The read-only bag accessors made each tracked-field read site a nested
ternary with two accessor calls, and each method probe evaluated the bag
twice. Large JavaScript programs have a branch per class and property
(and per-class key tables copy the computed fallback), so three.js grew
from 703 MB to 946 MB of IR and its in-process compile ran out of the
2 GB worker heap in CI.
Move the absent-bag handling into shared helpers instead:
%dyn.class.readPropertiesOrEmpty is rebuilt in finalize like
%dyn.class.readProperties but returns a fresh, unstored empty object for
an instance without a bag, and %dyn.class.bagHas/bagHasComputed test a
key on a possibly undefined bag. Every read site is one call again, and
the three.js IR is back to 719 MB (2.16 GB peak RSS, main 2.15 GB).
The read-only bag accessor returns the receiver itself for non-instances,
so an undefined bag can also mean an undefined receiver. Substitute the
empty bag only for instances: a read through undefined must still throw
Node's "Cannot read properties of undefined" TypeError (1544, 2162, 2449,
js-optional-class-fields).
A class instance keeps its own dynamic properties in a lazily created bag
(`%dynProperties`). Untyped reads went through the bag accessor that
creates and stores the bag on first use: selecting a method checks the bag
for an own property shadowing it, and the named and computed fallbacks,
`in`/own probes, Reflect.get, for-in and accessor reads all looked their key
up there. So a pure read stored into the object. On a published object the
frozen-object guard rejects that store with "Cannot assign to read only
property '%dynProperties'", where Node reads without error.
Read-only bag accessors now never store. The untyped
%dyn.class.readProperties is rebuilt from the settled bag dispatch without
its lazy stores, and typed read helpers return a prototype-backed bag
instead of storing it. Every read path uses the read-only accessor: key
tests treat an absent bag as having no own keys, and lookups that must see
Object.prototype read from a fresh, unstored empty object. Writes keep the
storing accessor.
Found with tsc-ts at --checkers 8 on vercel/eve: a checker thread read
`host.commonSourceDirectory()` through an untyped interface value whose
object is the published Program.
Integer induction counters live in unsigned 64-bit slots, so every read
as a number was a uitofp i64 (a 6-7 instruction sequence on x86-64) and
every nested start an fptoui. The runtime's push path also round-tripped
the array length through a double for its bound check.
The values are at most 2^32 - 1: on 64-bit targets convert counters with
sitofp and loop starts with fptosi, convert array lengths and validated
indices through int64_t in scr_array.c, and test the push bound on the
integer length. 32-bit targets keep the unsigned conversions.
tsc-ts Excalidraw: uitofp i64 sequences 32.5 M -> 4.0 M, -0.66%
instructions on top of the throw-path change.
With runtime bitcode import, scr_throw_obj, scr_error_new and the other
throw entry points were inlined into the error paths of small compiled
functions. The inlined bodies needed callee-saved registers that every
call then saved and restored, and they made the helpers too large to
inline into their callers (1047 inlined throw bodies in tsc-ts).
Mark the 25 functions that only run while raising a JS exception
cold and noinline. The LLVM helper never imports noinline bodies, so
the throw paths stay calls. tsc-ts Excalidraw: -0.44% instructions.
Every SCR_ELEM_REF array stored its element type's retain, release and trace entry points in its own header (24 bytes), so ScrArr was 80 bytes: an 80-byte block for arrays of acyclic elements and a 96-byte block for cycle-capable ones. The three pointers now live in one constant ScrArrOps descriptor per element type, which the compiler emits once per module (@sc_arrops.*) and the runtime keeps static, and the header holds a pointer to it plus a 4-byte `cyc` flag beside `elem` that the inline RC fast paths test. ScrArr is 64 bytes: arrays take 64- and 80-byte blocks.
scr_arr_new_ref(retain, release, trace, cap) becomes scr_arr_new_ops(ops, cap); scr_set_to_arr_ref takes the result's descriptor from its caller instead of building an array from the set's key adapters. The backend names the %ScrArr fields in SCR_ARR_FIELD. The layout change bumps the runtime ABI marker to scr_runtime_abi_v13.
Malte Ubl