Currently we're initializing the vtable pointers of a class only after

the bases are completely initialized.  This won't work --- base
initializer expressions can rely on the vtables having been set up.
Check for uses of 'this' in the initializers and force a vtable
initialization if found.

This might not be good enough;  we might need to extend this to handle
the possibility of arbitrary code finding an external reference to this
(not yet completely-constructed!) object and accessing through it,
in which case we'll probably find ourselves doing a lot more unnecessary
stores.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@114153 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 30 insertions, 0 deletions

diff --git a/lib/CodeGen/CGClass.cpp b/lib/CodeGen/CGClass.cpp
index a6ac0acfb9..c8f23f3f0c 100644
--- a/lib/CodeGen/CGClass.cpp
+++ b/lib/CodeGen/CGClass.cpp
@@ -14,6 +14,7 @@
 #include "CGDebugInfo.h"
 #include "CodeGenFunction.h"
 #include "clang/AST/CXXInheritance.h"
+#include "clang/AST/EvaluatedExprVisitor.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtCXX.h"
 
@@ -334,6 +335,29 @@ namespace {
       CGF.EmitCXXDestructorCall(D, Dtor_Base, BaseIsVirtual, Addr);
     }
   };
+
+  /// A visitor which checks whether an initializer uses 'this' in a
+  /// way which requires the vtable to be properly set.
+  struct DynamicThisUseChecker : EvaluatedExprVisitor<DynamicThisUseChecker> {
+    typedef EvaluatedExprVisitor<DynamicThisUseChecker> super;
+
+    bool UsesThis;
+
+    DynamicThisUseChecker(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(CXXThisExpr *E) { UsesThis = true; }
+  };
+}
+
+static bool BaseInitializerUsesThis(ASTContext &C, const Expr *Init) {
+  DynamicThisUseChecker Checker(C);
+  Checker.Visit(const_cast<Expr*>(Init));
+  return Checker.UsesThis;
 }
 
 static void EmitBaseInitializer(CodeGenFunction &CGF, 
@@ -355,6 +379,12 @@ static void EmitBaseInitializer(CodeGenFunction &CGF,
   if (CtorType == Ctor_Base && isBaseVirtual)
     return;
 
+  // If the initializer for the base (other than the constructor
+  // itself) accesses 'this' in any way, we need to initialize the
+  // vtables.
+  if (BaseInitializerUsesThis(CGF.getContext(), BaseInit->getInit()))
+    CGF.InitializeVTablePointers(ClassDecl);
+
   // We can pretend to be a complete class because it only matters for
   // virtual bases, and we only do virtual bases for complete ctors.
   llvm::Value *V =