Reapply "Modules: Cache PCMs in memory and avoid a use-after-free"
This reverts commit r298185, effectively reapplying r298165, after fixing the
new unit tests (PR32338). The memory buffer generator doesn't null-terminate
the MemoryBuffer it creates; this version of the commit informs getMemBuffer
about that to avoid the assert.
Original commit message follows:
----
Clang's internal build system for implicit modules uses lock files to
ensure that after a process writes a PCM it will read the same one back
in (without contention from other -cc1 commands). Since PCMs are read
from disk repeatedly while invalidating, building, and importing, the
lock is not released quickly. Furthermore, the LockFileManager is not
robust in every environment. Other -cc1 commands can stall until
timeout (after about eight minutes).
This commit changes the lock file from being necessary for correctness
to a (possibly dubious) performance hack. The remaining benefit is to
reduce duplicate work in competing -cc1 commands which depend on the
same module. Follow-up commits will change the internal build system to
continue after a timeout, and reduce the timeout. Perhaps we should
reconsider blocking at all.
This also fixes a use-after-free, when one part of a compilation
validates a PCM and starts using it, and another tries to swap out the
PCM for something new.
The PCMCache is a new type called MemoryBufferCache, which saves memory
buffers based on their filename. Its ownership is shared by the
CompilerInstance and ModuleManager.
- The ModuleManager stores PCMs there that it loads from disk, never
touching the disk if the cache is hot.
- When modules fail to validate, they're removed from the cache.
- When a CompilerInstance is spawned to build a new module, each
already-loaded PCM is assumed to be valid, and is frozen to avoid
the use-after-free.
- Any newly-built module is written directly to the cache to avoid the
round-trip to the filesystem, making lock files unnecessary for
correctness.
Original patch by Manman Ren; most testcases by Adrian Prantl!
llvm-svn: 298278
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 91319be..babef5d 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -70,15 +70,15 @@
Preprocessor::Preprocessor(std::shared_ptr<PreprocessorOptions> PPOpts,
DiagnosticsEngine &diags, LangOptions &opts,
- SourceManager &SM, HeaderSearch &Headers,
- ModuleLoader &TheModuleLoader,
+ SourceManager &SM, MemoryBufferCache &PCMCache,
+ HeaderSearch &Headers, ModuleLoader &TheModuleLoader,
IdentifierInfoLookup *IILookup, bool OwnsHeaders,
TranslationUnitKind TUKind)
: PPOpts(std::move(PPOpts)), Diags(&diags), LangOpts(opts), Target(nullptr),
AuxTarget(nullptr), FileMgr(Headers.getFileMgr()), SourceMgr(SM),
- ScratchBuf(new ScratchBuffer(SourceMgr)), HeaderInfo(Headers),
- TheModuleLoader(TheModuleLoader), ExternalSource(nullptr),
- Identifiers(opts, IILookup),
+ PCMCache(PCMCache), ScratchBuf(new ScratchBuffer(SourceMgr)),
+ HeaderInfo(Headers), TheModuleLoader(TheModuleLoader),
+ ExternalSource(nullptr), Identifiers(opts, IILookup),
PragmaHandlers(new PragmaNamespace(StringRef())),
IncrementalProcessing(false), TUKind(TUKind), CodeComplete(nullptr),
CodeCompletionFile(nullptr), CodeCompletionOffset(0),