-Warc-retain-cycles: look through [^{...} copy] and Block_copy(^{...})

Retain cycles happen in the case where a block is persisted past its
life on the stack, and the way that occurs is by copying the block.
We should thus look through any explicit copies we see.

Note that Block_copy is actually a type-safe wrapper for _Block_copy,
which does all the real work.

<rdar://problem/12219663>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164039 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Sema/SemaChecking.cpp

@@ -5429,6 +5429,24 @@ static Expr *findCapturingExpr(Sema &S, Expr *e, RetainCycleOwner &owner) {
   assert(owner.Variable && owner.Loc.isValid());
 
   e = e->IgnoreParenCasts();
+
+  // Look through [^{...} copy] and Block_copy(^{...}).
+  if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(e)) {
+    Selector Cmd = ME->getSelector();
+    if (Cmd.isUnarySelector() && Cmd.getNameForSlot(0) == "copy") {
+      e = ME->getInstanceReceiver();
+      if (!e)
+        return 0;
+      e = e->IgnoreParenCasts();
+    }
+  } else if (CallExpr *CE = dyn_cast<CallExpr>(e)) {
+    if (CE->getNumArgs() == 1) {
+      FunctionDecl *Fn = dyn_cast_or_null<FunctionDecl>(CE->getCalleeDecl());
+      if (Fn && Fn->getIdentifier()->isStr("_Block_copy"))
+        e = CE->getArg(0)->IgnoreParenCasts();
+    }
+  }
+  
   BlockExpr *block = dyn_cast<BlockExpr>(e);
   if (!block || !block->getBlockDecl()->capturesVariable(owner.Variable))
     return 0;

test/SemaObjC/warn-retain-cycle.m

@@ -1,5 +1,7 @@
 // RUN: %clang_cc1 -fsyntax-only -fobjc-runtime-has-weak -fobjc-arc -fblocks -verify -Wno-objc-root-class %s
 
+void *_Block_copy(const void *block);
+
 @interface Test0
 - (void) setBlock: (void(^)(void)) block;
 - (void) addBlock: (void(^)(void)) block;
@@ -153,3 +155,32 @@ void testBlockVariable() {
   };
 }
 
+
+@interface NSObject
+- (id)copy;
+
+- (void (^)(void))someRandomMethodReturningABlock;
+@end
+
+
+void testCopying(Test0 *obj) {
+  typedef void (^block_t)(void);
+
+  [obj setBlock:[^{ // expected-note{{block will be retained by the captured object}}
+    [obj actNow]; // expected-warning{{capturing 'obj' strongly in this block is likely to lead to a retain cycle}}
+  } copy]];
+
+  [obj addBlock:(__bridge_transfer block_t)_Block_copy((__bridge void *)^{ // expected-note{{block will be retained by the captured object}}
+    [obj actNow]; // expected-warning{{capturing 'obj' strongly in this block is likely to lead to a retain cycle}}
+  })];
+  
+  [obj addBlock:[^{
+    [obj actNow]; // no-warning
+  } someRandomMethodReturningABlock]];
+  
+  extern block_t someRandomFunctionReturningABlock(block_t);
+  [obj setBlock:someRandomFunctionReturningABlock(^{
+    [obj actNow]; // no-warning
+  })];
+}
+