clang/Modules: Refactor CompilerInstance::loadModule, NFC
Refactor the logic on CompilerInstance::loadModule and a couple of
surrounding methods in order to clarify what's going on.
- Rename ModuleLoader::loadModuleFromSource to compileModuleFromSource
and fix its documentation, since it never loads a module. It just
creates/compiles one.
- Rename one of the overloads of compileModuleImpl to compileModule,
making it more obvious which one calls the other.
- Rename compileAndLoadModule to compileModuleAndReadAST. This
clarifies the relationship between this helper and its caller,
CompilerInstance::loadModule (the old name implied the opposite
relationship). It also (correctly) indicates that more needs to be
done to load the module than this function is responsible for.
- Split findOrCompileModuleAndReadAST out of loadModule. Besides
reducing nesting for this code thanks to early returns and the like,
this refactor clarifies the logic in loadModule, particularly around
calls to ModuleMap::cacheModuleLoad and
ModuleMap::getCachedModuleLoad. findOrCompileModuleAndReadAST also
breaks early if the initial ReadAST call returns Missing or OutOfDate,
allowing the last ditch call to compileModuleAndReadAST to come at the
end of the function body.
- Additionally split out selectModuleSource, clarifying the logic
due to early returns.
- Add ModuleLoadResult::isNormal and OtherUncachedFailure, so that
loadModule knows whether to cache the result.
OtherUncachedFailure was added to keep this patch NFC, but there's
a chance that these cases were uncached by accident, through
copy/paste/modify failures. These should be audited as a
follow-up (maybe we can eliminate this case).
- Do *not* lift the setting of `ModuleLoadFailed = true` to
loadModule because there isn't a clear pattern for when it's set.
This should be reconsidered in a follow-up, in case it would be
correct to set `ModuleLoadFailed` whenever no module is returned
and the result is either Normal or OtherUncachedFailure.
- Add some header documentation where it was missing, and fix it where
it was wrong.
This should have no functionality change.
https://reviews.llvm.org/D70556