[PATCH v3] vect: Verify that GET_MODE_UNITS is greater than one for vect_grouped_store_supported

[Kevin Lee <kevinl@rivosinc.com>]

This patch properly guards gcc_assert (multiple_p (m_full_nelts, 
m_npatterns)) in vec_perm_indices indices (sel, 2, nelt) for VNx1 vectors.

Based on the feedback from Richard Biener and Richard Sandiford,
multiple_p has been used instead of maybe_lt to compare nelt with the
minimum size 2.

Bootstrap and testing done on x86_64-pc-linux-gnu. Would this be ok for trunk?

Patch V1: https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614463.html
Patch V2: https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614700.html
 
Kevin Lee <kevinl@rivosinc.com>
gcc/ChangeLog:

	* tree-vect-data-refs.cc (vect_grouped_store_supported): Add new
condition
---
 gcc/tree-vect-data-refs.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
index 8daf7bd7dd3..df393ba723d 100644
--- a/gcc/tree-vect-data-refs.cc
+++ b/gcc/tree-vect-data-refs.cc
@@ -5399,6 +5399,8 @@ vect_grouped_store_supported (tree vectype, unsigned HOST_WIDE_INT count)
 	  poly_uint64 nelt = GET_MODE_NUNITS (mode);
 
 	  /* The encoding has 2 interleaved stepped patterns.  */
+    if(!multiple_p (nelt, 2))
+      return false;
 	  vec_perm_builder sel (nelt, 2, 3);
 	  sel.quick_grow (6);
 	  for (i = 0; i < 3; i++)
-- 
2.25.1