[simonbyrne]

My point isn't that fast-math isn't useful: it very much is. The problem is that it is a whole grab bag of things that can do very dangerous things. Rather than using a sledgehammer, you should try to be selective and enable only the useful optimizations, e.g. you could just enable -ffp-contract=fast and -fno-math-errno.

[djmips]

One thing I don't think you pointed out is that tracking down issues with NaNs seems hard with fast-math since, I believe, it also disables any exceptions that might be useful to being alerted to their formation?