diff --git a/clang/lib/Lex/HeaderMap.cpp b/clang/lib/Lex/HeaderMap.cpp
index 478462c..0432e09 100644
--- a/clang/lib/Lex/HeaderMap.cpp
+++ b/clang/lib/Lex/HeaderMap.cpp
@@ -201,18 +201,29 @@
 /// this HeaderMap.  If so, open it and return its FileEntry.
 const FileEntry *HeaderMap::LookupFile(
     StringRef Filename, FileManager &FM) const {
+
+  SmallString<1024> Path;
+  StringRef Dest = lookupFilename(Filename, Path);
+  if (Dest.empty())
+    return 0;
+
+  return FM.getFile(Dest);
+}
+
+StringRef HeaderMap::lookupFilename(StringRef Filename,
+                                    SmallVectorImpl<char> &DestPath) const {
   const HMapHeader &Hdr = getHeader();
   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
 
   // If the number of buckets is not a power of two, the headermap is corrupt.
   // Don't probe infinitely.
   if (NumBuckets & (NumBuckets-1))
-    return 0;
+    return StringRef();
 
   // Linearly probe the hash table.
   for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
     HMapBucket B = getBucket(Bucket & (NumBuckets-1));
-    if (B.Key == HMAP_EmptyBucketKey) return 0; // Hash miss.
+    if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
 
     // See if the key matches.  If not, probe on.
     if (!Filename.equals_lower(getString(B.Key)))
@@ -220,9 +231,11 @@
 
     // If so, we have a match in the hash table.  Construct the destination
     // path.
-    SmallString<1024> DestPath;
-    DestPath += getString(B.Prefix);
-    DestPath += getString(B.Suffix);
-    return FM.getFile(DestPath.str());
+    StringRef Prefix = getString(B.Prefix);
+    StringRef Suffix = getString(B.Suffix);
+    DestPath.clear();
+    DestPath.append(Prefix.begin(), Prefix.end());
+    DestPath.append(Suffix.begin(), Suffix.end());
+    return StringRef(DestPath.begin(), DestPath.size());
   }
 }