Index: llvm/include/llvm/ADT/iterator.h
===================================================================
--- llvm/include/llvm/ADT/iterator.h
+++ llvm/include/llvm/ADT/iterator.h
@@ -86,6 +86,12 @@
     tmp -= n;
     return tmp;
   }
+  DifferenceTypeT operator-(const DerivedT &i) const {
+    static_assert(
+        IsRandomAccess,
+        "The '-' operator is only defined for random access iterators.");
+    return i - *static_cast<const DerivedT *>(this);
+  }
 
   DerivedT &operator++() {
     return static_cast<DerivedT *>(this)->operator+=(1);
@@ -114,6 +120,13 @@
     return !static_cast<const DerivedT *>(this)->operator==(RHS);
   }
 
+  bool operator<(const DerivedT &RHS) const {
+    static_assert(
+        IsRandomAccess,
+        "Relational operators are only defined for random access iterators.");
+    return !static_cast<const DerivedT *>(this)->operator>(RHS) &&
+           !static_cast<const DerivedT *>(this)->operator==(RHS);
+  }
   bool operator>(const DerivedT &RHS) const {
     static_assert(
         IsRandomAccess,