[PATCH] libstdc++: Add [[no_unique_address]] to repeat_view::_M_value [PR121402]

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

-- >8 --

        PR libstdc++/121402

libstdc++-v3/ChangeLog:

        * include/std/ranges (repeat_view::_M_value): Add
        [[no_unique_address]].
        * testsuite/std/ranges/adaptors/sizeof.cc
        [__cpp_lib_ranges_repeat]: New test.
---
 libstdc++-v3/include/std/ranges                      | 2 +-
 libstdc++-v3/testsuite/std/ranges/adaptors/sizeof.cc | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 8365bed17a6e..2cc17eb0f074 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -7874,7 +7874,7 @@ namespace views::__adaptor
       && (__detail::__is_integer_like<_Bound> || same_as<_Bound, 
unreachable_sentinel_t>)
   class repeat_view : public view_interface<repeat_view<_Tp, _Bound>>
   {
-    __detail::__box<_Tp> _M_value;
+    [[no_unique_address]] __detail::__box<_Tp> _M_value;
     [[no_unique_address]] _Bound _M_bound = _Bound();
 
     class _Iterator;
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/sizeof.cc 
b/libstdc++-v3/testsuite/std/ranges/adaptors/sizeof.cc
index 0a84b0f1dcbe..45f53c783ec1 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/sizeof.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/sizeof.cc
@@ -22,6 +22,8 @@
 
 namespace ranges = std::ranges;
 
+struct Empty { };
+
 auto pred_f(int x) { return x%2 == 0; };
 auto pred_l = [] (int x) { return x%2 == 0; };
 
@@ -53,3 +55,7 @@ static_assert
 #if __cpp_lib_ranges_slide
 static_assert(sizeof(ranges::slide_view<V>) == 3*ptr);
 #endif
+
+#if __cpp_lib_ranges_repeat
+static_assert(sizeof(ranges::repeat_view<Empty, size_t>) == 1*ptr);
+#endif
-- 
2.53.0.144.g73fd77805f