[SLPVectorizer] Fix divide-by-zero after D99719

Will add a test case later.

(cherry-picked from 8e5f3d0)

Author: MaskRay

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -3426,7 +3426,8 @@ computeExtractCost(ArrayRef<Value *> VL, FixedVectorType *VecTy,
                    TargetTransformInfo &TTI) {
   unsigned NumOfParts = TTI.getNumberOfParts(VecTy);
 
-  if (ShuffleKind != TargetTransformInfo::SK_PermuteSingleSrc || !NumOfParts)
+  if (ShuffleKind != TargetTransformInfo::SK_PermuteSingleSrc || !NumOfParts ||
+      VecTy->getNumElements() < NumOfParts)
     return TTI.getShuffleCost(ShuffleKind, VecTy);
 
   bool AllConsecutive = true;