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

[vivek pandya via cfe-dev]

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?

Note: I want to parse this string at MI level if possible or at IR level to
create a RegMask out of that.

Sincerely,
Vivek
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