Commit 86ced617 authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r295150:

r295150 | ahatanak | 2017-02-14 21:15:28 -0800 (Tue, 14 Feb 2017) | 13 lines

[Sema] Disallow returning a __block variable via a move.

r274291 made changes to prefer calling a move constructor to calling a
copy constructor when returning from a function. This caused programs to
crash when a __block variable in the heap was moved out and used later.

This commit fixes the bug by disallowing moving out of __block variables


Differential Revision:


git-svn-id: 91177308-0d34-0410-b5e6-96231b3b80d8
parent 155bc5fa
......@@ -2743,15 +2743,17 @@ bool Sema::isCopyElisionCandidate(QualType ReturnType, const VarDecl *VD,
// ...automatic...
if (!VD->hasLocalStorage()) return false;
// Return false if VD is a __block variable. We don't want to implicitly move
// out of a __block variable during a return because we cannot assume the
// variable will no longer be used.
if (VD->hasAttr<BlocksAttr>()) return false;
if (AllowParamOrMoveConstructible)
return true;
// ...non-volatile...
if (VD->getType().isVolatileQualified()) return false;
// __block variables can't be allocated in a way that permits NRVO.
if (VD->hasAttr<BlocksAttr>()) return false;
// Variables with higher required alignment than their type's ABI
// alignment cannot use NRVO.
if (!VD->getType()->isDependentType() && VD->hasAttr<AlignedAttr>() &&
// RUN: %clang_cc1 -fsyntax-only -verify -fblocks -Wno-objc-root-class %s
// RUN: %clang_cc1 -fsyntax-only -verify -fblocks -Wno-objc-root-class -std=c++11 %s
@protocol NSObject;
void bar(id(^)(void));
......@@ -144,3 +144,17 @@ namespace DependentReturn {
template void f<X>(X);
namespace MoveBlockVariable {
struct B0 {
struct B1 { // expected-note 2 {{candidate constructor (the implicit}}
B1(B0&&); // expected-note {{candidate constructor not viable}}
B1 test_move() {
__block B0 b;
return b; // expected-error {{no viable conversion from returned value of type 'MoveBlockVariable::B0' to function return type 'MoveBlockVariable::B1'}}
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