[nsajko]

The relevant GCC man page entries are even more clear than the OpenCL spec excerpt.

-ffast-math:

> This option is not turned on by any -O option besides -Ofast since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions.

It also point to the -funsafe-math-optimizations sub-option, where it is said that:

> Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards. When used at link time, it may include libraries or startup files that change the default FPU control word or other similar optimizations. [...]