[Bug tree-optimization/68614] New: ICE at -O3 on x86_64-linux-gnu (verify_ssa failed)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68614

            Bug ID: 68614
           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 5.2.x. 

$ 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/6.0.0/lto-wrapper
Target: x86_64-pc-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 20151128 (experimental) [trunk revision 231032] (GCC) 
$ 
$ gcc-trunk -O2 -c small.c
$ gcc-5.2 -O3 -c small.c
$ 
$ gcc-trunk -O3 -c small.c
small.c: In function âfn1â:
small.c:4:1: error: definition in block 2 follows the use
 fn1 ()
 ^~~

for SSA_NAME: _18 in statement:
vectp.19_36 = &b[_18];
small.c:4:1: internal compiler error: verify_ssa failed
0xcf9adc verify_ssa(bool, bool)
        ../../gcc-trunk/gcc/tree-ssa.c:1039
0xa28f8d execute_function_todo
        ../../gcc-trunk/gcc/passes.c:1965
0xa2982b execute_todo
        ../../gcc-trunk/gcc/passes.c:2010
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[3], c[3][5];

void
fn1 ()
{
  int e;
  for (a = 2; a >= 0; a--)
    for (e = 0; e < 4; e++)
      c[a][e] = b[a];
}