[Bug tree-optimization/67109] New: ICE at -O3 on x86_64-linux-gnu in vect_analyze_slp_instance, at tree-vect-slp.c:1793

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67109

            Bug ID: 67109
           Summary: ICE at -O3 on x86_64-linux-gnu in
                    vect_analyze_slp_instance, at tree-vect-slp.c:1793
           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 the 64-bit mode (but not in the 32-bit mode). 

It is a regression from 5.1.x (I didn't check 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 20150803 (experimental) [trunk revision 226526] (GCC) 
$ 
$ gcc-trunk -m64 -O2 -c small.c
small.c: In function ‘fn1’:
small.c:12:9: warning: iteration 1u invokes undefined behavior
[-Waggressive-loop-optimizations]
    b[a] ^= 1;
         ^
small.c:10:7: note: containing loop
       for (; c < 5; c++)
       ^
$ gcc-trunk -m32 -O3 -c small.c
small.c: In function ‘fn1’:
small.c:12:9: warning: iteration 1u invokes undefined behavior
[-Waggressive-loop-optimizations]
    b[a] ^= 1;
         ^
small.c:10:7: note: containing loop
       for (; c < 5; c++)
       ^
$ 
$ gcc-5.1 -m64 -O3 -c small.c
small.c: In function ‘fn1’:
small.c:12:9: warning: iteration 1u invokes undefined behavior
[-Waggressive-loop-optimizations]
    b[a] ^= 1;
         ^
small.c:10:7: note: containing loop
       for (; c < 5; c++)
       ^
$ 
$ gcc-trunk -m64 -O3 -c small.c
small.c: In function ‘fn1’:
small.c:12:9: warning: iteration 1u invokes undefined behavior
[-Waggressive-loop-optimizations]
    b[a] ^= 1;
         ^
small.c:10:7: note: containing loop
       for (; c < 5; c++)
       ^
small.c:5:1: internal compiler error: in vect_analyze_slp_instance, at
tree-vect-slp.c:1793
 fn1 ()
 ^
0xcf91c5 vect_analyze_slp_instance
        ../../gcc-trunk/gcc/tree-vect-slp.c:1793
0xcf9ab7 vect_analyze_slp(_loop_vec_info*, _bb_vec_info*, unsigned int)
        ../../gcc-trunk/gcc/tree-vect-slp.c:1879
0xcf9eee vect_slp_analyze_bb_1
        ../../gcc-trunk/gcc/tree-vect-slp.c:2426
0xcf9eee vect_slp_analyze_bb(basic_block_def*)
        ../../gcc-trunk/gcc/tree-vect-slp.c:2552
0xcfce22 execute
        ../../gcc-trunk/gcc/tree-vectorizer.c:702
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.
$ 


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


unsigned int a;
int b[1], c, d;

void
fn1 ()
{
  for (; d;)
    {
      a = c = 0;
      for (; c < 5; c++)
        {
          b[a] ^= 1;
          a--;
        }
    }
}