bc36279c
by Wolfgang Jeltsch at 2026-04-30T09:38:31+02:00
Introduce a cache of home module name providers
This contribution introduces to the module graph a cache that maps home
module names to sets of units providing them and changes the finder to
use that cache. This is a performance optimization, especially for
multi-home-unit builds.
The particular changes are as follows:
* In `GHC.Unit.Module.Graph`, `ModuleGraph` is extended with a new
field `mg_home_module_name_providers_map`, exposed as
`mgHomeModuleNameProvidersMap`. This is a cache that assigns to each
home module name the set of IDs of home units that define it.
Operations that construct module graphs are updated such that this
cache stays synchronized.
* In `GHC.Unit.Finder`, `findImportedModule` is changed to pull
`mgHomeModuleNameProvidersMap` from `hsc_mod_graph` and pass it to
`findImportedModuleNoHsc`, which now does not search home units in
arbitrary order but prioritizes those units that the cache mentions
as potential providers of the requested module.
Resolves #27055.
Co-authored-by: Wolfgang Jeltsch <wolfgang@well-typed.com>