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From: robert_dewar@my-dejanews.com
Subject: Re: should I be interested in ada?
Date: 1999/02/19
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In article <36CD44CF.A61DAE96@erols.com>,
  dnagle@erols.com wrote:
> Hello,
>
> Does Ada enforce anti-aliasing rules regarding the global
> variables?

The anti-aliasing rules are in some respects weaker,
although in other respects stronger (the stronger typing
for example allows better aliasing information to be
built). You can construct artificial examples which give
a theoretical optimization advantage in either direction.
How important this is in practice is anyone's guess.


> Do the Ada constructs which have been given as
> substitutes for Fortran 95 array syntax have an implied
> order of operation? If I say
>
> real, dimension( n, n) :: a, b
>                ! f95-speak for 2 nxn arrays of reals
>
> and then say
>
> a = b          ! f95 array assignment
>
> The order in which the assignments occur if unspecified.

Actually here Ada has an advantage, it does not even
see the assignment of b to a as a "series of assignment"
in any sense, Rather it is an assignment of a composite
object, and yes of course the compiler is free to achieve
this in any manner it pleases.

However, other aggregate operations in Fortran that imply
parallelism may not be so easy to model in Ada.

> I really am simply courious.  I see many things in Ada
> which. I find attractive and I want to know about the
> optimization issues.

Nick proposed that "the high level language is
theoretically compltely immaterial [to the optimization
issue]", and that of course is completely wrong.

It is definitely the case that there are various
theoretical differences, but as always, the difficulty
with any optimization issues is knowing how much
difference it will make in practice, and that is
hard to know. Usually such theoretical differences
are swamped by other engineering issues, i.e. "other
things being equal" is a condition that is not  in
practice easy to meet.


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