Re: Optimizing Boundary Checks

[Vinzent Hoefler <ada.rocks@jlfencey.com>]

Preben Randhol wrote:

>Vinzent Hoefler wrote:
>> 
>> Well, the compiler *could* see that the type Index_Range always
>> satisfies the same constraint as for the array. I don't know for sure,
>> but I'd think, it does, because somehow it must store the constraints
>> for any type anyway and I strongly doubt that an optimizer would work
>> on type names instead of actual numbers describing their constraints.
>
>For the second example I was thinking that the Index_Range was not
>defined at all.

Well, I guess, it's the same, it depends on what you code, I'd say. If
you say

|for i in 1 .. 10 loop
|   foo(i) := ...

and foo's index constraint is 1 .. 10, too, then the
compiler/optimizer *might* detect it doesn't need a range check here.

In cases where the actual value cannot be (easily) determined at
compiler time, the compiler is required to generate a range check.
Say, we call some function that returns an Integer, it is not easily
determinable that the function always returns values in bounds
(obviously, the contract doesn't tell us that here). So the compiler
generates a range check here, of course. Just see my other posting. :)


Vinzent.

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