Re: Optimization tradeoffs (time vs. space)

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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