[llvm] Remove `UnsafeFPMath` usage in `visitFSUBForFMACombine` (PR #145637)

[via llvm-commits]

https://github.com/paperchalice created https://github.com/llvm/llvm-project/pull/145637

None

>From a3d17618f65bbd62f3b1649121f5949b44e1af69 Mon Sep 17 00:00:00 2001
From: PaperChalice <liujunchang97 at outlook.com>
Date: Wed, 25 Jun 2025 13:41:07 +0800
Subject: [PATCH] Remove `UnsafeFPMath` usage in `visitFSUBForFMACombine`

---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 91f696e8fe88e..6b8baea404c2d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17010,8 +17010,7 @@ SDValue DAGCombiner::visitFSUBForFMACombine(SDNode *N) {
     return SDValue();
 
   const SDNodeFlags Flags = N->getFlags();
-  bool AllowFusionGlobally = (Options.AllowFPOpFusion == FPOpFusion::Fast ||
-                              Options.UnsafeFPMath || HasFMAD);
+  bool AllowFusionGlobally = (Options.AllowFPOpFusion == FPOpFusion::Fast || HasFMAD);
 
   // If the subtraction is not contractable, do not combine.
   if (!AllowFusionGlobally && !N->getFlags().hasAllowContract())
@@ -17167,7 +17166,7 @@ SDValue DAGCombiner::visitFSUBForFMACombine(SDNode *N) {
   }
 
   auto isReassociable = [&Options](SDNode *N) {
-    return Options.UnsafeFPMath || N->getFlags().hasAllowReassociation();
+    return N->getFlags().hasAllowReassociation();
   };
 
   auto isContractableAndReassociableFMUL = [&isContractableFMUL,
@@ -17181,7 +17180,7 @@ SDValue DAGCombiner::visitFSUBForFMACombine(SDNode *N) {
 
   // More folding opportunities when target permits.
   if (Aggressive && isReassociable(N)) {
-    bool CanFuse = Options.UnsafeFPMath || N->getFlags().hasAllowContract();
+    bool CanFuse = N->getFlags().hasAllowContract();
     // fold (fsub (fma x, y, (fmul u, v)), z)
     //   -> (fma x, y (fma u, v, (fneg z)))
     if (CanFuse && isFusedOp(N0) &&