Performance optimization (allocation inside a for loop)

[Francesco Potorti`]

>I gave the idea a second thought - maybe it has some merits. Sometimes
>you really want to use an array as a stack in Octave to avoid going
>through a loop twice, so Octave can try to optimize such usage.

Two thoughts only:

 1) if stack operations are one target of this optimisation, then it
    would better to have a hysteresis behaviour, that is, deallocate
    one chunk only when the free space is 2*chunk big; more generally,
    deallocate so that at least a whole unused chunk remains unused

 2) 1kB for chunk size is very little today.  I would have considered
    one memory page size at least, but since marginal improvements are
    smaller for big chunks, maybe the current choice is good.  Only a
    benchmark can tell, I suppose.

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