------- Comment #5 from steven at gcc dot gnu dot org 2010-01-28 10:17 -------
FWIW, DF rescanning runs with -g1 and not with -g0 because copy propagation
updates a debug_insn:
LOCAL COPY-PROP: Replacing reg 63 in insn 28 with reg 72
(insn 27 26 28 4 PR42889.c:7 (set (reg/v:SI 63 [ x ])
(reg:SI 72)) 47 {*movsi_1} (expr_list:REG_DEAD (reg:SI 72)
(nil)))
(debug_insn 28 27 29 4 PR42889.c:7 (var_location:SI x (reg:SI 72)) -1 (nil))
This clobbers the DF solution and triggers a re-run of all the DF problems. And
that, in turn, causes the extra DCE run.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42889
