indexReadInBounds proves only `i < xs.length`, not that `i` is a
non-negative integer. For `if (f(xs[i]!))` the forwarded-assertion path
used to pass a missing element as undefined; accepting `if` conditions for
every caller turned such reads into the dense bounds trap, which throws for
a negative index where Node passes undefined (tsc-ts: isMatchableRegion and
compareSymbolChains changed ABI). The `if`-condition position is now an
opt-in fact, used by the present-read proof, which also proves the index a
non-negative integer counter.
Code holding the array could detach its buffer between the guard and the
read, so the present-read proof must refuse it. With a genuine NaN also
reaching the parameter and a consumer that observes undefined, the
parameter stays `number | undefined`.
A typed-array read that may name a missing element lowers to a boxed
`number | undefined`, and the optional-value analysis widens every
parameter it reaches for all callers. Two patterns in tsc-ts's relater
boxed its hottest relation methods this way, failing the build's scalar
ABI check ("Boxed numeric arguments in Checker.isTypeAssignableTo"):
- `const regular = this.regularTypes[id]; const sourceId = regular >= 0
? regular : id;` The read is NaN-coded, but its occurrence in the true
arm was rebuilt as `number | undefined`, so `sourceId` and the
parameters of isSimpleTypeRelatedTo and structuredTypeRelatedTo were
boxed. A comparison with a number that is never NaN is false for
undefined and NaN alike, so an occurrence of a never-reassigned binding
under such a guard is a plain, non-NaN number. The analysis now treats
it as one wherever it flows.
- `for (let i = 0; i < sources.length; i++) isTypeAssignableTo(sources[i],
targets[i])` over two Uint32Arrays allocated with the same length. The
parameters also receive a JSON field that may be NaN, so NaN-coding
cannot carry them (`source === target` must tell NaN from undefined).
The reads are now proven present instead: the index is a non-negative
integer counter that only its own function writes, a dominating guard
bounds it by the array's length or by the length of a parallel typed
array allocated with the same length, and each array is a `const`
fixed-length typed array referenced only through element accesses and
`.length`, so no code can detach its buffer. A proven-present read
lowers to the plain element read and is never optional.
indexReadInBounds also accepts a read inside an `if` condition and takes
an optional same-length fact. Reads the proofs do not cover keep the
established lowering: an inclusive bound, a shorter parallel array, a
decreasing or fractional counter, a counter a closure writes, and an
array that escapes all still read undefined, as the new corpus program
typed-array-present-reads checks against Node.
Every class slice used to opt out of transparent huge pages, so each
4 KiB the bump pointers crossed cost a page fault. Those faults (fault
entry, memcg charge, LRU insertion and the page clear) were 6-14% of
tsc-ts samples in the kernel. Backing the whole reservation with huge
pages removes most of them, but makes the 2 MiB page around every bump
pointer resident at once. A worker executable has up to 32 class slices
per script thread, so tRPC at 8 checkers grew from 558 to 955 MB.
A slice now starts on small pages. Once it has carved 8 MiB, the rest
of its range switches to huge pages (MADV_HUGEPAGE). Only slices that
already hold 8 MiB pay for a partial last huge page. The reservation is
huge-page aligned, so the switch point and every slice start on a 2 MiB
boundary. The slow path raises a slice's bump limit in two steps (to the
switch point, then to the slice end), so the inline fast paths are
unchanged. The policy is Linux-only; other targets keep one limit per
slice, as before. The allocator checks now build with _GNU_SOURCE on
Linux like the runtime packs, so the madvise advice is compiled in and
checked (alignment, contiguous carving across the switch, VmFlags nh/hg).
Measured with tsc-ts best-v1 (parallel-check + 6247795 e24057a 64d9af6
1c42c55), built with this runtime vs origin/main, on two Linux Vercel
Sandboxes (8 vCPU; 5-7 interleaved runs, medians). Columns: wall, max
RSS, minor faults; "all" is MADV_HUGEPAGE on the whole reservation:
single-threaded wall RSS faults all: wall / RSS
Excalidraw -6.1% +0.8% 331k -> 112k -10.0% / +3.5%
Playwright -1.8% +1.0% 371k -> 111k -8.4% / +3.2%
TypeORM -7.2% +0.9% 259k -> 75k -11.8% / +4.1%
tRPC -5.0% +2.0% 101k -> 47k -9.0% / +11.3%
tsc-ts self-check -2.9% +2.6% 158k -> 64k -3.1% / +8.4%
--checkers 8
Excalidraw -2.9% +2.6% 1075k -> 508k -6.3% / +10.6%
Playwright -10.0% +2.6% 739k -> 381k -10.3% / +12.2%
TypeORM -5.9% +2.2% 372k -> 232k -10.1% / +27.7%
tRPC -2.5% +2.5% 159k -> 125k -4.3% / +71.2%
tsc-ts self-check -4.0% +3.9% 213k -> 172k -12.1% / +46.3%
Switching at 2 or 4 MiB was up to about 1.5 points faster single-threaded
but cost up to +11% RSS at 8 checkers. 16 MiB gave back most of the gain.
Prefaulting small pages with MADV_POPULATE_WRITE did not reduce sys time.
Collapsing the small-page prefix with MADV_COLLAPSE at the switch did not
help either. The runtime benchmark suite (--layouts=4 --runs=16) shows a
geomean change of -1.2%: inventory-report -9.9%, validate-errors -5.3%,
log-summary -2.9%, and regex-logs +2.1%. regex-logs peaks at 6.8 MB and
never reaches the switch point; with one binary the policy measures -0.9%
there, so its delta comes from code layout.
The NaN-coded read analysis memoized lookups whose answer can be null
(symbols, eligible functions, call sites, plain-number returns) and read
them back with `map.get(key)!`. Under Node that returns the cached null,
but in the natively compiled compiler `!` is a checked extraction, which
threw "null is not representable" while lowering programs
(self-hosting-native-frontend, the native CLI bootstrap contracts). Read
the cache through an undefined check instead.
Every two-argument Math.min/Math.max was an out-of-line call to
scr_math_min/scr_math_max (94 sites in tsc-ts, including
compareCodePoints and IdentifierTable.intern). LLVM's minimum/maximum
intrinsics have exactly their semantics: NaN propagates and -0 orders
below +0. On x86-64 they lower to minsd/maxsd with inline NaN and
signed-zero handling, on arm64 to fmin/fmax.
A typed-array element read answers undefined for an index outside
[0, length), so the default lowering returns a heap-boxed
`number | undefined` and widens every binding, parameter and return the
read reaches. In the tsc-ts scanner that boxed every character read and
turned every character predicate (isLineBreak, isIdentifierPart, ...)
into a function taking a boxed union.
Most consumers cannot tell undefined from NaN: relational, arithmetic
and bitwise operators, truthiness, Math functions, String.fromCharCode,
typed-array indexing, switch over number cases, and equality with a
number that is never undefined. The new analysis (nan-coded-reads.ts)
follows reads through local bindings, parameters of directly called
functions and methods (no overrides, no value uses), and their returns.
A slot is NaN-coded when every value it receives is a NaN-coded read or
slot, or any other number (converted with ToNumber on entry), and either:
- it never holds a genuine NaN (integer elements, integer constants,
guarded integer arithmetic), so NaN stands for undefined exactly; any
consumer that takes the value whole (an argument, a stored or returned
value, a literal element, concatenation) gets the exact
`number | undefined` rebuilt, and the optional-read analysis treats
that occurrence as optional, so it lowers as before; or
- every consumer is NaN-insensitive.
Equality of two NaN-coded values that never hold a genuine NaN also
answers true for two NaNs, as undefined === undefined does. Any other
slot keeps the established union lowering; asserted reads (`t[i]!`) are
unchanged.
tsc-ts best-v1 (scriptc main + this commit vs main, Linux sandbox,
Xeon 2.5 GHz, interleaved, medians of 5, diagnostics identical):
| app | parse | total (single-threaded) | wall --checkers 8 |
| --- | --- | --- | --- |
| tRPC | 1.263 -> 0.866 s (-31.4%) | 3.035 -> 2.527 s (-16.7%) | -13.0% |
| Excalidraw | 2.637 -> 1.865 s (-29.3%) | 14.99 -> 14.04 s (-6.3%) | -16.2% |
| Playwright | 3.150 -> 2.202 s (-30.1%) | 12.93 -> 12.14 s (-6.1%) | -12.4% |
| TypeORM | 2.562 -> 2.036 s (-20.5%) | 10.93 -> 10.46 s (-4.3%) | -8.6% |
| self-check | 2.080 -> 1.529 s (-26.5%) | 7.06 -> 6.68 s (-5.4%) | -15.1% |
The tsc-ts IR has 646 instead of 697 scr_union_new_f64 sites (the rest
are cold), 22 instead of 168 typed-read helper calls, and 217 instead of
572 scr_union_get_f64 calls; the scanner's hot functions allocate no
union boxes. Binary size -0.2%.
Baseline x86-64 has no rounding instruction, so every llvm.trunc became
a call to libm's trunc. The typed-array read helper paid that call on
every read: it decided presence with `i >= 0 && i < length &&
Math.trunc(i) === i` before the inline element load.
- Math.trunc (and the DataView offset truncation) now take an integer
round trip on x86-64 targets: values of magnitude below 2^52 go through
fptosi/sitofp with the sign restored by copysign (so -0.5 and -0 give
-0); larger values, NaN and the infinities are already integral and
keep their value. Other targets keep llvm.trunc, which is one
instruction there.
- The ToUint32 slow path is only reached for magnitudes above 2^53 (and
non-finite values), which are integers, so its truncation was a no-op
and is gone.
- For integer element kinds, the read helper performs the element read
that yields NaN for an invalid index (one inline index check) and
answers undefined exactly when that read is NaN: an integer element is
never NaN. Float element kinds keep the range and integrality test.
A closure created above the `let`/`const` it captures holds the binding
in a TDZ box whose NULL payload slot marks "not yet initialized". A
union of one reference arm with `null` and/or `undefined` (`Set<T> |
null`, `string | undefined`, `C | null`) is represented as the bare arm
pointer with NULL standing for the unit arm, so storing that unit value
made the box indistinguishable from the temporal dead zone: every later
read or write threw "Cannot access 'x' before initialization" although
the declaration had run.
The self-hosted compiler trips on exactly this shape in
lowerer.ts (`let dynamicViews: Set<string> | null = null`, read by a
callback created earlier), which made scriptc 0.2.8 fail to build
tsc-ts's relater with SC3004. Node evaluates the source correctly; the
native code was wrong.
TDZ boxes of nullable-union bindings now start at the module's immortal
NULLABLE_ABSENT sentinel and the TDZ test compares against it. No value
of the binding can hold that sentinel, and every RC entry point and the
cycle collector already skip it, so box release, trace and the
initializing store need no other change.
Corpus: 4596-tdz-nullable-forward-capture.
The class method census marks a method name as replaceable when a
function-typed property write uses that name, so a scanner storing its
error callback in `this.onError` made every call of any class's
`onError` method go through the checked property bag. That bag is a
dynamic store naming any property, so the int32 slot analysis also gave up
int32 storage for every class field exposed to dynamic code.
A function-typed write now marks the name only when an instance of a class
that has the method can inhabit the receiver's type: an assignability check
against the instance types of the method's owners, with `this` in an
instance member read as its class. Generic or anonymous owners, `this`
outside instance members, type parameters, `any` and `unknown` receivers
keep the conservative answer. Writes through interfaces or subclasses that
can reach a method still replace it.
Test: class-method-mutations.test.ts. Corpus:
4597-callback-field-method-name.
A class extending Error without its own constructor (or one passing
options to super) initializes the builtin prefix through the
error.ctorOptions helper, whose message and options arguments are dynamic.
The int32 slot analysis did not list that helper among the dynamic helpers
that never store into a live class view, so a single such class anywhere in
a program counted as a dynamic store naming every property: every f64
field of every class exposed to dynamic code lost its int32 storage, and
the integer facts of the functions reading those fields went with it.
error.ctorOptions runs scr_error_init_options, the same initializer
error.newOptions (already listed) runs: it stamps the receiver's
runtime-owned error prefix and only reads `options.cause`. In the native
tsc-ts self-check, two such classes cost 7% total time and 10% check time.
Unit test: int32-slots.test.ts. Corpus: 4596-error-subclass-int-fields
pins Error subclasses forwarding message and options beside integer
fields.
A field shared by every class arm of a union could only be read or
written when all arms declared it with one IR type. Syntax-tree code
commonly narrows a node to several classes with `instanceof` where one
class declares the field optional and another required (`initializer:
Expression | undefined` beside `initializer: Expression`), or as a
subclass beside its base, and both forms were refused.
Reads now dispatch on the union tag, read each arm's own slot, and widen
it to the arm field type every other one converts into without a check
(a union wrap or class upcast); the caller narrows the result to the
checker's flow type as before. Writes evaluate the value once as the arm
field type that every other arm's storage accepts and widen it per arm.
Arms whose field types are unrelated keep the existing refusal.
Corpus: 4594-union-class-field-mixed-types.
A parameter typed as a base class becomes runtime-optional storage
(`Base | undefined`) when a caller can pass an array hole. After
`instanceof` narrowed it to several subclasses and a guard such as
`node.label === undefined` ended its active runtime-optional state, the
next `node.label` lowered the receiver as the storage union, which has no
retag to the checker's class union, and the shared field read or write was
refused. Union property reads and union field writes now convert such a
receiver with the checked extraction and class test that typed slots
already use.
Corpus: 4595-union-class-field-optional-receiver.
- Synchronize published packages and the compiler surface manifest at v0.2.8, and bump the runtime ABI marker to v9.
- Add release notes for worker graph sharing, catchable deep recursion, parallel code generation, runtime performance, and compatibility fixes.
The natively built emitter records an allocation stack for every object
under ASan, so emitting its own module takes several times longer than
the plain build and now runs close to the 300 s per-stage limit on shared
runners. Sanitized runs get a 900 s per-stage limit and a matching test
budget; plain runs keep the existing limits.
A shorthand property and an object literal passed as an argument no
longer widen the declared record layout of the binding or parameter
that receives them. A widened layout made every existing record that
flowed into that binding or parameter convert to a copy, so later
writes through the copy were lost. Those literals keep a missing
element in their own fields and convert, with a check, into a declared
record.
The debug-variables fixture iterates an array whose elements may be
undefined, so its loop binding keeps the union layout the debugger
check inspects.
sync-versions stamps packages/threads with the CLI version (0.2.7 now),
the release workflow checks that version and publishes the package
before scriptc, and RELEASING.md lists it with the packages that always
release together. npm trusted publishing must be configured for
@scriptc/threads before the next release: a package without it fails
before upload.
The new docs page (/docs/threads) explains @scriptc/threads: a runnable
example that publishes a million-order ledger and sends it to four
workers, verified under Node.js 24 and as a scriptc executable; what
publish accepts and refuses, and that a refused publish leaves the graph
unchanged; the frozen-object TypeErrors of the write guard; a comparison
with Node's structured clone (constant-time sends, preserved classes and
identity, immortal objects) and the three rules that make a program
behave the same under both; the automatic sharing of deeply frozen
untyped data; and the cost model. The limitations page gains a Published
graphs section (immortality, class and identity differences, write-check
evaluation order, private fields) and links the new page from the
worker-threads section.
This is the first page added since the migration, so the route-test
fixture now accepts pages without a legacy URL, and the agent guide's
checklist for new pages names the fixture.
A published string can never record facts in its header later, so
publication proves ASCII before marking (every UTF-16 index mapper
answers ASCII strings by identity) and primes the Map key hash only for
short strings: hashing every source text cost more than the rest of the
walk, and the map code already skips caching into immortal strings.
Strings are marked when pushed instead of going through the worklist.
SCRIPTC_PUBLISH_TRACE reports object counts and walk/commit times.
The new @scriptc/threads package exports publish(value) and
sharesPublishedGraphs. Node.js runs its JavaScript: publish validates
the whole graph (plain objects, arrays, class instances, Maps, Sets and
primitives other than symbols), then deep-freezes it, and published Maps
and Sets reject mutation. scriptc builds lower both exports to
intrinsics and never compile the package body.
In scriptc, publish makes the graph immutable and immortal: a
compiler-emitted walker per static type (llvm/publish.ts) marks every
object rc == SIZE_MAX through a runtime worklist (scr_publish.c), so
retains, releases and the collector skip it and nothing frees it, and
the objects leave the collector's buffers. Hierarchy members dispatch on
the concrete class; arrays, maps, sets, strings and dyn subgraphs have
runtime walkers. Static types over-approximate a graph, so an
unpublishable type gets a refusing walker that fails only when a value
is present, and every mark is logged so a refusal restores the whole
graph, exactly like the Node implementation's validate-first order.
A typed-ref capsule over a published object travels through postMessage
and workerData as a pointer (a fresh capsule in the receiver; vtables,
adapters and type keys are process-wide); immortal dyn graphs inside a
message are shared the same way. Iterating a published map no longer
writes its iteration depth.
Stores into the static types a program publishes (computed by
backend/publication.ts, a class with its whole hierarchy) carry a guard
that throws Node's frozen-object TypeErrors, and may-throw counts them.
The corpus program pins the contract against Node: shared and cyclic
class graphs with arrays, maps, sets and records read identically on
both threads, every write form fails with Node's message, unpublished
instances of the same classes stay writable, a refused publish leaves
its graph unchanged, and a worker-published graph reaches the main
thread. packages/threads/README.md documents the contract and the
differences (prototypes and identity across messages).
Each mark records its object kind, so a successful publish takes the
objects out of the RC audit's live counts (immortal objects are never
freed).
Dates (time values) and process streams (descriptors) are scalars in
scriptc, so their walkers refuse a date field or root directly instead
of pushing its bits as a pointer; the refusal corpus program pins the
statically typed refusals (date, function, RegExp, typed array and Error
values in class and record fields, and a date root) against Node.
Main lowers a discarded or union-typed `xs.pop()` to a length
truncation; those stores now carry a `pop` marker so a published array
fails with pop's own TypeError ("Cannot delete property 'N'", or the
length message for an empty array, whose `length = 0` store the emitter
drops unless the array type can be published).
The inline half of a class or record release sent NULL, last and
immortal references to the out-of-line slow release. Static literals
were the only immortal objects then; a published graph is released as
often as ordinary objects (tsc-ts checking a published program spent
more time in the no-op calls of Node releases than in any checker
function). The rarely taken branch now tests for immortal first; the
common decrement path is unchanged.
A postMessage or workerData graph whose objects and arrays are all
frozen, ordinary and hold only primitives, strings and such containers
is now shared by pointer: every node and string becomes immortal
(rc == SIZE_MAX, so retains, releases and the cycle collector skip it
and nothing frees it), strings cache their key hash first, and the
nodes leave the sender's cycle buffers. Posting an already published
root is O(1). Anything else is cloned as before; SCRIPTC_PUBLISH=0
turns publication off and SCRIPTC_PUBLISH_TRACE=1 reports each choice.
With the receiver freezing what it receives (Node's clone is not
frozen) and no identity comparison across messages, the behavior
matches Node's structured clone. Published nodes leave the RC audit's live counts, since they are never
freed, and the small-integer dyn cache becomes process-wide (filled
before main): a published graph can outlive the thread that created its
nodes, and the thread-local table died with its thread.
The new corpus program pins that
contract both ways, including a worker-published graph read after the
worker exited and a shallowly frozen graph that must still be cloned.
Deferred collection diagnostics now stay attached to their declaration until a
copy reaches the final report, so a discarded probe buffer or a successful
nested collection can no longer drop them. Uses of a binding whose type names
a rejected class report that class's diagnostic before the inherited-blocker
cascade.
Positional arguments of Math.hypot now take the same undefined-to-NaN
conversion as Math.max, Math.min and the fixed-arity statics, and a
direct indexed read that can miss converts the same way as a binding
holding one.
A for-of loop over an array whose own facts show a hole or a stored
undefined binds T | undefined, and the typed parameters, locals, record
fields and Math arguments it reaches widen to hold it. Loops over arrays
the element-state analysis proves free of holes read each element
directly, without a per-element state test.
Object literals built from a missing-element read keep the property as
undefined in shorthand and long form, through spreads, nested records,
arrays of records, annotated locals and literal arguments to typed
parameters.
A worker's messages and its uncaught 'error' event reach the parent on
separate channels in Node, so their relative order is not specified and
can differ under load. The fixture now records both and reports them when
the worker exits, which Node and native executables deliver after both.
Concurrent builds of different entries with the same file name share
the default .ll path in a common output directory. The helper read that
shared file in place, so one build could compile the other program's
LLVM text. The helper now always reads a private copy written in large
batches, as before partitioning.
The partition debug-information test also matches the Mach-O
__debug_info section name, so it checks the same property on macOS.
Malte Ubl