[CodeGen] Fix a warning in DAGTypeLegalizer::PromoteIntRes_EXTRACT_SUBVECTOR

[david-arm]

Summary

Fixes up one warning in this test:

sve-sext-zext.ll

[fpetrogalli]

@david-arm , can you please update the patch adding context?

Thanks!

Francesco

[sdesmalen]

nit: The title and commit message speaks of fixing warnings (in some test), but I think many people who don't follow our developments closely will not know what those 'warnings' relate to. Perhaps you can phrase the title as [CodeGen] Fix wrong use of getVectorNumElements in PromoteIntRes_EXTRACT_SUBVECTOR. Also I think it's worth explaining in the commit message why you're moving this code, e.g. getVectorNumElements is not safe for scalable vectors and should normally use getVectorElementCount instead. But because at this point in the code only fixed-width vectors are used, the use of getVectorNumElements is valid.

LGTM otherwise.

[fpetrogalli]

LGTM! Thank you

llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

 }
 
 
 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);
   SDValue BaseIdx = N->getOperand(1);
 
   // TODO: We may be able to use this for types other than scalable
   // vectors and fix those tests that expect BUILD_VECTOR to be used
   if (OutVT.isScalableVector()) {
if (OutVT.isScalableVector())
     report_fatal_error("Unable to promote scalable types using BUILD_VECTOR");
 
   SDValue InOp0 = N->getOperand(0);
   if (getTypeAction(InOp0.getValueType()) == TargetLowering::TypePromoteInteger)
     InOp0 = GetPromotedInteger(N->getOperand(0));
 
   EVT InVT = InOp0.getValueType();
 
+  unsigned OutNumElems = OutVT.getVectorNumElements();
   SmallVector<SDValue, 8> Ops;
   Ops.reserve(OutNumElems);
   for (unsigned i = 0; i != OutNumElems; ++i) {
 
     // Extract the element from the original vector.
     SDValue Index = DAG.getNode(ISD::ADD, dl, BaseIdx.getValueType(),
       BaseIdx, DAG.getConstant(i, dl, BaseIdx.getValueType()));
     SDValue Ext = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl,