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| //===- DependencyScanningFilesystem.cpp - clang-scan-deps fs --------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h"
#include "clang/Lex/DependencyDirectivesSourceMinimizer.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Threading.h"
using namespace clang;
using namespace tooling;
using namespace dependencies;
CachedFileSystemEntry CachedFileSystemEntry::createFileEntry(
StringRef Filename, llvm::vfs::FileSystem &FS, bool Minimize) {
// Load the file and its content from the file system.
llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>> MaybeFile =
FS.openFileForRead(Filename);
if (!MaybeFile)
return MaybeFile.getError();
llvm::ErrorOr<llvm::vfs::Status> Stat = (*MaybeFile)->status();
if (!Stat)
return Stat.getError();
llvm::vfs::File &F = **MaybeFile;
llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MaybeBuffer =
F.getBuffer(Stat->getName());
if (!MaybeBuffer)
return MaybeBuffer.getError();
llvm::SmallString<1024> MinimizedFileContents;
// Minimize the file down to directives that might affect the dependencies.
const auto &Buffer = *MaybeBuffer;
SmallVector<minimize_source_to_dependency_directives::Token, 64> Tokens;
if (!Minimize || minimizeSourceToDependencyDirectives(
Buffer->getBuffer(), MinimizedFileContents, Tokens)) {
// Use the original file unless requested otherwise, or
// if the minimization failed.
// FIXME: Propage the diagnostic if desired by the client.
CachedFileSystemEntry Result;
Result.MaybeStat = std::move(*Stat);
Result.Contents.reserve(Buffer->getBufferSize() + 1);
Result.Contents.append(Buffer->getBufferStart(), Buffer->getBufferEnd());
// Implicitly null terminate the contents for Clang's lexer.
Result.Contents.push_back('\0');
Result.Contents.pop_back();
return Result;
}
CachedFileSystemEntry Result;
size_t Size = MinimizedFileContents.size();
Result.MaybeStat = llvm::vfs::Status(Stat->getName(), Stat->getUniqueID(),
Stat->getLastModificationTime(),
Stat->getUser(), Stat->getGroup(), Size,
Stat->getType(), Stat->getPermissions());
// The contents produced by the minimizer must be null terminated.
assert(MinimizedFileContents.data()[MinimizedFileContents.size()] == '\0' &&
"not null terminated contents");
// Even though there's an implicit null terminator in the minimized contents,
// we want to temporarily make it explicit. This will ensure that the
// std::move will preserve it even if it needs to do a copy if the
// SmallString still has the small capacity.
MinimizedFileContents.push_back('\0');
Result.Contents = std::move(MinimizedFileContents);
// Now make the null terminator implicit again, so that Clang's lexer can find
// it right where the buffer ends.
Result.Contents.pop_back();
// Compute the skipped PP ranges that speedup skipping over inactive
// preprocessor blocks.
llvm::SmallVector<minimize_source_to_dependency_directives::SkippedRange, 32>
SkippedRanges;
minimize_source_to_dependency_directives::computeSkippedRanges(Tokens,
SkippedRanges);
PreprocessorSkippedRangeMapping Mapping;
for (const auto &Range : SkippedRanges) {
if (Range.Length < 16) {
// Ignore small ranges as non-profitable.
// FIXME: This is a heuristic, its worth investigating the tradeoffs
// when it should be applied.
continue;
}
Mapping[Range.Offset] = Range.Length;
}
Result.PPSkippedRangeMapping = std::move(Mapping);
return Result;
}
CachedFileSystemEntry
CachedFileSystemEntry::createDirectoryEntry(llvm::vfs::Status &&Stat) {
assert(Stat.isDirectory() && "not a directory!");
auto Result = CachedFileSystemEntry();
Result.MaybeStat = std::move(Stat);
return Result;
}
DependencyScanningFilesystemSharedCache::
DependencyScanningFilesystemSharedCache() {
// This heuristic was chosen using a empirical testing on a
// reasonably high core machine (iMacPro 18 cores / 36 threads). The cache
// sharding gives a performance edge by reducing the lock contention.
// FIXME: A better heuristic might also consider the OS to account for
// the different cost of lock contention on different OSes.
NumShards = std::max(2u, llvm::hardware_concurrency() / 4);
CacheShards = std::make_unique<CacheShard[]>(NumShards);
}
/// Returns a cache entry for the corresponding key.
///
/// A new cache entry is created if the key is not in the cache. This is a
/// thread safe call.
DependencyScanningFilesystemSharedCache::SharedFileSystemEntry &
DependencyScanningFilesystemSharedCache::get(StringRef Key) {
CacheShard &Shard = CacheShards[llvm::hash_value(Key) % NumShards];
std::unique_lock<std::mutex> LockGuard(Shard.CacheLock);
auto It = Shard.Cache.try_emplace(Key);
return It.first->getValue();
}
/// Whitelist file extensions that should be minimized, treating no extension as
/// a source file that should be minimized.
///
/// This is kinda hacky, it would be better if we knew what kind of file Clang
/// was expecting instead.
static bool shouldMinimize(StringRef Filename) {
StringRef Ext = llvm::sys::path::extension(Filename);
if (Ext.empty())
return true; // C++ standard library
return llvm::StringSwitch<bool>(Ext)
.CasesLower(".c", ".cc", ".cpp", ".c++", ".cxx", true)
.CasesLower(".h", ".hh", ".hpp", ".h++", ".hxx", true)
.CasesLower(".m", ".mm", true)
.CasesLower(".i", ".ii", ".mi", ".mmi", true)
.CasesLower(".def", ".inc", true)
.Default(false);
}
static bool shouldCacheStatFailures(StringRef Filename) {
StringRef Ext = llvm::sys::path::extension(Filename);
if (Ext.empty())
return false; // This may be the module cache directory.
return shouldMinimize(Filename); // Only cache stat failures on source files.
}
llvm::ErrorOr<const CachedFileSystemEntry *>
DependencyScanningWorkerFilesystem::getOrCreateFileSystemEntry(
const StringRef Filename) {
if (const CachedFileSystemEntry *Entry = getCachedEntry(Filename)) {
return Entry;
}
// FIXME: Handle PCM/PCH files.
// FIXME: Handle module map files.
bool KeepOriginalSource = IgnoredFiles.count(Filename) ||
!shouldMinimize(Filename);
DependencyScanningFilesystemSharedCache::SharedFileSystemEntry
&SharedCacheEntry = SharedCache.get(Filename);
const CachedFileSystemEntry *Result;
{
std::unique_lock<std::mutex> LockGuard(SharedCacheEntry.ValueLock);
CachedFileSystemEntry &CacheEntry = SharedCacheEntry.Value;
if (!CacheEntry.isValid()) {
llvm::vfs::FileSystem &FS = getUnderlyingFS();
auto MaybeStatus = FS.status(Filename);
if (!MaybeStatus) {
if (!shouldCacheStatFailures(Filename))
// HACK: We need to always restat non source files if the stat fails.
// This is because Clang first looks up the module cache and module
// files before building them, and then looks for them again. If we
// cache the stat failure, it won't see them the second time.
return MaybeStatus.getError();
else
CacheEntry = CachedFileSystemEntry(MaybeStatus.getError());
} else if (MaybeStatus->isDirectory())
CacheEntry = CachedFileSystemEntry::createDirectoryEntry(
std::move(*MaybeStatus));
else
CacheEntry = CachedFileSystemEntry::createFileEntry(
Filename, FS, !KeepOriginalSource);
}
Result = &CacheEntry;
}
// Store the result in the local cache.
setCachedEntry(Filename, Result);
return Result;
}
llvm::ErrorOr<llvm::vfs::Status>
DependencyScanningWorkerFilesystem::status(const Twine &Path) {
SmallString<256> OwnedFilename;
StringRef Filename = Path.toStringRef(OwnedFilename);
const llvm::ErrorOr<const CachedFileSystemEntry *> Result =
getOrCreateFileSystemEntry(Filename);
if (!Result)
return Result.getError();
return (*Result)->getStatus();
}
namespace {
/// The VFS that is used by clang consumes the \c CachedFileSystemEntry using
/// this subclass.
class MinimizedVFSFile final : public llvm::vfs::File {
public:
MinimizedVFSFile(std::unique_ptr<llvm::MemoryBuffer> Buffer,
llvm::vfs::Status Stat)
: Buffer(std::move(Buffer)), Stat(std::move(Stat)) {}
llvm::ErrorOr<llvm::vfs::Status> status() override { return Stat; }
const llvm::MemoryBuffer *getBufferPtr() const { return Buffer.get(); }
llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
getBuffer(const Twine &Name, int64_t FileSize, bool RequiresNullTerminator,
bool IsVolatile) override {
return std::move(Buffer);
}
std::error_code close() override { return {}; }
private:
std::unique_ptr<llvm::MemoryBuffer> Buffer;
llvm::vfs::Status Stat;
};
llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>
createFile(const CachedFileSystemEntry *Entry,
ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings) {
if (Entry->isDirectory())
return llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>(
std::make_error_code(std::errc::is_a_directory));
llvm::ErrorOr<StringRef> Contents = Entry->getContents();
if (!Contents)
return Contents.getError();
auto Result = std::make_unique<MinimizedVFSFile>(
llvm::MemoryBuffer::getMemBuffer(*Contents, Entry->getName(),
/*RequiresNullTerminator=*/false),
*Entry->getStatus());
if (!Entry->getPPSkippedRangeMapping().empty() && PPSkipMappings)
(*PPSkipMappings)[Result->getBufferPtr()] =
&Entry->getPPSkippedRangeMapping();
return llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>(
std::unique_ptr<llvm::vfs::File>(std::move(Result)));
}
} // end anonymous namespace
llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>
DependencyScanningWorkerFilesystem::openFileForRead(const Twine &Path) {
SmallString<256> OwnedFilename;
StringRef Filename = Path.toStringRef(OwnedFilename);
const llvm::ErrorOr<const CachedFileSystemEntry *> Result =
getOrCreateFileSystemEntry(Filename);
if (!Result)
return Result.getError();
return createFile(Result.get(), PPSkipMappings);
}
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