Re: Value range tracing

jeremy@suede.sw.oz.au (Jeremy Fitzhardinge) writes:
>I'm wondering if people bother with value range tracing. That is,
>keeping track of the possible range of variables at each point in the
>program.
...
>Is this kind of thing useful? Is it useful enough to implement?
...
>propagation. Rather than saying "this particular value is here", you
>can say "this range is possible". On the other hand, ranges are


APEX, my APL compiler, has the ability to keep track of information such as


This array has upper/lower bounds of u,l.
This array is a permutation vector. [That is, 3 1 2 4 is a permutation
      of 1 2 3 4].
This array is sorted up/down.


And so on.


Advantages are in code generation. For example, bounds info may
indicate that you can use a table for doing set membership in linear
time. Sorted info lets you search it quickly [and also do
sort REALLY fast 8^}]. Knowing it's a permutation vector gives you
the ability to use a bucket sort on the data, or to do vector
indexed assignment in parallel.


Lots of possibilities once you start to carry arrays around at
the IL level.


Bob
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