From 9e87090db48de50007aeb1ebc58553696cd7a1c0 Mon Sep 17 00:00:00 2001
From: Georg Lehmann <dadschoorse@gmail.com>
Date: Mon, 4 May 2026 16:16:05 +0200
Subject: [PATCH] nir/loop_analyze: do not count fmul towards the limit when
 only used by fadd
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As always with loop unrolling, don't look too closely at stats, but they
confirm more loops are now unrolled.

Foz-DB Navi10:
Totals from 66 (0.09% of 72319) affected shaders:
MaxWaves: 1464 -> 1424 (-2.73%); split: +0.82%, -3.55%
Instrs: 101778 -> 173128 (+70.10%)
CodeSize: 544148 -> 905392 (+66.39%)
VGPRs: 3652 -> 3788 (+3.72%); split: -0.77%, +4.49%
SpillSGPRs: 105 -> 75 (-28.57%)
Latency: 1197088 -> 1033471 (-13.67%); split: -17.08%, +3.41%
InvThroughput: 315257 -> 293245 (-6.98%); split: -13.29%, +6.31%
VClause: 1663 -> 3057 (+83.82%); split: -0.12%, +83.94%
SClause: 2797 -> 4496 (+60.74%); split: -0.21%, +60.96%
Copies: 6472 -> 11219 (+73.35%); split: -0.08%, +73.42%
Branches: 2695 -> 4697 (+74.29%); split: -0.56%, +74.84%
PreSGPRs: 3418 -> 3619 (+5.88%); split: -0.79%, +6.67%
PreVGPRs: 3305 -> 3423 (+3.57%); split: -1.06%, +4.63%
VALU: 73061 -> 124934 (+71.00%)
SALU: 11775 -> 20803 (+76.67%); split: -0.99%, +77.66%
VMEM: 2729 -> 4627 (+69.55%)
SMEM: 3796 -> 5869 (+54.61%); split: -0.18%, +54.79%

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>
---
 src/compiler/nir/nir_loop_analyze.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/compiler/nir/nir_loop_analyze.c b/src/compiler/nir/nir_loop_analyze.c
index 208dd9fd895..6e72b1fbafb 100644
--- a/src/compiler/nir/nir_loop_analyze.c
+++ b/src/compiler/nir/nir_loop_analyze.c
@@ -26,6 +26,7 @@
 #include "util/ralloc.h"
 #include "nir.h"
 #include "nir_constant_expressions.h"
+#include "nir_search_helpers.h"
 
 typedef struct {
    /* The loop we store information for */
@@ -97,6 +98,10 @@ instr_cost(loop_info_state *state, nir_instr *instr,
    } else if (nir_op_is_vec_or_mov(alu->op)) {
       /* movs and vecs are likely free. */
       return 0;
+   } else if ((alu->op == nir_op_fmul || alu->op == nir_op_fmulz) &&
+              is_only_used_by_fadd(alu)) {
+      /* If we can fuse fma/mad, do not count the mul. */
+      return 0;
    }
 
    if (alu->op == nir_op_flrp) {