Windows breakage -- again

[Johan Tibell]

On Thu, Jul 17, 2014 at 12:23 AM, Páli Gábor János <pali.gabor at gmail.com> wrote:
> 2014-07-16 23:56 GMT+02:00 Johan Tibell <johan.tibell at gmail.com>:
>> My reading of the docs was that if the platform doesn't support the needed
>> instructions then GCC will generated a call to e.g. __sync_fetch_and_add_1,
>> where that function *is provided by GCC* as a fallback.
>
> I guess GCC would expect that somebody else will implement the given
> functionality by an external function.
>
>> Now I'm wondering if I'm supposed to supply that fallback.
>
> I was told that you cannot reliably emulate those operations in user
> mode, without loss in performance.

I think loss on performance is OK on i386, but not loss of
correctness. In my mind we have 3 options:

 1. Raise a compile time error saying that these operations aren't
supported on your platform (somewhat hard to detect as it depends on
GCC).
 2. Raise a runtime error saying the same (easy to detect, just raise
from the fallback functions).
 3. Provide some fallback.

I don't know how to do (3), but it seems like the best option if possible.