[gcc(refs/users/mikael/heads/pr121185_v01)] libstdc++: Ensure std::hash<__int128> is defined [PR96710]

[Mikael Morin]

https://gcc.gnu.org/g:43f8e460b5b9b32d45b6bd3e6f1174e3e9ffed85

commit 43f8e460b5b9b32d45b6bd3e6f1174e3e9ffed85
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri May 16 13:33:23 2025 +0100

    libstdc++: Ensure std::hash<__int128> is defined [PR96710]
    
    This is a follow-up to r16-2190-g4faa42ac0dee2c which ensures that
    std::hash is always enabled for signed and unsigned __int128. The
    standard requires std::hash to be enabled for all arithmetic types.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/96710
            * include/bits/functional_hash.h (hash<__int128>): Define for
            strict modes.
            (hash<unsigned __int128>): Likewise.
            * testsuite/20_util/hash/int128.cc: New test.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/include/bits/functional_hash.h   |  9 +++++++++
 libstdc++-v3/testsuite/20_util/hash/int128.cc | 20 ++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/libstdc++-v3/include/bits/functional_hash.h b/libstdc++-v3/include/bits/functional_hash.h
index e84c9ee04be2..8456089f768d 100644
--- a/libstdc++-v3/include/bits/functional_hash.h
+++ b/libstdc++-v3/include/bits/functional_hash.h
@@ -199,6 +199,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3 unsigned)
 #endif
 
+#if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
+  // In strict modes __GLIBCXX_TYPE_INT_N_0 is not defined for __int128,
+  // but we want to always treat signed/unsigned __int128 as integral types.
+  __extension__
+  _Cxx_hashtable_define_trivial_hash(__int128)
+  __extension__
+  _Cxx_hashtable_define_trivial_hash(__int128 unsigned)
+#endif
+
 #undef _Cxx_hashtable_define_trivial_hash
 
   struct _Hash_impl
diff --git a/libstdc++-v3/testsuite/20_util/hash/int128.cc b/libstdc++-v3/testsuite/20_util/hash/int128.cc
new file mode 100644
index 000000000000..7c3a1baa0ec6
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/hash/int128.cc
@@ -0,0 +1,20 @@
+// { dg-do run { target c++11 } }
+// { dg-add-options strict_std }
+
+#include <functional>
+#include <testsuite_hooks.h>
+
+int main()
+{
+#ifdef __SIZEOF_INT128__
+  std::hash<__int128> h;
+  __int128 i = (__int128)0x123456789;
+  VERIFY( h(i) == i );
+  VERIFY( h(-i) == (std::size_t)-i );
+  VERIFY( h(~i) == (std::size_t)~i );
+  std::hash<unsigned __int128> hu;
+  unsigned __int128 u = i;
+  VERIFY( hu(u) == u );
+  VERIFY( hu(~u) == (std::size_t)~u );
+#endif
+}