[Bug tree-optimization/121004] float_var*0.0f if we know a is either -0.0 or 0.0 can be just done as copysign(0.0, a)

[harald at gigawatt dot nl via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121004

--- Comment #3 from Harald van Dijk <harald at gigawatt dot nl> ---
I think comment #0's f could be optimised even more to just return a;