[PATCH] D31343: Add an attribute plugin example

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

In D31343#1902903 <https://reviews.llvm.org/D31343#1902903>, @john.brawn wrote:

> I've been looking into attribute merging, and as far as I can tell there's two things going on:
>
> - In SemaDeclAttr.cpp, the various handleXyzAttr functions may call mergeXyzAttr to handle clashes with other attributes within the same declaration.
> - In SemaDecl.cpp, several functions call mergeDeclAttributes, which calls mergeXyzAttr, to handle clashes with attributes in a previous declaration of the same thing.


Agreed.

> For the first kind, the handleDeclAttribute function defined for a plugin attribute can check for and handle clashes with other attributes.

Agreed.

> For the second kind, at that point we're using subclasses of Attr which means we're beyond the scope of plugin attributes which just work in the realm of ParsedAttrs.

Yeah, we are using semantic attributes at that point rather than parsed attributes.

> So I think things are OK, though I guess it depends on what exactly your plugin is doing - our use-case is that the plugin-defined attribute is just used to set an AnnotateAttr, which is used to tell a plugin-defined LLVM pass that it needs to do something in that function, so we don't need anything special to happen with regards to attribute merging.

I think things are fine for your example plugin. The scenario I'm worried about is when users want to add their own semantic attributes that need to be merged, or if they're using an existing semantic attribute but need to add custom merging logic to it for their own needs.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D31343/new/

https://reviews.llvm.org/D31343