More precise constant globals

Author: vouillon

compiler/lib-wasm/code_generation.mli

@@ -200,6 +200,8 @@ 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

@@ -600,6 +600,14 @@ module Value = struct
   let int_asr = 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
@@ -856,7 +864,9 @@ 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
 
@@ -874,7 +884,9 @@ 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
 
@@ -894,11 +906,6 @@ 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 byte_string s =
     let b = Buffer.create (String.length s) in
     String.iter s ~f:(function
@@ -1031,13 +1038,15 @@ module Constant = struct
             if b then return c else store_in_global c
         | Const_named name -> store_in_global ~name c
         | Mutated ->
+            let* typ = Type.string_type in
             let name = Code.Var.fresh_n "const" in
+            let* placeholder = array_placeholder typ in
             let* () =
               register_global
                 ~constant:true
                 name
-                { mut = true; typ = Type.value }
-                (W.RefI31 (Const (I32 0l)))
+                { mut = true; typ = Ref { nullable = false; typ = Type typ } }
+                placeholder
             in
             let* () = register_init_code (instr (W.GlobalSet (name, c))) in
             return (W.GlobalGet name))