* dce.c (reset_unmarked_insns_debug_uses): New.
(delete_unmarked_insns): Skip debug insns.
(prescan_insns_for_dce): Likewise.
(rest_of_handle_ud_dce): Reset debug uses of removed sets.
* reg-stack.c (subst_stack_regs_in_debug_insn): Signal when no
active reg can be found.
(subst_all_stack_regs_in_debug_insn): New.  Reset debug insn then.
(convert_regs_1): Use it.

From-SVN: r174699