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

7 files changed, 80 insertions, 59 deletions

diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index e2136ac27bd..94ec7961d3e 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -2050,7 +2050,7 @@ AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
     DiagnoseSwitchLabelsFallthrough(S, AC, !FallThroughDiagFull);
   }
 
-  if (S.getLangOpts().ObjCARCWeak &&
+  if (S.getLangOpts().ObjCWeak &&
       !Diags.isIgnored(diag::warn_arc_repeated_use_of_weak, D->getLocStart()))
     diagnoseRepeatedUseOfWeak(S, fscope, D, AC.getParentMap());
 
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 5099867b199..4aecd08d9fe 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -489,9 +489,9 @@ CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
                    QualType *TheOffendingDestType = nullptr,
                    Qualifiers *CastAwayQualifiers = nullptr) {
   // If the only checking we care about is for Objective-C lifetime qualifiers,
-  // and we're not in ARC mode, there's nothing to check.
+  // and we're not in ObjC mode, there's nothing to check.
   if (!CheckCVR && CheckObjCLifetime && 
-      !Self.Context.getLangOpts().ObjCAutoRefCount)
+      !Self.Context.getLangOpts().ObjC1)
     return false;
     
   // Casting away constness is defined in C++ 5.2.11p8 with reference to
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index 84936745b9a..06d9e375db8 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -4912,7 +4912,7 @@ void Sema::CodeCompleteObjCPropertyFlags(Scope *S, ObjCDeclSpec &ODS) {
     Results.AddResult(CodeCompletionResult("atomic"));
 
   // Only suggest "weak" if we're compiling for ARC-with-weak-references or GC.
-  if (getLangOpts().ObjCARCWeak || getLangOpts().getGC() != LangOptions::NonGC)
+  if (getLangOpts().ObjCWeak || getLangOpts().getGC() != LangOptions::NonGC)
     if (!ObjCPropertyFlagConflicts(Attributes, ObjCDeclSpec::DQ_PR_weak))
       Results.AddResult(CodeCompletionResult("weak"));
 
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 047ff152cf8..f9e75893bf3 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9815,9 +9815,9 @@ Sema::ActOnCXXForRangeIdentifier(Scope *S, SourceLocation IdentLoc,
 void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
   if (var->isInvalidDecl()) return;
 
-  // In ARC, don't allow jumps past the implicit initialization of a
+  // In Objective-C, don't allow jumps past the implicit initialization of a
   // local retaining variable.
-  if (getLangOpts().ObjCAutoRefCount &&
+  if (getLangOpts().ObjC1 &&
       var->hasLocalStorage()) {
     switch (var->getType().getObjCLifetime()) {
     case Qualifiers::OCL_None:
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 1b43f92128e..badb2ef118f 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -1702,7 +1702,7 @@ Sema::BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
 
   MarkDeclRefReferenced(E);
 
-  if (getLangOpts().ObjCARCWeak && isa<VarDecl>(D) &&
+  if (getLangOpts().ObjCWeak && isa<VarDecl>(D) &&
       Ty.getObjCLifetime() == Qualifiers::OCL_Weak &&
       !Diags.isIgnored(diag::warn_arc_repeated_use_of_weak, E->getLocStart()))
       recordUseOfEvaluatedWeak(E);
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
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index d1bf6cc6bb2..e53c7792e50 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -4408,7 +4408,7 @@ TypeSourceInfo *Sema::GetTypeForDeclaratorCast(Declarator &D, QualType FromTy) {
   TypeSourceInfo *ReturnTypeInfo = nullptr;
   QualType declSpecTy = GetDeclSpecTypeForDeclarator(state, ReturnTypeInfo);
 
-  if (getLangOpts().ObjCAutoRefCount) {
+  if (getLangOpts().ObjC1) {
     Qualifiers::ObjCLifetime ownership = Context.getInnerObjCOwnership(FromTy);
     if (ownership != Qualifiers::OCL_None)
       transferARCOwnership(state, declSpecTy, ownership);
@@ -5092,11 +5092,6 @@ static bool handleObjCOwnershipTypeAttr(TypeProcessingState &state,
     return true;
   }
 
-  // Consume lifetime attributes without further comment outside of
-  // ARC mode.
-  if (!S.getLangOpts().ObjCAutoRefCount)
-    return true;
-
   IdentifierInfo *II = attr.getArgAsIdent(0)->Ident;
   Qualifiers::ObjCLifetime lifetime;
   if (II->isStr("none"))
@@ -5114,6 +5109,14 @@ static bool handleObjCOwnershipTypeAttr(TypeProcessingState &state,
     return true;
   }
 
+  // Just ignore lifetime attributes other than __weak and __unsafe_unretained
+  // outside of ARC mode.
+  if (!S.getLangOpts().ObjCAutoRefCount &&
+      lifetime != Qualifiers::OCL_Weak &&
+      lifetime != Qualifiers::OCL_ExplicitNone) {
+    return true;
+  }
+
   SplitQualType underlyingType = type.split();
 
   // Check for redundant/conflicting ownership qualifiers.
@@ -5164,24 +5167,36 @@ static bool handleObjCOwnershipTypeAttr(TypeProcessingState &state,
     type = S.Context.getAttributedType(AttributedType::attr_objc_ownership,
                                        origType, type);
 
-  // Forbid __weak if the runtime doesn't support it.
+  // Sometimes, __weak isn't allowed.
   if (lifetime == Qualifiers::OCL_Weak &&
-      !S.getLangOpts().ObjCARCWeak && !NonObjCPointer) {
+      !S.getLangOpts().ObjCWeak && !NonObjCPointer) {
 
-    // Actually, delay this until we know what we're parsing.
+    // Use a specialized diagnostic if the runtime just doesn't support them.
+    unsigned diagnostic =
+      (S.getLangOpts().ObjCWeakRuntime ? diag::err_arc_weak_disabled
+                                       : diag::err_arc_weak_no_runtime);
+
+    // In any case, delay the diagnostic until we know what we're parsing.
     if (S.DelayedDiagnostics.shouldDelayDiagnostics()) {
       S.DelayedDiagnostics.add(
           sema::DelayedDiagnostic::makeForbiddenType(
               S.getSourceManager().getExpansionLoc(AttrLoc),
-              diag::err_arc_weak_no_runtime, type, /*ignored*/ 0));
+              diagnostic, type, /*ignored*/ 0));
     } else {
-      S.Diag(AttrLoc, diag::err_arc_weak_no_runtime);
+      S.Diag(AttrLoc, diagnostic);
     }
 
     attr.setInvalid();
     return true;
   }
 
+  // If we accepted __weak, we might still need to warn about it.
+  if (lifetime == Qualifiers::OCL_Weak &&
+      !S.getLangOpts().ObjCAutoRefCount &&
+      S.getLangOpts().ObjCWeak) {
+    S.Diag(AttrLoc, diag::warn_objc_weak_compat);
+  }
+
   // Forbid __weak for class objects marked as
   // objc_arc_weak_reference_unavailable
   if (lifetime == Qualifiers::OCL_Weak) {
@@ -5189,9 +5204,9 @@ static bool handleObjCOwnershipTypeAttr(TypeProcessingState &state,
           type->getAs<ObjCObjectPointerType>()) {
       if (ObjCInterfaceDecl *Class = ObjT->getInterfaceDecl()) {
         if (Class->isArcWeakrefUnavailable()) {
-            S.Diag(AttrLoc, diag::err_arc_unsupported_weak_class);
-            S.Diag(ObjT->getInterfaceDecl()->getLocation(),
-                   diag::note_class_declared);
+          S.Diag(AttrLoc, diag::err_arc_unsupported_weak_class);
+          S.Diag(ObjT->getInterfaceDecl()->getLocation(),
+                  diag::note_class_declared);
         }
       }
     }