 18495 (-2.42%)
LDPs: 23957 -> 22121 (-7.66%)
Preamble Instrs: 11100893 -> 11100673 (-0.00%)
Early Preamble: 122185 -> 122188 (+0.00%)
Last helper: 11913048 -> 11914963 (+0.02%); split: -0.04%, +0.06%
Subgroup size: 12925248 -> 12926272 (+0.01%)
Cat0: 9246551 -> 9240417 (-0.07%); split: -0.13%, +0.07%
Cat1: 2335781 -> 2341487 (+0.24%); split: -0.29%, +0.53%
Cat2: 18445905 -> 18445930 (+0.00%)
Cat6: 515382 -> 514732 (-0.13%)
Cat7: 1635575 -> 1637224 (+0.10%); split: -0.09%, +0.19%

Totals from 2293 (1.39% of 164705) affected shaders:
MaxWaves: 21622 -> 24802 (+14.71%)
Instrs: 3399456 -> 3400052 (+0.02%); split: -0.49%, +0.51%
CodeSize: 6576806 -> 6597292 (+0.31%); split: -0.24%, +0.55%
NOPs: 774365 -> 768091 (-0.81%); split: -1.54%, +0.73%
MOVs: 226724 -> 232959 (+2.75%); split: -2.73%, +5.48%
COVs: 48005 -> 48016 (+0.02%)
Full: 50599 -> 44571 (-11.91%)
(ss): 88248 -> 88966 (+0.81%); split: -1.85%, +2.66%
(sy): 41345 -> 41013 (-0.80%); split: -3.03%, +2.23%
(ss)-stall: 396793 -> 391497 (-1.33%); split: -2.11%, +0.78%
(sy)-stall: 1594786 -> 1551883 (-2.69%); split: -5.06%, +2.37%
STPs: 1147 -> 689 (-39.93%)
LDPs: 2535 -> 699 (-72.43%)
Preamble Instrs: 707407 -> 707187 (-0.03%)
Early Preamble: 180 -> 183 (+1.67%)
Last helper: 1538341 -> 1540256 (+0.12%); split: -0.35%, +0.47%
Subgroup size: 149248 -> 150272 (+0.69%)
Cat0: 857696 -> 851562 (-0.72%); split: -1.43%, +0.72%
Cat1: 275565 -> 281271 (+2.07%); split: -2.44%, +4.51%
Cat2: 1139467 -> 1139492 (+0.00%)
Cat6: 22505 -> 21855 (-2.89%)
Cat7: 129600 -> 131249 (+1.27%); split: -1.15%, +2.42%

Signed-off-by: Job Noorman <jnoorman@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36714>
This commit is contained in:
Job Noorman
2025-08-19 15:30:23 +02:00
committed by Marge Bot
parent ca15116fa1
commit 77c1c688dc
1 changed files with 15 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/freedreno/ir3/ir3_array_to_ssa.c
+15 -23
View File
@@ -121,40 +121,32 @@ remove_trivial_phi(struct ir3_instruction *phi)
phi->data = phi->dsts[0];
struct ir3_register *unique_def = NULL;
bool unique_def_valid = false;
bool unique = true;
for (unsigned i = 0; i < phi->block->predecessors_count; i++) {
struct ir3_register *src = phi->srcs[i];
/* If there are any undef sources, then the remaining sources may not
* dominate the phi node, even if they are all equal. So we need to
* bail out in this case.
*
* This seems to be a bug in the original paper.
*/
if (!src->def) {
unique = false;
break;
if (src->def) {
struct ir3_instruction *src_instr = src->def->instr;
/* phi sources which point to the phi itself don't count for
* figuring out if the phi is trivial
*/
if (src_instr == phi)
continue;
if (src_instr->opc == OPC_META_PHI) {
src->def = remove_trivial_phi(src->def->instr);
}
}
struct ir3_instruction *src_instr = src->def->instr;
/* phi sources which point to the phi itself don't count for
* figuring out if the phi is trivial
*/
if (src_instr == phi)
continue;
if (src_instr->opc == OPC_META_PHI) {
src->def = remove_trivial_phi(src->def->instr);
}
if (unique_def) {
if (unique_def_valid) {
if (unique_def != src->def) {
unique = false;
break;
}
} else {
unique_def = src->def;
unique_def_valid = true;
}
}