* combine.c (try_combine): Use NULL_RTX instead of '0' where
        appropriate in calls to gen_rtx().
        * cse.c (cse_main): Likewise.
        * emit-rtl.c (gen_label_rtx): Likewise.
        * expr.c (init_expr_once): Likewise.
        * haifa-sched.c (flush_pending_lists, sched_analyze_insn,
        sched_analyze, init_rgn_data_dependences,
        compute_block_backward_dependences): Likewise.
        * sched.c (schedule_insns): Likewise.
        * varasm.c (immed_double_const): Likewise.

From-SVN: r15630