Direct-call lowering: rt.InvokeValue → direct Go calls

[nnunley]

Tracking issue for direct-call lowering — lifting the rt.LookupVar → Var.Deref → rt.InvokeValue trampoline into direct Go calls in the -tags gogen_ir lowered tree. Sub-issue of #258. Reconciled against main @ d4c36cf2 (#251), 2026-06-19.

Already in main

• Infrastructure: emit-typed-direct-call, resolve-call-entry (handles :native?), lookup-direct-callable, *lowered-registry*, *native-imports-used* (lower_go.lg/pipeline.lg).
• Slice 1 — intra-namespace direct calls: MERGED in feat(lower-go): intra-namespace direct-call lowering (slice 1) #168 (2026-06-02).

Pending slices (sub-issues)

• Slice 2 — native-module cross-ns direct calls (branch feat/native-direct-calls, ticket lg-dq58). Seeds *lowered-registry* from (rt/native-modules) and emits the Go imports so the dormant :native? path activates end-to-end. Eliminates 94 seq trampolines → corefns.Seq. Perf-neutral (these native calls are cold). Implemented on-branch (3 commits); needs rebase onto current main + bundle regen.
• Slice 3 — global-lowered-registry: hot cross-ns lowered direct calls (planned follow-on, named in the lg-dq58 commit). Targets the hot trampolines — cross-ns calls into lowered licm/typeinfer/build. This is where the actual perf win is; Slice 2 deliberately leaves it.

Adjacent (not filed here)

• Lambda lifting — queued after direct-call per the roadmap; distinct optimization, no branch yet.
• Structured Go emission (ir.structurize) is already merged in main — lower-body is structured-first (if/for/break/continue for reducible CFGs) and falls back to the goto emitter when structurize reports :fallbacks > 0. It is the proper-emission mechanism, not pending direct-call work. Its residual fallbacks are exactly the gogen_ir: close ir.structurize fallbacks for the 18 func-decl-bail defns #263 bucket (driving structurize :fallbacks → 0).

Superseded branches (archive, not filed)

• feat/direct-call-intra-ns → landed as feat(lower-go): intra-namespace direct-call lowering (slice 1) #168.
• direct-call-boundary → dormant origin scaffold; superseded by feat/native-direct-calls.
• ir-exploration → 54-commit accumulator; mine for tests/notes, not a single issue.

[nnunley]

Retroactive links — the merged direct-call foundation this tracks:

• feat(lower-go): intra-namespace direct-call lowering (slice 1) #168 — intra-namespace direct-call lowering (slice 1)
• feat(lower-go): registry-driven intra-namespace direct-call lowering (slice 2) #188 — registry-driven intra-namespace direct-call lowering (slice 2)
• feat(lower-go): cross-ns IFn dispatch via cached vars (rt.CachedVarFn) #189 — cross-ns IFn dispatch via cached vars (rt.CachedVarFn)
• perf(lower-go): exact-key registry resolution (resolve-then-get, no scan) #193 — exact-key registry resolution (resolve-then-get)

Pending slices #271/#272 build on these.

[nnunley]

Status (roadmap alignment, EPIC-012): the three slices are merged — slice 1 intra-ns (#168), slice 2 native-module cross-ns (#343, closed #271), slice 3 global cross-package registry (#345, closed #272). Residual under this umbrella: IFn-typed direct calls (callee held in a var/typed param) — still trampolines by design until the concrete-vm-type track (ITER-0026/0028, #284/#282) lands. Keeping open as the umbrella for that residual.