Index: include/llvm/Support/RandomNumberGenerator.h
===================================================================
--- include/llvm/Support/RandomNumberGenerator.h	(revision 229790)
+++ include/llvm/Support/RandomNumberGenerator.h	(working copy)
@@ -33,6 +33,9 @@
 public:
   /// Returns a random number in the range [0, Max).
   uint_fast64_t operator()();
+  /// Returns a random number in the range [0, Limit).
+  /// Limit must be in range [1, Max].
+  uint_fast64_t operator()(uint_fast64_t Limit);
 
 private:
   /// Seeds and salts the underlying RNG engine.
Index: lib/Support/RandomNumberGenerator.cpp
===================================================================
--- lib/Support/RandomNumberGenerator.cpp	(revision 229790)
+++ lib/Support/RandomNumberGenerator.cpp	(working copy)
@@ -53,3 +53,18 @@
 uint_fast64_t RandomNumberGenerator::operator()() {
   return Generator();
 }
+
+uint_fast64_t RandomNumberGenerator::operator()(uint_fast64_t Limit) {
+  assert(Limit > 0 && Limit <= Generator.max());
+  uint_fast64_t Value, Remainder;
+  // If Limit doesn't divide Generator.max(), the value range doesn't
+  // factorise into equal stripes as the last stripe is partial.
+  // This is the case if Limit + Value - Remainder is too large.
+  // The expression is reorganised slightly to avoid possible
+  // (unsigned) overflow.
+  do {
+    Value = Generator();
+    Remainder = Value % Limit;
+  } while (Value - Remainder > Generator.max() - Limit);
+  return Remainder;
+}