[gcc r15-1342] libstdc++: Make std::type_info::operator== always_inline for C++23 [PR110572]

[Jonathan Wakely]

https://gcc.gnu.org/g:6af8d8e618ed27dae3432c96484de4360bd893ab

commit r15-1342-g6af8d8e618ed27dae3432c96484de4360bd893ab
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jun 11 15:52:30 2024 +0100

    libstdc++: Make std::type_info::operator== always_inline for C++23 [PR110572]
    
    Commit r12-6266-g3633cc54284450 implemented P1328 for C++23, making
    std::type_info::operator== usable in constant expressions. For targets
    such as mingw-w64 where that function was not previously inline, making
    it constexpr required making it inline for C++23 and later. For
    statically linked programs this can result in multiple definition
    errors, because there's a non-inline definition in libstdc++.a as well.
    
    For those targets make it always_inline for C++23, so that there is no
    symbol generated for the inline definition, and the non-inline
    definition in libstdc++.a will be the only definition.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/110572
            * libsupc++/typeinfo (type_info::operator==): Add always_inline
            attribute for targets where the ABI requries equality to be
            non-inline.
            * testsuite/18_support/type_info/110572.cc: New test.

Diff:
---
 libstdc++-v3/libsupc++/typeinfo                       |  3 +++
 libstdc++-v3/testsuite/18_support/type_info/110572.cc | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/libstdc++-v3/libsupc++/typeinfo b/libstdc++-v3/libsupc++/typeinfo
index fcc3077d0609..35e72bb18ee5 100644
--- a/libstdc++-v3/libsupc++/typeinfo
+++ b/libstdc++-v3/libsupc++/typeinfo
@@ -188,6 +188,9 @@ namespace std
 #endif
 
 #if __GXX_TYPEINFO_EQUALITY_INLINE || __cplusplus > 202002L
+# if ! __GXX_TYPEINFO_EQUALITY_INLINE
+  [[__gnu__::__always_inline__]]
+# endif
   _GLIBCXX23_CONSTEXPR inline bool
   type_info::operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT
   {
diff --git a/libstdc++-v3/testsuite/18_support/type_info/110572.cc b/libstdc++-v3/testsuite/18_support/type_info/110572.cc
new file mode 100644
index 000000000000..64081879b77d
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/type_info/110572.cc
@@ -0,0 +1,11 @@
+// { dg-options "-static-libstdc++" }
+// { dg-require-static-libstdcxx }
+// { dg-require-cpp-feature-test __cpp_rtti }
+// { dg-do link }
+
+#include <typeinfo>
+
+int main()
+{
+  return typeid(0) == typeid(0u);
+}