[Bug c++/109470] New: unexpected const & behavior

["johannes.kellner at wandelbots dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109470

            Bug ID: 109470
           Summary: unexpected const & behavior
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johannes.kellner at wandelbots dot com
  Target Milestone: ---

Hello, I am filing this ticket, as I had source code, where this funny Min
template created a seg fault when compiling release (optimized code).
I changed the this to an example - to check the behavior and the first to show
is this UNEXPECTED/INVALID? behavior:

#include <string>
#include <cassert>

template<typename TYPE>
const TYPE& Min(const TYPE& lhs, const TYPE& rhs)
{
   if (lhs < rhs) return lhs;
   return rhs;
}

int main()
{
   size_t lenght = 16;
   const int MAX = 32;

   const int& dst = Min(MAX, (int)lenght);
   assert(dst <= MAX);
   return dst;
}

Expected behavior: return 16

If compiled with gcc 12.2 and -O0: returns 16
If compiled with gcc 12.2 and -O1: returns 0  UNEXPECTED !!!

I assume, that something with the extension of lifetime, 
for the result of `(int)lenght` fails in the optimized code.

I found this unexpected behavior, because this Min function was used to
calculate the size for a memcpy. And if compiled with optimization, dst became
invalid (very large), just after the call to Min.

We tested with gcc10 but have the same problem with gcc12.

Please feel free to contact me for details.