Expand: Enable vector mode for by pieces compares

Expand: Enable vector mode for by pieces compares

Vector mode compare instructions are efficient for equality compare on
rs6000. This patch refactors the codes of by pieces operation to enable
vector mode for compare.

gcc/
	PR target/111449
	* expr.cc (can_use_qi_vectors): New function to return true if
	we know how to implement OP using vectors of bytes.
	(qi_vector_mode_supported_p): New function to check if optabs
	exists for the mode and certain by pieces operations.
	(widest_fixed_size_mode_for_size): Replace the second argument
	with the type of by pieces operations.  Call can_use_qi_vectors
	and qi_vector_mode_supported_p to do the check.  Call
	scalar_mode_supported_p to check if the scalar mode is supported.
	(by_pieces_ninsns): Pass the type of by pieces operation to
	widest_fixed_size_mode_for_size.
	(class op_by_pieces_d): Remove m_qi_vector_mode.  Add m_op to
	record the type of by pieces operations.
	(op_by_pieces_d::op_by_pieces_d): Change last argument to the
	type of by pieces operations, initialize m_op with it.  Pass
	m_op to function widest_fixed_size_mode_for_size.
	(op_by_pieces_d::get_usable_mode): Pass m_op to function
	widest_fixed_size_mode_for_size.
	(op_by_pieces_d::smallest_fixed_size_mode_for_size): Call
	can_use_qi_vectors and qi_vector_mode_supported_p to do the
	check.
	(op_by_pieces_d::run): Pass m_op to function
	widest_fixed_size_mode_for_size.
	(move_by_pieces_d::move_by_pieces_d): Set m_op to MOVE_BY_PIECES.
	(store_by_pieces_d::store_by_pieces_d): Set m_op with the op.
	(can_store_by_pieces): Pass the type of by pieces operations to
	widest_fixed_size_mode_for_size.
	(clear_by_pieces): Initialize class store_by_pieces_d with
	CLEAR_BY_PIECES.
	(compare_by_pieces_d::compare_by_pieces_d): Set m_op to
	COMPARE_BY_PIECES.