flambda-backend: Make header size unconditional (Marshal) (ocaml-fl…

…ambda#2095)

* Make header size unconditional (`Marshal`).

* Bootstrap

runtime4/intern.c

@@ -922,7 +922,7 @@ CAMLprim value caml_marshal_data_size(value buff, value ofs)
   default:
     caml_failwith("Marshal.data_size: bad object");
   }
-  return Val_long((header_len - 20) + data_len);
+  return Val_long((header_len - 16) + data_len);
 }
 
 /* Resolution of code pointers */

stdlib/marshal.ml

@@ -50,10 +50,7 @@ external from_channel: in_channel -> 'a = "caml_input_value"
 external from_bytes_unsafe: bytes -> int -> 'a = "caml_input_value_from_bytes"
 external data_size_unsafe: bytes -> int -> int = "caml_marshal_data_size"
 
-external runtime5 : unit -> bool = "%runtime5"
-let runtime5 = runtime5 ()
-
-let header_size = if runtime5 then 16 else 20
+let header_size = 16
 
 let data_size buff ofs =
   if ofs < 0 || ofs > Bytes.length buff - header_size

testsuite/tests/statmemprof/callstacks.flat-float-array.reference

@@ -56,7 +56,7 @@ Called from Callstacks.test in file "callstacks.ml", line 94, characters 2-10
 Called from Stdlib__List.iter in file "list.ml", line 116, characters 12-15
 Called from Callstacks in file "callstacks.ml", line 101, characters 2-27
 -----------
-Raised by primitive operation at Stdlib__Marshal.from_bytes in file "marshal.ml", line 70, characters 9-35
+Raised by primitive operation at Stdlib__Marshal.from_bytes in file "marshal.ml", line 67, characters 9-35
 Called from Callstacks.alloc_unmarshal in file "callstacks.ml", line 64, characters 12-87
 Called from Callstacks.test in file "callstacks.ml", line 94, characters 2-10
 Called from Stdlib__List.iter in file "list.ml", line 116, characters 12-15