Re: Invalid control file checksum with AVX-512 during initdb on a clang19 -O0 build - Mailing list pgsql-bugs
On Wed, Jun 11, 2025 at 11:57PM John Naylor <johncnaylorls@gmail.com> wrote:
>
> On Thu, Jun 12, 2025 at 4:42AM Nathan Bossart <nathandbossart@gmail.com> wrote:
> >
> > (I've CC'd the committer of the feature.)
> >
> > On Wed, Jun 11, 2025 at 11:10:31AM -0700, Soumyadeep Chakraborty wrote:
> > > Note that this only reproduces with clang-19 -O0 and NOT -O3. I haven't
> > > tried with other versions of clang.
> > >
> > > OTOH, gcc-14 is cool with both -O0 and -O3, with AVX-512 getting picked
> > > for both cases, for CRC instructions.
> >
> > I'm wondering if there's anything else this could be besides a compiler
> > bug. It's interesting that -O0 is the broken case. Have you tried looking
> > for differences in the assembly code?
Unfortunately, I haven't had a chance to dig into the assembly yet.
>
> Hmm, clang at -O0 is the same in versions 18, 19, and 20. The change
> from v17 is easy enough to workaround as in the attached, which
> produces identical output as master at -O2. Does this fix it for you?
> If that's not it, it may be more difficult, as the change at -O0 from
> v16 to v17 is large, so it's hard to see what's going on.
>
It unfortunately doesn't. I still get the same checksum failure. I tried
-O0 clang-19, clang-18 and clang-17. I've uploaded the rr recordings
and initdb output with your patch applied and the debug logs I had.
Regards,
Deep
>
> On Thu, Jun 12, 2025 at 4:42AM Nathan Bossart <nathandbossart@gmail.com> wrote:
> >
> > (I've CC'd the committer of the feature.)
> >
> > On Wed, Jun 11, 2025 at 11:10:31AM -0700, Soumyadeep Chakraborty wrote:
> > > Note that this only reproduces with clang-19 -O0 and NOT -O3. I haven't
> > > tried with other versions of clang.
> > >
> > > OTOH, gcc-14 is cool with both -O0 and -O3, with AVX-512 getting picked
> > > for both cases, for CRC instructions.
> >
> > I'm wondering if there's anything else this could be besides a compiler
> > bug. It's interesting that -O0 is the broken case. Have you tried looking
> > for differences in the assembly code?
Unfortunately, I haven't had a chance to dig into the assembly yet.
>
> Hmm, clang at -O0 is the same in versions 18, 19, and 20. The change
> from v17 is easy enough to workaround as in the attached, which
> produces identical output as master at -O2. Does this fix it for you?
> If that's not it, it may be more difficult, as the change at -O0 from
> v16 to v17 is large, so it's hard to see what's going on.
>
It unfortunately doesn't. I still get the same checksum failure. I tried
-O0 clang-19, clang-18 and clang-17. I've uploaded the rr recordings
and initdb output with your patch applied and the debug logs I had.
Regards,
Deep
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