https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99767
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- Note for quite some of the failed-DCE PRs we could "fix up" at RTL expansion time by teaching rewrite_out_of_ssa to DCE all zero-use defs where it already does /* Eliminate PHIs which are of no use, such as virtual or dead phis. */ eliminate_useless_phis (); for example by walking all SSA names and seeding a bitmap for simple_dce_from_worklist.
