Deadcode elimination of cyclic values

CHANGES.md

@@ -32,6 +32,7 @@
 * Compiler: more efficient code generation from bytecode (#1972)
 * Runtime: use Dataview to convert between floats and bit representation
 * Compiler: speed-up compilation by improving the scheduling of optimization passes (#1962)
+* Compiler: deadcode elimination of cyclic values (#1978)
 
 ## Bug fixes
 * Compiler: fix stack overflow issues with double translation (#1869)

compiler/lib/deadcode.ml

@@ -97,6 +97,14 @@ and mark_reachable st pc =
     let block = Addr.Map.find pc st.blocks in
     List.iter block.body ~f:(fun i ->
         match i with
+        | Let (_, Prim (Extern "caml_update_dummy", [ Pv x; Pv y ])) ->
+            if st.live.(Var.idx x) = 0
+            then
+              (* We will keep this instruction only if x is live *)
+              add_def st.defs x (Field_update y)
+            else (
+              mark_var st x;
+              mark_var st y)
         | Let (_, e) -> if not (pure_expr st.pure_funs e) then mark_expr st e
         | Event _ | Assign _ -> ()
         | Set_field (x, _, _, y) -> (
@@ -131,6 +139,7 @@ and mark_reachable st pc =
 
 let live_instr st i =
   match i with
+  | Let (_, Prim (Extern "caml_update_dummy", [ Pv x; Pv _ ])) -> st.live.(Var.idx x) > 0
   | Let (x, e) -> st.live.(Var.idx x) > 0 || not (pure_expr st.pure_funs e)
   | Assign (x, _) | Set_field (x, _, _, _) -> st.live.(Var.idx x) > 0
   | Event _ | Offset_ref _ | Array_set _ -> true

compiler/tests-compiler/dune.inc

@@ -869,6 +869,21 @@
  (preprocess
   (pps ppx_expect)))
 
+(library
+ ;; compiler/tests-compiler/update_dummy.ml
+ (name update_dummy_15)
+ (enabled_if true)
+ (modules update_dummy)
+ (libraries js_of_ocaml_compiler unix str jsoo_compiler_expect_tests_helper)
+ (inline_tests
+  (enabled_if true)
+  (deps
+   (file %{project_root}/compiler/bin-js_of_ocaml/js_of_ocaml.exe)
+   (file %{project_root}/compiler/bin-jsoo_minify/jsoo_minify.exe)))
+ (flags (:standard -open Jsoo_compiler_expect_tests_helper))
+ (preprocess
+  (pps ppx_expect)))
+
 (library
  ;; compiler/tests-compiler/variable_declaration_output.ml
  (name variable_declaration_output_15)

compiler/tests-compiler/update_dummy.ml

@@ -0,0 +1,21 @@
+open Util
+
+let%expect_test "deadcode elimination of cyclic values" =
+  let program =
+    compile_and_parse
+      {|
+      let f () =
+        let rec x = 1 :: x in
+        let rec y = 1 :: y in
+        snd (x, y)
+  |}
+  in
+  print_fun_decl program (Some "f");
+  [%expect
+    {|
+    function f(param){
+     var y = [];
+     runtime.caml_update_dummy(y, [0, 1, y]);
+     return y;
+    }
+    //end |}]