[Bug tree-optimization/70780] New: wrong code at -O2 and -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70780

            Bug ID: 70780
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            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 -O2
and -O3 in both 32-bit and 64-bit modes.

This is a regression from 5.3.x. 


$ 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 20160424 (experimental) [trunk revision 235394] (GCC) 
$ 
$ gcc-trunk -Os small.c; ./a.out
$ gcc-5.3 -O2 small.c; ./a.out
$ 
$ gcc-trunk -O2 small.c
$ ./a.out
Segmentation fault (core dumped)
$ 


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


int a, b, c, *d, e;

static int
fn1 () 
{
  if (a)
    goto l1;
 l2: while (b)
       if (*d)
         return c;
  for (e = 0; e; e++)
    {
      goto l2;
    l1:;
    }
  return 0; 
}

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