dce.c: Use rtx subclasses

dce.c: Use rtx subclasses

gcc/
	* dce.c (worklist): Strengthen from vec<rtx> to vec<rtx_insn *>.
	(deletable_insn_p): Strengthen param "insn" from rtx to
	rtx_insn *.  Add checked cast to rtx_call_insn when invoking
	find_call_stack_args, since this is guarded by CALL_P (insn).
	(marked_insn_p): Strengthen param "insn" from rtx to
	rtx_insn *.
	(mark_insn): Likewise.  Add checked cast to rtx_call_insn when
	invoking find_call_stack_args, since this is guarded by
	CALL_P (insn).
	(mark_nonreg_stores_1): Strengthen cast of "data" from rtx to
	rtx_insn *; we know this is an insn since this was called by
	mark_nonreg_stores.
	(mark_nonreg_stores_2): Likewise.
	(mark_nonreg_stores): Strengthen param "insn" from rtx to
	rtx_insn *.
	(find_call_stack_args): Strengthen param "call_insn" from rtx to
	rtx_call_insn *; strengthen locals "insn" and "prev_insn" from rtx
	to rtx_insn *.
	(remove_reg_equal_equiv_notes_for_defs): Strengthen param "insn"
	from rtx to rtx_insn *.
	(reset_unmarked_insns_debug_uses): Likewise for locals "insn",
	"next", "ref_insn".
	(delete_unmarked_insns): Likewise for locals "insn", "next".
	(prescan_insns_for_dce): Likewise for locals "insn", "prev".
	(mark_reg_dependencies): Likewise for param "insn".
	(rest_of_handle_ud_dce): Likewise for local "insn".
	(word_dce_process_block): Likewise.
	(dce_process_block): Likewise.

From-SVN: r214316