Re: Loop jamming!?

Christopher Glaeser <cdg@nullstone.com>
22 Jul 1997 20:57:58 -0400

          From comp.compilers
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Loop jamming!? wjhung@csie.nctu.edu.tw (1997-06-24)
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Re: Loop jamming!? cdg@nullstone.com (Christopher Glaeser) (1997-07-18)
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Re: Loop jamming!? jan@fsnif.neuroinformatik.ruhr-uni-bochum.de (Jan Vorbrueggen) (1997-07-31)
Re: Loop jamming!? cliff.click@Eng.Sun.COM (cliffc) (1997-08-07)
[2 later articles]
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From: Christopher Glaeser <cdg@nullstone.com>
Newsgroups: comp.compilers
Date: 22 Jul 1997 20:57:58 -0400
Organization: Nullstone Corporation
References: 97-07-089 97-07-102
Keywords: optimize, architecture

> >> In the extreme case, the slower loop is not slowed down any more
> >> by merging another loop with it.
> >
> >Not true. In the extreme case, performance can actually decrease. This
> >can occur, for example, when the fusion of the loops cause cache
> >conflicts that were not present when the loops are run separately.
>
> Of course, both cases can be true (but for different extreme cases).


I understood "In the extreme case, the slower loop is not slowed down"
to mean there are *no* programs that will slow as a result of loop
jamming. I contend such programs *do* exist. These two assertions can
not both be true. Either such programs exist, or they do not.


If I have misinterpreted the meaning of the original sentence, then
please explain what is "extreme" about the "extreme case". An example
would be helpful.


Best regards,
Christopher Glaeser cdg@nullstone.com
Nullstone Corporation http://www.nullstone.com
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