Ignore results from ops on ref benchmarks

This prevents the `get` op from being optimized away and makes some other
operations also more realistic.

bench.Dockerfile

@@ -1,6 +1,6 @@
 FROM ocaml/opam:debian-ocaml-5.3
+WORKDIR /bench-dir
 RUN sudo ln -sf /usr/bin/opam-2.1 /usr/bin/opam
-WORKDIR bench-dir
 RUN sudo chown opam .
 COPY *.opam ./
 RUN opam remote add origin https://github.com/ocaml/opam-repository.git && \

bench/bench_atomic.ml

@@ -10,8 +10,7 @@ module Atomic = struct
       modify ~backoff:(Backoff.once backoff) x f
 end
 
-type t =
-  | Op : string * int * 'a * ('a Atomic.t -> unit) * ('a Atomic.t -> unit) -> t
+type t = Op : string * int * 'a * ('a Atomic.t -> _) * ('a Atomic.t -> _) -> t
 
 let run_one ~budgetf ?(n_iter = 500 * Util.iter_factor)
     (Op (name, extra, value, op1, op2)) =
@@ -23,8 +22,8 @@ let run_one ~budgetf ?(n_iter = 500 * Util.iter_factor)
   let work _ () =
     let rec loop i =
       if i > 0 then begin
-        op1 loc;
-        op2 loc;
+        op1 loc |> ignore;
+        op2 loc |> ignore;
         loop (i - 2)
       end
     in
@@ -36,18 +35,17 @@ let run_one ~budgetf ?(n_iter = 500 * Util.iter_factor)
 
 let run_suite ~budgetf =
   [
-    (let get x = Atomic.get x |> ignore in
+    (let get x = Atomic.get x in
      Op ("get", 10, 42, get, get));
     (let incr x = Atomic.incr x in
      Op ("incr", 1, 0, incr, incr));
     (let push x = Atomic.modify x (fun xs -> 101 :: xs)
      and pop x = Atomic.modify x (function [] -> [] | _ :: xs -> xs) in
      Op ("push & pop", 2, [], push, pop));
-    (let cas01 x = Atomic.compare_and_set x 0 1 |> ignore
-     and cas10 x = Atomic.compare_and_set x 1 0 |> ignore in
+    (let cas01 x = Atomic.compare_and_set x 0 1
+     and cas10 x = Atomic.compare_and_set x 1 0 in
      Op ("cas int", 1, 0, cas01, cas10));
-    (let xchg1 x = Atomic.exchange x 1 |> ignore
-     and xchg0 x = Atomic.exchange x 0 |> ignore in
+    (let xchg1 x = Atomic.exchange x 1 and xchg0 x = Atomic.exchange x 0 in
      Op ("xchg int", 1, 0, xchg1, xchg0));
     (let swap x = Atomic.modify x (fun (x, y) -> (y, x)) in
      Op ("swap", 2, (4, 2), swap, swap));

bench/bench_ref.ml

@@ -26,7 +26,7 @@ module Ref = struct
       modify ~backoff:(Backoff.once backoff) x f
 end
 
-type t = Op : string * int * 'a * ('a Ref.t -> unit) * ('a Ref.t -> unit) -> t
+type t = Op : string * int * 'a * ('a Ref.t -> _) * ('a Ref.t -> _) -> t
 
 let run_one ~budgetf ?(n_iter = 500 * Util.iter_factor)
     (Op (name, extra, value, op1, op2)) =
@@ -38,8 +38,8 @@ let run_one ~budgetf ?(n_iter = 500 * Util.iter_factor)
   let work _ () =
     let rec loop i =
       if i > 0 then begin
-        op1 loc;
-        op2 loc;
+        op1 loc |> ignore;
+        op2 loc |> ignore;
         loop (i - 2)
       end
     in
@@ -51,18 +51,17 @@ let run_one ~budgetf ?(n_iter = 500 * Util.iter_factor)
 
 let run_suite ~budgetf =
   [
-    (let get x = Ref.get x |> ignore in
+    (let get x = Ref.get x in
      Op ("get", 10, 42, get, get));
     (let incr x = Ref.incr x in
      Op ("incr", 1, 0, incr, incr));
     (let push x = Ref.modify x (fun xs -> 101 :: xs)
      and pop x = Ref.modify x (function [] -> [] | _ :: xs -> xs) in
      Op ("push & pop", 2, [], push, pop));
-    (let cas01 x = Ref.compare_and_set x 0 1 |> ignore
-     and cas10 x = Ref.compare_and_set x 1 0 |> ignore in
+    (let cas01 x = Ref.compare_and_set x 0 1
+     and cas10 x = Ref.compare_and_set x 1 0 in
      Op ("cas int", 1, 0, cas01, cas10));
-    (let xchg1 x = Ref.exchange x 1 |> ignore
-     and xchg0 x = Ref.exchange x 0 |> ignore in
+    (let xchg1 x = Ref.exchange x 1 and xchg0 x = Ref.exchange x 0 in
      Op ("xchg int", 1, 0, xchg1, xchg0));
     (let swap x = Ref.modify x (fun (x, y) -> (y, x)) in
      Op ("swap", 2, (4, 2), swap, swap));

bench/bench_ref_mutex.ml

@@ -18,7 +18,7 @@ module Ref = struct
     before
 end
 
-type t = Op : string * 'a * ('a Ref.t -> unit) * ('a Ref.t -> unit) -> t
+type t = Op : string * 'a * ('a Ref.t -> _) * ('a Ref.t -> _) -> t
 
 (** For some reason allocating the mutex inside [run_one] tends to cause
     performance hiccups, i.e. some operations appear to be 10x slower than
@@ -34,10 +34,10 @@ let run_one ~budgetf ?(n_iter = 250 * Util.iter_factor)
     let rec loop i =
       if i > 0 then begin
         Mutex.lock mutex;
-        op1 loc;
+        op1 loc |> ignore;
         Mutex.unlock mutex;
         Mutex.lock mutex;
-        op2 loc;
+        op2 loc |> ignore;
         Mutex.unlock mutex;
         loop (i - 2)
       end
@@ -50,18 +50,17 @@ let run_one ~budgetf ?(n_iter = 250 * Util.iter_factor)
 
 let run_suite ~budgetf =
   [
-    (let get x = !x |> ignore in
+    (let get x = !x in
      Op ("get", 42, get, get));
     (let incr x = x := !x + 1 in
      Op ("incr", 0, incr, incr));
     (let push x = x := 101 :: !x
      and pop x = match !x with [] -> () | _ :: xs -> x := xs in
      Op ("push & pop", [], push, pop));
-    (let cas01 x = Ref.compare_and_set x 0 1 |> ignore
-     and cas10 x = Ref.compare_and_set x 1 0 |> ignore in
+    (let cas01 x = Ref.compare_and_set x 0 1
+     and cas10 x = Ref.compare_and_set x 1 0 in
      Op ("cas int", 0, cas01, cas10));
-    (let xchg1 x = Ref.exchange x 1 |> ignore
-     and xchg0 x = Ref.exchange x 0 |> ignore in
+    (let xchg1 x = Ref.exchange x 1 and xchg0 x = Ref.exchange x 0 in
      Op ("xchg int", 0, xchg1, xchg0));
     (let swap x =
        let l, r = !x in