Index: clang/lib/CodeGen/CGDebugInfo.h
===================================================================
--- clang/lib/CodeGen/CGDebugInfo.h
+++ clang/lib/CodeGen/CGDebugInfo.h
@@ -148,7 +148,7 @@
   llvm::BumpPtrAllocator DebugInfoNames;
   StringRef CWDName;
 
-  llvm::StringMap<llvm::TrackingMDRef> DIFileCache;
+  llvm::DenseMap<const char *, llvm::TrackingMDRef> DIFileCache;
   llvm::DenseMap<const FunctionDecl *, llvm::TrackingMDRef> SPCache;
   /// Cache declarations relevant to DW_TAG_imported_declarations (C++
   /// using declarations and global alias variables) that aren't covered
Index: clang/lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- clang/lib/CodeGen/CGDebugInfo.cpp
+++ clang/lib/CodeGen/CGDebugInfo.cpp
@@ -397,6 +397,17 @@
     // createFile() below for canonicalization if the source file was specified
     // with an absolute path.
     FileName = TheCU->getFile()->getFilename();
+    for (auto It : DIFileCache) {
+      // StringRef operator== does a content comparison.
+      if (FileName == It.first) {
+        // Got a string match, use the existing DIFile if possible.
+        if (llvm::Metadata *V = It.second)
+          return cast<llvm::DIFile>(V);
+        // Fall through to create the DIFile but use the original string.
+        FileName = It.first;
+        break;
+      }
+    }
   } else {
     PresumedLoc PLoc = SM.getPresumedLoc(Loc);
     FileName = PLoc.getFilename();