To reduce the number of modules we build in explicit builds (which use strict context hash), we prune unused header search paths. This essentially merges parts of the dependency graph.
Determining whether a search path was used to discover a module (through implicit module maps) proved to be somewhat complicated. Initial support landed in D102923, while D113676 attempts to fix some bugs.
However, now that we don't use implicit module maps in explicit builds (since D120465), we don't need to consider such search paths as used anymore. Modules are no longer discovered through the header search mechanism, so we can drop such search paths (provided they are not needed for other reasons).
This patch removes whatever support for detecting such usage we had, since it's buggy and not required anymore.
Depends on D120465.
Reviewed By: dexonsmith
Differential Revision: https://reviews.llvm.org/D121295
For dependency scanning, it would be useful to collect header search paths (provided on command-line via `-I` and friends) that were actually used during preprocessing. This patch adds that feature to `HeaderSearch` along with a new remark that reports such paths as they get used.
Previous version of this patch tried to use the existing `LookupFileCache` to report used paths via `HitIdx`. That doesn't work for `ComputeUserEntryUsage` (which is intended to be called *after* preprocessing), because it indexes used search paths by the file name. This means the values get overwritten when the code contains `#include_next`.
Note that `HeaderSearch` doesn't use `HeaderSearchOptions::UserEntries` directly. Instead, `InitHeaderSearch` pre-processes them (adds platform-specific paths, removes duplicates, removes paths that don't exist) and creates `DirectoryLookup` instances. This means we need a mechanism for translating between those two. It's not possible to go from `DirectoryLookup` back to the original `HeaderSearch`, so `InitHeaderSearch` now tracks the relationships explicitly.
Depends on D111557.
Reviewed By: dexonsmith
Differential Revision: https://reviews.llvm.org/D102923
Jan Svoboda