From 8df9e2438bee1289183b7cbf76b521d4c66237d3 Mon Sep 17 00:00:00 2001
From: Fariborz Jahanian <fjahanian@apple.com>
Date: Thu, 12 Jun 2014 20:57:14 +0000
Subject: 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 | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

(limited to 'clang/lib/Sema')

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index fc87b231d64..9f7a8bf7b38 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -7286,10 +7286,12 @@ namespace {
   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 @@ namespace {
       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 @@ static Expr *findCapturingExpr(Sema &S, Expr *e, RetainCycleOwner &owner) {
 
   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,
-- 
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