https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91993
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Created attachment 47971 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47971&action=edit gcc10-pr91993-wip.patch As implemented in this completely untested (so far) patch, which makes the -Wconversion warning go away both in the case of comma operator with user side-effects as well as -fsanitize=undefined.
