[llvm] [KnownFPClass] Correct denormal mode handling for `KnownFPClass::minMaxLike` (PR #220148)

[Matt Arsenault via llvm-commits]

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@@ -2258,6 +2258,13 @@ simplifyDemandedFPClassMinMax(KnownFPClass &Known, Intrinsic::ID IID,
                               KnownFPClass KnownLHS, KnownFPClass KnownRHS,
                               const Function &F, bool NSZ) {
   bool OrderedZeroSign = !NSZ;
+  Type *EltTy = CI->getType()->getScalarType();
+  DenormalMode Mode = F.getDenormalMode(EltTy->getFltSemantics());
+  // Prevent folding of the operand if a subnormal output/input could flush to
+  // zero.
+  bool CanReturnOperand =
+      Mode == DenormalMode::getIEEE() ||
+      (KnownLHS.isKnownNeverSubnormal() && KnownRHS.isKnownNeverSubnormal());
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arsenm wrote:

This doesn't feel like the right way to express this. "CanReturnOperand" is too mechanics focused, and not a logic/value adjustment to the existing checks 

https://github.com/llvm/llvm-project/pull/220148