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From: "schlie at comcast dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/18424] [3.4/4.0 Regression] ~6x+ performance regression, constant trees not being computed.
Date: Thu, 09 Dec 2004 15:52:00 -0000	[thread overview]
Message-ID: <20041209155218.7834.qmail@sourceware.org> (raw)
In-Reply-To: <20041111023501.18424.schlie@comcast.net>


------- Additional Comments From schlie at comcast dot net  2004-12-09 15:52 -------
Subject: Re:  [3.4/4.0 Regression] ~6x+ performance
 regression, constant trees not being computed.

Sorry, lost the fact that only a single bit needs to remain significant in
the resulting trasform:


   (((long)x & (1 << 28)) == 0)
=>
   ((((byte)(sub-word (long)x 3) >> 4) & 1) == 0)
=>
   ((((byte)x' >> 4) & 1) == 0) :: (((byte)x' & 0x10) == 0)

> From: schlie at comcast dot net <gcc-bugzilla@gcc.gnu.org>
>    i.e. 
> 
>   (((long)x & (1 << 28)) == 0) => (((sub-word (long)x 3) >> 4) == 0)
>    => (((byte)x >> 4) == 0)
> 
>   (then possibly => (((byte)x & 0x10) == 0) which I believe avr's
>    back-end knows how to transform into a [bit-test x 5] )
> 
> Might this be possible, as it would seem generally useful as well?
> 
> Thanks again, -paul-




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18424


  parent reply	other threads:[~2004-12-09 15:52 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-11-11  2:35 [Bug c/18424] New: 3.4.3 ~6x+ performance regression vs 3.3.1, " schlie at comcast dot net
2004-11-11  2:48 ` [Bug middle-end/18424] " pinskia at gcc dot gnu dot org
2004-11-11  2:49 ` pinskia at gcc dot gnu dot org
2004-11-11  2:52 ` pinskia at gcc dot gnu dot org
2004-11-11  3:15 ` schlie at comcast dot net
2004-11-11  3:18 ` pinskia at gcc dot gnu dot org
2004-11-11  3:56 ` schlie at comcast dot net
2004-11-11  4:33 ` schlie at comcast dot net
2004-11-11  4:41 ` pinskia at gcc dot gnu dot org
2004-11-11  4:59 ` schlie at comcast dot net
2004-11-11  5:04 ` pinskia at gcc dot gnu dot org
2004-11-11 15:52 ` schlie at comcast dot net
2004-11-11 16:22 ` joseph at codesourcery dot com
2004-11-11 16:30 ` ericw at evcohs dot com
2004-11-11 17:19 ` schlie at comcast dot net
2004-11-11 20:29 ` schlie at comcast dot net
2004-11-16 23:58 ` dmixm at marine dot febras dot ru
2004-11-17  7:22 ` schlie at comcast dot net
2004-12-09 12:51 ` [Bug middle-end/18424] [3.4/4.0 Regression] ~6x+ performance regression, " giovannibajo at libero dot it
2004-12-09 15:00 ` roger at eyesopen dot com
2004-12-09 15:23 ` schlie at comcast dot net
2004-12-09 15:52 ` schlie at comcast dot net [this message]
2004-12-11  1:49 ` cvs-commit at gcc dot gnu dot org
2004-12-14  1:47 ` cvs-commit at gcc dot gnu dot org
2004-12-14  2:11 ` pinskia at gcc dot gnu dot org
2004-12-14  2:13 ` schlie at comcast dot net
2004-12-14  5:04 ` ericw at evcohs dot com
2004-12-14 12:33 ` schlie at comcast dot net
2004-12-14 14:18 ` ericw at evcohs dot com
2004-12-14 23:20 ` giovannibajo at libero dot it
2004-12-21  7:59 ` schlie at comcast dot net
2004-12-21  8:02 ` schlie at comcast dot net
2004-12-21 16:02 ` pinskia at gcc dot gnu dot org

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