[ADT] Add makeIntrusiveRefCnt helper function

Works like std::make_unique but for IntrusiveRefCntPtr objects.
See https://lists.llvm.org/pipermail/llvm-dev/2021-January/147729.html

Reviewed By: dblaikie, MaskRay

Differential Revision: https://reviews.llvm.org/D94440

llvm/include/llvm/ADT/IntrusiveRefCntPtr.h

@@ -297,6 +297,12 @@ template <class T> struct simplify_type<const IntrusiveRefCntPtr<T>> {
   }
 };
 
+/// Factory function for creating intrusive ref counted pointers.
+template <typename T, typename... Args>
+IntrusiveRefCntPtr<T> makeIntrusiveRefCnt(Args &&...A) {
+  return IntrusiveRefCntPtr<T>(new T(std::forward<Args>(A)...));
+}
+
 } // end namespace llvm
 
 #endif // LLVM_ADT_INTRUSIVEREFCNTPTR_H

llvm/unittests/ADT/IntrusiveRefCntPtrTest.cpp

@@ -53,6 +53,22 @@ TYPED_TEST(IntrusiveRefCntPtrTest, InteropsWithUniquePtr) {
   EXPECT_EQ(0, NumInstances);
 }
 
+TYPED_TEST(IntrusiveRefCntPtrTest, MakeIntrusiveRefCnt) {
+  EXPECT_EQ(0, NumInstances);
+  {
+    auto S1 = makeIntrusiveRefCnt<TypeParam>();
+    auto S2 = makeIntrusiveRefCnt<const TypeParam>();
+    EXPECT_EQ(2, NumInstances);
+    static_assert(
+        std::is_same<decltype(S1), IntrusiveRefCntPtr<TypeParam>>::value,
+        "Non-const type mismatch");
+    static_assert(
+        std::is_same<decltype(S2), IntrusiveRefCntPtr<const TypeParam>>::value,
+        "Const type mismatch");
+  }
+  EXPECT_EQ(0, NumInstances);
+}
+
 struct InterceptRefCounted : public RefCountedBase<InterceptRefCounted> {
   InterceptRefCounted(bool *Released, bool *Retained)
     : Released(Released), Retained(Retained) {}