Reuse getBinOpIdentity in createAnyOfTargetReduction [nfc]

Consolidating code so that we have one copy instead of multiple reasoning
about identity element.  Note that we're (deliberately) not passing
the FMF flags to common utility to preserve behavior in this change.

Author: preames

llvm/lib/Transforms/Utils/LoopUtils.cpp

@@ -1210,6 +1210,11 @@ Value *llvm::createAnyOfTargetReduction(IRBuilderBase &Builder, Value *Src,
 Value *llvm::createSimpleTargetReduction(IRBuilderBase &Builder, Value *Src,
                                          RecurKind RdxKind) {
   auto *SrcVecEltTy = cast<VectorType>(Src->getType())->getElementType();
+  auto getIdentity = [&]() {
+    Intrinsic::ID ID = getReductionIntrinsicID(RdxKind);
+    unsigned Opc = getArithmeticReductionInstruction(ID);
+    return ConstantExpr::getBinOpIdentity(Opc, SrcVecEltTy);
+  };
   switch (RdxKind) {
   case RecurKind::Add:
   case RecurKind::Mul:
@@ -1227,10 +1232,9 @@ Value *llvm::createSimpleTargetReduction(IRBuilderBase &Builder, Value *Src,
     return Builder.CreateUnaryIntrinsic(getReductionIntrinsicID(RdxKind), Src);
   case RecurKind::FMulAdd:
   case RecurKind::FAdd:
-    return Builder.CreateFAddReduce(ConstantFP::getNegativeZero(SrcVecEltTy),
-                                    Src);
+    return Builder.CreateFAddReduce(getIdentity(), Src);
   case RecurKind::FMul:
-    return Builder.CreateFMulReduce(ConstantFP::get(SrcVecEltTy, 1.0), Src);
+    return Builder.CreateFMulReduce(getIdentity(), Src);
   default:
     llvm_unreachable("Unhandled opcode");
   }