Allow SmallPtrSet to be used with a std::insert_iterator

Currently, the SmallPtrSet type allows inserting elements but it does
not support inserting elements with a positional hint. The lack of this
signature means that you cannot use SmallPtrSet with
std::insert_iterator or std::inserter(), which makes some code
constructs more awkward. This adds an overload of insert() that can be
used in these scenarios.

The positional hint is unused by SmallPtrSet and the call is equivalent
to calling insert() without a hint.

llvm/include/llvm/ADT/SmallPtrSet.h

@@ -366,6 +366,13 @@ public:
     return std::make_pair(makeIterator(p.first), p.second);
   }
 
+  /// Insert the given pointer with an iterator hint that is ignored. This is
+  /// identical to calling insert(Ptr), but allows SmallPtrSet to be used by
+  /// std::insert_iterator and std::inserter().
+  iterator insert(iterator, PtrType Ptr) {
+    return insert(Ptr).first;
+  }
+
   /// erase - If the set contains the specified pointer, remove it and return
   /// true, otherwise return false.
   bool erase(PtrType Ptr) {

llvm/unittests/ADT/SmallPtrSetTest.cpp

@@ -395,3 +395,16 @@ TEST(SmallPtrSetTest, Contains) {
   EXPECT_TRUE(Set.contains(&buf[1]));
   EXPECT_TRUE(Set.contains(&buf[2]));
 }
+
+TEST(SmallPtrSetTest, InsertIterator) {
+  SmallPtrSet<int *, 5> Set;
+  int Vals[5] = {11, 22, 33, 44, 55};
+  int *Buf[5] = {&Vals[0], &Vals[1], &Vals[2], &Vals[3], &Vals[4]};
+
+  for (int *Ptr : Buf)
+    Set.insert(Set.begin(), Ptr);
+
+  // Ensure that all of the values were copied into the set.
+  for (const auto *Ptr : Buf)
+    EXPECT_TRUE(Set.contains(Ptr));
+}