[ObjC] Allow declaring __strong pointer fields in structs in Objective-C

ARC mode.

Declaring __strong pointer fields in structs was not allowed in
Objective-C ARC until now because that would make the struct non-trivial
to default-initialize, copy/move, and destroy, which is not something C
was designed to do. This patch lifts that restriction.

Special functions for non-trivial C structs are synthesized that are
needed to default-initialize, copy/move, and destroy the structs and
manage the ownership of the objects the __strong pointer fields point
to. Non-trivial structs passed to functions are destructed in the callee
function.

rdar://problem/33599681

Differential Revision: https://reviews.llvm.org/D41228

llvm-svn: 326307

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 41633f90c34..7f524c5591c 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -1151,6 +1151,7 @@ static bool HasFeature(const Preprocessor &PP, StringRef Feature) {
       // Objective-C features
       .Case("objc_arr", LangOpts.ObjCAutoRefCount) // FIXME: REMOVE?
       .Case("objc_arc", LangOpts.ObjCAutoRefCount)
+      .Case("objc_arc_fields", true)
       .Case("objc_arc_weak", LangOpts.ObjCWeak)
       .Case("objc_default_synthesize_properties", LangOpts.ObjC2)
       .Case("objc_fixed_enum", LangOpts.ObjC2)