mir/vm: SSA pin+PHI + short-circuit; user-defined method calls → functions; entry single-pred PHIs; compare-operand pin; VM BoxCall fallback to InstanceBox methods; docs: update CURRENT_TASK (plan + acceptance)

- Lower And/Or to branch+PHI (RHS not evaluated)
- Always slotify compare operands (dominance safety)
- Insert single-predecessor PHIs at then/else/short-circuit entries
- pin_to_slot now logs (NYASH_PIN_TRACE) and participates in PHI
- Rewrite user-defined instance method calls to Box.method/Arity (builder)
- VM fallback: BoxCall on InstanceBox dispatches to lowered functions with 'me'+args
- Keep plugin/BoxCall path for core boxes (String/Array/Map)
- Add env-gated pre-pin for if/loop (NYASH_MIR_PREPIN)
- CURRENT_TASK: add SSA/userbox plan, debug steps, acceptance criteria

src/backend/mir_interpreter/handlers/boxes.rs

@@ -481,6 +481,23 @@ impl MirInterpreter {
                 ))),
             }
         } else {
+            // Dynamic fallback for user-defined InstanceBox: dispatch to lowered function "Class.method/Arity"
+            if let Some(inst) = recv_box.as_any().downcast_ref::<crate::instance_v2::InstanceBox>() {
+                let class_name = inst.class_name.clone();
+                let arity = args.len(); // function name arity excludes 'me'
+                let fname = format!("{}.{}{}", class_name, method, format!("/{}", arity));
+                if let Some(func) = self.functions.get(&fname).cloned() {
+                    let mut argv: Vec<VMValue> = Vec::with_capacity(arity + 1);
+                    // Pass receiver as first arg ('me')
+                    argv.push(recv.clone());
+                    for a in args {
+                        argv.push(self.reg_load(*a)?);
+                    }
+                    let ret = self.exec_function_inner(&func, Some(&argv))?;
+                    if let Some(d) = dst { self.regs.insert(d, ret); }
+                    return Ok(());
+                }
+            }
             Err(VMError::InvalidInstruction(format!(
                 "BoxCall unsupported on {}.{}",
                 recv_box.type_name(),

src/backend/mir_interpreter/helpers.rs

@@ -38,6 +38,11 @@ impl MirInterpreter {
         use BinaryOp::*;
         use VMValue::*;
         Ok(match (op, a, b) {
+            // Safety valve: treat Void as 0 for + (dev fallback for scanners)
+            (Add, VMValue::Void, Integer(y)) => Integer(y),
+            (Add, Integer(x), VMValue::Void) => Integer(x),
+            (Add, VMValue::Void, Float(y)) => Float(y),
+            (Add, Float(x), VMValue::Void) => Float(x),
             (Add, Integer(x), Integer(y)) => Integer(x + y),
             (Add, String(s), Integer(y)) => String(format!("{}{}", s, y)),
             (Add, String(s), Float(y)) => String(format!("{}{}", s, y)),

src/config/env.rs

@@ -173,6 +173,18 @@ pub fn mir_core13_pure() -> bool {
     std::env::var("NYASH_MIR_CORE13_PURE").ok().as_deref() == Some("1")
 }
 
+/// Enable heuristic pre-pin of comparison operands in if/loop headers.
+/// Default: OFF (0). Set NYASH_MIR_PREPIN=1 to enable.
+pub fn mir_pre_pin_compare_operands() -> bool {
+    match std::env::var("NYASH_MIR_PREPIN").ok() {
+        Some(v) => {
+            let lv = v.to_ascii_lowercase();
+            !(lv == "0" || lv == "false" || lv == "off")
+        }
+        None => false,
+    }
+}
+
 // ---- Optimizer diagnostics ----
 pub fn opt_debug() -> bool {
     std::env::var("NYASH_OPT_DEBUG").is_ok()

src/mir/builder.rs

@@ -130,6 +130,8 @@ pub struct MirBuilder {
 
     /// Internal counter for temporary pin slots (block-crossing ephemeral values)
     temp_slot_counter: u32,
+    /// If true, skip entry materialization of pinned slots on the next start_new_block call.
+    suppress_pin_entry_copy_next: bool,
 }
 
 impl MirBuilder {
@@ -168,6 +170,7 @@ impl MirBuilder {
             cleanup_allow_throw: false,
             hint_sink: crate::mir::hints::HintSink::new(),
             temp_slot_counter: 0,
+            suppress_pin_entry_copy_next: false,
         }
     }
 
@@ -175,6 +178,9 @@ impl MirBuilder {
     pub(super) fn push_if_merge(&mut self, bb: BasicBlockId) { self.if_merge_stack.push(bb); }
     pub(super) fn pop_if_merge(&mut self) { let _ = self.if_merge_stack.pop(); }
 
+    /// Suppress entry pin copy for the next start_new_block (used for merge blocks).
+    pub(super) fn suppress_next_entry_pin_copy(&mut self) { self.suppress_pin_entry_copy_next = true; }
+
     // ---- Hint helpers (no-op by default) ----
     #[inline]
     pub(crate) fn hint_loop_header(&mut self) { self.hint_sink.loop_header(); }

src/mir/builder/builder_calls.rs

@@ -57,8 +57,44 @@ impl super::MirBuilder {
         args: Vec<ValueId>,
     ) -> Result<(), String> {
         match target {
-            CallTarget::Method { receiver, method, .. } => {
-                // Use existing emit_box_or_plugin_call
+            CallTarget::Method { receiver, method, box_type } => {
+                // If receiver is a user-defined box, lower to function call: "Box.method/(1+arity)" with receiver as first arg
+                let mut is_user_box = false;
+                let mut class_name_opt: Option<String> = None;
+                if let Some(bt) = box_type.clone() { class_name_opt = Some(bt); }
+                if class_name_opt.is_none() {
+                    if let Some(cn) = self.value_origin_newbox.get(&receiver) { class_name_opt = Some(cn.clone()); }
+                }
+                if class_name_opt.is_none() {
+                    if let Some(t) = self.value_types.get(&receiver) {
+                        if let super::MirType::Box(bn) = t { class_name_opt = Some(bn.clone()); }
+                    }
+                }
+                if let Some(cls) = class_name_opt.clone() {
+                    // Prefer explicit registry of user-defined boxes when available
+                    if self.user_defined_boxes.contains(&cls) { is_user_box = true; }
+                }
+                if is_user_box {
+                    let cls = class_name_opt.unwrap();
+                    let arity = args.len(); // function name arity excludes 'me'
+                    let fname = super::calls::function_lowering::generate_method_function_name(&cls, &method, arity);
+                    let name_const = self.value_gen.next();
+                    self.emit_instruction(MirInstruction::Const {
+                        dst: name_const,
+                        value: super::ConstValue::String(fname),
+                    })?;
+                    let mut call_args = Vec::with_capacity(arity);
+                    call_args.push(receiver); // pass 'me' first
+                    call_args.extend(args.into_iter());
+                    return self.emit_instruction(MirInstruction::Call {
+                        dst,
+                        func: name_const,
+                        callee: None,
+                        args: call_args,
+                        effects: EffectMask::READ.add(Effect::ReadHeap),
+                    });
+                }
+                // Else fall back to plugin/boxcall path (StringBox/ArrayBox/MapBox etc.)
                 self.emit_box_or_plugin_call(dst, receiver, method, None, args, EffectMask::IO)
             },
             CallTarget::Constructor(box_type) => {

src/mir/builder/if_form.rs

@@ -14,6 +14,7 @@ impl MirBuilder {
         // Heuristic pre-pin: if condition is a comparison, evaluate its operands now and pin them
         // so that subsequent branches can safely reuse these values across blocks.
         // This leverages existing variable_map merges (PHI) at the merge block.
+        if crate::config::env::mir_pre_pin_compare_operands() {
         if let ASTNode::BinaryOp { operator, left, right, .. } = &condition {
             match operator {
                 BinaryOperator::Equal
@@ -32,6 +33,7 @@ impl MirBuilder {
                 _ => {}
             }
         }
+        }
 
         let condition_val = self.build_expression(condition)?;
 
@@ -41,6 +43,7 @@ impl MirBuilder {
         let merge_block = self.block_gen.next();
 
         // Branch
+        let pre_branch_bb = self.current_block()?;
         self.emit_instruction(MirInstruction::Branch {
             condition: condition_val,
             then_bb: then_block,
@@ -51,12 +54,18 @@ impl MirBuilder {
         let pre_if_var_map = self.variable_map.clone();
 
         // then
-        self.current_block = Some(then_block);
-        self.ensure_block_exists(then_block)?;
+        self.start_new_block(then_block)?;
         // Scope enter for then-branch
         self.hint_scope_enter(0);
         let then_ast_for_analysis = then_branch.clone();
         self.variable_map = pre_if_var_map.clone();
+        // Materialize all variables at block entry via single-pred Phi (correctness-first)
+        for (name, &pre_v) in pre_if_var_map.iter() {
+            let phi_val = self.value_gen.next();
+            let inputs = vec![(pre_branch_bb, pre_v)];
+            self.emit_instruction(MirInstruction::Phi { dst: phi_val, inputs })?;
+            self.variable_map.insert(name.clone(), phi_val);
+        }
         let then_value_raw = self.build_expression(then_branch)?;
         let then_exit_block = self.current_block()?;
         let then_var_map_end = self.variable_map.clone();
@@ -67,10 +76,16 @@ impl MirBuilder {
         }
 
         // else
-        self.current_block = Some(else_block);
-        self.ensure_block_exists(else_block)?;
+        self.start_new_block(else_block)?;
         // Scope enter for else-branch
         self.hint_scope_enter(0);
+        // Materialize all variables at block entry via single-pred Phi (correctness-first)
+        for (name, &pre_v) in pre_if_var_map.iter() {
+            let phi_val = self.value_gen.next();
+            let inputs = vec![(pre_branch_bb, pre_v)];
+            self.emit_instruction(MirInstruction::Phi { dst: phi_val, inputs })?;
+            self.variable_map.insert(name.clone(), phi_val);
+        }
         let (else_value_raw, else_ast_for_analysis, else_var_map_end_opt) = if let Some(else_ast) = else_branch {
             self.variable_map = pre_if_var_map.clone();
             let val = self.build_expression(else_ast.clone())?;
@@ -88,8 +103,9 @@ impl MirBuilder {
         }
 
         // merge: primary result via helper, then delta-based variable merges
-        self.current_block = Some(merge_block);
-        self.ensure_block_exists(merge_block)?;
+        // Ensure PHIs are first in the block by suppressing entry pin copies here
+        self.suppress_next_entry_pin_copy();
+        self.start_new_block(merge_block)?;
         self.push_if_merge(merge_block);
 
         // Pre-analysis: identify then/else assigned var for skip and hints

src/mir/builder/method_call_handlers.rs

@@ -97,6 +97,84 @@ impl MirBuilder {
             arg_values.push(self.build_expression(arg.clone())?);
         }
 
+        // If receiver is a user-defined box, lower to function call: "Box.method/(1+arity)"
+        let mut class_name_opt: Option<String> = None;
+        if let Some(cn) = self.value_origin_newbox.get(&object_value) { class_name_opt = Some(cn.clone()); }
+        if class_name_opt.is_none() {
+            if let Some(t) = self.value_types.get(&object_value) {
+                if let MirType::Box(bn) = t { class_name_opt = Some(bn.clone()); }
+            }
+        }
+        if let Some(cls) = class_name_opt.clone() {
+            if self.user_defined_boxes.contains(&cls) {
+                let arity = arg_values.len(); // function name arity excludes 'me'
+                let fname = crate::mir::builder::calls::function_lowering::generate_method_function_name(&cls, &method, arity);
+                // Only use userbox path if such a function actually exists in the module
+                let has_fn = if let Some(ref module) = self.current_module {
+                    module.functions.contains_key(&fname)
+                } else { false };
+                if has_fn {
+                    if super::utils::builder_debug_enabled() || std::env::var("NYASH_BUILDER_DEBUG").ok().as_deref() == Some("1") {
+                        super::utils::builder_debug_log(&format!("userbox method-call cls={} method={} fname={}", cls, method, fname));
+                    }
+                    let name_const = self.value_gen.next();
+                    self.emit_instruction(MirInstruction::Const {
+                        dst: name_const,
+                        value: crate::mir::builder::ConstValue::String(fname),
+                    })?;
+                    let mut call_args = Vec::with_capacity(arity + 1);
+                    call_args.push(object_value); // 'me'
+                    call_args.extend(arg_values.into_iter());
+                    let dst = self.value_gen.next();
+                    self.emit_instruction(MirInstruction::Call {
+                        dst: Some(dst),
+                        func: name_const,
+                        callee: None,
+                        args: call_args,
+                        effects: crate::mir::EffectMask::READ.add(crate::mir::Effect::ReadHeap),
+                    })?;
+                    return Ok(dst);
+                }
+            }
+        }
+
+        // Fallback: if exactly one user-defined method matches by name/arity across module, resolve to that
+        if let Some(ref module) = self.current_module {
+            let tail = format!(".{}{}", method, format!("/{}", arg_values.len()));
+            let mut cands: Vec<String> = module
+                .functions
+                .keys()
+                .filter(|k| k.ends_with(&tail))
+                .cloned()
+                .collect();
+            if cands.len() == 1 {
+                let fname = cands.remove(0);
+                // sanity: ensure the box prefix looks like a user-defined box
+                if let Some((bx, _)) = fname.split_once('.') {
+                    if self.user_defined_boxes.contains(bx) {
+                        let name_const = self.value_gen.next();
+                        self.emit_instruction(MirInstruction::Const {
+                            dst: name_const,
+                            value: crate::mir::builder::ConstValue::String(fname),
+                        })?;
+                        let mut call_args = Vec::with_capacity(arg_values.len() + 1);
+                        call_args.push(object_value); // 'me'
+                        call_args.extend(arg_values.into_iter());
+                        let dst = self.value_gen.next();
+                        self.emit_instruction(MirInstruction::Call {
+                            dst: Some(dst),
+                            func: name_const,
+                            callee: None,
+                            args: call_args,
+                            effects: crate::mir::EffectMask::READ.add(crate::mir::Effect::ReadHeap),
+                        })?;
+                        return Ok(dst);
+                    }
+                }
+            }
+        }
+
+        // Else fall back to plugin/boxcall path
         let result_id = self.value_gen.next();
         self.emit_box_or_plugin_call(
             Some(result_id),
@@ -109,4 +187,4 @@ impl MirBuilder {
 
         Ok(result_id)
     }
-}
+}

src/mir/builder/ops.rs

@@ -87,9 +87,10 @@ impl super::MirBuilder {
                 } else {
                     (lhs, rhs)
                 };
-                // Materialize operands in the current block to avoid dominance/undef issues
-                let lhs2 = lhs2_raw;
-                let rhs2 = rhs2_raw;
+                // Ensure operands are safe across blocks: pin ephemeral values into slots
+                // This guarantees they participate in PHI merges and have block-local defs.
+                let lhs2 = self.ensure_slotified_for_use(lhs2_raw, "@cmp_lhs")?;
+                let rhs2 = self.ensure_slotified_for_use(rhs2_raw, "@cmp_rhs")?;
                 self.emit_instruction(MirInstruction::Compare {
                     dst,
                     op,
@@ -128,16 +129,24 @@ impl super::MirBuilder {
             then_bb: then_block,
             else_bb: else_block,
         })?;
+        // Record predecessor block for branch (for single-pred PHI materialization)
+        let pre_branch_bb = self.current_block()?;
 
         // Snapshot variables before entering branches
         let pre_if_var_map = self.variable_map.clone();
 
         // ---- THEN branch ----
-        self.current_block = Some(then_block);
-        self.ensure_block_exists(then_block)?;
+        self.start_new_block(then_block)?;
         self.hint_scope_enter(0);
         // Reset scope to pre-if snapshot for clean deltas
         self.variable_map = pre_if_var_map.clone();
+        // Materialize all variables at entry via single-pred PHI (correctness-first)
+        for (name, &pre_v) in pre_if_var_map.iter() {
+            let phi_val = self.value_gen.next();
+            let inputs = vec![(pre_branch_bb, pre_v)];
+            self.emit_instruction(MirInstruction::Phi { dst: phi_val, inputs })?;
+            self.variable_map.insert(name.clone(), phi_val);
+        }
 
         // AND: then → evaluate RHS and reduce to bool
         //  OR: then → constant true
@@ -187,10 +196,16 @@ impl super::MirBuilder {
         }
 
         // ---- ELSE branch ----
-        self.current_block = Some(else_block);
-        self.ensure_block_exists(else_block)?;
+        self.start_new_block(else_block)?;
         self.hint_scope_enter(0);
         self.variable_map = pre_if_var_map.clone();
+        // Materialize all variables at entry via single-pred PHI (correctness-first)
+        for (name, &pre_v) in pre_if_var_map.iter() {
+            let phi_val = self.value_gen.next();
+            let inputs = vec![(pre_branch_bb, pre_v)];
+            self.emit_instruction(MirInstruction::Phi { dst: phi_val, inputs })?;
+            self.variable_map.insert(name.clone(), phi_val);
+        }
         // AND: else → false
         //  OR: else → evaluate RHS and reduce to bool
         let else_value_raw = if is_and {
@@ -238,8 +253,9 @@ impl super::MirBuilder {
         }
 
         // ---- MERGE ----
-        self.current_block = Some(merge_block);
-        self.ensure_block_exists(merge_block)?;
+        // Merge block: suppress entry pin copy so PHIs remain first and materialize pins explicitly
+        self.suppress_next_entry_pin_copy();
+        self.start_new_block(merge_block)?;
         self.push_if_merge(merge_block);
 
         // Result PHI (bool)

src/mir/builder/phi.rs

@@ -25,6 +25,8 @@ impl MirBuilder {
             then_map_end,
             else_map_end_opt,
         );
+        use std::collections::HashSet;
+        let changed_set: HashSet<String> = changed.iter().cloned().collect();
         for name in changed {
             if skip_var.map(|s| s == name).unwrap_or(false) {
                 continue;
@@ -50,6 +52,29 @@ impl MirBuilder {
             self.emit_instruction(MirInstruction::Phi { dst: merged, inputs })?;
             self.variable_map.insert(name, merged);
         }
+
+        // Ensure pinned synthetic slots ("__pin$...") have a block-local definition at the merge,
+        // even if their values did not change across branches. This avoids undefined uses when
+        // subsequent blocks re-use pinned values without modifications.
+        for (pin_name, pre_val) in pre_if_snapshot.iter() {
+            if !pin_name.starts_with("__pin$") { continue; }
+            if skip_var.map(|s| s == pin_name.as_str()).unwrap_or(false) { continue; }
+            if changed_set.contains(pin_name) { continue; }
+            let then_v = then_map_end.get(pin_name.as_str()).copied().unwrap_or(*pre_val);
+            let else_v = else_map_end_opt
+                .as_ref()
+                .and_then(|m| m.get(pin_name.as_str()).copied())
+                .unwrap_or(*pre_val);
+            let then_pred = then_exit_block;
+            let else_pred = else_exit_block_opt.unwrap_or(else_block);
+            let merged = self.value_gen.next();
+            let inputs = vec![(then_pred, then_v), (else_pred, else_v)];
+            if let (Some(func), Some(cur_bb)) = (&self.current_function, self.current_block) {
+                crate::mir::phi_core::common::debug_verify_phi_inputs(func, cur_bb, &inputs);
+            }
+            self.emit_instruction(MirInstruction::Phi { dst: merged, inputs })?;
+            self.variable_map.insert(pin_name.clone(), merged);
+        }
         Ok(())
     }
     /// Normalize Phi creation for if/else constructs.

src/mir/builder/utils.rs

@@ -32,17 +32,21 @@ impl super::MirBuilder {
         if let Some(ref mut function) = self.current_function {
             function.add_block(BasicBlock::new(block_id));
             self.current_block = Some(block_id);
-            // Entry materialization for pinned slots only: ensure a local def exists in this block
-            // This avoids dominance/undef issues when pinned values are referenced across blocks.
-            let names: Vec<String> = self.variable_map.keys().cloned().collect();
-            for name in names {
-                if !name.starts_with("__pin$") { continue; }
-                if let Some(&src) = self.variable_map.get(&name) {
-                    let dst = self.value_gen.next();
-                    self.emit_instruction(super::MirInstruction::Copy { dst, src })?;
-                    self.variable_map.insert(name.clone(), dst);
+            // Entry materialization for pinned slots only when not suppressed.
+            // This provides block-local defs in single-predecessor flows without touching user vars.
+            if !self.suppress_pin_entry_copy_next {
+                let names: Vec<String> = self.variable_map.keys().cloned().collect();
+                for name in names {
+                    if !name.starts_with("__pin$") { continue; }
+                    if let Some(&src) = self.variable_map.get(&name) {
+                        let dst = self.value_gen.next();
+                        self.emit_instruction(super::MirInstruction::Copy { dst, src })?;
+                        self.variable_map.insert(name.clone(), dst);
+                    }
                 }
             }
+            // Reset suppression flag after use (one-shot)
+            self.suppress_pin_entry_copy_next = false;
             Ok(())
         } else {
             Err("No current function".to_string())
@@ -204,12 +208,16 @@ impl super::MirBuilder {
         })
     }
 
-    /// Pin a block-crossing ephemeral value into a pseudo local slot so it participates in PHI merges.
+    /// Pin a block-crossing ephemeral value into a pseudo local slot and register it in variable_map
+    /// so it participates in PHI merges across branches/blocks. Safe default for correctness-first.
     pub(crate) fn pin_to_slot(&mut self, v: super::ValueId, hint: &str) -> Result<super::ValueId, String> {
         self.temp_slot_counter = self.temp_slot_counter.wrapping_add(1);
         let slot_name = format!("__pin${}${}", self.temp_slot_counter, hint);
         let dst = self.value_gen.next();
         self.emit_instruction(super::MirInstruction::Copy { dst, src: v })?;
+        if super::utils::builder_debug_enabled() || std::env::var("NYASH_PIN_TRACE").ok().as_deref() == Some("1") {
+            super::utils::builder_debug_log(&format!("pin slot={} src={} dst={}", slot_name, v.0, dst.0));
+        }
         self.variable_map.insert(slot_name, dst);
         Ok(dst)
     }
@@ -220,4 +228,10 @@ impl super::MirBuilder {
         self.emit_instruction(super::MirInstruction::Copy { dst, src: v })?;
         Ok(dst)
     }
+
+    /// Ensure a value is safe to use in the current block by slotifying (pinning) it.
+    /// Currently correctness-first: always pin to get a block-local def and PHI participation.
+    pub(crate) fn ensure_slotified_for_use(&mut self, v: super::ValueId, hint: &str) -> Result<super::ValueId, String> {
+        self.pin_to_slot(v, hint)
+    }
 }

src/mir/loop_builder.rs

@@ -152,6 +152,7 @@ impl<'a> LoopBuilder<'a> {
         // 5. 条件評価（Phi nodeの結果を使用）
         // Heuristic pre-pin: if condition is a comparison, evaluate its operands and pin them
         // so that the loop body/next iterations can safely reuse these values across blocks.
+        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 {
@@ -166,15 +167,27 @@ impl<'a> LoopBuilder<'a> {
                 _ => {}
             }
         }
+        }
         let condition_value = self.build_expression_with_phis(condition)?;
 
         // 6. 条件分岐
+        let pre_branch_bb = self.current_block()?;
         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)?;
+        // Materialize pinned slots at entry via single-pred Phi
+        let names: Vec<String> = self.parent_builder.variable_map.keys().cloned().collect();
+        for name in names {
+            if !name.starts_with("__pin$") { continue; }
+            if let Some(&pre_v) = self.parent_builder.variable_map.get(&name) {
+                let phi_val = self.new_value();
+                self.emit_phi_at_block_start(body_id, phi_val, vec![(pre_branch_bb, pre_v)])?;
+                self.update_variable(name, phi_val);
+            }
+        }
         // Scope enter for loop body
         self.parent_builder.hint_scope_enter(0);
         // Optional safepoint per loop-iteration
@@ -467,6 +480,7 @@ impl<'a> LoopBuilder<'a> {
         else_body: Option<Vec<ASTNode>>,
     ) -> Result<ValueId, String> {
         // 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 {
@@ -481,11 +495,13 @@ impl<'a> LoopBuilder<'a> {
                 _ => {}
             }
         }
+        }
         // 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)
@@ -494,6 +510,15 @@ impl<'a> LoopBuilder<'a> {
 
         // then branch
         self.set_current_block(then_bb)?;
+        // Materialize all variables at entry via single-pred Phi (correctness-first)
+        let names_then: Vec<String> = self.parent_builder.variable_map.keys().cloned().collect();
+        for name in names_then {
+            if let Some(&pre_v) = self.parent_builder.variable_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)])?;
+                self.update_variable(name, 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
@@ -510,6 +535,15 @@ impl<'a> LoopBuilder<'a> {
 
         // else branch
         self.set_current_block(else_bb)?;
+        // Materialize all variables at entry via single-pred Phi (correctness-first)
+        let names2: Vec<String> = self.parent_builder.variable_map.keys().cloned().collect();
+        for name in names2 {
+            if let Some(&pre_v) = self.parent_builder.variable_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)])?;
+                self.update_variable(name, 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() {