# ✅ How a built-in's result reaches a condition — the operand chain

The previous iteration named the branches and stated plainly that this was still
missing: *"naming the branch does not by itself give the clear condition — that
needs the operand chain feeding each compare."* It is read now, and it closes.

## ⚠️ First: the corpus already had half of it, and I had written the stale file

[`isl-bytecode.md`](isl-bytecode.md) — which **owns** the opcode table — already
named ops 21–24 (`push.i` / `push.f` / `pop.i` / `pop.f`) and ops 13–18 as the
six branches. My own [`isl-branches.md`](isl-branches.md), written one iteration
earlier, said `op23` and `op21` were unread. **The stale file was mine.**

Verified rather than assumed, from the thunks and handlers:

| op | moves | verified by |
|---|---|---|
| 21 `push.i` | `[phase+168]` → deque at `phase+44` | thunk: `addi r4,r30,168` / `addi r3,r30,44` |
| 22 `push.f` | `[phase+184]` → deque at `phase+64` | thunk: `addi r4,r30,184` / `addi r3,r30,64` |
| 23 `pop.i` | → `[phase+168]` | handler `0x82271C30`, only r3-offset touched is **168** |
| 24 `pop.f` | → `[phase+184]` | handler `0x82271CB8`, only r3-offset touched is **184** |

With `isl-bytecode.md`'s operand-kind table (`special[0] = [phase+164]`,
`special[1] = [phase+168]`), `pop.i` lands in **`special[1]`**.

## ✅ The built-in table is a thin dispatch layer over a vtable

Each of the 147 entries is a **stub**, not an implementation. The stub resolves
the `local[]` argument base and tail-calls a fixed slot of the `ScriptPhase`
vtable at `[phase+0]`:

```
82272DFC  addi r3, r31, 20     ; local[] base
82272E00  bl   0x82454A40      ; resolve
82272E04  lwz  r11, 0(r31)     ; the vptr
82272E10  lwz  r11, 184(r11)   ; <- fixed slot, one per built-in
82272E14  b    0x822724F0      ; mtspr CTR / bcctrl, then return 0
```

Measured over all 147:

| | count |
|---|---|
| dispatched through a `ScriptPhase` vtable slot | **112** |
| write `[phase+164]` (`special[0]`) inline in the stub | 17 |
| write `[phase+184]` inline | 0 |

**Every named predicate is in the vtable group** — `unit_state` 184,
`unit_alive` 188, `hp_pct_test` 64, `dist_lt` 56, `unit_hp_pct` 256,
`is_engaged` 252, `group_ratio_pct` 196, `timer_elapsed` 372,
`player_gauge0/1_test` 396/400 — which is the control: the split is not
arbitrary, it separates engine queries from script-local bookkeeping.

## ✅ The vtable is at `0x820A84BC`, derived self-checkingly

Not guessed from a stride — the trap this corpus already paid for. Derived from
a **known implementation**:

1. `isl-bytecode.md` documents built-in **39** `MARK_LAST_PHASE` as `[phase+300] = 2`.
2. The function `0x8226B498` is exactly `addi r11,r0,2 ; stw r11,300(r3) ; blr`.
3. It appears as a data word at exactly **one** address: `0x820A8570`.
4. Built-in 39's stub uses slot **180** → base = `0x820A8570 − 180` = **`0x820A84BC`**.

**The check, which was not used in the derivation:** built-in **40**
`mark_not_last` (`[phase+300] = 1`) uses slot **176**, so the base predicts
`0x820A84A8`… and slot 176 holds `0x8226B4A8`, which is
`addi r11,r0,1 ; stw r11,300(r3) ; blr` — the `= 1` stub sitting immediately
after the `= 2` one. Predicted and confirmed.

**Third, independent:** the database's own `vptr_writes` lists
`0x820A84BC` as a vtable, written at `0x82261B80`.

## ✅ And the result lands in `special[0]`

`unit_state` is slot 184 → **`0x8226ADF0`**. It indexes `[phase+324]` — the unit
array `isl-builtins.md` already documents — by `local[4]`, reads the record, and
writes its answer to **`[phase+164]` = `special[0]`** at both its normal exit
(`0x8226AEC4`) and its early exit (`0x8226AF48`).

That completes the chain, and the phase-3 poll loop now reads end to end:

```
call   unit_state(ADT308)      ; result -> special[0]
pop.i                          ; special[1] <- the pushed comparand
cmp.i  special[0], special[1]
beq    -> 0xFEB4               ; loop back while they are equal
```

**A built-in's return value is `special[0]`; the comparand is popped into
`special[1]`; the compare and branch do the rest.** That is the shape of every
clear condition in the corpus.

## 🟡 Not settled

* **The other 111 vtable slots are not read.** The base is now known, so each is
  a lookup rather than a search — but knowing where `hp_pct_test` lives is not
  the same as having read it.
* **Which comparand each site pushes.** The loop above compares against whatever
  `push.i` put on the deque; recovering that per site needs the push tracked
  through the decode, which `isl.py` does not do.
* **The 35 non-vtable built-ins**, and `op21`/`op22`'s generic deque helpers
  (`0x82175C20`, `0x82274BA0`), were not read — only their arguments.
* ~~**The vtable's length.**~~ ✅ **SETTLED (2026-08-27): 113 slots (0…112).**

## ✅ (2026-08-27) The class is `silph::SilphScriptPhase`, the vtable is 113 slots, and there is a SECOND one

The MSVC RTTI locator sits at `vtable[-1]`. At **`0x820A84B8`** it is `0x8210DDC0`,
whose type descriptor `0x8289CD18` spells **`.?AVSilphScriptPhase@silph@@`** — so
the class is named, not inferred.

The vtable **ends at `0x820A867C`, 113 entries**. The terminator is not "a
non-code word" — a scan on that rule runs straight past the end, which is why an
earlier pass reported "≥200 slots, no non-code word in the first 200". The real
terminator is **the next class's COL**: `0x820A8680` holds `0x8210DD74`, and a
second vtable begins at `0x820A8684`.

**Cross-check, independent of the RTTI:** the 147 built-in stubs between them
reference **109 distinct slots, minimum 0, maximum 110** — every one inside
0…112. A wrong length would have stubs pointing past the end.

### The second class: `silph::SilphScriptPhaseDemo`

`0x8210DD74` → type descriptor `0x8289CCC0` = **`.?AVSilphScriptPhaseDemo@silph@@`**,
vtable at `0x820A8684`, **also 113 slots**. It **overrides 109 of the 113**, and
the overwhelming majority point at a single shared stub, `0x8226C160`. So the Demo
phase implements almost none of the script surface — it keeps a handful of real
methods (slot 15 → `sub_82391BA8`, slot 111 `Update` → `sub_82275800`,
slot 112 → `sub_8237EF08`) and stubs the rest.

🔑 That explains a loose end from [isl-timers](isl-timers.md): the stopwatch
advance `sub_822710D0` has **two** callers, `sub_82263408` and `sub_82275800`.
They are the two classes' `Update` methods — same slot 111, base and derived.

### And both "unread spawner callers" are placed

`isl-coroutine-spawner.md` lists `sub_82273910` and `sub_82264058` as unread
callers of the spawner. They are a **matched pair**:

| | slot | class |
|---|---|---|
| `sub_82264058` | **0** | `SilphScriptPhase` |
| `sub_82273910` | **0** | `SilphScriptPhaseDemo` |

Slot 0 in this ABI is the scalar deleting destructor, so these are the two
classes' teardown paths — not two separate mysteries. 🟡 *Why* a destructor
reaches the spawner is not read here.

## ✅ (2026-08-27) A script load builds TWO phase objects, not one

Each vtable constant is materialised at exactly **two** sites — its constructor
and its destructor — and `vptr_writes` agrees:

| class | ctor | dtor |
|---|---|---|
| `SilphScriptPhase` | `sub_8225FEF8` (`0x8225FF28`) | `sub_82261B60` |
| `SilphScriptPhaseDemo` | `sub_82260568` (`0x82260660`) | `sub_82260FF8` |

⚠️ **A wrong turn worth recording.** `sub_8225FEF8`'s *only* caller is
`sub_82260568`, which looks exactly like "base ctor called from derived ctor" —
i.e. **every phase is a Demo**. That would make the built-in dispatch inert,
since the Demo vtable no-ops almost everything. Reading the constructor kills it:
`sub_82260568` **allocates and builds two separate objects.**

```
822605C8  bl 0x82150EF8          ; allocate 10216 bytes      <- object A
822605EC  bl 0x8225FEF8          ; SilphScriptPhase ctor on A
   …
82260658  bl 0x822700C0          ; the sibling initialiser on B
82260660  addi r11, r11, -31100  ; 0x820A8684
82260664  stw  r11, 0(r29)       ; Demo vptr onto B
82260690  stw  r29, 8(r30)
```

Both get the same four arguments. They land at **`Y+4` (the main phase)** and
**`Y+8` (the demo phase)** — which is why the load path read earlier resolves the
ScriptPhase through `Y+4`. *A constructor calling another class's constructor is
not proof of inheritance; check which object each vptr lands on.*

📏 The allocation is **10216 bytes**, consistent with the highest field this
corpus has read, `[phase+10160]`.

### ✅ There are THREE classes, not two — the base is `SilphScriptPhaseBase`

`sub_8225FEF8` opens by calling `sub_822700C0`, which stamps **its own** vptr
`0x820A8E44`; `sub_8225FEF8` then overwrites it with `0x820A84BC`. That *is* the
derived-constructor pattern, on one object. `0x820A8E44`'s COL gives
**`.?AVSilphScriptPhaseBase@silph@@`**, and it is **113 slots** like the other two.

```
silph::SilphScriptPhaseBase   0x820A8E44   ctor sub_822700C0
   ├── silph::SilphScriptPhase      0x820A84BC   ctor sub_8225FEF8
   └── silph::SilphScriptPhaseDemo  0x820A8684   ctor inlined in sub_82260568
```

The Demo object is built by calling the **base** ctor and stamping the Demo vptr,
which is why `sub_822700C0` appears on both paths — and why the two objects are
separate allocations rather than one.

🔑 The base ctor is also what stores the load's kind argument
(`or r26, r7, r7` → `stw r26, 152(r30)`). That field is now identified as a
**0-based stage index** — see [isl-condition-builtins](isl-condition-builtins.md).

## ✅ What the Demo vtable's overrides actually are: no-ops

The 109 overridden slots point at three shared stubs, and all three do nothing:

```
8226C160   stw r11(=0), 164(r3)                  ; special[0] = 0 ; return
822748B8   stw r10(=0), 164(r11) ; r3 = 0        ; same, and return code 0
822748A8   lfd f0, 25600(0x820B) ; stfd f0, 176  ; [phase+176] = 0.0
```

It keeps only four real methods: slot 15 → `sub_82391BA8`, **slot 111 `Update` →
`sub_82275800`**, slot 112 → `sub_8237EF08`, and its destructor.

🟡 **What a "Demo" phase is — a reading, from the corpus's own vocabulary.**
`DEMO` is one of the **eight cutscene text families** already decoded here
(`MSG_DEMO_<id>_<page>_<line>` — see
[isl-message-dialogue-link](isl-message-dialogue-link.md) and the movie↔subtitle
work), so "demo" means *cutscene* in this codebase. A second phase object,
built from the same script load, with every gameplay built-in stubbed to a no-op
and only `Update` alive, reads as **the cutscene script runner**. Stated as a
reading: nothing here shows it executing cutscene bytecode.

🔑 **A new handle on the stalled `X+12` question.** The Demo class's single
construction site is inside `sub_8225EC78` (the script load):
`sub_82260568(Y, r26, [X+12])` at `0x8225ED5C` — the kind is passed **straight
into the constructor as its third argument**, alongside `[r30+12]` again at
`0x822605E8` and `0x82260654`.