perf: function-constructor objects (new F(), x instanceof F) are 78–566× slower than Node (F.prototype and builtin identity re-derived from side tables per operation) #10507

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. The pre-ES6 object model (function F(){},
F.prototype.m = …, new F(), x instanceof F, new this.constructor(v)) never gets a class id or a cached
prototype: every new F() runs js_new_function_construct (10,464 instructions for an empty constructor vs 625
for new KE() of an empty class) and every x instanceof F runs the dynamic ladder (3,770 vs 185).

Reproduction

fnctor.ts:

// Pre-ES6 object model (decimal.js, dayjs, lodash): `function F(){}` constructors, `x instanceof F`, `new x.constructor(v)`.
const variant = process.argv[2]; const N = Number(process.argv[3]);
function E(this: any) { }
class KE { }
function clone() {                                   // decimal.js: the constructor is a closure made by clone()
  function Dec(this: any, v: number): any { const x = this; if (!(x instanceof Dec)) return new (Dec as any)(v); x.constructor = Dec; x.d = v; }
  Dec.prototype.plus = function (this: any, y: number) { const Ctor = this.constructor; return new Ctor((this.d + y) % 1000003); };
  return Dec;
}
const D: any = clone();
class C { d: number; constructor(v: number) { this.d = v; } plus(y: number) { return new C((this.d + y) % 1000003); } }
const fe: any = new (E as any)(); const ke: any = new KE(); const keep: any[] = new Array(1024);
function run(n: number): number {
  let s = 0;
  if (variant === "new_fn_empty") for (let i = 0; i < n; i++) { keep[i & 1023] = new (E as any)(); s += 1; }
  else if (variant === "new_class_empty") for (let i = 0; i < n; i++) { keep[i & 1023] = new KE(); s += 1; }
  else if (variant === "instanceof_fn") for (let i = 0; i < n; i++) s += fe instanceof E ? 1 : 0;
  else if (variant === "instanceof_class") for (let i = 0; i < n; i++) s += ke instanceof KE ? 1 : 0;
  else if (variant === "decimal_fn") { let x = new D(1); for (let i = 0; i < n; i++) x = x.plus(i); s = x.d; }
  else if (variant === "decimal_class") { let x = new C(1); for (let i = 0; i < n; i++) x = x.plus(i); s = x.d; }
  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 fnctor.ts -o fnctor
for v in new_fn_empty new_class_empty instanceof_fn instanceof_class decimal_fn decimal_class; do node fnctor.ts $v 1000000; ./fnctor $v 1000000; done

Measurements

Median of 3, N = 1,000,000, shared host (loaded; instruction counts are the load-independent figure).

Checksums identical. The empty-constructor and instanceof rows contain no property adds, so they isolate this
mechanism from #10496 (adds never cached), which accounts for ~35 % of the decimal_fn row.

perf record (inclusive):

• new_fn_empty: js_new_function_construct 91 % → js_get_global_this_builtin_value 36 %,
  closure_get_dynamic_prop 17 %, get_accessor_descriptor 12 %, identify_global_builtin_constructor 12 %,
  extends_target_must_throw 7 %, object_set_static_prototype_impl 7 %, synthetic_class_id_for_function 5 %,
  SipHash 4 %.
• instanceof_fn: js_instanceof_dynamic 68 % → builtin_ctor_class_id_from_value 28 %, closure_get_dynamic_prop
  27 %, js_instanceof_dynamic_tail 20 %, js_object_has_own_symbol (Symbol.hasInstance) 18 %,
  synthetic_class_id_for_function 17 %, identify_global_builtin_constructor 15 %, well_known_symbol 14 %.
• decimal_fn: js_new_function_construct 79 %, js_put_value_set_ic_miss 35 % (the adds), js_instanceof_dynamic 9 %.

Impact

From the audit profiles (v0.5.1587):

• decimal.js 10.6 (26.7× Node overall, objects-group report): js_new_function_construct 8.8 %, instanceof
  dynamic tail 15.6 %, plus the property adds and prototype-method calls of the same object model — ≈ 46 % of Perry
  time is this model. Every operation runs new Ctor(…) with Ctor = x.constructor and
  isDecimalInstance(y) (y instanceof Decimal); Decimal is a closure created inside clone().
• dayjs (85× Node, strings-group report): the Dayjs constructor chain — the audit's function-constructor
  microbenchmark was 141× vs 52× for the same code as a class.
• typescript 5.8 (transpileModule, large-group report): js_new_function_construct →
  replay_class_object_constructor 15.2 % inclusive (NodeObject/TokenObject/SymbolObject constructors — class
  expressions constructed through a variable, which enter the same function; overlaps perf: new on a class expression is 159× slower than Node vs 7× for the identical declaration (constructor this.x = fields inferred only for declarations) #10499).
• lodash: Stack/MapCache/ListCache/Hash are function constructors (≈ 1 %).

Mechanism

• crates/perry-runtime/src/object/class_registry/construct.rs:242 js_new_function_construct (verified), per call:
  bound-function / boxed-primitive / RegExp / Proxy / non-constructable-builtin checks; is_function_prototype_object_value
  (:321, resolves globalThis.Function.prototype by name — see perf: missing-property reads on functions are ~2,600× and Object.hasOwn/getPrototypeOf 40–90× slower than Node (Function.prototype re-resolved by name per call) #10497); bound_native_callable_module_and_method
  (:324); identify_global_builtin_constructor (:470); arrow and extends_target_must_throw checks (:1046);
  synthetic_class_id_for_function (:1049, a hash lookup keyed by the function); allocation; then
  closure_get_dynamic_prop(fp, "prototype") (:1083) and a static-prototype side-table insert for the instance.
• crates/perry-runtime/src/closure/dynamic_props.rs:900 closure_get_dynamic_prop (verified): first
  get_accessor_descriptor(ptr, prop) (:919; when the per-object summary admits a possible entry it looks up
  (ptr, key.to_string()) — a String allocation + SipHash, crates/perry-runtime/src/object/descriptor_state.rs), then locks the process-global
  Mutex<PtrHashMap<usize, ClosureProps>> (:94, :936) and hashes the &str name. F.prototype therefore costs up to a
  string allocation, two hash lookups and a mutex on every new and every instanceof (inferred from source + profile).
• crates/perry-runtime/src/object/instanceof.rs:166 js_instanceof_dynamic (verified): Proxy unwrap, Temporal
  kind, own Symbol.hasInstance probe (:225), builtin_ctor_class_id_from_value (:127, reads the closure's
  name dynamic prop and string-matches it, :292), identify_global_builtin_constructor (:481),
  intl_instanceof (:541), and only then js_instanceof_dynamic_tail (:626), which reads F.prototype from the
  closure side table again and walks the chain.
• None of these answers is cached per closure, although for an ordinary user function none of them can change
  except F.prototype (a write that can bump an epoch).

What fast looks like

• Give a user function used with new a per-closure constructor record (synthetic class id, "is ordinary user
  function" bit, cached prototype object pointer + epoch) established on first new/instanceof; later calls do a
  header check + epoch compare and allocate with the cached prototype. Skip the builtin-identity ladder for closures
  whose func_ptr is not one of the builtin thunks (a pointer compare, done once).
• Targets on this benchmark: new_fn_empty ≤ 2× new_class_empty (≤ 1,300 instructions), instanceof_fn ≤ 2×
  instanceof_class, decimal_fn ≤ 3× decimal_class once perf: adding a property with o.k = v is ~100× slower than Node (static-key write IC primes only overwrites; no add-transition cache) #10496 and perf: method calls on untyped receivers (prototype methods, fn.call, push on any) are 44–520× slower than Node (no call-site cache; name re-resolved per call) #10505 are fixed.

Notes

• The ES-class rows show the gap is specific to the function-constructor path (class construction was addressed in
  closed perf: new Klass(v,w) is 63% slower than the equivalent object literal (28.5x vs 17.4x Node) #7512).
• Open correctness issues on the same path: x instanceof F is always false when F is an imported non-class constructor (ES5 function, factory-made function, CJS module.exports = F); namespace access and local aliases work #10477 (x instanceof F false for imported non-class constructors),
  Object.create(proto).constructor is a bogus class reference instead of proto.constructor; ctor instanceof ctor then segfaults (lodash isEqual(cloneDeep(x), x)) #10478 (Object.create(proto).constructor bogus class reference), arguments in a class constructor is empty when the class is constructed through a value, and padded to the declared parameter count on a static new #10484 (arguments in a class constructor
  constructed through a value). A fix that caches the constructor record should keep those in view.
• Sibling drafts: perf: adding a property with o.k = v is ~100× slower than Node (static-key write IC primes only overwrites; no add-transition cache) #10496 (property adds in the constructor body), perf: method calls on untyped receivers (prototype methods, fn.call, push on any) are 44–520× slower than Node (no call-site cache; name re-resolved per call) #10505 (prototype-method calls on the
  instances), perf: missing-property reads on functions are ~2,600× and Object.hasOwn/getPrototypeOf 40–90× slower than Node (Function.prototype re-resolved by name per call) #10497 (Function.prototype resolved by name).