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


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168740 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 19 insertions, 7 deletions

diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp
index 7ed3942332..5b7fb4656d 100644
--- a/lib/Sema/SemaInit.cpp
+++ b/lib/Sema/SemaInit.cpp
@@ -3846,14 +3846,15 @@ enum InvalidICRKind { IIK_okay, IIK_nonlocal, IIK_nonscalar };
 
 /// Determines whether this expression is an acceptable ICR source.
 static InvalidICRKind isInvalidICRSource(ASTContext &C, Expr *e,
-                                         bool isAddressOf) {
+                                         bool isAddressOf, bool &isWeakAccess) {
   // Skip parens.
   e = e->IgnoreParens();
 
   // Skip address-of nodes.
   if (UnaryOperator *op = dyn_cast<UnaryOperator>(e)) {
     if (op->getOpcode() == UO_AddrOf)
-      return isInvalidICRSource(C, op->getSubExpr(), /*addressof*/ true);
+      return isInvalidICRSource(C, op->getSubExpr(), /*addressof*/ true,
+                                isWeakAccess);
 
   // Skip certain casts.
   } else if (CastExpr *ce = dyn_cast<CastExpr>(e)) {
@@ -3862,7 +3863,7 @@ static InvalidICRKind isInvalidICRSource(ASTContext &C, Expr *e,
     case CK_BitCast:
     case CK_LValueBitCast:
     case CK_NoOp:
-      return isInvalidICRSource(C, ce->getSubExpr(), isAddressOf);
+      return isInvalidICRSource(C, ce->getSubExpr(), isAddressOf, isWeakAccess);
 
     case CK_ArrayToPointerDecay:
       return IIK_nonscalar;
@@ -3876,6 +3877,11 @@ static InvalidICRKind isInvalidICRSource(ASTContext &C, Expr *e,
 
   // If we have a declaration reference, it had better be a local variable.
   } else if (isa<DeclRefExpr>(e)) {
+    // set isWeakAccess to true, to mean that there will be an implicit 
+    // load which requires a cleanup.
+    if (e->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
+      isWeakAccess = true;
+    
     if (!isAddressOf) return IIK_nonlocal;
 
     VarDecl *var = dyn_cast<VarDecl>(cast<DeclRefExpr>(e)->getDecl());
@@ -3885,10 +3891,11 @@ static InvalidICRKind isInvalidICRSource(ASTContext &C, Expr *e,
 
   // If we have a conditional operator, check both sides.
   } else if (ConditionalOperator *cond = dyn_cast<ConditionalOperator>(e)) {
-    if (InvalidICRKind iik = isInvalidICRSource(C, cond->getLHS(), isAddressOf))
+    if (InvalidICRKind iik = isInvalidICRSource(C, cond->getLHS(), isAddressOf,
+                                                isWeakAccess))
       return iik;
 
-    return isInvalidICRSource(C, cond->getRHS(), isAddressOf);
+    return isInvalidICRSource(C, cond->getRHS(), isAddressOf, isWeakAccess);
 
   // These are never scalar.
   } else if (isa<ArraySubscriptExpr>(e)) {
@@ -3907,8 +3914,13 @@ static InvalidICRKind isInvalidICRSource(ASTContext &C, Expr *e,
 /// indirect copy/restore.
 static void checkIndirectCopyRestoreSource(Sema &S, Expr *src) {
   assert(src->isRValue());
-
-  InvalidICRKind iik = isInvalidICRSource(S.Context, src, false);
+  bool isWeakAccess = false;
+  InvalidICRKind iik = isInvalidICRSource(S.Context, src, false, isWeakAccess);
+  // If isWeakAccess to true, there will be an implicit 
+  // load which requires a cleanup.
+  if (S.getLangOpts().ObjCAutoRefCount && isWeakAccess)
+    S.ExprNeedsCleanups = true;
+  
   if (iik == IIK_okay) return;
 
   S.Diag(src->getExprLoc(), diag::err_arc_nonlocal_writeback)