[SLP][REVEC] Make GetMinMaxCost support FixedVectorType when REVEC is

enabled.

Author: HanKuanChen

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -10777,6 +10777,8 @@ BoUpSLP::getEntryCost(const TreeEntry *E, ArrayRef<Value *> VectorizedVals,
     // If the selects are the only uses of the compares, they will be
     // dead and we can adjust the cost by removing their cost.
     if (VI && SelectOnly) {
+      assert((!Ty->isVectorTy() || SLPReVec) &&
+             "Expected only for scalar type.");
       auto *CI = cast<CmpInst>(VI->getOperand(0));
       IntrinsicCost -= TTI->getCmpSelInstrCost(
           CI->getOpcode(), Ty, Builder.getInt1Ty(), CI->getPredicate(),