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# ===========================================================================
# https://www.gnu.org/software/autoconf-archive/ax_cxx_restrict_this.html
# ===========================================================================
#
# SYNOPSIS
#
# AX_CXX_RESTRICT_THIS
#
# DESCRIPTION
#
# Determine whether the C++ compiler supports qualifying a member function
# with a restricted "this" pointer. Define "restrict_this" to the correct
# spelling; use like this:
#
# T::fn() restrict_this { /* code */ }
#
# Otherwise, define "restrict_this" to be empty.
#
# Note: the syntax above is a GCC extension. If your C++ compiler has a
# different way of applying the 'restricted' qualifier to the "this"
# pointer, please consider reporting it.
#
# LICENSE
#
# Copyright (c) 2010 Riccardo Murri <riccardo.murri@gmail.com>
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation, either version 3 of the License, or (at your
# option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
# Public License for more details.
#
# Under Section 7 of GPL version 3, you are granted additional permissions
# described in the Autoconf Configure Script Exception, version 3.0, as
# published by the Free Software Foundation.
#
# You should have received a copy of the GNU General Public License and a
# copy of the Autoconf Configure Script Exception along with this program;
# see the files COPYINGv3 and COPYING.EXCEPTION respectively. If not, see
# <https://www.gnu.org/licenses/>.
#serial 2
AC_DEFUN([AX_CXX_RESTRICT_THIS],
[AC_CACHE_CHECK([whether C++ supports GCC's restrict "this" syntax], ax_cv_cxx_restrict_this,
[ax_cv_cxx_restrict_this=no
AC_LANG_PUSH([C++])
# The order here caters to the fact that C++ does not require restrict.
for ac_kw in __restrict __restrict__ _Restrict restrict; do
AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
[[#define restrict_this $ac_kw
class Foo {
private:
int x_;
public:
Foo(int x) : x_(x) { };
int bar(Foo* other);
};
int Foo::bar(Foo* other) restrict_this { return this->x_ + other->x_; }
]],
[[
Foo a(3), b(5);
return (8 == a.bar(&b));
]])],
[ax_cv_cxx_restrict_this=$ac_kw])
test "$ax_cv_cxx_restrict_this" != no && break
done
AC_LANG_POP([C++])
])
AH_VERBATIM([restrict_this],
[/* Define to the keyword(s) used to specify that a member function's
"this" pointer is unaliased. Define to nothing if this is not
supported. */
#undef restrict_this])
case $ax_cv_cxx_restrict_this in
no) AC_DEFINE([restrict_this], []) ;;
*) AC_DEFINE_UNQUOTED([restrict_this], [$ax_cv_cxx_restrict_this]) ;;
esac
])# AC_C_RESTRICT
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