[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
implicitly.
rdar://problem/28181080
Differential Revision: https://reviews.llvm.org/D29908
llvm-svn: 295150
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index a8832e9..390e1b5 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2743,15 +2743,17 @@
// ...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>() &&