Handle poly_int vector sizes in get_vec_alignment_for_array_type

get_vectype_for_scalar_type returns a variable-length vector type
for SVE, whereas get_vec_alignment_for_array_type assumed it would
always be an INTEGER_CST.

This is needed to build libstdc++-v3/src/closures.cc for SVE
(and probably many other places besides -- this was just the
first hit).

2018-01-12  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-vectorizer.c (get_vec_alignment_for_array_type): Handle
	polynomial type sizes.

From-SVN: r256586

gcc/ChangeLog

 2018-01-12  Richard Sandiford  <richard.sandiford@linaro.org>
 
+	* tree-vectorizer.c (get_vec_alignment_for_array_type): Handle
+	polynomial type sizes.
+
+2018-01-12  Richard Sandiford  <richard.sandiford@linaro.org>
+
 	* gimplify.c (gimple_add_tmp_var_fn): Allow variables to have a
 	poly_uint64 size, rather than requiring an unsigned HOST_WIDE_INT size.
 	(gimple_add_tmp_var): Likewise.

gcc/tree-vectorizer.c

@@ -1015,12 +1015,13 @@ static unsigned
 get_vec_alignment_for_array_type (tree type) 
 {
   gcc_assert (TREE_CODE (type) == ARRAY_TYPE);
+  poly_uint64 array_size, vector_size;
 
   tree vectype = get_vectype_for_scalar_type (strip_array_types (type));
   if (!vectype
-      || !TYPE_SIZE (type)
-      || TREE_CODE (TYPE_SIZE (type)) != INTEGER_CST
-      || tree_int_cst_lt (TYPE_SIZE (type), TYPE_SIZE (vectype)))
+      || !poly_int_tree_p (TYPE_SIZE (type), &array_size)
+      || !poly_int_tree_p (TYPE_SIZE (vectype), &vector_size)
+      || maybe_lt (array_size, vector_size))
     return 0;
 
   return TYPE_ALIGN (vectype);