[Bug c++/119154] GCC 15.0 std module with compiled with -O3 breaks when loaded with -O0 (not -O1, -O2 and -Ofast)

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119154

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Though
===pr119154-1.C===
#include "pr119154-1.h"
import foo;
int main(){return 0;}
===pr119154-1.h===
extern "C" {
extern wchar_t *wmemset (wchar_t *__s, wchar_t __c, __SIZE_TYPE__ __n) noexcept
(true);
#ifdef _FORTIFY_SOURCE
extern wchar_t *__wmemset_chk (wchar_t *__s, wchar_t __c, __SIZE_TYPE__ __n,
__SIZE_TYPE__ __ns) noexcept (true);
extern wchar_t *__wmemset_alias (wchar_t *__s, wchar_t __c, __SIZE_TYPE__ __n)
noexcept (true) __asm__ ("wmemset");
extern wchar_t *__wmemset_chk_warn (wchar_t *__s, wchar_t __c, __SIZE_TYPE__
__n, __SIZE_TYPE__ __ns) noexcept (true) __asm__ ("__wmemset_chk")
__attribute__((__warning__ ("wmemset called with length bigger than size of
destination buffer")));
extern __inline __attribute__ ((__always_inline__)) __attribute__
((__gnu_inline__)) __attribute__ ((__artificial__)) wchar_t *
__attribute__ ((__leaf__)) wmemset (wchar_t *__s, wchar_t __c, __SIZE_TYPE__
__n) noexcept (true)
{
  return (((__builtin_object_size (__s, 0)) == (long unsigned int) -1 ||
(((__typeof (__n)) 0 < (__typeof (__n)) -1 || (__builtin_constant_p (__n) &&
(__n) > 0)) && __builtin_constant_p ((((long unsigned int) (__n)) <=
((__builtin_object_size (__s, 0))) / ((sizeof (wchar_t))))) && (((long unsigned
int) (__n)) <= ((__builtin_object_size (__s, 0))) / ((sizeof (wchar_t)))))) ?
__wmemset_alias (__s, __c, __n) : ((((__typeof (__n)) 0 < (__typeof (__n)) -1
|| (__builtin_constant_p (__n) && (__n) > 0)) && __builtin_constant_p ((((long
unsigned int) (__n)) <= (__builtin_object_size (__s, 0)) / (sizeof (wchar_t))))
&& !(((long unsigned int) (__n)) <= (__builtin_object_size (__s, 0)) / (sizeof
(wchar_t)))) ? __wmemset_chk_warn (__s, __c, __n, (__builtin_object_size (__s,
0)) / (sizeof (wchar_t))) : __wmemset_chk (__s, __c, __n,
(__builtin_object_size (__s, 0)) / (sizeof (wchar_t)))));
}
#endif
}
===pr119154-2.C===
module;
#include "pr119154-1.h"
#include "pr119154-2.h"
export module foo;
export namespace foo
{
  using foo::wmemset;
}
===pr119154-2.h===
extern "C++"
{
namespace foo
{
  using ::wmemset;
}
}

g++  -std=c++23 -O3 -fmodules -S pr119154-2.C -D_FORTIFY_SOURCE
g++  -std=c++23 -O0 -fmodules -S pr119154-1.C

doesn't reproduce it.  Note, one of the templates actualy uses wmemset:
      static constexpr char_type*
      assign(char_type* __s, size_t __n, char_type __a)
      {
 if (__n == 0)
   return __s;

 if (std::__is_constant_evaluated())
   return __gnu_cxx::char_traits<char_type>::assign(__s, __n, __a);

 return wmemset(__s, __a, __n);
      }
That is something that doesn't happen in the above testcase.