perf: closes #753 — Eager/Deferred init split for dynamic import()#768
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…mic import() Follow-up to #100/#752. The dynamic-import resolver registered every target as a regular Import with `is_dynamic: true` and put it in the eager init chain at program start — functionally correct, but a heavy locale bundle or optional feature module was paid upfront even when no dispatch site ever fired. Reachability classification (compile.rs): fixed-point pass starting from the entry, propagating Eager across non-type-only static imports and re-export sources. Everything unmarked is Deferred. Writes the result to each Module::init_kind (HIR field from #100, no codegen consulted it before). Codegen (codegen.rs + expr.rs): - Entry main filters `deferred_module_prefixes` out of the eager init call sequence — Deferred modules only fire from dispatch sites. - Each non-entry module gains a 3-block wrapper `<prefix>__init` (load `@__perry_init_done_<prefix>`, icmp ne 0, cond_br to ret-or-do; do block stores 1, calls dep wrappers transitively, then calls `<prefix>__init_body`). Existing body code keeps every semantic; rename to `_body` is invisible to other code paths. - `Expr::DynamicImport` (single + multi-path arms) calls `<target>__init` before loading `@__perry_ns_<target_prefix>`. For Eager targets the guard short-circuits; for Deferred targets it's the only invocation that builds the namespace. - Entry emits a no-op `<entry_prefix>__init` stub so a non-entry module dispatching `await import("./entry.ts")` resolves at link. The entry's actual body still runs in main; the stub just satisfies the dispatch's unconditional init call. Module init deps (per-module: static-import + re-export sources) are plumbed to the wrapper's do block so a Deferred module that reaches another Deferred only through its own re-export chain still initializes the source before its namespace populator runs. Cache key hashes deferred_module_prefixes (sorted) and module_init_deps (ordered) so a program that gains or loses a dynamic-import reachability path invalidates the entry's cached .o. Acceptance: - All 7 dynamic-import gap tests from #100 (literal, ternary, template, reexport, tla, cycle, init_time) byte-equal `node --experimental-strip-types`. - New test_gap_dynamic_import_deferred.ts covers the Deferred-only case: marker module's top-level console.log fires only on the dispatch branch, never on the no-arg path. - cargo test --workspace green (excluding cross-host UI crates). Benchmark (heavy.ts builds a 1M-entry int array at top level, main.ts dynamically imports it only when argv[2] === 'use'): | | PRE-#753 | POST-#753 | |--------------|-----------------------|-----------------------| | no-arg | 8.4 ms ± 1.6 (min 7.4) | 4.8 ms ± 2.2 (min 3.1) | | use | 7.6 ms ± 0.4 (min 7.1) | 8.4 ms ± 0.7 (min 7.5) | hyperfine -N -w 5 -r 30. No-arg branch drops by 43% on mean / 58% on min — that 4 ms is the for-loop that no longer runs at startup. The `use` branch is statistically indistinguishable; the heavy init still runs, just lazily, with one extra call indirection.
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Summary
import()).<prefix>__initfires lazily from eachExpr::DynamicImportdispatch site.<prefix>__initbecomes an idempotent guard wrapper around<prefix>__init_body, with transitive dep init so a Deferred → re-export → Deferred chain still populates its namespace correctly.Closes #753.
Benchmark
bench_heavy.tsbuilds a 1M-entry int array at top level;bench_main.tsdynamically imports it only whenprocess.argv[2] === 'use'.hyperfine -N -w 5 -r 30:use(deferred loaded)No-arg branch drops by ~43% on mean / ~58% on min — that 4 ms is the for-loop that no longer runs at startup. The
usebranch is statistically indistinguishable (heavy init still runs, just lazily with one extra call indirection).Test plan
node --experimental-strip-types:literal,ternary,template,reexport,tla,cycle,init_time.test_gap_dynamic_import_deferred.ts— marker module's top-levelconsole.logfires only on the dispatch branch (argv[2]=1), suppressed on the no-arg path. Byte-equal to Node on both branches.cargo test --release --workspacegreen (excluding cross-host UI crates).dynamic_import_cycle_a.tsnow compiles standalone (entry no-op__initstub satisfies cycle_b's dispatch-site reference)..o.Version bump +
CHANGELOG.mdentry will land in a follow-up commit on this branch once CI is green.