# Re: Optimization tradeoffs (time vs. space)

## roy@phri.uucp (Roy Smith)10 Aug 88 14:00:19 GMT

From comp.compilers

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Re: Optimization tradeoffs (time vs. space) roy@phri.uucp (1988-08-10)
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 From: roy@phri.uucp (Roy Smith) Newsgroups: comp.compilers Date: 10 Aug 88 14:00:19 GMT References: <1989@ima.ISC.COM> Organization: Public Health Research Inst. (NY, NY)

midkiff@uicsrd.csrd.uiuc.edu (Sam Midkiff) writes:
> One dramatic space/time tradeoff occurs in vectorizing and parallelizing
> compilers. The transformation is called "scalar expansion". For example,
> consider the loop:
>
> do i = 1, n
> a = b + c
> d = a + e
> end

I'm confused. Since b, c, and e are all constants (invariant
inside the loop), can't you just re-write this as

a = b + c
d = a + e

without the loop at all? Unless, of course, you meant to write "a(i)"
instead of "a", etc, which I would guess is what you meant (and is
certainly the example given in the CACM paper you mentioned).
--
Roy Smith, System Administrator
Public Health Research Institute
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net
"The connector is the network"
[Mea culpa for not asking him to clarify it --John]
--

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