re PR tree-optimization/51581 (Integer division by constant is not vectorized)

	PR tree-optimization/51581
	* tree-vect-stmts.c (permute_vec_elements): Add forward decl.
	(vectorizable_operation): Handle vectorization of MULT_HIGHPART_EXPR
	also using VEC_WIDEN_MULT_*_EXPR or builtin_mul_widen_* plus
	VEC_PERM_EXPR if vector MULT_HIGHPART_EXPR isn't supported.
	* tree-vect-patterns.c (vect_recog_divmod_pattern): Use
	MULT_HIGHPART_EXPR instead of VEC_WIDEN_MULT_*_EXPR and shifts.

	* gcc.dg/vect/pr51581-4.c: New test.

From-SVN: r189053