[Bug libstdc++/87544] alloc-size-larger-than incorrectly triggered

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87544

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Maybe this:

--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -1726,7 +1726,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       static size_type
       _S_max_size(const _Tp_alloc_type& __a) _GLIBCXX_NOEXCEPT
       {
-       const size_t __diffmax = __gnu_cxx::__numeric_traits<ptrdiff_t>::__max;
+       // std::distance(begin(), end()) cannot be greater than PTRDIFF_MAX,
+       // and realistically we can't store more than PTRDIFF_MAX/sizeof(T)
+       // (even if std::allocator_traits<A>::max_size() says we can).
+       const size_t __diffmax
+         = __gnu_cxx::__numeric_traits<ptrdiff_t>::__max / sizeof(_Tp);
        const size_t __allocmax = _Alloc_traits::max_size(__a);
        return (std::min)(__diffmax, __allocmax);
       }