[clang] [llvm] [clang][deps] Cache `VFS::getRealPath()` (PR #68645)

[Ben Langmuir via cfe-commits]

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@@ -130,11 +130,11 @@ DependencyScanningFilesystemSharedCache::CacheShard::
     getOrEmplaceEntryForFilename(StringRef Filename,
                                  llvm::ErrorOr<llvm::vfs::Status> Stat) {
   std::lock_guard<std::mutex> LockGuard(CacheLock);
-  auto Insertion = EntriesByFilename.insert({Filename, nullptr});
-  if (Insertion.second)
-    Insertion.first->second =
+  const CachedFileSystemEntry *StoredEntry = CacheByFilename[Filename].first;
+  if (!StoredEntry)
+    StoredEntry =
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benlangmuir wrote:

The original code modified the value in the cache, but doesn't this new code only put the value in the local variable StoredEntry (i.e. it's not a reference just a copy)?

https://github.com/llvm/llvm-project/pull/68645