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::ast::ASTNode;
use std::collections::{HashMap, HashSet};

// 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,
    collect_phi_incoming_if_reachable,
};

/// 不完全なPhi nodeの情報
#[derive(Debug, Clone)]
struct IncompletePhi {
    /// Phi nodeの結果ValueId
    phi_id: ValueId,
    /// 変数名
    var_name: String,
    /// 既知の入力値 (predecessor block id, value)
    known_inputs: Vec<(BasicBlockId, ValueId)>,
}

/// 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,

    /// ループ内で追跡する変数の不完全Phi node
    incomplete_phis: HashMap<BasicBlockId, Vec<IncompletePhi>>,

    /// 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>)>,

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

// (removed) extract_assigned_var_local was a local helper used during
// diagnostics and is no longer referenced. Keep the file lean and avoid
// dead_code warnings.

impl<'a> LoopBuilder<'a> {
    // =============================================================
    // 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)
    }

    /// Handle a `break` statement: jump to loop exit and continue in a fresh unreachable block.
    fn do_break(&mut self) -> Result<ValueId, String> {
        if let Some(exit_bb) = crate::mir::builder::loops::current_exit(self.parent_builder) {
            self.jump_with_pred(exit_bb)?;
        }
        self.switch_to_unreachable_block_with_void()
    }

    /// Handle a `continue` statement: snapshot vars, jump to loop header, then continue in a fresh unreachable block.
    fn do_continue(&mut self) -> Result<ValueId, String> {
        // Snapshot variables at current block to be considered as a predecessor input
        let snapshot = self.get_current_variable_map();
        let cur_block = self.current_block()?;
        self.block_var_maps.insert(cur_block, snapshot.clone());
        self.continue_snapshots.push((cur_block, snapshot));

        if let Some(header) = self.loop_header {
            self.jump_with_pred(header)?;
        }

        self.switch_to_unreachable_block_with_void()
    }

    // =============================================================
    // 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 {
        // フェーズM: no_phi_mode初期化削除
        Self {
            parent_builder: parent,
            incomplete_phis: HashMap::new(),
            block_var_maps: HashMap::new(),
            loop_header: None,
            continue_snapshots: Vec::new(),
            // フェーズM: no_phi_modeフィールド削除
        }
    }

    /// SSA形式でループを構築
    pub fn build_loop(
        &mut self,
        condition: ASTNode,
        body: Vec<ASTNode>,
    ) -> Result<ValueId, String> {
        // Pre-scan body for simple carrier pattern (up to 2 assigned variables, no break/continue)
        fn collect_assigns(n: &ASTNode, vars: &mut Vec<String>, has_ctrl: &mut bool) {
            match n {
                ASTNode::Assignment { target, .. } => {
                    if let ASTNode::Variable { name, .. } = target.as_ref() {
                        if !vars.iter().any(|v| v == name) {
                            vars.push(name.clone());
                        }
                    }
                }
                ASTNode::Break { .. } | ASTNode::Continue { .. } => { *has_ctrl = true; }
                ASTNode::If { then_body, else_body, .. } => {
                    let tp = ASTNode::Program { statements: then_body.clone(), span: crate::ast::Span::unknown() };
                    collect_assigns(&tp, vars, has_ctrl);
                    if let Some(eb) = else_body {
                        let ep = ASTNode::Program { statements: eb.clone(), span: crate::ast::Span::unknown() };
                        collect_assigns(&ep, vars, has_ctrl);
                    }
                }
                ASTNode::Program { statements, .. } => {
                    for s in statements { collect_assigns(s, vars, has_ctrl); }
                }
                _ => {}
            }
        }
        let mut assigned_vars: Vec<String> = Vec::new();
        let mut has_ctrl = false;
        for st in &body { collect_assigns(st, &mut assigned_vars, &mut has_ctrl); }
        if !has_ctrl && !assigned_vars.is_empty() && assigned_vars.len() <= 2 {
            // Emit a carrier hint (no-op sink by default; visible with NYASH_MIR_TRACE_HINTS=1)
            self.parent_builder.hint_loop_carrier(assigned_vars.clone());
        }

        // 1. ブロックの準備
        let preheader_id = self.current_block()?;
        let (header_id, body_id, after_loop_id) =
            crate::mir::builder::loops::create_loop_blocks(self.parent_builder);
        self.loop_header = Some(header_id);
        self.continue_snapshots.clear();

        // 2. Preheader -> Header へのジャンプ
        self.emit_jump(header_id)?;
        let _ = crate::mir::builder::loops::add_predecessor(self.parent_builder, header_id, preheader_id);

        // 3. Headerブロックの準備（unsealed状態）
        self.set_current_block(header_id)?;
        // Hint: loop header (no-op sink)
        self.parent_builder.hint_loop_header();
        let _ = self.mark_block_unsealed(header_id);

        // 4. ループ変数のPhi nodeを準備
        // ここでは、ループ内で変更される可能性のある変数を事前に検出するか、
        // または変数アクセス時に遅延生成する
        self.prepare_loop_variables(header_id, preheader_id)?;

        // 5. 条件評価（Phi nodeの結果を使用）
        let condition_value = self.build_expression_with_phis(condition)?;

        // 6. 条件分岐
        self.emit_branch(condition_value, body_id, after_loop_id)?;
        let _ = crate::mir::builder::loops::add_predecessor(self.parent_builder, body_id, header_id);
        let _ = crate::mir::builder::loops::add_predecessor(self.parent_builder, after_loop_id, header_id);

        // 7. ループボディの構築
        self.set_current_block(body_id)?;
        // Scope enter for loop body
        self.parent_builder.hint_scope_enter(0);
        // Optional safepoint per loop-iteration
        if std::env::var("NYASH_BUILDER_SAFEPOINT_LOOP")
            .ok()
            .as_deref()
            == Some("1")
        {
            self.emit_safepoint()?;
        }

        // ボディをビルド
        for stmt in body {
            self.build_statement(stmt)?;
        }
        // 8. Latchブロック（ボディの最後）からHeaderへ戻る
        // 現在の挿入先が latch（最後のブロック）なので、そのブロックIDでスナップショットを保存する
        let latch_id = self.current_block()?;
        // Hint: loop latch (no-op sink)
        self.parent_builder.hint_loop_latch();
        // Scope leave for loop body
        self.parent_builder.hint_scope_leave(0);
        let latch_snapshot = self.get_current_variable_map();
        // 以前は body_id に保存していたが、複数ブロックのボディや continue 混在時に不正確になるため
        // 実際の latch_id に対してスナップショットを紐づける
        self.block_var_maps.insert(latch_id, latch_snapshot);
        // Only jump back to header if the latch block is not already terminated
        {
            let need_jump = {
                if let Some(ref fun_ro) = self.parent_builder.current_function {
                    if let Some(bb) = fun_ro.get_block(latch_id) {
                        !bb.is_terminated()
                    } else {
                        true
                    }
                } else {
                    true
                }
            };
            if need_jump {
                self.emit_jump(header_id)?;
                let _ = crate::mir::builder::loops::add_predecessor(
                    self.parent_builder,
                    header_id,
                    latch_id,
                );
            }
        }

        // 9. Headerブロックをシール（全predecessors確定）
        self.seal_block(header_id, latch_id)?;

        // 10. ループ後の処理
        self.set_current_block(after_loop_id)?;
        // Pop loop context
        crate::mir::builder::loops::pop_loop_context(self.parent_builder);

        // void値を返す
        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）
    fn prepare_loop_variables(
        &mut self,
        header_id: BasicBlockId,
        preheader_id: BasicBlockId,
    ) -> Result<(), String> {
        // 現在の変数マップから、ループで使用される可能性のある変数を取得
        let current_vars = self.get_current_variable_map();
        // preheader時点のスナップショット（後でphi入力の解析に使う）
        self.block_var_maps
            .insert(preheader_id, current_vars.clone());

        // 各変数に対して不完全なPhi nodeを作成
        let mut incomplete_phis = Vec::new();
        for (var_name, &value_before) in &current_vars {
            let phi_id = self.new_value();

            // 不完全なPhi nodeを作成（preheaderからの値のみ設定）
            let incomplete_phi = IncompletePhi {
                phi_id,
                var_name: var_name.clone(),
                known_inputs: vec![(preheader_id, value_before)],
            };

            incomplete_phis.push(incomplete_phi);

            // フェーズM: no_phi_mode分岐削除（常にPHI使用）

            // 変数マップを更新（Phi nodeの結果を使用）
            self.update_variable(var_name.clone(), phi_id);
        }

        // 不完全なPhi nodeを記録
        self.incomplete_phis.insert(header_id, incomplete_phis);

        Ok(())
    }

    /// ブロックをシールし、不完全なPhi nodeを完成させる
    fn seal_block(&mut self, block_id: BasicBlockId, latch_id: BasicBlockId) -> Result<(), String> {
        // 不完全なPhi nodeを取得
        if let Some(incomplete_phis) = self.incomplete_phis.remove(&block_id) {
            for mut phi in incomplete_phis {
                for (cid, snapshot) in &self.continue_snapshots {
                    if let Some(v) = snapshot.get(&phi.var_name) {
                        phi.known_inputs.push((*cid, *v));
                    }
                }

                let value_after = self
                    .get_variable_at_block(&phi.var_name, latch_id)
                    .ok_or_else(|| format!("Variable {} not found at latch block", phi.var_name))?;

                phi.known_inputs.push((latch_id, value_after));

                // フェーズM: 常にPHI命令を使用（no_phi_mode分岐削除）
                self.emit_phi_at_block_start(block_id, phi.phi_id, phi.known_inputs)?;
                self.update_variable(phi.var_name.clone(), phi.phi_id);
            }
        }

        // ブロックをシール済みとしてマーク
        self.mark_block_sealed(block_id)?;

        Ok(())
    }

    // --- 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 {
        self.parent_builder.value_gen.next()
    }

    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> {
        self.parent_builder
            .emit_instruction(MirInstruction::Branch {
                condition,
                then_bb,
                else_bb,
            })
    }

    fn emit_safepoint(&mut self) -> Result<(), String> {
        self.parent_builder
            .emit_instruction(MirInstruction::Safepoint)
    }

    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> {
        // 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) {
                // Phi命令は必ずブロックの先頭に配置
                let phi_inst = MirInstruction::Phi { dst, inputs };
                block.instructions.insert(0, phi_inst);
                Ok(())
            } else {
                Err(format!("Block {} not found", block_id))
            }
        } else {
            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())
        }
    }

    fn mark_block_unsealed(&mut self, _block_id: BasicBlockId) -> Result<(), String> {
        // ブロックはデフォルトでunsealedなので、特に何もしない
        // （既にBasicBlock::newでsealed: falseに初期化されている）
        Ok(())
    }

    fn mark_block_sealed(&mut self, block_id: BasicBlockId) -> Result<(), String> {
        if let Some(ref mut function) = self.parent_builder.current_function {
            if let Some(block) = function.get_block_mut(block_id) {
                block.seal();
                Ok(())
            } else {
                Err(format!("Block {} not found", block_id))
            }
        } 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) {
        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_expression_with_phis(&mut self, expr: ASTNode) -> Result<ValueId, String> {
        // Phi nodeの結果を考慮しながら式を構築
        self.parent_builder.build_expression(expr)
    }

    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)?);
                    // Stop early if this block has been terminated (e.g., break/continue)
                    let cur_id = self.current_block()?;
                    let terminated = {
                        if let Some(ref fun_ro) = self.parent_builder.current_function {
                            if let Some(bb) = fun_ro.get_block(cur_id) {
                                bb.is_terminated()
                            } else {
                                false
                            }
                        } else {
                            false
                        }
                    };
                    if terminated {
                        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> {
        // 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();
        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 pre_then_var_value = pre_if_var_map.clone();

        // then branch
        self.set_current_block(then_bb)?;
        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
        )?;

        // else branch
        self.set_current_block(else_bb)?;
        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
        )?;

        // Continue at merge
        self.set_current_block(merge_bb)?;
        // collect assigned variables in both branches
        fn collect_assigned_vars(ast: &ASTNode, out: &mut std::collections::HashSet<String>) {
            match ast {
                ASTNode::Assignment { target, .. } => {
                    if let ASTNode::Variable { name, .. } = target.as_ref() { out.insert(name.clone()); }
                }
                ASTNode::Program { statements, .. } => { for s in statements { collect_assigned_vars(s, out); } }
                ASTNode::If { then_body, else_body, .. } => {
                    let tp = ASTNode::Program { statements: then_body.clone(), span: crate::ast::Span::unknown() };
                    collect_assigned_vars(&tp, out);
                    if let Some(eb) = else_body {
                        let ep = ASTNode::Program { statements: eb.clone(), span: crate::ast::Span::unknown() };
                        collect_assigned_vars(&ep, out);
                    }
                }
                _ => {}
            }
        }

        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() };
        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() };
            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();
        for var_name in vars.into_iter() {
            let then_val = then_var_map_end.get(&var_name).copied().or_else(|| pre_then_var_value.get(&var_name).copied());
            let else_val = else_var_map_end_opt.as_ref().and_then(|m| m.get(&var_name).copied()).or_else(|| pre_then_var_value.get(&var_name).copied());

            if let (Some(tv), Some(ev)) = (then_val, else_val) {
                let mut incomings: Vec<(BasicBlockId, ValueId)> = Vec::new();
                if let Some(pred) = then_pred_to_merge { incomings.push((pred, tv)); }
                if let Some(pred) = else_pred_to_merge { incomings.push((pred, ev)); }
                match incomings.len() {
                    0 => {}
                    1 => {
                        let (_pred, v) = incomings[0];
                        self.parent_builder.variable_map.insert(var_name, v);
                    }
                    _ => {
                        let phi_id = self.new_value();
                        // フェーズM: 常にPHI命令を使用（no_phi_mode分岐削除）
                        self.emit_phi_at_block_start(merge_bb, phi_id, incomings)?;
                        self.parent_builder.variable_map.insert(var_name, phi_id);
                    }
                }
            }
        }
        let void_id = self.new_value();
        self.emit_const(void_id, ConstValue::Void)?;
        Ok(void_id)
    }
}