Flag to generate the new exception handling instructions

Wasmtime only supports these instructions. We should eventually use
instead of the legacy instructions, but they are not allowed by default
in node.

Author: vouillon

compiler/bin-wasm_of_ocaml/compile.ml

@@ -84,6 +84,7 @@ let preprocessor_variables () =
         | `Disabled | `Jspi -> "jspi"
         | `Cps -> "cps"
         | `Double_translation -> assert false) )
+  ; "exnref", Wat_preprocess.Bool (Config.Flag.exnref ())
   ]
 
 let with_runtime_files ~runtime_wasm_files f =

compiler/bin-wasm_of_ocaml/gen/gen.ml

@@ -75,7 +75,7 @@ let check_js_file fname =
 (* Keep the two variables below in sync with function build_runtime in
    ../compile.ml *)
 
-let default_flags = []
+let default_flags = [ "exnref", `B false ]
 
 let interesting_runtimes = [ [ "effects", `S "jspi" ]; [ "effects", `S "cps" ] ]
 

compiler/lib-wasm/binaryen.ml

@@ -135,11 +135,11 @@ let optimize
     ~output_file
     () =
   command
-    ("wasm-opt"
-     :: (common_options ()
-        @ (match options with
-          | Some o -> o
-          | None -> optimization_options profile)
-        @ [ Filename.quote input_file; "-o"; Filename.quote output_file ])
+    (("wasm-opt" :: (if Config.Flag.exnref () then [ "--emit-exnref" ] else []))
+    @ common_options ()
+    @ (match options with
+      | Some o -> o
+      | None -> optimization_options profile)
+    @ [ Filename.quote input_file; "-o"; Filename.quote output_file ]
     @ opt_flag "--input-source-map" opt_input_sourcemap
     @ opt_flag "--output-source-map" opt_output_sourcemap)

compiler/lib/config.ml

@@ -106,6 +106,8 @@ module Flag = struct
   let es6 = o ~name:"es6" ~default:false
 
   let load_shapes_auto = o ~name:"load-shapes-auto" ~default:false
+
+  let exnref = o ~name:"exnref" ~default:false
 end
 
 module Param = struct

compiler/lib/config.mli

@@ -76,6 +76,8 @@ module Flag : sig
 
   val load_shapes_auto : unit -> bool
 
+  val exnref : unit -> bool
+
   val enable : string -> unit
 
   val disable : string -> unit