@gribozavr: in response to the above:

* it's not because we explicitly list `-fno-X` flags for `strict` and `precise` that we expect things to be different than `defaultprec`. It just makes this robust against changes in the default (which I don't expect to happen here, but fine).
* the help for `-ffast-math` mentions "has no effect on optimizations" (only enabled `-D__FAST_MATH_`), while the other flags used in `loose` and `veryloose` explicitly mention to have effect on optimisations...

With GCC, just using `-ffast-math` will do the trick (and we probably should do that in `gcc.py`), but from Clang's documentation I understand the `-ffast-math` flag has a different meaning for Clang specifically...