[clang] [clang] Implement `__is_virtual_base_of()` intrinsic (PR #100393)

[Aaron Ballman via cfe-commits]

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@@ -6027,6 +6027,33 @@ static bool EvaluateBinaryTypeTrait(Sema &Self, TypeTrait BTT, const TypeSourceI
     return cast<CXXRecordDecl>(rhsRecord->getDecl())
       ->isDerivedFrom(cast<CXXRecordDecl>(lhsRecord->getDecl()));
   }
+  case BTT_IsVirtualBaseOf: {
+    const RecordType *BaseRecord = LhsT->getAs<RecordType>();
+    const RecordType *DerivedRecord = RhsT->getAs<RecordType>();
+
+    if (!BaseRecord || !DerivedRecord) {
+      DiagnoseVLAInCXXTypeTrait(Self, Lhs, tok::kw___is_virtual_base_of);
+      DiagnoseVLAInCXXTypeTrait(Self, Rhs, tok::kw___is_virtual_base_of);
+      return false;
+    }
+
+    if (BaseRecord->isUnionType() || DerivedRecord->isUnionType())
+      return false;
+
+    if (!BaseRecord->isStructureOrClassType() ||
+        !DerivedRecord->isStructureOrClassType())
+      return false;
+
+    if (Self.RequireCompleteType(Rhs->getTypeLoc().getBeginLoc(), RhsT,
+                                 diag::err_incomplete_type))
+      return false;
+
+    if (Self.Context.hasSameUnqualifiedType(LhsT, RhsT))
+      return false;
----------------
AaronBallman wrote:

I think this actually does *more* work instead of less; most code will not pass in the same type as both arguments, right? So that means this check won't catch anything useful most of the time, but the below check still will catch this case (I believe).

https://github.com/llvm/llvm-project/pull/100393