commit 8df9e2438bee1289183b7cbf76b521d4c66237d3
author Fariborz Jahanian <fjahanian@apple.com> Thu Jun 12 20:57:14 2014 +0000
committer Fariborz Jahanian <fjahanian@apple.com> Thu Jun 12 20:57:14 2014 +0000
tree 26411864f3ae3fcede78432a0d4b2c85b53926ea
parent d104c31fc0b62dca30debb8a4647aea44eb79ec9

Objective-C ARC. Blocks that strongly capture themselves
to call themselves will get the warning:
"Capturing <itself> strongly in this block is likely to
lead to a retain cycle". Cut down on the amount of noise
by noticing that user at some point sets the captured variable
to null in order to release it (and break the cycle). 
// rdar://16944538

llvm-svn: 210823

clang/lib/Sema/SemaChecking.cpp

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index fc87b23..9f7a8bf 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -7286,10 +7286,12 @@
   struct FindCaptureVisitor : EvaluatedExprVisitor<FindCaptureVisitor> {
     FindCaptureVisitor(ASTContext &Context, VarDecl *variable)
       : EvaluatedExprVisitor<FindCaptureVisitor>(Context),
-        Variable(variable), Capturer(nullptr) {}
-
+        Context(Context), Variable(variable), Capturer(nullptr),
+        VarWillBeReased(false) {}
+    ASTContext &Context;
     VarDecl *Variable;
     Expr *Capturer;
+    bool VarWillBeReased;
 
     void VisitDeclRefExpr(DeclRefExpr *ref) {
       if (ref->getDecl() == Variable && !Capturer)
@@ -7314,6 +7316,21 @@
       if (OVE->getSourceExpr())
         Visit(OVE->getSourceExpr());
     }
+    void VisitBinaryOperator(BinaryOperator *BinOp) {
+      if (!Variable || VarWillBeReased || BinOp->getOpcode() != BO_Assign)
+        return;
+      Expr *LHS = BinOp->getLHS();
+      if (const DeclRefExpr *DRE = dyn_cast_or_null<DeclRefExpr>(LHS)) {
+        if (DRE->getDecl() != Variable)
+          return;
+        if (Expr *RHS = BinOp->getRHS()) {
+          RHS = RHS->IgnoreParenCasts();
+          llvm::APSInt Value;
+          VarWillBeReased =
+            (RHS && RHS->isIntegerConstantExpr(Value, Context) && Value == 0);
+        }
+      }
+    }
   };
 }
 
@@ -7351,7 +7368,7 @@
 
   FindCaptureVisitor visitor(S.Context, owner.Variable);
   visitor.Visit(block->getBlockDecl()->getBody());
-  return visitor.Capturer;
+  return visitor.VarWillBeReased ? nullptr : visitor.Capturer;
 }
 
 static void diagnoseRetainCycle(Sema &S, Expr *capturer,