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List:       gcc-bugs
Subject:    [Bug rtl-optimization/27883] [4.0/4.1 regression] in schedule_insns, at sched-rgn.c:3038 on mips
From:       "amylaar at gcc dot gnu dot org" <gcc-bugzilla () gcc ! gnu ! org>
Date:       2006-10-31 14:34:52
Message-ID: 20061031143452.3379.qmail () sourceware ! org
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------- Comment #17 from amylaar at gcc dot gnu dot org  2006-10-31 14:34 -------
(In reply to comment #4)
> It is curious that life2 is running immediately before sched, instead of
> immediately after combine.  If we ran it immediately after combine, we could
> get rid of the REG_DEAD/REG_UNUSED support in distribute_notes, which is
> probably the most complicated, and most buggy, part of combine.  This would
> also speed up the compiler a little bit.

The combiner itself relies on REG_DEAD notes to find out what it can combine.
If you leave an invalid REG_DEAD note, it can lead to wrong code being emitted.
If you don't leave in valid REG_DEAD notes in their proper place, multi-step
instruction combinations will stop working - and with the three insn limit on
any single combination, this is likely to stop quite a lot of combinations.
Most combiner bridge patterns will become useless.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27883

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