Rather than storing a single flat list of SourceLocations where the diagnostic
state changes (in source order), we now store a separate list for each FileID
in which there is a diagnostic state transition. (State for other files is
built and cached lazily, on demand.) This has two consequences:
1) We can now sensibly support modules, and properly track the diagnostic state
for modular headers (this matters when, for instance, triggering instantiation
of a template defined within a module triggers diagnostics).
2) It's much faster than the old approach, since we can now just do a binary
search on the offsets within the FileID rather than needing to call
isBeforeInTranslationUnit to determine source order (which is surprisingly
slow). For some pathological (but real world) files, this reduces total
compilation time by more than 10%.
For now, the diagnostic state points for modules are loaded eagerly. It seems
feasible to defer this until diagnostic state information for one of the
module's files is needed, but that's not part of this patch.
llvm-svn: 293123
Richard Smith