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From: "johannes.kellner at wandelbots dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109470] New: unexpected const & behavior
Date: Tue, 11 Apr 2023 07:43:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109470

            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 s=
how
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 =3D 16;
   const int MAX =3D 32;

   const int& dst =3D Min(MAX, (int)lenght);
   assert(dst <=3D 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,=20
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 bec=
ame
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.=