mfbt/OperatorNewExtensions.h
author L10n Bumper Bot <release+l10nbumper@mozilla.com>
Thu, 08 Nov 2018 03:00:11 -0800
changeset 501100 1cd4f2d571554c4dc89cf1be1d98683c0d14f797
parent 352850 522135225936a32c7b084ba7eea082ee025ea7d5
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
no bug - Bumping Fennec l10n changesets r=release a=l10n-bump DONTBUILD an -> 336e061995b9 ar -> f6834a7d7374 as -> d2c76e616a66 ast -> fcb8f3455237 az -> c4caf3b07cf2 be -> 697eb1022498 bg -> 7bf1f448f743 bn-BD -> 5f7a87adee06 bn-IN -> 49ce3195c4c2 br -> 41cf35b7c5b5 bs -> 4a14aee27904 ca -> 9373e8ce86d4 cak -> a40d767541ba cs -> 4b99defb0525 cy -> 4c948fed2584 de -> 017a7e7a267a dsb -> aadebeccf5ba el -> 2d28a78dcef5 en-CA -> 55ad9171a9f0 en-GB -> 296422b495e9 en-ZA -> c1b5d2128914 eo -> c68e87667d9f es-AR -> bff0a788c711 es-CL -> 1d3efd2532ea es-ES -> 4d1feb70b0e2 es-MX -> fceda607d0f4 et -> 58a8262a0cc7 eu -> 7cebfd46208b fa -> cbc040d58476 ff -> 46f5aec275ea fi -> 235ab13d261e fr -> 8ee417b64f99

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* A version of |operator new| that eschews mandatory null-checks. */

#ifndef mozilla_OperatorNewExtensions_h
#define mozilla_OperatorNewExtensions_h

#include "mozilla/Assertions.h"

// Credit goes to WebKit for this implementation, cf.
// https://bugs.webkit.org/show_bug.cgi?id=74676
namespace mozilla {
enum NotNullTag {
  KnownNotNull,
};
} // namespace mozilla

/*
 * The logic here is a little subtle.  [expr.new] states that if the allocation
 * function being called returns null, then object initialization must not be
 * done, and the entirety of the new expression must return null.  Non-throwing
 * (noexcept) functions are defined to return null to indicate failure.  The
 * standard placement operator new is defined in such a way, and so it requires
 * a null check, even when that null check would be extraneous.  Functions
 * declared without such a specification are defined to throw std::bad_alloc if
 * they fail, and return a non-null pointer otherwise.  We compile without
 * exceptions, so any placement new overload we define that doesn't declare
 * itself as noexcept must therefore avoid generating a null check.  Below is
 * just such an overload.
 *
 * You might think that MOZ_NONNULL might perform the same function, but
 * MOZ_NONNULL isn't supported on all of our compilers, and even when it is
 * supported, doesn't work on all the versions we support.  And even keeping
 * those limitations in mind, we can't put MOZ_NONNULL on the global,
 * standardized placement new function in any event.
 *
 * We deliberately don't add MOZ_NONNULL(3) to tag |p| as non-null, to benefit
 * hypothetical static analyzers.  Doing so makes |MOZ_ASSERT(p)|'s internal
 * test vacuous, and some compilers warn about such vacuous tests.
 */
inline void*
operator new(size_t, mozilla::NotNullTag, void* p)
{
  MOZ_ASSERT(p);
  return p;
}

#endif // mozilla_OperatorNewExtensions_h