[Bug tree-optimization/71518] New: wrong code at -O3 on x86_64-linux-gnu in 64-bit mode (not in 32-bit mode)

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71518

            Bug ID: 71518
           Summary: wrong code at -O3 on x86_64-linux-gnu in 64-bit mode
                    (not in 32-bit mode)
           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 and 6.1.x miscompile the following code on
x86_64-linux-gnu at -O3 in the 64-bit mode (but not in the 32-bit mode).

This is a regression from 5.4.x, and goes away with -fno-tree-vectorize. 


$ 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 20160612 (experimental) [trunk revision 237336] (GCC) 
$ 
$ gcc-trunk -m32 -O3 small.c; ./a.out
$ gcc-trunk -m64 -O2 small.c; ./a.out
$ gcc-5.4 -O3 small.c; ./a.out
$ 
$ gcc-trunk -m64 -O3 small.c
$ ./a.out
Segmentation fault (core dumped)
$ 
$ gcc-6.1 -m64 -O3 small.c
$ ./a.out
Segmentation fault (core dumped)
$ 


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


int a, *b[9], c, d, e; 

static int
fn1 ()
{
  for (c = 6; c >= 0; c--)
    for (d = 0; d < 2; d++)
      {
        b[d * 2 + c] = 0;
        e = a > 1 ? : 0;
        if (e == 2) 
          return 0;
      }
  return 0;
}

int
main ()
{
  fn1 ();
  return 0; 
}