linux-kernel - Re: [PATCH 2/2] arm: lib: xor-neon: disable clang vectorization

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Message-ID: <20201112215033.GA438824@rani.riverdale.lan>
Date:   Thu, 12 Nov 2020 16:50:33 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Adrian Ratiu <adrian.ratiu@...labora.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Russell King <linux@...linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH 2/2] arm: lib: xor-neon: disable clang vectorization

On Wed, Nov 11, 2020 at 04:15:59PM +0200, Adrian Ratiu wrote:
> On Tue, 10 Nov 2020, Nick Desaulniers <ndesaulniers@...gle.com> 
> wrote:
> > 
> > Yes, though additionally Arvind points out that this code is 
> > kind of curious if there was overlap; maybe the parameters 
> > should just be restrict-qualified. 
> >
> 
> For now I think I'll just re-send the GCC changes and leave the 
> Clang optimization as is, until we better understand what's 
> happening and what's the best way to enable it.
> 

Note that the __restrict__ keywords also help GCC -- it saves it from
having to emit the non-vectorized version and switch between the two at
runtime. If we can verify it's safe, it's a good thing to add all
around.