That's the way a number of those special flags work. They are a contract to the compiler saying "act like this can't happen, I promise it won't".

The picking and choosing specific flags enable might be better in general. The flag `-funsafe-math-optimizations` seems to be useful as general-purpose, although as this article mentions, some of those optimizations need the more unsafe ones to become active.

I would say that `-ffast-math` is a dangerously safe-sounding flag, `-funsafe-fast-math` would be better IMO.