GlobalISel: Drop original type pointeriness in minScalarSameAs

[arsenm]

Summary

It is not useful to report WidenScalar for a pointer value, so always
report a scalar value in the target size. This allows using this to
clamp the scalar operand to the pointer size in operations like
G_PTR_ADD or G_PTRMASK.

[aemerson]

LGTM.

[arsenm]

8e62ffdef1c8e50cc0f108b1d67a37bcb6089279

llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h

public:
   LegalizeRuleSet &minScalarSameAs(unsigned TypeIdx, unsigned LargeTypeIdx) {
     typeIdx(TypeIdx);
     return widenScalarIf(
         [=](const LegalityQuery &Query) {
           return Query.Types[LargeTypeIdx].getScalarSizeInBits() >
                  Query.Types[TypeIdx].getSizeInBits();
         },
         [=](const LegalityQuery &Query) {
-          LLT T = Query.Types[LargeTypeIdx];
-          return std::make_pair(TypeIdx,
-                                T.isVector() ? T.getElementType() : T);
+          const LLT Ty = Query.Types[TypeIdx];
+          const LLT LargeTy = Query.Types[LargeTypeIdx];
+          LLT NewEltTy = LLT::scalar(LargeTy.getScalarSizeInBits());
+          return std::make_pair(TypeIdx, Ty.changeElementType(NewEltTy));
         });
   }
 
   /// Conditionally widen the scalar or elt to match the size of another.
   LegalizeRuleSet &minScalarEltSameAsIf(LegalityPredicate Predicate,
                                    unsigned TypeIdx, unsigned LargeTypeIdx) {
     typeIdx(TypeIdx);
     return widenScalarIf(