[llvm] 199af46 - Add hashing support for std::tuple

[Dmitri Gribenko via llvm-commits]

Author: Michael Forster
Date: 2020-07-16T19:01:25+02:00
New Revision: 199af46e50aa3576657bff58769571b0a5dc92df

URL: https://github.com/llvm/llvm-project/commit/199af46e50aa3576657bff58769571b0a5dc92df
DIFF: https://github.com/llvm/llvm-project/commit/199af46e50aa3576657bff58769571b0a5dc92df.diff

LOG: Add hashing support for std::tuple

Summary:
All tuple values are passed directly to hash_combine. This is inspired by the implementation used for Swift:

https://github.com/llvm/llvm-project-staging/commit/4a1b4edbe1d1969284c1528e2950ac81b25edc8f
https://github.com/llvm/llvm-project-staging/commit/845f3829b91522920a59c351b9011af01c5c7f87

Reviewers: gribozavr2

Reviewed By: gribozavr2

Subscribers: dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D83887

Added: 
    

Modified: 
    llvm/include/llvm/ADT/Hashing.h
    llvm/unittests/ADT/HashingTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/ADT/Hashing.h b/llvm/include/llvm/ADT/Hashing.h
index 9ee310c879fd..cb53b7fa7469 100644
--- a/llvm/include/llvm/ADT/Hashing.h
+++ b/llvm/include/llvm/ADT/Hashing.h
@@ -52,6 +52,7 @@
 #include <cassert>
 #include <cstring>
 #include <string>
+#include <tuple>
 #include <utility>
 
 namespace llvm {
@@ -112,6 +113,10 @@ template <typename T> hash_code hash_value(const T *ptr);
 template <typename T, typename U>
 hash_code hash_value(const std::pair<T, U> &arg);
 
+/// Compute a hash_code for a tuple.
+template <typename... Ts>
+hash_code hash_value(const std::tuple<Ts...> &arg);
+
 /// Compute a hash_code for a standard string.
 template <typename T>
 hash_code hash_value(const std::basic_string<T> &arg);
@@ -645,6 +650,26 @@ hash_code hash_value(const std::pair<T, U> &arg) {
   return hash_combine(arg.first, arg.second);
 }
 
+// Implementation details for the hash_value overload for std::tuple<...>(...).
+namespace hashing {
+namespace detail {
+
+template <typename... Ts, std::size_t... Indices>
+hash_code hash_value_tuple_helper(const std::tuple<Ts...> &arg,
+                                  std::index_sequence<Indices...> indices) {
+  return hash_combine(std::get<Indices>(arg)...);
+}
+
+} // namespace detail
+} // namespace hashing
+
+template <typename... Ts>
+hash_code hash_value(const std::tuple<Ts...> &arg) {
+  // TODO: Use std::apply when LLVM starts using C++17.
+  return ::llvm::hashing::detail::hash_value_tuple_helper(
+      arg, typename std::index_sequence_for<Ts...>());
+}
+
 // Declared and documented above, but defined here so that any of the hashing
 // infrastructure is available.
 template <typename T>

diff  --git a/llvm/unittests/ADT/HashingTest.cpp b/llvm/unittests/ADT/HashingTest.cpp
index 66d63d437a46..d2cda3afdda0 100644
--- a/llvm/unittests/ADT/HashingTest.cpp
+++ b/llvm/unittests/ADT/HashingTest.cpp
@@ -101,6 +101,17 @@ TEST(HashingTest, HashValueStdPair) {
             hash_value(std::make_pair(obj1, std::make_pair(obj2, obj3))));
 }
 
+TEST(HashingTest, HashValueStdTuple) {
+  EXPECT_EQ(hash_combine(), hash_value(std::make_tuple()));
+  EXPECT_EQ(hash_combine(42), hash_value(std::make_tuple(42)));
+  EXPECT_EQ(hash_combine(42, 'c'), hash_value(std::make_tuple(42, 'c')));
+
+  EXPECT_NE(hash_combine(43, 42), hash_value(std::make_tuple(42, 43)));
+  EXPECT_NE(hash_combine(42, 43), hash_value(std::make_tuple(42ull, 43ull)));
+  EXPECT_NE(hash_combine(42, 43), hash_value(std::make_tuple(42, 43ull)));
+  EXPECT_NE(hash_combine(42, 43), hash_value(std::make_tuple(42ull, 43)));
+}
+
 TEST(HashingTest, HashValueStdString) {
   std::string s = "Hello World!";
   EXPECT_EQ(hash_combine_range(s.c_str(), s.c_str() + s.size()), hash_value(s));