[FFmpeg-devel] [PATCH] x86/intmath: allow the source operand for icc/icl ff_ctzll to be a memory location

[Ganesh Ajjanagadde]

On Sat, Oct 24, 2015 at 7:03 PM, James Almer <jamrial at gmail.com> wrote:
> On 10/24/2015 7:48 PM, Ganesh Ajjanagadde wrote:
>> On Sat, Oct 24, 2015 at 6:08 PM, James Almer <jamrial at gmail.com> wrote:
>>> This gives the compiler some flexibility
>>>
>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>> ---
>>>  libavutil/x86/intmath.h | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavutil/x86/intmath.h b/libavutil/x86/intmath.h
>>> index 7881e3c..10d3e7f 100644
>>> --- a/libavutil/x86/intmath.h
>>> +++ b/libavutil/x86/intmath.h
>>> @@ -36,7 +36,7 @@ static av_always_inline av_const int ff_ctzll_x86(long long v)
>>>  {
>>>  #   if ARCH_X86_64
>>>      uint64_t c;
>>> -    __asm__("bsfq %1,%0" : "=r" (c) : "r" (v));
>>> +    __asm__ ("bsfq %1,%0" : "=r" (c) : "rm" (v));
>>>      return c;
>>>  #   else
>>>      return ((uint32_t)v == 0) ? _bit_scan_forward((uint32_t)(v >> 32)) + 32 : _bit_scan_forward((uint32_t)v);
>>> --
>>> 2.6.2
>>
>> This question may be silly, but can you clarify when this asm code is
>> used instead of __builtin_ctzll? For instance, I think on GNU/Linux,
>> x86-64, sufficiently modern GCC (even with asm enabled), we should
>> always use the builtin: the compiler knows best what to do with its
>> builtin.
>
> This is ICC/ICL, not GCC.

Ah, now I recall that _bit_scan_forward64 was not always available on
ICC. Anyway, this is just a heads up to whoever uses ICC/ICL and the
like: you may want to find out to which versions this built in
applies.

>
>
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