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nyash-codex acb6720d9b Phase 61: structural if-sum+break lowering (dev-only)

2025-12-12 22:15:41 +09:00

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Phase 56: Ownership-Relay Design

Overview

「読むのは自由、管理は直下 owned だけ」アーキテクチャの設計文書。

Phase 56 は インターフェース設計のみ。実装は Phase 57 以降。

Core Definitions

owned (所有)

変数を定義したスコープが唯一の owner
Loop直下の local x → そのループが owned
body-local（if/block内の local）→ 最も内側の enclosing loop が owned

例:

fn outer() {
    local a = 0    // owned by outer
    loop {
        local b = 0    // owned by this loop
        if cond {
            local c = 0    // owned by enclosing loop (not if!)
        }
    }
}

carriers (管理対象)

carriers = writes ∩ owned
そのスコープが定義 AND 更新する変数のみ
loop_step の引数として管理

重要: Carrier は「所有 AND 更新」のみ。読み取り専用の owned 変数は carrier ではない。

captures (読み取り参照)

captures = reads \ owned (かつ carriers ではない)
祖先スコープの変数への read-only アクセス
CapturedEnv / ConditionEnv 経由

例:

local limit = 100
loop {
    local sum = 0
    if sum < limit {  // limit は capture (read-only)
        sum++         // sum は carrier (owned + written)
    }
}

relay (中継)

内側スコープが祖先 owned を更新する場合
更新責務を owner へ昇格（relay up）
中間ループは引数として素通し

例:

loop outer {
    local total = 0    // owned by outer
    loop inner {
        total++        // relay to outer (inner doesn't own total)
    }
}
// outer の exit PHI で total を merge

Invariants (不変条件)

Ownership Uniqueness: 各変数は唯一の owner を持つ
Carrier Locality: carriers = writes ∩ owned (借用なし)
Relay Propagation: writes \ owned → owner に昇格
Capture Read-Only: captures は read-only (PHI 不要)

Shadowing Rules

local x = 0          // outer owned
loop {
    local x = 1      // inner owned (shadows outer)
    // 外の x は capture 可能だが、inner の x が優先
    print(x)         // inner の x (1)
}
print(x)             // outer の x (0)

Shadowing = 新しい ownership 発生
名前解決は最内スコープ優先
外の x は capture として参照可能だが、内の x が存在する限り内が優先

Multi-Writer Merge

loop outer {
    local total = 0
    if a { loop inner1 { total++ } }  // relay to outer
    if b { loop inner2 { total-- } }  // relay to outer
}
// outer の exit PHI で merge

Relay は「更新意図の伝達」
実際の PHI merge は owner 側で実行
複数の内側ループが同じ変数を relay → owner の exit PHI で統合

JoinIR Mapping

Current System → New System

Current	New
CarrierInfo.carriers	OwnershipPlan.owned_vars (where is_written=true)
promoted_loopbodylocals	(absorbed into owned analysis)
CapturedEnv	OwnershipPlan.captures
ConditionEnv	OwnershipPlan.condition_captures
(implicit)	OwnershipPlan.relay_writes

OwnershipPlan Structure

pub struct OwnershipPlan {
    pub scope_id: ScopeId,
    pub owned_vars: Vec<ScopeOwnedVar>,  // All owned vars (carriers = is_written subset)
    pub relay_writes: Vec<RelayVar>,
    pub captures: Vec<CapturedVar>,
    pub condition_captures: Vec<CapturedVar>,
}

設計意図:

owned_vars: このスコープが所有する変数（更新されるものは carriers）
relay_writes: 祖先の変数への書き込み（owner へ昇格）
captures: 祖先の変数への読み取り専用参照
condition_captures: captures のうち、条件式で使われるもの

Implementation Phases

Phase 56: Design + interface skeleton (this phase) ✅
Phase 57: OwnershipAnalyzer implementation (dev-only)
Phase 58: P2 plumbing (dev-only)
Phase 59: P3 plumbing (dev-only)
Phase 60: Single-hop relay threading for fixtures (dev-only)
Phase 61: P3 側の接続点を決めて段階接続（dev-only）
- まずは fixtures ルート（Program(JSON v0)）で、if-sum+break を別箱として構造的に接続する
- 詳細: docs/development/current/main/PHASE_61_SUMMARY.md
- MIR→JoinIR の本番ルート（pattern3_with_if_phi.rs）へ寄せるのは別フェーズで設計→接続

Module Boundary

src/mir/join_ir/ownership/ - 責務は「解析のみ」

This module does:

✅ Collect reads/writes from AST/ProgramJSON
✅ Determine variable ownership (owned/relay/capture)
✅ Produce OwnershipPlan for downstream lowering

This module does NOT:

❌ Generate MIR instructions
❌ Modify JoinIR structures
❌ Perform lowering transformations

Lowering/MIR生成は既存モジュールが担当。

Example Ownership Plans

Example 1: Simple Loop

local sum = 0
loop {
    sum++
}

OwnershipPlan (loop scope):

owned_vars: [sum (is_written=true)]
relay_writes: []
captures: []

Example 2: Nested Loop with Relay

local total = 0
loop outer {
    loop inner {
        total++
    }
}

OwnershipPlan (inner loop):

owned_vars: []
relay_writes: [total → relay to outer]
captures: []

OwnershipPlan (outer loop):

owned_vars: [total (is_written=true, via relay)]
relay_writes: []
captures: []

Example 3: Capture + Carrier

local limit = 100
loop {
    local sum = 0
    if sum < limit {
        sum++
    }
}