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Section 03: Remove Workarounds & Simplify

Status: Complete Goal: With elem_dec_fn stored in the RC header, the ordering workarounds in the ARC lowering are no longer needed. Remove them to simplify the code.

Depends on: Section 02 (codegen must use header-based cleanup first).

Ordering within this section: Steps 03.1, 03.1.5, and 03.2 remove the for-loop workarounds and MUST be done together (they share state: for_coll_counter, ForYieldContext::coll_param, and __for_coll_N bindings). Step 03.2.5 (removing elem_dec_fn from the iterator API) is an independent change that can be done before or after the workaround removal, but doing it last is recommended to keep the removal steps focused and testable as a single unit.

03.1 Remove Phantom Binding from lower_for

File: compiler/ori_arc/src/lower/control_flow/loops.rs

The phantom __for_coll_N mutable binding was added to thread the collection through the loop header, forcing AIMS to add RcInc. With the header storing elem_dec_fn, the ordering no longer matters — whoever reaches zero reads the function from the header.

Note: The source code comment at loops.rs:169-176 says the phantom is needed for “List, Set, Map”, but the actual match expression at line 177 only handles List | Set — Map is excluded. This is a pre-existing documentation bug in the source code.

  • Remove the needs_phantom check and scope.bind_mutable(coll_name, iter_val) block (lines 177-184 in loops.rs) (2026-03-21)
  • Remove the comments explaining the workaround (lines 169-176) (2026-03-21)
  • Verify: the __for_coll name is not referenced anywhere else in the compiler (grep -r "__for_coll" compiler/ → 0 results) (2026-03-21)
  • [BUG FIX] Set.iter() was using emit_list_iter directly, treating the hash table as a contiguous array — exposed by phantom removal. Fixed: emit_set_iter now converts via ori_set_to_list + explicit set buffer ori_set_buffer_rc_dec (2026-03-21)

Cleanup (03.1)

  • [WASTE] compiler/ori_arc/src/lower/control_flow/loops.rs:169-184 — Removed phantom binding code and stale comment. ALL __for_coll references updated:
    • loops.rs:177-184 — phantom binding creation code removed (2026-03-21)
    • for_iterator.rs:192-207 — dummy reference after ori_iter_drop removed (Section 03.2) (2026-03-21)
    • for_yield.rs:60-62 — prepare_iterator() doc comment updated (2026-03-21)
    • for_yield.rs:86-96 — prepare_iterator() coll logic removed (Section 03.1.5) (2026-03-21)
    • expr/mod.rs:108-112 — for_coll_counter field removed. Initialization sites at lower/mod.rs:168 and lower/calls/lambda.rs:126 also removed (2026-03-21)
    • borrowed_defs.rs:208-209 — doc comment updated to describe generic mechanism without referencing removed phantom (2026-03-21)
    • walk_dec.rs:79 — comment updated (2026-03-21)
    • list_builtins.rs:143-147 — comment updated to reference header-based approach (2026-03-21)

03.1.5 Remove For-Yield Collection Threading

Files: compiler/ori_arc/src/lower/control_flow/for_yield.rs, compiler/ori_arc/src/lower/expr/mod.rs, compiler/ori_arc/src/lower/control_flow/mod.rs

The for-yield path has its own independent collection-phantom mechanism parallel to the for-do __for_coll_N binding. prepare_iterator() returns coll_var = Some(iter_val) for List/Set, which lower_for_yield_iterator() threads through header/exit blocks as coll_param/exit_coll_param block parameters, and emits a dummy let after ori_iter_drop. ForYieldContext::coll_param is used by lower_break/lower_continue to prepend the phantom to jump args. With the header storing elem_dec_fn, all of this is unnecessary.

  • In for_yield.rs prepare_iterator(): simplified return type to (ArcVarId, Idx), removed coll variable logic (2026-03-21)
  • In for_yield.rs lower_for_yield_iterator(): removed coll_var parameter and all coll_param/exit_coll_param block parameter threading (2026-03-21)
  • In for_yield.rs exit block: removed dummy reference to exit_coll_param after ori_iter_drop (2026-03-21)
  • In for_yield.rs lower_for_yield_iterator() doc comment: updated block diagram — removed coll_param from header and exit_prep jump args (2026-03-21)
  • In for_yield.rs lower_for_yield_iterator(): removed #[expect(clippy::too_many_arguments)] (2026-03-21)
  • In for_yield.rs ForYieldContext construction: removed coll_param field initialization (2026-03-21)
  • In expr/mod.rs ForYieldContext: removed coll_param field (2026-03-21)
  • In for_yield_option.rs:158: removed coll_param: None and updated comment at line 88 (2026-03-21)
  • In control_flow/mod.rs lower_break(): removed coll_param from for-yield break path (2026-03-21)
  • In control_flow/mod.rs lower_continue(): removed coll_param from for-yield continue path (2026-03-21)
  • [NOTE] control_flow/mod.rs shrunk from 494 to ~475 lines after coll_param removal. Safe margin restored. (2026-03-21)
  • In for_yield.rs lower_for_yield() call site: updated destructuring from 3-tuple to 2-tuple (2026-03-21)

Cleanup (03.1.5)

  • [WASTE] for_yield.rs — lower_for_yield_iterator shrunk ~40 lines. #[expect(clippy::too_many_arguments)] removed. #[expect(clippy::too_many_lines)] retained (function still > 50 lines but well under 100). (2026-03-21)
  • [NOTE] for_yield.rs shrunk from 390 to ~345 lines. No split needed. (2026-03-21)

03.2 Remove Dummy Reference from lower_for_iterator

File: compiler/ori_arc/src/lower/control_flow/for_loops/for_iterator.rs

The dummy Let after ori_iter_drop was added to keep the collection alive past the iterator drop. No longer needed.

  • Remove the __for_coll_N lookup and emit_let(coll_ty, ArcValue::Var(exit_param)) block (lines ~192-207 in for_iterator.rs) (2026-03-21)
  • Remove the comments explaining the ordering guarantee (2026-03-21)

03.2.5 Remove Dead elem_dec_fn Parameter from Iterator API

Files: compiler/ori_rt/src/iterator/sources.rs, compiler/ori_rt/src/iterator/state.rs, compiler/ori_llvm/src/codegen/arc_emitter/builtins/collections/list_builtins.rs, compiler/ori_llvm/src/codegen/runtime_decl/runtime_functions.rs, compiler/ori_llvm/src/evaluator/runtime_mappings.rs

With the header storing elem_dec_fn, the parameter in ori_iter_from_list and the field in IterState::List are redundant (the header provides the function). Section 02.2 chose Option A (keep parameter for defense-in-depth while the header approach was unproven). Now that the header approach is proven stable by Sections 02-04, the redundant parameter is removed.

WARNING — ABI sync point: This step changes the ori_iter_from_list signature from 5 to 4 parameters. All 4 locations MUST be updated in a single commit: (1) ori_rt/src/iterator/sources.rs (runtime impl), (2) runtime_functions.rs (LLVM IR declaration), (3) list_builtins.rs (codegen call site), (4) runtime_mappings.rs (JIT symbol). Partial updates cause linker errors or silent memory corruption.

  • Remove elem_dec_fn parameter from ori_iter_from_list function signature in sources.rs (currently at line 32). Also: (2026-03-22)
    • Remove elem_dec_fn, from the IterState::List { ... } construction at line 41 (field must be removed from both the struct definition AND this construction site). (2026-03-22)
    • Update the function doc comment (lines 20-25) — remove the reference to elem_dec_fn = None for test data. The doc should explain that element cleanup is entirely header-based (V5 RC header). (2026-03-22)
  • Remove elem_dec_fn field from IterState::List in state.rs (field at line 62; List variant starts at line 56). Also update the variant doc comment at lines 43-55 — remove the paragraph explaining elem_dec_fn defense-in-depth (lines 51-55), since the field will no longer exist. The doc should explain that element cleanup is entirely header-based. (2026-03-22)
  • Update IterState::List Drop (state.rs:162-178): the drop() match arm currently destructures elem_dec_fn (line 168) and passes *elem_dec_fn to ori_buffer_rc_dec (line 176). With the field removed, pass None instead — ori_buffer_rc_dec reads the function from the V5 RC header via load_elem_dec_fn at cleanup time. The destructuring pattern at lines 163-169 must also remove the elem_dec_fn field. Safety: passing None is safe because the header was populated at construction time (Section 02.1) and ori_buffer_rc_dec always reads from the header in its drop path (drop_elements_and_free calls load_elem_dec_fn). (2026-03-22)
  • Update emit_list_iter in list_builtins.rs: remove the elem_dec_fn argument from the call to ori_iter_from_list (currently passes real function at line 148, call at line 152 — this becomes unnecessary when header provides it). Also: (2026-03-22)
    • Update the function doc comment (lines 115-129): remove the “real elem_dec_fn” explanation and the “Defense-in-depth” paragraph. Replace with a note that element cleanup is entirely header-based (V5 RC header). (2026-03-22)
    • Remove the comment block at lines 143-147 explaining why elem_dec_fn is passed and referencing __for_coll. (2026-03-22)
    • Remove let elem_dec_fn = self.get_or_generate_elem_dec_fn(elem_ty); at line 148. (2026-03-22)
    • Update the emit_rt_call args from &[data_ptr, len, cap, elem_size_val, elem_dec_fn] to &[data_ptr, len, cap, elem_size_val]. (2026-03-22)
  • Update ori_iter_from_list declaration in runtime_functions.rs (line 1305): remove the 5th parameter (Ty::Ptr for elem_dec_fn) and update the inline comment at line 1307. Note: runtime_functions.rs is 1528 lines — self-documenting exemption from the 500-line limit (pure static data table), but verify no logic has crept in. (2026-03-22)
  • Update Rust unit tests in compiler/ori_rt/src/iterator/tests.rs that call ori_iter_from_list with 5 args — update to 4 args. There are 30+ call sites across all iterator tests (next, map, filter, take, skip, enumerate, zip, chain, flatten, flat_map, cycle, collect, for_each, fold, slice drop). Each passes None as the 5th arg — remove that argument from every call. (2026-03-22)
  • Update ori_iter_from_list JIT symbol mapping in compiler/ori_llvm/src/evaluator/runtime_mappings.rs (line 204) to match the new 4-parameter signature — no change needed: JIT mapping is a function pointer cast, parameter count derived from runtime_functions.rs declaration (already updated). (2026-03-22)
  • Run timeout 150 cargo test -p ori_rt and timeout 150 cargo test -p ori_llvm --test aot to verify — 350 + 1876 tests pass (2026-03-22)

Cleanup (03.2.5)

  • [STYLE] compiler/ori_rt/src/iterator/mod.rs:43,60 — Remove 2 decorative banners (// ── Extern C API — Core ──..., // ── Extern C API — Cleanup ──...). Replace with plain section comments. (2026-03-22)
  • [STYLE] compiler/ori_rt/src/iterator/tests.rs — Remove 20 decorative banners across test file (e.g., // ── List iterator ───, // ── Range iterator ──, etc.). Replace with plain section comments. Since this file has 30+ ori_iter_from_list calls being modified, clean banners in the same commit. (2026-03-22)

03.3 Verify No Regressions

  • Run timeout 150 cargo test -p ori_llvm --test aot — 1876 passed, 0 failed, 17 ignored (2026-03-22)
  • Run timeout 150 ./test-all.sh — 13,551 passed, 0 failed (2026-03-22)
  • Run ./clippy-all.sh — zero warnings (2026-03-22)
  • Run ./fmt-all.sh — clean (2026-03-22)
  • Verify ARC IR for [str] iteration is cleaner (no phantom __for_coll_N param in loop header, no coll_param in for-yield loop header) — verified with ORI_DUMP_AFTER_ARC=1, no matches for __for_coll or coll_param (2026-03-22)
  • Verify ori_iter_from_list takes 4 parameters (not 5) in the LLVM IR output — confirmed: declare ptr @ori_iter_from_list(ptr, i64, i64, i64) (2026-03-22)

03.R Third Party Review Findings

  • [TPR-03-002][low] plans/rc-header-elem-dec/section-03-remove-workarounds.md:4 — Section 03 status metadata contradicts the document body and index. Resolved: Aligned frontmatter (status: complete, third_party_review.status: resolved), body status text (**Status:** Complete), and index entry on 2026-03-22.

  • [TPR-03-003][low] compiler/ori_llvm/src/codegen/arc_emitter/builtins/collections/list_builtins.rs:118 — emit_list_iter’s doc comment still claims the function explicitly emits ori_list_rc_inc, but the implementation no longer does that. Resolved: Updated doc comment on 2026-03-22 to describe the actual ownership path — caller is responsible for RC inc (via ARC arg-ownership or emit_slice_aware_rc_inc in emit_auto_iter).

  • [TPR-03-001][high] compiler/ori_llvm/src/codegen/arc_emitter/builtins/mod.rs:397 — Auto-iterator promotion still routes Set receivers through emit_list_iter, so methods like Set.fold() still iterate the hash-table buffer as if it were a contiguous list. Resolved: Validated and fixed on 2026-03-22. Split TypeInfo::List | TypeInfo::Set match arm in emit_auto_iter() so Set routes through emit_set_iter(). Added 5 semantic pin tests: set_auto_fold, set_auto_count, set_auto_any, set_auto_all, set_str_auto_fold.

03.N Completion Checklist

Workaround Removal (03.1, 03.1.5, 03.2)

  • No references to __for_coll in compiler code (verified: grep -rn "__for_coll" compiler/ → 0 results) (2026-03-22)
  • No references to coll_param in for-yield collection-threading context (verified: grep -rn "coll_param" compiler/ori_arc/src/lower/ → 0 results) (2026-03-22)
  • No dummy reference after ori_iter_drop in exit block (both for-do and for-yield paths) — exit blocks only call ori_iter_drop + scope restore (2026-03-22)
  • lower_for is simpler (no phantom binding logic) (2026-03-22)
  • lower_for_iterator is simpler (no exit-block dummy reference) (2026-03-22)
  • lower_for_yield_iterator is simpler (no coll_var/coll_param threading, no exit-block dummy reference) (2026-03-22)
  • ForYieldContext::coll_param field removed from expr/mod.rs — only 3 fields: list_ptr, elem_size, list_push_name (2026-03-22)
  • lower_break and lower_continue in control_flow/mod.rs no longer prepend coll_param to jump args (2026-03-22)
  • prepare_iterator in for_yield.rs no longer returns collection variable for phantom threading — returns (ArcVarId, Idx) (2026-03-22)
  • for_coll_counter field removed from ArcLowerer in expr/mod.rs (2026-03-22)
  • for_coll_counter: 0 initialization removed from lower/mod.rs and lower/calls/lambda.rs (2026-03-22)
  • propagate_borrowed_closure in borrowed_defs.rs updated (no stale __for_coll references) (2026-03-22)
  • for_yield_option.rs updated (no coll_param: None in ForYieldContext construction) (2026-03-22)
  • for_yield_option.rs comment updated (no reference to coll_param) (2026-03-22)
  • lower_for_yield_iterator doc comment block diagram updated (no coll_param in jump args) (2026-03-22)
  • lower_for_yield_iterator #[expect(clippy::too_many_arguments)] removed (only too_many_lines remains with justification) (2026-03-22)

Iterator API Cleanup (03.2.5)

  • ori_iter_from_list takes 4 parameters (dead elem_dec_fn removed) (2026-03-22)
  • ori_iter_from_list doc comment updated to reflect header-based cleanup (no elem_dec_fn parameter) (2026-03-22)
  • ori_iter_from_list JIT symbol mapping in evaluator/runtime_mappings.rs — no change needed (function pointer cast) (2026-03-22)
  • IterState::List has no elem_dec_fn field (2026-03-22)
  • IterState::List doc comment updated: header-based cleanup, no defense-in-depth reference (2026-03-22)
  • IterState::List Drop match arm destructuring pattern updated (no elem_dec_fn field) (2026-03-22)
  • 30+ ori_iter_from_list calls in iterator/tests.rs updated from 5 args to 4 args (2026-03-22)
  • emit_list_iter in list_builtins.rs doc comment and code updated — no reference to elem_dec_fn parameter or __for_coll phantom (2026-03-22)
  • Decorative banners in iterator/mod.rs and iterator/tests.rs replaced with plain section comments (2026-03-22)

Verification

  • All tests pass (timeout 150 ./test-all.sh) — 13,551 passed, 0 failed (2026-03-22)
  • All tests pass in release build (cargo b --release && timeout 150 cargo test -p ori_llvm --test aot --release) — 1876 passed (2026-03-22)
  • ./clippy-all.sh — zero warnings (2026-03-22)
  • lower_for_yield_iterator function length: 211 lines (exceeds 100-line target but justified with #[expect(clippy::too_many_lines)] — inherently sequential SSA merge logic) (2026-03-22)
  • control_flow/mod.rs file length: 494 lines (under 500-line limit) (2026-03-22)