postreload-gcse.c: Use rtx_insn in various places

postreload-gcse.c: Use rtx_insn in various places

gcc/
	* postreload-gcse.c (struct occr): Strengthen field "insn" from
	rtx to rtx_insn *.
	(struct unoccr): Likewise.
	(struct modifies_mem): Likewise.
	(alloc_mem): Likewise for local "insn".
	(insert_expr_in_table): Likewise for param "insn".
	(dump_expr_hash_table_entry): Likewise for local "insn".
	(oprs_unchanged_p): Likewise for param "insn".
	(load_killed_in_block_p): Likewise for local "setter".
	(record_last_reg_set_info): Likewise for param "insn".
	(record_last_reg_set_info_regno): Likewise.
	(record_last_mem_set_info): Likewise.
	(record_last_set_info): Likewise for local "last_set_insn".
	(record_opr_changes): Likewise for param "insn".
	(hash_scan_set): Likewise.
	(compute_hash_table): Likewise for local "insn".
	(get_avail_load_store_reg): Likewise for param "insn".
	(eliminate_partially_redundant_load): Likewise, also for locals
	"avail_insn", "next_pred_bb_end".  Replace use of NULL_RTX with
	RTX for insns.
	(eliminate_partially_redundant_loads): Likewise for local "insn".

From-SVN: r214356