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

[Vlad Serebrennikov 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);
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Endilll wrote:

I don't want to introduce even more VLA extensions in C++ mode (this builtin is exposed only in C++ mode). This began with https://github.com/llvm/llvm-project/pull/88473#discussion_r1562040787

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