[clang] [llvm] [llvm][clang] Trace VFS calls (PR #88326)

[Jan Svoboda via llvm-commits]

https://github.com/jansvoboda11 updated https://github.com/llvm/llvm-project/pull/88326

>From b395e907fcb3895941b58e0d00ef69f14b07c4ae Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Fri, 12 Apr 2024 10:47:13 -0700
Subject: [PATCH] [llvm][support] Implement tracing virtual file system

---
 .../DependencyScanningFilesystemTest.cpp      | 26 +---------
 llvm/include/llvm/Support/VirtualFileSystem.h | 48 ++++++++++++++++++
 llvm/lib/Support/VirtualFileSystem.cpp        | 13 +++++
 .../Support/VirtualFileSystemTest.cpp         | 50 +++++++++++++++++++
 4 files changed, 113 insertions(+), 24 deletions(-)

diff --git a/clang/unittests/Tooling/DependencyScanning/DependencyScanningFilesystemTest.cpp b/clang/unittests/Tooling/DependencyScanning/DependencyScanningFilesystemTest.cpp
index 697b7d70ff035a..c1a06c1f5ea20e 100644
--- a/clang/unittests/Tooling/DependencyScanning/DependencyScanningFilesystemTest.cpp
+++ b/clang/unittests/Tooling/DependencyScanning/DependencyScanningFilesystemTest.cpp
@@ -13,33 +13,11 @@
 
 using namespace clang::tooling::dependencies;
 
-namespace {
-struct InstrumentingFilesystem
-    : llvm::RTTIExtends<InstrumentingFilesystem, llvm::vfs::ProxyFileSystem> {
-  unsigned NumStatusCalls = 0;
-  unsigned NumGetRealPathCalls = 0;
-
-  using llvm::RTTIExtends<InstrumentingFilesystem,
-                          llvm::vfs::ProxyFileSystem>::RTTIExtends;
-
-  llvm::ErrorOr<llvm::vfs::Status> status(const llvm::Twine &Path) override {
-    ++NumStatusCalls;
-    return ProxyFileSystem::status(Path);
-  }
-
-  std::error_code getRealPath(const llvm::Twine &Path,
-                              llvm::SmallVectorImpl<char> &Output) override {
-    ++NumGetRealPathCalls;
-    return ProxyFileSystem::getRealPath(Path, Output);
-  }
-};
-} // namespace
-
 TEST(DependencyScanningWorkerFilesystem, CacheStatusFailures) {
   auto InMemoryFS = llvm::makeIntrusiveRefCnt<llvm::vfs::InMemoryFileSystem>();
 
   auto InstrumentingFS =
-      llvm::makeIntrusiveRefCnt<InstrumentingFilesystem>(InMemoryFS);
+      llvm::makeIntrusiveRefCnt<llvm::vfs::TracingFileSystem>(InMemoryFS);
 
   DependencyScanningFilesystemSharedCache SharedCache;
   DependencyScanningWorkerFilesystem DepFS(SharedCache, InstrumentingFS);
@@ -65,7 +43,7 @@ TEST(DependencyScanningFilesystem, CacheGetRealPath) {
   InMemoryFS->addFile("/bar", 0, llvm::MemoryBuffer::getMemBuffer(""));
 
   auto InstrumentingFS =
-      llvm::makeIntrusiveRefCnt<InstrumentingFilesystem>(InMemoryFS);
+      llvm::makeIntrusiveRefCnt<llvm::vfs::TracingFileSystem>(InMemoryFS);
 
   DependencyScanningFilesystemSharedCache SharedCache;
   DependencyScanningWorkerFilesystem DepFS(SharedCache, InstrumentingFS);
diff --git a/llvm/include/llvm/Support/VirtualFileSystem.h b/llvm/include/llvm/Support/VirtualFileSystem.h
index 4b1ca0c3d262b6..1d851d4d9aea51 100644
--- a/llvm/include/llvm/Support/VirtualFileSystem.h
+++ b/llvm/include/llvm/Support/VirtualFileSystem.h
@@ -1125,6 +1125,54 @@ class YAMLVFSWriter {
   void write(llvm::raw_ostream &OS);
 };
 
+/// File system that tracks the number of calls to the underlying file system.
+/// This is particularly useful when wrapped around \c RealFileSystem to add
+/// lightweight tracking of expensive syscalls.
+class TracingFileSystem
+    : public llvm::RTTIExtends<TracingFileSystem, ProxyFileSystem> {
+public:
+  static const char ID;
+
+  std::size_t NumStatusCalls = 0;
+  std::size_t NumOpenFileForReadCalls = 0;
+  std::size_t NumDirBeginCalls = 0;
+  std::size_t NumGetRealPathCalls = 0;
+  std::size_t NumIsLocalCalls = 0;
+
+  TracingFileSystem(llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS)
+      : RTTIExtends(std::move(FS)) {}
+
+  ErrorOr<Status> status(const Twine &Path) override {
+    ++NumStatusCalls;
+    return ProxyFileSystem::status(Path);
+  }
+
+  ErrorOr<std::unique_ptr<File>> openFileForRead(const Twine &Path) override {
+    ++NumOpenFileForReadCalls;
+    return ProxyFileSystem::openFileForRead(Path);
+  }
+
+  directory_iterator dir_begin(const Twine &Dir, std::error_code &EC) override {
+    ++NumDirBeginCalls;
+    return ProxyFileSystem::dir_begin(Dir, EC);
+  }
+
+  std::error_code getRealPath(const Twine &Path,
+                              SmallVectorImpl<char> &Output) override {
+    ++NumGetRealPathCalls;
+    return ProxyFileSystem::getRealPath(Path, Output);
+  }
+
+  std::error_code isLocal(const Twine &Path, bool &Result) override {
+    ++NumIsLocalCalls;
+    return ProxyFileSystem::isLocal(Path, Result);
+  }
+
+protected:
+  void printImpl(raw_ostream &OS, PrintType Type,
+                 unsigned IndentLevel) const override;
+};
+
 } // namespace vfs
 } // namespace llvm
 
diff --git a/llvm/lib/Support/VirtualFileSystem.cpp b/llvm/lib/Support/VirtualFileSystem.cpp
index 32b480028e71b4..fe8924585e1ceb 100644
--- a/llvm/lib/Support/VirtualFileSystem.cpp
+++ b/llvm/lib/Support/VirtualFileSystem.cpp
@@ -2877,8 +2877,21 @@ recursive_directory_iterator::increment(std::error_code &EC) {
   return *this;
 }
 
+void TracingFileSystem::printImpl(raw_ostream &OS, PrintType Type,
+                                  unsigned IndentLevel) const {
+  printIndent(OS, IndentLevel);
+  OS << "TracingFileSystem\n";
+  if (Type == PrintType::Summary)
+    return;
+
+  if (Type == PrintType::Contents)
+    Type = PrintType::Summary;
+  getUnderlyingFS().print(OS, Type, IndentLevel + 1);
+}
+
 const char FileSystem::ID = 0;
 const char OverlayFileSystem::ID = 0;
 const char ProxyFileSystem::ID = 0;
 const char InMemoryFileSystem::ID = 0;
 const char RedirectingFileSystem::ID = 0;
+const char TracingFileSystem::ID = 0;
diff --git a/llvm/unittests/Support/VirtualFileSystemTest.cpp b/llvm/unittests/Support/VirtualFileSystemTest.cpp
index 49a2e19e4f74cd..c692590eca2725 100644
--- a/llvm/unittests/Support/VirtualFileSystemTest.cpp
+++ b/llvm/unittests/Support/VirtualFileSystemTest.cpp
@@ -3395,3 +3395,53 @@ TEST(RedirectingFileSystemTest, ExternalPaths) {
 
   EXPECT_EQ(CheckFS->SeenPaths, Expected);
 }
+
+TEST(TracingFileSystemTest, TracingWorks) {
+  auto InMemoryFS = makeIntrusiveRefCnt<vfs::InMemoryFileSystem>();
+  auto TracingFS =
+      makeIntrusiveRefCnt<vfs::TracingFileSystem>(std::move(InMemoryFS));
+
+  EXPECT_EQ(TracingFS->NumStatusCalls, 0u);
+  EXPECT_EQ(TracingFS->NumOpenFileForReadCalls, 0u);
+  EXPECT_EQ(TracingFS->NumDirBeginCalls, 0u);
+  EXPECT_EQ(TracingFS->NumGetRealPathCalls, 0u);
+  EXPECT_EQ(TracingFS->NumIsLocalCalls, 0u);
+
+  (void)TracingFS->status("/foo");
+  EXPECT_EQ(TracingFS->NumStatusCalls, 1u);
+  EXPECT_EQ(TracingFS->NumOpenFileForReadCalls, 0u);
+  EXPECT_EQ(TracingFS->NumDirBeginCalls, 0u);
+  EXPECT_EQ(TracingFS->NumGetRealPathCalls, 0u);
+  EXPECT_EQ(TracingFS->NumIsLocalCalls, 0u);
+
+  (void)TracingFS->openFileForRead("/foo");
+  EXPECT_EQ(TracingFS->NumStatusCalls, 1u);
+  EXPECT_EQ(TracingFS->NumOpenFileForReadCalls, 1u);
+  EXPECT_EQ(TracingFS->NumDirBeginCalls, 0u);
+  EXPECT_EQ(TracingFS->NumGetRealPathCalls, 0u);
+  EXPECT_EQ(TracingFS->NumIsLocalCalls, 0u);
+
+  std::error_code EC;
+  (void)TracingFS->dir_begin("/foo", EC);
+  EXPECT_EQ(TracingFS->NumStatusCalls, 1u);
+  EXPECT_EQ(TracingFS->NumOpenFileForReadCalls, 1u);
+  EXPECT_EQ(TracingFS->NumDirBeginCalls, 1u);
+  EXPECT_EQ(TracingFS->NumGetRealPathCalls, 0u);
+  EXPECT_EQ(TracingFS->NumIsLocalCalls, 0u);
+
+  SmallString<128> RealPath;
+  (void)TracingFS->getRealPath("/foo", RealPath);
+  EXPECT_EQ(TracingFS->NumStatusCalls, 1u);
+  EXPECT_EQ(TracingFS->NumOpenFileForReadCalls, 1u);
+  EXPECT_EQ(TracingFS->NumDirBeginCalls, 1u);
+  EXPECT_EQ(TracingFS->NumGetRealPathCalls, 1u);
+  EXPECT_EQ(TracingFS->NumIsLocalCalls, 0u);
+
+  bool IsLocal;
+  (void)TracingFS->isLocal("/foo", IsLocal);
+  EXPECT_EQ(TracingFS->NumStatusCalls, 1u);
+  EXPECT_EQ(TracingFS->NumOpenFileForReadCalls, 1u);
+  EXPECT_EQ(TracingFS->NumDirBeginCalls, 1u);
+  EXPECT_EQ(TracingFS->NumGetRealPathCalls, 1u);
+  EXPECT_EQ(TracingFS->NumIsLocalCalls, 1u);
+}