objective-C arc: load of a __weak object happens via call to

objc_loadWeak. This retains and autorelease the weakly-refereced
object. This hidden autorelease sometimes makes __weak variable alive even
after the weak reference is erased, because the object is still referenced
by an autorelease pool. This patch overcomes this behavior by loading a 
weak object via call to objc_loadWeakRetained(), followng it by objc_release
at appropriate place, thereby removing the hidden autorelease. // rdar://10849570

llvm-svn: 168740

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 840f04f0da8..66beb34128e 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -504,6 +504,12 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
     T = T.getUnqualifiedType();
 
   UpdateMarkingForLValueToRValue(E);
+  
+  // Loading a __weak object implicitly retains the value, so we need a cleanup to 
+  // balance that.
+  if (getLangOpts().ObjCAutoRefCount &&
+      E->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
+    ExprNeedsCleanups = true;
 
   ExprResult Res = Owned(ImplicitCastExpr::Create(Context, T, CK_LValueToRValue,
                                                   E, 0, VK_RValue));