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

It appears to be a 7 regression.

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/home/absozero/trunk/root-gcc/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc/configure --prefix=/home/absozero/trunk/root-gcc --enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 7.0.0 20160515 (experimental) [trunk revision 236250] (GCC) 



$ gcc-trunk -O3 abc.c
abc.c: In function ‘main’:
abc.c:6:5: internal compiler error: Segmentation fault
 int main() {
     ^~~~
0xbaa52f crash_signal
	../../gcc/gcc/toplev.c:333
0xbe18e0 bb_seq_addr
	../../gcc/gcc/gimple.h:1654
0xbe18e0 gsi_last_bb
	../../gcc/gcc/gimple-iterator.h:163
0xbe18e0 last_stmt(basic_block_def*)
	../../gcc/gcc/tree-cfg.c:2640
0xc38900 create_edge_for_control_dependence
	../../gcc/gcc/tree-loop-distribution.c:282
0xc39bb6 create_rdg_cd_edges
	../../gcc/gcc/tree-loop-distribution.c:327
0xc39bb6 build_rdg
	../../gcc/gcc/tree-loop-distribution.c:458
0xc39f0b distribute_loop
	../../gcc/gcc/tree-loop-distribution.c:1418
0xc3cdc7 execute
	../../gcc/gcc/tree-loop-distribution.c:1791
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.

$ cat abc.c
typedef unsigned size_t;
struct {
  unsigned char buf[sizeof(long)];
} a;
size_t b;
int main() {
  size_t c, i;
  unsigned char *d;
  for (; c < sizeof(long);) {
    d = a.buf;
    b = 0;
    for (; b < i; b++)
      *d++ = '\0';
    for (; c < b; c++)
      *d++ = 'a';
    c = 0;
    for (; i < sizeof(long); i++)
      ;
  }
}