PR debug/43478

	PR debug/43478
	* df-problems.c (struct dead_debug_use, struct dead_debug): New.
	(dead_debug_init, dead_debug_finish): New functions.
	(dead_debug_add, dead_debug_insert_before): Likewise.
	(df_note_bb_compute): Initialize a dead_debug object, add dead
	debug uses to it, insert debug bind insns before death insns,
	reset debug insns that refer to pending uses at the end.
	* rtl.h (make_debug_expr_from_rtl): New prototype.
	* varasm.c (make_debug_expr_from_rtl): New function.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@159063 138bc75d-0d04-0410-961f-82ee72b054a4