While writing some test cases, and some of the tests check for the result of a NaN.
I tried using
Assertion `std::isnan(x)' failed.
NaN != NaN
assert(x == x)
This is embarrassing.
The reason the compiler (GCC in this case) was optimising away the comparison and
false was because someone in my team had turned on
From the docs:
-ffast-math Sets -fno-math-errno, -funsafe-math-optimizations, -fno-trapping-math, -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans and fcx-limited-range. This option causes the preprocessor macro __FAST_MATH__ to be defined. This option should never be turned on by any -O option since it can result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions.
Notice the ending sentence -
-ffast-math is unsafe.