[Bug rtl-optimization/42889] [4.5 Regression] "-fcompare-debug failure (length)" with "-O1 -fgcse"

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- 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
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                 CC|                            |rguenth at gcc dot gnu dot
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42889