vect: Teach vectorizer how to handle bitfield accesses

vect: Teach vectorizer how to handle bitfield accesses

gcc/ChangeLog:

	* tree-if-conv.cc (if_convertible_loop_p_1): Move ordering of loop bb's from
	here...
	(tree_if_conversion): ... to here.  Also call bitfield lowering when
	appropriate.
	(version_loop_for_if_conversion): Adapt to enable loop versioning when we only
	need to lower bitfields.
	(ifcvt_split_critical_edges): Relax condition of expected loop form as this is
	checked earlier.
	(get_bitfield_rep): New function.
	(lower_bitfield): Likewise.
	(bitfields_to_lower_p): Likewise.
	(need_to_lower_bitfields): New global boolean.
	(need_to_ifcvt): Likewise.
	* tree-vect-data-refs.cc (vect_find_stmt_data_reference): Improve diagnostic
	message.
	* tree-vect-patterns.cc (vect_recog_temp_ssa_var): Add default value for last
	parameter.
	(vect_recog_bitfield_ref_pattern): New.
	(vect_recog_bit_insert_pattern): New.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/vect-bitfield-read-1.c: New test.
	* gcc.dg/vect/vect-bitfield-read-2.c: New test.
	* gcc.dg/vect/vect-bitfield-read-3.c: New test.
	* gcc.dg/vect/vect-bitfield-read-4.c: New test.
	* gcc.dg/vect/vect-bitfield-read-5.c: New test.
	* gcc.dg/vect/vect-bitfield-read-6.c: New test.
	* gcc.dg/vect/vect-bitfield-write-1.c: New test.
	* gcc.dg/vect/vect-bitfield-write-2.c: New test.
	* gcc.dg/vect/vect-bitfield-write-3.c: New test.
	* gcc.dg/vect/vect-bitfield-write-4.c: New test.
	* gcc.dg/vect/vect-bitfield-write-5.c: New test.