[llvm] [llvm] Fix fabs simplification (PR #152825)

[Oliver Hunt via llvm-commits]

https://github.com/ojhunt updated https://github.com/llvm/llvm-project/pull/152825

>From 4bebc84bfc096e0adbd785a3b0addf0221f1ff3b Mon Sep 17 00:00:00 2001
From: Oliver Hunt <oliver at apple.com>
Date: Fri, 8 Aug 2025 20:58:57 -0700
Subject: [PATCH] [llvm] Fix fabs simplification

The existing code hits the std::optional<bool> is of comparing
to a bool being "correct" for the std::optional and the intended
comparison.

This corrects the comparison while reinforcing the idea that we
need some way to diagnose this.

Fixes #152824
---
 llvm/lib/Analysis/InstructionSimplify.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 5907e21065331..622c67200ac51 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -6304,7 +6304,8 @@ static Value *simplifyUnaryIntrinsic(Function *F, Value *Op0,
   Value *X;
   switch (IID) {
   case Intrinsic::fabs:
-    if (computeKnownFPSignBit(Op0, Q) == false)
+    if (std::optional<bool> KnownSignBit = computeKnownFPSignBit(Op0, Q);
+        !KnownSignBit || *KnownSignBit == false)
       return Op0;
     break;
   case Intrinsic::bswap: