Re: [PATCH] handle bzero/bcopy in DSE and aliasing (PR 80933, 80934)

[Martin Sebor <msebor at gmail dot com>]

On 06/07/2017 02:01 PM, Marc Glisse wrote:
> On Wed, 7 Jun 2017, Bernhard Reutner-Fischer wrote:
>
> > On 7 June 2017 16:46:53 CEST, Martin Sebor <msebor@gmail.com> wrote:
> > > On 06/07/2017 02:23 AM, Richard Biener wrote:
> > > > On Wed, Jun 7, 2017 at 5:26 AM, Martin Sebor <msebor@gmail.com>
> > > wrote:
> > > > > > Note I'd be _much_ more sympathetic to simply canonicalizing all of
> > > > > > bzero and bcopy
> > > > > > to memset / memmove and be done with all the above complexity.
> > > > >
> > > > >
> > > > > Attached is an updated patch along these lines.  Please let me
> > > > > know if it matches your expectations.
> > > >
> > > > I think you attached the wrong patch.
> > >
> > > Yes I did, sorry.  The correct one is attached.
> >
> > Under POSIX.1-2008 "optimizing" bzero or bcmp is IMO plain wrong.
> >
> > It's like optimizing foo() to a random built-in but maybe that's just
> > me. If your libc provides a define to a standard function for these
> > under a compat knob then fine but otherwise you should fix that.
> > *shrug*. Joseph?
>
> The patch optimizes __builtin_bzero, which should be ok. The question
> (independent from this patch) is then under what conditions bzero should
> be detected as a builtin.

Yes.  The problem is that unlike for C and C++, GCC doesn't have
a mechanism to select the target version of POSIX.  I think it
should.

But there is a subtle problem with the patch that needs fixing.
Bcopy should not be transformed to memcpy but rather memmove.
I'll fix that before committing.

Martin