# Phase 80-1: Inline Slots Switch Dispatch — Results

## Goal

Reduce per-op comparison/branch overhead in inline-slots routing for the hot classes by replacing the sequential `if (class_idx==X)` chain with a `switch (class_idx)` dispatch when enabled.

Scope:
- Alloc hot path: `core/box/tiny_front_hot_box.h`
- Free legacy fallback: `core/box/tiny_legacy_fallback_box.h`

## Change Summary

- New env gate box: `core/box/tiny_inline_slots_switch_dispatch_box.h`
  - ENV: `HAKMEM_TINY_INLINE_SLOTS_SWITCHDISPATCH=0/1` (default 0)
- When enabled, uses switch dispatch for C4/C5/C6 (and excludes C2/C3 work, which is NO-GO).
- Reversible: set `HAKMEM_TINY_INLINE_SLOTS_SWITCHDISPATCH=0` to restore the original if-chain.

## A/B (Mixed SSOT, 10-run)

Workload:
- `ITERS=20000000`, `WS=400`, `RUNS=10`
- `scripts/run_mixed_10_cleanenv.sh`

Results:

Baseline (SWITCHDISPATCH=0, if-chain):
- Mean: `51.98M ops/s`

Treatment (SWITCHDISPATCH=1, switch):
- Mean: `52.84M ops/s`

Delta:
- `+1.65%` ✅ **GO** (threshold +1.0%)

## perf stat (single-run sanity)

Key deltas (treatment vs baseline):
- Cycles: `-1.6%`
- Instructions: `-1.5%`
- Branches: `-2.9%` ✅
- Cache-misses: `-6.7%`
- Throughput (single): `+3.7%`

Interpretation:
- Switch dispatch removes repeated failed comparisons for the hot inline-slot classes, reducing branches/instructions without causing cache-miss explosions.

## Promotion

Promoted to Mixed SSOT defaults:
- `core/bench_profile.h`: `HAKMEM_TINY_INLINE_SLOTS_SWITCHDISPATCH=1`
- `scripts/run_mixed_10_cleanenv.sh`: `HAKMEM_TINY_INLINE_SLOTS_SWITCHDISPATCH=1`

Rollback:
```sh
export HAKMEM_TINY_INLINE_SLOTS_SWITCHDISPATCH=0
```