[m-rev.] for review: Optimise dependency file index maps.

[Peter Wang]

On Tue, 29 Nov 2022 12:07:16 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> 
> 
> On Mon, 28 Nov 2022 17:40:58 +1100, Peter Wang <novalazy at gmail.com> wrote:
> 
> > On Mon, 28 Nov 2022 16:47:26 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> > > 
> > > 2022-11-28 15:06 GMT+11:00 "Peter Wang" <novalazy at gmail.com>:
> > > > Replace the type used in the mappings between dependency_file and
> > > > dependency_file_index from dependency_file, which refers to targets by
> > > > module_name, to a similar type that refers to targets by module_index.
> > > 
> > > I didn't understand that sentence until I read the diff, which is not good
> > > for something that is supposed to explain the diff.
> > > 
> > 
> > Ok, I've rewritten it.
> 
> Are you going to commit this? I would like to have a go at
> rewriting this area of code to eliminate its "higher-order code
> piled on top of more higher-order code" approach with
> something much simpler.

We can get another decent speedup by caching the results of computing
imports_012 (and maybe interface_file_dependencies). It seems fairly
simple, but I'll wait if you are working on mmc --make.

Peter