[Bug tree-optimization/71661] 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=71661

            Bug ID: 71661
           Summary: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit
                    and 64-bit modes)
           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.

It should be different from PR 71550, which seems to have become latent for the
latest trunk. 


$ 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 20160625 (experimental) [trunk revision 237780] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
$ gcc-6.1 -O3 small.c; ./a.out
$ 
$ gcc-trunk -O3 small.c  
$ ./a.out
Segmentation fault (core dumped)
$ 
$ gcc-trunk -O3 pr71550.c; ./a.out
$ gcc-trunk -O0 pr71550.c; ./a.out
$ 


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


int a, b;

void
fn1 ()
{
  unsigned c = 0;
  int d;
  b = a;
  if (a < 0)
    goto L1;
  for (; a < 1; a++)
    d = 0;
  for (; d < 2; d++)
    {
      for (c = 0; c < 3; c++)
      L1:
        a = 2;
    }
}

int
main ()
{
  fn1 ();
  return 0;
}