Re: Using POPCNT and other advanced bit manipulation instructions

On Thu, Feb 14, 2019 at 4:38 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> And, while I'm complaining: why the devil is use of the compiler builtins
> gated by HAVE__GET_CPUID? This is unbelievably Intel-centric, because
> it prevents use of the builtins on other architectures. If the builtin
> exists, we should use it, full stop. There's no reason to expect that it
> would be slower than hand-rolled code, regardless of the architecture.

FWIW a quick test of __builtin_popcount(n) compiles as CNT on a Debian
ARM system, without any special compiler flags.

> I'd be inclined to rip out all of the run-time-detection logic here;
> I doubt any of it is buying anything that's worth the price of an
> indirect call.

No view on that but apparently there were Intel Atom and AMD C chips
sold in the early part of this decade that lack POPCNT so I suspect
the distros can't ship software that requires it with no fallback.

--
Thomas Munro
http://www.enterprisedb.com