Re: [PATCH 2/2] fix clang -Wtautological-compare with unsigned enum
- From
John Keeping <john@keeping.me.uk>
- Date
- Jan 17, 2013, 11:00 UTC
- Message-ID
- <20130117110008.GD4574@serenity.lan>
- In-Reply-To
- <CALWbr2wk+78zxGKCo-hCOwMuMOzdGspYvMu7PA6o0OYM3Y3m4A@mail.gmail.com>
On Thu, Jan 17, 2013 at 11:32:39AM +0100, Antoine Pelisse wrote:
> John, could you confirm that you trigger the -Wtautological-compare > warning with your version of clang ?
Yes, the warning is still there with both 3.2 and a recent trunk build but this patch squelches it.
> And that this patch makes clang compilation warning-free (with the > very latest clang) ?
There is one remaining warning on pu which hasn't been discussed in this thread as far as I can see. I'll send a patch shortly.
There's also a warning that triggers with clang 3.2 but not clang trunk, which I think is a legitimate warning - perhaps someone who understands integer type promotion better than me can explain why the code is OK (patch->score is declared as 'int'):
builtin/apply.c:1044:47: warning: comparison of constant 18446744073709551615
with expression of type 'int' is always false
[-Wtautological-constant-out-of-range-compare]
if ((patch->score = strtoul(line, NULL, 10)) == ULONG_MAX)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~Show 53 quoted lines
> On Wed, Jan 16, 2013 at 11:47 PM, Antoine Pelisse <apelisse@gmail.com> wrote:
> > Create a GREP_HEADER_FIELD_MIN so we can check that the field value is
> > sane and silent the clang warning.
> >
> > Clang warning happens because the enum is unsigned (this is
> > implementation-defined, and there is no negative fields) and the check
> > is then tautological.
> >
> > Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
> > ---
> > I tried to consider discussion [1] and this [2] discussion on clang's list
> >
> > With these two patches and the patch from Max Horne, I'm finally able to
> > compile with CC=clang CFLAGS=-Werror.
> >
> > [1]: http://thread.gmane.org/gmane.comp.version-control.git/184908
> > [2]: http://clang-developers.42468.n3.nabble.com/Possibly-invalid-enum-tautology-warning-td3233140.html
> >
> > grep.c | 3 ++-
> > grep.h | 3 ++-
> > 2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/grep.c b/grep.c
> > index 4bd1b8b..bb548ca 100644
> > --- a/grep.c
> > +++ b/grep.c
> > @@ -625,7 +625,8 @@ static struct grep_expr *prep_header_patterns(struct grep_opt *opt)
> > for (p = opt->header_list; p; p = p->next) {
> > if (p->token != GREP_PATTERN_HEAD)
> > die("bug: a non-header pattern in grep header list.");
> > - if (p->field < 0 || GREP_HEADER_FIELD_MAX <= p->field)
> > + if (p->field < GREP_HEADER_FIELD_MIN ||
> > + GREP_HEADER_FIELD_MAX <= p->field)
> > die("bug: unknown header field %d", p->field);
> > compile_regexp(p, opt);
> > }
> > diff --git a/grep.h b/grep.h
> > index 8fc854f..e4a1df5 100644
> > --- a/grep.h
> > +++ b/grep.h
> > @@ -28,7 +28,8 @@ enum grep_context {
> > };
> >
> > enum grep_header_field {
> > - GREP_HEADER_AUTHOR = 0,
> > + GREP_HEADER_FIELD_MIN = 0,
> > + GREP_HEADER_AUTHOR = GREP_HEADER_FIELD_MIN,
> > GREP_HEADER_COMMITTER,
> > GREP_HEADER_REFLOG,
> >
> > --
> > 1.8.1.1.435.g20d29be.dirty
> >