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079c40e886
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: 298165
77 lines
2.5 KiB
C++
77 lines
2.5 KiB
C++
//===--- GeneratePCH.cpp - Sema Consumer for PCH Generation -----*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the PCHGenerator, which as a SemaConsumer that generates
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// a PCH file.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/AST/ASTContext.h"
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#include "clang/Lex/HeaderSearch.h"
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#include "clang/Lex/Preprocessor.h"
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#include "clang/Sema/SemaConsumer.h"
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#include "clang/Serialization/ASTWriter.h"
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#include "llvm/Bitcode/BitstreamWriter.h"
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using namespace clang;
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PCHGenerator::PCHGenerator(
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const Preprocessor &PP, StringRef OutputFile, StringRef isysroot,
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std::shared_ptr<PCHBuffer> Buffer,
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ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
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bool AllowASTWithErrors, bool IncludeTimestamps)
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: PP(PP), OutputFile(OutputFile), isysroot(isysroot.str()),
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SemaPtr(nullptr), Buffer(Buffer), Stream(Buffer->Data),
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Writer(Stream, Buffer->Data, PP.getPCMCache(), Extensions,
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IncludeTimestamps),
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AllowASTWithErrors(AllowASTWithErrors) {
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Buffer->IsComplete = false;
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}
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PCHGenerator::~PCHGenerator() {
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}
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void PCHGenerator::HandleTranslationUnit(ASTContext &Ctx) {
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// Don't create a PCH if there were fatal failures during module loading.
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if (PP.getModuleLoader().HadFatalFailure)
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return;
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bool hasErrors = PP.getDiagnostics().hasErrorOccurred();
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if (hasErrors && !AllowASTWithErrors)
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return;
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Module *Module = nullptr;
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if (PP.getLangOpts().isCompilingModule()) {
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Module = PP.getHeaderSearchInfo().lookupModule(
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PP.getLangOpts().CurrentModule, /*AllowSearch*/ false);
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if (!Module) {
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assert(hasErrors && "emitting module but current module doesn't exist");
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return;
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}
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}
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// Emit the PCH file to the Buffer.
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assert(SemaPtr && "No Sema?");
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Buffer->Signature =
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Writer.WriteAST(*SemaPtr, OutputFile, Module, isysroot,
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// For serialization we are lenient if the errors were
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// only warn-as-error kind.
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PP.getDiagnostics().hasUncompilableErrorOccurred());
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Buffer->IsComplete = true;
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}
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ASTMutationListener *PCHGenerator::GetASTMutationListener() {
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return &Writer;
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}
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ASTDeserializationListener *PCHGenerator::GetASTDeserializationListener() {
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return &Writer;
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}
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