From daa3d5292fad6d10439cbc6a523a0c273d39d8ff Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Sch=C3=BCrmann?= <daniel@schuermann.dev>
Date: Thu, 2 Apr 2026 08:46:26 +0200
Subject: [PATCH] nir/opt_if: allow undef instructions on ELSE side for
 if-simplification

Totals from 72 (0.04% of 202440) affected shaders: (Navi48)

Instrs: 213900 -> 213873 (-0.01%); split: -0.03%, +0.02%
CodeSize: 1215012 -> 1214924 (-0.01%); split: -0.01%, +0.01%
Latency: 4458993 -> 4458679 (-0.01%)
Copies: 18840 -> 18816 (-0.13%)
Branches: 5044 -> 5043 (-0.02%)
VALU: 116547 -> 116529 (-0.02%)
SALU: 28686 -> 28669 (-0.06%)
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40738>
---
 src/compiler/nir/nir_opt_if.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index d5a6fc12ac7..bab4fb9cfba 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -702,7 +702,8 @@ is_block_empty_or_constant(nir_block *block)
       return false;
 
    nir_foreach_instr(instr, block) {
-      if (instr->type != nir_instr_type_load_const)
+      if (instr->type != nir_instr_type_load_const &&
+          instr->type != nir_instr_type_undef)
          return false;
    }