The following code causes an ICE when compiled with the current gcc trunk at -O3 on x86_64-linux (both 32-bit and 64-bit modes). This is a regression from 4.8.x.

$ gcc-trunk -v
gcc version 4.9.0 20130811 (experimental) [trunk revision 201651] (GCC) 
$ gcc-trunk -O2 -c small.c  
$ gcc-4.8 -O3 -c small.c
$ gcc-trunk -O3 -c small.c
small.c: In function ‘foo’:
small.c:5:6: internal compiler error: Segmentation fault
 void foo ()
      ^
0x7e02bf crash_signal
	../../gcc-trunk/gcc/toplev.c:335
0x808dfb ssa_default_def(function*, tree_node*)
	../../gcc-trunk/gcc/tree-dfa.c:314
0x8090c0 get_or_create_ssa_default_def(function*, tree_node*)
	../../gcc-trunk/gcc/tree-dfa.c:362
0x822a1a get_reaching_def
	../../gcc-trunk/gcc/tree-into-ssa.c:1184
0x8289ca maybe_replace_use
	../../gcc-trunk/gcc/tree-into-ssa.c:1784
0x8289ca rewrite_update_stmt
	../../gcc-trunk/gcc/tree-into-ssa.c:1967
0x8289ca rewrite_update_enter_block
	../../gcc-trunk/gcc/tree-into-ssa.c:2136
0xb43e9a walk_dominator_tree(dom_walk_data*, basic_block_def*)
	../../gcc-trunk/gcc/domwalk.c:210
0x8216e3 rewrite_blocks
	../../gcc-trunk/gcc/tree-into-ssa.c:2216
0x827c7e update_ssa(unsigned int)
	../../gcc-trunk/gcc/tree-into-ssa.c:3319
0x940aa8 insert_range_assertions
	../../gcc-trunk/gcc/tree-vrp.c:6102
0x940aa8 execute_vrp
	../../gcc-trunk/gcc/tree-vrp.c:9515
0x940aa8 execute
	../../gcc-trunk/gcc/tree-vrp.c:9616
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.
$ 



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short a;
int b, c;
int d[1][4][2];

void foo ()
{
  int *e;
  for (b = 1;; b--)
    {
      if (*e)
	break;
      for (c = 2; c >= 0; c--)
        {
	  *e |= d[0][3][b] != a;
	  int *f = &d[0][3][b];
	  *f = 0;
        }
    }
}