AILang/docs/journals/2026-05-12-iter-hs.2.md

iter hs.2 — Static-Str sentinel-slot retrofit

Date: 2026-05-12 Started from: 51a096cf83 Status: DONE Tasks completed: 3 of 3

Summary

Second iter of the heap-Str ABI milestone. Surgical codegen-side retrofit of hs.1's static-Str global layout: per the amended parent spec (docs/specs/2026-05-12-heap-str-abi.md) the sentinel rc-header slot drops. Language Str literals now emit as <{ i64, [N+1 x i8] }> <{ i64 N, [N+1 x i8] c"…\00" }> instead of the hs.1 shape <{ i64, i64, [N+1 x i8] }> <{ i64 -1, i64 N, …}>. The explicit len field becomes the first (and only non-byte) field on which the IR-Str pointer lands via constexpr-GEP i32 0, i32 0. The +8 GEP consumer-side calls (@puts, @ail_str_eq, @ail_str_compare, inline @strcmp) do not change — the bytes still sit 8 bytes past the len-field. Static-Str pointers are kept out of ailang_rc_dec at the codegen level via move-tracking (iter 18d.3) and non-escape lowering (iter 18b), so no header slot is needed at the global.

Change surface: three format-string sites and two doc-comments in crates/ailang-codegen/src/lib.rs, rename + assertion update of two IR-shape tests in the same crate's test module, plus snapshot regeneration of crates/ail/tests/snapshots/hello.ll. No runtime changes, no checker changes, no new fixtures. Static-Str globals are now 8 bytes smaller per literal.

Acceptance verified end-to-end: cargo test --workspace green (every test result ok, 0 failures across the workspace), bench/cross_lang.py exit 0 (byte-identical stdout across all ail/c benchmark pairs), bench/compile_check.py exit 0, bench/check.py exit 0 within the known latency.explicit_at_rc.* nondeterminism tolerance.

Per-task notes

• iter hs.2.1: renamed static_str_global_uses_packed_struct_with_sentinel_and_len → static_str_global_uses_packed_struct_with_len; updated its doc-comment and assertion substring (struct loses leading i64, , initialiser loses leading i64 -1, ). Updated assertion in static_str_callsite_pointer_is_payload_via_constexpr_gep (name preserved — "payload" still describes the len-field-as-pointer-target; struct loses leading i64, , GEP indices i32 0, i32 1 → i32 0, i32 0). RED confirmed: both tests fail against hs.1 emission with the expected assertion-substring mismatch. The four +8 GEP tests stayed green.
• iter hs.2.2: flipped the global-emission loop format string at lib.rs:471 to the 2-field shape; flipped both Literal::Str arms (emit_const_def ~ lib.rs:933, lower_term ~ lib.rs:1255) to emit constexpr-GEP i32 0, i32 0 onto the 2-field struct type; updated the two doc-comments on the str_literals field (lib.rs:561) and on intern_str_literal (lib.rs:2596) to the amended-spec wording. All five edits exactly per plan text. Static_str_ tests GREEN, _calls_ tests GREEN, full cargo test -p ailang-codegen GREEN (33 tests).
• iter hs.2.3: regenerated crates/ail/tests/snapshots/hello.ll via UPDATE_SNAPSHOTS=1 cargo test -p ail --test ir_snapshot hello. The two affected lines (the @.str_hello_str_0 global and its constexpr- GEP at %v1) flipped to the new shape; the outer i64 8 byte offset preserved. Workspace cargo test --workspace green; cross_lang.py, compile_check.py, check.py all green.

Concerns

(none)

Known debt

(none)

Files touched

• crates/ailang-codegen/src/lib.rs — three format strings, two doc-comments, two test names + assertions + doc-comments
• crates/ail/tests/snapshots/hello.ll — regenerated snapshot (2 lines content change, byte offsets preserved)

Stats

bench/orchestrator-stats/2026-05-12-iter-hs.2.json