tree-ssa-pre.c (NECESSARY): Remove.

tree-ssa-pre.c (NECESSARY): Remove.

2017-09-06  Richard Biener  <rguenther@suse.de>

	* tree-ssa-pre.c (NECESSARY): Remove.
	(create_expression_by_pieces): Do not touch pass-local flags.
	(insert_into_preds_of_block): Likewise.
	(do_pre_regular_insertion): Likewise.
	(eliminate_insert): Likewise.
	(eliminate_dom_walker::before_dom_children): Likewise.
	(fini_eliminate): Do not look at inserted_exprs.
	(mark_operand_necessary): Remove.
	(remove_dead_inserted_code): Replace with simple work-list
	algorithm based on inserted_exprs and SSA uses.
	(pass_pre::execute): Re-order fini_eliminate and
	remove_dead_inserted_code.

From-SVN: r251798