diff --git a/src/mir/builder/exprs.rs b/src/mir/builder/exprs.rs
index 2294a8bf..c8bf09bd 100644
--- a/src/mir/builder/exprs.rs
+++ b/src/mir/builder/exprs.rs
@@ -1,6 +1,6 @@
 // Expression lowering split from builder.rs to keep files lean
 use super::{ConstValue, MirInstruction, ValueId};
-use crate::ast::{ASTNode, AssignStmt, ReturnStmt};
+use crate::ast::{ASTNode, AssignStmt, ReturnStmt, BinaryExpr, CallExpr};
 
 impl super::MirBuilder {
     // Main expression dispatcher
@@ -19,12 +19,11 @@ impl super::MirBuilder {
         match ast {
             ASTNode::Literal { value, .. } => self.build_literal(value),
 
-            ASTNode::BinaryOp {
-                left,
-                operator,
-                right,
-                ..
-            } => self.build_binary_op(*left, operator, *right),
+            node @ ASTNode::BinaryOp { .. } => {
+                // Use BinaryExpr for clear destructuring (no behavior change)
+                let e = BinaryExpr::try_from(node).expect("ASTNode::BinaryOp must convert");
+                self.build_binary_op(*e.left, e.operator, *e.right)
+            }
 
             ASTNode::UnaryOp {
                 operator, operand, ..
@@ -87,9 +86,10 @@ impl super::MirBuilder {
                 }
             }
 
-            ASTNode::FunctionCall {
-                name, arguments, ..
-            } => self.build_function_call(name.clone(), arguments.clone()),
+            node @ ASTNode::FunctionCall { .. } => {
+                let c = CallExpr::try_from(node).expect("ASTNode::FunctionCall must convert");
+                self.build_function_call(c.name, c.arguments)
+            }
 
             ASTNode::Call {
                 callee, arguments, ..
diff --git a/src/mir/builder/loops.rs b/src/mir/builder/loops.rs
index 3d9e7594..43035252 100644
--- a/src/mir/builder/loops.rs
+++ b/src/mir/builder/loops.rs
@@ -1,5 +1,14 @@
 //! Small loop utilities for MirBuilder
-use super::BasicBlockId;
+use super::{BasicBlockId, MirBuilder};
+
+/// Create header/body/after blocks for a loop and push loop context.
+pub(crate) fn create_loop_blocks(builder: &mut MirBuilder) -> (BasicBlockId, BasicBlockId, BasicBlockId) {
+    let header = builder.block_gen.next();
+    let body = builder.block_gen.next();
+    let after = builder.block_gen.next();
+    push_loop_context(builder, header, after);
+    (header, body, after)
+}
 
 /// Push loop context (header/exit) onto the MirBuilder stacks.
 pub(crate) fn push_loop_context(
@@ -36,3 +45,19 @@ pub(crate) fn in_loop(builder: &super::MirBuilder) -> bool {
 pub(crate) fn depth(builder: &super::MirBuilder) -> usize {
     builder.loop_header_stack.len()
 }
+
+/// Add predecessor edge metadata to a basic block.
+pub(crate) fn add_predecessor(
+    builder: &mut MirBuilder,
+    block: BasicBlockId,
+    pred: BasicBlockId,
+) -> Result<(), String> {
+    if let Some(ref mut function) = builder.current_function {
+        if let Some(bb) = function.get_block_mut(block) {
+            bb.add_predecessor(pred);
+            return Ok(());
+        }
+        return Err(format!("Block {} not found", block));
+    }
+    Err("No current function".to_string())
+}
diff --git a/src/mir/loop_builder.rs b/src/mir/loop_builder.rs
index 6f1ed4ce..bcc35eb3 100644
--- a/src/mir/loop_builder.rs
+++ b/src/mir/loop_builder.rs
@@ -103,21 +103,14 @@ impl<'a> LoopBuilder<'a> {
     ) -> Result<ValueId, String> {
         // 1. ブロックの準備
         let preheader_id = self.current_block()?;
-        let header_id = self.new_block();
-        let body_id = self.new_block();
-        let after_loop_id = self.new_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();
-        // Push loop context to parent builder (for nested break/continue lowering)
-        crate::mir::builder::loops::push_loop_context(
-            self.parent_builder,
-            header_id,
-            after_loop_id,
-        );
 
         // 2. Preheader -> Header へのジャンプ
         self.emit_jump(header_id)?;
-        let _ = self.add_predecessor(header_id, preheader_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)?;
@@ -133,8 +126,8 @@ impl<'a> LoopBuilder<'a> {
 
         // 6. 条件分岐
         self.emit_branch(condition_value, body_id, after_loop_id)?;
-        let _ = self.add_predecessor(body_id, header_id);
-        let _ = self.add_predecessor(after_loop_id, header_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)?;
@@ -159,7 +152,7 @@ impl<'a> LoopBuilder<'a> {
         // 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);
         self.emit_jump(header_id)?;
-        let _ = self.add_predecessor(header_id, latch_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)?;
@@ -539,7 +532,7 @@ impl<'a> LoopBuilder<'a> {
                 let cur_block = self.current_block()?;
                 if let Some(exit_bb) = crate::mir::builder::loops::current_exit(self.parent_builder) {
                     self.emit_jump(exit_bb)?;
-                    let _ = self.add_predecessor(exit_bb, cur_block);
+                    let _ = crate::mir::builder::loops::add_predecessor(self.parent_builder, exit_bb, cur_block);
                 }
                 // Continue building in a fresh (unreachable) block to satisfy callers
                 let next_block = self.new_block();
@@ -556,7 +549,7 @@ impl<'a> LoopBuilder<'a> {
 
                 if let Some(header) = self.loop_header {
                     self.emit_jump(header)?;
-                    let _ = self.add_predecessor(header, cur_block);
+                    let _ = crate::mir::builder::loops::add_predecessor(self.parent_builder, header, cur_block);
                 }
 
                 let next_block = self.new_block();