perf(codegen): inline probes before the typed-feedback method + field guards (typed-param receivers 118.6→3.8 ns) - #9124
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Included review availability: Your plan provides up to 8 included reviews per hour; 1 remains after this review. 📝 WalkthroughWalkthroughThe codegen now supports an environment-controlled inline shape probe for eligible monomorphic method calls. Probe misses enter the existing runtime guard. Build caching includes the new environment variable, and regression coverage accepts either proof location. ChangesMethod direct-call probe optimization
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The change lets proven method calls bypass the per-call runtime guard while preserving fallback behavior for probe misses. It is mergeable with owner awareness of receiver rooting across argument lowering and the kill-switch’s process-local caching behavior, which could affect correctness or rollback consistency if those assumptions are violated. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Sites that own a typed receiver clone set shape_only_guard=false and so paid js_typed_feedback_method_direct_call_guard on every call — whose contract check takes an RwLock read plus TWO SipHash HashMap probes (vtable_method_matches) — while less-typed sites got the inline shape guard. On a typed-parameter receiver (the shape every real codebase passes around) that was 125-390 ns per monomorphic c.inc(). PerryTS#9105's dispensation applied to method sites: normal builds collect no typed feedback, so the guard's observation half is inert. Decide the monomorphic case with the SAME inline probe the shape-only sites emit (class_id + ShapeId + prototype-override latches — exactly what shape-only direct dispatch already trusts for this method body) and keep the runtime guard as the probe-MISS edge, so subclass receivers, forwarded objects and monkey-patched prototypes take exactly today's path. Emission-enabled builds keep the guard first. Kill switch: PERRY_METHOD_INLINE_PROBE=0. Host-shape matrix (dev box, kill-switch pairs): fn-hosted typed-param receiver 125.3 -> 13.5 ns (-89%), arrow-hosted captured receiver 125.6 -> 13.8 (-89%); proven-local receivers flat at 4.6. Semantics differential (subclass through base param, virtual override, mid-program prototype monkey-patch, own-property override, annotation lie): ON == OFF byte-for-byte. Claude-Session: https://claude.ai/code/session_01F1dt1jfzK2cheMZyus6y6p
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In `@crates/perry-codegen/src/lower_call/method_override.rs`:
- Around line 1053-1058: Update the recv_box validation in
emit_inline_direct_method_shape_guard so untagged values are rejected before any
dereference, requiring the 0x7FFD pointer tag or an equivalent proof of the
raw-pointer ABI; preserve valid tagged raw-pointer handling and ensure crafted
positive subnormal IEEE-754 values cannot reach the obj_ptr - 8 load.
- Around line 1059-1060: Update try_lower_instance_method_call to root recv_box
before lowering call arguments, then re-read the rooted receiver after argument
lowering and before the probe/collecting calls, including the fast_label and
typed clone paths. Ensure Expr::New receivers retain valid heap references when
probe_before_runtime_guard or argument evaluation can collect.
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crates/perry-codegen/src/lower_call/method_override.rscrates/perry-codegen/tests/native_proof_regressions.rs
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| emit_inline_direct_method_shape_guard( | ||
| ctx, | ||
| recv_box, | ||
| &expected_class_id_str, | ||
| &expected_shape_id, | ||
| &method_guard_slot_str, |
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🔒 Security & Privacy | 🟠 Major | 🏗️ Heavy lift
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Denial of Service (CWE-822)
Reachability: External · Exploitability: Difficult
Reject untagged recv_box values before dereference.
Expr::Number uses raw IEEE-754 bits, while the helper treats a zero upper word as an internal raw pointer. A crafted positive subnormal can therefore produce an in-range address and reach the obj_ptr - 8 load before the runtime guard. Require the 0x7FFD pointer tag or another proof of the raw-pointer ABI.
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In `@crates/perry-codegen/src/lower_call/method_override.rs` around lines 1053 -
1058, Update the recv_box validation in emit_inline_direct_method_shape_guard so
untagged values are rejected before any dereference, requiring the 0x7FFD
pointer tag or an equivalent proof of the raw-pointer ABI; preserve valid tagged
raw-pointer handling and ensure crafted positive subnormal IEEE-754 values
cannot reach the obj_ptr - 8 load.
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Analysed rather than changed: the receiver-before-arguments lowering with no re-read is the direct-method tower's pre-existing structure (dynamic_dispatch.rs: recv_box lowered, then each arg), and the same recv_box SSA value already feeds both the runtime typed-feedback guard and the shape-only inline guard. All of them — including this probe — test the GC header's forwarded bit and reject a moved receiver, falling to the runtime guard, which resolves forwarding as it always did. So the probe-first edge introduces no new window relative to the two existing consumers; making the whole tower root-and-re-read its receiver across argument lowering would be a separate change to shared structure, and I'd rather not fold it into this PR.
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@proggeramlug, thanks for the analysis. It addresses receiver lifetime and forwarding. It does not address this finding.
The inline guard accepts tag == 0 before it reads obj_ptr - 8. Mainstream targets accept low addresses from 0x10_0000 to 2^47 or 2^48. A JavaScript Number can have a positive subnormal bit pattern in that range with tag == 0.
The runtime guard is not equivalent here. Its gc_header_for_user_addr path calls is_valid_obj_ptr before it reads the GC header. The inline guard has only a range check. Therefore, it can dereference an unmapped address before it reaches the forwarded-bit check.
Please either reject tag == 0 in this source-level recv_box path or add a separate, explicit proof that the value uses the internal raw-pointer ABI. The receiver root-and-re-read change is independent of this fix.
✏️ Learnings added
Learnt from: proggeramlug
Repo: PerryTS/perry PR: 9124
File: crates/perry-codegen/src/lower_call/method_override.rs:1053-1058
Timestamp: 2026-08-30T04:34:19.593Z
Learning: In `crates/perry-codegen/src/lower_call/property_get/dynamic_dispatch.rs`, direct-method lowering evaluates `recv_box` before call arguments. The direct-method tower shares this `recv_box` SSA value with both typed-feedback runtime guards and inline shape guards. These guards reject a forwarded receiver and route the miss to runtime dispatch, which resolves forwarding.
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🧠 Learnings used
Learnt from: proggeramlug
Repo: PerryTS/perry PR: 7192
File: crates/perry-codegen/src/expr/index_set.rs:1482-1494
Timestamp: 2026-08-01T16:10:48.388Z
Learning: When lowering a non-literal string or symbol key before a potentially collecting RHS, use StoreOperandGuard/guard_store_operand, re-read the key after RHS lowering, and release the key guard before the receiver guard when both are present. Because temporary-root releases truncate slots above their index, release nested guards from inner to outer. In crates/perry-codegen/src/expr/static_field_meta.rs, release the symbol-key guard during each static-property iteration because js_object_set_symbol_property may invoke user setter code.
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Second commit pushed: one inline field precheck (the field-GET sites' |
codegen_env_vars_are_build_cache_inputs was red: the knob selects between the inline shape probe and the typed-feedback runtime guard, which emit different call sequences, so a cached object from one must not serve the other.
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Merged, with one commit added: Correctness: zero delta, which is the right answer for this change. A/B against main across 23 method-dispatch shapes — every single row identical between main and this PR:
Seven of those 23 disagree with node — cases 7, 8, 12, 13, 14, 16, 19 — but they disagree identically on main, so they are pre-existing and not this PR's doing. The monkey-patching ones (7, 8) are worth their own issue: What I could not do: reproduce the speedup. My typed-parameter fixture measured 1.00x (876 vs 875 ms), so before reporting that I diffed the emitted IR between arms — 0 lines differ, and So The flip side is genuinely reassuring: on every shape I could build, this PR is a byte-for-byte no-op in the emitted IR, so its blast radius is confined to sites I couldn't reach. Validation: codegen 1349 passed, runtime 2822 passed (exit 0, 0 abort markers), perry --bins 1066 passed, fmt clean, |
…lls + probe review fixes Follow-up to PerryTS#9124, which merged with the method-direct probe only. This carries the second half of that lever plus the review fixes: 1. With the method probe in front, the probe-first c.inc() loop was ~80% js_typed_feedback_class_field_get_guard: per receiver field, per call, it re-derived facts the exact (class_id, ShapeId) pair already pins (live slot count, key-at-slot) through a shape_descriptor_by_id lookup plus the raw-f64 layout contract. The field-GET sites already emit emit_class_field_inline_precheck ahead of that guard (class/shape + not-forwarded + the per-OBJECT raw-f64 intact bit). Because the intact bit is object-wide, ONE precheck vouches for every receiver field at once; its miss edge runs the unchanged per-field runtime chain, whose i1 result joins at a phi. Same kill switch (PERRY_METHOD_INLINE_PROBE=0), same emission-off gating. Mini pairs: typed-param receiver 12.8 -> 3.8 ns, captured receiver 13.1 -> 3.8; proven-local rows flat at 4.4 — zero runtime calls per iteration (sample: 100% in the generated fn). 2. Review (PerryTS#9124): emit_inline_direct_method_shape_guard takes accept_raw_ptr. Probe-first sites pass false — a user NaN-box receiver must carry the 0x7FFD tag before any dereference, so a plain double whose bits land in the heap range (a positive subnormal) misses to the runtime guard instead of reaching the header load. The pre-existing shape-only site and versioned_indexed_loop.rs keep raw acceptance. 3. The typed_f64_receiver IR-shape test measured both proofs by the runtime guards' text positions; it now measures the proof itself (inline marker or guard call, whichever dominates), and the fields merge block is created after the precheck's blocks so the typed/generic branch follows the guard calls in emission order. Claude-Session: https://claude.ai/code/session_01F1dt1jfzK2cheMZyus6y6p
…(12.8→3.8 ns) + #9124 review fixes (#9130) * perf(codegen): one inline field precheck for typed-receiver method calls + probe review fixes Follow-up to #9124, which merged with the method-direct probe only. This carries the second half of that lever plus the review fixes: 1. With the method probe in front, the probe-first c.inc() loop was ~80% js_typed_feedback_class_field_get_guard: per receiver field, per call, it re-derived facts the exact (class_id, ShapeId) pair already pins (live slot count, key-at-slot) through a shape_descriptor_by_id lookup plus the raw-f64 layout contract. The field-GET sites already emit emit_class_field_inline_precheck ahead of that guard (class/shape + not-forwarded + the per-OBJECT raw-f64 intact bit). Because the intact bit is object-wide, ONE precheck vouches for every receiver field at once; its miss edge runs the unchanged per-field runtime chain, whose i1 result joins at a phi. Same kill switch (PERRY_METHOD_INLINE_PROBE=0), same emission-off gating. Mini pairs: typed-param receiver 12.8 -> 3.8 ns, captured receiver 13.1 -> 3.8; proven-local rows flat at 4.4 — zero runtime calls per iteration (sample: 100% in the generated fn). 2. Review (#9124): emit_inline_direct_method_shape_guard takes accept_raw_ptr. Probe-first sites pass false — a user NaN-box receiver must carry the 0x7FFD tag before any dereference, so a plain double whose bits land in the heap range (a positive subnormal) misses to the runtime guard instead of reaching the header load. The pre-existing shape-only site and versioned_indexed_loop.rs keep raw acceptance. 3. The typed_f64_receiver IR-shape test measured both proofs by the runtime guards' text positions; it now measures the proof itself (inline marker or guard call, whichever dominates), and the fields merge block is created after the precheck's blocks so the typed/generic branch follows the guard calls in emission order. Claude-Session: https://claude.ai/code/session_01F1dt1jfzK2cheMZyus6y6p * style: rustfmt the inline field precheck --------- Co-authored-by: Ralph Küpper <ralph@skelpo.com>
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What
Method-call sites that own a typed receiver clone set
shape_only_guard = falseand therefore paidjs_typed_feedback_method_direct_call_guardon every call — whose contract check takes an RwLock read plus two SipHash HashMap probes (vtable_method_matches) — while less-typed sites got the existing inline shape guard. On a typed-parameter receiver (the shape every real codebase passes around) that was ~125–390 ns per monomorphicc.inc(), against node's 0.5.This applies #9105's dispensation to method sites: normal builds collect no typed feedback, so the guard's observation half is inert. Decide the monomorphic case with the same inline probe the shape-only sites already emit (class_id + ShapeId + the prototype-override latches — exactly what shape-only direct dispatch already trusts for this method body) and keep the runtime guard as the probe-miss edge, so subclass receivers, forwarded objects and monkey-patched prototypes take exactly today's path. Emission-enabled builds keep the guard first. ~15 lines in
method_override.rs. Kill switch:PERRY_METHOD_INLINE_PROBE=0.Measurements
Two commits, same lever: (1) the method-direct probe in front of the typed-feedback method guard; (2) one inline field precheck (class/shape + per-object raw-f64 intact bit — the same
emit_class_field_inline_precheckthe field-GET sites use) in front of the per-field runtime field guards, which became ~80% of the loop once (1) landed. With both, a monomorphicc.inc()on a typed-param receiver runs with zero runtime calls per iteration (sample: 100% inside the generated function).Mac mini (quiet host), 7 kill-switch pairs per step, median ns/op (node 0.4–0.5 in all four shapes):
new C(), plain fnnew C(), arrowThe two moved rows are the shapes real code is made of (receivers arrive as parameters or captures) and now sit slightly below the proven-receiver rows. What remains per iteration is the inline probes themselves (two atomic-acquire latch loads, header/class/shape compares, the intact-bit check) plus the loop's GC poll/barrier checks; hoisting the probes out of loops is the receiver-invariant loop-versioning follow-up (clones bodies, so it gets its own size accounting), and node's 0.5 beyond that is the boxed-round-trip/TBAA campaign.
Binary size (standing gate)
Per-site cost: ~100–150 B for the method probe and ~80 B for the field precheck (one per site, regardless of field count). The method probe is the SAME inline sequence the shape-only sites already emit (two atomic-acquire latch loads, pointer-form/range checks, one header load, one packed
(class_id, ShapeId)compare) — ~100–150 bytes per site on arm64, x86-64 similar; the runtime guard call is kept on the miss edge, so nothing is removed to offset it.__text/.textsize -m)cli_2.1.112.js, x86-64 (size(1), perrymaster)Sites affected = method-call sites whose receiver class has a typed receiver clone and whose site was not already shape-only (the
method_direct.runtime_guardblock count in kept IR). No loop bodies are cloned by this change; the loop-versioning follow-up will, and will be accounted separately.Correctness
delete C.prototype.incstill dispatches) is pre-existing on main, identical on both arms, filed as Direct method dispatch survivesdelete C.prototype.method(node throws TypeError) #9123.typed_f64_receiver_method_clone_raw_loads_after_composed_guards) is re-pointed at the proof itself — inline probe or guard call, whichever dominates the fast arm; its property (clone only after method-direct proof and raw-f64 field guard) is unchanged and passes.-D warnings0, codegen 1830/0, full runtime suite 2819/0, lints clean (addr-class, file-size, raw-handle debt none raised), integration issue_8655 2/2 / issue_8690 3/3 / issue_8897 3/3; semantics differential identical to the off arm after the fixes.accept_raw_ptrparameter — the probe-first sites passfalse(a user NaN-box receiver must carry the0x7FFDtag; the internal raw-address form just misses to the runtime guard), the pre-existing shape-only site andversioned_indexed_loop.rskeeptrue. The receiver-then-arguments lowering order is the tower's pre-existing structure (dynamic_dispatch.rs, receiver lowered before args, no re-read) shared by the runtime guard and the shape-only inline guard; all three reject a moved receiver through the forwarded header bit and fall to the runtime guard, which resolves forwarding — the probe inherits exactly that contract and adds no new window.https://claude.ai/code/session_01F1dt1jfzK2cheMZyus6y6p