[clang] [CIR] Add support for initializing classes with multiple vtables (PR #155275)

[Erich Keane via cfe-commits]

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@@ -126,6 +127,32 @@ static bool isInitializerOfDynamicClass(const CXXCtorInitializer *baseInit) {
   return baseClassDecl->isDynamicClass();
 }
 
+namespace {
+/// A visitor which checks whether an initializer uses 'this' in a
+/// way which requires the vtable to be properly set.
+struct DynamicThisUseChecker
+    : ConstEvaluatedExprVisitor<DynamicThisUseChecker> {
+  using super = ConstEvaluatedExprVisitor<DynamicThisUseChecker>;
+
+  bool usesThis;
+
+  DynamicThisUseChecker(const ASTContext &c) : super(c), usesThis(false) {}
+
+  // Black-list all explicit and implicit references to 'this'.
+  //
+  // Do we need to worry about external references to 'this' derived
+  // from arbitrary code?  If so, then anything which runs arbitrary
+  // external code might potentially access the vtable.
+  void VisitCXXThisExpr(const CXXThisExpr *e) { usesThis = true; }
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erichkeane wrote:

This is strange and seems insufficient... but I see it is from classic codegen, so *shrug* guess this is good enough.

https://github.com/llvm/llvm-project/pull/155275