flambda-backend: Add "-dcfg" flag to ocamlopt (#254)

* Use Format to print Cfg instructions

Extends the interface to use Format, but does not change the formatting,
which leaves much to be desired and will be improved later.
Add functions [dump_basic] and [dump_terminator] to implement
"-dcfg" compiler flag.
Keep the functions [print_basic] and [print_terminator] for printing
in dot format to a file.

* Add -dcfg compiler flag to ocamlopt

* Update asmgen to dump cfg

* Fix asmgen tests

* Keep preserve_orig_labels=true

* Fix formatting

Author: gretay-js

driver/main_args.ml

@@ -799,6 +799,10 @@ let mk_dcamlprimc f =
   "-dcamlprimc", Arg.Unit f, " (undocumented)"
 ;;
 
+let mk_dcfg f =
+  "-dcfg", Arg.Unit f, " (undocumented)"
+;;
+
 let mk_dcmm f =
   "-dcmm", Arg.Unit f, " (undocumented)"
 ;;
@@ -1388,6 +1392,7 @@ module type Optcommon_options = sig
   val _dflambda_verbose : unit -> unit
   val _drawclambda : unit -> unit
   val _dclambda : unit -> unit
+  val _dcfg : unit -> unit
   val _dcmm : unit -> unit
   val _dsel : unit -> unit
   val _dcombine : unit -> unit
@@ -1867,6 +1872,7 @@ struct
     mk_dfexpr F._dfexpr;
     mk_dflexpect F._dflexpect;
     mk_dclosure_offsets F._dclosure_offsets;
+    mk_dcfg F._dcfg;
     mk_dcmm F._dcmm;
     mk_dsel F._dsel;
     mk_dcombine F._dcombine;
@@ -2040,6 +2046,7 @@ module Make_opttop_options (F : Opttop_options) = struct
     mk_dclambda F._dclambda;
     mk_drawflambda F._drawflambda;
     mk_dflambda F._dflambda;
+    mk_dcfg F._dcfg;
     mk_dcmm F._dcmm;
     mk_dsel F._dsel;
     mk_dcombine F._dcombine;
@@ -2219,6 +2226,7 @@ module Default = struct
     let _dalloc = set dump_regalloc
     let _davail () = dump_avail := true
     let _dclambda = set dump_clambda
+    let _dcfg = set dump_cfg
     let _dcmm = set dump_cmm
     let _dcombine = set dump_combine
     let _dcse = set dump_cse

driver/main_args.mli

@@ -204,6 +204,7 @@ module type Optcommon_options = sig
   val _dflambda_verbose : unit -> unit
   val _drawclambda : unit -> unit
   val _dclambda : unit -> unit
+  val _dcfg : unit -> unit
   val _dcmm : unit -> unit
   val _dsel : unit -> unit
   val _dcombine : unit -> unit

utils/clflags.ml

@@ -117,6 +117,7 @@ let optimize_for_speed = ref true       (* -compact *)
 and opaque = ref false                  (* -opaque *)
 
 and dump_cmm = ref false                (* -dcmm *)
+let dump_cfg = ref false                (* -dcfg *)
 let dump_selection = ref false          (* -dsel *)
 let dump_cse = ref false                (* -dcse *)
 let dump_live = ref false               (* -dlive *)

utils/clflags.mli

@@ -116,6 +116,7 @@ val dump_instr : bool ref
 val keep_camlprimc_file : bool ref
 val keep_asm_file : bool ref
 val optimize_for_speed : bool ref
+val dump_cfg : bool ref
 val dump_cmm : bool ref
 val dump_selection : bool ref
 val dump_cse : bool ref