[Bug middle-end/93806] Wrong optimization: instability of floating-point results with -funsafe-math-optimizations leads to nonsense

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93806

--- Comment #9 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Alexander Cherepanov from comment #8)
> A similar problem happens with -fno-signed-zeros -fno-trapping-math. Not
> sure if a separate PR should be filed...

Concerning -fno-signed-zeros, your code has undefined behavior since the sign
of zero is significant in "1 / x == 1 / 0.", i.e. changing the sign of 0
changes the result. If you use this option, you are telling GCC that this
cannot be the case. Thus IMHO, this is not a bug.

I would say that -fno-trapping-math should have no effect because there are no
traps by default (for floating point). But since your code has undefined
behavior, this is not necessarily surprising.