linux-kernel - Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC

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Message-ID: <CAKwvOdkicQtiY13ey7uUgF9PsHGMYQbaWzYTUcY7GhYWL=xb3w@mail.gmail.com>
Date:   Tue, 19 Jan 2021 14:05:30 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Adrian Ratiu <adrian.ratiu@...labora.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "kernel@...labora.com" <kernel@...labora.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning

On Tue, Jan 19, 2021 at 2:04 PM David Laight <David.Laight@...lab.com> wrote:
>
> From: Adrian Ratiu
> > Sent: 19 January 2021 13:17
> > To: linux-arm-kernel@...ts.infradead.org
> >
> > Drop warning because kernel now requires GCC >= v4.9 after
> > commit 6ec4476ac825 ("Raise gcc version requirement to 4.9")
> > and clarify that -ftree-vectorize now always needs enabling
> > for GCC by directly testing the presence of CONFIG_CC_IS_GCC.
> ...
> > -#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
> > +#ifdef CONFIG_CC_IS_GCC
> >  #pragma GCC optimize "tree-vectorize"
> > -#else
>
> I thought that #pragma optimise was very likely to remove
> a random subset of the command line parameters leading to
> incorrect/unexpected code.
>
> As such the extra option needs to passed in as a per source
> file compiler option.

Yes, patch 2 in the series removes it from .c source, and passes
-ftree-vectorize during Kbuild.

>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>


-- 
Thanks,
~Nick Desaulniers