DCE cleanup by JonoPrest · Pull Request #8 · JonoPrest/rescript-compiler

JonoPrest · 2026-06-15T11:10:45Z

No description provided.

Adds scripts/dce/run-dce.sh + README to run reanalyze DCE over the compiler's own OCaml source. The vendored rescript-tools reanalyze can't do this: the compiler's OCaml is built by host OCaml 5.3 (cmt magic Caml1999I035), while the vendored ml library only reads the 4.06-era ReScript cmt format, so it dies with Cmi_format.Error. Instead we build the standalone reanalyze against host compiler-libs, using the OCaml-5.3 support from rescript-lang/reanalyze#203 (pinned, not yet merged). It works end-to-end and produces a full report. Raw output is currently dominated by entry-point false positives (dune emits only .cmti for the bsc main, and jsoo isn't built in the default profile), so making it actionable needs root/entry-point fixes — documented in the README along with the lowest-noise starting categories (redundant/unused optional args) and the CI-gating proposal.

…ability blocker Two findings from triaging the DCE output: 1. Roots: a plain `dune build` emits only .cmti for modules with an .mli (incl the bsc main), so reanalyze missed the entry-point bodies and over-reported. Switch the runner to `dune build @check`, which emits impl .cmt for every module. Fixes the Bs_version-class false positives (Dead Value ~2740->2130, Dead Module ~203->146). 2. Blocker: even with roots fixed, reanalyze#203 flags obviously-live core modules as dead (Ast_helper has 510 in-tree refs; Lam_compile, Js_dump, Lam_convert likewise). Per the PR, its 5.3 value-dependency tracking is derived 'just based on the type' in cmt_infos and is incomplete (rescript-lang/reanalyze#202). So cross-reference-based categories aren't trustworthy yet. Documented in the README.

Investigated why obviously-live modules (Ast_helper, Lam_compile, Js_dump) are flagged dead. reanalyze's DCE is location-keyed, and OCaml 5.3 broke that on two fronts: cmt_declaration_dependencies is uid-based and carries few edges, and the dominant typedtree-walk reference source relies on Texp_ident val_loc that no longer matches declaration registration cross-module. Confirmed by experiment (local reanalyze branch): a global uid->decl pre-pass is a necessary foundation but insufficient; resolving references via val_uid alone regresses (2129->2526 dead values) because declarations are still keyed by the old location. The real fix keys both declarations and references by uid - a core refactor, not a patch.

JonoPrest

DCE notes.

JonoPrest · 2026-06-15T11:13:15Z

  | Batch of ('k * 'v option) list

 let set k v = (k, Some v)
-let remove k = (k, None)


DCE-confirmed cleanup: removed unused reactive exports. Covers reactive.mli too.

JonoPrest

DCE notes 1.

JonoPrest · 2026-06-15T11:14:05Z

 (** Emit a delta *)
 let emit t delta = t.emit delta

-(** Process a file if changed. Emits delta to subscribers. *)


DCE: trimmed dead APIs; trimmed reactive interfaces. Covers reactive_file_collection.mli too.

JonoPrest · 2026-06-15T11:14:05Z


 let empty = {issues = []}

-let add_issue result issue = {issues = issue :: result.issues}


DCE: removed unused result helpers. Covers analysis_result.mli too.

JonoPrest · 2026-06-15T11:14:05Z

             ({cd_attributes; cd_loc; cd_args} :
               Typedtree.constructor_declaration)
           ->
-             let _process_inline_records =


DCE: dropped inline record bindings.

JonoPrest · 2026-06-15T11:14:05Z

 val of_reactive : (string, Cross_file_items.t) Reactive.t -> t
 (** Wrap reactive collection directly (no intermediate collection) *)

-val iter_optional_arg_calls :


DCE: hid item store iterators.

JonoPrest · 2026-06-15T11:14:05Z

@@ -1,4 +0,0 @@
-(** Dead code analysis - cmt file processing.


DCE: removed dead code alias.

JonoPrest · 2026-06-15T11:14:07Z


 type mutable_flag = Js_op.mutable_flag
 type binop = Js_op.binop
-type int_op = Js_op.int_op


DCE: trimmed js op types.

JonoPrest · 2026-06-15T11:14:07Z


 val eq_expression : J.expression -> J.expression -> bool

-val eq_statement : J.statement -> J.statement -> bool


DCE: trimmed js debug exports.

JonoPrest · 2026-06-15T11:14:07Z

  close_in ic;
  v

-let from_file_with_digest name : t * Digest.t =


DCE: trimmed cmj readers. Covers js_cmj_format.mli too.

JonoPrest · 2026-06-15T11:14:07Z

    (fun cxt f s -> statement top cxt f s)
    (if top then P.at_least_two_lines else P.newline)

-let string_of_block (block : J.block) =


DCE: trimmed js debug exports; trimmed js dump literals. Covers js_dump.mli too.

JonoPrest · 2026-06-15T11:14:07Z


 let new_ = "new"

-let array = "Array"


DCE: trimmed js dump literals.

JonoPrest

DCE notes.

JonoPrest · 2026-06-15T11:15:46Z

 (* let mk ?comment exp : t =
   {expression_desc = exp ; comment  } *)

-let var ?comment id : t = {expression_desc = Var (Id id); comment}


DCE: trimmed JS expression helpers and optional comment args. Covers js_exp_make.mli too.

JonoPrest

DCE notes 1.

JonoPrest · 2026-06-15T11:20:36Z

 val set : 'k -> 'v -> 'k * 'v option
 (** Create a batch entry that sets a key *)

-val remove : 'k -> 'k * 'v option


DCE: trimmed dead APIs; trimmed reactive interfaces; removed unused reactive exports.

JonoPrest · 2026-06-15T11:20:36Z


 (** {1 Processing} *)

-val process_files : ('raw, 'v) t -> string list -> unit


DCE: trimmed dead APIs; trimmed reactive interfaces.

JonoPrest · 2026-06-15T11:20:36Z

 val empty : t
 (** Empty result with no issues *)

-val add_issue : t -> Issue.t -> t


DCE: removed unused result helpers.

JonoPrest · 2026-06-15T11:20:36Z

 val builder_to_list : builder -> (Lexing.position * Decl.t) list
 (** Extract all declarations as a list for reactive merge *)

-val create_from_hashtbl : Decl.t Pos_hash.t -> t


DCE: trimmed reactive exports; removed stale declaration helpers.

JonoPrest · 2026-06-15T11:20:36Z

 val assert_failure : t
 val decode_error : t
 val division_by_zero : t
-val end_of_file : t


DCE: removed unused exception names.

JonoPrest · 2026-06-15T11:20:38Z

    x.times <- x0 + y0;
    if captured then x.captured <- true

-let pp_info fmt (x : used_info) =


DCE: trimmed lambda helpers. Covers lam_pass_count.mli too.

JonoPrest · 2026-06-15T11:20:38Z


 let simplify_lets (lam : Lam.t) : Lam.t =
  let occ = Lam_pass_count.collect_occurs lam in
-  (* Ext_log.dwarn ~__POS__ "@[%a@]@." Lam_pass_count.pp_occ_tbl occ ; *)


DCE: trimmed lambda helpers.

JonoPrest · 2026-06-15T11:20:38Z

  | Some (Constant (Const_js_false | Const_js_null | Const_js_undefined _)) ->
    Eval_false
  | Some
-      ( Normal_optional _ | ImmutableBlock _ | MutableBlock _ | Constant _


DCE: trimmed dead APIs.

JonoPrest · 2026-06-15T11:20:38Z


 type ident = Ident.t

-type record_representation =


DCE: trimmed lambda debug API; removed runtime apply primitive; removed undefined primitive. Covers lam_primitive.mli too.

JonoPrest · 2026-06-15T11:20:38Z

  | Pinit_mod -> fprintf ppf "init_mod!"
  | Pupdate_mod -> fprintf ppf "update_mod!"
  | Pjs_apply -> fprintf ppf "#apply"
-  | Pjs_runtime_apply -> fprintf ppf "#runtime_apply"


DCE: trimmed lambda debug API; removed runtime apply primitive; removed undefined primitive. More of the same in this file. Covers lam_print.mli too.

JonoPrest

DCE notes 2.

JonoPrest · 2026-06-15T11:21:50Z




-let is_function (lam : Lam.t) = 


DCE: removed lam function helper. Covers lam_util.mli too.

JonoPrest · 2026-06-15T11:21:50Z


 val read_ast_exn : fname:string -> 'a kind -> 'a

-val magic_sep_char : char


DCE: trimmed lambda helpers.

JonoPrest · 2026-06-15T11:21:50Z

 type error =
  | Cmj_not_found of string
  | Js_not_found of string
-  | Bs_cyclic_depends of string list


DCE: trimmed bs exception. Covers bs_exception.mli too.

JonoPrest · 2026-06-15T11:21:50Z


 type string_action =
  | String_call of (string -> unit)
-  | String_set of string ref


DCE: trimmed arg spec variants; removed unused args finish. Covers bsc_args.mli too.

JonoPrest · 2026-06-15T11:21:50Z

      a.!(i + len - 1 - k) <- t
    done

-let reverse_in_place a = reverse_range a 0 (Array.length a)


DCE: trimmed array helpers. Covers ext_array.mli too.

JonoPrest · 2026-06-15T11:21:51Z


 type t = Parsetree.pattern

-let is_unit_cont ~yes ~no (p : t) =


DCE: trimmed frontend helpers. Covers ast_pat.mli too.

JonoPrest · 2026-06-15T11:21:51Z

  in
  List.rev acc

-(** Note this is okay with enums, for variants,


DCE: trimmed frontend helpers. Covers ast_polyvar.mli too.

JonoPrest · 2026-06-15T11:21:51Z

  Str.include_ ~loc
    (Incl.mk ~loc
       (Mod.constraint_ ~loc (Mod.structure ~loc stru) (Mty.signature ~loc sign)))
-


DCE: trimmed frontend helpers. Covers ast_structure.mli too.

JonoPrest · 2026-06-15T11:21:51Z


 type exn += Error of int (* offset *) * error

-val pp_error : Format.formatter -> error -> unit


DCE: rooted utf8 test hook for DCE.

JonoPrest · 2026-06-15T11:21:51Z

 *)

 type pos = {
-  lnum: int;


DCE: rooted unicode test helpers for DCE. Covers ast_utf8_string_interp.mli too.

JonoPrest

DCE notes 3.

JonoPrest · 2026-06-15T11:23:03Z

 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)

-type untagged_variant = OnlyOneUnknown | AtMostOneObject | AtMostOneArray


DCE: trimmed frontend constants. Covers bs_syntaxerr.mli too.

JonoPrest · 2026-06-15T11:23:03Z


 val cst_string : string -> delim -> cst

-val empty_label : label


DCE: trimmed frontend constants.

JonoPrest · 2026-06-15T11:23:03Z


 type constructor_tag = {
  cstr_name: Ast_untagged_variants.tag;
-  const: int;


DCE: trimmed frontend constants. Covers lam_constant.mli too.

JonoPrest · 2026-06-15T11:23:03Z

 type bs_version = int * int * int

 type t = {
-  bsb_project_root: string;


DCE: trimmed gentype config.

JonoPrest · 2026-06-15T11:23:03Z

@@ -1,7 +1,5 @@
 open Gentype_common

-let concat = Filename.concat


DCE: trimmed gentype config.

JonoPrest · 2026-06-15T11:23:05Z

  interesting in case of errors.
 *)

-open Annot


DCE: trimmed debug helpers; trimmed call annotations. Covers stypes.mli too.

JonoPrest · 2026-06-15T11:23:05Z

 val modtype : t -> module_type -> module_type
 val signature : t -> signature -> signature
 val modtype_declaration : t -> modtype_declaration -> modtype_declaration
-val module_declaration : t -> module_declaration -> module_declaration


DCE: trimmed typing exports.

JonoPrest · 2026-06-15T11:23:05Z

    let c = compare x v in
    if c = 0 then d else find_str x (if c < 0 then l else r)

-let rec mem x = function


DCE: trimmed debug helpers. Covers tbl.mli too.

JonoPrest · 2026-06-15T11:23:05Z


 and transl_cases_try cases = List.map transl_case_try cases

-and transl_apply ?(inlined = Default_inline)


DCE: made apply metadata explicit.

JonoPrest · 2026-06-15T11:23:05Z


 type error
 (* exception Error of Location.t * error *)
-


DCE: trimmed ml exports.

JonoPrest

DCE notes 4.

JonoPrest · 2026-06-15T11:24:18Z

 (* Forward declaration, to be filled in by Typemod.type_open *)

 let type_open :
-    (?used_slot:bool ref ->


DCE: narrowed typecore helpers; removed unused open slot; trimmed typing exports. Covers typecore.mli too.

JonoPrest · 2026-06-15T11:24:18Z

 open Types
 open Typetexp

-type native_repr_kind = Unboxed | Untagged


DCE: trimmed ml exports; removed free_variables env. Covers typedecl.mli too.

JonoPrest · 2026-06-15T11:24:18Z


 (* Compute the environment after opening a module *)

-let type_open_ ?used_slot ?toplevel ovf env loc lid =


DCE: removed unused open slot; trimmed typing exports. Covers typemod.mli too.

JonoPrest · 2026-06-15T11:24:18Z

      [Tobject (_, `Some (`A.ct', [t1;...;tn]')] ==> [(t1, ..., tn) A.ct].
      where A.ct is the type of some class.

-      There are also special cases for so-called "class-types", cf. [Typeclass]


DCE: trimmed ctype.

JonoPrest · 2026-06-15T11:24:18Z

 *)
 module Color = struct
  (* use ANSI color codes, see https://en.wikipedia.org/wiki/ANSI_escape_code *)
-  type[@warning "-37"] color =


DCE: trimmed syntax CLI colors.

JonoPrest · 2026-06-15T11:24:18Z

@@ -1,3 +1,3 @@
 (* Interface to print source code to res.
 * Takes a filename called "input" and returns the corresponding formatted res syntax *)
-val print : ?ignore_parse_errors:bool -> string -> string [@@dead "+print"]


DCE: fixed live printer annotation.

JonoPrest · 2026-06-15T11:24:18Z

 * We don't support custom operators. *)
 let parenthesized_ident _name = true

-(* TODO: better allocation strategy for the buffer *)


DCE: trimmed outcome printers.

JonoPrest · 2026-06-15T11:24:18Z

 val has_inline_record_definition_attribute : Parsetree.attributes -> bool
 val has_res_pat_variant_spread_attribute : Parsetree.attributes -> bool
 val has_dict_pattern_attribute : Parsetree.attributes -> bool
-val has_dict_spread_attribute : Parsetree.attributes -> bool


DCE: trimmed syntax helpers.

JonoPrest · 2026-06-15T11:24:18Z

  in
  skip_whitespace_and_check scanner.offset

-let peek_minus scanner = peek_char scanner '-'


DCE: trimmed syntax helpers. Covers res_scanner.mli too.

JonoPrest · 2026-06-15T11:24:18Z

@@ -1,4 +1,4 @@
-type input = Filename of string | Source of string


DCE: trimmed syntax print engine.

JonoPrest added 30 commits June 11, 2026 11:01

dce: add baseline report

6adae89

dce: remove unused process_file kind

bab4af9

dce: remove unused cmt filters

9748813

dce: remove unused outputprefix args

e77d9df

dce: simplify disjoint_union

3442961

dce: fix live printer annotation

d9079af

dce: simplify array test asserts

f399489

dce: simplify hash stub asserts

b607181

dce: simplify hashtable test asserts

58881af

dce: inline jsx loc assert

96eec83

dce: simplify list test asserts

3b524c6

dce: simplify map test asserts

d7e3fb7

dce: simplify string test asserts

0fde7b9

dce: simplify utf8 test asserts

8a3989a

dce: simplify util test asserts

79cb287

dce: simplify raise assertion

4875980

dce: note live reanalyze stats

8115b5f

dce: require ppx restore flag

f724fdd

dce: remove unused open slot

fc9a119

dce: narrow typed completions helper

c02633f

dce: require apply metadata

0352606

dce: narrow js mapper app helpers

b3d08ab

dce: note live ast helper labels

43c60d5

dce: remove unused args finish

250c180

dce: narrow pipeable filter

5330642

dce: require pipe transform flag

65fb4b0

dce: note live type contexts

2204004

JonoPrest added 22 commits June 12, 2026 16:20

dce: trim js exp optionals

5499095

dce: trim js numeric optionals

7f4df5b

dce: trim js arithmetic optionals

233c4c8

dce: note untagged switch liveness

551753c

dce: note namespace helpers

69efd3c

dce: remove unused ext sys helper

87ab438

dce: note location hooks

dd8833e

dce: remove js file kind record

8c8294f

dce: remove lam function helper

a24fe29

dce: remove unused debugger literal

df879b4

dce: remove unused dynamic check helper

c8ae11e

dce: remove unused misc output helper

9cc6b61

dce: remove identifiable helper

5d9c3d3

dce: note ext pervasives tests

a14bf9f

dce: trim hash set poly exports

cbc5179

dce: trim lam print export

ec30a41

dce: require parse error flag

9dab4fa

dce: remove analysis version state

4746f43

dce: trim cmt format exports

9d9b4b2

dce: remove cmt deprecated text

4d25b06

dce: trim map set core helpers

8ee8257

dce: clarify map set findings

bcd1f66

JonoPrest commented Jun 15, 2026

View reviewed changes

dce: track reanalyze branch

1b1e3f6


		let empty = {issues = []}

		let add_issue result issue = {issues = issue :: result.issues}

		@@ -1,4 +0,0 @@
		(** Dead code analysis - cmt file processing.


		val eq_expression : J.expression -> J.expression -> bool

		val eq_statement : J.statement -> J.statement -> bool


		(** {1 Processing} *)

		val process_files : ('raw, 'v) t -> string list -> unit


		val read_ast_exn : fname:string -> 'a kind -> 'a

		val magic_sep_char : char


		type t = Parsetree.pattern

		let is_unit_cont ~yes ~no (p : t) =


		type exn += Error of int (* offset ) error

		val pp_error : Format.formatter -> error -> unit


		val cst_string : string -> delim -> cst

		val empty_label : label

		@@ -1,7 +1,5 @@
		open Gentype_common

		let concat = Filename.concat


		and transl_cases_try cases = List.map transl_case_try cases

		and transl_apply ?(inlined = Default_inline)


		(* Compute the environment after opening a module *)

		let type_open_ ?used_slot ?toplevel ovf env loc lid =

		@@ -1,4 +1,4 @@
		type input = Filename of string \| Source of string

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JonoPrest commented Jun 15, 2026

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