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

[Zoltan Somogyi]

2022-11-23 12:28 GMT+11:00 "Peter Wang" <novalazy at gmail.com>:
> For a do-nothing build of Prince with intermodule optimisation enabled,
> mmc --make spends a large fraction of its time computing foreign imports,
> or rather looking up the cached results of such. (There are 650 modules,
> and the results for each module are looked up tens to hundreds of
> thousands of times each.)

Do you know where those lookups are coming from? Speeding up
the lookups is good, but eliminating them would be even better.

When I converted the compiler from Fergus's "lists of items"
representation to using file-kind-specific parse trees, I noted
that there were a lot of operations that scanned item lists
looking for foreign imports, together with a varying set of
other kinds of items. I thought I eliminated most of the
redundant passes, though I did not try to eliminate them all,
having bigger fish to fry. But if a single piece of info is looked up
10k+ times, then this fish was bigger than I thought :-)

Zoltan.