re PR target/62128 (Use vpalignr for AVX2 rotation)

re PR target/62128 (Use vpalignr for AVX2 rotation)

	PR target/62128
	* config/i386/i386.c (expand_vec_perm_1): Try expand_vec_perm_palignr
	if it expands to a single insn only.
	(expand_vec_perm_palignr): Add SINGLE_INSN_ONLY_P argument.  If true,
	fail unless in_order is true.  Add forward declaration.
	(expand_vec_perm_vperm2f128): Fix up comment about which permutation
	is useful for one_operand_p.
	(ix86_expand_vec_perm_const_1): Adjust expand_vec_perm_palignr caller.

From-SVN: r215796