Add partial implementation of std::to_address() as llvm::to_address()

Summary:
Following on from the review for D58088, this patch provides the
prerequisite to_address() implementation that's needed to have
pointer_iterator support unique_ptr.

The late bound return should be removed once we move to C++14 to better
align with the C++20 declaration. Also, this implementation can be removed
once we move to C++20 where it's defined as std::to_addres()

The std::pointer_traits<>::to_address(p) variations of these overloads has
not been implemented.

Reviewers: dblaikie, paquette

Reviewed By: dblaikie

Subscribers: dexonsmith, kristina, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58421

llvm-svn: 354491

include/llvm/ADT/STLExtras.h

@@ -1576,6 +1576,19 @@ bool hasNItemsOrMore(
   return true;
 }
 
+/// Returns a raw pointer that represents the same address as the argument.
+///
+/// The late bound return should be removed once we move to C++14 to better
+/// align with the C++20 declaration. Also, this implementation can be removed
+/// once we move to C++20 where it's defined as std::to_addres()
+///
+/// The std::pointer_traits<>::to_address(p) variations of these overloads has
+/// not been implemented.
+template <class Ptr> auto to_address(const Ptr &P) -> decltype(P.operator->()) {
+  return P.operator->();
+}
+template <class T> constexpr T *to_address(T *P) { return P; }
+
 } // end namespace llvm
 
 #endif // LLVM_ADT_STLEXTRAS_H

unittests/ADT/STLExtrasTest.cpp

@@ -446,4 +446,27 @@ TEST(STLExtrasTest, splat) {
   EXPECT_FALSE(is_splat(V));
 }
 
+TEST(STLExtrasTest, to_address) {
+  int *V1 = new int;
+  EXPECT_EQ(V1, to_address(V1));
+
+  // Check fancy pointer overload for unique_ptr
+  std::unique_ptr<int> V2 = make_unique<int>(0);
+  EXPECT_EQ(V2.get(), to_address(V2));
+
+  V2.reset(V1);
+  EXPECT_EQ(V1, to_address(V2));
+  V2.release();
+
+  // Check fancy pointer overload for shared_ptr
+  std::shared_ptr<int> V3 = std::make_shared<int>(0);
+  std::shared_ptr<int> V4 = V3;
+  EXPECT_EQ(V3.get(), V4.get());
+  EXPECT_EQ(V3.get(), to_address(V3));
+  EXPECT_EQ(V4.get(), to_address(V4));
+
+  V3.reset(V1);
+  EXPECT_EQ(V1, to_address(V3));
+}
+
 } // namespace