linux-kernel - Re: [PATCH] crypto: blake2b - Fix clang optimization for ARMv7-M

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Message-ID: <20200509014330.GA2153306@ubuntu-s3-xlarge-x86>
Date:   Fri, 8 May 2020 18:43:30 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        David Sterba <dsterba@...e.com>,
        Horia Geantă <horia.geanta@....com>,
        Eric Biggers <ebiggers@...gle.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] crypto: blake2b - Fix clang optimization for ARMv7-M

On Fri, May 08, 2020 at 11:31:07PM +0200, Arnd Bergmann wrote:
> On Wed, May 6, 2020 at 7:12 AM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> > > -
> > > +#ifdef CONFIG_CC_IS_CLANG
> >
> > Given your comment in the bug:
> >
> > "The code is written to assume no loops are unrolled"
> >
> > Does it make sense to make this unconditional and take compiler
> > heuristics out of it?
> >
> > > +#pragma nounroll /* https://bugs.llvm.org/show_bug.cgi?id=45803 */
> > > +#endif
> > >       for (i = 0; i < 8; ++i)
> > >               S->h[i] = S->h[i] ^ v[i] ^ v[i + 8];
> 
> No, that would not work, as gcc does not support this pragma.
> 
>         Arnd

Ah fair enough.

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>