[Bug middle-end/82479] missing popcount builtin detection

[kugan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82479

--- Comment #1 from kugan at gcc dot gnu.org ---
gcc trunk generates:
PopCount:
        mov     w2, 0
        cbz     x0, .L1
        .p2align 3
.L3:
        sub     x1, x0, #1
        add     w2, w2, 1
        ands    x0, x0, x1
        bne     .L3
.L1:
        mov     w0, w2
        ret