[clang-tidy][NFC] Remove the double look-up on IncludeInserter

[njames93]

Summary

Refactor out the double lookup in IncludeInserter when trying to get the IncludeSorter for a specified FileID.

[aaron.ballman]

LGTM

clang-tools-extra/clang-tidy/utils/IncludeInserter.h

public:
   /// error or if inclusion directive already exists.
   llvm::Optional<FixItHint>
   CreateIncludeInsertion(FileID FileID, llvm::StringRef Header, bool IsAngled);
 
 private:
   void AddInclude(StringRef FileName, bool IsAngled,
                   SourceLocation HashLocation, SourceLocation EndLocation);
 
+  IncludeSorter &getOrCreate(FileID FileID);
+
   llvm::DenseMap<FileID, std::unique_ptr<IncludeSorter>> IncludeSorterByFile;
   llvm::DenseMap<FileID, std::set<std::string>> InsertedHeaders;
   const SourceManager &SourceMgr;
   const LangOptions &LangOpts;
   const IncludeSorter::IncludeStyle Style;
   friend class IncludeInserterCallback;
 };
 
 } // namespace utils
 } // namespace tidy
 } // namespace clang
 #endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_INCLUDEINSERTER_H

clang-tools-extra/clang-tidy/utils/IncludeInserter.cpp

IncludeInserter::IncludeInserter(const SourceManager &SourceMgr,
     : SourceMgr(SourceMgr), LangOpts(LangOpts), Style(Style) {}
 
 IncludeInserter::~IncludeInserter() {}
 
 std::unique_ptr<PPCallbacks> IncludeInserter::CreatePPCallbacks() {
   return std::make_unique<IncludeInserterCallback>(this);
 }
 
+IncludeSorter &IncludeInserter::getOrCreate(FileID FileID) {
+  // std::unique_ptr is cheap to construct, so force a construction now to save
+  // the lookup needed if we were to insert into the map.
+  std::unique_ptr<IncludeSorter> &Entry = IncludeSorterByFile[FileID];
+  if (!Entry) {
+    // If it wasn't found, Entry will be default constructed to nullptr.
+    Entry = std::make_unique<IncludeSorter>(
+        &SourceMgr, &LangOpts, FileID,
+        SourceMgr.getFilename(SourceMgr.getLocForStartOfFile(FileID)), Style);
+  }
+  return *Entry;
+}
+
 llvm::Optional<FixItHint>
 IncludeInserter::CreateIncludeInsertion(FileID FileID, StringRef Header,
                                         bool IsAngled) {
   // We assume the same Header will never be included both angled and not
   // angled.
   if (!InsertedHeaders[FileID].insert(std::string(Header)).second)
     return llvm::None;
 
-  if (IncludeSorterByFile.find(FileID) == IncludeSorterByFile.end()) {
-    // This may happen if there have been no preprocessor directives in this
-    // file.
-    IncludeSorterByFile.insert(std::make_pair(
-        FileID,
-        std::make_unique<IncludeSorter>(
-            &SourceMgr, &LangOpts, FileID,
-            SourceMgr.getFilename(SourceMgr.getLocForStartOfFile(FileID)),
-            Style)));
-  }
-  return IncludeSorterByFile[FileID]->CreateIncludeInsertion(Header, IsAngled);
+  return getOrCreate(FileID).CreateIncludeInsertion(Header, IsAngled);
 }
 
 void IncludeInserter::AddInclude(StringRef FileName, bool IsAngled,
                                  SourceLocation HashLocation,
                                  SourceLocation EndLocation) {
   FileID FileID = SourceMgr.getFileID(HashLocation);
-  if (IncludeSorterByFile.find(FileID) == IncludeSorterByFile.end()) {
-    IncludeSorterByFile.insert(std::make_pair(
-        FileID, std::make_unique<IncludeSorter>(
-                    &SourceMgr, &LangOpts, FileID,
-                    SourceMgr.getFilename(HashLocation), Style)));
-  }
-  IncludeSorterByFile[FileID]->AddInclude(FileName, IsAngled, HashLocation,
-                                          EndLocation);
+  getOrCreate(FileID).AddInclude(FileName, IsAngled, HashLocation, EndLocation);
 }
 
 } // namespace utils
 } // namespace tidy
 } // namespace clang