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brw: Lower all phis to scalar

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The next commit will cause some very specific phis to not be lowered to
scalar, and that's the reason the callback is used instead of
nir_lower_all_phis_to_scalar.

It's worth noting that the comment in nir_lower_phis_to_scalar.c
specifically calls out Deus Ex as the reason some phis should not be
lowered. At least on current BRW, zero shaders from Deus Ex trace were
affected for spills or fills on any Intel platform.

shader-db:

All Intel platforms had similar results. (Lunar Lake shown)
total instructions in shared programs: 17050005 -> 17051449 (<.01%)
instructions in affected programs: 41032 -> 42476 (3.52%)
helped: 29 / HURT: 159

total cycles in shared programs: 876411976 -> 876433702 (<.01%)
cycles in affected programs: 1455550 -> 1477276 (1.49%)
helped: 40 / HURT: 150

fossil-db:

All Intel platforms had similar results. (Lunar Lake shown)
Totals:
Instrs: 916599633 -> 916694854 (+0.01%); split: -0.00%, +0.01%
CodeSize: 14705971792 -> 14708302384 (+0.02%); split: -0.00%, +0.02%
Send messages: 40870114 -> 40870113 (-0.00%)
Cycle count: 102360965889 -> 102364169753 (+0.00%); split: -0.00%, +0.01%
Spill count: 3460669 -> 3460240 (-0.01%)
Fill count: 4988325 -> 4987891 (-0.01%)
Max live registers: 192914542 -> 192918153 (+0.00%); split: -0.00%, +0.00%
Max dispatch width: 48848112 -> 48848128 (+0.00%)
Non SSA regs after NIR: 141633613 -> 141671589 (+0.03%); split: -0.00%, +0.03%

Totals from 5713 (0.28% of 2010434) affected shaders:
Instrs: 5215921 -> 5311142 (+1.83%); split: -0.09%, +1.91%
CodeSize: 88940784 -> 91271376 (+2.62%); split: -0.20%, +2.82%
Send messages: 284751 -> 284750 (-0.00%)
Cycle count: 275671864 -> 278875728 (+1.16%); split: -0.74%, +1.90%
Spill count: 857 -> 428 (-50.06%)
Fill count: 845 -> 411 (-51.36%)
Max live registers: 667776 -> 671387 (+0.54%); split: -0.86%, +1.40%
Max dispatch width: 160416 -> 160432 (+0.01%)
Non SSA regs after NIR: 1127904 -> 1165880 (+3.37%); split: -0.10%, +3.47%

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Tested-by: Matt Corallo <git@bluematt.me>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41172>
This commit is contained in:
Ian Romanick 2026-04-23 19:42:09 -07:00 • committed by Marge Bot
parent 71508d90aa
commit 09b43966ba
1 changed files with 7 additions and 1 deletions
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8
src/intel/compiler/brw/brw_nir.c
View file

@ -1698,6 +1698,12 @@ brw_nir_tag_speculative_access(nir_shader *nir)
nir_metadata_all, NULL);
}
static uint8_t
brw_nir_lower_phis_to_scalar_cb(const nir_instr *instr, const void *_)
{
return 1;
}
#define OPT BRW_NIR_PASS
#define LOOP_OPT BRW_NIR_LOOP_PASS
#define LOOP_OPT_NOT_IDEMPOTENT BRW_NIR_LOOP_PASS_NOT_IDEMPOTENT
@ -1735,7 +1741,7 @@ brw_nir_optimize(brw_pass_tracker *pt)
LOOP_OPT(nir_opt_copy_prop);
LOOP_OPT(nir_lower_phis_to_scalar, NULL, NULL);
LOOP_OPT(nir_lower_phis_to_scalar, brw_nir_lower_phis_to_scalar_cb, NULL);
LOOP_OPT(nir_opt_copy_prop);
LOOP_OPT(nir_opt_dce);