[llvm-dev] [RFC] Memory region declaration intrinsic

[Roman Lebedev via llvm-dev]

On Wed, Dec 8, 2021 at 2:07 AM Eli Friedman <efriedma at quicinc.com> wrote:
>
> > -----Original Message-----
> > From: Roman Lebedev <lebedev.ri at gmail.com>
> > Sent: Tuesday, December 7, 2021 2:39 PM
> > To: llvm-dev at lists.llvm.org
> > Cc: Eli Friedman <efriedma at quicinc.com>; Johannes Doerfert
> > <jdoerfert at anl.gov>; Clement Courbet <courbet at google.com>; Nuno Lopes
> > <nunoplopes at sapo.pt>; Nikita Popov <nikita.ppv at gmail.com>; Peter
> > Collingbourne <peter at pcc.me.uk>; Philip Reames <listmail at philipreames.com>
> > Subject: Re: [RFC] Memory region declaration intrinsic
> >
> > On Wed, Dec 8, 2021 at 12:57 AM Eli Friedman <efriedma at quicinc.com> wrote:
> > >
> > > How does this interact with "inbounds" markings on GEPs?  Can the result of a
> > non-inbounds GEP point outside the specified region?
> > Uh, it's a trick question, isn't it? :)
> >
> > Right now I would basically say that "inbounds" markings on GEPs is
> > orthogonal here, because this intrinsic simply "clamps" the underlying
> > "allocated object".
> > (and naturally, you can't unclamp it afterwards *in this def-use chain*)
> >
> > I.e. if you go out of the specified bounds with `inbounds` you get
> > poison (and i think you can't go back from there?); but if you go
> > out of the specified bounds without `inbounds` it's not poison,
> > but dereferencing said pointer is still UB.
> >
> > Let me know if this isn't a proper answer,
> > or if i have talked myself into a corner here :)
>
> This seems fine, sure.  Please update your proposed LangRef patch so this is clear.
Thank you!
Okay, tried to improve the langref, let me know if there's anything
obvious missing / can be improved.

> -Eli
Roman