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nir,amd: reassociate fadd to create more fma/mad

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ACO's backend fusing is quite competent, but it cannot reorder adds.
This adds a simple algebraic pass to do that for us.

Foz-DB Navi10:
Totals from 13568 (18.76% of 72319) affected shaders:
MaxWaves: 304722 -> 304004 (-0.24%); split: +0.10%, -0.33%
Instrs: 15084252 -> 14993010 (-0.60%); split: -0.61%, +0.00%
CodeSize: 81480188 -> 81372600 (-0.13%); split: -0.17%, +0.04%
VGPRs: 741580 -> 743680 (+0.28%); split: -0.10%, +0.38%
SpillSGPRs: 9418 -> 9434 (+0.17%)
Latency: 154602014 -> 154312940 (-0.19%); split: -0.29%, +0.10%
InvThroughput: 44628554 -> 44442595 (-0.42%); split: -0.47%, +0.05%
VClause: 300035 -> 300054 (+0.01%); split: -0.31%, +0.31%
SClause: 370992 -> 370640 (-0.09%); split: -0.15%, +0.06%
Copies: 1162401 -> 1162800 (+0.03%); split: -0.30%, +0.33%
Branches: 300646 -> 300654 (+0.00%); split: -0.00%, +0.01%
PreSGPRs: 673675 -> 675057 (+0.21%); split: -0.00%, +0.21%
PreVGPRs: 633017 -> 634768 (+0.28%); split: -0.29%, +0.57%
VALU: 10800351 -> 10712041 (-0.82%); split: -0.82%, +0.00%
SALU: 1752917 -> 1753203 (+0.02%); split: -0.04%, +0.06%

Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41348>
This commit is contained in:
Georg Lehmann 2026-05-04 16:57:49 +02:00 • committed by Marge Bot
parent 9e87090db4
commit 1716cbff37
6 changed files with 44 additions and 14 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
src/amd/ci/traces-amd.yml
View file

@ -68,7 +68,7 @@ traces:
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3
src/amd/vulkan/radv_shader.c
View file

@ -277,6 +277,9 @@ radv_optimize_nir_algebraic_early(nir_shader *nir)
void
radv_optimize_nir_algebraic_late(nir_shader *nir)
{
if (nir->info.stage != MESA_SHADER_VERTEX && nir->info.stage != MESA_SHADER_GEOMETRY)
NIR_PASS(_, nir, nir_opt_reassociate_for_fma);
/* Do late algebraic optimization to turn add(a,
* neg(b)) back into subs, then the mandatory cleanup
* after algebraic. Note that it may produce fnegs,

1
src/compiler/nir/nir.h
View file

@ -6688,6 +6688,7 @@ bool nir_opt_algebraic_late(nir_shader *shader);
bool nir_opt_algebraic_distribute_src_mods(nir_shader *shader);
bool nir_opt_algebraic_integer_promotion(nir_shader *shader);
bool nir_opt_reassociate_matrix_mul(nir_shader *shader);
bool nir_opt_reassociate_for_fma(nir_shader *shader);
bool nir_opt_constant_folding(nir_shader *shader);
bool nir_opt_fp_math_ctrl(nir_shader *shader);

23
src/compiler/nir/nir_opt_algebraic.py
View file

@ -4246,6 +4246,23 @@ before_lower_int64_optimizations = [
(('iadd', ('u2u64', a), ('u2u64', a)), ('ishl', ('u2u64', a), 1)),
]
reassoc_fma_optimizations = [
# Try to reassociate fadd to make more adds have a fmul source
(('~fadd', ('fadd(is_used_once)', 'a(is_fmul)', ('fadd(is_used_once)', 'b(is_fmul)', ('fadd(is_used_once)', 'c(is_fmul)', 'd(is_fmul)'))), 'e(is_not_fmul)'),
('fadd', a, ('fadd', b, ('fadd', c, ('fadd', d, e))))),
(('~fadd', ('fadd(is_used_once)', 'a(is_fmul)', ('fadd(is_used_once)', 'b(is_fmul)', 'c(is_fmul)')), 'd(is_not_fmul)'),
('fadd', a, ('fadd', b, ('fadd', c, d)))),
(('~fadd', ('fadd(is_used_once)', 'a(is_fmul)', 'b(is_fmul)'), 'c(is_not_fmul)'),
('fadd', a, ('fadd', b, c))),
(('~fadd', ('fneg(is_used_once)', ('fadd(is_used_once)', 'a(is_fmul)', ('fadd(is_used_once)', 'b(is_fmul)', ('fadd(is_used_once)', 'c(is_fmul)', 'd(is_fmul)')))), 'e(is_not_fmul)'),
('fadd', ('fneg', a), ('fneg', ('fadd', b, ('fadd', c, ('fadd', d, ('fneg', e))))))),
(('~fadd', ('fneg(is_used_once)', ('fadd(is_used_once)', 'a(is_fmul)', ('fadd(is_used_once)', 'b(is_fmul)', 'c(is_fmul)'))), 'd(is_not_fmul)'),
('fadd', ('fneg', a), ('fneg', ('fadd', b, ('fadd', c, ('fneg', d)))))),
(('~fadd', ('fneg(is_used_once)', ('fadd(is_used_once)', 'a(is_fmul)', 'b(is_fmul)')), 'c(is_not_fmul)'),
('fadd', ('fneg', a), ('fadd', ('fneg', b), c))),
]
# Those optimizations try to reverse integer promotion found in e.g. OpenCL C. Those should be ran
# before any bit_size lowering is done.
integer_promotion_optimizations = []
@ -4321,6 +4338,12 @@ passes.append(nir_algebraic.AlgebraicPass(
build_tests=build_tests
))
passes.append(nir_algebraic.AlgebraicPass(
"nir_opt_reassociate_for_fma",
reassoc_fma_optimizations,
build_tests=build_tests
))
if build_tests:
with open(args.out_tests, "w", encoding='utf-8') as f:
for p in passes:

3
src/gallium/drivers/radeonsi/gfx/si_shader_nir.c
View file

@ -94,6 +94,9 @@ void si_nir_opts(struct si_screen *sscreen, struct nir_shader *nir, bool has_arr
void si_nir_late_opts(nir_shader *nir)
{
if (nir->info.stage != MESA_SHADER_VERTEX && nir->info.stage != MESA_SHADER_GEOMETRY)
NIR_PASS(_, nir, nir_opt_reassociate_for_fma);
bool more_late_algebraic = true;
while (more_late_algebraic) {
more_late_algebraic = false;

22
src/gallium/drivers/zink/ci/traces-zink.yml
View file

@ -99,9 +99,9 @@ traces:
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