[clang-tidy][NFC] optimize cache for config option

Current implement will cache ConfigOptions for each path, it will create lots of copy of options when project have deep nested folder structure.
New implement use vector to store options and only cache the index to reduce memory usage and avoid meanless copy

Author: HerrCai0907

clang-tools-extra/clang-tidy/ClangTidyOptions.cpp

@@ -337,33 +337,34 @@ FileOptionsBaseProvider::FileOptionsBaseProvider(
 void FileOptionsBaseProvider::addRawFileOptions(
     llvm::StringRef AbsolutePath, std::vector<OptionsSource> &CurOptions) {
   auto CurSize = CurOptions.size();
-
   // Look for a suitable configuration file in all parent directories of the
   // file. Start with the immediate parent directory and move up.
-  StringRef Path = llvm::sys::path::parent_path(AbsolutePath);
-  for (StringRef CurrentPath = Path; !CurrentPath.empty();
-       CurrentPath = llvm::sys::path::parent_path(CurrentPath)) {
-    std::optional<OptionsSource> Result;
-
-    auto Iter = CachedOptions.find(CurrentPath);
-    if (Iter != CachedOptions.end())
-      Result = Iter->second;
-
-    if (!Result)
-      Result = tryReadConfigFile(CurrentPath);
-
-    if (Result) {
-      // Store cached value for all intermediate directories.
-      while (Path != CurrentPath) {
+  StringRef RootPath = llvm::sys::path::parent_path(AbsolutePath);
+  auto MemorizedConfigFile =
+      [this, &RootPath](StringRef CurrentPath) -> std::optional<OptionsSource> {
+    auto Iter = CachedOptions.Memorized.find(CurrentPath);
+    if (Iter != CachedOptions.Memorized.end())
+      return CachedOptions.Storage[Iter->second];
+    std::optional<OptionsSource> OptionsSource = tryReadConfigFile(CurrentPath);
+    if (OptionsSource) {
+      const size_t Index = CachedOptions.Storage.size();
+      CachedOptions.Storage.emplace_back(OptionsSource.value());
+      while (RootPath != CurrentPath) {
         LLVM_DEBUG(llvm::dbgs()
-                   << "Caching configuration for path " << Path << ".\n");
-        if (!CachedOptions.count(Path))
-          CachedOptions[Path] = *Result;
-        Path = llvm::sys::path::parent_path(Path);
+                   << "Caching configuration for path " << RootPath << ".\n");
+        CachedOptions.Memorized[RootPath] = Index;
+        RootPath = llvm::sys::path::parent_path(RootPath);
       }
-      CachedOptions[Path] = *Result;
-
-      CurOptions.push_back(*Result);
+      CachedOptions.Memorized[CurrentPath] = Index;
+      RootPath = llvm::sys::path::parent_path(CurrentPath);
+    }
+    return OptionsSource;
+  };
+  for (StringRef CurrentPath = RootPath; !CurrentPath.empty();
+       CurrentPath = llvm::sys::path::parent_path(CurrentPath)) {
+    if (std::optional<OptionsSource> Result =
+            MemorizedConfigFile(CurrentPath)) {
+      CurOptions.emplace_back(Result.value());
       if (!Result->first.InheritParentConfig.value_or(false))
         break;
     }

clang-tools-extra/clang-tidy/ClangTidyOptions.h

@@ -241,7 +241,10 @@ class FileOptionsBaseProvider : public DefaultOptionsProvider {
   /// \c ConfigHandlers.
   std::optional<OptionsSource> tryReadConfigFile(llvm::StringRef Directory);
 
-  llvm::StringMap<OptionsSource> CachedOptions;
+  struct OptionsCache {
+    llvm::StringMap<size_t> Memorized;
+    llvm::SmallVector<OptionsSource, 4U> Storage;
+  } CachedOptions;
   ClangTidyOptions OverrideOptions;
   ConfigFileHandlers ConfigHandlers;
   llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS;