Who cares about performance (or Intel's CPU errata)?

[Stefan Kanthak]

Just to show how SLOPPY, INCONSEQUENTIAL and INCOMPETENT GCC's developers are:

--- dontcare.c ---
int ispowerof2(unsigned __int128 argument) {
    return __builtin_popcountll(argument) + __builtin_popcountll(argument >> 64) == 1;
}
--- EOF ---

GCC 13.3    gcc -march=haswell -O3

https://gcc.godbolt.org/z/PPzYsPzMc
ispowerof2(unsigned __int128):
        popcnt  rdi, rdi
        popcnt  rsi, rsi
        add     esi, edi
        xor     eax, eax
        cmp     esi, 1
        sete    al
        ret

OOPS: what about Intel's CPU errata regarding the false dependency on POPCNTs output?

See https://gcc.godbolt.org/z/jdjTc3EET for comparison!

FIX YOUR BUGS, KIDS!

Stefan