Recommit r370502: Make `vector` unconditionally move elements when

exceptions are disabled.

The patch was reverted due to some confusion about non-movable types. ie
types
that explicitly delete their move constructors. However, such types do
not meet
the requirement for `MoveConstructible`, which is required by
`std::vector`:

Summary:

`std::vector<T>` is free choose between using copy or move operations
when it
needs to resize. The standard only candidates that the correct exception
safety
guarantees are provided. When exceptions are disabled these guarantees
are
trivially satisfied. Meaning vector is free to optimize it's
implementation by
moving instead of copying.

This patch makes `std::vector` unconditionally move elements when
exceptions are
disabled. This optimization is conforming according to the current
standard wording.

There are concerns that moving in `-fno-noexceptions`mode will be a
surprise to
users. For example, a user may be surprised to find their code is slower
with
exceptions enabled than it is disabled. I'm sympathetic to this
surprised, but
I don't think it should block this optimization.

Reviewers: mclow.lists, ldionne, rsmith
Reviewed By: ldionne
Subscribers: zoecarver, christof, dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D62228

llvm-svn: 371867

2 files changed, 45 insertions, 45 deletions

diff --git a/libcxx/test/std/containers/sequences/vector/vector.modifiers/resize.copy_only.pass.sh.cpp b/libcxx/test/std/containers/sequences/vector/vector.modifiers/resize.copy_only.pass.sh.cpp
deleted file mode 100644
index b24736e22b6..00000000000
--- a/libcxx/test/std/containers/sequences/vector/vector.modifiers/resize.copy_only.pass.sh.cpp
+++ /dev/null
@@ -1,45 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++98, c++03
-
-// RUN: %build -fno-exceptions
-// RUN: %run
-
-// RUN: %build
-// RUN: %run
-
-// UNSUPPORTED: c++98, c++03
-
-// <vector>
-
-// Test that vector won't try to call the move constructor when resizing if
-// the class has a deleted move constructor (but a working copy constructor).
-
-#include <vector>
-
-class CopyOnly {
-public:
-  CopyOnly() { }
-
-  CopyOnly(CopyOnly&&) = delete;
-  CopyOnly& operator=(CopyOnly&&) = delete;
-
-  CopyOnly(const CopyOnly&) = default;
-  CopyOnly& operator=(const CopyOnly&) = default;
-};
-
-int main() {
-    std::vector<CopyOnly> x;
-    x.emplace_back();
-
-    CopyOnly c;
-    x.push_back(c);
-
-    return 0;
-}
diff --git a/libcxx/test/std/containers/sequences/vector/vector.modifiers/resize_not_move_insertable.fail.cpp b/libcxx/test/std/containers/sequences/vector/vector.modifiers/resize_not_move_insertable.fail.cpp
new file mode 100644
index 00000000000..2b4a5a9e2cd
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/vector/vector.modifiers/resize_not_move_insertable.fail.cpp
@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+
+// <vector>
+
+// Test that vector produces a decent diagnostic for user types that explicitly
+// delete their move constructor. Such types don't meet the Cpp17CopyInsertible
+// requirements.
+
+#include <vector>
+
+template <int>
+class BadUserNoCookie {
+public:
+  BadUserNoCookie() { }
+
+  BadUserNoCookie(BadUserNoCookie&&) = delete;
+  BadUserNoCookie& operator=(BadUserNoCookie&&) = delete;
+
+  BadUserNoCookie(const BadUserNoCookie&) = default;
+  BadUserNoCookie& operator=(const BadUserNoCookie&) = default;
+};
+
+int main() {
+  // expected-error@memory:* 2 {{"The specified type does not meet the requirements of Cpp17MoveInsertable"}}
+  {
+
+    std::vector<BadUserNoCookie<1> > x;
+    x.emplace_back();
+  }
+  {
+    std::vector<BadUserNoCookie<2>> x;
+    BadUserNoCookie<2> c;
+    x.push_back(c);
+  }
+    return 0;
+}