[Bug tree-optimization/37242] missed FRE opportunity because of signedness of addition

[dimhen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37242

--- Comment #24 from Dmitry G. Dyachenko <dimhen at gmail dot com> ---
r257061 optimize too

gcc version 8.0.1 20180125 (experimental) [trunk revision 257061] (GCC)