[cfe-dev] Help required for adding a new attribute

[vivek pandya via cfe-dev]

On Mon, Jul 11, 2016 at 6:03 PM, Aaron Ballman <aaron at aaronballman.com>
wrote:

> On Mon, Jul 11, 2016 at 6:47 AM, vivek pandya via cfe-dev
> <cfe-dev at lists.llvm.org> wrote:
> > Hello Clang Developers,
> >
> > I want to add a new attribute which is required to work with function
> > declaration as shown in example given below:
> >
> > extern void foo(int param) __attribute__((regmask("R8,R11")));
> >
> > int foo2(int param) {
> > foo(param);
> > return param;
> > }
> >
> > For this I have done following changes:
> >
> > Attr.td
> >
> > def RegMask : Attr {
> >   let Spellings = [GNU<"regmask">];
> >   let Args = [StringArgument<"ClobbersList">];
> >   let Subjects = SubjectList<[Function]>;
> >   let Documentation = [Undocumented];
> > }
> >
> > lib/Sema/SemaDeclAttr.cpp
> >
> > static void handleRegMaskAttr(Sema &S, Decl *D, const AttributeList
> &Attr) {
> >   // Make sure that there is a string literal as the annotation's single
> >   // argument.
> >   StringRef Str;
> >   if (!S.checkStringLiteralArgumentAttr(Attr, 0, Str))
> >     return;
> >
> >   D->addAttr(::new (S.Context)
> >              AnnotateAttr(Attr.getRange(), S.Context, Str,
> >                           Attr.getAttributeSpellingListIndex()));
> >   llvm::dbgs() << "Reg Mask attribute : " << Str << "\n";
> > }
> >
> > above method is very similar to handleAnnotateAttr
> >
> > and use this method inside ProcessDeclAttribute method as follows :
> >
> > // Attribute to help interprocedural register allocation
> >   case AttributeList::AT_RegMask:
> >     handleRegMaskAttr(S, D, Attr);
> >     break;
> >   }
> >
> > but this does not work for me, it works on function definitions but not
> with
> > function declaration.
> >
> > Am I missing here any thing?
>
> The attribute should inherit from InheritableAttr instead of just
> Attr. That should cause it to be inherited by later redeclarations.
>
I think my question is not clear, in the example given above foo and foo2
both are different function and what I want is that foo is extern function
for current module and for this declaration I want regmask attribute as a
string.
Why should I need InheritableAttr when foo is not going to be redeclared in
the current module?

>
> > Note: I want to parse this string at MI level if possible or at IR level
> to
> > create a RegMask out of that.
>
> How do you intend to report diagnostics to the user if the parsed
> string contains something unexpected?
>
If I am not able to use clang's diagnostics then I believe I should take
help of some thing like LLVM_ERROR.
-Vivek

>
> ~Aaron
>
> >
> > Sincerely,
> > Vivek
> >
> > _______________________________________________
> > cfe-dev mailing list
> > cfe-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> >
>
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