ADT: Add hash_value overload for Optional

Add a `hash_value` for Optional so that other data structures with
optional fields can easily hash them. I have a use for this in an
upcoming patch.

Differential Revision: https://reviews.llvm.org/D92676

2 files changed, 22 insertions, 0 deletions

diff --git a/llvm/include/llvm/ADT/Optional.h b/llvm/include/llvm/ADT/Optional.h
index be32178..daa9ee6 100644
--- a/llvm/include/llvm/ADT/Optional.h
+++ b/llvm/include/llvm/ADT/Optional.h
@@ -15,6 +15,7 @@
 #ifndef LLVM_ADT_OPTIONAL_H
 #define LLVM_ADT_OPTIONAL_H
 
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/None.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/type_traits.h"
@@ -299,6 +300,10 @@ public:
 #endif
 };
 
+template <class T> llvm::hash_code hash_value(const Optional<T> &O) {
+  return O ? hash_combine(true, *O) : hash_value(false);
+}
+
 template <typename T, typename U>
 constexpr bool operator==(const Optional<T> &X, const Optional<U> &Y) {
   if (X && Y)
diff --git a/llvm/unittests/ADT/OptionalTest.cpp b/llvm/unittests/ADT/OptionalTest.cpp
index 17a7640..c7fa796 100644
--- a/llvm/unittests/ADT/OptionalTest.cpp
+++ b/llvm/unittests/ADT/OptionalTest.cpp
@@ -599,4 +599,21 @@ TEST(OptionalTest, UseInUnitTests) {
   EXPECT_NONFATAL_FAILURE(EXPECT_EQ(llvm::None, Comparable::get()), "object");
 }
 
+TEST(OptionalTest, HashValue) {
+  // Check that None, false, and true all hash differently.
+  Optional<bool> B, B0 = false, B1 = true;
+  EXPECT_NE(hash_value(B0), hash_value(B));
+  EXPECT_NE(hash_value(B1), hash_value(B));
+  EXPECT_NE(hash_value(B1), hash_value(B0));
+
+  // Check that None, 0, and 1 all hash differently.
+  Optional<int> I, I0 = 0, I1 = 1;
+  EXPECT_NE(hash_value(I0), hash_value(I));
+  EXPECT_NE(hash_value(I1), hash_value(I));
+  EXPECT_NE(hash_value(I1), hash_value(I0));
+
+  // Check None hash the same way regardless of type.
+  EXPECT_EQ(hash_value(B), hash_value(I));
+}
+
 } // end anonymous namespace