Index: clang-tidy/ClangTidy.cpp
===================================================================
--- clang-tidy/ClangTidy.cpp
+++ clang-tidy/ClangTidy.cpp
@@ -42,6 +42,8 @@
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include <algorithm>
+#include <string>
+#include <unordered_map>
 #include <utility>
 
 using namespace clang::ast_matchers;
@@ -237,8 +239,13 @@
     if (FilePath.empty())
       return SourceLocation();
 
-    const FileEntry *File = SourceMgr.getFileManager().getFile(FilePath);
-    FileID ID = SourceMgr.createFileID(File, SourceLocation(), SrcMgr::C_User);
+    std::string Path = FilePath.str();
+    if (Path2FileID.find(Path) == Path2FileID.end()) {
+      const FileEntry *File = SourceMgr.getFileManager().getFile(FilePath);
+      Path2FileID[Path] =
+          SourceMgr.createFileID(File, SourceLocation(), SrcMgr::C_User);
+    }
+    FileID ID = Path2FileID[Path];
     return SourceMgr.getLocForStartOfFile(ID).getLocWithOffset(Offset);
   }
 
@@ -248,6 +255,7 @@
         << Message.Message;
   }
 
+  std::unordered_map<std::string, FileID> Path2FileID;
   FileManager Files;
   LangOptions LangOpts; // FIXME: use langopts from each original file
   IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts;