[ADT] Adds equality operator for SmallPtrSet

[yrouban]

Summary

This change makes it easier to migrate existing code that uses std::set (which support equality comparison) to SmallPtrSet.

[tellenbach]

llvm/include/llvm/ADT/SmallPtrSet.h

422

NIT: Can this be const?

llvm/unittests/ADT/SmallPtrSetTest.cpp

334

Can you add a unit test for testing the inequality of different-sized sets?

335

Can you use a smaller buffer and initialize it?

[yrouban]

Addressed all comments.

[tellenbach]

Thanks for addressing the comments, LGTM.

llvm/include/llvm/ADT/SmallPtrSet.h

private:
   /// Create an iterator that dereferences to same place as the given pointer.
   iterator makeIterator(const void *const *P) const {
     if (shouldReverseIterate())
       return iterator(P == EndPointer() ? CurArray : P + 1, CurArray, *this);
     return iterator(P, EndPointer(), *this);
   }
 };
 
+/// 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
 /// SmallPtrSetImplBase for details of the algorithm.
 template<class PtrType, unsigned SmallSize>
 class SmallPtrSet : public SmallPtrSetImpl<PtrType> {
   // In small mode SmallPtrSet uses linear search for the elements, so it is
   // not a good idea to choose this value too high. You may consider using a

llvm/unittests/ADT/SmallPtrSetTest.cpp

 TEST(SmallPtrSetTest, ConstNonPtrTest) {
   SmallPtrSet<TestPair, 8> IntSet;
   int A[1];
   TestPair Pair(&A[0], 1);
   IntSet.insert(Pair);
   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);
+}