Relax the conversion rules for Objective-C GC qualifiers a

bit by allowing __weak and __strong to be added/dropped as part of
implicit conversions (qualification conversions in C++). A little
history: GCC lets one add/remove/change GC qualifiers just about
anywhere, implicitly. Clang did roughly the same before, but we
recently normalized the semantics of qualifiers across the board to
get a semantics that we could reason about (yay). Unfortunately, this
tightened the screws a bit too much for GC qualifiers, where it's
common to add/remove these qualifiers at will.

Overall, we're still in better shape than we were before: we don't
permit directly changing the GC qualifier (e.g., __weak -> __strong),
so type safety is improved. More importantly, we're internally
consistent in our handling of qualifiers, and the logic that allows
adding/removing GC qualifiers (but not adding/removing address
spaces!) only touches two obvious places.

Fixes <rdar://problem/9402499>.

llvm-svn: 131065

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 64f04de87aa..602ecd66027 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -2197,6 +2197,13 @@ Sema::IsQualificationConversion(QualType FromType, QualType ToType,
     Qualifiers FromQuals = FromType.getQualifiers();
     Qualifiers ToQuals = ToType.getQualifiers();
     
+    // Allow addition/removal of GC attributes but not changing GC attributes.
+    if (FromQuals.getObjCGCAttr() != ToQuals.getObjCGCAttr() &&
+        (!FromQuals.hasObjCGCAttr() || !ToQuals.hasObjCGCAttr())) {
+      FromQuals.removeObjCGCAttr();
+      ToQuals.removeObjCGCAttr();
+    }
+    
     //   -- for every j > 0, if const is in cv 1,j then const is in cv
     //      2,j, and similarly for volatile.
     if (!CStyle && !ToQuals.compatiblyIncludes(FromQuals))