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, 6 insertions, 8 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 94e3e7ca29b..e774e115344 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -4946,8 +4946,6 @@ bool ASTContext::BlockRequiresCopying(QualType Ty,
   
   // If we have lifetime, that dominates.
   if (Qualifiers::ObjCLifetime lifetime = qs.getObjCLifetime()) {
-    assert(getLangOpts().ObjCAutoRefCount);
-    
     switch (lifetime) {
       case Qualifiers::OCL_None: llvm_unreachable("impossible");
         
@@ -4981,14 +4979,14 @@ bool ASTContext::getByrefLifetime(QualType Ty,
   if (Ty->isRecordType()) {
     HasByrefExtendedLayout = true;
     LifeTime = Qualifiers::OCL_None;
-  }
-  else if (getLangOpts().ObjCAutoRefCount)
-    LifeTime = Ty.getObjCLifetime();
-  // MRR.
-  else if (Ty->isObjCObjectPointerType() || Ty->isBlockPointerType())
+  } else if ((LifeTime = Ty.getObjCLifetime())) {
+    // Honor the ARC qualifiers.
+  } else if (Ty->isObjCObjectPointerType() || Ty->isBlockPointerType()) {
+    // The MRR rule.
     LifeTime = Qualifiers::OCL_ExplicitNone;
-  else
+  } else {
     LifeTime = Qualifiers::OCL_None;
+  }
   return true;
 }