perf: function-valued stores served by the store IC with a body check (ConstFn key-add)

[proggeramlug]

Function-valued stores (this.k = F, o.cb = fn) no longer miss the store IC on every store. Stacked on #11787; retarget to main after it merges.

Instructions per op

Row	base	this PR
new C() storing this.k = C	5,013	2,189
this.cb = fn, 16 closures of one body	5,085	2,267
o.cb = fn overwrite	2,026	202
#10507 decimal row	5,003	2,387
controls (number key-add, class decimal, empty ctor)	–	unchanged

A function-valued key-add now costs about 156 instructions more than a number key-add, down from about 2,985.

How it works

• The store site gets a fifth word holding its one ConstFn body, set the first time a function store is cached.
• A cached function store is served inline only when the value is a closure of that body: one GC-header kind load, one info compare and one capture-flag test. Anything else takes the slow path, which deprecates the lane as before.
• The runtime key-add memo applies the same check.
• The new guard bits are in perry-abi and pinned by the layout test.

tsc and Zod (n=5; output matches node)

• tsc: −0.07%, full collections 81/81.
• Zod: +0.08%, full collections 0/0.
• RSS is equal within run-to-run spread.

Verification

• runtime 4827/0; codegen lib 1913/0; native_proof_regressions 291/0.
• fmt, file size, gc_call_effects and gc-root-dominance (40/40 seeded caught) pass.
• Gap A/B on 229 tests: 0 regressions.
• Sabotage:
  • the runtime memo skipping the body check, and a site claiming any body, each turn a unit test red;
  • the emitted check ignoring the body is caught only by the codegen IR test assert_constfn_body_compare, because no current JS program can observe it.

Limits: one body per site, so a site alternating two bodies still misses for the second. Arrows that capture this take the slow path. Class-field stores were not measured.

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📥 Commits

Reviewing files that changed from the base of the PR and between ea38090 and 88eed19.

📒 Files selected for processing (29)

• changelog.d/11787-function-constructors.md
• changelog.d/11798-constfn-function-stores.md
• crates/perry-abi/src/lib.rs
• crates/perry-codegen/src/expr/put_value_store_ic.rs
• crates/perry-codegen/src/expr/write_pic_barrier_tests.rs
• crates/perry-codegen/src/fn_info.rs
• crates/perry-codegen/src/lower_call/property_get/dynamic_dispatch.rs
• crates/perry-codegen/tests/native_proof_regressions.rs
• crates/perry-runtime/src/closure/dispatch.rs
• crates/perry-runtime/src/closure/dispatch/value_call.rs
• crates/perry-runtime/src/closure/mod.rs
• crates/perry-runtime/src/closure/shape.rs
• crates/perry-runtime/src/object/alloc_basic.rs
• crates/perry-runtime/src/object/class_registry.rs
• crates/perry-runtime/src/object/class_registry/construct.rs
• crates/perry-runtime/src/object/class_registry/construct/compiled_function.rs
• crates/perry-runtime/src/object/class_registry/construct/compiled_function_tests.rs
• crates/perry-runtime/src/object/class_registry/state.rs
• crates/perry-runtime/src/object/instanceof/dynamic_dispatch.rs
• crates/perry-runtime/src/object/meta_accessors.rs
• crates/perry-runtime/src/object/meta_record.rs
• crates/perry-runtime/src/object/mod.rs
• crates/perry-runtime/src/proxy/put_value/cached_constfn_tests.rs
• crates/perry-runtime/src/proxy/put_value/packed_add.rs
• crates/perry-runtime/src/proxy/put_value/packed_add_tests.rs
• crates/perry-runtime/src/proxy/put_value/packed_set.rs
• test-files/_helpers/constfn_store_worker.ts
• test-files/test_gap_10507_function_constructors.ts
• test-files/test_gap_constfn_function_stores.ts

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