[all-commits] [llvm/llvm-project] 6e4dcb: [clang][deps] Print tracing VFS data (#108056)

[Jan Svoboda via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6e4dcbb21dab47e520f2cd19e7017af27328669e
      https://github.com/llvm/llvm-project/commit/6e4dcbb21dab47e520f2cd19e7017af27328669e
  Author: Jan Svoboda <jan_svoboda at apple.com>
  Date:   2024-09-11 (Wed, 11 Sep 2024)

  Changed paths:
    M clang/include/clang/Tooling/DependencyScanning/DependencyScanningService.h
    M clang/include/clang/Tooling/DependencyScanning/DependencyScanningTool.h
    M clang/include/clang/Tooling/DependencyScanning/DependencyScanningWorker.h
    M clang/lib/Basic/FileManager.cpp
    M clang/lib/Frontend/CompilerInstance.cpp
    M clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp
    M clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp
    A clang/test/ClangScanDeps/verbose.test
    A clang/test/Misc/print-stats-vfs.test
    M clang/tools/clang-scan-deps/ClangScanDeps.cpp

  Log Message:
  -----------
  [clang][deps] Print tracing VFS data (#108056)

Clang's `-cc1 -print-stats` shows lots of useful internal data including
basic `FileManager` stats. Since this layer caches some results, it is
unclear how that information translates to actual filesystem accesses.
This PR uses `llvm::vfs::TracingFileSystem` to provide that missing
information.

Similar mechanism is implemented for `clang-scan-deps`'s verbose mode
(`-v`). IO contention proved to be a real bottleneck a couple of times
already and this new feature should make those easier to detect in the
future. The tracing VFS is inserted below the caching FS and above the
real FS.



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