loop-invariant.c: Use rtx_insn in various places

loop-invariant.c: Use rtx_insn in various places

gcc/
	* loop-invariant.c (struct use): Strengthen field "insn" from rtx
	to rtx_insn *.
	(struct invariant): Likewise.
	(hash_invariant_expr_1): Likewise for param "insn".
	(invariant_expr_equal_p): Likewise for param "insn1", "insn2".
	(find_exits): Likewise for local "insn".
	(create_new_invariant): Likewise for param "insn".
	(check_dependencies): Likewise.
	(find_invariant_insn): Likewise.
	(record_uses): Likewise.
	(find_invariants_insn): Likewise.
	(find_invariants_bb): Likewise for local "insn".
	(get_pressure_class_and_nregs): Likewise for param "insn".
	(calculate_loop_reg_pressure): Likewise for local "insn".

From-SVN: r214343