https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60540
--- Comment #10 from Rich Felker <bugdal at aerifal dot cx> --- GCC can choose the behavior for any undefined behavior it wants, and GCC absolutely can make transformations based on behaviors it guarantees or that Annex F guarantees on targets for which it implements the requirements of Annex F. On this particular target, and on every target of any modern relevance, (float)16777217 has well-defined behavior. On ones with floating point environment (most/all hardfloat), it has side effects (inexact), so can't be elided without the flags to make gcc ignore those side effects.
