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, 44 insertions, 38 deletions

diff --git a/clang/lib/Sema/SemaObjCProperty.cpp b/clang/lib/Sema/SemaObjCProperty.cpp
index 374e5ccd918..04465958c1c 100644
--- a/clang/lib/Sema/SemaObjCProperty.cpp
+++ b/clang/lib/Sema/SemaObjCProperty.cpp
@@ -663,8 +663,10 @@ static void checkARCPropertyImpl(Sema &S, SourceLocation propertyImplLoc,
   // We're fine if they match.
   if (propertyLifetime == ivarLifetime) return;
 
-  // These aren't valid lifetimes for object ivars;  don't diagnose twice.
-  if (ivarLifetime == Qualifiers::OCL_None ||
+  // None isn't a valid lifetime for an object ivar in ARC, and
+  // __autoreleasing is never valid; don't diagnose twice.
+  if ((ivarLifetime == Qualifiers::OCL_None &&
+       S.getLangOpts().ObjCAutoRefCount) ||
       ivarLifetime == Qualifiers::OCL_Autoreleasing)
     return;
 
@@ -953,18 +955,46 @@ Decl *Sema::ActOnPropertyImplDecl(Scope *S,
     ObjCPropertyDecl::PropertyAttributeKind kind 
       = property->getPropertyAttributes();
 
-    // Add GC __weak to the ivar type if the property is weak.
-    if ((kind & ObjCPropertyDecl::OBJC_PR_weak) && 
-        getLangOpts().getGC() != LangOptions::NonGC) {
-      assert(!getLangOpts().ObjCAutoRefCount);
-      if (PropertyIvarType.isObjCGCStrong()) {
-        Diag(PropertyDiagLoc, diag::err_gc_weak_property_strong_type);
-        Diag(property->getLocation(), diag::note_property_declare);
+    bool isARCWeak = false;
+    if (kind & ObjCPropertyDecl::OBJC_PR_weak) {
+      // Add GC __weak to the ivar type if the property is weak.
+      if (getLangOpts().getGC() != LangOptions::NonGC) {
+        assert(!getLangOpts().ObjCAutoRefCount);
+        if (PropertyIvarType.isObjCGCStrong()) {
+          Diag(PropertyDiagLoc, diag::err_gc_weak_property_strong_type);
+          Diag(property->getLocation(), diag::note_property_declare);
+        } else {
+          PropertyIvarType =
+            Context.getObjCGCQualType(PropertyIvarType, Qualifiers::Weak);
+        }
+
+      // Otherwise, check whether ARC __weak is enabled and works with
+      // the property type.
       } else {
-        PropertyIvarType =
-          Context.getObjCGCQualType(PropertyIvarType, Qualifiers::Weak);
+        if (!getLangOpts().ObjCWeak) {
+          if (getLangOpts().ObjCWeakRuntime) {
+            Diag(PropertyDiagLoc, diag::err_arc_weak_disabled);
+          } else {
+            Diag(PropertyDiagLoc, diag::err_arc_weak_no_runtime);
+          }
+          Diag(property->getLocation(), diag::note_property_declare);
+        } else {
+          isARCWeak = true;
+          if (const ObjCObjectPointerType *ObjT =
+                PropertyIvarType->getAs<ObjCObjectPointerType>()) {
+            const ObjCInterfaceDecl *ObjI = ObjT->getInterfaceDecl();
+            if (ObjI && ObjI->isArcWeakrefUnavailable()) {
+              Diag(property->getLocation(),
+                   diag::err_arc_weak_unavailable_property)
+                << PropertyIvarType;
+              Diag(ClassImpDecl->getLocation(), diag::note_implemented_by_class)
+                << ClassImpDecl->getName();
+            }
+          }
+        }
       }
     }
+
     if (AtLoc.isInvalid()) {
       // Check when default synthesizing a property that there is 
       // an ivar matching property name and issue warning; since this
@@ -987,7 +1017,7 @@ Decl *Sema::ActOnPropertyImplDecl(Scope *S,
     if (!Ivar) {
       // In ARC, give the ivar a lifetime qualifier based on the
       // property attributes.
-      if (getLangOpts().ObjCAutoRefCount &&
+      if ((getLangOpts().ObjCAutoRefCount || isARCWeak) &&
           !PropertyIvarType.getObjCLifetime() &&
           PropertyIvarType->isObjCRetainableType()) {
 
@@ -1002,24 +1032,6 @@ Decl *Sema::ActOnPropertyImplDecl(Scope *S,
           Qualifiers::ObjCLifetime lifetime =
             getImpliedARCOwnership(kind, PropertyIvarType);
           assert(lifetime && "no lifetime for property?");
-          if (lifetime == Qualifiers::OCL_Weak) {
-            bool err = false;
-            if (const ObjCObjectPointerType *ObjT =
-                PropertyIvarType->getAs<ObjCObjectPointerType>()) {
-              const ObjCInterfaceDecl *ObjI = ObjT->getInterfaceDecl();
-              if (ObjI && ObjI->isArcWeakrefUnavailable()) {
-                Diag(property->getLocation(),
-                     diag::err_arc_weak_unavailable_property) << PropertyIvarType;
-                Diag(ClassImpDecl->getLocation(), diag::note_implemented_by_class)
-                  << ClassImpDecl->getName();
-                err = true;
-              }
-            }
-            if (!err && !getLangOpts().ObjCARCWeak) {
-              Diag(PropertyDiagLoc, diag::err_arc_weak_no_runtime);
-              Diag(property->getLocation(), diag::note_property_declare);
-            }
-          }
           
           Qualifiers qs;
           qs.addObjCLifetime(lifetime);
@@ -1027,13 +1039,6 @@ Decl *Sema::ActOnPropertyImplDecl(Scope *S,
         }
       }
 
-      if (kind & ObjCPropertyDecl::OBJC_PR_weak &&
-          !getLangOpts().ObjCAutoRefCount &&
-          getLangOpts().getGC() == LangOptions::NonGC) {
-        Diag(PropertyDiagLoc, diag::error_synthesize_weak_non_arc_or_gc);
-        Diag(property->getLocation(), diag::note_property_declare);
-      }
-
       Ivar = ObjCIvarDecl::Create(Context, ClassImpDecl,
                                   PropertyIvarLoc,PropertyIvarLoc, PropertyIvar,
                                   PropertyIvarType, /*Dinfo=*/nullptr,
@@ -1121,7 +1126,8 @@ Decl *Sema::ActOnPropertyImplDecl(Scope *S,
         // Fall thru - see previous comment
       }
     }
-    if (getLangOpts().ObjCAutoRefCount)
+    if (getLangOpts().ObjCAutoRefCount || isARCWeak ||
+        Ivar->getType().getObjCLifetime())
       checkARCPropertyImpl(*this, PropertyLoc, property, Ivar);
   } else if (PropertyIvar)
     // @dynamic