svn commit: r278474 - head/sys/sys

[Jung-uk Kim]

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On 02/09/2015 16:55, Jung-uk Kim wrote:
> On 02/09/2015 16:08, John Baldwin wrote:
>> On Monday, February 09, 2015 09:03:24 PM John Baldwin wrote:
>>> Author: jhb Date: Mon Feb  9 21:03:23 2015 New Revision:
>>> 278474 URL: https://svnweb.freebsd.org/changeset/base/278474
>>> 
>>> Log: Use __builtin_popcnt() to implement a BIT_COUNT() 
>>> operation for bitsets and use this to implement CPU_COUNT() to 
>>> count the number of CPUs in a cpuset.
>>> 
>>> MFC after:	2 weeks
> 
>> Yes, __builtin_popcnt() works with GCC 4.2.  It should also
>> allow the compiler to DTRT in userland uses of this if -msse4.2
>> is enabled.
> 
> Back in 2012, when I submitted a similar patch, bde noted 
> __builtin_popcount*() cannot be used with GCC 4.2 for *kernel* 
> because it emits a library call.
> 
> http://docs.freebsd.org/cgi/mid.cgi?20121116171923.L1135

BTW, __POPCNT__ macro may be used to detect availability of POPCNT
instruction when compiled with Clang.

Jung-uk Kim
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