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Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
From: |
Ian Lance Taylor |
Subject: |
Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..." |
Date: |
31 Dec 2006 18:11:50 -0800 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.4 |
address@hidden (Richard Kenner) writes:
> > > > Note that -fwrapv also _enables_ some transformations on signed
> > > > integers that are disabled otherwise. We for example constant fold
> > > > -CST for -fwrapv while we do not if signed overflow is undefined.
> > > > Would you change those?
> > >
> > > I don't understand the rationale for not wrapping constant folding when
> > > signed overflow is undefined: what's the harm in "defining" it as wrapping
> > > for that purpose? If it's undefined, then why does it matter what we
> > > fold it to? So we might as well fold it to what traditional code expects.
> >
> > If flag_wrapv is false, we can't do any optimization which may
> > introduce signed overflow when it did not already exist.
>
> But how would that happen here? If we constant-fold something that would
> have overflowed by wrapping, we are ELIMINATING a signed overflow, not
> INTRODUCING one. Or do I misunderstand what folding we're talking about here?
http://gcc.gnu.org/PR27116 is what led to the patch.
Ian
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", (continued)
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Ian Lance Taylor, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Seongbae Park, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Paul Eggert, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Robert Dewar, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Guenther, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Guenther, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Ian Lance Taylor, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...",
Ian Lance Taylor <=
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- RE: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Dave Korn, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Karl Berry, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Bruce Korb, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Robert Dewar, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Paul Eggert, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Ian Lance Taylor, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Daniel Berlin, 2006/12/31