[Bug tree-optimization/66951] New: ICE at -O3 on x86_64-linux-gnu, verify_ssa failed

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66951

            Bug ID: 66951
           Summary: ICE at -O3 on x86_64-linux-gnu, verify_ssa failed
           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 20150719 (experimental) [trunk revision 225987] (GCC) 
$ 
$ gcc-trunk -O2 -c small.c
$ gcc-5.1 -O3 -c small.c
$ 
$ gcc-trunk -O3 -c small.c
small.c: In function ‘fn1’:
small.c:4:1: error: definition in block 18 does not dominate use in block 9
 fn1 ()
 ^
for SSA_NAME: .MEM_48 in statement:
# VUSE <.MEM_48>
vect__9.18_58 = MEM[(int *)vectp_b.16_56];
small.c:4:1: internal compiler error: verify_ssa failed
0xd6a819 verify_ssa(bool, bool)
        ../../gcc-trunk/gcc/tree-ssa.c:1047
0xaaea3d execute_function_todo
        ../../gcc-trunk/gcc/passes.c:1955
0xaaf253 execute_todo
        ../../gcc-trunk/gcc/passes.c:2005
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, b[16], c, d;

void
fn1 ()
{
  for (; d; d++)
    {
      for (a = 0; a < 2; a++)
        ;
      c ^= b[d];
    }
}