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Re: nonnull, -Wnonnull, and do/while
- From: Marek Polacek <polacek at redhat dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Mark Wielaard <mjw at redhat dot com>, stefan dot sobernig at wu dot ac dot at, gcc at gcc dot gnu dot org
- Date: Tue, 16 Feb 2016 11:17:35 +0100
- Subject: Re: nonnull, -Wnonnull, and do/while
- Authentication-results: sourceware.org; auth=none
- References: <56C2EF2C dot 4050508 at thinkersfoot dot net> <20160216100438 dot GR3163 at redhat dot com> <20160216101121 dot GO3017 at tucnak dot redhat dot com>
On Tue, Feb 16, 2016 at 11:11:21AM +0100, Jakub Jelinek wrote:
> On Tue, Feb 16, 2016 at 11:04:38AM +0100, Marek Polacek wrote:
> > On Tue, Feb 16, 2016 at 10:43:08AM +0100, Stefan Sobernig wrote:
> > > Under a recent gcc 6 [*], we run into -Wnonnull warnings using the
> > > nonnull attribute:
> > Yes, this warning has been enhanced for GCC 6.
> > > test.c: In function 'f':
> > > test.c:16:14: warning: nonnull argument 's' compared to NULL [-Wnonnull]
> > > } while (s != NULL);
> > >
> > > Am I missing sth.? Is this a false positive?
> > Well, it's just that "s" has the nonnull attribute so the compiler thinks it
> > should never be null in which case comparing it to null should be redundant.
> > Doesn't seem like a false positive to me, but maybe someone else feels
> > otherwise.
> The nonnull attribute should be solely about the value that is passed to the
> function, it doesn't tell anything about the value of the argument after
> it is changed. So IMHO this warning change should be reverted and instead
> we should warn somewhere soon after going into SSA, only when
> the SSA_NAME_IS_DEFAULT_DEF of the PARM_DECL which has non-NULL attribute
> is compared to NULL.
In that case I take back what I wrote, sorry.