Re: [RFC PATCH] x86/hweight: Get rid of the special calling convention

[H. Peter Anvin]

On 05/04/2016 12:31 PM, Brian Gerst wrote:
>>
>> -       asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT)
>> -                    : "="REG_OUT (res)
>> -                    : REG_IN (w));
>> +       if (likely(static_cpu_has(X86_FEATURE_POPCNT))) {
>> +               asm volatile("popcnt %[w], %[res]" : [res] "=r" (res) : [w] "r" (w));
> 
> Do all supported versions of the assembler know of the popcnt
> instruction?  That's why is was open coded before.  The problem is
> Intel and AMD are constantly adding new instructions and it's a long
> cycle for the user's assembler to get updated.
> 

Most likely not.  It would be nice to have some more uniform solution to
that.  I'm wondering if we could use the -Wa option to load some kind of
macro package.

	-hpa