[STLExtras] Add append_range helper.

[silvas]

Summary

This is convenient in a lot of cases, such as when the thing you want
to append is someReallyLongFunctionName() that you'd rather not
write twice or assign to a variable for the paired begin/end calls.

[silvas]

I initially called this append, but that seemed to conflict with a function elsewhere in the codebase. It seems like map_range is probably making a similar decision to avoid a function with as generic a name as map.

[dblaikie]

Looks good!

llvm/include/llvm/ADT/STLExtras.h

 /// Wrapper function to remove a value from a container:
 ///
 /// C.erase(remove(C.begin(), C.end(), V), C.end());
 template <typename Container, typename ValueType>
 void erase_value(Container &C, ValueType V) {
   C.erase(std::remove(C.begin(), C.end(), V), C.end());
 }
 
+/// Wrapper function to append a range to a container.
+///
+/// C.insert(C.end(), R.begin(), R.end());
+template <typename Container, typename Range>
+inline void append_range(Container &C, Range &&R) {
+  C.insert(C.end(), R.begin(), R.end());
+}
+
 /// Given a sequence container Cont, replace the range [ContIt, ContEnd) with
 /// the range [ValIt, ValEnd) (which is not from the same container).
 template<typename Container, typename RandomAccessIterator>
 void replace(Container &Cont, typename Container::iterator ContIt,
              typename Container::iterator ContEnd, RandomAccessIterator ValIt,
              RandomAccessIterator ValEnd) {
   while (true) {
     if (ValIt == ValEnd) {

llvm/unittests/ADT/STLExtrasTest.cpp

TEST(STLExtrasTest, EraseIf) {
   erase_if(V, [](int i) { return i % 2 == 0; });
   EXPECT_EQ(4u, V.size());
   EXPECT_EQ(1, V[0]);
   EXPECT_EQ(3, V[1]);
   EXPECT_EQ(5, V[2]);
   EXPECT_EQ(7, V[3]);
 }
 
+TEST(STLExtrasTest, AppendRange) {
+  auto AppendVals = {3};
+  std::vector<int> V = {1, 2};
+  append_range(V, AppendVals);
+  EXPECT_EQ(1, V[0]);
+  EXPECT_EQ(2, V[1]);
+  EXPECT_EQ(3, V[2]);
+}
+
 namespace some_namespace {
 struct some_struct {
   std::vector<int> data;
   std::string swap_val;
 };
 
 std::vector<int>::const_iterator begin(const some_struct &s) {
   return s.data.begin();