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From: gl8f@astsun.astro.Virginia.EDU (Greg Lindahl)
Newsgroups: comp.lang.misc
Subject: Re: Aggressive optimization
Message-ID: <1990Nov8.031353.10405@murdoch.acc.Virginia.EDU>
Date: 8 Nov 90 03:13:53 GMT
References: <2701@l.cc.purdue.edu> <5009@lanl.gov> <6PX6-O@xds13.ferranti.com>
Sender: news@murdoch.acc.Virginia.EDU
Organization: Department of Astronomy, University of Virginia
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In article <6PX6-O@xds13.ferranti.com> peter@ficc.ferranti.com (Peter da Silva) writes:
>What's wrong with:
>
>	if(array_a_and_array_b_overlap)
>		use_safe_code
>	else
>		use_fast_code_that_doesn't_work_for_aliased_arrays.

Of course, this won't catch every situation where aliasing can occur.
However, you might be happy to know that Cray's Fortran compiler will
insert tests into runtime code to see if particular loops are vector
or scalar, in situations where a variable determines the behavior.
I've yet to see a C compiler which does this, although some (Convex)
do some compile-time checking for aliasing in array references.

See my reply to Dan for situations where this won't catch all
Fortran-style non-aliased expressions.