[gcc r12-7244] libstdc++: Add missing constexpr to uses-allocator construction utilities [PR104542]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:6cfb7ffb659fd6b87a21312021ab023a06e8f6be

commit r12-7244-g6cfb7ffb659fd6b87a21312021ab023a06e8f6be
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Feb 15 12:47:39 2022 +0000

    libstdc++: Add missing constexpr to uses-allocator construction utilities [PR104542]
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/104542
            * include/bits/uses_allocator_args.h (make_obj_using_allocator)
            (uninitialized_construct_using_allocator): Add constexpr.
            * testsuite/20_util/uses_allocator/make_obj.cc: Check constexpr.
            * testsuite/20_util/uses_allocator/uninitialized_construct.cc: New test.

Diff:
---
 libstdc++-v3/include/bits/uses_allocator_args.h    |  4 +--
 .../testsuite/20_util/uses_allocator/make_obj.cc   | 30 +++++++++++++++++++++-
 .../uses_allocator/uninitialized_construct.cc      | 17 ++++++++++++
 3 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/bits/uses_allocator_args.h b/libstdc++-v3/include/bits/uses_allocator_args.h
index a3aa37d8e78..d92dd1f0901 100644
--- a/libstdc++-v3/include/bits/uses_allocator_args.h
+++ b/libstdc++-v3/include/bits/uses_allocator_args.h
@@ -196,7 +196,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, typename _Alloc, typename... _Args>
-    inline _Tp
+    constexpr _Tp
     make_obj_using_allocator(const _Alloc& __a, _Args&&... __args)
     {
       return std::make_from_tuple<_Tp>(
@@ -205,7 +205,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, typename _Alloc, typename... _Args>
-    inline _Tp*
+    constexpr _Tp*
     uninitialized_construct_using_allocator(_Tp* __p, const _Alloc& __a,
 					    _Args&&... __args)
     {
diff --git a/libstdc++-v3/testsuite/20_util/uses_allocator/make_obj.cc b/libstdc++-v3/testsuite/20_util/uses_allocator/make_obj.cc
index cd4497e8410..2dd0f819657 100644
--- a/libstdc++-v3/testsuite/20_util/uses_allocator/make_obj.cc
+++ b/libstdc++-v3/testsuite/20_util/uses_allocator/make_obj.cc
@@ -142,7 +142,7 @@ test01()
   VERIFY( c2.alloc_id == 1 );
 }
 
-void 
+void
 test02()
 {
   decltype(auto) b
@@ -389,6 +389,34 @@ test08()
   std::make_obj_using_allocator<X>(a);
 }
 
+constexpr bool
+test_pr104542()
+{
+  // PR libstdc++/104542 - missing constexpr
+  std::allocator<void> a;
+  int i = std::make_obj_using_allocator<int>(a, 1);
+
+  struct X {
+    using allocator_type = std::allocator<long>;
+    constexpr X(std::allocator_arg_t, std::allocator<int>, int i) : i(i+1) { }
+    int i;
+  };
+
+  X x = std::make_obj_using_allocator<X>(a, i);
+
+  struct Y {
+    using allocator_type = std::allocator<char>;
+    constexpr Y(X x, std::allocator<int>) : i(x.i+1) { }
+    int i;
+  };
+
+  Y y = std::make_obj_using_allocator<Y>(a, x);
+
+  return y.i == 3;
+}
+
+static_assert( test_pr104542() );
+
 int
 main()
 {
diff --git a/libstdc++-v3/testsuite/20_util/uses_allocator/uninitialized_construct.cc b/libstdc++-v3/testsuite/20_util/uses_allocator/uninitialized_construct.cc
new file mode 100644
index 00000000000..f403cbe99cc
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/uses_allocator/uninitialized_construct.cc
@@ -0,0 +1,17 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+#include <memory>
+
+constexpr bool
+test_pr104542()
+{
+  // PR libstdc++/104542 - missing constexpr
+  std::allocator<int> a;
+  int* p = a.allocate(1);
+  int i = *std::uninitialized_construct_using_allocator<int>(p, a, 999);
+  a.deallocate(p, 1);
+  return i == 999;
+}
+
+static_assert( test_pr104542() );