Add hash_value support for tuples.

include/llvm/ADT/Hashing.h

@@ -53,6 +53,7 @@
 #include <cassert>
 #include <cstring>
 #include <string>
+#include <tuple>
 #include <utility>
 
 namespace llvm {
@@ -656,6 +657,33 @@ hash_code hash_value(const std::basic_string<T> &arg) {
   return hash_combine_range(arg.begin(), arg.end());
 }
 
+template<unsigned ...Indices>
+struct UnsignedConstantIndexSet { };
+
+template<unsigned I, unsigned N, unsigned ...Indices>
+struct MakeUnsignedConstantIndexSet {
+  typedef typename MakeUnsignedConstantIndexSet<I+1, N, Indices..., I>::Type
+    Type;
+};
+
+template<unsigned N, unsigned ...Indices>
+struct MakeUnsignedConstantIndexSet<N, N, Indices...> {
+  typedef UnsignedConstantIndexSet<Indices...> Type;
+};
+
+template <typename ...Ts, unsigned ...Indices>
+hash_code hash_value_tuple_helper(const std::tuple<Ts...> &arg,
+                                  UnsignedConstantIndexSet<Indices...> indices) {
+  return hash_combine(hash_value(std::get<Indices>(arg))...);
+}
+
+template <typename ...Ts>
+hash_code hash_value(const std::tuple<Ts...> &arg) {
+  return hash_value_tuple_helper(
+           arg, 
+           typename MakeUnsignedConstantIndexSet<0, sizeof...(Ts)>::Type());
+}
+
 } // namespace llvm
 
 #endif