opaque

Author: mshinwell

boot/ocamlc

@@ -597,10 +597,6 @@ let (^^) (Format (fmt1, str1)) (Format (fmt2, str2)) =
   Format (CamlinternalFormatBasics.concat_fmt fmt1 fmt2,
           str1 ^ "%," ^ str2)
 
-(* Optimisation *)
-
-external opaque : 'a -> 'a = "%opaque"
-
 (* Miscellaneous *)
 
 external sys_exit : int -> 'a = "caml_sys_exit"

boot/ocamldep

@@ -502,10 +502,6 @@ let ( ^^ ) (Format (fmt1, str1)) (Format (fmt2, str2)) =
   Format (CamlinternalFormatBasics.concat_fmt fmt1 fmt2,
           str1 ^ "%," ^ str2)
 
-(* Optimisation *)
-
-external opaque : 'a -> 'a = "%opaque"
-
 (* Miscellaneous *)
 
 external sys_exit : int -> 'a = "caml_sys_exit"

boot/ocamllex

@@ -1098,15 +1098,6 @@ val ( ^^ ) :
   [f1], then results from [f2].
 *)
 
-(** {6 Optimisation} *)
-
-external opaque : 'a -> 'a = "%opaque"
-(** Semantically, [opaque v] behaves as the identity function; but when
-    used with Flambda mode, for the purposes of optimisation passes such
-    expression is side-effecting and yields an unknown result.  This may
-    be used to prevent necessary code in applications such as benchmarks from
-    being optimised away. *)
-
 (** {6 Program termination} *)
 
 val exit : int -> 'a

otherlibs/threads/pervasives.ml

@@ -280,3 +280,20 @@ val enable_runtime_warnings: bool -> unit
 
 val runtime_warnings_enabled: unit -> bool
 (** Return whether runtime warnings are currently enabled. *)
+
+(** {6 Optimization} *)
+
+external opaque_identity : 'a -> 'a = "%opaque"
+(** For the purposes of optimization, [opaque_identity] behaves like an
+    unknown (and thus possibly side-effecting) function.
+
+    At runtime, [opaque_identity] disappears altogether.
+
+    A typical use of this function is to prevent pure computations from being
+    optimized away in benchmarking loops.  For example:
+    {[
+      for _round = 1 to 100_000 do
+        ignore (Sys.opaque_identity (my_pure_computation ()))
+      done
+    }]
+*)