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/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index bf15460..f660429 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -13,6 +13,7 @@
#include "clang/AST/Decl.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/FileManager.h"
+#include "clang/Basic/MemoryBufferCache.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/Version.h"
@@ -55,9 +56,15 @@
CompilerInstance::CompilerInstance(
std::shared_ptr<PCHContainerOperations> PCHContainerOps,
- bool BuildingModule)
- : ModuleLoader(BuildingModule), Invocation(new CompilerInvocation()),
- ThePCHContainerOperations(std::move(PCHContainerOps)) {}
+ MemoryBufferCache *SharedPCMCache)
+ : ModuleLoader(/* BuildingModule = */ SharedPCMCache),
+ Invocation(new CompilerInvocation()),
+ PCMCache(SharedPCMCache ? SharedPCMCache : new MemoryBufferCache),
+ ThePCHContainerOperations(std::move(PCHContainerOps)) {
+ // Don't allow this to invalidate buffers in use by others.
+ if (SharedPCMCache)
+ getPCMCache().finalizeCurrentBuffers();
+}
CompilerInstance::~CompilerInstance() {
assert(OutputFiles.empty() && "Still output files in flight?");
@@ -128,6 +135,8 @@
return ModuleManager;
}
void CompilerInstance::setModuleManager(IntrusiveRefCntPtr<ASTReader> Reader) {
+ assert(PCMCache.get() == &Reader->getModuleManager().getPCMCache() &&
+ "Expected ASTReader to use the same PCM cache");
ModuleManager = std::move(Reader);
}
@@ -370,7 +379,7 @@
getDiagnostics(), getLangOpts(), &getTarget());
PP = std::make_shared<Preprocessor>(
Invocation->getPreprocessorOptsPtr(), getDiagnostics(), getLangOpts(),
- getSourceManager(), *HeaderInfo, *this, PTHMgr,
+ getSourceManager(), getPCMCache(), *HeaderInfo, *this, PTHMgr,
/*OwnsHeaderSearch=*/true, TUKind);
PP->Initialize(getTarget(), getAuxTarget());
@@ -1073,9 +1082,11 @@
Invocation->getModuleHash() && "Module hash mismatch!");
// Construct a compiler instance that will be used to actually create the
- // module.
+ // module. Since we're sharing a PCMCache,
+ // CompilerInstance::CompilerInstance is responsible for finalizing the
+ // buffers to prevent use-after-frees.
CompilerInstance Instance(ImportingInstance.getPCHContainerOperations(),
- /*BuildingModule=*/true);
+ &ImportingInstance.getPreprocessor().getPCMCache());
auto &Inv = *Invocation;
Instance.setInvocation(std::move(Invocation));