Define weak and __weak to mean ARC-style weak references, even in MRC.

Previously, __weak was silently accepted and ignored in MRC mode.
That makes this a potentially source-breaking change that we have to
roll out cautiously.  Accordingly, for the time being, actual support
for __weak references in MRC is experimental, and the compiler will
reject attempts to actually form such references.  The intent is to
eventually enable the feature by default in all non-GC modes.
(It is, of course, incompatible with ObjC GC's interpretation of
__weak.)

If you like, you can enable this feature with
  -Xclang -fobjc-weak
but like any -Xclang option, this option may be removed at any point,
e.g. if/when it is eventually enabled by default.

This patch also enables the use of the ARC __unsafe_unretained qualifier
in MRC.  Unlike __weak, this is being enabled immediately.  Since
variables are essentially __unsafe_unretained by default in MRC,
the only practical uses are (1) communication and (2) changing the
default behavior of by-value block capture.

As an implementation matter, this means that the ObjC ownership
qualifiers may appear in any ObjC language mode, and so this patch
removes a number of checks for getLangOpts().ObjCAutoRefCount
that were guarding the processing of these qualifiers.  I don't
expect this to be a significant drain on performance; it may even
be faster to just check for these qualifiers directly on a type
(since it's probably in a register anyway) than to do N dependent
loads to grab the LangOptions.

rdar://9674298

llvm-svn: 251041

1 files changed, 3 insertions, 11 deletions

diff --git a/clang/lib/Basic/Targets.cpp b/clang/lib/Basic/Targets.cpp
index 01b10082047..e3d8602b695 100644
--- a/clang/lib/Basic/Targets.cpp
+++ b/clang/lib/Basic/Targets.cpp
@@ -118,19 +118,11 @@ static void getDarwinDefines(MacroBuilder &Builder, const LangOptions &Opts,
   if (Opts.Sanitize.has(SanitizerKind::Address))
     Builder.defineMacro("_FORTIFY_SOURCE", "0");
 
-  if (!Opts.ObjCAutoRefCount) {
+  // Darwin defines __weak, __strong, and __unsafe_unretained even in C mode.
+  if (!Opts.ObjC1) {
     // __weak is always defined, for use in blocks and with objc pointers.
     Builder.defineMacro("__weak", "__attribute__((objc_gc(weak)))");
-
-    // Darwin defines __strong even in C mode (just to nothing).
-    if (Opts.getGC() != LangOptions::NonGC)
-      Builder.defineMacro("__strong", "__attribute__((objc_gc(strong)))");
-    else
-      Builder.defineMacro("__strong", "");
-
-    // __unsafe_unretained is defined to nothing in non-ARC mode. We even
-    // allow this in C, since one might have block pointers in structs that
-    // are used in pure C code and in Objective-C ARC.
+    Builder.defineMacro("__strong", "");
     Builder.defineMacro("__unsafe_unretained", "");
   }