https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78685
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> --- If -Og does not force user variables/parameters to stack nor forces an artificial use of the var at the end of their scope, then it will always happen, the rest is purely best effort, see if the var value can be computed from something else and punt if it can't. The problem is mainly register allocation, if the var is seen by RA as dead after certain point, then the RA doesn't try to keep it alive in some register or memory. In particular on this testcase, DW_OP_GNU_entry_value is emitted (as last resort) for the count variable, and similarly for argc in main (again, it isn't used after the function call). So, in this particular case it might help if glibc tried to provide better debug info for __libc_start_main and/or _start (if the argc and/or argv values can be easily computed; though, e.g. computing argc from argv array might not be correct, because main could have changed it). For the potential -Og change to be more useful, it would mean adding some artificial stmts at the end of scope of user vars (e.g. where we poison vars for -fsanitize-user-after-scope) that would not expand into a real assembly insn(s), but something like (use (var)) and would convince the RA to keep them alive somewhere.
