[PATCH] libstdc++: Implement __integral_constant_like in terms of __constexpr_wrapper_like.

[Tomasz Kamiński]

This implements LWG4486. integral-constant-like and constexpr-wrapper-like
exposition-only concept duplication.

libstdc++-v3/ChangeLog:

	* include/bits/simd_details.h (simd::__constexpr_wrapper_like):
	Move to...
	* include/std/concepts (std::__constexpr_wrapper_like): Moved
	from bits/simd_details.h.
	* include/std/span (std::__integral_constant_like): Define in
	terms of __constexpr_wrapper_like.
	* testsuite/std/simd/traits_impl.cc: Added using declaration
	for std::__constexpr_wrapper_like.
---

Tested on x86_64-linux locally. OK for trunk/stage-1?
I done it, to double check if they are in sync. This impacts span in C++20 mode,
so maybe it is safer to keep it for stage-1. From other seems safe, i.e. should
work as soon as test passes.

 libstdc++-v3/include/bits/simd_details.h       | 7 -------
 libstdc++-v3/include/std/concepts              | 9 +++++++++
 libstdc++-v3/include/std/span                  | 8 +++-----
 libstdc++-v3/testsuite/std/simd/traits_impl.cc | 1 +
 4 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/libstdc++-v3/include/bits/simd_details.h b/libstdc++-v3/include/bits/simd_details.h
index 31bd6ac45ab..408a344d2ec 100644
--- a/libstdc++-v3/include/bits/simd_details.h
+++ b/libstdc++-v3/include/bits/simd_details.h
@@ -1030,13 +1030,6 @@ namespace simd
   /** @internal
    * C++26 [simd.expos]
    */
-  template<typename _Tp>
-    concept __constexpr_wrapper_like
-      = convertible_to<_Tp, decltype(_Tp::value)>
-	  && equality_comparable_with<_Tp, decltype(_Tp::value)>
-	  && bool_constant<_Tp() == _Tp::value>::value
-	  && bool_constant<static_cast<decltype(_Tp::value)>(_Tp()) == _Tp::value>::value;
-
   // [simd.ctor] explicit(...) of broadcast ctor
   template <auto _From, typename _To>
     concept __non_narrowing_constexpr_conversion
diff --git a/libstdc++-v3/include/std/concepts b/libstdc++-v3/include/std/concepts
index 7673443f33a..328096a89e3 100644
--- a/libstdc++-v3/include/std/concepts
+++ b/libstdc++-v3/include/std/concepts
@@ -421,6 +421,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	       && ! requires(_Tp&& __t, _Up&& __u)
 	         { static_cast<_Up&&>(__u).operator<=>(static_cast<_Tp&&>(__t)); }));
   }
+
+  // [expos.only.entity]
+  template<typename _Tp>
+    concept __constexpr_wrapper_like
+      = convertible_to<_Tp, decltype(_Tp::value)>
+	&& equality_comparable_with<_Tp, decltype(_Tp::value)>
+	&& bool_constant<_Tp() == _Tp::value>::value
+	&& bool_constant<static_cast<decltype(_Tp::value)>(_Tp()) == _Tp::value>::value;
+
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 #endif // __cpp_lib_concepts
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index a5f5bf48f90..1215ce826f6 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -467,15 +467,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   {
     // _GLIBCXX_RESOLVE_LIB_DEFECTS
     // 4351. integral-constant-like needs more remove_cvref_t
+    // 4486. integral-constant-like and constexpr-wrapper-like exposition-only
+    //       concept duplicatiob
     template<typename _Tp>
       concept __integral_constant_like =
 	is_integral_v<remove_cvref_t<decltype(_Tp::value)>>
 	&& !is_same_v<bool, remove_cvref_t<decltype(_Tp::value)>>
-	&& convertible_to<_Tp, decltype(_Tp::value)>
-	&& equality_comparable_with<_Tp, decltype(_Tp::value)>
-	&& bool_constant<_Tp() == _Tp::value>::value
-	&& bool_constant<static_cast<decltype(_Tp::value)>(_Tp()) == _Tp::value>
-	     ::value;
+	&& __constexpr_wrapper_like<_Tp>;
 
     template<typename _Tp>
       constexpr size_t __maybe_static_ext = dynamic_extent;
diff --git a/libstdc++-v3/testsuite/std/simd/traits_impl.cc b/libstdc++-v3/testsuite/std/simd/traits_impl.cc
index f73a9e3beb5..2f705c7df2f 100644
--- a/libstdc++-v3/testsuite/std/simd/traits_impl.cc
+++ b/libstdc++-v3/testsuite/std/simd/traits_impl.cc
@@ -16,6 +16,7 @@ using std::float32_t;
 using std::float64_t;
 
 using namespace std::simd;
+using std::__constexpr_wrapper_like;
 
 template <int = 0>
 void test()
-- 
2.53.0