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Modules: Remove ModuleLoader::OtherUncachedFailure, NFC

Authored by dexonsmith on Apr 30 2021, 2:14 PM.

Description

Modules: Remove ModuleLoader::OtherUncachedFailure, NFC

5cca622310c10fdf6f921b6cce26f91d9f14c762 refactored
CompilerInstance::loadModule, splitting out
findOrCompileModuleAndReadAST, but was careful to avoid making any
functional changes. It added ModuleLoader::OtherUncachedFailure to
facilitate this and left behind FIXMEs asking why certain failures
weren't cached.

After a closer look, I think we can just remove this and simplify the
code. This changes the behaviour of the following (simplified) code from
CompilerInstance::loadModule, causing a failure to be cached more often:

if (auto MaybeModule = MM.getCachedModuleLoad(*Path[0].first))
  return *MaybeModule;
if (ModuleName == getLangOpts().CurrentModule)
  return MM.cacheModuleLoad(PP.lookupModule(...));
ModuleLoadResult Result = findOrCompileModuleAndReadAST(...);
if (Result.isNormal()) // This will be 'true' more often.
  return MM.cacheModuleLoad(..., Module);
return Result;

MM here is a ModuleMap owned by the Preprocessor. Here are the cases
where findOrCompileModuleAndReadAST starts returning a "normal" failed
result:

  • Emitted diag::err_module_not_found, where there's no module map found.
  • Emitted diag::err_module_build_disabled, where implicitly building modules is disabled.
  • Emitted diag::err_module_cycle, which detects module cycles in the implicit modules build system.
  • Emitted diag::err_module_not_built, which avoids building a module in this CompilerInstance if another one tried and failed already.
  • compileModuleAndReadAST() was called and failed to build.

The four errors are all fatal, and last item also reports a fatal error,
so it this extra caching has no functionality change... but even if it
did, it seems fine to cache these failed results within a ModuleMap
instance (note that each CompilerInstance has its own Preprocessor and
ModuleMap).

Differential Revision: https://reviews.llvm.org/D101667