loop-iv.c: Use rtx_insn (also touches cfgloop.h and loop-unroll.c)

loop-iv.c: Use rtx_insn (also touches cfgloop.h and loop-unroll.c)

gcc/
	* cfgloop.h (iv_analyze): Strengthen param 1 "insn" from rtx to
	rtx_insn *.
	(iv_analyze_result): Likewise.
	(iv_analyze_expr): Likewise.
	(biv_p): Likewise.

	* loop-iv.c (iv_get_reaching_def): Strengthen param "insn" and
	local "def_insn" from rtx to rtx_insn *.
	(get_biv_step_1): Likewise for local "insn".
	(iv_analyze_expr): Likewise for param "insn".
	(iv_analyze_def): Likewise for local "insn".
	(iv_analyze_op): Likewise for param "insn".
	(iv_analyze): Likewise.
	(iv_analyze_result): Likewise.
	(biv_p): Likewise.
	(suitable_set_for_replacement): Likewise.
	(simplify_using_initial_values): Likewise for local "insn".
	(iv_number_of_iterations): Likewise for param "insn".
	(check_simple_exit): Add checked cast to rtx_insn when invoking
	iv_number_of_iterations for now (until get_condition is
	strengthened).

	* loop-unroll.c (analyze_iv_to_split_insn): Strengthen param
	"insn" from rtx to rtx_insn *.
	(analyze_insns_in_loop): Likewise for local "insn".

From-SVN: r214344