Array placeholder

Author: vouillon

compiler/lib-wasm/code_generation.ml

@@ -565,6 +565,26 @@ let should_make_global x st = Var.Set.mem x st.context.globalized_variables, st
 
 let value_type st = st.context.value_type, st
 
+let get_constant x st = Var.Hashtbl.find_opt st.context.constants x, st
+
+let placeholder_value typ f =
+  let* c = get_constant typ in
+  match c with
+  | None ->
+      let x = Var.fresh () in
+      let* () = register_constant typ (W.GlobalGet x) in
+      let* () =
+        register_global
+          ~constant:true
+          x
+          { mut = false; typ = Ref { nullable = false; typ = Type typ } }
+          (f typ)
+      in
+      return (W.GlobalGet x)
+  | Some c -> return c
+
+let array_placeholder typ = placeholder_value typ (fun typ -> ArrayNewFixed (typ, []))
+
 let rec store ?(always = false) ?typ x e =
   let* e = e in
   match e with

compiler/lib-wasm/code_generation.mli

@@ -201,3 +201,9 @@ val function_body :
   -> (Wasm_ast.var * Wasm_ast.value_type) list * Wasm_ast.instruction list
 
 val variable_type : Code.Var.t -> Wasm_ast.value_type option t
+
+val array_placeholder : Code.Var.t -> expression
+
+val default_value :
+     Wasm_ast.value_type
+  -> (Wasm_ast.expression * Wasm_ast.value_type * Wasm_ast.ref_type option) t

compiler/lib-wasm/gc_target.ml

@@ -428,7 +428,7 @@ module Value = struct
 
   let dummy_block =
     let* t = Type.block_type in
-    return (W.ArrayNewFixed (t, []))
+    array_placeholder t
 
   let as_block e =
     let* t = Type.block_type in