DF usage in loop-invariant.c (PR46590)

DF usage in loop-invariant.c (PR46590)

- df_live is already present at -O2, so we only need to add it and
  mark all blocks dirty for -O

- df_process_deferred_rescans should be enough to force a rescan of
  blocks affected by moving invariants, but calling it in find_defs
  means that we don't do any rescans for the final loop

2019-04-04  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR rtl-optimization/46590
	* loop-invariant.c (find_defs): Move df_remove_problem and
	df_process_deferred_rescans to move_invariants.
	Move df_live_add_problem and df_live_set_all_dirty calls
	to move_invariants.
	(move_invariants): Likewise.
	(move_loop_invariants): Likewise, making the df_live calls
	conditional on -O.  Remove the problem again if we added it
	locally.

From-SVN: r270142