[LegalizeVectorTypes] When widening don't check for libcalls if promoted (#111297)

When widening some FP ops, LegalizeVectorTypes will check to see if the
widened op may be scalarized and then turned into a bunch of libcalls,
and if so unroll early to avoid unnecessary libcalls of the padded undef
elements.

It checks if the widened op is legal or custom to see if it will be
scalarized, but promoted ops will also avoid scalarization.

This relaxes the check to account for this which fixes some illegal
vector types on RISC-V from being scalarized when they could be widened.

Author: lukel97

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

@@ -4441,7 +4441,7 @@ void DAGTypeLegalizer::WidenVectorResult(SDNode *N, unsigned ResNo) {
     // libcalls on the undef elements.
     EVT VT = N->getValueType(0);
     EVT WideVecVT = TLI.getTypeToTransformTo(*DAG.getContext(), VT);
-    if (!TLI.isOperationLegalOrCustom(N->getOpcode(), WideVecVT) &&
+    if (!TLI.isOperationLegalOrCustomOrPromote(N->getOpcode(), WideVecVT) &&
         TLI.isOperationExpand(N->getOpcode(), VT.getScalarType())) {
       Res = DAG.UnrollVectorOp(N, WideVecVT.getVectorNumElements());
       return true;