Re: Using POPCNT and other advanced bit manipulation instructions

Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> and we have defined pg_popcount64() like this:

> static int
> pg_popcount64_sse42(uint64 word)
> {
>     return __builtin_popcountl(word);
> }

That is clearly completely broken.


> If that's correct, then I think we need something like this patch.  But
> it makes me wonder whether we need a configure test for
> __builtin_popcountll() and friends.  I wonder if there's any compiler
> that implements __builtin_popcountl() but not __builtin_popcountll() ...
> and if not, then the test for __builtin_popcountl() should be removed,
> and have everything rely on the one for __builtin_popcount().

AFAICS, this is a gcc-ism, and it looks like they've probably had
all width variants for the same amount of time.  I'd take out the
test for __builtin_popcountl(), and assume that testing for
__builtin_popcount() is sufficient until proven differently.

            regards, tom lane