[m-rev.] for review: Cache transitive foreign imports.

[Peter Wang]

On Fri, 25 Nov 2022 05:08:36 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> 
> 2022-11-24 14:45 GMT+11:00 "Peter Wang" <novalazy at gmail.com>:
> > We previously cached the foreign imports of a module.
> > find_module_foreign_imports always needs to compute the transitive
> > foreign imports (i.e. including the foreign imports of transitively
> > implementation-imported modules), so it had to take the union of a bunch
> > of sets after looking up cached results.
> > 
> > This change caches the transitive foreign imports of a module, avoiding
> > the bitset union operations, many/most of which turn out to be redundant.
> > It reduces the average run time for a do-nothing build of Prince on my
> > machine from 5.9 s to 3.1 s, for a speed up of ~47%.
> 
> That's great. Did you profile it to see whether there are any
> obvious remaining bottlenecks?

Yes, we can cache indirect_imports as well.

> 
> > compiler/make.dependencies.m:
> >     Cache transitive foreign module imports instead of direct foreign
> >     module imports.
> > 
> >     Delete code to make use va_map; it is no longer used.
> 
> Some word is missing there.

Fixed, thanks.

Peter