1 files changed, 30 insertions, 0 deletions
diff --git a/lib/AST/ExprCXX.cpp b/lib/AST/ExprCXX.cpp
index 526c484677..692c2c3760 100644
--- a/lib/AST/ExprCXX.cpp
+++ b/lib/AST/ExprCXX.cpp
@@ -482,6 +482,36 @@ CXXDynamicCastExpr *CXXDynamicCastExpr::CreateEmpty(ASTContext &C,
   return new (Buffer) CXXDynamicCastExpr(EmptyShell(), PathSize);
 }
 
+/// isAlwaysNull - Return whether the result of the dynamic_cast is proven
+/// to always be null. For example:
+///
+/// struct A { };
+/// struct B final : A { };
+/// struct C { };
+///
+/// C *f(B* b) { return dynamic_cast<C*>(b); }
+bool CXXDynamicCastExpr::isAlwaysNull() const
+{
+  QualType SrcType = getSubExpr()->getType();
+  QualType DestType = getType();
+
+  if (const PointerType *SrcPTy = SrcType->getAs<PointerType>()) {
+    SrcType = SrcPTy->getPointeeType();
+    DestType = DestType->castAs<PointerType>()->getPointeeType();
+  }
+
+  const CXXRecordDecl *SrcRD = 
+    cast<CXXRecordDecl>(SrcType->castAs<RecordType>()->getDecl());
+
+  if (!SrcRD->hasAttr<FinalAttr>())
+    return false;
+
+  const CXXRecordDecl *DestRD = 
+    cast<CXXRecordDecl>(DestType->castAs<RecordType>()->getDecl());
+
+  return !DestRD->isDerivedFrom(SrcRD);
+}
+
 CXXReinterpretCastExpr *
 CXXReinterpretCastExpr::Create(ASTContext &C, QualType T, ExprValueKind VK,
                                CastKind K, Expr *Op,