[gcc r11-3501] libstdc++: Reduce the size of an unbounded iota_view

[Patrick Palka]

https://gcc.gnu.org/g:623443357e6092067b4cf98cc6c0aeff7560b98d

commit r11-3501-g623443357e6092067b4cf98cc6c0aeff7560b98d
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Sep 28 11:54:57 2020 -0400

    libstdc++: Reduce the size of an unbounded iota_view
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ranges (iota_view::_M_bound): Give it
            [[no_unique_address]].
            * testsuite/std/ranges/iota/iota_view.cc: Check that an
            unbounded iota_view has minimal size.

Diff:
---
 libstdc++-v3/include/std/ranges                     | 2 +-
 libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index ed04fa0001d..964a2b616a6 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -511,7 +511,7 @@ namespace ranges
       };
 
       _Winc _M_value = _Winc();
-      _Bound _M_bound = _Bound();
+      [[no_unique_address]] _Bound _M_bound = _Bound();
 
     public:
       iota_view() = default;
diff --git a/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc b/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
index 65d166fbd3b..8a33e10a093 100644
--- a/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
+++ b/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
@@ -77,6 +77,9 @@ test04()
   VERIFY( it == v.end() );
 }
 
+// Verify we optimize away the 'bound' data member of an unbounded iota_view.
+static_assert(sizeof(std::ranges::iota_view<char>) == 1);
+
 int
 main()
 {