From: Jeffrey A Law <law@hurl.cygnus.com>
To: Zack Weinberg <zack@rabi.columbia.edu>
Cc: Jamie Lokier <egcs@tantalophile.demon.co.uk>, egcs@egcs.cygnus.com
Subject: Re: gcc-2.7 creates faster code than pgcc-1.1.1
Date: Thu, 04 Mar 1999 18:09:00 -0000 [thread overview]
Message-ID: <13506.920599740@hurl.cygnus.com> (raw)
In-Reply-To: Your message of Thu, 04 Mar 1999 20:04:53 MST. < 199903050104.UAA15335@octiron.phys.columbia.edu >
In message < 199903050104.UAA15335@octiron.phys.columbia.edu >you write:
> A related issue: I see us generate a lot of code like this for loops over
> strings:
>
> loop:
> xorl %eax, %eax
> movb (%esi), %al
> incl %esi
> movb %al, (%edi)
> incl %edi
> testl %eax
> jne loop
>
> After the first iteration, the xorl is unnecessary. We ought to be able to
> hoist it out of the loop.
True, but I don't believe the loop optimizer is prepared to do that since it
doesn't keep track of what bits are active vs what bits are inactive in a
value.
jeff
WARNING: multiple messages have this Message-ID
From: Jeffrey A Law <law@hurl.cygnus.com>
To: Zack Weinberg <zack@rabi.columbia.edu>
Cc: Jamie Lokier <egcs@tantalophile.demon.co.uk>, egcs@egcs.cygnus.com
Subject: Re: gcc-2.7 creates faster code than pgcc-1.1.1
Date: Wed, 31 Mar 1999 23:46:00 -0000 [thread overview]
Message-ID: <13506.920599740@hurl.cygnus.com> (raw)
Message-ID: <19990331234600.OyBYaAMp-p03aMj78zV8W-tLkpLV7ibmeIHSqgDhF4w@z> (raw)
In-Reply-To: <199903050104.UAA15335@octiron.phys.columbia.edu>
In message < 199903050104.UAA15335@octiron.phys.columbia.edu >you write:
> A related issue: I see us generate a lot of code like this for loops over
> strings:
>
> loop:
> xorl %eax, %eax
> movb (%esi), %al
> incl %esi
> movb %al, (%edi)
> incl %edi
> testl %eax
> jne loop
>
> After the first iteration, the xorl is unnecessary. We ought to be able to
> hoist it out of the loop.
True, but I don't believe the loop optimizer is prepared to do that since it
doesn't keep track of what bits are active vs what bits are inactive in a
value.
jeff
next prev parent reply other threads:[~1999-03-04 18:09 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-03-04 3:40 Терехин Вячеслав
[not found] ` < 001401be6633$fed21a60$a18330d4@main.medtech.ru >
1999-03-04 13:20 ` Jamie Lokier
[not found] ` < 19990304222018.A21939@pcep-jamie.cern.ch >
1999-03-04 17:05 ` Zack Weinberg
[not found] ` < 199903050104.UAA15335@octiron.phys.columbia.edu >
1999-03-04 18:09 ` Jeffrey A Law [this message]
1999-03-31 23:46 ` Jeffrey A Law
1999-03-31 23:46 ` Zack Weinberg
1999-03-31 23:46 ` Jamie Lokier
1999-03-31 23:46 ` Терехин Вячеслав
-- strict thread matches above, loose matches on Subject: below --
1999-03-09 1:19 Òåðåõèà Âÿ÷åñëà â
1999-03-31 23:46 ` Òåðåõèà Âÿ÷åñëà â
1999-03-04 23:11 Терехин Вячеслав
[not found] ` < 005601be66d7$ae033480$288230d4@main.medtech.ru >
1999-03-05 9:22 ` Alfred Perlstein
[not found] ` < Pine.BSF.3.96.990305121935.7355C-100000@cygnus.rush.net >
1999-03-05 13:02 ` Richard Henderson
1999-03-31 23:46 ` Richard Henderson
1999-03-31 23:46 ` Alfred Perlstein
1999-03-05 15:52 ` H.J. Lu
1999-03-31 23:46 ` H.J. Lu
1999-03-31 23:46 ` Терехин Вячеслав
1999-03-04 14:31 H.J. Lu
[not found] ` < m10Igdx-000AUaC@shanghai.varesearch.com >
1999-03-04 16:04 ` Martin v. Loewis
[not found] ` < 199903050001.BAA00973@mira.isdn.cs.tu-berlin.de >
1999-03-04 16:46 ` H.J. Lu
[not found] ` < m10Iil3-000393C@ocean.lucon.org >
1999-03-04 17:03 ` Joe Buck
[not found] ` < 199903050102.RAA06944@atrus.synopsys.com >
1999-03-04 17:06 ` H.J. Lu
1999-03-31 23:46 ` H.J. Lu
1999-03-31 23:46 ` Joe Buck
1999-03-05 6:52 ` craig
[not found] ` < 19990305145306.4796.qmail@deer >
1999-03-05 9:18 ` Jeffrey A Law
1999-03-31 23:46 ` Jeffrey A Law
1999-03-31 23:46 ` craig
1999-03-31 23:46 ` H.J. Lu
1999-03-04 18:08 ` Jeffrey A Law
[not found] ` < 13494.920599668@hurl.cygnus.com >
1999-03-04 20:03 ` H.J. Lu
[not found] ` < m10Ilq3-00000YC@ocean.lucon.org >
1999-03-04 20:14 ` Jeffrey A Law
1999-03-31 23:46 ` Jeffrey A Law
1999-03-31 23:46 ` H.J. Lu
1999-03-31 23:46 ` Jeffrey A Law
1999-03-31 23:46 ` Martin v. Loewis
1999-03-31 23:46 ` H.J. Lu
[not found] <19990218210259.A720@loki.midheimar>
1999-02-19 0:09 ` [Q] alpha egc -> motorolla dragonball Scott Howard
[not found] ` < 36CD1CD3.1FC47334@objsw.com >
1999-02-19 11:04 ` Jeffrey A Law
1999-02-28 22:53 ` Jeffrey A Law
1999-02-28 22:53 ` Scott Howard
1998-07-14 11:29 porting EGCS to the Cray T3E Julian C. Cummings
1998-07-14 11:29 ` Jeffrey A Law
1997-12-12 3:55 1.0 sucessfull, install params questions Hermann Lauer
1997-12-12 8:55 ` Jeffrey A Law
1997-12-12 10:18 ` Michael Poole
[not found] ` <law@hurl.cygnus.com>
1997-12-12 15:46 ` Hermann Lauer
1998-07-14 14:29 ` porting EGCS to the Cray T3E Julian C. Cummings
1998-07-14 13:20 ` Jeffrey A Law
1998-07-14 16:57 ` Julian C. Cummings
1998-07-14 14:29 ` Jeffrey A Law
[not found] ` < 1845.919451010@hurl.cygnus.com >
1999-02-19 11:09 ` [Q] alpha egc -> motorola dragonball David Edelsohn
1999-02-28 22:53 ` David Edelsohn
[not found] ` < 13506.920599740@hurl.cygnus.com >
1999-03-04 20:04 ` gcc-2.7 creates faster code than pgcc-1.1.1 David Edelsohn
[not found] ` < 9903050403.AA36338@marc.watson.ibm.com >
1999-03-04 20:31 ` Jeffrey A Law
[not found] ` < 13939.920608288@hurl.cygnus.com >
1999-03-05 6:53 ` craig
[not found] ` < 19990305143358.4747.qmail@deer >
1999-03-05 9:30 ` Jeffrey A Law
[not found] ` < 15755.920655014@hurl.cygnus.com >
1999-03-05 10:18 ` Joe Buck
1999-03-31 23:46 ` Joe Buck
1999-03-05 10:19 ` craig
1999-03-31 23:46 ` craig
1999-03-31 23:46 ` Jeffrey A Law
1999-03-31 23:46 ` craig
1999-03-31 23:46 ` Jeffrey A Law
1999-03-07 11:01 ` Zack Weinberg
1999-03-31 23:46 ` Zack Weinberg
1999-03-31 23:46 ` David Edelsohn
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