Support objc_nonlazy_class attribute on Objective-C implementations

[erik.pilkington]

Summary

Fixes rdar://49523079

[rjmccall]

Should we have a special has_feature test to check that this attribute is allowed on implementations? We've done that in the past when expanding the set of subjects for an attribute. But that's not necessary if we haven't made this attribute part of a public Xcode release yet, because then the attribute is just understood to always apply to implementations; I can't remember when exactly this was added and what releases it's made it into.

[aaron.ballman]

LGTM, modulo the __has_feature question.

[erik.pilkington]

In D60544#1462869, @rjmccall wrote:

Should we have a special has_feature test to check that this attribute is allowed on implementations? We've done that in the past when expanding the set of subjects for an attribute. But that's not necessary if we haven't made this attribute part of a public Xcode release yet, because then the attribute is just understood to always apply to implementations; I can't remember when exactly this was added and what releases it's made it into.

I think we can sneak by without a __has_feature for this, D56555 isn't in LLVM 8 nor Xcode 10.2.

[rjmccall]

Great, SGTM.

clang/include/clang/Basic/Attr.td

 def ObjCRootClass : InheritableAttr {
   let Spellings = [Clang<"objc_root_class">];
   let Subjects = SubjectList<[ObjCInterface], ErrorDiag>;
   let Documentation = [Undocumented];
 }
 
 def ObjCNonLazyClass : Attr {
   let Spellings = [Clang<"objc_nonlazy_class">];
-  let Subjects = SubjectList<[ObjCInterface], ErrorDiag>;
+  let Subjects = SubjectList<[ObjCInterface, ObjCImpl], ErrorDiag>;
   let LangOpts = [ObjC];
   let Documentation = [ObjCNonLazyClassDocs];
 }
 
 def ObjCSubclassingRestricted : InheritableAttr {
   let Spellings = [Clang<"objc_subclassing_restricted">];
   let Subjects = SubjectList<[ObjCInterface], ErrorDiag>;
   let Documentation = [ObjCSubclassingRestrictedDocs];

clang/include/clang/Basic/AttrDocs.td

 This attribute can be added to an Objective-C ``@interface`` declaration to
 ensure that this class cannot be subclassed.
   }];
 }
 
 def ObjCNonLazyClassDocs : Documentation {
   let Category = DocCatDecl;
   let Content = [{
-This attribute can be added to an Objective-C ``@interface`` declaration to
-add the class to the list of non-lazily initialized classes. A non-lazy class
-will be initialized eagerly when the Objective-C runtime is loaded.  This is
-required for certain system classes which have instances allocated in
-non-standard ways, such as the classes for blocks and constant strings.  Adding
-this attribute is essentially equivalent to providing a trivial `+load` method 
-but avoids the (fairly small) load-time overheads associated with defining and
-calling such a method.
+This attribute can be added to an Objective-C ``@interface`` or
+``@implementation`` declaration to add the class to the list of non-lazily
+initialized classes. A non-lazy class will be initialized eagerly when the
+Objective-C runtime is loaded. This is required for certain system classes which
+have instances allocated in non-standard ways, such as the classes for blocks
+and constant strings. Adding this attribute is essentially equivalent to
+providing a trivial `+load` method but avoids the (fairly small) load-time
+overheads associated with defining and calling such a method.
   }];
 }
 
 def SelectAnyDocs : Documentation {
   let Category = DocCatDecl;
   let Content = [{
 This attribute appertains to a global symbol, causing it to have a weak
 definition (

clang/lib/CodeGen/CGObjCMac.cpp

     if (HiddenVisibility)
       GV->setVisibility(llvm::GlobalValue::HiddenVisibility);
   return GV;
 }
 
 bool CGObjCNonFragileABIMac::ImplementationIsNonLazy(
     const ObjCImplDecl *OD) const {
   return OD->getClassMethod(GetNullarySelector("load")) != nullptr ||
-         OD->getClassInterface()->hasAttr<ObjCNonLazyClassAttr>();
+         OD->getClassInterface()->hasAttr<ObjCNonLazyClassAttr>() ||
+         OD->hasAttr<ObjCNonLazyClassAttr>();
 }
 
 void CGObjCNonFragileABIMac::GetClassSizeInfo(const ObjCImplementationDecl *OID,
                                               uint32_t &InstanceStart,
                                               uint32_t &InstanceSize) {
   const ASTRecordLayout &RL =
     CGM.getContext().getASTObjCImplementationLayout(OID);
 

clang/test/CodeGenObjC/non-lazy-classes.m

-// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -Wno-objc-root-class -emit-llvm -o - %s | \
-// RUN: FileCheck %s
-// CHECK: @"OBJC_LABEL_NONLAZY_CLASS_$" = private global [2 x {{.*}}]{{.*}}@"OBJC_CLASS_$_A"{{.*}},{{.*}}@"OBJC_CLASS_$_D"{{.*}} section "__DATA,__objc_nlclslist,regular,no_dead_strip", align 8
-// CHECK: @"OBJC_LABEL_NONLAZY_CATEGORY_$" = private global [1 x {{.*}}] {{.*}}@"\01l_OBJC_$_CATEGORY_A_$_Cat"{{.*}}, section "__DATA,__objc_nlcatlist,regular,no_dead_strip", align 8
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -Wno-objc-root-class -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: @"OBJC_LABEL_NONLAZY_CLASS_$" = private global [3 x {{.*}}]{{.*}}@"OBJC_CLASS_$_A"{{.*}},{{.*}}@"OBJC_CLASS_$_D"{{.*}},{{.*}}"OBJC_CLASS_$_E"{{.*}} section "__DATA,__objc_nlclslist,regular,no_dead_strip", align 8
+// CHECK: @"OBJC_LABEL_NONLAZY_CATEGORY_$" = private global [2 x {{.*}}] {{.*}}@"\01l_OBJC_$_CATEGORY_A_$_Cat"{{.*}},{{.*}}@"\01l_OBJC_$_CATEGORY_E_$_MyCat"{{.*}}, section "__DATA,__objc_nlcatlist,regular,no_dead_strip", align 8
 
 @interface A @end
 @implementation A
 +(void) load {
 }
 @end
 
 @interface A (Cat) @end

 @interface C : A @end
 @implementation C
 @end
 
 __attribute__((objc_nonlazy_class))
 @interface D @end
 
 @implementation D @end
+
+@interface E @end
+
+__attribute__((objc_nonlazy_class))
+@implementation E @end
+
+__attribute__((objc_nonlazy_class))
+@implementation E (MyCat) @end

clang/test/Misc/pragma-attribute-supported-attributes-list.test

 // CHECK-NEXT: ObjCBridge (SubjectMatchRule_record, SubjectMatchRule_type_alias)
 // CHECK-NEXT: ObjCBridgeMutable (SubjectMatchRule_record)
 // CHECK-NEXT: ObjCBridgeRelated (SubjectMatchRule_record)
 // CHECK-NEXT: ObjCDesignatedInitializer (SubjectMatchRule_objc_method)
 // CHECK-NEXT: ObjCException (SubjectMatchRule_objc_interface)
 // CHECK-NEXT: ObjCExplicitProtocolImpl (SubjectMatchRule_objc_protocol)
 // CHECK-NEXT: ObjCExternallyRetained (SubjectMatchRule_variable_not_is_parameter, SubjectMatchRule_function, SubjectMatchRule_block, SubjectMatchRule_objc_method)
 // CHECK-NEXT: ObjCMethodFamily (SubjectMatchRule_objc_method)
-// CHECK-NEXT: ObjCNonLazyClass (SubjectMatchRule_objc_interface)
+// CHECK-NEXT: ObjCNonLazyClass (SubjectMatchRule_objc_interface, SubjectMatchRule_objc_implementation)
 // CHECK-NEXT: ObjCPreciseLifetime (SubjectMatchRule_variable)
 // CHECK-NEXT: ObjCRequiresPropertyDefs (SubjectMatchRule_objc_interface)
 // CHECK-NEXT: ObjCRequiresSuper (SubjectMatchRule_objc_method)
 // CHECK-NEXT: ObjCReturnsInnerPointer (SubjectMatchRule_objc_method, SubjectMatchRule_objc_property)
 // CHECK-NEXT: ObjCRootClass (SubjectMatchRule_objc_interface)
 // CHECK-NEXT: ObjCRuntimeName (SubjectMatchRule_objc_interface, SubjectMatchRule_objc_protocol)
 // CHECK-NEXT: ObjCRuntimeVisible (SubjectMatchRule_objc_interface)
 // CHECK-NEXT: ObjCSubclassingRestricted (SubjectMatchRule_objc_interface)

clang/test/SemaObjC/attr-objc-non-lazy.m

 @protocol B
 @end
 
 __attribute__((objc_nonlazy_class)) // expected-error {{'objc_nonlazy_class' attribute only applies to Objective-C interfaces}}
 void foo();
 
 @interface E
 @end
-// expected-error@+1 {{'objc_nonlazy_class' attribute only applies to Objective-C interfaces}}
+
 __attribute__((objc_nonlazy_class))
 @implementation E
 @end
+
+__attribute__((objc_nonlazy_class))
+@implementation E (MyCat)
+@end