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Re: match.pd: Three new patterns
- From: Richard Biener <rguenther at suse dot de>
- To: Marek Polacek <polacek at redhat dot com>
- Cc: Marc Glisse <marc dot glisse at inria dot fr>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 23 Jun 2015 10:22:35 +0200 (CEST)
- Subject: Re: match.pd: Three new patterns
- Authentication-results: sourceware.org; auth=none
- References: <20150612121332 dot GH2756 at redhat dot com> <alpine dot DEB dot 2 dot 20 dot 1506131138460 dot 2373 at laptop-mg dot saclay dot inria dot fr> <20150618154117 dot GD10139 at redhat dot com> <20150619152304 dot GH10139 at redhat dot com> <alpine dot DEB dot 2 dot 20 dot 1506191725520 dot 1586 at laptop-mg dot saclay dot inria dot fr> <20150622190319 dot GM10139 at redhat dot com> <alpine dot LSU dot 2 dot 11 dot 1506230951200 dot 31770 at zhemvz dot fhfr dot qr> <20150623081350 dot GO10139 at redhat dot com>
On Tue, 23 Jun 2015, Marek Polacek wrote:
> On Tue, Jun 23, 2015 at 09:56:33AM +0200, Richard Biener wrote:
> > > I think you're right about TYPE_SATURATING so I've dropped that and instead
> > > replaced it with TYPE_OVERFLOW_TRAPS. That should do the right thing
> > > together with TYPE_OVERFLOW_SANITIZED.
> >
> > Are you sure? The point is that if the minus or the plus in the original
> > expression saturate the result isn't correct, no?
>
> Yes, but I thought that TYPE_SATURATING is only true for fixed-point, i.e.
> those _Accum/_Sat/_Fract (?), and you can't do bitwise & or | on them, which
> means that the TYPE_SATURATING check wouldn't be necessary.
Who says you can't do bitwise ops on them? I can't see that being
enforced in the GIMPLE checking in tree-cfg.c. Yes, there is no
such thing as a "saturating" bitwise and but bitwise and should
just work fine.
You can check with a arm cross what the C FE does when you use
bitwise ops but I believe the regular and/ior md patterns work
just fine (there are no special modes/registers but they seem
to be shared with regular registers, just special operations
are available).
Richard.
>
> > As said, removing TYPE_SATURATING doesn't sound correct. I'm not sure
> > about TYPE_OVERFLOW_TRAPS - we're certainly removing traps elsewhere
> > (look for the scarce use of this flag in fold-const.c and match.pd
> > where I only preserved those that were originally in fold-const.c).
> >
> > So, TYPE_OVERFLOW_TRAPS is your choice but TYPE_SATURATING is
> > required IMHO.
>
> Ok, I guess I'll add TYPE_SATURATING back, even though I'm not clear
> on that one, and commit.
>
> Thanks,
>
> Marek
>
>
--
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Dilip Upmanyu, Graham Norton, HRB 21284 (AG Nuernberg)