> > What is that even supposed to mean?!
>
> It's a term used to describe a practice that shouldn't work but it does in practice because of an unanticipated obscure feature and nobody understand why.

You're using the term to describe basic compiler mechanisms like
register allocation and loading/storing from memory though, so I'm not
seeing how this makes any sense.

It's not that "unanticipated and obscure" that when you do
__builtin_compute_sha or something, it would load a _BitInt(384) from
memory into a register to perform that special operation. It's not any
different from loading an int from four bytes of memory into eax in
order to perform addition.

It's also not "unanticipated and obscure" that when _BitInt(384) is
the return type of a function, that the result is passed via the SHA
acceleration register or via the stack or something, depending on the
ABI. It's the same principle as passing an int via eax and passing
larger types like structs on the stack (or having an extra result
parameter that tells you the address of the returned object).