[Bug tree-optimization/84407] incorrect constant propagation with -frounding-math

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84407

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
Cf. bug 57245 (a similar bug for truncation from wider floating-point 
types).