[llvm-dev] The semantics of nonnull attribute

[Juneyoung Lee via llvm-dev]

Hello,

>  Would it be correct to resolve this by saying that dereferenceable(N)
> *implies* not_poison? This would be helpful as a clarification of how
> it all fits together.

Yes, I think it makes sense.

On Wed, Feb 19, 2020 at 12:14 PM Nicolai Hähnle <nhaehnle at gmail.com> wrote:

> On Wed, Feb 19, 2020 at 3:51 AM Juneyoung Lee via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I think not_poison (Johannes's used keyword) makes sense. We can
> simulate the original UB semantics by simply attaching it, as explained.
> > For the attributes other than nonnull, we may need more discussion;
> align attribute seems to be okay with defining it as poison,
> dereferenceable may need UB even without nonnull (because it needs to be
> non-poison as shown Nuno's hoisting example).
>
> For reference, the hoisting example was:
>
> f(dereferenceable(4) %p) {
>   loop() {
>     %v = load %p
>     use(%v)
>   }
> }
> =>
> f(dereferenceable(4) %p) {
>   %v = load %p
>   loop() {
>     use(%v)
>   }
> }
>
> Would it be correct to resolve this by saying that dereferenceable(N)
> *implies* not_poison? This would be helpful as a clarification of how
> it all fits together.
>
> Cheers,
> Nicolai
>


-- 

Juneyoung Lee
Software Foundation Lab, Seoul National University
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