[PATCH 2/4] libstdc++: Reduce the size of a subrange with empty sentinel type

[Jonathan Wakely]

On 28/09/20 00:48 -0400, Patrick Palka via Libstdc++ wrote:
>libstdc++-v3/ChangeLog:
>
>	* include/bits/ranges_util.h (subrange::_M_end): Give it
>	[[no_unique_adcress]].
>	* testsuite/std/ranges/subrange/sizeof.cc: New test.

OK.

> libstdc++-v3/include/bits/ranges_util.h       |  2 +-
> .../testsuite/std/ranges/subrange/sizeof.cc   | 28 +++++++++++++++++++
> 2 files changed, 29 insertions(+), 1 deletion(-)
> create mode 100644 libstdc++-v3/testsuite/std/ranges/subrange/sizeof.cc
>
>diff --git a/libstdc++-v3/include/bits/ranges_util.h b/libstdc++-v3/include/bits/ranges_util.h
>index 694ae796399..a98658ff5c8 100644
>--- a/libstdc++-v3/include/bits/ranges_util.h
>+++ b/libstdc++-v3/include/bits/ranges_util.h
>@@ -208,7 +208,7 @@ namespace ranges
> 	= _Kind == subrange_kind::sized && !sized_sentinel_for<_Sent, _It>;
>
>       _It _M_begin = _It();
>-      _Sent _M_end = _Sent();
>+      [[no_unique_address]] _Sent _M_end = _Sent();
>
>       template<typename, bool = _S_store_size>
> 	struct _Size
>diff --git a/libstdc++-v3/testsuite/std/ranges/subrange/sizeof.cc b/libstdc++-v3/testsuite/std/ranges/subrange/sizeof.cc
>new file mode 100644
>index 00000000000..7e95e196c6c
>--- /dev/null
>+++ b/libstdc++-v3/testsuite/std/ranges/subrange/sizeof.cc
>@@ -0,0 +1,28 @@
>+// Copyright (C) 2020 Free Software Foundation, Inc.
>+//
>+// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option)
>+// any later version.
>+
>+// This library 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.
>+
>+// You should have received a copy of the GNU General Public License along
>+// with this library; see the file COPYING3.  If not see
>+// <http://www.gnu.org/licenses/>.
>+
>+// { dg-options "-std=gnu++2a" }
>+// { dg-do compile { target c++2a } }
>+
>+#include <iterator>
>+#include <ranges>
>+
>+// Verify we optimize away the 'end' data member of a subrange with an empty
>+// sentinel type.
>+static_assert(sizeof(std::ranges::subrange<std::counted_iterator<int*>,
>+					   std::default_sentinel_t>)
>+	      == sizeof(std::counted_iterator<int*>));
>-- 
>2.28.0.618.g9bc233ae1c
>