Re: Extended doubt regarding the bug 93432

[Krishna Narayanan <krishnanarayanan132002@gmail.com>]

Yes Sir,
 I will go through the dump from uninit pass with required optimizations.I
will try the tree-ssa-uninit.cc on gdb.
Thanks and Regards,
Krishna Narayanan.


On Wed, Feb 9, 2022 at 3:20 AM Martin Sebor <msebor@gmail.com> wrote:

> On 2/8/22 10:37, Jonathan Wakely via Gcc-help wrote:
> > On Tue, 8 Feb 2022 at 17:18, Krishna Narayanan <
> > krishnanarayanan132002@gmail.com> wrote:
> >
> >> Thanks for your response,Could you please clarify if this is a bug?
> >>
> >
> > It warns with -O1, which is the documented behaviour:
> >
> >        The effectiveness of some warnings depends on optimizations also
> > being enabled. For example -Wsuggest-final-types is more
> >        effective with link-time optimization and -Wmaybe-uninitialized
> does
> > not warn at all unless optimization is enabled.
>
> Yes, although the latter sentence is no longer completely accurate.
> Since GCC 11 -Wmaybe-uninitialized doesn't need optimization to trigger
> for code that passes an uninitialized object to a function that takes
> a const reference.  Let me update the manual with that.
>
> > So no, I don't think it' a bug. GCC is behaving as designed. Ideally it
> > would be better at warning without optimization, but changing that would
> be
> > hard.
>
> It might be tricky to handle this case without causing false positives
> in others.
>
> Krishna, to understand why some of these cases are diagnosed and others
> aren't, you need to look at either the dump from the uninit pass
> (-fdump-tree-uninit) with -O1 and above, or at some early dump (e.g.,
> -fdump-tree-ssa) at -O0.  Here's a link to the former on Godbolt for
> your example:
>
>    https://gcc.godbolt.org/z/89c4s7o6E
>
> The best way is of course to step through GCC in a debugger (for
> the uninitialized warnings the code is in gcc/tree-ssa-uninit.cc).
>
> Martin
>
> >
> >
> >
> >
> >
> >> Regards,
> >> Krishna Narayanan.
> >>
> >> On Tue, Feb 8, 2022 at 10:28 PM Jonathan Wakely <jwakely.gcc@gmail.com>
> >> wrote:
> >>
> >>>
> >>>
> >>> On Tue, 8 Feb 2022 at 16:25, Krishna Narayanan via Gcc-help <
> >>> gcc-help@gcc.gnu.org> wrote:
> >>>
> >>>> Hello,
> >>>> As an extension to the bug 93432
> >>>> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93432), I would like to
> >>>> add a few more points,here in the given code
> >>>> (https://godbolt.org/z/sYjqjqh3d) there is a warning averted but
> there
> >>>> is no warning shown for this code
> >>>> (https://gcc.godbolt.org/z/oo5sf4oec) .
> >>>> I tried it with "-fno-strict-aliasing -fwrapv
> >>>> -fno-aggressive-loop-optimizations" and "fsanitize=undefined".There
> >>>> are no errors for gcc but clang has runtime errors,the error for
> >>>> clang: https://gcc.godbolt.org/z/1hq8x1o8E .
> >>>>
> >>>> Can we have a warning in the second case as well? It will be much more
> >>>> convenient as there is a lapse of initialization.
> >>>>
> >>>
> >>> Yes, ideally it would warn.
> >>>
> >>>
> >>>
> >>
>
>