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Subject: Re: [PATCH v2] lib/zlib_inflate/inffast: Check config in C to avoid
 unused function warning
To:     Paul Menzel <pmenzel@molgen.mpg.de>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>
Cc:     Zhen Lei <thunder.leizhen@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
References: <20210920074633.13089-1-pmenzel@molgen.mpg.de>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <00f8d7d7-cb13-203e-5a37-aee34a3258ff@csgroup.eu>
Date:   Mon, 20 Sep 2021 10:36:53 +0200
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Le 20/09/2021 à 09:46, Paul Menzel a écrit :
> Building Linux for ppc64le with Ubuntu clang version 12.0.0-3ubuntu1~21.04.1
> shows the warning below.
> 
>      arch/powerpc/boot/inffast.c:20:1: warning: unused function 'get_unaligned16' [-Wunused-function]
>      get_unaligned16(const unsigned short *p)
>      ^
>      1 warning generated.
> 
> Fix it, by moving the check from the preprocessor to C, so the compiler
> sees the use.
> 
> Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
> ---
>   lib/zlib_inflate/inffast.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/zlib_inflate/inffast.c b/lib/zlib_inflate/inffast.c
> index f19c4fbe1be7..fb87a3120f0f 100644
> --- a/lib/zlib_inflate/inffast.c
> +++ b/lib/zlib_inflate/inffast.c
> @@ -254,11 +254,8 @@ void inflate_fast(z_streamp strm, unsigned start)
>   			sfrom = (unsigned short *)(from);
>   			loops = len >> 1;
>   			do
> -#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> -			    *sout++ = *sfrom++;
> -#else
> -			    *sout++ = get_unaligned16(sfrom++);
> -#endif
> +			    *sout++ = IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ?
> +				*sfrom++ : get_unaligned16(sfrom++);

I think it would be more readable as

do {
         if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
                 *sout++ = *sfrom++;
         else
                 *sout++ = get_unaligned16(sfrom++);
} while (--loops);


>   			while (--loops);
>   			out = (unsigned char *)sout;
>   			from = (unsigned char *)sfrom;
>