Emission size — reachability-gated dead-code elimination (umbrella)

• Type: feature (codegen / optimization) — Track A
• Status: backlog
• Opened: 2026-06-30 (merge of feature-lazy-standard-unit-emission + chore-runtime-emission-size, found redundant in triage)
• Relation: the concrete passes here would be hosted by [[feature-optimization-levels]]'s pass framework (kept separate; cross-linked).

Goal

Shrink emitted binaries by emitting only reachable code. Two overlapping fronts, unified here:

1. Routine-level DCE for uses-unit bodies (was feature-lazy-standard-unit- emission): a uses textfile/builtin pulls in whole unit bodies even when only one routine is called. hello.pas still emits ~31.6 KB vs a ~29 KB reachable baseline. Emit a unit routine only if reached from the program entry.

2. Finer runtime-support emission (was chore-runtime-emission-size): the implicit runtime helpers (string/dynarray/managed/exception support) are emitted coarsely; gate each on actual use.

Both are the same mechanism: build a call/reachability graph from the entry point and skip unreferenced routine bodies. Do it once, cover both fronts.

Acceptance

hello (and other minimal programs) shrink measurably (toward the ~29 KB baseline) with no behavior change; self-host byte-identical; make test + cross green. Ideally lands as an -O-gated pass under [[feature-optimization-levels]].

Notes

• Merged from two redundant tickets (2026-06-30 triage). History in git.