[llvm] Fixes [AArch64] Assertion `EltCnt.isKnownEven() && "Cannot halve vector with odd number of elements."' failed. (PR #166528)

[Benjamin Maxwell via llvm-commits]

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@@ -1333,6 +1333,11 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
           TargetLowering::TypeSplitVector;
       if ((SplitSrc || SplitDst) && SrcVTy->getElementCount().isVector() &&
           DstVTy->getElementCount().isVector()) {
+        auto SrcEltCnt = SrcVTy->getElementCount();
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MacDue wrote:

You should just change the `SrcVTy->getElementCount().isVector()` and `DstVTy->getElementCount().isVector()` checks above  this to use `.isKnownEven()` rather than `.isVector()`.

https://github.com/llvm/llvm-project/pull/166528