Add a new attribute CFNoRelease.

[gottesmm]

Summary

This attribute will allow users to annotate opaque c functions as not
decrementing any reference counts in the functions body or any function that is
called by the given function.

This will improve ARC optimization.

[gottesmm]

Added documentation.

[aaron.ballman]

It's a bit strange to add an attribute that has absolutely no semantic effect whatsoever. Where is this attribute intended to be queried within the compiler? Are there additional functionality patches coming for this?

include/clang/Basic/Attr.td

540

Please, no undocumented new attributes. You should modify AttrDocs.td and include that reference here.

test/SemaObjC/attr-cf_no_release.m

31

Not that lots of test are bad, but a lot of these tests are duplicates and can be removed. For instance, really only need one test for ObjC methods, one for properties, one for params, etc. It would be good to add a test ensuring that the attribute accepts no arguments.

[gottesmm]

I think that my response via email did not hit phabriactor. So sorry for the delay.

Yes there is a forthcoming patch for CodeGen which will place an attribute on the relevant functions. The attribute will be queried in the middle end optimizer. The reason why there has been a bit of a delay is I realized I wanted to talk to a few more people about this attribute internally.

We may want to expand its use to essentially mean "no-arc", i.e. this is a c function that uses pure c-code.

There are other possibilities as well so stay tuned.

[gottesmm]

include/clang/Basic/Attr.td

540

Ok. I was just following what was done in the surrounding code. I am fine with adding something to AttrDocs.td once we pin down exactly what we want.

test/SemaObjC/attr-cf_no_release.m

31

Ok.

[aaron.ballman]

In D16708#340359, @gottesmm wrote:

I think that my response via email did not hit phabriactor. So sorry for the delay.

No worries!

Yes there is a forthcoming patch for CodeGen which will place an attribute on the relevant functions. The attribute will be queried in the middle end optimizer. The reason why there has been a bit of a delay is I realized I wanted to talk to a few more people about this attribute internally.

We may want to expand its use to essentially mean "no-arc", i.e. this is a c function that uses pure c-code.

There are other possibilities as well so stay tuned.

Okay, I would recommend the future patch include that middle end component as well. It gives better context for the attribute side of things.

include/clang/Basic/Attr.td

540

Yeah, the surrounding code was grandfathered in. It really should be documented as well. ;-)

include/clang/Basic/Attr.td

 }
 
 def CFConsumed : InheritableParamAttr {
   let Spellings = [GNU<"cf_consumed">];
   let Subjects = SubjectList<[ParmVar]>;
   let Documentation = [Undocumented];
 }
 
+// cf_no_release indicates that the call graph reachable from the given function
+// does not decrement reference counts in a manner that is visible to the
+// compiler.
+def CFNoRelease : InheritableAttr {
+  let Spellings = [GNU<"cf_no_release">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [Undocumented];
+}
+
 def Cleanup : InheritableAttr {
   let Spellings = [GCC<"cleanup">];
   let Args = [FunctionArgument<"FunctionDecl">];
   let Subjects = SubjectList<[Var]>;
   let Documentation = [Undocumented];
 }
 
 def Cold : InheritableAttr {

lib/Sema/SemaDeclAttr.cpp

static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
 
   case AttributeList::AT_CFConsumed:
   case AttributeList::AT_NSConsumed:
     handleNSConsumedAttr(S, D, Attr);
     break;
   case AttributeList::AT_NSConsumesSelf:
     handleSimpleAttribute<NSConsumesSelfAttr>(S, D, Attr);
     break;
-
+  case AttributeList::AT_CFNoRelease:
+    handleSimpleAttribute<CFNoReleaseAttr>(S, D, Attr);
+    break;
   case AttributeList::AT_NSReturnsAutoreleased:
   case AttributeList::AT_NSReturnsNotRetained:
   case AttributeList::AT_CFReturnsNotRetained:
   case AttributeList::AT_NSReturnsRetained:
   case AttributeList::AT_CFReturnsRetained:
     handleNSReturnsRetainedAttr(S, D, Attr);
     break;
   case AttributeList::AT_WorkGroupSizeHint:

test/SemaObjC/attr-cf_no_release.m

+// RUN: %clang_cc1 -fobjc-arc -verify -fsyntax-only %s
+// Make sure we accept the cf_no_release attribute in all of the appropriate places.
+
+#define CF_NO_RELEASE __attribute__((cf_no_release))
+
+int x CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+
+typedef struct __CFFoo *CFFooRef;
+
+int valid1() CF_NO_RELEASE;
+void valid2() CF_NO_RELEASE;
+CFFooRef valid3() CF_NO_RELEASE;
+id valid4() CF_NO_RELEASE;
+
+@interface Test
+- (int)invalid1 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+- (void)invalid2 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+- (CFFooRef)invalid3 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+- (id)invalid4 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+
+@property int invalidProp1 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+@property void invalidProp2 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+@property CFFooRef invalidProp3 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+@property id invalidProp4 CF_NO_RELEASE; // expected-warning{{'cf_no_release' attribute only applies to functions}}
+@end
+
+void invalidParam(int a CF_NO_RELEASE, // expected-warning{{'cf_no_release' attribute only applies to functions}}
+                  int *b CF_NO_RELEASE, // expected-warning{{'cf_no_release' attribute only applies to functions}}
+                  id c CF_NO_RELEASE, // expected-warning{{'cf_no_release' attribute only applies to functions}}
+                  void *d CF_NO_RELEASE, // expected-warning{{'cf_no_release' attribute only applies to functions}}
+                  CFFooRef e CF_NO_RELEASE); // expected-warning{{'cf_no_release' attribute only applies to functions}}