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Section 07: ARC Pipeline

Context: J10 showed 3 identical drop functions (_ori_drop$202, _ori_drop$202.1, _ori_drop$202.2) for [int] — all calling ori_rc_free(ptr, i64 24, i64 8). Each list literal gets its own copy despite having the same layout.

07.1 Fix M12 — Deduplicate Drop Functions

Journey: J10 | Severity: MEDIUM File(s): compiler/ori_llvm/src/codegen/arc_emitter/ (drop function generation)

; Current — 3 identical functions:
define void @"_ori_drop$202"(ptr %0) { call @ori_rc_free(ptr, i64 24, i64 8); ret void }
define void @"_ori_drop$202.1"(ptr %0) { ... identical ... }
define void @"_ori_drop$202.2"(ptr %0) { ... identical ... }

Fix: Deduplicate by canonical drop-function identity, NOT by (alloc_size, alloc_align). Two types can share layout (size + align) but require different drop behavior — e.g., [str] needs recursive ARC traversal of elements while [int] does not, even if both have the same allocation size. Keying by layout would alias incompatible drop logic and cause use-after-free or leaked memory.

The existing drop_fn_cache already keys by type index (Idx), which is correct for type identity. The bug is that multiple pool entries for the same concrete type (e.g., three [int] list literals) get different Idx values, generating duplicate drop functions.

Correct key: Mangled type name (the same string used for _ori_drop$<mangled> naming). Types with identical mangled names have identical drop behavior by construction. This deduplicates within a type while keeping different types separate.

  • Find where drop functions are generated in the ARC emitter (drop_gen.rs)
  • Fix: use get_or_declare_void_function instead of declare_void_function + check function_has_body to skip body regeneration
  • Same fix applied to elem_dec and elem_inc functions in element_fn_gen.rs
  • Verify: multi-function program with [str] generates exactly 1 _ori_drop$3 (was 2 before fix)
  • Verify: Programs with [str] + [int] generate separate drop functions (different traversal logic)
  • Verify: 1179 AOT tests pass

07.2 Completion Checklist

  • Each unique canonical type produces exactly one drop/elem_dec/elem_inc function
  • Multi-type programs still have correct separate functions (different type names → different functions)
  • Types with same layout but different drop logic are NOT merged (keyed by Idx, not layout)
  • cargo test -p ori_llvm --tests — 1179 pass
  • Valgrind verification deferred to Section 11

Exit Criteria: No duplicate drop functions in IR. Verified with [str]+[int] test: exactly 1 _ori_drop$3.