[sledge] Dump program to file between frontend and backend

Summary:
`sledge -c foo.bc` generates a binary file `foo.bc.llair` which can be
analyzed with `sledge foo.bc.llair`, and converted to textual form
with `sledge -c foo.bc.llair -o foo.llair`. Binary files are not
compatible between debug and release builds.

Reviewed By: mbouaziz

Differential Revision: D10389473

fbshipit-source-id: dfcabf33b

sledge/src/import/import.ml

@@ -22,6 +22,7 @@ include (
         (* prematurely deprecated, remove and use Stdlib instead *)
          and module Filename := Base.Filename
          and module Format := Base.Format
+         and module Marshal := Base.Marshal
          and module Scanf := Base.Scanf
          and type ('ok, 'err) result := ('ok, 'err) Base.result)
       [@warning "-3"]

sledge/src/import/import.mli

@@ -22,6 +22,7 @@ include module type of (
         (* prematurely deprecated, remove and use Stdlib instead *)
          and module Filename := Base.Filename
          and module Format := Base.Format
+         and module Marshal := Base.Marshal
          and module Scanf := Base.Scanf
          and type ('ok, 'err) result := ('ok, 'err) Base.result)
       [@warning "-3"]

sledge/src/sledge.ml

@@ -9,8 +9,17 @@
 
 let main ~input ~output ~compile_only =
   try
+    let program =
+      if String.is_suffix input ~suffix:".llair" then
+        In_channel.with_file input ~f:(fun ic ->
+            (Marshal.from_channel ic : Llair.t) )
+      else
         let program = Frontend.translate input in
         Trace.flush () ;
+        Out_channel.with_file (input ^ ".llair") ~f:(fun oc ->
+            Marshal.to_channel oc program [Marshal.Closures] ) ;
+        program
+    in
     Option.iter output ~f:(function
       | "-" -> Format.printf "%a@." Llair.pp program
       | filename ->