[ADT] Wrapper for std::accumulate accepting a range. (llvm#158702)

(cherry picked from commit 7e71877)

Author: mtrofin

llvm/include/llvm/ADT/STLExtras.h

@@ -35,6 +35,7 @@
 #include <iterator>
 #include <limits>
 #include <memory>
+#include <numeric>
 #include <optional>
 #include <tuple>
 #include <type_traits>
@@ -1731,6 +1732,12 @@ template <typename R> constexpr size_t range_size(R &&Range) {
     return static_cast<size_t>(std::distance(adl_begin(Range), adl_end(Range)));
 }
 
+/// Wrapper for std::accumulate.
+template <typename R, typename E> auto accumulate(R &&Range, E &&Init) {
+  return std::accumulate(adl_begin(Range), adl_end(Range),
+                         std::forward<E>(Init));
+}
+
 /// Provide wrappers to std::for_each which take ranges instead of having to
 /// pass begin/end explicitly.
 template <typename R, typename UnaryFunction>

llvm/unittests/ADT/STLExtrasTest.cpp

@@ -1602,6 +1602,16 @@ TEST(STLExtrasTest, Fill) {
   EXPECT_THAT(V2, ElementsAre(Val, Val, Val, Val));
 }
 
+TEST(STLExtrasTest, Accumulate) {
+  EXPECT_EQ(accumulate(std::vector<int>(), 0), 0);
+  EXPECT_EQ(accumulate(std::vector<int>(), 3), 3);
+  std::vector<int> V1 = {1, 2, 3, 4, 5};
+  EXPECT_EQ(accumulate(V1, 0), std::accumulate(V1.begin(), V1.end(), 0));
+  EXPECT_EQ(accumulate(V1, 10), std::accumulate(V1.begin(), V1.end(), 10));
+  EXPECT_EQ(accumulate(drop_begin(V1), 7),
+            std::accumulate(V1.begin() + 1, V1.end(), 7));
+}
+
 struct Foo;
 struct Bar {};