Re: Estimating loop iterations

glen herrmannsfeldt <gah@ugcs.caltech.edu>
7 May 2005 16:58:29 -0400

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Related articles
Estimating loop iterations drizzle76@gmail.com (drizzle) (2005-05-06)
Re: Estimating loop iterations gah@ugcs.caltech.edu (glen herrmannsfeldt) (2005-05-07)
Re: Estimating loop iterations sandyam@india.hp.com (sandya) (2005-05-07)
Re: Estimating loop iterations Trevor.Jenkins@suneidesis.com (2005-05-08)
Re: Estimating loop iterations gah@ugcs.caltech.edu (glen herrmannsfeldt) (2005-05-08)
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From: glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups: comp.compilers,comp.lang.fortran
Date: 7 May 2005 16:58:29 -0400
Organization: Compilers Central
References: 05-05-030
Keywords: Fortran, optimize
Posted-Date: 07 May 2005 16:58:29 EDT

drizzle wrote:


> Can anyone point me to any literature on estimating number of times
> a loop would iterate. I noticed gcc 4 can estimate based on access
> functions, size of data used etc in the loop. Anybody know what paper
> is it based on ?


> [Where is the Fortran FREQUENCY statement now that we need it? -John]


I wondered about it a year or two ago. I saw it in the 704 Fortran
manual when I was looking for something else. It seems that it
didn't last very long. Since its use was optional, I am not sure
why it would go away. The compiler could always ignore it.


The C reg attribute is sometimes used as an indication that a
variable is used more than others, but compilers are allowed to
ignore that.


Other than FREQUENCY, it is interesting how many Fortran features
are pretty much unchanged since Fortran I.


-- glen
[I heard that FREQUENCY went away both because nobody used it and because
at least with 1960 optimizing technology, it didn't tell the compiler anything
useful. -John]


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