Index: llvm/trunk/include/llvm/Support/Path.h
===================================================================
--- llvm/trunk/include/llvm/Support/Path.h
+++ llvm/trunk/include/llvm/Support/Path.h
@@ -87,6 +87,9 @@
   reverse_iterator &operator++();    // preincrement
   bool operator==(const reverse_iterator &RHS) const;
   bool operator!=(const reverse_iterator &RHS) const { return !(*this == RHS); }
+
+  /// @brief Difference in bytes between this and RHS.
+  ptrdiff_t operator-(const reverse_iterator &RHS) const;
 };
 
 /// @brief Get begin iterator over \a path.
Index: llvm/trunk/lib/Support/Path.cpp
===================================================================
--- llvm/trunk/lib/Support/Path.cpp
+++ llvm/trunk/lib/Support/Path.cpp
@@ -353,6 +353,10 @@
          Position == RHS.Position;
 }
 
+ptrdiff_t reverse_iterator::operator-(const reverse_iterator &RHS) const {
+  return Position - RHS.Position;
+}
+
 StringRef root_path(StringRef path) {
   const_iterator b = begin(path),
                  pos = b,