[gcc r13-5079] libstdc++: Fix std::span constraint for sizeof(size_t) < sizeof(int) [PR108221]

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

https://gcc.gnu.org/g:b39f4333d18cc58b1a655c537a78fefe95b82609

commit r13-5079-gb39f4333d18cc58b1a655c537a78fefe95b82609
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jan 9 10:45:31 2023 +0000

    libstdc++: Fix std::span constraint for sizeof(size_t) < sizeof(int) [PR108221]
    
    The default constructor has a constraint that is always false if
    arithmetic on size_t values promotes to int. Rewrite the constraint
    exactly as written in the standard, which works correctly.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/108221
            * include/std/span (span::span()): Un-simplify constraint to
            work for size_t of lesser rank than int.

Diff:
---
 libstdc++-v3/include/std/span | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index 251fed91abf..b336332b190 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -145,7 +145,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       constexpr
       span() noexcept
-      requires ((_Extent + 1u) <= 1u)
+      requires (_Extent == dynamic_extent || _Extent == 0)
       : _M_ptr(nullptr), _M_extent(0)
       { }