[Bug middle-end/125817] __builtin_popcountg() doesn't work for large _BitInt()

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125817

Drea Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED
          Component|c                           |middle-end

--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
This union:

union ln {
        unsigned _BitInt(256)  ln;
        unsigned _BitInt(1)    e[256];
};

Does not do what you think it does.

`unsigned _BitInt(1)` has 7bit padding.
So when you do:

        l.e[5] = true;
        l.e[4] = true;
        l.e[2] = true;
        l.e[7] = true;
        l.e[20] = true;
        l.e[30] = true;
        l.e[60] = true;
        l.e[77] = true;

It does not set bit 6, 4,2, etc. but rather 5*8, 4*8, 2*8, etc. bit of the
whole union.