[SLP][REVEC] Fix false assumption of the source for castToScalarTyElem.

The argument V may come from adjustExtracts, which is the vector operand
of ExtractElementInst. In addition, it is not existed in getTreeEntry.

The vector operand of ExtractElementInst may have a type of <1 x Ty>,
ensuring that the number of elements in ScalarTy and VecTy are equal.

reference: #99411

Author: HanKuanChen

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -11850,8 +11850,7 @@ class BoUpSLP::ShuffleInstructionBuilder final : public BaseShuffleAnalysis {
   Value *castToScalarTyElem(Value *V,
                             std::optional<bool> IsSigned = std::nullopt) {
     auto *VecTy = cast<VectorType>(V->getType());
-    assert(getNumElements(ScalarTy) < getNumElements(VecTy) &&
-           (getNumElements(VecTy) % getNumElements(ScalarTy) == 0));
+    assert(getNumElements(VecTy) % getNumElements(ScalarTy) == 0);
     if (VecTy->getElementType() == ScalarTy->getScalarType())
       return V;
     return Builder.CreateIntCast(

llvm/test/Transforms/SLPVectorizer/revec-fix-99411.ll

@@ -2,6 +2,11 @@
 ; RUN: opt -mtriple x86_64-unknown-linux-gnu -passes=slp-vectorizer -S %s | FileCheck %s
 
 define void @e() {
+; CHECK-LABEL: @e(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    store <2 x i64> zeroinitializer, ptr null, align 8
+; CHECK-NEXT:    ret void
+;
 entry:
   %0 = extractelement <1 x i64> zeroinitializer, i64 0
   %bf.value = and i64 %0, 0