https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115576
--- Comment #5 from user202729 <user202729 at protonmail dot com> --- I think this can be resolved by implementing some code in combine.cc to replace: (set:TI (reg:TI 101) (zero_extend:TI (...:DI ...))) (set:DI (reg:DI ...) (subreg:DI (reg:TI 101) 8)) with (set:TI (reg:TI 101) (zero_extend:TI (...:DI ...))) (set:DI (reg:DI ...) (const_int 0)) This certainly is always an improvement, because 0 is simpler than extracting the subregister. After that, a few other passes of combine rescanning should be able to constant fold the 0 forward. Unfortunately, I don't know how to modify combine.cc or some other files to handle this pattern. Can anyone give a suggestion? (maybe add a define_peephole2 in common.md ? )
