[ADT] Teach PointerUnion to support assignment directly from nullptr to

clear it out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207471 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/PointerUnion.h

@@ -155,6 +155,12 @@ namespace llvm {
       return (PT1 *)Val.getAddrOfPointer();
     }
 
+    /// \brief Assignment from nullptr which just clears the union.
+    const PointerUnion &operator=(std::nullptr_t) {
+      Val.initWithPointer(nullptr);
+      return *this;
+    }
+    
     /// Assignment operators - Allow assigning into this union from either
     /// pointer type, setting the discriminator to remember what it came from.
     const PointerUnion &operator=(const PT1 &RHS) {
@@ -299,6 +305,12 @@ namespace llvm {
       return T();
     }
 
+    /// \brief Assignment from nullptr which just clears the union.
+    const PointerUnion3 &operator=(std::nullptr_t) {
+      Val = nullptr;
+      return *this;
+    }
+    
     /// Assignment operators - Allow assigning into this union from either
     /// pointer type, setting the discriminator to remember what it came from.
     const PointerUnion3 &operator=(const PT1 &RHS) {
@@ -408,6 +420,12 @@ namespace llvm {
       return T();
     }
 
+    /// \brief Assignment from nullptr which just clears the union.
+    const PointerUnion4 &operator=(std::nullptr_t) {
+      Val = nullptr;
+      return *this;
+    }
+    
     /// Assignment operators - Allow assigning into this union from either
     /// pointer type, setting the discriminator to remember what it came from.
     const PointerUnion4 &operator=(const PT1 &RHS) {

unittests/ADT/PointerUnionTest.cpp

@@ -46,6 +46,12 @@ TEST_F(PointerUnionTest, Null) {
   EXPECT_TRUE((bool)a);
   EXPECT_TRUE((bool)b);
   EXPECT_FALSE(n);
+
+  EXPECT_NE(n, b);
+  EXPECT_EQ(b, c);
+  b = nullptr;
+  EXPECT_EQ(n, b);
+  EXPECT_NE(b, c);
 }
 
 TEST_F(PointerUnionTest, Is) {