[llvm] [InstCombine] Generalize ignoreSignBitOfZero/NaN to handle more cases (PR #141015)

[Matt Arsenault via llvm-commits]

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@@ -2803,15 +2830,70 @@ static bool ignoreSignBitOfNaN(Instruction &I) {
   if (!I.hasOneUse())
     return false;
   Instruction *User = I.user_back();
+  if (auto *FPOp = dyn_cast<FPMathOperator>(User)) {
+    if (FPOp->hasNoNaNs())
+      return true;
+  }
 
-  // fcmp ignores the sign bit of NaN.
-  if (User->getOpcode() == Instruction::FCmp)
+  switch (User->getOpcode()) {
+  case Instruction::FPToSI:
+  case Instruction::FPToUI:
     return true;
+  // Proper FP math operations ignore the sign bit of NaN.
+  case Instruction::FAdd:
+  case Instruction::FSub:
+  case Instruction::FMul:
+  case Instruction::FDiv:
+  case Instruction::FRem:
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arsenm wrote:

fdiv and frem cases untested 

https://github.com/llvm/llvm-project/pull/141015