Refactor tree-vrp.c

Refactor tree-vrp.c

Refactor tree-vrp.c to eliminate all global variables except
'x_vrp_values', which will require that 'thread_outgoing_edges'
to accept an extra argument and pass it to the 'simplify' callback.

It also removes every access to 'cfun', retrieving the function being
compiled from the pass engine.

gcc/ChangeLog
2020-05-12  Giuliano Belinassi  <giuliano.belinassi@usp.br>

	* tree-vrp.c (class vrp_insert): New.
	(insert_range_assertions): Move to class vrp_insert.
	(dump_all_asserts): Same as above.
	(dump_asserts_for): Same as above.
	(live): Same as above.
	(need_assert_for): Same as above.
	(live_on_edge): Same as above.
	(finish_register_edge_assert_for): Same as above.
	(find_switch_asserts): Same as above.
	(find_assert_locations): Same as above.
	(find_assert_locations_1): Same as above.
	(find_conditional_asserts): Same as above.
	(process_assert_insertions): Same as above.
	(register_new_assert_for): Same as above.
	(vrp_prop): New variable fun.
	(vrp_initialize): New parameter.
	(identify_jump_threads): Same as above.
	(execute_vrp): Same as above.