Index: include/llvm/ADT/STLExtras.h
===================================================================
--- include/llvm/ADT/STLExtras.h
+++ include/llvm/ADT/STLExtras.h
@@ -1038,6 +1038,11 @@
   return std::distance(Range.begin(), Range.end());
 }
 
+template <class T, std::size_t N>
+constexpr size_t size(const T (&array)[N]) noexcept {
+  return N;
+}
+
 //===----------------------------------------------------------------------===//
 //     Extra additions to <memory>
 //===----------------------------------------------------------------------===//
Index: unittests/ADT/STLExtrasTest.cpp
===================================================================
--- unittests/ADT/STLExtrasTest.cpp
+++ unittests/ADT/STLExtrasTest.cpp
@@ -364,4 +364,10 @@
   EXPECT_EQ(5, count);
 }
 
+TEST(STLExtrasTest, ArraySize) {
+  int a1[] = {1, 2, 3, 4};
+
+  EXPECT_EQ(size(a1), 4);
+}
+
 } // namespace