Re: fast array assignement

robert.corbett_at_sun.com
Date: 02/07/05 

Date: 6 Feb 2005 21:04:07 -0800

> It is surprising
> to me that now, almost 15 years after array syntax was standardized
> in the language, optimizers aren't doing a better job with array
> syntax.

It is no surprise to me. Optimizing array expressions is hard.
Consider an example that was presented before on c.l.f.
Someone wanted to know why the expression

      COUNT( (/ a, b, c, d /) ) == 4

where a, b, c, and d are logical expressions took longer to execute
than

      a .and. b .and. c .and. d

Most compilers figure out that the array constructor has a small
fixed-size value, and so dynamic allocation is unnecessary. A few
understand that evaluating the count does not require storing the
elements of the constructor. If any compiler does the transformation
into logical conjunctions, it is because a special case was tossed in
as a result of the earlier posting on c.l.f.

                Sincerely,

                 Bob Corbett

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