refactor(phi): Phase 59b PhiInputCollector inline in loop_builder.rs

Inline PhiInputCollector usage in loop_builder.rs continue merge logic.
This is the last remaining callsite of PhiInputCollector.

Changes:
- Inline sanitize pattern (BTreeMap for dedup and sort)
- Inline optimize_same_value logic
- Comment out use statement

This completes the PhiInputCollector usage elimination from:
- loopform_builder.rs (Phase 59)
- loop_builder.rs (Phase 59b)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/mir/loop_builder.rs

@@ -24,7 +24,8 @@ use super::{BasicBlockId, ConstValue, MirInstruction, ValueId};
 use crate::ast::ASTNode;
 use crate::mir::control_form::{is_control_form_trace_on, ControlForm, IfShape, LoopShape};
 use crate::mir::phi_core::loopform_builder::{LoopFormBuilder, LoopFormOps};
-use crate::mir::phi_core::phi_input_collector::PhiInputCollector;
+// Phase 59b: PhiInputCollector は loop_builder.rs 内にインライン化済み
+// use crate::mir::phi_core::phi_input_collector::PhiInputCollector;
 use std::collections::{BTreeMap, BTreeSet}; // Phase 25.1: 決定性確保
 
 // Phase 15 段階的根治戦略：制御フローユーティリティ
@@ -517,22 +518,39 @@ impl<'a> LoopBuilder<'a> {
                 }
             }
 
-            // 各変数について PHI ノードを生成（Phase 26-B-3: PhiInputCollector使用）
+            // 各変数について PHI ノードを生成
+            // ========================================
+            // Phase 59b: PhiInputCollector インライン化
+            // ========================================
             let mut merged = BTreeMap::new();
             for (var_name, inputs) in all_vars {
-                // Phase 26-B-3: Use PhiInputCollector
-                let mut collector = PhiInputCollector::new();
-                collector.add_snapshot(&inputs);
-                collector.sanitize();
+                // Step 1: sanitize (BTreeMap で重複削除＆ソート)
+                let mut sanitized: BTreeMap<BasicBlockId, ValueId> = BTreeMap::new();
+                for (bb, val) in &inputs {
+                    sanitized.insert(*bb, *val);
+                }
+                let final_inputs: Vec<(BasicBlockId, ValueId)> = sanitized.into_iter().collect();
 
-                // Phase 25.2: optimize_same_value() で最適化判定
-                let result_value = if let Some(same_val) = collector.optimize_same_value() {
+                // Step 2: optimize_same_value
+                let same_value = if final_inputs.is_empty() {
+                    None
+                } else if final_inputs.len() == 1 {
+                    Some(final_inputs[0].1)
+                } else {
+                    let first_val = final_inputs[0].1;
+                    if final_inputs.iter().all(|(_, val)| *val == first_val) {
+                        Some(first_val)
+                    } else {
+                        None
+                    }
+                };
+
+                // Step 3: PHI 生成 or 同一値を使用
+                let result_value = if let Some(same_val) = same_value {
                     // 全て同じ値 or 単一入力 → PHI 不要
                     same_val
                 } else {
                     // 異なる値を持つ場合は PHI ノードを生成
-                    let final_inputs = collector.finalize();
-
                     let phi_id = self.new_value();
 
                     if let Some(ref mut func) = self.parent_builder.current_function {