[Bug tree-optimization/66372] New: ICE on valid code at -O3 on x86_64-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66372

            Bug ID: 66372
           Summary: ICE on valid 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 following code causes an ICE when compiled with the current gcc trunk at
-O3 on x86_64-linux-gnu in both 32-bit and 64-bit modes. 

It is a regression from 5.1.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/6.0.0/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 6.0.0 20150601 (experimental) [trunk revision 223995] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
$ gcc-5.1 -O3 small.c; ./a.out
$ 
$ gcc-trunk -O3 small.c
small.c: In function âmainâ:
small.c:29:1: internal compiler error: Segmentation fault
 main ()
 ^
0xb1212f crash_signal
        ../../gcc-trunk/gcc/toplev.c:380
0xcf4811 thread_through_all_blocks(bool)
        ../../gcc-trunk/gcc/tree-ssa-threadupdate.c:2693
0xc3310b execute
        ../../gcc-trunk/gcc/tree-ssa-dom.c:1244
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.
$ 


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


int a, c, d, e, f;

int
fn1 ()
{
  for (;;)
    {
      if (a)
        break;
      unsigned int g = 1;
    lbl:
      c = g;
      for (g = 0; g < 1; g++)
        {
          if (c)
            continue;
          int h[1];
          f = h[0];
          for (; d; d = 0)
            if (e)
              goto lbl;
        }
      return 0;
    }
  return 0;
}

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