[gcc r17-354] libstdc++: Remove non-concepts fallback for std::make_shared_for_overwrite

[Jonathan Wakely]

https://gcc.gnu.org/g:5d225c5aa3d40cbf479d99c0bb2ca22291a11568

commit r17-354-g5d225c5aa3d40cbf479d99c0bb2ca22291a11568
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue May 5 14:03:04 2026 +0100

    libstdc++: Remove non-concepts fallback for std::make_shared_for_overwrite
    
    Clang 10 added support for concepts, so we no longer need to support
    C++20 compilers that don't define __cpp_concepts.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/shared_ptr.h (_UnboundedArray, _BoundedArray)
            (_NotUnboundedArray): Remove fallback definition for C++20
            compilers that don't define __cpp_concepts.
            * include/bits/shared_ptr_base.h (_Sp_counted_ptr_inplace):
            Remove fallback declaration of _Sp_overwrite_tag partial
            specialization.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/include/bits/shared_ptr.h      | 18 ------------------
 libstdc++-v3/include/bits/shared_ptr_base.h |  5 -----
 2 files changed, 23 deletions(-)

diff --git a/libstdc++-v3/include/bits/shared_ptr.h b/libstdc++-v3/include/bits/shared_ptr.h
index fd00384df223..ada32d3d3cb9 100644
--- a/libstdc++-v3/include/bits/shared_ptr.h
+++ b/libstdc++-v3/include/bits/shared_ptr.h
@@ -114,38 +114,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __glibcxx_shared_ptr_arrays >= 201707L
   // Constraint for overloads taking array types with unknown bound, U[].
-#if __cpp_concepts
   template<typename _Tp>
     requires is_array_v<_Tp> && (extent_v<_Tp> == 0)
     using _UnboundedArray = _Tp;
-#else
-  template<typename _Tp>
-    using _UnboundedArray
-      = __enable_if_t<__is_array_unknown_bounds<_Tp>::value, _Tp>;
-#endif
 
   // Constraint for overloads taking array types with known bound, U[N].
-#if __cpp_concepts
   template<typename _Tp>
     requires (extent_v<_Tp> != 0)
     using _BoundedArray = _Tp;
-#else
-  template<typename _Tp>
-    using _BoundedArray
-      = __enable_if_t<__is_array_known_bounds<_Tp>::value, _Tp>;
-#endif
 
 #if __glibcxx_smart_ptr_for_overwrite
   // Constraint for overloads taking either non-array or bounded array, U[N].
-#if __cpp_concepts
   template<typename _Tp>
     requires (!is_array_v<_Tp>) || (extent_v<_Tp> != 0)
     using _NotUnboundedArray = _Tp;
-#else
-  template<typename _Tp>
-    using _NotUnboundedArray
-      = __enable_if_t<!__is_array_unknown_bounds<_Tp>::value, _Tp>;
-#endif
 #endif // smart_ptr_for_overwrite
 #endif // shared_ptr_arrays
 
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index b92e3a4c90e4..cfaee6df37b1 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -727,14 +727,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Partial specialization used for make_shared_for_overwrite<non-array>().
   // This partial specialization is used when the allocator's value type
   // is the special _Sp_overwrite_tag type.
-#if __cpp_concepts
   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
     requires is_same_v<typename _Alloc::value_type, _Sp_overwrite_tag>
     class _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> final
-#else
-  template<typename _Tp, template<typename> class _Alloc, _Lock_policy _Lp>
-    class _Sp_counted_ptr_inplace<_Tp, _Alloc<_Sp_overwrite_tag>, _Lp> final
-#endif
     : public _Sp_counted_base<_Lp>
     {
       [[no_unique_address]] _Alloc _M_alloc;