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perf: functions using arguments are ~590× slower than Node (per-call registry-tracked object with side-table descriptors; residual after #10063) #10509

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perf: functions using arguments are ~590× slower than Node (per-call registry-tracked object with side-table descriptors; residual after #10063)#10509
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package-auditFound by the 2026 package audit: compiling real npm packages from source instead of native bindingsperformanceRuntime, compile-time, build-size, or memory performance

Description

@proggeramlug
proggeramlug
opened on Sep 17, 2026

Found by the package performance audit (real npm packages compiled from source, profiled against Node 26.5.1) and
re-measured on Perry 7661bc0 (v0.5.1589), Linux x64. #10063 (closed by #10081) removed the per-index attribute
entries, but every call of a function that mentions arguments still allocates an arguments object, registers it in a
thread-local HashMap (with its own inner HashMap), installs length attributes and — in strict code — a
callee thrower accessor in the string-keyed descriptor side tables, and the GC later prunes those entries. Reads
then resolve by name. A merge()-style function costs 38,400 instructions per call vs 279 with named parameters.

Reproduction

args.js:

// `arguments` objects: dayjs `cfg.args = arguments` (escapes), validator/lodash `arguments.length` / `arguments[i]` reads.
"use strict";
const variant = process.argv[2]; const N = Number(process.argv[3]);
const keep = new Array(1024);
function makeArgs(date, c) { const cfg = typeof c === "object" ? c : {}; cfg.date = date; cfg.args = arguments; return cfg; }
function makeRest(...a) { const cfg = typeof a[1] === "object" ? a[1] : {}; cfg.date = a[0]; cfg.args = a; return cfg; }
function mergeArgs() { const obj = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : {}; const d = arguments.length > 1 ? arguments[1] : undefined; return d ? obj : obj; }
function mergeNamed(a, b) { const obj = a !== undefined ? a : {}; return b ? obj : obj; }
function run(n) {
  let s = 0;
  if (variant === "escape_arguments") for (let i = 0; i < n; i++) { const o = makeArgs(i, { k: 1 }); keep[i & 1023] = o; s += o.date + o.args.length; }
  else if (variant === "escape_rest") for (let i = 0; i < n; i++) { const o = makeRest(i, { k: 1 }); keep[i & 1023] = o; s += o.date + o.args.length; }
  else if (variant === "read_arguments") for (let i = 0; i < n; i++) { const o = mergeArgs({ date: i }, keep); s += o.date; }
  else if (variant === "read_named") for (let i = 0; i < n; i++) { const o = mergeNamed({ date: i }, keep); s += o.date; }
  return s;
}
run(N / 5 | 0); const t0 = performance.now(); const cs = run(N);
console.log(`variant=${variant} checksum=${cs} ms=${(performance.now() - t0).toFixed(2)}`);
PERRY_NO_AUTO_OPTIMIZE=1 perry compile args.js -o args
for v in read_arguments read_named escape_arguments escape_rest; do node args.js $v 500000; ./args $v 500000; done

Measurements

Median of 3, N = 500,000, shared host (loaded; instruction counts are the load-independent figure).

variant (strict mode) Node loop ms Perry loop ms ratio Perry instructions / iter Node wall Perry wall
mergeArgs(...) — reads arguments.length, arguments[0], arguments[1] 4.7 2,748 586× 38,398 64 ms 3,354 ms
mergeNamed(a, b) (control) 0.8 8.0 10× 279 59 ms 29 ms
makeArgs(...) — cfg.args = arguments (escapes) 11.1 3,177 287× 54,359 71 ms 3,974 ms
makeRest(...a) — cfg.args = a (control) 16.0 595.5 37× 12,638 94 ms 730 ms

Checksums identical. Sloppy mode (same file without "use strict", 3 runs each): read_arguments 525×,
31,002 instructions/iter; escape_arguments 354×, 72,654 instructions/iter — so the strict callee accessor is not
the only cost.

perf record of read_arguments (inclusive): mergeArgs 68 % → js_arguments_object_alloc 33 %
(install_fresh_accessor_property 10 %, set_property_attrs 9 %, thrower_closure_value 9 %),
get_field_ic_miss_impl → arguments_object_get_field 14–20 %, js_dyn_index_get → arguments_object_get_index
11–13 %; copying-minor GC 29.5 % (finalize_dead_copied_minor_from_space_side_allocations 13 %,
prune_dead_descriptor_owner_entries_young 12 %, scan_descriptor_roots_mut 12 %). In escape_arguments a further
43 % is the property adds cfg.date =/cfg.args = (#10496).

Impact

From the audit profiles (v0.5.1587; strings- and objects-group reports):

  • dayjs: cfg.args = arguments in every dayjs() call — 4.4 % of dayjs overall, 6.0 % of add/diff.
  • validator: util/merge (arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {}, Babel's
    default-parameter output) — 6.3 % of isEmail, 8.2 % of isURL (7.2 % mean).
  • lodash: closure calls / arguments objects 10.5 / 12 / 24 % of cloneDeep / get / sortBy (memoize
    func.apply(this, arguments), baseRest); jsonwebtoken ≈ 5 %.
  • Babel/TypeScript down-levelled default and rest parameters emit exactly the mergeArgs shape, so this is common
    in any package compiled to ES5.

Mechanism

  • crates/perry-runtime/src/object/arguments.rs:212-302 js_arguments_object_alloc (verified), per call: handle
    scope, keys array for len, js_object_alloc, one js_object_set_field per argument and length; then
    • strict (restricted_callee != 0, :253-270): set_property_attrs(obj, "length".to_string(), …) and
      install_fresh_accessor_property(obj, "callee".to_string(), thrower) — two String allocations and entries in the
      (usize, String)-keyed descriptor tables;
    • sloppy (:271-285): a callee field plus set_property_attrs_batch for length/callee;
    • :289-300: ARGUMENTS_OBJECTS.insert(obj, ArgumentsMeta { mapped: HashMap::new(), … }) into a thread-local map.
  • Reads: arguments.length misses the IC and resolves by name through arguments_object_get_field
    (arguments.rs:401); arguments[i] goes js_dyn_index_get → arguments_object_get_index (arguments.rs:362,
    called from crates/perry-runtime/src/value/dyn_index.rs:424), each consulting the registry (verified by profile).
  • Every dead arguments object leaves descriptor-table and registry entries that the copying minor must prune
    (crates/perry-runtime/src/object/descriptor_state.rs:1799 prune_dead_descriptor_owner_entries_young, verified).
  • The residual is the same mechanism perf(runtime): three-argument arguments-object loop costs 267–627x Node #10063 hypothesised (allocation + descriptor/registry bookkeeping + GC), minus
    the per-index attributes fix(runtime): reduce arguments object construction overhead #10081 removed.

What fast looks like

  • Codegen: when arguments does not escape (only arguments.length, arguments[i] with no writes, no
    arguments passed/stored/apply'd, no sloppy mapped-parameter aliasing), lower those reads to the incoming
    argument count and argument slots — no object at all (read_arguments ≤ 2× read_named).
  • Runtime, for escaping objects: a dedicated arguments shape whose length/callee attributes are fixed by the
    shape (no per-object descriptor entries, no registry insert in strict mode where nothing is mapped), so
    escape_arguments costs about what escape_rest does (≤ 1.5×) and GC has nothing to prune.

Notes

Activity

  1. proggeramlug
    added
    performanceRuntime, compile-time, build-size, or memory performance
    package-auditFound by the 2026 package audit: compiling real npm packages from source instead of native bindings
    on Sep 17, 2026
  2. proggeramlug
    added 2 commits that reference this issue on Sep 25, 2026

    perf(codegen): read-only `arguments[k]` no longer builds an Arguments…

    0da3536

    perf(codegen): read-only `arguments[k]` no longer builds an Arguments…

    7a64428

  3. proggeramlug commented on Sep 30, 2026

    @proggeramlug
    proggeramlug
    on Sep 30, 2026
    ContributorAuthor

    Current target (2026-09-30): the escaping arguments object (cfg.args = arguments) is 82× Node; read-only arguments is 7× its named-parameter twin

    Package impact (#11464)

    Bucket row 6, closures / boxed captures / arguments, is 4.6% of equal-weight excess. It is ≥5% in 9 packages. Share of each package's excess: dayjs 12, qs 9, moment 8, axios 7, decimal.js 7, fastify 7, rate-limiter-flexible 6, ioredis 5, node-forge 5.

    Most of that bucket is not box cells or arguments. Most of it enters under the method dispatcher (js_typed_feedback_native_call_method_by_id) and the IC miss. Its top chains end in function-object property leaves (closure_get_dynamic_prop, is_closure_ptr, closure_is_key_deleted). The part that enters through box and arguments entry points is small:

    workload entry → leaf instr/iter % of excess
    dayjs/diff_startof js_arguments_object_alloc 239k 2.6
    dayjs/parse_format js_arguments_object_alloc 58k 2.9
    dayjs/parse_format js_closure_set_box_capture_ptr → is_registered_box_ptr 46k 2.3
    qs/stringify_nested js_closure_set_box_capture_ptr (side-channel factories) 263k 1.7
    qs/parse_nested js_closure_set_box_capture_ptr 37k 1.0
    mongodb/batch_query box_get_bits_named 3.07M 1.4
    rate-limiter-flexible/get_penalty box_get_bits_named + js_box_set_bits + set_box_capture_ptr 4.5k 3.2
    moment/parse_format js_arguments_object_alloc 36k 1.0
    redis/set_get set_box_capture_ptr + js_box_release 86k 1.3

    Boxes also add root-scan work to the copying minor (the gc_minor bucket). The data cannot separate that share.

    For this issue, the arguments rows are dayjs (cfg.args = arguments in every dayjs() call: 2.6–2.9% of excess) and moment (1.0%). These are the escaping shape, and they were profiled on a build that already had #11349. Three more chains pay arguments-registry probes on paths that never use arguments, measured as % of the workload's Perry instructions:

    workload path instr/iter % of Perry
    node-forge/sha256 js_object_get_index_polymorphic → is_arguments_object 212k 2.6
    big.js js_dyn_index_set_strict → arguments_object_set_index (big.mjs:872 c[j] = 0) 3.9M 1.8
    commander js_class_field_add → arguments_object_set_field 64k 1.7

    The big.js site may be gone after #11588. I did not re-profile it.

    What landed since the issue was filed

    Reproducer, fresh numbers (the issue's args.js, strict, instructions per call)

    function mergeArgs() { const obj = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : {}; const d = arguments.length > 1 ? arguments[1] : undefined; return d ? obj : obj; }
function mergeNamed(a, b) { const obj = a !== undefined ? a : {}; return b ? obj : obj; }
function makeArgs(date, c) { const cfg = typeof c === "object" ? c : {}; cfg.date = date; cfg.args = arguments; return cfg; }
function makeRest(...a) { const cfg = typeof a[1] === "object" ? a[1] : {}; cfg.date = a[0]; cfg.args = a; return cfg; }
    variant Perry, 7661bc0 (issue) Perry, main Node Perry/Node
    read_named (control) 279 155 56 2.8×
    read_arguments 38,398 1,083 144 7.5×
    escape_rest (control) 12,638 4,635 292 15.9×
    escape_arguments 54,359 20,353 250 81.5×

    (The issue's column used whole-process ÷ 1.2·N. Main's uses two-N.)

    Acceptance target

    • Issue's own targets: read_arguments ≤ 2× read_named (now 7.0×) and escape_arguments ≤ 1.5× escape_rest (now 4.4×).
    • No ARGUMENTS_OBJECTS or descriptor-table entries for strict escaping objects.
    • The registry probes above should vanish from plain Array and class-field paths.
    • No regression on dayjs, moment, validator, commander and big.js.

    Package check (Linux, needs perf). Build with cargo build --release -p perry -p perry-runtime-static -p perry-stdlib-static, then run:

    (cd benchmarks/packages && npm ci --ignore-scripts)
python3 scripts/package_bench.py compile --perry-bin-dir /tmp/pb --filter dayjs --filter moment --filter validator --filter commander --filter big.js
python3 scripts/package_bench.py run --perry-bin-dir /tmp/pb --arms node,perry --modes instr --filter dayjs --filter moment --filter validator --filter commander --filter big.js --out /tmp/pb/instr.json

    Run it once on a base-commit build and once on the branch, and compare instructions per iteration. --filter is a workload-id substring, and control/* always runs. For attribution, run profile --callgraph on PERRY_KEEP_SYMBOLS=1 binaries (see benchmarks/packages/PROFILE.md).

    Fresh numbers were measured on origin/main 5fbc2c3 (v0.5.1654) with cargo build --release -p perry -p perry-runtime-static -p perry-stdlib-static. Binaries were compiled with PERRY_NO_AUTO_OPTIMIZE=1 and compared with Node 26.5.1 on Linux x86-64 using perf stat -e instructions:u. Each figure is the median of 3 runs at two sizes of N, with per-op = ΔI/ΔN. N1 is at least 200k operations (20k calls for the factory bench), which keeps most of Node's JIT warm-up inside the constant term. Output was byte-identical to Node on every row. The #11464 figures come from benchmarks/packages/profile/callgraph.{md,json}, measured at Perry 36420d2 with auto-optimize. node-forge was measured from 2febf42 binaries. "% of excess" means the share of a package's (Perry − Node) instructions per iteration.

  4. proggeramlug
    added a commit that references this issue on Oct 3, 2026

    perf(arguments): an arguments object is born with its final shape (#1…

    adaa2d3

  5. proggeramlug commented on Oct 3, 2026

    @proggeramlug
    proggeramlug
    on Oct 3, 2026
    ContributorAuthor

    Partial progress in #11794: escape_arguments 16,365 → 7,799 instructions/op (node 179, still ~44×); read_arguments unchanged at 1,064. Leaving open.

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