[llvm] Add contains(KeyType) -> bool methods to DenseSet

Matches C++20 API addition.

Differential Revision: https://reviews.llvm.org/D83449

llvm/include/llvm/ADT/DenseSet.h

@@ -173,6 +173,11 @@ public:
     return ConstIterator(TheMap.find(V));
   }
 
+  /// Check if the set contains the given element.
+  bool contains(const_arg_type_t<ValueT> V) const {
+    return TheMap.find(V) != TheMap.end();
+  }
+
   /// Alternative version of find() which allows a different, and possibly less
   /// expensive, key type.
   /// The DenseMapInfo is responsible for supplying methods

llvm/unittests/ADT/DenseSetTest.cpp

@@ -227,7 +227,7 @@ TEST(DenseSetCustomTest, ConstTest) {
   Map.insert(B);
   EXPECT_EQ(Map.count(B), 1u);
   EXPECT_EQ(Map.count(C), 1u);
-  EXPECT_NE(Map.find(B), Map.end());
-  EXPECT_NE(Map.find(C), Map.end());
+  EXPECT_TRUE(Map.contains(B));
+  EXPECT_TRUE(Map.contains(C));
 }
 }