[PATCH] D72097: [LifetimeAnalysis] Do not forbid void deref type in gsl::Pointer/gsl::Owner annotations

Thu Jan 2 12:40:10 PST 2020

xazax.hun added a comment.

In D72097#1801777 <https://reviews.llvm.org/D72097#1801777>, @gribozavr2 wrote:

> Could you provide a more fleshed out example of a case where it is useful?

Sure! The `std::any` could be one example (`std::variant` is similar, but ultimately, we migh want to be able to enumerate multiple types in that case rather than just using void).

The specific example I found was an allocator: https://fuchsia-review.googlesource.com/c/fuchsia/+/340159/3/zircon/kernel/lib/fbl/include/fbl/arena.h#25

This might not be super important as it might be unlikely that we will ever find a problem where an arena is destroyed before an object allocated there is dereferenced, but still, it is good to cover this use case as well.

> Could you update the documentation for the attribute? I'm forgetting if there's a spec for this attribute -- is this extension part of that spec?

`void` is currently not mentioned in the documentation, but adding an example and the interpretation would help indeed, thanks!

> Do you foresee any issues or further special cases? For example, IIRC, 'operator*' is required to return DerefType. I have a hard time understanding how one would define 'operator*' in such an owner.

I think those types that have `void` as deref types are unlikely to implement `operator*`. There might be some skeletons but I am not aware of anything at the moment.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72097/new/

https://reviews.llvm.org/D72097