Give caml_send* arguments the correct types (#10498)

One of the arguments is a derived pointer.  It must therefore be declared with type Addr.

The derived pointer is live throughout a loop.  If we let the Polling pass have its way, it inserts an Ipoll instruction in this loop, and the derived pointer is live across the Ipoll, which is wrong and rejected at compile-time.

We instruct the Polling pass to not add poll points to caml_send* functions, just like it does not add poll points to caml_apply* functions.  This fixes the issue and is safe, as caml_send* cannot cause an infinite loop by itself.

Co-authored-by: Vincent Laviron <vincent.laviron@gmail.com>
(cherry picked from commit e608b7c)

Changes

@@ -579,6 +579,13 @@ OCaml 4.13.0
   with -dsource
   (Matt Else, review by Florian Angeletti)
 
+- #10461, #10498: `caml_send*` helper functions take derived pointers
+  as arguments.  Those must be declared with type Addr instead of Val.
+  Moreover, poll point insertion must be disabled for `caml_send*`,
+  otherwise the derived pointer is live across a poll point.
+  (Vincent Laviron and Xavier Leroy, review by Xavier Leroy and Sadiq Jaffer)
+
+
 OCaml 4.12, maintenance version
 -------------------------------
 

asmcomp/cmm_helpers.ml

@@ -1865,7 +1865,7 @@ let send_function arity =
   let cache = cache in
   let fun_name = "caml_send" ^ Int.to_string arity in
   let fun_args =
-    [obj, typ_val; tag, typ_int; cache, typ_val]
+    [obj, typ_val; tag, typ_int; cache, typ_addr]
     @ List.map (fun id -> (id, typ_val)) (List.tl args) in
   let fun_dbg = placeholder_fun_dbg ~human_name:fun_name in
   Cfunction

asmcomp/polling.ml

@@ -24,6 +24,7 @@ module String = Misc.Stdlib.String
 
 let function_is_assumed_to_never_poll func =
   String.starts_with ~prefix:"caml_apply" func
+  || String.starts_with ~prefix:"caml_send" func
 
 (* Detection of recursive handlers that are not guaranteed to poll
    at every loop iteration. *)