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From: dwells@fits.acc.Virginia.EDU (Don Wells)
Newsgroups: comp.arch
Subject: Re: Vector_Assembly (was: It looks like he's at it again!)
Summary: assembly_sometimes_worth_it_on_vector_CPUs
Message-ID: <1990Jul12.202223.17675@murdoch.acc.Virginia.EDU>
Date: 12 Jul 90 20:22:23 GMT
References: <1990Jul10.072443.4844@cs.UAlberta.CA> <63692@sgi.sgi.com> <9896@celit.fps.com>
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In article <9896@celit.fps.com> dave@fps.com (Dave Smith) writes:
>In article <63692@sgi.sgi.com> karsh@trifolium.sgi.com (Bruce Karsh) writes:
> >In article <1990Jul10.072443.4844@cs.UAlberta.CA> cdshaw@cs.UAlberta.CA (Chris Shaw) writes:
> >>The basic problem with assembly coding by hand vs assembly coding by compiler
> >>is that IT DOESN'T SCALE. There are extremely limited application areas where
> >>coding by hand is much faster....  Some examples:
> >	Graphics Rendering Seismic Deconvolution Audio Signal Processing...
>David L. Smith>FPS Computing, San Diego>ucsd!celerity!dave or dave@fps.com

You can count me on the side of those who think that HLL is generally
the only approach that makes economic sense. However, I know of one
important exception:
				Vector CPUs

Many vector CPUs have vector instructions that their compilers do not
invoke. A notable example is the vector compress. In some cases,
usually various forms of IFs in loops, the compilers do not take
advantage of the instruction set and produce code that can be easily
beaten by use of assembly language. Of course the real problem is
weakness in the compilers: the best vectorizing compilers *do* utilize
these instructions for IF-loops and, when doing so, can generally beat
hand-coding.  There will still remain a *small* (N-->0 as limit) group
of bit-smashing applications where one occasionally will find that
hand-coded vector instructions will beat the compiler...

Donald C. Wells, Associate Scientist | NSFnet: dwells@nrao.edu [192.33.115.2]
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