PR debug/46171
	* df-problems.c (struct dead_debug_use, struct dead_debug): Move
	earlier.
	(df_set_unused_notes_for_mw, df_create_unused_note): Add DEBUG
	argument, call dead_debug_reset when adding REG_UNUSED note.
	(dead_debug_reset): New function.
	(df_note_bb_compute): Adjust df_set_unused_notes_for_mw and
	df_create_unused_note callers.

	* gcc.dg/pr46171.c: New test.

From-SVN: r166504