Nullable globals + more precise constant globals

Author: vouillon

compiler/lib-wasm/code_generation.ml

@@ -537,7 +537,13 @@ and expression_type (e : W.expression) st =
   | GlobalGet x ->
       ( (try
            let typ = (Var.Map.find x st.context.constant_globals).typ in
-           if Poly.equal typ st.context.value_type then None else Some typ
+           if Poly.equal typ st.context.value_type
+           then None
+           else
+             Some
+               (match typ with
+               | Ref { typ; nullable = true } -> Ref { typ; nullable = false }
+               | _ -> typ)
          with Not_found -> None)
       , st )
   | Seq (_, e') -> expression_type e' st
@@ -638,10 +644,13 @@ let rec store ?(always = false) ?typ x e =
                 match typ with
                 | Some typ -> return typ
                 | None -> (
-                    let* typ = expression_type e in
-                    match typ with
-                    | None -> value_type
-                    | Some typ -> return typ)
+                    if always
+                    then value_type
+                    else
+                      let* typ = expression_type e in
+                      match typ with
+                      | None -> value_type
+                      | Some typ -> return typ)
               in
               let* default, typ', cast = default_value typ in
               let* () =
@@ -653,7 +662,6 @@ let rec store ?(always = false) ?typ x e =
               in
               register_global ~constant:true x { mut = true; typ = typ' } default
           in
-          let* () = register_constant x (W.GlobalGet x) in
           instr (GlobalSet (x, e))
         else
           let* typ =

compiler/lib-wasm/code_generation.mli

@@ -207,6 +207,8 @@ val function_body :
 
 val variable_type : Code.Var.t -> Wasm_ast.value_type option t
 
+val expression_type : Wasm_ast.expression -> Wasm_ast.value_type option t
+
 val array_placeholder : Code.Var.t -> expression
 
 val default_value :

compiler/lib-wasm/gc_target.ml

@@ -606,6 +606,14 @@ module Value = struct
   let int_asr = binop Arith.( asr )
 end
 
+let store_in_global ?(name = "const") c =
+  let name = Code.Var.fresh_n name in
+  let* typ = expression_type c in
+  let* () =
+    register_global name { mut = false; typ = Option.value ~default:Type.value typ } c
+  in
+  return (W.GlobalGet name)
+
 module Memory = struct
   let wasm_cast ty e =
     let* e = e in
@@ -865,7 +873,9 @@ module Memory = struct
     in
     let* ty = Type.int32_type in
     let* e = e in
-    return (W.StructNew (ty, [ GlobalGet int32_ops; e ]))
+    let e' = W.StructNew (ty, [ GlobalGet int32_ops; e ]) in
+    let* b = is_small_constant e in
+    if b then store_in_global e' else return e'
 
   let box_int32 e = make_int32 ~kind:`Int32 e
 
@@ -883,7 +893,9 @@ module Memory = struct
     in
     let* ty = Type.int64_type in
     let* e = e in
-    return (W.StructNew (ty, [ GlobalGet int64_ops; e ]))
+    let e' = W.StructNew (ty, [ GlobalGet int64_ops; e ]) in
+    let* b = is_small_constant e in
+    if b then store_in_global e' else return e'
 
   let box_int64 e = make_int64 e
 
@@ -903,11 +915,6 @@ module Constant = struct
      strings are encoded as a sequence of bytes in the wasm module. *)
   let string_length_threshold = 64
 
-  let store_in_global ?(name = "const") c =
-    let name = Code.Var.fresh_n name in
-    let* () = register_global name { mut = false; typ = Type.value } c in
-    return (W.GlobalGet name)
-
   let str_js_utf8 s =
     let b = Buffer.create (String.length s) in
     String.iter s ~f:(function