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Date: Wed, 28 Jan 2004 10:20:37 -0500
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: In-Out Parameters for functions
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Date: 2004-01-28T10:20:37-05:00
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Dmitry A. Kazakov wrote:
> for I in A'Range loop
>    Sum := Sum + A (I) + B (I - A'First + B'First);
> end loop;

For code like this, I would expect the compiler to be
generating all sorts of induction variables. There's
never going to be a loop constant to hoist. The
generated code should look something like this (in C):

n = A_Last - A_First + 1;
if (B_Last - B_First + 1 < n) raise Program_Error;
pa = &A[A_First];
pb = &B[B_First];
while (n-- > 0) sum += *pa++ + *pb++;

In any case, the compiler would be free to rearrange its
calculations any way it likes as long as the results are
the same as doing them in the proper order. If the compiler
cannot determine that this is the case, then the code is
probably tricky enough such that doing it in the defined
order is helpful.