linux-kernel - Re: [PATCH] powerpc: workaround clang codegen bug in dcbz

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Date:   Mon, 29 Jul 2019 13:49:11 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Arnd Bergmann <arnd@...db.de>,
        kbuild test robot <lkp@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] powerpc: workaround clang codegen bug in dcbz

On Mon, Jul 29, 2019 at 1:47 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Mon, Jul 29, 2019 at 01:45:35PM -0700, Nick Desaulniers wrote:
> > On Mon, Jul 29, 2019 at 1:32 PM Nathan Chancellor
> > <natechancellor@...il.com> wrote:
> > >
> > > On Mon, Jul 29, 2019 at 01:25:41PM -0700, Nick Desaulniers wrote:
> > > > But I'm not sure how the inlined code generated would be affected.
> > >
> > > For the record:
> > >
> > > https://godbolt.org/z/z57VU7
> > >
> > > This seems consistent with what Michael found so I don't think a revert
> > > is entirely unreasonable.
> >
> > Thanks for debugging/reporting/testing and the Godbolt link which
> > clearly shows that the codegen for out of line versions is no
> > different.  The case I can't comment on is what happens when those
> > `static inline` functions get inlined (maybe the original patch
> > improves those cases?).
> > --
> > Thanks,
> > ~Nick Desaulniers
>
> I'll try to build with various versions of GCC and compare the
> disassembly of the one problematic location that I found and see
> what it looks like.

Also, guess I should have included the tag:
Fixes: 6c5875843b87 ("powerpc: slightly improve cache helpers")
-- 
Thanks,
~Nick Desaulniers