1 //===- DependencyScanningFilesystem.cpp - clang-scan-deps fs --------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h"
10 #include "clang/Lex/DependencyDirectivesSourceMinimizer.h"
11 #include "llvm/Support/MemoryBuffer.h"
12 #include "llvm/Support/Threading.h"
13
14 using namespace clang;
15 using namespace tooling;
16 using namespace dependencies;
17
createFileEntry(StringRef Filename,llvm::vfs::FileSystem & FS,bool Minimize)18 CachedFileSystemEntry CachedFileSystemEntry::createFileEntry(
19 StringRef Filename, llvm::vfs::FileSystem &FS, bool Minimize) {
20 // Load the file and its content from the file system.
21 llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>> MaybeFile =
22 FS.openFileForRead(Filename);
23 if (!MaybeFile)
24 return MaybeFile.getError();
25 llvm::ErrorOr<llvm::vfs::Status> Stat = (*MaybeFile)->status();
26 if (!Stat)
27 return Stat.getError();
28
29 llvm::vfs::File &F = **MaybeFile;
30 llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MaybeBuffer =
31 F.getBuffer(Stat->getName());
32 if (!MaybeBuffer)
33 return MaybeBuffer.getError();
34
35 llvm::SmallString<1024> MinimizedFileContents;
36 // Minimize the file down to directives that might affect the dependencies.
37 const auto &Buffer = *MaybeBuffer;
38 SmallVector<minimize_source_to_dependency_directives::Token, 64> Tokens;
39 if (!Minimize || minimizeSourceToDependencyDirectives(
40 Buffer->getBuffer(), MinimizedFileContents, Tokens)) {
41 // Use the original file unless requested otherwise, or
42 // if the minimization failed.
43 // FIXME: Propage the diagnostic if desired by the client.
44 CachedFileSystemEntry Result;
45 Result.MaybeStat = std::move(*Stat);
46 Result.Contents.reserve(Buffer->getBufferSize() + 1);
47 Result.Contents.append(Buffer->getBufferStart(), Buffer->getBufferEnd());
48 // Implicitly null terminate the contents for Clang's lexer.
49 Result.Contents.push_back('\0');
50 Result.Contents.pop_back();
51 return Result;
52 }
53
54 CachedFileSystemEntry Result;
55 size_t Size = MinimizedFileContents.size();
56 Result.MaybeStat = llvm::vfs::Status(Stat->getName(), Stat->getUniqueID(),
57 Stat->getLastModificationTime(),
58 Stat->getUser(), Stat->getGroup(), Size,
59 Stat->getType(), Stat->getPermissions());
60 // The contents produced by the minimizer must be null terminated.
61 assert(MinimizedFileContents.data()[MinimizedFileContents.size()] == '\0' &&
62 "not null terminated contents");
63 // Even though there's an implicit null terminator in the minimized contents,
64 // we want to temporarily make it explicit. This will ensure that the
65 // std::move will preserve it even if it needs to do a copy if the
66 // SmallString still has the small capacity.
67 MinimizedFileContents.push_back('\0');
68 Result.Contents = std::move(MinimizedFileContents);
69 // Now make the null terminator implicit again, so that Clang's lexer can find
70 // it right where the buffer ends.
71 Result.Contents.pop_back();
72
73 // Compute the skipped PP ranges that speedup skipping over inactive
74 // preprocessor blocks.
75 llvm::SmallVector<minimize_source_to_dependency_directives::SkippedRange, 32>
76 SkippedRanges;
77 minimize_source_to_dependency_directives::computeSkippedRanges(Tokens,
78 SkippedRanges);
79 PreprocessorSkippedRangeMapping Mapping;
80 for (const auto &Range : SkippedRanges) {
81 if (Range.Length < 16) {
82 // Ignore small ranges as non-profitable.
83 // FIXME: This is a heuristic, its worth investigating the tradeoffs
84 // when it should be applied.
85 continue;
86 }
87 Mapping[Range.Offset] = Range.Length;
88 }
89 Result.PPSkippedRangeMapping = std::move(Mapping);
90
91 return Result;
92 }
93
94 CachedFileSystemEntry
createDirectoryEntry(llvm::vfs::Status && Stat)95 CachedFileSystemEntry::createDirectoryEntry(llvm::vfs::Status &&Stat) {
96 assert(Stat.isDirectory() && "not a directory!");
97 auto Result = CachedFileSystemEntry();
98 Result.MaybeStat = std::move(Stat);
99 return Result;
100 }
101
102 DependencyScanningFilesystemSharedCache::
DependencyScanningFilesystemSharedCache()103 DependencyScanningFilesystemSharedCache() {
104 // This heuristic was chosen using a empirical testing on a
105 // reasonably high core machine (iMacPro 18 cores / 36 threads). The cache
106 // sharding gives a performance edge by reducing the lock contention.
107 // FIXME: A better heuristic might also consider the OS to account for
108 // the different cost of lock contention on different OSes.
109 NumShards =
110 std::max(2u, llvm::hardware_concurrency().compute_thread_count() / 4);
111 CacheShards = std::make_unique<CacheShard[]>(NumShards);
112 }
113
114 /// Returns a cache entry for the corresponding key.
115 ///
116 /// A new cache entry is created if the key is not in the cache. This is a
117 /// thread safe call.
118 DependencyScanningFilesystemSharedCache::SharedFileSystemEntry &
get(StringRef Key)119 DependencyScanningFilesystemSharedCache::get(StringRef Key) {
120 CacheShard &Shard = CacheShards[llvm::hash_value(Key) % NumShards];
121 std::unique_lock<std::mutex> LockGuard(Shard.CacheLock);
122 auto It = Shard.Cache.try_emplace(Key);
123 return It.first->getValue();
124 }
125
126 /// Whitelist file extensions that should be minimized, treating no extension as
127 /// a source file that should be minimized.
128 ///
129 /// This is kinda hacky, it would be better if we knew what kind of file Clang
130 /// was expecting instead.
shouldMinimize(StringRef Filename)131 static bool shouldMinimize(StringRef Filename) {
132 StringRef Ext = llvm::sys::path::extension(Filename);
133 if (Ext.empty())
134 return true; // C++ standard library
135 return llvm::StringSwitch<bool>(Ext)
136 .CasesLower(".c", ".cc", ".cpp", ".c++", ".cxx", true)
137 .CasesLower(".h", ".hh", ".hpp", ".h++", ".hxx", true)
138 .CasesLower(".m", ".mm", true)
139 .CasesLower(".i", ".ii", ".mi", ".mmi", true)
140 .CasesLower(".def", ".inc", true)
141 .Default(false);
142 }
143
144
shouldCacheStatFailures(StringRef Filename)145 static bool shouldCacheStatFailures(StringRef Filename) {
146 StringRef Ext = llvm::sys::path::extension(Filename);
147 if (Ext.empty())
148 return false; // This may be the module cache directory.
149 return shouldMinimize(Filename); // Only cache stat failures on source files.
150 }
151
152 llvm::ErrorOr<const CachedFileSystemEntry *>
getOrCreateFileSystemEntry(const StringRef Filename)153 DependencyScanningWorkerFilesystem::getOrCreateFileSystemEntry(
154 const StringRef Filename) {
155 if (const CachedFileSystemEntry *Entry = getCachedEntry(Filename)) {
156 return Entry;
157 }
158
159 // FIXME: Handle PCM/PCH files.
160 // FIXME: Handle module map files.
161
162 bool KeepOriginalSource = IgnoredFiles.count(Filename) ||
163 !shouldMinimize(Filename);
164 DependencyScanningFilesystemSharedCache::SharedFileSystemEntry
165 &SharedCacheEntry = SharedCache.get(Filename);
166 const CachedFileSystemEntry *Result;
167 {
168 std::unique_lock<std::mutex> LockGuard(SharedCacheEntry.ValueLock);
169 CachedFileSystemEntry &CacheEntry = SharedCacheEntry.Value;
170
171 if (!CacheEntry.isValid()) {
172 llvm::vfs::FileSystem &FS = getUnderlyingFS();
173 auto MaybeStatus = FS.status(Filename);
174 if (!MaybeStatus) {
175 if (!shouldCacheStatFailures(Filename))
176 // HACK: We need to always restat non source files if the stat fails.
177 // This is because Clang first looks up the module cache and module
178 // files before building them, and then looks for them again. If we
179 // cache the stat failure, it won't see them the second time.
180 return MaybeStatus.getError();
181 else
182 CacheEntry = CachedFileSystemEntry(MaybeStatus.getError());
183 } else if (MaybeStatus->isDirectory())
184 CacheEntry = CachedFileSystemEntry::createDirectoryEntry(
185 std::move(*MaybeStatus));
186 else
187 CacheEntry = CachedFileSystemEntry::createFileEntry(
188 Filename, FS, !KeepOriginalSource);
189 }
190
191 Result = &CacheEntry;
192 }
193
194 // Store the result in the local cache.
195 setCachedEntry(Filename, Result);
196 return Result;
197 }
198
199 llvm::ErrorOr<llvm::vfs::Status>
status(const Twine & Path)200 DependencyScanningWorkerFilesystem::status(const Twine &Path) {
201 SmallString<256> OwnedFilename;
202 StringRef Filename = Path.toStringRef(OwnedFilename);
203 const llvm::ErrorOr<const CachedFileSystemEntry *> Result =
204 getOrCreateFileSystemEntry(Filename);
205 if (!Result)
206 return Result.getError();
207 return (*Result)->getStatus();
208 }
209
210 namespace {
211
212 /// The VFS that is used by clang consumes the \c CachedFileSystemEntry using
213 /// this subclass.
214 class MinimizedVFSFile final : public llvm::vfs::File {
215 public:
MinimizedVFSFile(std::unique_ptr<llvm::MemoryBuffer> Buffer,llvm::vfs::Status Stat)216 MinimizedVFSFile(std::unique_ptr<llvm::MemoryBuffer> Buffer,
217 llvm::vfs::Status Stat)
218 : Buffer(std::move(Buffer)), Stat(std::move(Stat)) {}
219
220 static llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>
221 create(const CachedFileSystemEntry *Entry,
222 ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings);
223
status()224 llvm::ErrorOr<llvm::vfs::Status> status() override { return Stat; }
225
226 llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
getBuffer(const Twine & Name,int64_t FileSize,bool RequiresNullTerminator,bool IsVolatile)227 getBuffer(const Twine &Name, int64_t FileSize, bool RequiresNullTerminator,
228 bool IsVolatile) override {
229 return std::move(Buffer);
230 }
231
close()232 std::error_code close() override { return {}; }
233
234 private:
235 std::unique_ptr<llvm::MemoryBuffer> Buffer;
236 llvm::vfs::Status Stat;
237 };
238
239 } // end anonymous namespace
240
create(const CachedFileSystemEntry * Entry,ExcludedPreprocessorDirectiveSkipMapping * PPSkipMappings)241 llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>> MinimizedVFSFile::create(
242 const CachedFileSystemEntry *Entry,
243 ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings) {
244 if (Entry->isDirectory())
245 return llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>(
246 std::make_error_code(std::errc::is_a_directory));
247 llvm::ErrorOr<StringRef> Contents = Entry->getContents();
248 if (!Contents)
249 return Contents.getError();
250 auto Result = std::make_unique<MinimizedVFSFile>(
251 llvm::MemoryBuffer::getMemBuffer(*Contents, Entry->getName(),
252 /*RequiresNullTerminator=*/false),
253 *Entry->getStatus());
254 if (!Entry->getPPSkippedRangeMapping().empty() && PPSkipMappings)
255 (*PPSkipMappings)[Result->Buffer->getBufferStart()] =
256 &Entry->getPPSkippedRangeMapping();
257 return llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>(
258 std::unique_ptr<llvm::vfs::File>(std::move(Result)));
259 }
260
261 llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>
openFileForRead(const Twine & Path)262 DependencyScanningWorkerFilesystem::openFileForRead(const Twine &Path) {
263 SmallString<256> OwnedFilename;
264 StringRef Filename = Path.toStringRef(OwnedFilename);
265
266 const llvm::ErrorOr<const CachedFileSystemEntry *> Result =
267 getOrCreateFileSystemEntry(Filename);
268 if (!Result)
269 return Result.getError();
270 return MinimizedVFSFile::create(Result.get(), PPSkipMappings);
271 }
272