[Bug tree-optimization/58696] New: wrong code at -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58696

            Bug ID: 58696
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk produces wrong code for the following testcase on
x86_64-linux when compiled at -O3 in both 32-bit and 64-bit modes. 

This is a regression from 4.8.x.


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure
--enable-languages=c,c++,objc,obj-c++,fortran,lto --disable-werror
--enable-checking=release --with-gmp=/usr/local/gcc-trunk
--with-mpfr=/usr/local/gcc-trunk --with-mpc=/usr/local/gcc-trunk
--with-cloog=/usr/local/gcc-trunk --prefix=/usr/local/gcc-trunk
Thread model: posix
gcc version 4.9.0 20131011 (experimental) [trunk revision 203458] (GCC) 
$ 
$ gcc-trunk -O2 small.c; a.out
0
$ gcc-4.8 -O3 small.c; a.out
0
$ gcc-trunk -O3 small.c; a.out
1
$ 


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


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

int a[20], b, c; 

int
fn1 ()
{
  int d, e, f, g = 0; 

  a[12] = 1;
  for (e = 0; e < 3; e++)
    for (d = 0; d < 2; d++)
      {
    for (f = 0; f < 2; f++)
      {
        g ^= a[12] > 1;
        if (g)
          return 0;
        if (b)
          break;
      }
    for (c = 0; c < 1; c++)
      a[d] = a[e * 3 + 9]; 
      }
  return 0;
}

int
main ()
{
  fn1 ();
  printf ("%d\n", a[0]);
  return 0;
}