Re: Last call for bikeshedding on attribute sym/exalias/reverse_alias

[Roy Jacobson <roi.jacobson1@gmail.com>]

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There's a related [[preferred_name]] attribute in Clang but it's not a
success story. If you come up with something more usable I think we'll be
happy to implement it as well :)

https://clang.llvm.org/docs/AttributeReference.html#preferred-name


On Fri, 8 Sept 2023, 11:34 Jonathan Wakely via Gcc, <gcc@gcc.gnu.org> wrote:

> On Fri, 8 Sept 2023, 06:26 Alexandre Oliva via Gcc, <gcc@gcc.gnu.org>
> wrote:
>
> > Since 2020 I've been trying to introduce an attribute that operates a
> > bit like alias, but instead of defining a declaration as an alias to
> > another defined declaration, it merely exposes the present declaration
> > with an alternate mnemonic symbol name, so that it can be further
> > aliased, imported or referenced elsewhere with an invariant name, rather
> > than with a mangled name.  E.g.:
> >
> > // C++
> > namespace foo {
> >   int __attribute__ ((__???__ ("FOOVAR")))
> >   var = 42; // FOOVAR is an asm alias to the mangled name for foo::var
> > }
> >
> > --  Ada
> > package Foo is
> >   Var : Integer;
> >   pragma Import (CPP, FooVar, "FOOVAR");
> >   --  use the mnemonic alias rather than the mangled name.
> >
> >
> > The implementation also handles C++ cdtors, modifying the mnemonic alias
> > of each clone so that they don't clash, and typeinfo objects generated
> > for classes when the attribute is associated with a class.
> >
>
> Very cool, we have immediate uses for this in libstdc++.
>
> Personally I think calling it some form of "alias" focuses on the
> implementation details of how its done behind the scenes, not what its
> practical effects are. On the other hand, it would relate it to the
> existing alias attribute which is related.
>
> I think "symname" or "symalias" would be better than just "sym".
>
> Have you contacted anybody in the llvm community to see if they would
> implement it, or maybe already have something similar by another name?
>
>
>
>
> >
> > There don't seem to be objections to the feature per se, but discussions
> > about it have invariably got stuck in debating the attribute name.
> >
> > https://gcc.gnu.org/pipermail/gcc-patches/2020-August/551614.html
> > https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624560.html
> > https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624977.html
> >
> >
> > The customer report that motivated this development didn't require its
> > full generality, and asm("symbol") satisfies it.  But I've implemented
> > the feature, I find it useful, others seem to have liked it, and so I'd
> > like it to find its way into GCC.  However, I'm advised to not spend
> > much more time on it.
> >
> > So, instead of updating the patch for every suggested attribute name, my
> > last-attempt plan is to try to reach consensus on the attribute name,
> > and then adjust the patch and submit it one more time.  If that doesn't
> > succeed, I'll leave it for anyone else to take it from there.
> >
> > Attribute sym, named after symver, is the one in the latest version of
> > the patch.  mnemonic_alias, convenience_alias and asm_alias are other
> > possibilities that comes to mind.  The 2020-August thread has many more.
> >
> > --
> > Alexandre Oliva, happy hacker            https://FSFLA.org/blogs/lxo/
> >    Free Software Activist                   GNU Toolchain Engineer
> > More tolerance and less prejudice are key for inclusion and diversity
> > Excluding neuro-others for not behaving ""normal"" is *not* inclusive
> >
>