[m-rev.] for review: Speed up retrieval of foreign imports.

[Julien Fischer]

On Tue, 22 Nov 2022, Peter Wang wrote:

> On Tue, 22 Nov 2022 15:57:40 +1100 Peter Wang <novalazy at gmail.com> wrote:
>> 
>> This change replaces the representation of cached_foreign_imports from
>> tree234 to one based on version_array. It reduces the average run time
>> for a do-nothing build of Prince on my machine from 7.850 s to 6.505 s,
>> for a speedup of ~17%.
>> 
>> compiler/va_map.m:
>>     Add a module originally written for Prince.
>
> Actually the 2-level scheme employed by va_map isn't necessary for
> this use case. I will try using a flat version_array.

Which would have the advantage of working when targetting C# or Java,
unlike the current version of va_map.

Julien.