Re: [PATCH] Cygwin: Make gcc-specific code in <sys/cpuset.h> compiler-agnostic

[Mark Geisert <mark@maxrnd.com>]

Brian Inglis wrote:
> On 2023-07-07 12:54, Brian Inglis wrote:
>> On 2023-07-07 03:44, Corinna Vinschen wrote:
>>> Hi Mark,
>>>
>>> On Jul  7 00:41, Mark Geisert wrote:
>>>> The current version of <sys/cpuset.h> cannot be compiled by Clang due to
>>>> the use of __builtin* functions.  Their presence here was a dubious
>>>> optimization anyway, so their usage has been converted to standard
>>>> library functions.  A popcnt (population count of 1 bits in a word)
>>>> function is provided here because there isn't one in the standard library
>>>> or elsewhere in the Cygwin DLL.
>>>
>>> And clang really doesn't provide it?  That's unfortunate.
>>>
>>> Do you really think it's not worth to use it if it's available?
>>>
>>> You could workaround it like this:
>>>
>>>> +/* Modern CPUs have popcnt* instructions but the need here is not worth
>>>> + * worrying about builtins or inline assembler for different compilers. */
>>>> +static inline int
>>>> +__maskpopcnt (__cpu_mask mask)
>>>> +{
>>> #if (__GNUC__ >= 4)
>>>       return __builtin_popcountl (mask);
> 
> Missed the difference in spelling, but clang supports the same builtin functions 
> __builtin_popcount{,l,ll} et. al. or provides *optimized* inline functions if not 
> directly available as an instruction on the architecture.

Clang in its current version 16.0.x has __builtin_popcount*, but not in the 
ancient version 8.0.1 that is currently packaged for Cygwin.  I think that's what 
was behind Jon's earlier comment that perhaps we should remove clang from Cygwin 
unless/until somebody can adopt and maintain an up-to-date version.  :-(.

..mark