------- Comment #6 from rguenth at gcc dot gnu dot org 2010-01-28 11:05 -------
(In reply to comment #5)
> 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.
Ugh. It shouldn't trigger a DCE run at least. I guess it has to trigger
a re-run of the DF problems though.
I guess similar things could happen on the tree-level with scheduling
of cleanup_cfg after something changed. Double-ugh.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42889
