[llvm] [SelectionDAG] Remove UnsafeFPMath check in `visitFADDForFMACombine` (PR #127770)

[James Y Knight via llvm-commits]

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@@ -17855,11 +17856,17 @@ template <class MatchContextClass> SDValue DAGCombiner::visitFMA(SDNode *N) {
   }
 
   // FIXME: use fast math flags instead of Options.UnsafeFPMath
-  if (Options.UnsafeFPMath) {
-    if (N0CFP && N0CFP->isZero())
-      return N2;
-    if (N1CFP && N1CFP->isZero())
-      return N2;
+  // TODO: Finally migrate away from global TargetOptions.
+  if (Options.AllowFPOpFusion == FPOpFusion::Fast ||
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jyknight wrote:

I believe the "Options.AllowFPOpFusion == FPOpFusion::Fast" part of the condition is incorrect: -fp-contract=fast means you can translate mul/add to fma globally. It does _not_ mean you can ignore NaNs. Furthermore, no tests fail if I remove this part of the OR.

https://github.com/llvm/llvm-project/pull/127770