Re: Excessive copies of set elements in GMPL

On Fri, 24 Jul 2020, Andrew Makhorin wrote:

> The issue can be illustrated by the following example:
>
>  for (i = 0; i < 1000000; i++)
>  for (j = 0; j < 1000000; j++)
>  for (k = 0; k < 1000000; k++)
>    if (j == i+1 && j == j+2)
>      foo(i, j, k);
>
> Would you expect the C compiler to optimize this fragment in order not
> to perform obvious excessive computations?

My recollection is that gcc does make that
kind of optimization for linear constraints.
At the very least, most optimizing compilers
would hoist the j==i+1 test ouside the k loop.
That might be just enough to allow it to run in a practical amount of time:
a few trillion cycles plus whatever foo requires.

That said, the coder can, as noted,
provide equivalent code that requires no optimization.

-- 
Michael   [email protected]
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