UBSan: Fix alignment checks emitted in downcasts.

Summary:
UBSan was checking for alignment of the derived class on the pointer to
the base class, before converting. With some class hierarchies, this could
generate false positives.

Added test-case.

llvm-svn: 187948

1 files changed, 6 insertions, 6 deletions

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 73824afc17e..0e87d8311c1 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -2764,18 +2764,18 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) {
 
     LValue LV = EmitLValue(E->getSubExpr());
 
-    // C++11 [expr.static.cast]p2: Behavior is undefined if a downcast is
-    // performed and the object is not of the derived type.
-    if (SanitizePerformTypeCheck)
-      EmitTypeCheck(TCK_DowncastReference, E->getExprLoc(),
-                    LV.getAddress(), E->getType());
-
     // Perform the base-to-derived conversion
     llvm::Value *Derived =
       GetAddressOfDerivedClass(LV.getAddress(), DerivedClassDecl,
                                E->path_begin(), E->path_end(),
                                /*NullCheckValue=*/false);
 
+    // C++11 [expr.static.cast]p2: Behavior is undefined if a downcast is
+    // performed and the object is not of the derived type.
+    if (SanitizePerformTypeCheck)
+      EmitTypeCheck(TCK_DowncastReference, E->getExprLoc(),
+                    Derived, E->getType());
+
     return MakeAddrLValue(Derived, E->getType());
   }
   case CK_LValueBitCast: {