[Bug tree-optimization/71550] 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=71550

            Bug ID: 71550
           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.


$ 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 20160615 (experimental) [trunk revision 237485] (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)
$ 


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


int a = 3, b, c, f, g, h;
unsigned d;
char *e;

int
main ()
{
  for (; a; a--)
    {
      int i;
      if (h && i)
        __builtin_printf ("%d%d", c, f);
      i = 0;
      for (; i < 2; i++)
        if (g)
          for (; d < 10; d++)
            b = *e;
      i = 0;
      for (; i < 1; i++)
        ;
    }
  return 0;
}