[libc++] Fix std::move algorithm with trivial move-only types

As reported in https://reviews.llvm.org/D151953#4472195, the std::move
algorithm (and various other functions that relied on it) stopped working
after starting to use `__constexpr_memmove` in its implementation. This
patch fixes the underlying issue in `__constexpr_memmove` and adds tests
for various related algorithms and functions that were not exercising
trivial move-only types.

Differential Revision: https://reviews.llvm.org/D154613

4 files changed, 91 insertions, 4 deletions

diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move.pass.cpp
index 3795314..ce5cf05 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move.pass.cpp
@@ -18,10 +18,12 @@
 
 #include <algorithm>
 #include <cassert>
+#include <iterator>
 #include <memory>
 
-#include "test_macros.h"
+#include "MoveOnly.h"
 #include "test_iterators.h"
+#include "test_macros.h"
 
 class PaddedBase {
 public:
@@ -111,11 +113,32 @@ TEST_CONSTEXPR_CXX20 bool test() {
     assert(std::equal(a, a + 10, expected));
   }
 
+  // Make sure that the algorithm works with move-only types
+  {
+    // When non-trivial
+    {
+      MoveOnly from[3] = {1, 2, 3};
+      MoveOnly to[3] = {};
+      std::move(std::begin(from), std::end(from), std::begin(to));
+      assert(to[0] == MoveOnly(1));
+      assert(to[1] == MoveOnly(2));
+      assert(to[2] == MoveOnly(3));
+    }
+    // When trivial
+    {
+      TrivialMoveOnly from[3] = {1, 2, 3};
+      TrivialMoveOnly to[3] = {};
+      std::move(std::begin(from), std::end(from), std::begin(to));
+      assert(to[0] == TrivialMoveOnly(1));
+      assert(to[1] == TrivialMoveOnly(2));
+      assert(to[2] == TrivialMoveOnly(3));
+    }
+  }
+
   return true;
 }
 
-int main(int, char**)
-{
+int main(int, char**) {
   test();
 #if TEST_STD_VER >= 20
   static_assert(test());
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move_backward.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move_backward.pass.cpp
index 04ecd48..2ed4d37 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move_backward.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/move_backward.pass.cpp
@@ -17,10 +17,12 @@
 
 #include <algorithm>
 #include <cassert>
+#include <iterator>
 #include <memory>
 
-#include "test_macros.h"
+#include "MoveOnly.h"
 #include "test_iterators.h"
+#include "test_macros.h"
 
 class PaddedBase {
 public:
@@ -110,6 +112,28 @@ TEST_CONSTEXPR_CXX20 bool test() {
     assert(std::equal(a, a + 10, expected));
   }
 
+  // Make sure that the algorithm works with move-only types
+  {
+    // When non-trivial
+    {
+      MoveOnly from[3] = {1, 2, 3};
+      MoveOnly to[3] = {};
+      std::move_backward(std::begin(from), std::end(from), std::end(to));
+      assert(to[0] == MoveOnly(1));
+      assert(to[1] == MoveOnly(2));
+      assert(to[2] == MoveOnly(3));
+    }
+    // When trivial
+    {
+      TrivialMoveOnly from[3] = {1, 2, 3};
+      TrivialMoveOnly to[3] = {};
+      std::move_backward(std::begin(from), std::end(from), std::end(to));
+      assert(to[0] == TrivialMoveOnly(1));
+      assert(to[1] == TrivialMoveOnly(2));
+      assert(to[2] == TrivialMoveOnly(3));
+    }
+  }
+
   return true;
 }
 
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move.pass.cpp
index d98c319..aeff581 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move.pass.cpp
@@ -24,6 +24,7 @@
 #include <array>
 #include <cassert>
 #include <deque>
+#include <iterator>
 #include <ranges>
 #include <vector>
 
@@ -203,6 +204,7 @@ constexpr bool test() {
   test_proxy_in_iterators<ProxyIterator>();
 
   { // check that a move-only type works
+    // When non-trivial
     {
       MoveOnly a[] = {1, 2, 3};
       MoveOnly b[3];
@@ -219,6 +221,24 @@ constexpr bool test() {
       assert(b[1].get() == 2);
       assert(b[2].get() == 3);
     }
+
+    // When trivial
+    {
+      TrivialMoveOnly a[] = {1, 2, 3};
+      TrivialMoveOnly b[3];
+      std::ranges::move(a, std::begin(b));
+      assert(b[0].get() == 1);
+      assert(b[1].get() == 2);
+      assert(b[2].get() == 3);
+    }
+    {
+      TrivialMoveOnly a[] = {1, 2, 3};
+      TrivialMoveOnly b[3];
+      std::ranges::move(std::begin(a), std::end(a), std::begin(b));
+      assert(b[0].get() == 1);
+      assert(b[1].get() == 2);
+      assert(b[2].get() == 3);
+    }
   }
 
   { // check that a move-only type works for ProxyIterator
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move_backward.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move_backward.pass.cpp
index f6ca42b..9219cbb 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move_backward.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.move/ranges.move_backward.pass.cpp
@@ -24,6 +24,7 @@
 #include <array>
 #include <cassert>
 #include <deque>
+#include <iterator>
 #include <ranges>
 #include <vector>
 
@@ -189,6 +190,7 @@ constexpr bool test() {
   test_proxy_in_iterators<ProxyIterator>();
 
   { // check that a move-only type works
+    // When non-trivial
     {
       MoveOnly a[] = {1, 2, 3};
       MoveOnly b[3];
@@ -205,6 +207,24 @@ constexpr bool test() {
       assert(b[1].get() == 2);
       assert(b[2].get() == 3);
     }
+
+    // When trivial
+    {
+      TrivialMoveOnly a[] = {1, 2, 3};
+      TrivialMoveOnly b[3];
+      std::ranges::move_backward(a, std::end(b));
+      assert(b[0].get() == 1);
+      assert(b[1].get() == 2);
+      assert(b[2].get() == 3);
+    }
+    {
+      TrivialMoveOnly a[] = {1, 2, 3};
+      TrivialMoveOnly b[3];
+      std::ranges::move_backward(std::begin(a), std::end(a), std::end(b));
+      assert(b[0].get() == 1);
+      assert(b[1].get() == 2);
+      assert(b[2].get() == 3);
+    }
   }
 
   { // check that a move-only type works for ProxyIterator