rjmccall added inline comments.
================
Comment at: clang/include/clang/Basic/Attr.td:2655
+
+def Retain : InheritableAttr {
+ let Spellings = [GCC<"retain">];
----------------
MaskRay wrote:
> aaron.ballman wrote:
> > MaskRay wrote:
> > > aaron.ballman wrote:
> > > > MaskRay wrote:
> > > > > aaron.ballman wrote:
> > > > > > Should this be a target-specific attribute as it only has effects
> > > > > > on ELF targets?
> > > > > As I understand it, GCC `retain` is not warned on unsupported targets.
> > > > >
> > > > > Regardless of GCC's choice, I think not having a `warning: unknown
> > > > > attribute 'retain' ignored [-Wunknown-attributes]` diagnostic makes
> > > > > sense. `retain` will be usually used together with `used`. In Clang,
> > > > > `used` already has "retain" semantics on macOS and Windows (I don't
> > > > > know what they do on GCC; GCC folks want orthogonality for ELF and I
> > > > > agree). If `retain` is silently ignored on macOS and Windows, then
> > > > > users don't need to condition compile for different targets.
> > > > The other side of that is a user who writes only `retain` and expects
> > > > it to do something when it's actually being silently ignored. While
> > > > they may usually use it in conjunction with `used`, I'm more worried
> > > > about the situation where the user is possibly confused.
> > > `retain` without `used` can be used on some external linkage definitions,
> > > as well as internal linkage definitions which are referenced by live
> > > sections. I agree there could be some confusion, but hope with mccall's
> > > suggestion (thanks) the documentation is clear.
> > If `retain` without `used` is an expected usage pattern, then I think we
> > need a diagnostic when we ignore the `retain` attribute. I don't think it
> > is reasonable to expect users to read the documentation because they won't
> > know that they've misused the attribute when we silently ignore it.
> >
> > Alternatively, would it be possible to make `retain` useful on all targets?
> > e.g., when `retain` is used by itself on a declaration compiled for macOS
> > or Windows, the backend does whatever it would normally do for `used`?
> There is the normal behavior: `__attribute__((retain)) static void f1() {} //
> expected-warning {{unused function 'f1'}}`.
>
> Sema.cpp:1227 has the unused diagnostics. There are already many different
> versions of diagnostics. Do you suggest another diagnostic line for `used is
> needed`? If you think so, I'll need to figure out how to do that...
>
> Added some tests leveraging the existing diagnostic code.
We could definitely support retain-without-used with the ELF semantics on all
targets if we think they're useful.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D96838/new/
https://reviews.llvm.org/D96838
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