[CodeGen] Fix wrong use of getVectorNumElements in PromoteIntRes_EXTR…

…ACT_SUBVECTOR

Calling getVectorNumElements() is not safe for scalable vectors and we
should normally use getVectorElementCount() instead. However, for the
code changed in this patch I decided to simply move the instantiation of
the variable 'OutNumElems' lower down to the place where only fixed-width
vectors are used, and hence it is safe to call getVectorNumElements().

Fixes up one warning in this test:

  sve-sext-zext.ll

Differential Revision: https://reviews.llvm.org/D83195

llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

@@ -4334,7 +4334,6 @@ SDValue DAGTypeLegalizer::PromoteIntRes_EXTRACT_SUBVECTOR(SDNode *N) {
   EVT OutVT = N->getValueType(0);
   EVT NOutVT = TLI.getTypeToTransformTo(*DAG.getContext(), OutVT);
   assert(NOutVT.isVector() && "This type must be promoted to a vector type");
-  unsigned OutNumElems = OutVT.getVectorNumElements();
   EVT NOutVTElem = NOutVT.getVectorElementType();
 
   SDLoc dl(N);
@@ -4371,6 +4370,7 @@ SDValue DAGTypeLegalizer::PromoteIntRes_EXTRACT_SUBVECTOR(SDNode *N) {
 
   EVT InVT = InOp0.getValueType();
 
+  unsigned OutNumElems = OutVT.getVectorNumElements();
   SmallVector<SDValue, 8> Ops;
   Ops.reserve(OutNumElems);
   for (unsigned i = 0; i != OutNumElems; ++i) {