[Bug tree-optimization/67464] 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=67464

            Bug ID: 67464
           Summary: wrong code at -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 -O3
in both 32-bit and 64-bit modes. 

This is a regression from 5.2.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/6.0.0/lto-wrapper
Target: x86_64-pc-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 6.0.0 20150905 (experimental) [trunk revision 227508] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
01
$ gcc-5.2 -O3 small.c; ./a.out
01
$ 
$ gcc-trunk -O3 small.c
$ ./a.out
00
$ 


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


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

int a = 1, b, c, d, e, f, g;

void
fn1 ()
{
  c = b;
  for (; d; d--)
    ;
  for (f = 0; f < 1; f++)
    for (e = 0; e < 1; e++)
      c = 0;
}

int
main ()
{
  int h = a;
  b = h = g < 1 ? a : a < 0;
  for (a = 0; a < 1; a++)
    fn1 ();
  printf ("0");
  printf ("%d\n", b);  // b should be 1, not 0 
  return 0;
}