From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Fri, 19 Apr 2024 02:47:55 +0200 Subject: Adding upstream version 124.0.1. Signed-off-by: Daniel Baumann --- mfbt/OperatorNewExtensions.h | 50 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 mfbt/OperatorNewExtensions.h (limited to 'mfbt/OperatorNewExtensions.h') diff --git a/mfbt/OperatorNewExtensions.h b/mfbt/OperatorNewExtensions.h new file mode 100644 index 0000000000..a44a6bdeae --- /dev/null +++ b/mfbt/OperatorNewExtensions.h @@ -0,0 +1,50 @@ +/* -*- 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 -- cgit v1.2.3