[llvm][support] Implement tracing virtual file system (#88326)

LLVM-based tools often use the `llvm::vfs::FileSystem` instrastructure
to access the file system. This patch adds new kind of a VFS that
performs lightweight tracing of file system operations on an underlying
VFS. This is supposed to aid in investigating file system traffic
without resorting to instrumentation on the operating system level.
There will be follow-up patches that integrate this into Clang and its
dependency scanner.

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/lib/Support/VirtualFileSystem.cpp b/llvm/lib/Support/VirtualFileSystem.cpp
index 6d756f4..928c0b5 100644
--- a/llvm/lib/Support/VirtualFileSystem.cpp
+++ b/llvm/lib/Support/VirtualFileSystem.cpp
@@ -2945,8 +2945,34 @@ 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;
+
+  printIndent(OS, IndentLevel);
+  OS << "NumStatusCalls=" << NumStatusCalls << "\n";
+  printIndent(OS, IndentLevel);
+  OS << "NumOpenFileForReadCalls=" << NumOpenFileForReadCalls << "\n";
+  printIndent(OS, IndentLevel);
+  OS << "NumDirBeginCalls=" << NumDirBeginCalls << "\n";
+  printIndent(OS, IndentLevel);
+  OS << "NumGetRealPathCalls=" << NumGetRealPathCalls << "\n";
+  printIndent(OS, IndentLevel);
+  OS << "NumExistsCalls=" << NumExistsCalls << "\n";
+  printIndent(OS, IndentLevel);
+  OS << "NumIsLocalCalls=" << NumIsLocalCalls << "\n";
+
+  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;