Add a signaling Nans rts option to ghc?

[Ben Gamari]

Carter Schonwald <carter.schonwald at gmail.com> writes:

> Hello All!
> I had some interesting conversations yesterday with a few folks and the
> take away was that I might experiment with adding an off by default rts
> flag that on applicable architectures that makes all floating point
> computations that yield Nans signaling , plus mayve some HS side hooks to
> enable or disable that per green thread if it doesn't harm no fib.  Kinda
> like the way green threads track and save / restore the state of the magic
> c error tracking variable
>
Sounds reasonable to me; debugging floating point issues is certainly a
chore and this could only help. Regarding a per-thread handling I think
we'd certainly need to benchmark. Note that rts/posix/Signals.c already has
some logic to handle SIGFPE, although it has been disabled for over a
decade due to an infinite loop where the handler immediately threw
another FPE. It would be nice to have a solution to this issue; looping
is quite bad.

Do you lump infinities into the class of NaN values? I'm not sure how
much code would fail due to "legitimate" uses of infinity if so.

Cheers,

- Ben
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