[clang][Interp][NFC] Save IsUnion bit for Records

Now that we call this more often, try to keep pointer chasing to a
minimum.

clang/lib/AST/Interp/Record.cpp

@@ -16,7 +16,7 @@ Record::Record(const RecordDecl *Decl, BaseList &&SrcBases,
                FieldList &&SrcFields, VirtualBaseList &&SrcVirtualBases,
                unsigned VirtualSize, unsigned BaseSize)
     : Decl(Decl), Bases(std::move(SrcBases)), Fields(std::move(SrcFields)),
-      BaseSize(BaseSize), VirtualSize(VirtualSize) {
+      BaseSize(BaseSize), VirtualSize(VirtualSize), IsUnion(Decl->isUnion()) {
   for (Base &V : SrcVirtualBases)
     VirtualBases.push_back({ V.Decl, V.Offset + BaseSize, V.Desc, V.R });
 

clang/lib/AST/Interp/Record.h

@@ -53,7 +53,7 @@ class Record final {
   /// Returns the name of the underlying declaration.
   const std::string getName() const;
   /// Checks if the record is a union.
-  bool isUnion() const { return getDecl()->isUnion(); }
+  bool isUnion() const { return IsUnion; }
   /// Returns the size of the record.
   unsigned getSize() const { return BaseSize; }
   /// Returns the full size of the record, including records.
@@ -132,6 +132,8 @@ class Record final {
   unsigned BaseSize;
   /// Size of all virtual bases.
   unsigned VirtualSize;
+  /// If this record is a union.
+  bool IsUnion;
 };
 
 } // namespace interp