[Bug tree-optimization/78725] New: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes)

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78725

            Bug ID: 78725
           Summary: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit
                    and 64-bit modes)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 7.0.0 20161206 (experimental) [trunk revision 243299] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
1
$ gcc-6.2 -O3 small.c; ./a.out
1
$ 
$ gcc-trunk -O3 small.c; ./a.out
0
$ 


----------------------------------------------


int printf (const char *, ...);

int fn1 (int b, int c)
{
  return c < 0 || c > 31 ? 0 : b >> c;
}

unsigned char d = 255; 
int e, f;

int main ()
{
  for (; f < 2; f++)
    e = fn1 (1, d++);
  printf ("%d\n", e); 
  return 0; 
}