linux-kernel - Re: [PATCH v2] lib/zlib_inflate/inffast: Check config in C to avoid unused function warning

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Message-ID: <dcae41fe-b09b-eb0c-f518-f49e2ea36aa8@molgen.mpg.de>
Date:   Mon, 20 Sep 2021 10:47:28 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2] lib/zlib_inflate/inffast: Check config in C to avoid
 unused function warning

Dear Christophe,


Thank you for the review.

Am 20.09.21 um 10:36 schrieb Christophe Leroy:
> 
> 
> 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@...gen.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);

I prefer the ternary operator, as it’s less lines, and it’s clear, that 
only the variable assignment is affected by the condition. But as style 
is subjective, I sent v3.

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


Kind regards,

Paul