[gcc r11-3348] libstdc++: Use correct argument type for __use_alloc, again [PR 96803]

[gcc r11-3348] libstdc++: Use correct argument type for __use_alloc, again [PR 96803]

[Jonathan Wakely]

https://gcc.gnu.org/g:7825399092d572ce8ea82c4aa8dfeb65076b0e52

commit r11-3348-g7825399092d572ce8ea82c4aa8dfeb65076b0e52
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Sep 22 08:42:18 2020 +0100

    libstdc++: Use correct argument type for __use_alloc, again [PR 96803]
    
    While backporting 5494edae83ad33c769bd1ebc98f0c492453a6417 I noticed
    that it's still not correct. I made the allocator-extended constructor
    use the right type for the uses-allocator construction detection, but I
    used an rvalue when it should be a const lvalue.
    
    This should fix it properly this time.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/96803
            * include/std/tuple
            (_Tuple_impl(allocator_arg_t, Alloc, const _Tuple_impl<U...>&)):
            Use correct value category in __use_alloc call.
            * testsuite/20_util/tuple/cons/96803.cc: Check with constructors
            that require correct value category to be used.

Diff:
---
 libstdc++-v3/include/std/tuple                     |  2 +-
 libstdc++-v3/testsuite/20_util/tuple/cons/96803.cc | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index 06f56337ce4..11ad1991108 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -355,7 +355,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		    const _Tuple_impl<_Idx, _UHead, _UTails...>& __in)
 	: _Inherited(__tag, __a,
 		     _Tuple_impl<_Idx, _UHead, _UTails...>::_M_tail(__in)),
-	  _Base(__use_alloc<_Head, _Alloc, _UHead>(__a),
+	  _Base(__use_alloc<_Head, _Alloc, const _UHead&>(__a),
 		_Tuple_impl<_Idx, _UHead, _UTails...>::_M_head(__in))
 	{ }
 
diff --git a/libstdc++-v3/testsuite/20_util/tuple/cons/96803.cc b/libstdc++-v3/testsuite/20_util/tuple/cons/96803.cc
index 9d3c07d55b2..867a42150e0 100644
--- a/libstdc++-v3/testsuite/20_util/tuple/cons/96803.cc
+++ b/libstdc++-v3/testsuite/20_util/tuple/cons/96803.cc
@@ -38,4 +38,25 @@ test01()
   // std::tuple chooses wrong constructor for uses-allocator construction
   std::tuple<int> o;
   std::tuple<X> nok(std::allocator_arg, std::allocator<int>(), o);
+
+  std::tuple<int, int> oo;
+  std::tuple<X, X> nn(std::allocator_arg, std::allocator<int>(), oo);
+}
+
+struct Y
+{
+  using allocator_type = std::allocator<int>;
+
+  Y(const X&) { }
+  Y(const X&, const allocator_type&) { }
+
+  Y(X&&) { }
+  Y(std::allocator_arg_t, const allocator_type&, X&&) { }
+};
+
+void
+test02()
+{
+  std::tuple<X, X> o{1, 1};
+  std::tuple<Y, Y> oo(std::allocator_arg, std::allocator<int>(), o);
 }