# Phase‑20.12a — Hardcoding Cleanup (Lowering hygiene)

Scope (safe, reversible)
- Name normalization via table (SSOT) instead of `if` chains in `mir_call.py`.
- Tail/fastcc hinting: move logic toward helpers (no behavior change; stricter gating optional).
- Method by‑id: gated route (`NYASH_LLVM_METHOD_BY_ID=1`) using stable 64‑bit hash (FNV‑1a). Fallback to by‑name kept.
- Bench hooks (barrier/noop): normalized via alias table (dev only; AOT shim symbols).
- ErrorBox unification (first wave): replace ad‑hoc "Error: ..." StringBox in Divide/Modulo/Random/Time/HTTPServer with structured ErrorBox.
- Arithmetic Extended: minimal `compute_auto()` + `chain()` for Subtract/Mul/Div (delegating to legacy execute by default).
- PHI hardening: register block_phi_incomings on creation and auto‑enable PHI post‑process under strict mode to avoid empty PHI text lines.
- Bench externs: special‑case `Env.bench.print_i64/1`/`noop_i64/1`/`use_value/1` to `void(i64)` declarations and calls (fair, robust lowering path).

New micro benches (optimization‑resistant)
- `tools/bench/run_inproc_mix_alu_resisted.sh` — per‑iteration value sink (use_value) for ALU loop.
- `tools/bench/run_inproc_call_noop_resisted.sh` — per‑iteration no‑op call. C side mirrors via noinline+asm barrier.

Non‑goals (defer to 20.13)
- Full externs registry ingestion from Rust at runtime.
- Method by‑id defaulting and runtime registry integration.
- Wide refactors beyond lowering helpers (keep deltas minimal).

Why (benefits)
- Reduce ad‑hoc hardcoding in lowering; improve readability and testability.
- Keep `mir_call.py` focused on bridging, not string alias trivia.
- Prepare by‑id migration without changing defaults.

Gates
- `NYASH_LLVM_METHOD_BY_ID=1` → use `invoke_by_id` if available (fallback by‑name)
- `NYASH_LLVM_TAILCALL_STRICT=1` → strict tail placement (same CC, at block ret, unused dst)

Files
- `src/llvm_py/consts/externs.py`: add `ALIASES` (alias → canonical)
- `src/llvm_py/instructions/mir_call.py`: `_normalize_extern_name()` uses table lookups; optional by‑id path
- `lang/c-abi/shims/hako_kernel.c`: add `hako_bench_noop_i64()`

Validation
- IR dump pre/post: `NYASH_LLVM_DUMP_IR`, `NYASH_LLVM_DUMP_OPT_IR`
- Quick benches (in‑proc) unchanged semantics; div(2^k) requires `NYASH_LLVM_UDIV_POW2=1` + `NYASH_LLVM_ASSUME_UNSIGNED=1`

Rollback
- Remove `ALIASES` and revert `_normalize_extern_name` to explicit if‑chains.
- Disable `NYASH_LLVM_METHOD_BY_ID` gate.