4 files changed, 12 insertions, 16 deletions
diff --git a/clang/include/clang/AST/Expr.h b/clang/include/clang/AST/Expr.h
index 77684eee00c..7a9cfaeebe4 100644
--- a/clang/include/clang/AST/Expr.h
+++ b/clang/include/clang/AST/Expr.h
@@ -665,12 +665,14 @@ public:
 
   static bool hasAnyTypeDependentArguments(llvm::ArrayRef<Expr *> Exprs);
 
-  /// \brief If we have class type (or pointer to class type), return the
-  /// class decl. Return NULL otherwise.
+  /// \brief For an expression of class type or pointer to class type,
+  /// return the most derived class decl the expression is known to refer to.
   ///
   /// If this expression is a cast, this method looks through it to find the
-  /// most derived decl that can be infered from the expression.
-  const CXXRecordDecl *getMostDerivedClassDeclForType() const;
+  /// most derived decl that can be inferred from the expression.
+  /// This is valid because derived-to-base conversions have undefined
+  /// behavior if the object isn't dynamically of the derived type.
+  const CXXRecordDecl *getBestDynamicClassType() const;
 
   static bool classof(const Stmt *T) {
     return T->getStmtClass() >= firstExprConstant &&
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 22d15be6a87..15cf6602b71 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -33,7 +33,7 @@
 #include <cstring>
 using namespace clang;
 
-const CXXRecordDecl *Expr::getMostDerivedClassDeclForType() const {
+const CXXRecordDecl *Expr::getBestDynamicClassType() const {
   const Expr *E = this;
 
   while (true) {
@@ -51,15 +51,10 @@ const CXXRecordDecl *Expr::getMostDerivedClassDeclForType() const {
   }
 
   QualType DerivedType = E->getType();
-  if (DerivedType->isDependentType())
-    return NULL;
   if (const PointerType *PTy = DerivedType->getAs<PointerType>())
     DerivedType = PTy->getPointeeType();
 
   const RecordType *Ty = DerivedType->castAs<RecordType>();
-  if (!Ty)
-    return NULL;
-
   Decl *D = Ty->getDecl();
   return cast<CXXRecordDecl>(D);
 }
diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index 372eb5407c9..30324b97ef1 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -102,8 +102,7 @@ static bool canDevirtualizeMemberFunctionCalls(ASTContext &Context,
   //   b->f();
   // }
   //
-  const CXXRecordDecl *MostDerivedClassDecl =
-    Base->getMostDerivedClassDeclForType();
+  const CXXRecordDecl *MostDerivedClassDecl = Base->getBestDynamicClassType();
   if (MostDerivedClassDecl->hasAttr<FinalAttr>())
     return true;
 
@@ -228,8 +227,7 @@ RValue CodeGenFunction::EmitCXXMemberCallExpr(const CXXMemberCallExpr *CE,
   bool UseVirtualCall = MD->isVirtual() && !ME->hasQualifier()
                         && !canDevirtualizeMemberFunctionCalls(getContext(),
                                                                Base, MD);
-  const CXXRecordDecl *MostDerivedClassDecl =
-    Base->getMostDerivedClassDeclForType();
+  const CXXRecordDecl *MostDerivedClassDecl = Base->getBestDynamicClassType();
 
   llvm::Value *Callee;
   if (const CXXDestructorDecl *Dtor = dyn_cast<CXXDestructorDecl>(MD)) {
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index bc77e6fae7e..2a7a8b9f195 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -10854,8 +10854,9 @@ static void MarkExprReferenced(Sema &SemaRef, SourceLocation Loc,
   if (!MD)
     return;
   const Expr *Base = ME->getBase();
-  const CXXRecordDecl *MostDerivedClassDecl
-    = Base->getMostDerivedClassDeclForType();
+  if (Base->getType()->isDependentType())
+    return;
+  const CXXRecordDecl *MostDerivedClassDecl = Base->getBestDynamicClassType();
   if (!MostDerivedClassDecl)
     return;
   CXXMethodDecl *DM = MD->getCorrespondingMethodInClass(MostDerivedClassDecl);