[clang][deps] Cache VFS::getRealPath() and VFS::exists()
#8571
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This is an NFC change split from llvm#68645. (cherry picked from commit fe59cb2)
This is an NFC change split from llvm#68645. (cherry picked from commit edd7fed)
This is an NFC change split from llvm#68645. (cherry picked from commit c11976f)
This PR starts caching calls to `DependencyScanningWorkerFilesystem::getRealPath()` that we use whenever we canonicalize module map path. In the case of the real VFS, this functions performs an expensive syscall that we'd like to do as rarely as possible. This PR keeps the real path out of `CachedFileSystemEntry`, since that's **immutable**; populating the real path on creation of this data structure (every stat/open) would be expensive. (cherry picked from commit a11a432)
(cherry picked from commit a9111d4)
…esystem` to have it use cached `status` (llvm#88152) As-is, calls to `exists()` fallback on the implementation in `ProxyFileSystem::exists` which explicitly calls out to the underlying `FS`, which for the `DependencyScanningFilesystem` (overlay) is the real underlying filesystem. Instead, directly overloading `exists` allows us to have it rely on the cached `status` behavior used elsewhere by the `DependencyScanningFilesystem`. (cherry picked from commit 779ba60)
artemcm
approved these changes
Apr 12, 2024
|
@swift-ci please test |
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Cherry-pick of llvm#68645, llvm#88152 and related NFC commits
Explanation: The dependency scanner caches file system accesses under the assumption that input files are immutable. This PR adds caching of the
VFS::getRealPath()andVFS::exists()calls in order to reduce file system traffic and increase performance.Risk: Low. This is a performance optimization.
Testing: New unit tests were added for the implemented caching behavior.
Reviewed By: @benlangmuir, @jansvoboda11