Specialize ValueIsPresent for PointerUnion

Author: s-barannikov

llvm/include/llvm/ADT/PointerUnion.h

@@ -198,14 +198,14 @@ class PointerUnion
   }
 };
 
-template <typename... PTs>
-bool operator==(PointerUnion<PTs...> LHS, PointerUnion<PTs...> RHS) {
-  return (!LHS && !RHS) || LHS.getOpaqueValue() == RHS.getOpaqueValue();
+template <typename ...PTs>
+bool operator==(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
+  return lhs.getOpaqueValue() == rhs.getOpaqueValue();
 }
 
-template <typename... PTs>
-bool operator!=(PointerUnion<PTs...> LHS, PointerUnion<PTs...> RHS) {
-  return !operator==(LHS, RHS);
+template <typename ...PTs>
+bool operator!=(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
+  return lhs.getOpaqueValue() != rhs.getOpaqueValue();
 }
 
 template <typename ...PTs>
@@ -259,6 +259,17 @@ struct CastInfo<To, const PointerUnion<PTs...>>
                                           CastInfo<To, PointerUnion<PTs...>>> {
 };
 
+// The default implementation of isPresent() for nullable types returns true
+// if the active member is not the first one, even if its value is nullptr.
+// Override the default behavior to return false for all possible null values.
+template <typename... PTs>
+struct ValueIsPresent<PointerUnion<PTs...>,
+                      std::enable_if_t<IsNullable<PointerUnion<PTs...>>>> {
+  using Union = PointerUnion<PTs...>;
+  static bool isPresent(const Union &V) { return static_cast<bool>(V); }
+  static decltype(auto) unwrapValue(Union &V) { return V; }
+};
+
 // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
 // # low bits available = min(PT1bits,PT2bits)-1.
 template <typename ...PTs>

llvm/unittests/ADT/PointerUnionTest.cpp

@@ -53,16 +53,9 @@ TEST_F(PointerUnionTest, Comparison) {
   EXPECT_TRUE(i4 != l4);
   EXPECT_TRUE(f4 != l4);
   EXPECT_TRUE(l4 != d4);
-  EXPECT_TRUE(i4null == f4null);
-  EXPECT_FALSE(i4null != f4null);
-  EXPECT_TRUE(i4null == l4null);
-  EXPECT_FALSE(i4null != l4null);
-  EXPECT_TRUE(i4null == d4null);
-  EXPECT_FALSE(i4null != d4null);
-  EXPECT_FALSE(i4null == i4);
-  EXPECT_TRUE(i4null != i4);
-  EXPECT_FALSE(i4null == f4);
-  EXPECT_TRUE(i4null != f4);
+  EXPECT_TRUE(i4null != f4null);
+  EXPECT_TRUE(i4null != l4null);
+  EXPECT_TRUE(i4null != d4null);
 }
 
 TEST_F(PointerUnionTest, Null) {
@@ -215,6 +208,11 @@ TEST_F(PointerUnionTest, NewCastInfra) {
   EXPECT_FALSE(isa<float *>(d4null));
   EXPECT_FALSE(isa<long long *>(d4null));
 
+  EXPECT_FALSE(isa_and_present<int *>(i4null));
+  EXPECT_FALSE(isa_and_present<float *>(f4null));
+  EXPECT_FALSE(isa_and_present<long long *>(l4null));
+  EXPECT_FALSE(isa_and_present<double *>(d4null));
+
   // test cast<>
   EXPECT_EQ(cast<float *>(a), &f);
   EXPECT_EQ(cast<int *>(b), &i);