[Bug tree-optimization/81679] use attribute unused on function arguments as an optimization hint

["egallager at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81679

--- Comment #5 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to joseph@codesourcery.com from comment #4)
> On Wed, 2 Aug 2017, msebor at gcc dot gnu.org wrote:
> 
> > If there is a concern that the attribute could be used on declarations in
> > existing code that the optimization might break, then the attribute could be
> > specified differently (e.g., as a function attribute with an argument number
> > indicating which argument is unused; that would also differentiate it from the
> > existing function attribute).  Or the same feature could be provided under a
> > different attribute.  The main idea here is the ability to express the notion
> > that a function doesn't modify an object via its (non-const) pointer argument. 
> > The name for the feature is secondary (though "unused" is obviously a nice
> > fit).
> 
> The "unused" attribute always means "possibly unused, don't warn if 
> actually unused".  It would be a mistake to make it mean anything else.

...so close this as WONTFIX then?