[clang-tidy] Optimize readability-identifier-naming

- Reduce disk IO usage by adding cache to an realpath
  introduced by llvm#81985

Author: PiotrZSL

clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp

@@ -1414,13 +1414,21 @@ IdentifierNamingCheck::getDiagInfo(const NamingCheckId &ID,
                   }};
 }
 
+StringRef IdentifierNamingCheck::getRealFileName(StringRef FileName) const {
+  auto Iter = RealFileNameCache.try_emplace(FileName);
+  SmallString<256U> &RealFileName = Iter.first->getValue();
+  if (!Iter.second)
+    return RealFileName;
+  llvm::sys::fs::real_path(FileName, RealFileName);
+  return RealFileName;
+}
+
 const IdentifierNamingCheck::FileStyle &
 IdentifierNamingCheck::getStyleForFile(StringRef FileName) const {
   if (!GetConfigPerFile)
     return *MainFileStyle;
 
-  SmallString<128> RealFileName;
-  llvm::sys::fs::real_path(FileName, RealFileName);
+  StringRef RealFileName = getRealFileName(FileName);
   StringRef Parent = llvm::sys::path::parent_path(RealFileName);
   auto Iter = NamingStylesCache.find(Parent);
   if (Iter != NamingStylesCache.end())

clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.h

@@ -205,6 +205,7 @@ class IdentifierNamingCheck final : public RenamerClangTidyCheck {
                        const NamingCheckFailure &Failure) const override;
 
   const FileStyle &getStyleForFile(StringRef FileName) const;
+  StringRef getRealFileName(StringRef FileName) const;
 
   /// Find the style kind of a field in an anonymous record.
   StyleKind findStyleKindForAnonField(
@@ -222,6 +223,7 @@ class IdentifierNamingCheck final : public RenamerClangTidyCheck {
   /// Stores the style options as a vector, indexed by the specified \ref
   /// StyleKind, for a given directory.
   mutable llvm::StringMap<FileStyle> NamingStylesCache;
+  mutable llvm::StringMap<SmallString<256U>> RealFileNameCache;
   FileStyle *MainFileStyle;
   ClangTidyContext *Context;
   const bool GetConfigPerFile;