[llvm] [ExpandReductions] Add support for non-pow2 vector counts (PR #208738)

[Matt Arsenault via llvm-commits]

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@@ -112,11 +127,18 @@ bool expandReductions(Function &F, const TargetTransformInfo *TTI,
       Value *Vec = II->getArgOperand(0);
       auto *FTy = cast<FixedVectorType>(Vec->getType());
       unsigned NumElts = FTy->getNumElements();
-      if (!isPowerOf2_32(NumElts))
-        continue;
 
       if (FTy->getElementType() == Builder.getInt1Ty()) {
-        Rdx = Builder.CreateBitCast(Vec, Builder.getIntNTy(NumElts));
+        unsigned Width = PowerOf2Ceil(NumElts);
+        if (Width != NumElts) {
+          Constant *Identity = ID == Intrinsic::vector_reduce_and
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arsenm wrote:

We should have a more proper method to get the identity value for a given operation. Doesn't that exist already? 

https://github.com/llvm/llvm-project/pull/208738