Fix Gc.minor_{words,free} by removing [@@noalloc]

Author: stedolan

Changes

@@ -511,6 +511,9 @@ Next major version (4.05.0):
 - GPR#1075: Ensure that zero-sized float arrays have zero tags.
   (Mark Shinwell, Leo White)
 
+* GPR#1088: Gc.minor_words now returns accurate numbers.
+  (Stephen Dolan)
+
 Next minor version (4.04.1):
 ----------------------------
 

stdlib/gc.ml

@@ -47,15 +47,15 @@ external stat : unit -> stat = "caml_gc_stat"
 external quick_stat : unit -> stat = "caml_gc_quick_stat"
 external counters : unit -> (float * float * float) = "caml_gc_counters"
 external minor_words : unit -> (float [@unboxed])
-  = "caml_gc_minor_words" "caml_gc_minor_words_unboxed" [@@noalloc]
+  = "caml_gc_minor_words" "caml_gc_minor_words_unboxed"
 external get : unit -> control = "caml_gc_get"
 external set : control -> unit = "caml_gc_set"
 external minor : unit -> unit = "caml_gc_minor"
 external major_slice : int -> int = "caml_gc_major_slice"
 external major : unit -> unit = "caml_gc_major"
 external full_major : unit -> unit = "caml_gc_full_major"
 external compact : unit -> unit = "caml_gc_compaction"
-external get_minor_free : unit -> int = "caml_get_minor_free" [@@noalloc]
+external get_minor_free : unit -> int = "caml_get_minor_free"
 external get_bucket : int -> int = "caml_get_major_bucket" [@@noalloc]
 external get_credit : unit -> int = "caml_get_major_credit" [@@noalloc]
 external huge_fallback_count : unit -> int = "caml_gc_huge_fallback_count"

stdlib/gc.mli

@@ -171,7 +171,7 @@ external counters : unit -> float * float * float = "caml_gc_counters"
     is as fast as [quick_stat]. *)
 
 external minor_words : unit -> (float [@unboxed])
-  = "caml_gc_minor_words" "caml_gc_minor_words_unboxed" [@@noalloc]
+  = "caml_gc_minor_words" "caml_gc_minor_words_unboxed"
 (** Number of words allocated in the minor heap since the program was
     started. This number is accurate in byte-code programs, but only an
     approximation in programs compiled to native code.
@@ -219,7 +219,7 @@ val allocated_bytes : unit -> float
    started.  It is returned as a [float] to avoid overflow problems
    with [int] on 32-bit machines. *)
 
-external get_minor_free : unit -> int = "caml_get_minor_free" [@@noalloc]
+external get_minor_free : unit -> int = "caml_get_minor_free"
 (** Return the current size of the free space inside the minor heap.
 
     @since 4.03.0 *)

testsuite/tests/misc/gcwords.ml

@@ -0,0 +1,24 @@
+type t = Leaf of int | Branch of t * t
+
+let a = [| 0.0 |]
+
+let rec allocate_lots m = function
+  | 0 -> Leaf m
+  | n -> Branch (allocate_lots m (n-1), allocate_lots (m+1) (n-1))
+
+let measure f =
+  let a = Gc.minor_words () in
+  f ();
+  let c = Gc.minor_words () in
+  c -. a
+
+let () =
+  let n = measure (fun () -> a.(0) <- Gc.minor_words ()) in
+  (* Gc.minor_words should not allocate, although bytecode
+     generally boxes the floats *)
+  assert (n < 10.);
+  if Sys.backend_type = Sys.Native then assert (n = 0.);
+  let n = measure (fun () -> Sys.opaque_identity (allocate_lots 42 10)) in
+  (* This should allocate > 3k words (varying slightly by unboxing) *)
+  assert (n > 3000.);
+  print_endline "ok"

testsuite/tests/misc/gcwords.reference

@@ -0,0 +1 @@
+ok