Add a signaling Nans rts option to ghc?
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 Would this be something folks would be open to adding once I hack it out? Most modern CPUs have some built in support for this, but having better rts integration might make things way nicer. Plus part of the point of the sheer diversity of Nans as per the IEEE report is to encode the nature of the source of the nan error. (There are other parts of IEEE that I think should be ignored / we should change the behavior in a way that disagrees with IEEE choices that hinder debugging and such )
Carter Schonwald
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
Count me in as interested, I'd appreciate a feature to notice accidental NaNs in my code.
participants (3)
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Ben Gamari -
Carter Schonwald -
Niklas Hambüchen