hakorune/docs/archive/phases/phase-170-197/phase197_pattern4_update_semantics.md

Phase 197: Pattern 4 Update Semantics

Status: In Progress（197-B で ExitMeta/Boundary 経路の修正は完了） Date: 2025-12-06 Goal: Fix loop_continue_multi_carrier.hako to output correct values (25, 5)

Problem Statement

Current Behavior

• Output: 5, 5
• Expected: 25, 5

Root Cause

The update expressions for carriers are hardcoded in loop_with_continue_minimal.rs:310-317:

let rhs = if carrier_name == "count" {
    const_1  // count = count + 1
} else {
    i_next   // sum = sum + i_next (and other accumulators)
};

This works for the simple pattern where:

• count carriers always use +1
• Other carriers always use +i_next

However, this breaks semantic correctness because:

• sum = sum + i in the source code should use the current i value
• The current implementation uses i_next (the next iteration's value)

Test Case Analysis

From loop_continue_multi_carrier.hako:

local i = 0
local sum = 0
local count = 0
loop(i < 10) {
  i = i + 1          // i goes 1,2,3,4,5,6,7,8,9,10
  if (i % 2 == 0) {
    continue         // Skip even: 2,4,6,8,10
  }
  sum = sum + i      // sum = sum + i (current i)
  count = count + 1  // count = count + 1
}
// Expected: sum=25 (1+3+5+7+9), count=5

The update expressions should be:

• i: i = i + 1 (constant increment)
• sum: sum = sum + i (accumulate current i)
• count: count = count + 1 (constant increment)

Current Implementation Problem

In loop_with_continue_minimal.rs, the Select statement for carriers:

// carrier_next = carrier_param + rhs
loop_step_func.body.push(JoinInst::Compute(MirLikeInst::BinOp {
    dst: carrier_next,
    op: BinOpKind::Add,
    lhs: carrier_param,
    rhs,  // This is WRONG for sum!
}));

For sum:

• rhs = i_next (next iteration value)
• Should be: rhs = i_current (current iteration value)

197-B: ExitMeta / Boundary 経路の修正（完了）

さらに、Phase 197-B では「どの ValueId を出口として見るか」という経路も修正した:

• 問題:

  • もともと k_exit 関数のパラメータ（carrier_exit_ids = 例えば ValueId(20), ValueId(21)）を ExitMeta に入れていたが、
  • これらは JoinIR 関数インライン後の MIR では「定義されない」ValueId になってしまうケースがあった。
  • 一方、loop_step 内の Jump 引数（carrier_param_ids）は MIR マージ時に正しい ValueId に remap される。

• 修正内容:

  1. loop_with_continue_minimal.rs 側で、ExitMeta には k_exit のパラメータではなく、Jump の引数（carrier_param_ids）を使うよう変更。
  2. reconnect_boundary（mod.rs）に remapper パラメータを追加し、Boundary に書かれた JoinIR 側 ValueId を remapper 経由で MIR の ValueId に変換してから variable_map に接続。

この結果:

• carrier の出口 ValueId は「必ず MIR 上で定義がある値」になり、
• ExitBindingBuilder 〜 JoinInlineBoundary 〜 merge_joinir_mir_blocks までの配管が、multi-carrier でも破綻しない状態になった。

Solution Design

Phase 197-2: LoopUpdateAnalyzer

Create src/mir/join_ir/lowering/loop_update_analyzer.rs:

pub enum UpdateExpr {
    Const(i64),                                    // count = count + 1
    BinOp { lhs: String, op: BinOpKind, rhs: String }, // sum = sum + i
}

pub struct LoopUpdateAnalyzer;

impl LoopUpdateAnalyzer {
    pub fn analyze_carrier_updates(
        body: &[ASTNode],
        carriers: &[CarrierVar]
    ) -> HashMap<String, UpdateExpr> {
        // Extract update expressions from assignment statements
        // in the loop body
    }
}

Phase 197-3: Update Lowerer

Modify loop_with_continue_minimal.rs:

1. Call LoopUpdateAnalyzer::analyze_carrier_updates() at the start
2. Remove hardcoded if carrier_name == "count" logic
3. Use extracted UpdateExpr metadata to generate correct RHS:
   • For Const(n): Use const_n
   • For BinOp { rhs: "i", ... }: Use i_current (not i_next)

Expected Fix

After implementation:

• sum = sum + i will use current i value
• Output will be 25, 5 as expected

Implementation Steps

1. Task 197-1: Create this documentation
2. Task 197-2: Implement LoopUpdateAnalyzer
3. Task 197-3: Update loop_with_continue_minimal.rs to use metadata
4. Task 197-4: Test and verify output

References

• Test case: apps/tests/loop_continue_multi_carrier.hako
• Lowerer: src/mir/join_ir/lowering/loop_with_continue_minimal.rs
• Pattern detection: src/mir/builder/control_flow/joinir/patterns/pattern4_with_continue.rs Status: Historical