Use "unboxable" as the name of the best-effort unboxing attribute (oc…

…aml-flambda#2319)

middle_end/flambda2/docs/unboxed_params.md

@@ -11,10 +11,14 @@ this only applies when the type/layout of the unboxed value is one of the follow
 - boxed numbers (Float, Int32, Int64, Nativeint, Vec128)
 - records/pairs[1]
 
+Unboxing of variants will follow in the near future.
+
+This unboxing is best-effort: in particular, indirect calls to functions
+using this new optimization will still cause boxing.
 
 ## How does one unbox a parameter/return value ?
 
-The `[@unboxed]` annotations are used to specify what to unbox in this context.
+The `[@unboxable]` annotations are used to specify what to unbox in this context.
 These annotations can be put either on a function parameter, or on a function declaration
 to unbox its return value.
 
@@ -25,15 +29,15 @@ Here are some examples:
 let f_boxed x y = x +. y
 
 (* The same function, but this time with the return value unboxed *)
-let[@unboxed] f_return x y = x +. y
+let[@unboxable] f_return x y = x +. y
 
 (* Again, `f`, but with only the first argument unboxed.
    Note the parentheses around `x`, so that the annotation attaches to the parameter *)
-let f_first (x[@unboxed]) y = x +. y
+let f_first (x[@unboxable]) y = x +. y
 
 (* Let's define a version of `f` with the first parameter unboxed, and the return
    value unboxed, and mark it as never inline. *)
-let[@unboxed] f (x[@unboxed]) y = x +. y [@@inline never]
+let[@unboxable] f (x[@unboxable]) y = x +. y [@@inline never]
 
 (* Using the definition of `f` just above, this `main` function does not allocate,
    even with `f` not being inlined. *)
@@ -45,7 +49,7 @@ let main t y =
 
 ## What exactly happens ? What does it mean to unbox a parameter/return ?
 
-Contrary to layouts/kinds/jkinds, the `[@unboxed]` annotation does not really change
+Contrary to layouts/kinds/jkinds, the `[@unboxable]` annotation does not really change
 the calling convention of functions. However, these annotations alter the compilation
 strategy just enough so that the annotated function actually becomes a thin wrapper
 around the unboxed version of the function. Later, that wrapper can be inlined (without
@@ -58,7 +62,7 @@ code will look like:
 (* ***** Source code ***** *)
 
 (* here are the original `f` and `main` functions *)
-let[@unboxed] f (x[@unboxed]) y = x +. y [@@inline never]
+let[@unboxable] f (x[@unboxable]) y = x +. y [@@inline never]
 
 let main t y =
   let x = t +. 1. in

ocaml/lambda/printlambda.ml

@@ -944,7 +944,7 @@ let rec lam ppf = function
                 let { unbox_param } = p.attributes in
                 fprintf ppf "@ %a%s%a%s"
                   Ident.print p.name (alloc_kind p.mode) layout p.layout
-                  (if unbox_param then "[@unboxed]" else "")
+                  (if unbox_param then "[@unboxable]" else "")
               ) params
         | Tupled ->
             fprintf ppf " (";
@@ -956,7 +956,7 @@ let rec lam ppf = function
                  Ident.print ppf p.name;
                  Format.fprintf ppf "%s" (alloc_kind p.mode);
                  layout ppf p.layout;
-                 if unbox_param then Format.fprintf ppf "[@unboxed]"
+                 if unbox_param then Format.fprintf ppf "[@unboxable]"
               )
               params;
             fprintf ppf ")" in

ocaml/lambda/translattribute.ml

@@ -53,8 +53,8 @@ let is_loop_attribute =
 let is_opaque_attribute =
   [ ["opaque"; "ocaml.opaque"], true ]
 
-let is_unboxed_attribute =
-  [ ["unboxed"; "ocaml.unboxed"], true ]
+let is_unboxable_attribute =
+  [ ["unboxable"; "ocaml.unboxable"], true ]
 
 let find_attribute ?mark_used p attributes =
   let inline_attribute =
@@ -591,13 +591,13 @@ let add_opaque_attribute expr loc attributes =
 let add_unbox_return_attribute expr loc attributes =
   match expr with
   | Lfunction funct ->
-      let attr = find_attribute is_unboxed_attribute attributes in
+      let attr = find_attribute is_unboxable_attribute attributes in
       begin match attr with
       | None -> expr
       | Some _ ->
           if funct.attr.unbox_return then
             Location.prerr_warning loc
-              (Warnings.Duplicated_attribute "unboxed");
+              (Warnings.Duplicated_attribute "unboxable");
           let attr = { funct.attr with unbox_return = true } in
           lfunction_with_attr ~attr funct
       end
@@ -676,8 +676,8 @@ let add_function_attributes lam loc attr =
   lam
 
 let transl_param_attributes pat =
-      let attrs = pat.pat_attributes in
-      let unbox_param =
-        Option.is_some (find_attribute is_unboxed_attribute attrs)
-      in
-      { unbox_param }
+  let attrs = pat.pat_attributes in
+  let unbox_param =
+    Option.is_some (find_attribute is_unboxable_attribute attrs)
+  in
+  { unbox_param }