[ADT] Add a pop_back_val method to the SparseSet container.

The next commit will use it.

llvm-svn: 263455

include/llvm/ADT/SparseSet.h

@@ -263,6 +263,11 @@ public:
     return *insert(ValueT(Key)).first;
   }
 
+  ValueT pop_back_val() {
+    // Sparse does not need to be cleared, see find().
+    return Dense.pop_back_val();
+  }
+
   /// erase - Erases an existing element identified by a valid iterator.
   ///
   /// This invalidates all iterators, but erase() returns an iterator pointing

unittests/ADT/SparseSetTest.cpp

@@ -183,4 +183,24 @@ TEST(SparseSetTest, AltStructSet) {
   EXPECT_FALSE(Set.erase(5));
   EXPECT_TRUE(Set.erase(6));
 }
+
+TEST(SparseSetTest, PopBack) {
+  USet Set;
+  const unsigned UpperBound = 300;
+  Set.setUniverse(UpperBound);
+  for (unsigned i = 0; i < UpperBound; ++i)
+    Set.insert(i);
+
+  // Make sure pop back returns the values in the reverse order we
+  // inserted them.
+  unsigned Expected = UpperBound;
+  while (!Set.empty())
+    ASSERT_TRUE(--Expected == Set.pop_back_val());
+
+  // Insert again the same elements in the sparse set and make sure
+  // each insertion actually inserts the elements. I.e., check
+  // that the underlying data structure are properly cleared.
+  for (unsigned i = 0; i < UpperBound; ++i)
+    ASSERT_TRUE(Set.insert(i).second);
+}
 } // namespace