Re: [PATCH] Fix bootstrap failure (with g++ 4.8.5) in tree-if-conv.cc.

[Andrew Pinski <pinskia@gmail.com>]

On Mon, Jul 17, 2023 at 12:21 AM Tamar Christina via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> > -----Original Message-----
> > From: Richard Biener <richard.guenther@gmail.com>
> > Sent: Monday, July 17, 2023 7:19 AM
> > To: Roger Sayle <roger@nextmovesoftware.com>
> > Cc: gcc-patches@gcc.gnu.org; Tamar Christina <Tamar.Christina@arm.com>
> > Subject: Re: [PATCH] Fix bootstrap failure (with g++ 4.8.5) in tree-if-conv.cc.
> >
> > On Fri, Jul 14, 2023 at 8:56 PM Roger Sayle <roger@nextmovesoftware.com>
> > wrote:
> > >
> > >
> > >
> > > This patch fixes the bootstrap failure I'm seeing using gcc 4.8.5 as
> > >
> > > the host compiler.  Ok for mainline?  [I might be missing something]
> >
> > OK.   Btw, while I didn't spot this during review I would appreciate
> > if the code could use vec.[q]sort, this should work with a lambda as well I
> > think.
>
> That was my first use, but that hits https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99469

That is not hitting PR 99469 but rather it means your comparison is
not correct for an (unstable) sort.
That is qsort comparator should have this relationship `f(a,b) ==
!f(b, a)` and `f(a,a)` should also return false.
If you are running into this for qsort here, you will most likely run
into issues with std::sort later on too.

Thanks,
Andrew

>
> Regards,
> Tamar