[llvm] [InstCombine] InstCombine should fold frexp of select to select of frexp (PR #121227)

[Matt Arsenault via llvm-commits]

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@@ -4043,6 +4043,52 @@ InstCombinerImpl::foldExtractOfOverflowIntrinsic(ExtractValueInst &EV) {
   return nullptr;
 }
 
+static Value *foldFrexpOfSelect(ExtractValueInst &EV, CallInst *FrexpCall,
+                                SelectInst *SelectInst,
+                                InstCombiner::BuilderTy &Builder) {
+  // Helper to fold frexp of select to select of frexp.
+  Value *Cond = SelectInst->getCondition();
+  Value *TrueVal = SelectInst->getTrueValue();
+  Value *FalseVal = SelectInst->getFalseValue();
+  ConstantFP *ConstOp = nullptr;
+  Value *VarOp = nullptr;
+  bool ConstIsTrue = false;
+
+  if (auto *TrueConst = dyn_cast<ConstantFP>(TrueVal)) {
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arsenm wrote:

This won't handle the vector case. It's recommended to use m_APFloat to handle the scalar or vector case 

https://github.com/llvm/llvm-project/pull/121227