Re: [PATCH] add simple attribute introspection

[Eric Gallager <egall at gwmail dot gwu dot edu>]

On 10/10/18, Martin Sebor <msebor@gmail.com> wrote:
> While writing tests for fixes and enhancements for attribute
> handling I keep finding myself coming up with the same boiler-
> plate code to verify whether an attribute has or has not been
> successfully applied.  It's often error-prone because it
> depends on the subtle and unique effects each attribute has
> on optimizers or code generation in general.
>
> Implementing an API just for testing might perhaps be excessive
> but I suspect that users would find use for such a feature too.
> I can even envision wanting to selectively apply attributes to
> one's own symbols depending on their presence or absence on
> other symbols (as an extension to the patch I posted for pr81824
> that introduces the copy attribute to copy attributes from one
> symbol to another).
>
> The attached patch introduces a built-in function called
> __builtin_has_attribute that makes some of this possible.
> See the documentation and tests for details.

__builtin_has_attribute sounds confusingly close to the
__has_attribute macro, and yet from this description it sounds like it
does something different. Maybe clear that up?

>
> The C++ implementation is only tested using the C tests and
> I'm pretty sure it doesn't do the right thing for templates
> but I think it can be extended to do that in a followup patch
> or an update to this one.
>
> The C tests don't exhaustively exercise all attributes so it's
> quite possible there are gaps/bugs where the built-in doesn't
> return the right value due to missing special handling.
> Attribute format validation is nearly non-existent.  I view
> these shortcomings as minor and they too can be plugged in
> a followup patch.
>
> Ultimately, if this is viewed as useful as I'm hoping it will
> be, I'd like to move the special handling from has_attribute
> and to a callback function pointed from attribute_spec.  That
> way each attribute, front-end and back-end alike, could, in
> addition the attribute handler, implement its own special
> query routine without the details leaking into the rest of
> the compiler.
>
> Martin
>