[ADT] Add equality operator for SmallPtrSet

Reviewed By: tellenbach
Differential Revision: https://reviews.llvm.org/D69429

include/llvm/ADT/SmallPtrSet.h

@@ -409,6 +409,32 @@ private:
   }
 };
 
+/// Equality comparison for SmallPtrSet.
+///
+/// Iterates over elements of LHS confirming that each value from LHS is also in
+/// RHS, and that no additional values are in RHS.
+template <typename PtrType>
+bool operator==(const SmallPtrSetImpl<PtrType> &LHS,
+                const SmallPtrSetImpl<PtrType> &RHS) {
+  if (LHS.size() != RHS.size())
+    return false;
+
+  for (const auto *KV : LHS)
+    if (!RHS.count(KV))
+      return false;
+
+  return true;
+}
+
+/// Inequality comparison for SmallPtrSet.
+///
+/// Equivalent to !(LHS == RHS).
+template <typename PtrType>
+bool operator!=(const SmallPtrSetImpl<PtrType> &LHS,
+                const SmallPtrSetImpl<PtrType> &RHS) {
+  return !(LHS == RHS);
+}
+
 /// SmallPtrSet - This class implements a set which is optimized for holding
 /// SmallSize or less elements.  This internally rounds up SmallSize to the next
 /// power of two if it is not already a power of two.  See the comments above

unittests/ADT/SmallPtrSetTest.cpp

@@ -329,3 +329,41 @@ TEST(SmallPtrSetTest, ConstNonPtrTest) {
   EXPECT_EQ(IntSet.count(Pair), 1u);
   EXPECT_NE(IntSet.find(Pair), IntSet.end());
 }
+
+// Test equality comparison.
+TEST(SmallPtrSetTest, EqualityComparison) {
+  int buf[3];
+  for (int i = 0; i < 3; ++i)
+    buf[i] = 0;
+
+  SmallPtrSet<int *, 1> a;
+  a.insert(&buf[0]);
+  a.insert(&buf[1]);
+
+  SmallPtrSet<int *, 2> b;
+  b.insert(&buf[1]);
+  b.insert(&buf[0]);
+
+  SmallPtrSet<int *, 3> c;
+  c.insert(&buf[1]);
+  c.insert(&buf[2]);
+
+  SmallPtrSet<int *, 4> d;
+  d.insert(&buf[0]);
+
+  SmallPtrSet<int *, 5> e;
+  e.insert(&buf[0]);
+  e.insert(&buf[1]);
+  e.insert(&buf[2]);
+
+  EXPECT_EQ(a, b);
+  EXPECT_EQ(b, a);
+  EXPECT_NE(b, c);
+  EXPECT_NE(c, a);
+  EXPECT_NE(d, a);
+  EXPECT_NE(a, d);
+  EXPECT_NE(a, e);
+  EXPECT_NE(e, a);
+  EXPECT_NE(c, e);
+  EXPECT_NE(e, d);
+}