Test with an lto-build of libgfortran.

[Andrew Pinski]

On Wed, Sep 27, 2023 at 11:28 PM Richard Biener via Fortran
<fortran@gcc.gnu.org> wrote:
>
> On Wed, Sep 27, 2023 at 11:48 PM Jeff Law via Fortran
> <fortran@gcc.gnu.org> wrote:
> >
> >
> >
> > On 9/27/23 12:21, Toon Moene wrote:
> >
> > >
> > > The lto-ing of libgfortran did succeed, because I did get a new warning:
> > >
> > > gfortran -O3 -flto -flto-partition=none -static  -o xlintstrfz zchkrfp.o
> > > zdrvrfp.o zdrvrf1.o zdrvrf2.o zdrvrf3.o zdrvrf4.o zerrrfp.o zlatb4.o
> > > zlaipd.o zlarhs.o zsbmv.o zget04.o zpot01.o zpot03.o zpot02.o chkxer.o
> > > xerbla.o alaerh.o aladhd.o alahd.o alasvm.o ../../libtmglib.a
> > > ../../liblapack.a ../../librefblas.a
> > > In function 'xtoa_big',
> > >      inlined from 'write_z' at
> > > /home/toon/compilers/gcc/libgfortran/io/write.c:1296:11,
> > >      inlined from 'formatted_transfer_scalar_write' at
> > > /home/toon/compilers/gcc/libgfortran/io/transfer.c:2136:4:
> > > /home/toon/compilers/gcc/libgfortran/io/write.c:1222:6: warning: writing
> > > 1 byte into a region of size 0 [-Wstringop-overflow=]
> > >   1222 |   *q = '\0';
> > >        |      ^
> > > /home/toon/compilers/gcc/libgfortran/io/write.c: In function
> > > 'formatted_transfer_scalar_write':
> > > /home/toon/compilers/gcc/libgfortran/io/write.c:1291:8: note: at offset
> > > [34, 4294967294] into destination object 'itoa_buf' of size 33
> > >   1291 |   char itoa_buf[GFC_XTOA_BUF_SIZE];
> > >        |        ^
> > >
> > > which was (of course) not given with a non-lto libgfortran.
> > Yea.  This certainly can happen with LTO.  These warnings would
> > definitely be something worth investigating.
> >
> > Essentially the inlining enabled by LTO can expose a different set of
> > diagnostics.
>
> This particular place in libgfortran has
>
>   /* write_z, which calls xtoa_big, is called from transfer.c,
>      formatted_transfer_scalar_write.  There it is passed the kind as
>      argument, which means a maximum of 16.  The buffer is large
>      enough, but the compiler does not know that, so shut up the
>      warning here.  */
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wstringop-overflow"
>   *q = '\0';
> #pragma GCC diagnostic pop
>
> so obviously the #pragma doesn't survive through LTO.  Somehow I think
> this is a known bug, but maybe I misremember (I think we are not streaming
> any of the ad-hoc location parts).

Yes it is a known bug.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80922 .

Thanks,
Andrew


>
> Richard.
>
> >
> > Jeff