[JSC] Bytecode cache: lay the modules of a link out in one payload by an order file - #718
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…aid out by an order file BytecodeLinkEncoder takes every module of an embedder's link and writes ONE payload in regions: the heads (cache entry, key, top-level code, its functions' records) of the modules a recorded run evaluated or did not know, the function bodies that run decoded in the order it first decoded them, the heads of the modules it knew and did not evaluate, all other bodies in source order, and last the expression info. A region is complete before the next one starts, so every offset is final when it is written: references back are plain deltas, and a function record's body slots and a code block's expression-info slot are filled in when their target is written, as in a single-module payload. Array and string-content sharing are link-wide as a consequence. Collections are deferred while a link is open: queued bodies hold function code blocks that an executable may otherwise drop. A function is identified by bytecodeOrderSourceHash: a hash of its source text with identifiers, numbers and string contents collapsed and whitespace dropped, so the identity survives a minifier's renames and names no module. A module's cache entry may now start anywhere in its payload (CachedBytecode::entryOffset); every offset a Decoder keeps stays relative to the start of the payload. Every module's entry records the size of the whole payload, set when the link is finished, so a span shorter than that is a miss for each of them as it is for a payload of one module. EncoderStringTable::serialize can put the records of given strings first; the offsets array stays indexed by ordinal. Without an order file nothing changes: the per-module encoder is what runs and its output is byte for byte what it was.
…ayloads
With PersistentBytecodePayloads::enableOrderRecording and
DecoderStringTable::enableFirstUseRecording a VM remembers, in first-use order,
each function whose code it decoded from a persistent payload (not the
embedder's builtins), each module whose cache entry it decoded and each string
table record it read. bytecodeOrderFileContents renders that as the text of an
order file ("v1", then "F|M|S <hash>" lines) for the embedder to write;
BytecodeLinkEncoder consumes the same hashes. Nothing is recorded, hashed or
allocated unless recording was enabled: the lazy-decode path and the string
table's record() gain one predictable branch each.
… layout against another Decodes everything a payload holds for a source (every function, however deeply nested, without generating any, and each block's expression info) and digests, in tree order, each block's instructions, constant count, identifiers and expression info size. Two payloads of the same source decode to the same digest however they are laid out, which is how a BytecodeLinkEncoder payload is checked against the per-module ones.
… build did not have into a region of their own An order file may list, besides the functions its run decoded, the other functions its build had (appendHashesOfAllCachedFunctions lists a payload's). A function in neither list is new or changed since the recording: nothing is known about it, and the functions a program runs at startup are the ones that change. Their bodies go into the UNKNOWN region, right after the HOT one, in source order, instead of among the COLD bodies, where each one a run decodes costs a page of its own. Of the functions nested in an unknown function, the ones the run decoded stay with it (the HOT region is complete by then) and the ones it knew and did not decode are COLD. Without such a list there is no UNKNOWN region, as before.
…order of the code it belongs to The last region of a linked payload was written in the order the code blocks were encoded. It is now ordered like the regions before it: the expression info of the evaluated modules' top-level code, of the HOT bodies in their order, of the UNKNOWN bodies, of the other modules' top-level code and of the COLD bodies, so that the position tables a run reads (those of the code that throws) lie as close together as that code does. Arrays equal to an earlier one are still shared, and the first writer is now the hottest user.
A BytecodeOrderRecorder is thread-safe, stays registered for the life of the process and keeps what it names alive (source providers; strings are ordinals into the string table's bytes), so the thread that writes the order file sees what the VMs of Workers read too, whether or not they are still running. bytecodeOrderFileContents renders all of them, the first VM's first.
…of a link BytecodeLinkEncoder::addBuiltinFunction takes what encodeBuiltinFunction takes. The builtin's cache entry and its function's record are a head like a module's, and its body and the functions nested in it are placed by the order file like any other, by the same source hash. decodeBuiltinFunction reads the entry at the CachedBytecode's entry offset and counts as evaluating the builtin's source for a recording, and a recording lists builtin functions decoded from a payload with the rest.
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Preview build of f74048b: |
…he words with its first letter bytecodeOrderSourceHash compared every identifier-like run of up to ten characters with all 43 reserved words. It is called for every function of a link, and once per function of an executable when an order file is written, over the function's whole text including the functions nested in it. The hash values do not change.
… deferring GC; review fixes - A link no longer holds a DeferGC for its whole life. Explicit collections ignore the deferral depth, and a DeferGC inside a heap object ties the VM's deferral count to that object's lifetime. Every function code block of a module is rooted from addModule()/addBuiltinFunction() until the link ends instead. BytecodeLinkEncoder::vm() lets the embedder check it uses an encoder on the VM it was made for. The shared string table is required. - One enum names the regions (BytecodeLinkRegions); Encoder::LinkClass is defined from it and finish() closes a region where it writes it. - Hashes that come out of an order file are checked before they go into tables whose key traits reserve two values. - BytecodeOrderRecorder: ifRecording(VM&) replaces three copies of the lookup; modules are recorded once; PauseScope keeps digestOfAllCachedCode and the appendHashesOf... helpers, which decode everything, from being recorded as use; a VM has one string table while it records. - An order file's string hashes come from the table's records, without creating a string for each. - cacheEntryOf<Entry> checks the size and the alignment of a module's and of a builtin function's entry alike. - The recorder's users are under USE(BUN_JSC_ADDITIONS) like the recorder.
…ed payload by region The embedder tells a VM which persistent payload was written by BytecodeLinkEncoder and where its regions end (PersistentBytecodePayloads::setLinkedPayload). From then on every function code block decoded out of that payload is counted, with the bytes of its own arrays and record, under the region it lies in: HOT, UNKNOWN or COLD. This tells a program how well the order file its executable was built with still matches what it runs. Per VM. Where the code block is decoded the record's offset is already known; a VM without a linked payload pays one pointer compare.
…inding's name are keywords The hash collapses every name to one character because a minifier hands names out afresh in every build. With thousands of bindings in a scope it gets to `of`, `as`, `get`, `set`, and the table treated the contextual keywords as themselves: a binding renamed from `oe` to `of` changed the identity of every function that mentions it. `let`, `static`, `yield` and `await` stay: in module code they are reserved, and a minifier never assigns them.
…d functions not counted A function was named by the hash of all of its text. Writing an order file hashed every function's text once per enclosing function (3.5 s at the exit of a recording run of a large program, and as much again in every build laid out by an order file), and an edit renamed every function around it up to the module. bytecodeOrderHash(source, codeBlock) hashes the text with each function of the code block counted as one token, so all of a program's text is hashed once and an edit renames the innermost function around it only. A module or program is named the same way by its top-level text. The function that initializes a class's fields has the text of the whole scope the class is in: it is named by the fields it defines (not by the spelling of private names, which a minifier changes), and is not a nested range of that scope. A template literal is one token plus one for each function in it; other tokens stop at the next nested function, so a quote inside a regular expression cannot swallow one. The recorder keeps hashes instead of source providers and ranges: they are computed where the code is decoded, and nothing of a VM has to stay alive for the order file. ifRecording() is null while a PauseScope is alive. A builtin function is named when it is decoded, which takes its code: it is recorded as module and as function there. appendHashesOfAllCached(Builtin)Functions also return the module's hash and skip functions without code. bytecodeOrderSourceHash is no longer exported.
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Included review availability: 1 review is currently available. Your included PR review attempts over the past 7 days set your current allowance at 3 reviews per hour. WalkthroughThe change adds Bun-gated bytecode-order recording, normalized hashes, cached-code digests, and linked payload encoding. Cache entries now support shared-payload offsets, validated decoding, and linked-payload statistics. ChangesBytecode Order and Linked Payloads
Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to The incremental exception-handling change presents no identified merge-blocking risk. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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…e names of the functions nested in it Naming a function by its own text alone made one name of all functions that differ only in what is nested in them, so a hot function's twins were laid out hot with it. The name is now a hash of the function's own normalised text with, in the place of each function written directly in it, that function's name: two functions differ by anything written anywhere in them, as when all of their text was hashed, and every character is still read once per link (OrderIdentities, memoised per executable). Such a name takes the code of everything nested in the function, which a program that decodes lazily does not have. So a recorder no longer names anything while the program runs: it remembers where the record of the decoded code is in its persistent payload (one store under a lock instead of a hash of the function's text). When the program is done the embedder hands every payload to BytecodeOrderFile, which decodes each in full, names everything and prints what the recorders saw decoded as "F"/"M" lines and the rest as "K"/"N" lines. bytecodeOrderFileContents() and appendHashesOfAllCached*Functions() are gone, as is the hook in UnlinkedFunctionExecutable::unlinkedCodeBlockFor. BytecodeLinkEncoder::Result::matchedHotFunctions: how many of the order file's hot functions are functions of the link, so that an embedder can say when a file fits nothing of the program. A module's code is rooted before the module is named.
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Beyond the inline finding, I also checked the RELEASE_ASSERT in BytecodeOrderRecorder::didReadString (CachedBytecode.cpp:111) for a crash when a second DecoderStringTable of the same VM enables first-use recording — that is the documented one-table-per-recording-VM contract in CachedTypes.h, enforced deliberately rather than a latent bug.
Extended reasoning...
The change adds ~1260 lines under USE(BUN_JSC_ADDITIONS) across CachedBytecode., CachedTypes. and UnlinkedFunctionExecutable.*: a process-wide order recorder, source-hash function naming, order-file rendering, and a multi-module link encoder with six payload regions. It touches no auth, injection or data-exposure surface, but it is a large, cross-thread, GC-rooting-sensitive bytecode-cache layout change with no tests in this diff. One verified finding is posted inline (builtin payload hot functions lost from the order file), which by itself rules out approval; the didReadString single-table assert was examined and ruled out as an explicit embedder contract.
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In `@Source/JavaScriptCore/runtime/CachedTypes.cpp`:
- Around line 4583-4586: Gate the BytecodeOrderRecorder recording calls in the
function decode path and the module paths in decodeCodeBlockImpl and
decodeBuiltinFunction on decoder.canBorrowPayload(), so only persistent payloads
are recorded; leave decoding behavior unchanged.
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… the program, and only persistent payloads are recorded BytecodeOrderFile::addBuiltinFunction decoded through decodeBuiltinFunction with recoverable code, so the pass registered a slot of the VM's persistent payloads, and one created for the program's own provider would have handed the pass the program's executables (takeChildExecutables), whose code was decoded before the pass could learn where it is: the recorded function would be listed as not decoded. decodeBuiltinFunction takes a Decoder::RecoverableCode; the naming pass and digestOfAllCachedBuiltinCode pass No, as the module paths already did, which also keeps them out of the VM's per-region decode counts. A recorder knows code by the address of its record, so it records code of persistent payloads only (Decoder::canBorrowPayload): the bytes of any other payload can be freed and their addresses used again. contents() counts the records a recorder saw, inside a payload that was added, that got no name. It asserts there are none, and says so in a "#" line of the file otherwise (readers ignore lines of unknown kinds).
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Inline comments:
In `@Source/JavaScriptCore/runtime/CachedTypes.cpp`:
- Line 5898: Move payload registration in addModule and addBuiltinFunction until
after decoding and validation succeed: retain each cached bytecode span locally,
call didAddPayload only after decodeCodeBlockImpl returns a code block or
m_impl->add returns an identity, and return before registration on failure.
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…at were added BytecodeOrderFile::addModule and addBuiltinFunction noted the payload's bytes before the payload had decoded, so a payload that is not the source's still counted as added and any record of it a recorder had seen was reported as missing a name (the assertion in contents(), or its "#" line). The bytes are noted once the add has succeeded. addBuiltinFunction gave up on a builtin whose function has no code after decodeBuiltinFunction had succeeded, which is when a running program records the builtin as a module: that record had no name. The module is now named whether or not the function has code, the way the link encoder names it.
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…nkedCodeBlock throws
tryCreate returned nullptr as soon as getUnlinkedCodeBlock() came back null, which is how a syntax error comes back, and
so left its ThrowScope with an exception nobody had checked: a process running with validateExceptionChecks aborts there
("Unchecked JS exception", getUnlinkedCodeBlock / tryCreate). It takes a module whose source first fails to compile at
this point, such as one an embedder supplies analysis for (so nothing parsed it earlier) and no bytecode. The exception
is checked right after the call, as ScriptExecutable does; every null return of getUnlinkedCodeBlock throws.
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…rding ends when its file is written A link writes a function's record long after the function's module was added (with the body of the function around it, or when the link is finished), from what the executable holds then. VM::deleteAllCode, VM::shrinkFootprintNow and whoever else goes through Heap::deleteAllUnlinkedCodeBlocks empty executables, which no root prevents, and the payload then silently lacks those bodies (with a hook that deleted all code before finish(): 6 of 11 code blocks left). A recorder knows code by where it was decoded from, and a run that records should decode a record once, in the order the program first needs it. So a VM can be asked to keep its unlinked code (VM::keepUnlinkedCode, a count): a BytecodeLinkEncoder asks for as long as it lives, a BytecodeOrderRecorder for the rest of its VM's life. While anybody asks, Heap::deleteAllUnlinkedCodeBlocks neither clears executables nor returns code to its cache, ScriptExecutable::clearCode leaves a program's or module's top-level unlinked code, and the code cache is written but not emptied. Linked code is dropped as ever, and one branch on paths that are cold is all it costs a VM that neither links nor records. Code that ages out in a collection is not affected: a link roots every function code block, and code decoded from a cache never has the weak edge. Code that has to be generated differently (a debugger attached, a profiler turned on) is not held back: VM::deleteAllCodeToGenerateItAgain, used by Debugger::recompileAllJSFunctions and the inspector's profiler switches. In debug builds a link asserts that a function that had code when its module was added still has it when its record is written; nothing is added to a link after finish(). BytecodeOrderRecorder::PauseScope is gone. Its users (naming what a recording saw, which decodes everything; the digests; reading a class's field definitions while naming) only ever run when the recording is over, so recording simply ends when its file is written: creating a BytecodeOrderFile stops every recorder of the process.
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…d3140 The preview includes the ModuleProgramExecutable::tryCreate exception-check fix, so the failed-bytecode compile test runs with exception-check validation again.
…codes The link takes, with each module, the module's name and a sorted table from (function start, kind) to name, borrowed for the add call; the recorder reports raw events (payload, entry offset, start, kind), notes modules whose bytecode was rejected, and names nothing. Taking the recording ends it for the process. The source normaliser, its keyword table and the exit-time naming pass are gone. A function's place is decided when its module is added: COLD inside COLD or unevaluated code, else by its own name. A HOT function inside an UNKNOWN one is written ahead of its record, which points back at it. Encoder::DeferredBody replaces the Function<void()> of a deferred body. What should not happen during a link degrades to COLD instead of aborting the build.
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…ding is taken The recording is taken on whichever thread the embedder chooses, so the VM's keep is the recorder's flag (VM::keepUnlinkedCodeUntil) rather than a count only the VM's thread may touch: it ends for every VM the moment the recording does. A VM lets go of its recorder the next time it would record, and a recorder that is over returns before taking its lock.
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…UT, bytecodeOrderStats()) (#43811) ### What does this PR do? A `--compile --bytecode` executable maps its bytecode from disk and decodes functions lazily, so the pages it touches at startup are scattered over the whole payload: a large application keeps most of its bytecode resident after reading a small part of it. This adds order files: ```sh bun build --compile --bytecode ./app.ts --outfile myapp BUN_BYTECODE_ORDER_OUT=./myapp.order ./myapp # record what a run reads; written at exit (%p = pid) bun build --compile --bytecode --bytecode-order=./myapp.order ./app.ts --outfile myapp ``` also `Bun.build({ compile: { bytecodeOrder: string | string[] | false | null } })` (`false`, `null`, `[]` = none; several files are merged, first file first). There is no environment variable for consuming one. Requires oven-sh/WebKit#718. How it works - Order file: text, `v2`, then `F <hash>` function decoded to be run, `S` string read (both in first-use order), `M` module evaluated, `N` module present and not evaluated, `K` function present and not run. No source in it. A byte order mark and blank or `#` lines before the version line are skipped; malformed lines are ignored; a missing file is a build error; an unusable one (other version, UTF-16, lists nothing, none of its functions in the build) is a warning that says why. - Names are computed by Bun, not JavaScriptCore: `src/js_parser/function_identities.rs` parses the PRINTED chunk (parse only, no visit) and hashes each function's syntax. Locals, labels and private names are numbered by declaration, captured bindings by frame depth and index, module-level bindings by first mention, so minifier renames do not matter; property names and numbers count; the property a function is the value of is part of its name (`{ a: () => a, b: () => b }` are two); string VALUES and the paths chunks import each other by are left out (they change with every build); a nested function contributes its own name; a default constructor is named by its class's members; what is nested deeper than a fixed count in ONE function is a fixed tag. Nested functions are walked from a worklist, so nesting depth costs no stack. The parser records the three starts JavaScriptCore uses that are not AST locations (async arrow parameters, class element, expression body). - The same walker runs in the build (names handed to `JSC::BytecodeLinkEncoder` as `(start, kind) → name` tables) and in the recording run at exit (JavaScriptCore reports raw `(payload, entry offset, start, kind)` events; Bun names the text the executable embeds). Taking the recording ends it, so `BUN_BYTECODE_DIGEST_OUT`'s decode-everything pass is not recorded. A module whose bytecode the runtime rejected is listed neither as evaluated nor as not. A text that does not parse gets no names, with a warning; the file is written through temp + rename. - With an order file the linker writes ONE payload in regions: heads of evaluated modules · HOT · UNKNOWN (new or changed since the recording) · heads of never-evaluated modules · COLD · expression info; startup read-ahead covers the front through HOT. Internal modules are modules of the link too. `bytecodeOrderStats()` in `bun:jsc` returns decodes per region and region sizes (`null` without an ordered payload). - Without an order file the build path is the old one and the executable's module graph is byte-identical. Measured on a large compiled TUI application (≈2,000 chunks, ≈142k functions, 82 MB of bytecode), linux x64, 64 KB fault-around, n=3, MB of the embedded payload resident: | | at its idle prompt | after one interaction | decodes after the interaction (hot / unknown / cold) | |---|---|---|---| | no order file | 59.5 | 62.3 | | | order file from the same build | **20.5** (20.0–21.1) | **25.9** | 18,274 / 0 / 12 | | order file from the previous day's build | **23.2** (23.0–23.4) | **28.1** | 18,085 / 171 / 28 | Two merged entry points were measured with the previous naming scheme only (21.0 / 26.3; the second entry point 61.8 → 25.6 MB). Cold start to the first prompt (page cache dropped for the executable only, n=6 interleaved, final binary; median [min–max]): | | first prompt | major faults | read from disk | RssFile at the prompt | |---|---|---|---|---| | main | 1.01 s [0.96–1.12] | 598 | 76 MB | 105 MB | | no order file | 0.99 s [0.97–1.16] | 606 | 76 MB | 104 MB | | order file from the same build | **0.53 s** [0.48–0.57] | 185 | 22 MB | 65 MB | | order file from the previous day's build | **0.55 s** [0.52–0.68] | 202 | 24 MB | 68 MB | Warm start: main-thread instructions equal to main (1212 M vs 1208 M, n=5). A recording run's exit: 0.011 s → 0.25 s. The application's full build, n=3 interleaved on a shared box (load average 45–64 of 64 cores), final binary: | | wall | user CPU | peak RSS | |---|---|---|---| | main | 2:49 2:44 2:38 | 168–173 s | 4.93 GB | | no order file | 2:47 2:44 2:40 | 170–175 s | 4.89 GB | | with the same-build order file | 2:53 2:43 2:44 | 174–182 s | 5.37 GB | Wall time is unchanged (median 2:44 in all three); an order file costs about 3 s of CPU (naming on up to 8 threads, placement) and +0.47 GB peak RSS, because unlinked code stays alive until the payload is written. Normal parses pay three `Option` branches for the recorded starts. The recording lists 16,971 run and 104,894 not-run functions, no function without a name. ### How did you verify your code works? - No order file: executables byte-identical across builds (byte-identical to a build from main was checked earlier on this branch, on the large application and a 360-module test app); same order file: byte-identical executables. - `BUN_BYTECODE_DIGEST_OUT` (decode ALL embedded bytecode, one digest per module): unordered == same-build order file == day-old order file on the large application (2,104 modules, 149,415 code blocks, 0 undecodable), and in the tests. - Round trips (build → record → rebuild → run): an all-syntax fixture that runs every kind of function JavaScriptCore compiles (hashbang, non-ASCII banner, a JSON chunk without bytecode): 0 unknown, 0 cold, no unnamed function; sloppy CommonJS; `Bun.ModuleGraph` modules; a build whose SHARED chunk is edited between recording and layout: a second recording shows exactly one function and one module renamed; typescript.js (21.5k functions): 1,541 hot / 0 unknown / 0 cold; rejected bytecode (patched executable, Linux). - The invariant "build and run derive identical names from identical inputs": every round trip sets `BUN_BYTECODE_ORDER_NAMES_OUT` for the build and for a recording run of the same executable and asserts the two dumps EQUAL (module name and every start, kind, name, for every chunk and internal module): single chunk, `--splitting` with an entry in a subdirectory, CommonJS, `--minify`, a non-ASCII banner. - Unit tests of the walker through `bun:internal-for-testing`: renames (bindings, labels, private names, minifier), string edits, property keys, class fields and static blocks, default constructors, 600 nested arrows, 200,000-term expressions, two hand-derived golden hashes. - 42 order-file tests pass on release and on debug + ASAN with `BUN_JSC_validateExceptionChecks=1`; the new ones fail on the previous binary. Limitations - An order file's names come from the walker of the Bun that built the recording executable. A Bun upgrade that changes what the walker hashes bumps the order-file version (`v2` → `v3`), so a stale file is rejected with "was recorded by another version of Bun: record it again" instead of silently matching nothing; two hand-derived golden hashes in the tests are the tripwire for an accidental change. - A name follows the bundler's PRINTED output: platform/`define` differences and printer or minifier upgrades re-name the code they touch (it lands in UNKNOWN, next to HOT); record and build with the same minify settings. Functions with identical syntax share a name and hotness. - Not ordered: the prelinked module graph and module-info tables, source text. Expression info is ordered by code, not by what throws. - Run on linux x64 only locally (CI runs the round trips on every platform). A Windows-target build cannot be run on Linux: the test asserts that it names every chunk and internal module exactly as the host-target build does. A public path does not reach a compiled executable's chunk import paths (CLI or `Bun.build`), so there is no such variant to test. --------- Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
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[JSC] Bytecode cache: one payload per link, laid out by an order file the embedder names
What: an embedder that serializes many modules at once (
bun build --compile --bytecode) can encode them into ONE payload whose layoutfollows a recording of a previous run, so that what a program decodes at startup is contiguous in the file instead of spread over every
module's blob. JSC does not name code: the embedder does, and JSC places by those names and reports what it decodes.
How it works
BytecodeLinkEncoderowns oneEncoderfor the whole link. Regions are written to completion in file order: heads of evaluated modules ·HOT function bodies (recorded order) · UNKNOWN bodies (functions the recorded build did not have) · heads of modules known not to be
evaluated · COLD bodies (source order) · expression info. Every pointer is written once with its final value; no relocation pass. Array and
string sharing become link-wide. Every module's
CachedBytecodeis the shared payload plus anentryOffset.addModule/addBuiltinFunctiontakeBytecodeOrderNames: the module's name and a sorted table fromOrderFunctionKey { start, kind }to a 64-bit name, borrowed for the length of the call.startis the offset JSC itself keys a functionon in its linked source;
kindtells apart what may share a start (the function, the inner body of a generator or of an async function thatawaits, a class's field initializer, a default constructor).
Hintscarry the recorded names: hot functions in order, known functions,hot strings, evaluated and not-evaluated modules.
Resultreports how many hot names matched, how many functions went to HOT, and how manyfunctions of named modules have no name (an embedder warns on the first being zero or the last being non-zero).
that merely looks like a hot one, in code the run never reached), otherwise by its own name: HOT if recorded, UNKNOWN if the recorded
build did not have it. A HOT function inside an UNKNOWN one is written ahead, in HOT, and its record, written later, points back at it
(
Encoder::DeferredBody, which also replaces theFunction<void()>a deferred body used to be).BytecodeOrderRecorder(per VM, off unless the embedder enables it) reports raw events and names nothing:(payload, entry offset)of thesource,
(start, kind)of each function decoded in order to be run, each module decoded, each module whose bytecode was rejected (it ranfrom source, so the recording says nothing about it), and string-table ordinals read, all in first-use order.
bytecodeOrderRecording()merges every VM of the process and ends the recording for the process, so that a later decode-everything pass is not taken for the program.
VM::keepUnlinkedCode) while a link is open, because a function's record is written long after its module wasadded, and while a VM records, so that a recording does not depend on when the collector runs. The encoder roots every queued code block;
it does not defer GC.
complete) degrades to COLD and is counted, instead of aborting the embedder's build.
PersistentBytecodePayloadscounts function bodies decoded from HOT / UNKNOWN / COLD of a linked payload, for hit-rate metrics.OrderIdentities,BytecodeOrderFileand the exit-time pass that decoded all code to name it.
Costs
compiled TUI application to its first prompt: main-thread instructions equal to main within noise (1212 M vs 1208 M vs 1209 M ordered, n=5).
file, 0.55 s with a day-old one; major faults 598 -> 185 / 202; 76 MB -> 22 / 24 MB read. Its full build: wall time unchanged (median
2:44 with and without an order file, n=3), about 3 s more CPU, +0.47 GB peak RSS (unlinked code is kept until the payload is written).
encodeCodeBlockoutput is byte-identical.Validation (numbers and the table are in the Bun PR, oven-sh/bun#43811)
ordered payload and per-module payloads (2,104 modules, 149,415 code blocks on a large compiled TUI application, same-build and day-old
order files); output without an order file is byte-identical; output with one is deterministic.
(21.5k functions: 1,541 HOT / 0 / 0) and for a large compiled TUI application (18,274 / 0 / 12).
Limitations