Re: test at top ==> test at bottom

tim@apple.com (Tim Olson)
Fri, 14 May 1993 14:41:17 GMT

          From comp.compilers

Related articles
test at top ==> test at bottom max@nic.gac.edu (1993-04-28)
Re: test at top ==> test at bottom preston@dawn.cs.rice.edu (1993-04-29)
Re: test at top ==> test at bottom marcoz@CS.CMU.EDU (1993-04-30)
Re: test at top ==> test at bottom tim@apple.com (1993-05-14)
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Newsgroups: comp.compilers
From: tim@apple.com (Tim Olson)
Keywords: optimize
Organization: Apple Computer, Inc. / Somerset
References: 93-04-105
Date: Fri, 14 May 1993 14:41:17 GMT

max@nic.gac.edu (Max Hailperin) wrote:
> ... I haven't seen much in the literature
> on transformations that will turn test-at-the-top loops into
> test-at-the-bottom loops. Yet unless you've done so, you can't safely
> assume the loop will be done at least once.


This is commonly known as "loop inversion", and is a simple optimization
that is normally done by replicating and inverting the test condition,
placing it at the end of the loop instead of the unconditional jump back to
the test.


                -- Tim Olson
                Apple Computer Inc. / Somerset
--


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