hakorune/src/mir/loop_builder.rs

/*!
 * MIR Loop Builder - SSA形式でのループ構築専用モジュール
 *
 * Sealed/Unsealed blockとPhi nodeを使った正しいループ実装
 * Based on Gemini's recommendation for proper SSA loop handling
 */

use super::{BasicBlockId, ConstValue, MirInstruction, ValueId};
use crate::mir::control_form::{ControlForm, IfShape, LoopShape, is_control_form_trace_on};
use crate::mir::phi_core::loopform_builder::{LoopFormBuilder, LoopFormOps};
use crate::ast::ASTNode;
use std::collections::HashMap;

// Phase 15 段階的根治戦略：制御フローユーティリティ
use super::utils::{
    is_current_block_terminated,
    capture_actual_predecessor_and_jump,
};

/// ループ脱出の種類（箱化・共通化のための型）
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum LoopExitKind {
    /// break文（exit blockへジャンプ）
    Break,
    /// continue文（header blockへジャンプ）
    Continue,
}

/// ループビルダー - SSA形式でのループ構築を管理
pub struct LoopBuilder<'a> {
    /// 親のMIRビルダーへの参照
    parent_builder: &'a mut super::builder::MirBuilder,

    /// ブロックごとの変数マップ（スコープ管理）
    #[allow(dead_code)]
    block_var_maps: HashMap<BasicBlockId, HashMap<String, ValueId>>,

    /// ループヘッダーID（continueで使用）
    loop_header: Option<BasicBlockId>,

    /// continue文からの変数スナップショット
    continue_snapshots: Vec<(BasicBlockId, HashMap<String, ValueId>)>,

    /// break文からの変数スナップショット（exit PHI生成用）
    exit_snapshots: Vec<(BasicBlockId, HashMap<String, ValueId>)>,

    // フェーズM: no_phi_modeフィールド削除（常にPHI使用）
}


impl<'a> LoopBuilder<'a> {
    // Implement phi_core LoopPhiOps on LoopBuilder for in-place delegation

    /// Find the source value of a Copy instruction in a given block
    /// If `dst` is defined by a Copy instruction `dst = copy src`, return Some(src)
    /// Otherwise return None

    // =============================================================
    // Control Helpers — break/continue/jumps/unreachable handling
    // =============================================================

    /// Emit a jump to `target` from the current block and record predecessor metadata.
    fn jump_with_pred(&mut self, target: BasicBlockId) -> Result<(), String> {
        let cur_block = self.current_block()?;
        self.emit_jump(target)?;
        let _ = crate::mir::builder::loops::add_predecessor(self.parent_builder, target, cur_block);
        Ok(())
    }

    /// Switch insertion to a fresh (unreachable) block and place a Void const to keep callers satisfied.
    fn switch_to_unreachable_block_with_void(&mut self) -> Result<ValueId, String> {
        let next_block = self.new_block();
        self.set_current_block(next_block)?;
        let void_id = self.new_value();
        self.emit_const(void_id, ConstValue::Void)?;
        Ok(void_id)
    }

    /// 【箱化】ループ脱出の共通処理（break/continue統一化）
    ///
    /// Phase 25.1o: break と continue の共通パターンを抽出し、
    /// LoopExitKind で振る舞いを切り替える統一メソッド。
    ///
    /// # 処理フロー
    /// 1. 現在の変数マップをスナップショット
    /// 2. 適切なスナップショットリストに追加（Break → exit_snapshots, Continue → continue_snapshots）
    /// 3. ターゲットブロックへジャンプ（Break → exit, Continue → header）
    /// 4. unreachable ブロックに切り替え
    fn do_loop_exit(&mut self, kind: LoopExitKind) -> Result<ValueId, String> {
        // 1. スナップショット取得（共通処理）
        let snapshot = self.get_current_variable_map();
        let cur_block = self.current_block()?;

        // 2. スナップショット保存（kind別処理）
        match kind {
            LoopExitKind::Break => {
                if std::env::var("NYASH_LOOPFORM_DEBUG").ok().as_deref() == Some("1") {
                    eprintln!("[DEBUG/do_break] Saved snapshot from block {:?}, vars: {:?}",
                        cur_block, snapshot.keys().collect::<Vec<_>>());
                }
                self.exit_snapshots.push((cur_block, snapshot));
            }
            LoopExitKind::Continue => {
                self.block_var_maps.insert(cur_block, snapshot.clone());
                self.continue_snapshots.push((cur_block, snapshot));
            }
        }

        // 3. ターゲットブロックへジャンプ（kind別処理）
        match kind {
            LoopExitKind::Break => {
                if let Some(exit_bb) = crate::mir::builder::loops::current_exit(self.parent_builder) {
                    self.jump_with_pred(exit_bb)?;
                }
            }
            LoopExitKind::Continue => {
                if let Some(header) = self.loop_header {
                    self.jump_with_pred(header)?;
                }
            }
        }

        // 4. unreachable ブロックに切り替え（共通処理）
        self.switch_to_unreachable_block_with_void()
    }

    /// Handle a `break` statement: jump to loop exit and continue in a fresh unreachable block.
    /// 【箱化】do_loop_exit() への thin wrapper
    fn do_break(&mut self) -> Result<ValueId, String> {
        self.do_loop_exit(LoopExitKind::Break)
    }

    /// Handle a `continue` statement: snapshot vars, jump to loop header, then continue in a fresh unreachable block.
    /// 【箱化】do_loop_exit() への thin wrapper
    fn do_continue(&mut self) -> Result<ValueId, String> {
        self.do_loop_exit(LoopExitKind::Continue)
    }

    // =============================================================
    // Lifecycle — create builder, main loop construction
    // =============================================================
    /// 新しいループビルダーを作成
    pub fn new(parent: &'a mut super::builder::MirBuilder) -> Self {
        Self {
            parent_builder: parent,
            block_var_maps: HashMap::new(),
            loop_header: None,
            continue_snapshots: Vec::new(),
            exit_snapshots: Vec::new(),  // exit PHI用のスナップショット
        }
    }

    /// SSA形式でループを構築 (LoopForm v2 only)
    pub fn build_loop(
        &mut self,
        condition: ASTNode,
        body: Vec<ASTNode>,
    ) -> Result<ValueId, String> {
        // Phase 7-F: Legacy loop builder removed - LoopForm v2 is now the only implementation
        self.build_loop_with_loopform(condition, body)
    }

    /// SSA形式でループを構築 (LoopFormBuilder implementation)
    fn build_loop_with_loopform(
        &mut self,
        condition: ASTNode,
        body: Vec<ASTNode>,
    ) -> Result<ValueId, String> {
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[build_loop_with_loopform] === ENTRY ===");
            if let Some(ref func) = self.parent_builder.current_function {
                eprintln!("[build_loop_with_loopform] fn='{}', counter={}, func_ptr={:p}",
                         func.signature.name, func.next_value_id, func as *const _);
            }
            eprintln!("[build_loop_with_loopform] condition={:?}", condition);
            eprintln!("[build_loop_with_loopform] body.len()={}", body.len());
        }
        // Create loop structure blocks following LLVM canonical form
        // We need a dedicated preheader block to materialize loop entry copies
        let before_loop_id = self.current_block()?;

        // Capture variable snapshot BEFORE creating new blocks (at loop entry point)
        let current_vars = self.get_current_variable_map();

        // DEBUG: Show variable map before guard check
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[loopform] before_loop_id={:?}, variable_map size={}",
                     before_loop_id, current_vars.len());
            for (name, value) in &current_vars {
                eprintln!("  {} -> {:?}", name, value);
            }
        }

        // GUARD: Check for invalid ValueId(0) before proceeding
        // ValueId(0) indicates uninitialized variables - skip loop construction entirely
        for (name, value) in &current_vars {
            if value.0 == 0 {
                if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
                    eprintln!("[build_loop_with_loopform] ⚠️ GUARD: Detected ValueId(0) for '{}', skipping entire loop construction", name);
                    eprintln!("[build_loop_with_loopform] Returning ValueId(0) without emitting any instructions");
                }
                // Return ValueId(0) directly without emitting instructions
                // This allows the caller to retry loop construction with properly initialized variables
                return Ok(ValueId(0));
            }
        }

        let preheader_id = self.new_block();
        let header_id = self.new_block();
        let body_id = self.new_block();
        let latch_id = self.new_block();
        let exit_id = self.new_block();

        // Jump from current block to preheader
        let entry_block = self.current_block()?;
        self.emit_jump(preheader_id)?;
        // 📦 Hotfix 6: Add CFG predecessor for preheader (same as legacy version)
        crate::mir::builder::loops::add_predecessor(self.parent_builder, preheader_id, entry_block)?;

        // Initialize LoopFormBuilder with preheader and header blocks
        let mut loopform = LoopFormBuilder::new(preheader_id, header_id);

        // Pass 1: Prepare structure (allocate all ValueIds upfront)
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[loopform] Block IDs: preheader={:?}, header={:?}, body={:?}, latch={:?}, exit={:?}",
                     preheader_id, header_id, body_id, latch_id, exit_id);
            eprintln!("[loopform] variable_map at loop entry (size={}):", current_vars.len());
            let mut loop_count = 0;
            for (name, value) in &current_vars {
                loop_count += 1;
                eprintln!("  [{}] {} -> {:?}", loop_count, name, value);
                let is_param = self.is_parameter(name);
                eprintln!("    param={}", is_param);
            }
            eprintln!("[loopform] iterated {} times", loop_count);
            if let Some(ref func) = self.parent_builder.current_function {
                eprintln!("[loopform] BEFORE prepare_structure: fn='{}', counter={}, func_ptr={:p}",
                         func.signature.name, func.next_value_id, func as *const _);
            } else {
                eprintln!("[loopform] BEFORE prepare_structure: current_function=None");
            }
        }
        loopform.prepare_structure(self, &current_vars)?;
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            if let Some(ref func) = self.parent_builder.current_function {
                eprintln!("[loopform] AFTER prepare_structure: fn='{}', counter={}, func_ptr={:p}",
                         func.signature.name, func.next_value_id, func as *const _);
            } else {
                eprintln!("[loopform] AFTER prepare_structure: current_function=None");
            }
        }

        // Pass 2: Emit preheader (copies and jump to header)
        loopform.emit_preheader(self)?;
        // 📦 Hotfix 6: Add CFG predecessor for header from preheader (same as legacy version)
        crate::mir::builder::loops::add_predecessor(self.parent_builder, header_id, preheader_id)?;

        // Pass 3: Emit header PHIs (incomplete, only preheader edge)
        self.set_current_block(header_id)?;

        // Ensure header block exists before emitting PHIs
        self.parent_builder.ensure_block_exists(header_id)?;

        loopform.emit_header_phis(self)?;

        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[loopform] variable_map after emit_header_phis:");
            for (name, value) in self.get_current_variable_map().iter() {
                eprintln!("  {} -> {:?}", name, value);
            }
        }

        // Set up loop context for break/continue
        crate::mir::builder::loops::push_loop_context(self.parent_builder, header_id, exit_id);
        self.loop_header = Some(header_id);
        self.continue_snapshots.clear();
        self.exit_snapshots.clear();

        // Emit condition check in header
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[loopform/condition] BEFORE build_expression: current_block={:?}", self.current_block()?);
            if let Some(ref func) = self.parent_builder.current_function {
                eprintln!("[loopform/condition] BEFORE: fn='{}', counter={}, func_ptr={:p}",
                         func.signature.name, func.next_value_id, func as *const _);
            }
        }
        let cond_value = self.parent_builder.build_expression(condition)?;
        // Capture the ACTUAL block that emits the branch (might differ from header_id
        // if build_expression created new blocks)
        let branch_source_block = self.current_block()?;
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[loopform/condition] AFTER build_expression: branch_source_block={:?}", branch_source_block);
            if let Some(ref func) = self.parent_builder.current_function {
                eprintln!("[loopform/condition] AFTER: fn='{}', counter={}, func_ptr={:p}",
                         func.signature.name, func.next_value_id, func as *const _);
            }
        }
        self.emit_branch(cond_value, body_id, exit_id)?;
        // 📦 Hotfix 6: Add CFG predecessors for branch targets (Cytron et al. 1991 requirement)
        // This ensures exit_block.predecessors is populated before Exit PHI generation
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[loopform/condition] BEFORE add_predecessor: exit_id={:?}, branch_source={:?}", exit_id, branch_source_block);
        }
        crate::mir::builder::loops::add_predecessor(self.parent_builder, body_id, branch_source_block)?;
        crate::mir::builder::loops::add_predecessor(self.parent_builder, exit_id, branch_source_block)?;
        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[loopform/condition] AFTER emit_branch: current_block={:?}", self.current_block()?);
            eprintln!("[loopform/condition] Added predecessors: body={:?} exit={:?} from={:?}",
                body_id, exit_id, branch_source_block);
            // Verify predecessors were added
            if let Some(ref func) = self.parent_builder.current_function {
                if let Some(exit_block) = func.blocks.get(&exit_id) {
                    eprintln!("[loopform/condition] exit_block.predecessors = {:?}", exit_block.predecessors);
                }
            }
        }

        // Lower loop body
        self.set_current_block(body_id)?;
        for stmt in body {
            self.build_statement(stmt)?;
            if is_current_block_terminated(self.parent_builder)? {
                break;
            }
        }

        // Capture variable snapshot at end of body (before jumping to latch)
        let body_end_vars = self.get_current_variable_map();

        // Jump to latch if not already terminated
        let actual_latch_id = if !is_current_block_terminated(self.parent_builder)? {
            self.emit_jump(latch_id)?;
            latch_id
        } else {
            // Body is terminated (break/continue), use current block as latch
            self.current_block()?
        };

        // Latch: jump back to header
        self.set_current_block(latch_id)?;

        // Update variable map with body end values for sealing
        for (name, value) in body_end_vars {
            self.update_variable(name, value);
        }

        self.emit_jump(header_id)?;
        // 📦 Hotfix 6: Add CFG predecessor for header from latch (same as legacy version)
        crate::mir::builder::loops::add_predecessor(self.parent_builder, header_id, latch_id)?;

        // Pass 4: Seal PHIs with latch + continue values
        let continue_snaps = self.continue_snapshots.clone();
        loopform.seal_phis(self, actual_latch_id, &continue_snaps)?;

        // Exit block
        self.set_current_block(exit_id)?;

        // Phase 25.1h: ControlForm統合版に切り替え
        // continue / break のターゲットブロックをユニーク化して収集
        use std::collections::HashSet;
        let mut cont_set: HashSet<BasicBlockId> = HashSet::new();
        let mut break_set: HashSet<BasicBlockId> = HashSet::new();
        for (bb, _) in &self.continue_snapshots {
            cont_set.insert(*bb);
        }
        for (bb, _) in &self.exit_snapshots {
            break_set.insert(*bb);
        }
        let continue_targets: Vec<BasicBlockId> = cont_set.into_iter().collect();
        let break_targets: Vec<BasicBlockId> = break_set.into_iter().collect();

        let loop_shape = LoopShape {
            preheader: preheader_id,
            header: header_id,
            body: body_id,
            latch: latch_id,
            exit: exit_id,
            continue_targets,
            break_targets,
        };
        let form = ControlForm::from_loop(loop_shape.clone());

        // Region/GC 観測レイヤ（Phase 25.1l）:
        // NYASH_REGION_TRACE=1 のときだけ、Stage‑B 周辺ループの
        // Region 情報（entry/exit/slots）をログに出すよ。
        crate::mir::region::observer::observe_control_form(self.parent_builder, &form);

        // Build exit PHIs for break statements using ControlForm wrapper
        let exit_snaps = self.exit_snapshots.clone();
        crate::mir::phi_core::loopform_builder::build_exit_phis_for_control(
            &loopform,
            self,
            &form,
            &exit_snaps,
            branch_source_block,
        )?;

        // Pop loop context
        crate::mir::builder::loops::pop_loop_context(self.parent_builder);

        // ControlForm 観測: 環境フラグ（未設定時は既定ON）のとき LoopShape をダンプ
        if is_control_form_trace_on() {
            form.debug_dump();
            #[cfg(debug_assertions)]
            if let Some(ref func) = self.parent_builder.current_function {
                loop_shape.debug_validate(func);
            }
        }

        // Return void value
        let void_dst = self.new_value();
        self.emit_const(void_dst, ConstValue::Void)?;
        Ok(void_dst)
    }


    // =============================================================
    // PHI Helpers — prepare/finalize PHIs and block sealing
    // =============================================================
    /// ループ変数の準備（事前検出または遅延生成）
    ///
    /// ポリシー:
    /// - ループキャリア（ループ本体で再代入される変数）と pinned 変数のみを PHI 対象とする。
    /// - ループ不変のローカル（text_len / pattern_len など）は preheader 値をそのまま使い、
    ///   不要な PHI を張らないことで SSA 破綻（同一 ValueId の二重定義）を防ぐ。

    /// ブロックをシールし、不完全なPhi nodeを完成させる

    /// Exitブロックで変数のPHIを生成（breakポイントでの値を統一）

    // --- ヘルパーメソッド（親ビルダーへの委譲） ---

    fn current_block(&self) -> Result<BasicBlockId, String> {
        self.parent_builder
            .current_block
            .ok_or_else(|| "No current block".to_string())
    }

    fn new_block(&mut self) -> BasicBlockId {
        self.parent_builder.block_gen.next()
    }

    fn new_value(&mut self) -> ValueId {
        // Use function-local allocator via MirBuilder helper to keep
        // ValueId ranges consistent within the current function.
        self.parent_builder.next_value_id()
    }

    fn set_current_block(&mut self, block_id: BasicBlockId) -> Result<(), String> {
        self.parent_builder.start_new_block(block_id)
    }

    fn emit_jump(&mut self, target: BasicBlockId) -> Result<(), String> {
        self.parent_builder
            .emit_instruction(MirInstruction::Jump { target })
    }

    fn emit_branch(
        &mut self,
        condition: ValueId,
        then_bb: BasicBlockId,
        else_bb: BasicBlockId,
    ) -> Result<(), String> {
        // LocalSSA: ensure condition is materialized in the current block
        let condition_local = self.parent_builder.local_ssa_ensure(condition, 4);
        self.parent_builder
            .emit_instruction(MirInstruction::Branch {
                condition: condition_local,
                then_bb,
                else_bb,
            })
    }

    fn emit_const(&mut self, dst: ValueId, value: ConstValue) -> Result<(), String> {
        self.parent_builder
            .emit_instruction(MirInstruction::Const { dst, value })
    }

    /// ブロック先頭に PHI 命令を挿入（不変条件: PHI は常にブロック先頭）
    fn emit_phi_at_block_start(
        &mut self,
        block_id: BasicBlockId,
        dst: ValueId,
        inputs: Vec<(BasicBlockId, ValueId)>,
    ) -> Result<(), String> {
        let dbg = std::env::var("NYASH_BUILDER_DEBUG").ok().as_deref() == Some("1");
        if dbg {
            eprintln!(
                "[DEBUG] LoopBuilder::emit_phi_at_block_start: block={}, dst=%{}, inputs={:?}",
                block_id, dst.0, inputs
            );
        }
        // Phi nodeをブロックの先頭に挿入
        if let Some(ref mut function) = self.parent_builder.current_function {
            if let Some(block) = function.get_block_mut(block_id) {
                if dbg {
                    eprintln!(
                        "[DEBUG]   Block {} current instructions count: {}",
                        block_id,
                        block.instructions.len()
                    );
                }
                // Phi命令は必ずブロックの先頭に配置。ただし同一dstの既存PHIがある場合は差し替える。
                let mut replaced = false;
                let mut idx = 0;
                while idx < block.instructions.len() {
                    match &mut block.instructions[idx] {
                        MirInstruction::Phi { dst: d, inputs: ins } if *d == dst => {
                            *ins = inputs.clone();
                            replaced = true;
                            break;
                        }
                        MirInstruction::Phi { .. } => { idx += 1; }
                        _ => break,
                    }
                }
                if !replaced {
                    let phi_inst = MirInstruction::Phi { dst, inputs: inputs.clone() };
                    block.instructions.insert(0, phi_inst);
                }
                if dbg {
                    eprintln!("[DEBUG]   ✅ PHI instruction inserted at position 0");
                    eprintln!(
                        "[DEBUG]   Block {} after insert instructions count: {}",
                        block_id,
                        block.instructions.len()
                    );
                }
                // Verify PHI is still there
                if let Some(first_inst) = block.instructions.get(0) {
                    match first_inst {
                        MirInstruction::Phi { dst: phi_dst, .. } => {
                            if dbg {
                                eprintln!(
                                    "[DEBUG]   Verified: First instruction is PHI dst=%{}",
                                    phi_dst.0
                                );
                            }
                        }
                        other => {
                            if dbg {
                                eprintln!(
                                    "[DEBUG]   ⚠️  WARNING: First instruction is NOT PHI! It's {:?}",
                                    other
                                );
                            }
                        }
                    }
                }
                Ok(())
            } else {
                if dbg {
                    eprintln!("[DEBUG]   ❌ Block {} not found!", block_id);
                }
                Err(format!("Block {} not found", block_id))
            }
        } else {
            if dbg {
                eprintln!("[DEBUG]   ❌ No current function!");
            }
            Err("No current function".to_string())
        }
    }

    #[allow(dead_code)]
    fn add_predecessor(&mut self, block: BasicBlockId, pred: BasicBlockId) -> Result<(), String> {
        if let Some(ref mut function) = self.parent_builder.current_function {
            if let Some(block) = function.get_block_mut(block) {
                block.add_predecessor(pred);
                Ok(())
            } else {
                Err(format!("Block {} not found", block))
            }
        } else {
            Err("No current function".to_string())
        }
    }

    // =============================================================
    // Variable Map Utilities — snapshots and rebinding
    // =============================================================
    fn get_current_variable_map(&self) -> HashMap<String, ValueId> {
        self.parent_builder.variable_map.clone()
    }

    fn update_variable(&mut self, name: String, value: ValueId) {
        if std::env::var("NYASH_BUILDER_DEBUG").ok().as_deref() == Some("1") {
            eprintln!(
                "[DEBUG] LoopBuilder::update_variable: name={}, value=%{}",
                name, value.0
            );
        }
        self.parent_builder.variable_map.insert(name, value);
    }

    fn get_variable_at_block(&self, name: &str, block_id: BasicBlockId) -> Option<ValueId> {
        // まずブロックごとのスナップショットを優先
        if let Some(map) = self.block_var_maps.get(&block_id) {
            if let Some(v) = map.get(name) {
                return Some(*v);
            }
        }
        // フォールバック：現在の変数マップ（単純ケース用）
        self.parent_builder.variable_map.get(name).copied()
    }


    fn build_statement(&mut self, stmt: ASTNode) -> Result<ValueId, String> {
        match stmt {
            // Ensure nested bare blocks inside loops are lowered with loop-aware semantics
            ASTNode::Program { statements, .. } => {
                let mut last = None;
                for s in statements.into_iter() {
                    last = Some(self.build_statement(s)?);
                    // フェーズS修正：統一終端検出ユーティリティ使用
                    if is_current_block_terminated(self.parent_builder)? {
                        break;
                    }
                }
                Ok(last.unwrap_or_else(|| {
                    let void_id = self.new_value();
                    // Emit a void const to keep SSA consistent when block is empty
                    let _ = self.emit_const(void_id, ConstValue::Void);
                    void_id
                }))
            }
            ASTNode::If { condition, then_body, else_body, .. } =>
                self.lower_if_in_loop(*condition, then_body, else_body),
            ASTNode::Break { .. } => self.do_break(),
            ASTNode::Continue { .. } => self.do_continue(),
            other => self.parent_builder.build_expression(other),
        }
    }

    /// Lower an if-statement inside a loop, preserving continue/break semantics and emitting PHIs per assigned variable.
    fn lower_if_in_loop(
        &mut self,
        condition: ASTNode,
        then_body: Vec<ASTNode>,
        else_body: Option<Vec<ASTNode>>,
    ) -> Result<ValueId, String> {
        // Reserve a deterministic join id for debug region labeling (nested inside loop)
        let join_id = self.parent_builder.debug_next_join_id();
        // Pre-pin comparison operands to slots so repeated uses across blocks are safe
        if crate::config::env::mir_pre_pin_compare_operands() {
        if let ASTNode::BinaryOp { operator, left, right, .. } = &condition {
            use crate::ast::BinaryOperator as BO;
            match operator {
                BO::Equal | BO::NotEqual | BO::Less | BO::LessEqual | BO::Greater | BO::GreaterEqual => {
                    if let Ok(lhs_v) = self.parent_builder.build_expression((**left).clone()) {
                        let _ = self.parent_builder.pin_to_slot(lhs_v, "@loop_if_lhs");
                    }
                    if let Ok(rhs_v) = self.parent_builder.build_expression((**right).clone()) {
                        let _ = self.parent_builder.pin_to_slot(rhs_v, "@loop_if_rhs");
                    }
                }
                _ => {}
            }
        }
        }
        // Evaluate condition and create blocks
        let cond_val = self.parent_builder.build_expression(condition)?;
        let then_bb = self.new_block();
        let else_bb = self.new_block();
        let merge_bb = self.new_block();
        let pre_branch_bb = self.current_block()?;
        self.emit_branch(cond_val, then_bb, else_bb)?;

        // Capture pre-if variable map (used for phi normalization)
        let pre_if_var_map = self.get_current_variable_map();
        let trace_if = std::env::var("NYASH_IF_TRACE").ok().as_deref() == Some("1");
        // (legacy) kept for earlier merge style; now unified helpers compute deltas directly.

        // then branch
        self.set_current_block(then_bb)?;
        // Debug region: join then-branch (inside loop)
        self.parent_builder
            .debug_push_region(format!("join#{}", join_id) + "/then");
        // Materialize all variables at entry via single-pred Phi (correctness-first)
        let names_then: Vec<String> = self
            .parent_builder
            .variable_map
            .keys()
            .filter(|n| !n.starts_with("__pin$"))
            .cloned()
            .collect();
        for name in names_then {
            if let Some(&pre_v) = pre_if_var_map.get(&name) {
                let phi_val = self.new_value();
                self.emit_phi_at_block_start(then_bb, phi_val, vec![(pre_branch_bb, pre_v)])?;
                let name_for_log = name.clone();
                self.update_variable(name, phi_val);
                if trace_if {
                    eprintln!(
                        "[if-trace] then-entry phi var={} pre={:?} -> dst={:?}",
                        name_for_log, pre_v, phi_val
                    );
                }
            }
        }
        for s in then_body.iter().cloned() {
            let _ = self.build_statement(s)?;
            // フェーズS修正：統一終端検出ユーティリティ使用
            if is_current_block_terminated(self.parent_builder)? { 
                break; 
            }
        }
        let then_var_map_end = self.get_current_variable_map();
        // フェーズS修正：最強モード指摘の「実到達predecessor捕捉」を統一
        let then_pred_to_merge = capture_actual_predecessor_and_jump(
            self.parent_builder, 
            merge_bb
        )?;
        // Pop then-branch debug region
        self.parent_builder.debug_pop_region();

        // else branch
        self.set_current_block(else_bb)?;
        // Debug region: join else-branch (inside loop)
        self.parent_builder
            .debug_push_region(format!("join#{}", join_id) + "/else");
        // Materialize all variables at entry via single-pred Phi (correctness-first)
        let names2: Vec<String> = self
            .parent_builder
            .variable_map
            .keys()
            .filter(|n| !n.starts_with("__pin$"))
            .cloned()
            .collect();
        for name in names2 {
            if let Some(&pre_v) = pre_if_var_map.get(&name) {
                let phi_val = self.new_value();
                self.emit_phi_at_block_start(else_bb, phi_val, vec![(pre_branch_bb, pre_v)])?;
                let name_for_log = name.clone();
                self.update_variable(name, phi_val);
                if trace_if {
                    eprintln!(
                        "[if-trace] else-entry phi var={} pre={:?} -> dst={:?}",
                        name_for_log, pre_v, phi_val
                    );
                }
            }
        }
        let mut else_var_map_end_opt: Option<HashMap<String, ValueId>> = None;
        if let Some(es) = else_body.clone() {
            for s in es.into_iter() {
                let _ = self.build_statement(s)?;
                // フェーズS修正：統一終端検出ユーティリティ使用
                if is_current_block_terminated(self.parent_builder)? { 
                    break; 
                }
            }
            else_var_map_end_opt = Some(self.get_current_variable_map());
        }
        // フェーズS修正：else branchでも統一実到達predecessor捕捉
        let else_pred_to_merge = capture_actual_predecessor_and_jump(
            self.parent_builder, 
            merge_bb
        )?;
        // Pop else-branch debug region
        self.parent_builder.debug_pop_region();

        // Continue at merge
        self.set_current_block(merge_bb)?;
        // Debug region: join merge (inside loop)
        self.parent_builder
            .debug_push_region(format!("join#{}", join_id) + "/join");

        let mut vars: std::collections::HashSet<String> = std::collections::HashSet::new();
        let then_prog = ASTNode::Program { statements: then_body.clone(), span: crate::ast::Span::unknown() };
        crate::mir::phi_core::if_phi::collect_assigned_vars(&then_prog, &mut vars);
        if let Some(es) = &else_body {
            let else_prog = ASTNode::Program { statements: es.clone(), span: crate::ast::Span::unknown() };
            crate::mir::phi_core::if_phi::collect_assigned_vars(&else_prog, &mut vars);
        }

        // Reset to pre-if map before rebinding to ensure a clean environment
        self.parent_builder.variable_map = pre_if_var_map.clone();
        // Use shared helper to merge modified variables at merge block
        struct Ops<'b, 'a>(&'b mut LoopBuilder<'a>);
        impl<'b, 'a> crate::mir::phi_core::if_phi::PhiMergeOps for Ops<'b, 'a> {
            fn new_value(&mut self) -> ValueId { self.0.new_value() }
            fn emit_phi_at_block_start(
                &mut self,
                block: BasicBlockId,
                dst: ValueId,
                inputs: Vec<(BasicBlockId, ValueId)>,
            ) -> Result<(), String> { self.0.emit_phi_at_block_start(block, dst, inputs) }
            fn update_var(&mut self, name: String, value: ValueId) { self.0.parent_builder.variable_map.insert(name, value); }
            fn debug_verify_phi_inputs(&mut self, merge_bb: BasicBlockId, inputs: &[(BasicBlockId, ValueId)]) {
                if let Some(ref func) = self.0.parent_builder.current_function {
                    crate::mir::phi_core::common::debug_verify_phi_inputs(func, merge_bb, inputs);
                }
            }
        }
        // Reset to pre-if snapshot, then delegate to shared helper
        self.parent_builder.variable_map = pre_if_var_map.clone();

        // Phase 25.1h: ControlForm統合版に切り替え
        let if_shape = IfShape {
            cond_block: pre_branch_bb,
            then_block: then_bb,
            else_block: Some(else_bb),
            merge_block: merge_bb,
        };
        let form = ControlForm::from_if(if_shape.clone());

        // Region/GC 観測レイヤ（Phase 25.1l）:
        // NYASH_REGION_TRACE=1 のときだけ、Stage‑B 周辺 If 構造の
        // Region 情報（entry/exit/slots）をログに出すよ。
        crate::mir::region::observer::observe_control_form(self.parent_builder, &form);

        let mut ops = Ops(self);

        crate::mir::phi_core::if_phi::merge_modified_with_control(
            &mut ops,
            &form,
            &pre_if_var_map,
            &then_var_map_end,
            &else_var_map_end_opt,
            None,
            then_pred_to_merge,
            else_pred_to_merge,
        )?;

        // ControlForm 観測: 環境フラグ（未設定時は既定ON）のとき IfShape をダンプ
        if is_control_form_trace_on() {
            form.debug_dump();
            #[cfg(debug_assertions)]
            if let Some(ref func) = self.parent_builder.current_function {
                if_shape.debug_validate(func);
            }
        }
        let void_id = self.new_value();
        self.emit_const(void_id, ConstValue::Void)?;
        // Pop merge debug region
        self.parent_builder.debug_pop_region();
        Ok(void_id)
    }
}

// Implement phi_core LoopPhiOps on LoopBuilder for in-place delegation
impl crate::mir::phi_core::loop_phi::LoopPhiOps for LoopBuilder<'_> {
    fn new_value(&mut self) -> ValueId { self.new_value() }
    fn emit_phi_at_block_start(
        &mut self,
        block: BasicBlockId,
        dst: ValueId,
        inputs: Vec<(BasicBlockId, ValueId)>,
    ) -> Result<(), String> {
        self.emit_phi_at_block_start(block, dst, inputs)
    }
    fn update_var(&mut self, name: String, value: ValueId) { self.update_variable(name, value) }
    fn get_variable_at_block(&mut self, name: &str, block: BasicBlockId) -> Option<ValueId> {
        // Call the inherent method (immutable borrow) to avoid recursion
        LoopBuilder::get_variable_at_block(self, name, block)
    }
    fn debug_verify_phi_inputs(&mut self, merge_bb: BasicBlockId, inputs: &[(BasicBlockId, ValueId)]) {
        if let Some(ref func) = self.parent_builder.current_function {
            crate::mir::phi_core::common::debug_verify_phi_inputs(func, merge_bb, inputs);
        }
    }

    fn emit_copy_at_preheader(
        &mut self,
        preheader_id: BasicBlockId,
        dst: ValueId,
        src: ValueId,
    ) -> Result<(), String> {
        let dbg = std::env::var("NYASH_BUILDER_DEBUG").ok().as_deref() == Some("1");
        if dbg {
            eprintln!(
                "[DEBUG] emit_copy_at_preheader: preheader={}, dst=%{}, src=%{}",
                preheader_id, dst.0, src.0
            );
        }
        if let Some(ref mut function) = self.parent_builder.current_function {
            if let Some(block) = function.get_block_mut(preheader_id) {
                if dbg {
                    eprintln!("[DEBUG]   Adding Copy instruction to block {}", preheader_id);
                }
                block.add_instruction(MirInstruction::Copy { dst, src });
                Ok(())
            } else {
                if dbg {
                    eprintln!("[DEBUG]   ❌ Preheader block {} not found!", preheader_id);
                }
                Err(format!("Preheader block {} not found", preheader_id))
            }
        } else {
            if dbg {
                eprintln!("[DEBUG]   ❌ No current function!");
            }
            Err("No current function".to_string())
        }
    }

    fn add_predecessor_edge(
        &mut self,
        block: BasicBlockId,
        pred: BasicBlockId,
    ) -> Result<(), String> {
        self.add_predecessor(block, pred)
    }
}

// Implement LoopFormOps trait for LoopBuilder to support LoopFormBuilder integration
impl<'a> LoopFormOps for LoopBuilder<'a> {
    fn new_value(&mut self) -> ValueId {
        // CRITICAL: Must use MirFunction's next_value_id(), not MirBuilder's value_gen
        // Otherwise we get SSA violations because the two counters diverge
        let id = if let Some(ref mut func) = self.parent_builder.current_function {
            let before = func.next_value_id;
            let id = func.next_value_id();
            if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
                eprintln!("[LoopFormOps::new_value] fn='{}' counter: {} -> {}, allocated: {:?}",
                         func.signature.name, before, func.next_value_id, id);
            }
            id
        } else {
            // Fallback (should never happen in practice)
            let id = self.parent_builder.value_gen.next();
            if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
                eprintln!("[LoopFormOps::new_value] FALLBACK value_gen, allocated: {:?}", id);
            }
            id
        };
        id
    }

    fn ensure_counter_after(&mut self, max_id: u32) -> Result<(), String> {
        if let Some(ref mut func) = self.parent_builder.current_function {
            // 📦 Hotfix 1: Consider both parameter count and existing ValueIds
            let param_count = func.signature.params.len() as u32;
            let min_counter = param_count.max(max_id + 1);

            if func.next_value_id < min_counter {
                if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
                    eprintln!("[LoopFormOps::ensure_counter_after] fn='{}' params={}, max_id={}, adjusting counter {} -> {}",
                             func.signature.name, param_count, max_id, func.next_value_id, min_counter);
                }
                func.next_value_id = min_counter;
            }
            Ok(())
        } else {
            Err("No current function to adjust counter".to_string())
        }
    }

    fn block_exists(&self, block: BasicBlockId) -> bool {
        // 📦 Hotfix 2: Check if block exists in current function's CFG
        if let Some(ref func) = self.parent_builder.current_function {
            func.blocks.contains_key(&block)
        } else {
            false
        }
    }

    fn get_block_predecessors(&self, block: BasicBlockId) -> std::collections::HashSet<BasicBlockId> {
        // 📦 Hotfix 6: Get actual CFG predecessors for PHI validation
        if let Some(ref func) = self.parent_builder.current_function {
            if let Some(bb) = func.blocks.get(&block) {
                bb.predecessors.clone()
            } else {
                std::collections::HashSet::new()  // Non-existent blocks have no predecessors
            }
        } else {
            std::collections::HashSet::new()
        }
    }

    fn is_parameter(&self, name: &str) -> bool {
        // A parameter is a true function parameter that doesn't change across iterations
        // Pinned receivers (__pin$*$@*) are NOT parameters - they're carriers
        // because they can be reassigned in the loop body

        // Pinned variables are always carriers (loop-variant)
        if name.starts_with("__pin$") {
            return false;
        }

        // Check if it's the receiver
        if name == "me" {
            return true;
        }

        // Check if it's in the original function parameter names
        // This is more reliable than checking ValueIds, which can change through copies/PHIs
        let is_param = self.parent_builder.function_param_names.contains(name);

        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
            eprintln!("[is_parameter] {} -> {} (param_names = {:?})",
                     name, is_param, self.parent_builder.function_param_names);
        }

        is_param
    }

    fn set_current_block(&mut self, block: BasicBlockId) -> Result<(), String> {
        self.parent_builder.start_new_block(block)
    }

    fn emit_copy(&mut self, dst: ValueId, src: ValueId) -> Result<(), String> {
        self.parent_builder.emit_instruction(MirInstruction::Copy { dst, src })
    }

    fn emit_jump(&mut self, target: BasicBlockId) -> Result<(), String> {
        self.emit_jump(target)
    }

    fn emit_phi(
        &mut self,
        dst: ValueId,
        inputs: Vec<(BasicBlockId, ValueId)>,
    ) -> Result<(), String> {
        self.emit_phi_at_block_start(
            self.current_block()?,
            dst,
            inputs
        )
    }

    fn update_phi_inputs(
        &mut self,
        block: BasicBlockId,
        phi_id: ValueId,
        inputs: Vec<(BasicBlockId, ValueId)>,
    ) -> Result<(), String> {
        self.parent_builder.update_phi_instruction(block, phi_id, inputs)
    }

    fn update_var(&mut self, name: String, value: ValueId) {
        self.parent_builder.variable_map.insert(name, value);
    }

    fn get_variable_at_block(&self, name: &str, block: BasicBlockId) -> Option<ValueId> {
        // Use the inherent method to avoid recursion
        LoopBuilder::get_variable_at_block(self, name, block)
    }
}