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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/38785] huge performance regression on EEMBC bitmnp01
Date: Wed, 14 Jan 2009 20:51:00 -0000 [thread overview]
Message-ID: <20090114205113.5787.qmail@sourceware.org> (raw)
In-Reply-To: <bug-38785-5394@http.gcc.gnu.org/bugzilla/>
------- Comment #10 from rguenther at suse dot de 2009-01-14 20:51 -------
Subject: Re: huge performance regression on
EEMBC bitmnp01
On Wed, 14 Jan 2009, amylaar at gcc dot gnu dot org wrote:
> I think the disregard for conditional execution opportunities and the
> assumption that phi nodes have no execution cost are two separate issues.
> I'd like to address the latter first, because it causes exponential code and
> execution time growth.
>
> A phi node joining two constants has at least the cost of a constant load.
> A phi node joining two different variables which are initialized by a graph
> with constant leafs costs at least a reg-reg copy on one arm, plus the cost
> of its parents if these are needed solely for this phi node.
>
> Therefore, if an expression is only partially anticipatable, we should compare
> the cost of any phi node needed to compute it early with the estimated
> likelyhod that such a computatatio, once done, is actually needed, multiplied
> with the cost of the replaced operation.
>
> Can we use edge probabilities inside tree-pre to calculate execution
> probabilities?
>
> Can we calculate the cost of replaced expressions?
You would completely underestimate the optimization opportunities PRE
unleashes.
Richard.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38785
next prev parent reply other threads:[~2009-01-14 20:51 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-09 15:46 [Bug tree-optimization/38785] New: " amylaar at gcc dot gnu dot org
2009-01-09 15:55 ` [Bug tree-optimization/38785] " rguenth at gcc dot gnu dot org
2009-01-09 16:39 ` amylaar at gcc dot gnu dot org
2009-01-09 17:35 ` amylaar at gcc dot gnu dot org
2009-01-09 17:59 ` rguenth at gcc dot gnu dot org
2009-01-09 20:55 ` steven at gcc dot gnu dot org
2009-01-10 16:10 ` amylaar at gcc dot gnu dot org
2009-01-14 10:08 ` Joey dot ye at intel dot com
2009-01-14 10:54 ` steven at gcc dot gnu dot org
2009-01-14 18:47 ` amylaar at gcc dot gnu dot org
2009-01-14 20:51 ` rguenther at suse dot de [this message]
2009-01-14 22:06 ` amylaar at gcc dot gnu dot org
2009-01-15 11:36 ` amylaar at gcc dot gnu dot org
2009-01-20 23:02 ` steven at gcc dot gnu dot org
2009-03-04 22:58 ` amylaar at gcc dot gnu dot org
2009-03-05 0:32 ` amylaar at gcc dot gnu dot org
2009-03-31 16:08 ` [Bug tree-optimization/38785] [4.3/4.4/4.5 Regression] " jsm28 at gcc dot gnu dot org
2009-04-14 9:49 ` jakub at gcc dot gnu dot org
2009-07-15 21:12 ` steven at gcc dot gnu dot org
2009-07-15 21:35 ` steven at gcc dot gnu dot org
2009-07-23 21:51 ` drow at gcc dot gnu dot org
2009-07-23 22:23 ` stevenb dot gcc at gmail dot com
2009-08-04 12:46 ` rguenth at gcc dot gnu dot org
2010-01-29 20:33 ` amylaar at gcc dot gnu dot org
2010-02-19 12:18 ` rguenth at gcc dot gnu dot org
2010-02-19 12:29 ` amylaar at gcc dot gnu dot org
2010-02-19 13:19 ` matz at gcc dot gnu dot org
2010-02-19 14:08 ` drow at gcc dot gnu dot org
2010-02-19 23:33 ` stevenb dot gcc at gmail dot com
2010-05-22 18:28 ` [Bug tree-optimization/38785] [4.3/4.4/4.5/4.6 " rguenth at gcc dot gnu dot org
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