------- Comment #12 from hp at gcc dot gnu dot org 2009-05-13 13:09 ------- The relax_delay_slots (first) call finds that there's a branch to a redundant insn that it can eliminate. It does this by redirecting the branch to a new or existing label and deleting the insn, or rather move it and make it a USE-mark at the "new" label. When doing this, the old USE-mark quoted above (not related to the new USE-mark by other means being before it in the execution path) is now deemed unreachable and removed by jump.c:delete_related_insns. So, it seems a solution will include propagating existing USE-marks when redirecting branch labels, perhaps in reorg_redirect_jump or update_block.
-- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40086
