[Bug tree-optimization/71466] New: wrong code at -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71466

            Bug ID: 71466
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 7.0
            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: ---

The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -O3
in both 32-bit and 64-bit modes.

This is a regression from 6.1.x, and goes away with -fno-tree-vrp. 


$ 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 20160608 (experimental) [trunk revision 237199] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
0
$ gcc-6.1 -O3 small.c; ./a.out
0
$ gcc-trunk -O3 -fno-tree-vrp small.c; ./a.out
0
$ 
$ gcc-trunk -O3 small.c
$ ./a.out
$ 


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


int a, b, c, d;

void
fn1 ()
{
  for (c = 0; c < 2; c++)
    {
      int e, f = 1;
      for (e = 0; e < 2; e++)
        {
          if (!f)
            return;
          for (d = 0; d; d++)
            f = b;
        }
    }
}

int
main ()
{
  for (; a < 1; a++)
    {
      fn1 ();
      __builtin_printf ("0\n");
    }
  return 0;
}