[PATCH] Fix ICE with single element vector

[Andreas Krebbel]

I did run into an ICE with a single element vector triggered by
dividing the number of elements by 2 with exact_div here:

tree-vect-data-refs.c:5132

      else
        {
          /* If length is not equal to 3 then only power of 2 is supported.  */
          gcc_assert (pow2p_hwi (count));
          poly_uint64 nelt = GET_MODE_NUNITS (mode);

          /* The encoding has 2 interleaved stepped patterns.  */
          vec_perm_builder sel (nelt, 2, 3);
          sel.quick_grow (6);
          for (i = 0; i < 3; i++)
            {
              sel[i * 2] = i;
              sel[i * 2 + 1] = i + nelt;
            }
          vec_perm_indices indices (sel, 2, nelt);
          if (can_vec_perm_const_p (mode, indices))
            {
              for (i = 0; i < 6; i++)
                sel[i] += exact_div (nelt, 2);    <-----
              indices.new_vector (sel, 2, nelt);
              if (can_vec_perm_const_p (mode, indices))
                return true;
            }
        }

The patch adds a check to prevent this.

Ok?

-Andreas-

gcc/ChangeLog:

2018-04-16  Andreas Krebbel  <kreb...@linux.ibm.com>

        * tree-vect-data-refs.c (vect_grouped_store_supported): Exit for
        single element vectors.
---
 gcc/tree-vect-data-refs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index 161a886..01e28ca 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -5135,6 +5135,9 @@ vect_grouped_store_supported (tree vectype, unsigned 
HOST_WIDE_INT count)
          gcc_assert (pow2p_hwi (count));
          poly_uint64 nelt = GET_MODE_NUNITS (mode);
 
+         if (maybe_eq (nelt, 1U))
+           return false;
+
          /* The encoding has 2 interleaved stepped patterns.  */
          vec_perm_builder sel (nelt, 2, 3);
          sel.quick_grow (6);
-- 
2.9.1