[Bug tree-optimization/59715] New: wrong code at -Os and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59715

            Bug ID: 59715
           Summary: wrong code at -Os and above 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 (as well as 4.8.x and 4.7.x) miscompiles the following
code on x86_64-linux at -Os and above in both 32-bit and 64-bit modes.

This is a regression from 4.6.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 --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20140107 (experimental) [trunk revision 206387] (GCC) 
$ 
$ gcc-trunk -O1 small.c; a.out
0
$ gcc-4.6 -Os small.c; a.out
0
$ gcc-trunk -Os small.c; a.out
2
$ gcc-4.8 -Os small.c; a.out
2
$ gcc-4.7 -Os small.c; a.out
2
$ 


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


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

int a = 2, b;

int
main ()
{
  int c;
  if (!b)
    {
      b = a;
      c = a == 0 ? 1 : 1 % a;
      if (c)
    b = 0;
    }
  printf ("%d\n", b);
  return 0;
}