Re: [FFmpeg-devel] [PATCH 1/2] avutil/intmath: use AV_HAS_BUILTIN to detect builtin availability

From: "Martin Storsjö" <martin@martin.st>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/2] avutil/intmath: use AV_HAS_BUILTIN to detect builtin availability
Date: Wed, 11 Jun 2025 21:44:59 +0300 (EEST)
Message-ID: <559dd37b-57b6-79f-57e-be9eafc024a5@martin.st> (raw)
In-Reply-To: <CABPLASTXiD8X-wZ3dTGDMC4trUT3PMaoQ3V9kMaE6p_ibRxcJQ@mail.gmail.com>

On Wed, 11 Jun 2025, Kacper Michajlow wrote:

> On Mon, 31 Mar 2025 at 14:03, Kacper Michajłow <kasper93@gmail.com> wrote:
>>
>> Fixes use of bultins on clang x86_64-pc-windows-msvc which does not
>> define any __GNUC__. Also on other targets __GNUC__ is defined to 4 by
>> default, so any feature testing based on version is not really valid.
>>
>> Signed-off-by: Kacper Michajłow <kasper93@gmail.com>
>> ---
>>  libavutil/intmath.h     | 12 +++++-------
>>  libavutil/x86/intmath.h |  4 ++--
>>  2 files changed, 7 insertions(+), 9 deletions(-)
>>
>> diff --git a/libavutil/intmath.h b/libavutil/intmath.h
>> index 52e11a8d5f..b177a848c6 100644
>> --- a/libavutil/intmath.h
>> +++ b/libavutil/intmath.h
>> @@ -35,7 +35,7 @@
>>  #endif
>>
>>  #if HAVE_FAST_CLZ
>> -#if AV_GCC_VERSION_AT_LEAST(3,4)
>> +#if AV_GCC_VERSION_AT_LEAST(3,4) || AV_HAS_BUILTIN(__builtin_clz)
>>  #ifndef ff_log2
>>  #   define ff_log2(x) (31 - __builtin_clz((x)|1))
>>  #   ifndef ff_log2_16bit
>> @@ -90,18 +90,16 @@ static av_always_inline av_const int ff_log2_16bit_c(unsigned int v)
>>   */
>>
>>  #if HAVE_FAST_CLZ
>> -#if AV_GCC_VERSION_AT_LEAST(3,4)
>> -#ifndef ff_ctz
>> +#if !defined(ff_ctz) && (AV_GCC_VERSION_AT_LEAST(3,4) || AV_HAS_BUILTIN(__builtin_ctz))
>>  #define ff_ctz(v) __builtin_ctz(v)
>>  #endif
>> -#ifndef ff_ctzll
>> +#if !defined(ff_ctzll) && (AV_GCC_VERSION_AT_LEAST(3,4) || AV_HAS_BUILTIN(__builtin_ctzll))
>>  #define ff_ctzll(v) __builtin_ctzll(v)
>>  #endif
>> -#ifndef ff_clz
>> +#if !defined(ff_clz) && (AV_GCC_VERSION_AT_LEAST(3,4) || AV_HAS_BUILTIN(__builtin_clz))
>>  #define ff_clz(v) __builtin_clz(v)
>>  #endif
>>  #endif
>> -#endif
>>
>>  #ifndef ff_ctz
>>  #define ff_ctz ff_ctz_c
>> @@ -154,7 +152,7 @@ static av_always_inline av_const unsigned ff_clz_c(unsigned x)
>>  }
>>  #endif
>>
>> -#if AV_GCC_VERSION_AT_LEAST(3,4)
>> +#if AV_GCC_VERSION_AT_LEAST(3,4) || AV_HAS_BUILTIN(__builtin_parity)
>>  #ifndef av_parity
>>  #define av_parity __builtin_parity
>>  #endif
>> diff --git a/libavutil/x86/intmath.h b/libavutil/x86/intmath.h
>> index 4893a1f1b4..030ded6b6f 100644
>> --- a/libavutil/x86/intmath.h
>> +++ b/libavutil/x86/intmath.h
>> @@ -66,7 +66,7 @@ static av_always_inline av_const int ff_ctzll_x86(long long v)
>>
>>  #endif /* HAVE_FAST_CLZ */
>>
>> -#if defined(__GNUC__)
>> +#if defined(__GNUC__) || defined(__clang__)
>>
>>  /* Our generic version of av_popcount is faster than GCC's built-in on
>>   * CPUs that don't support the popcnt instruction.
>> @@ -81,7 +81,7 @@ static av_always_inline av_const int ff_ctzll_x86(long long v)
>>
>>  #if defined(__BMI2__)
>>
>> -#if AV_GCC_VERSION_AT_LEAST(5,1)
>> +#if AV_GCC_VERSION_AT_LEAST(5,1) || AV_HAS_BUILTIN(__builtin_ia32_bzhi_si)
>>  #if defined(ASSERT_LEVEL) && ASSERT_LEVEL >= 2
>>  #define av_zero_extend av_zero_extend_bmi2
>>  static av_always_inline av_const unsigned av_zero_extend_bmi2(unsigned a, unsigned p)
>> --
>> 2.45.1
>>
>
> bump

Can you specify the symptoms that are fixed? Is there a specific build 
configuration that fails, or is it a case of using more optimal builtins 
where suitable? (Same goes for 2/2 probably.)

// Martin
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