[Bug tree-optimization/58830] New: wrong code at -O3 on x86_64-linux-gnu (affecting 4.8.x, but not trunk or 4.7.x)

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58830

            Bug ID: 58830
           Summary: wrong code at -O3 on x86_64-linux-gnu (affecting
                    4.8.x, but not trunk or 4.7.x)
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The following testcase is miscompiled by 4.8.2 (as well 4.8.0 and 4.8.1) on
x86_64-linux at -O3 in both 32-bit and 64-bit modes. 

It works with the current gcc trunk, 4.7.x and 4.6.x. 

$ gcc-4.8.2 -v   
Using built-in specs.
COLLECT_GCC=gcc-4.8.2
COLLECT_LTO_WRAPPER=/usr/local/gcc-4.8.2/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.8.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.8.2/configure
--enable-languages=c,c++,objc,obj-c++,fortran,lto --enable-checking=release
--with-gmp=/home/su/software/local/gcc-4.8.2
--with-mpfr=/home/su/software/local/gcc-4.8.2
--with-mpc=/home/su/software/local/gcc-4.8.2
--with-cloog=/home/su/software/local/gcc-4.8.2
--prefix=/home/su/software/local/gcc-4.8.2
Thread model: posix
gcc version 4.8.2 (GCC) 
$ 
$ gcc-4.8.2 -O2 small.c; a.out
0
$ gcc-4.7.3 -O3 small.c; a.out
0
$ gcc-4.6.4 -O3 small.c; a.out
0
$ gcc-trunk -O3 small.c; a.out
0
$ 
$ gcc-4.8.2 -O3 small.c; a.out
2
$ gcc-4.8.1 -O3 small.c; a.out
2
$ gcc-4.8.0 -O3 small.c; a.out
2
$ 


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


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

int b, c, d, f, g, h, i, j[6], *l = &b, *m, n, *o, r; 
char k;

static int
foo ()
{
  char *p = &k;

  for (; d; d++)
    if (i)
      h = 0;
    else
      h = c || (r = 0);

  for (f = 0; f < 2; f++)
    {
      unsigned int q;
      *l = 0;
      if (n)
    *m = g;
      if (g)
    o = 0;
      for (q = -8; q >= 5; q++)
    (*p)--;
    }

  return 0;
}

int
main ()
{
  foo ();
  printf("%d\n",
j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[j[0]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
^ (k & 15)]);
  return 0;
}