perf: CallFrame 构造 this 判别位并入 bool 组省 8 字节

crates/oxide_vm/src/dispatch/call.rs

@@ -625,10 +625,11 @@ impl Vm {
             self.raise_error_kind("ReferenceError", "super() called more than once")?;
             return Ok(true);
         }
-        let Some(derived_this) = frame.constructed_this else {
+        if !frame.has_constructed_this {
             self.raise_error_kind("ReferenceError", "super() without derived this")?;
             return Ok(true);
-        };
+        }
+        let derived_this = frame.constructed_this;
         let callee = frame.callee;
 
         let new_target = self.regs[255];
@@ -1197,10 +1198,11 @@ impl Vm {
             self.raise_error_kind("ReferenceError", "super() called more than once")?;
             return Ok(true);
         }
-        let Some(derived_this) = frame.constructed_this else {
+        if !frame.has_constructed_this {
             self.raise_error_kind("ReferenceError", "super() without derived this")?;
             return Ok(true);
-        };
+        }
+        let derived_this = frame.constructed_this;
         let callee = frame.callee;
 
         let new_target = self.regs[255];

crates/oxide_vm/src/session_gc/tests.rs

@@ -102,7 +102,8 @@ fn gc_roots_contains_registers_frames_and_root_roots() {
         arguments_obj: JsValue::undefined(),
         construct_result_reg: None,
         strict: false,
-        constructed_this: Some(JsValue::from_js_object(child_session)),
+        constructed_this: JsValue::from_js_object(child_session),
+        has_constructed_this: true,
         is_derived_constructor: false,
         super_called: false,
         continuation: FrameContinuation::None,

crates/oxide_vm/src/suspended.rs

@@ -191,8 +191,8 @@ impl SuspendedFrame {
             f(frame.saved_new_target);
             f(frame.callee);
             f(frame.arguments_obj);
-            if let Some(ct) = frame.constructed_this {
-                f(ct);
+            if frame.has_constructed_this {
+                f(frame.constructed_this);
             }
         }
         for v in &self.spill_stack {
@@ -307,7 +307,8 @@ mod tests {
             callee: tag,
             arguments_obj: JsValue::undefined(),
             construct_result_reg: None,
-            constructed_this: Some(tag),
+            constructed_this: tag,
+            has_constructed_this: true,
             is_derived_constructor: false,
             super_called: false,
             strict: false,

crates/oxide_vm/src/vm/call.rs

@@ -381,7 +381,8 @@ impl Vm {
             callee,
             arguments_obj: JsValue::undefined(),
             construct_result_reg: construct.result_reg,
-            constructed_this: construct.constructed_this,
+            constructed_this: construct.constructed_this.unwrap_or(JsValue::undefined()),
+            has_constructed_this: construct.constructed_this.is_some(),
             is_derived_constructor: obj.is_derived_constructor(),
             super_called: false,
             strict: sub_is_strict,

crates/oxide_vm/src/vm/frames.rs

@@ -68,7 +68,13 @@ pub struct CallFrame {
     /// 无 mapped arguments 时为 undefined。GC 根（帧遍历期标记）。
     pub arguments_obj: JsValue,
     pub construct_result_reg: Option<u8>,
-    pub constructed_this: Option<JsValue>,
+    /// derived 构造器构造出的 this 值；仅当 `has_constructed_this` 为真时有效，
+    /// 标志为假时该槽为 undefined。
+    ///
+    /// 判别位并入结构体尾部 bool 组（单字节容纳四个 bool），字段本体只占
+    /// 裸 JsValue 的 8 字节，帧整体比 Option 包装省 8 字节。
+    pub constructed_this: JsValue,
+    pub has_constructed_this: bool,
     pub is_derived_constructor: bool,
     /// derived 构造帧是否已成功调用 super()（父构造器正常返回后置位）。
     ///
@@ -91,6 +97,18 @@ pub struct CallFrame {
     pub upvalues: *const [*mut Cell],
 }
 
+#[cfg(test)]
+mod tests {
+    use super::CallFrame;
+
+    /// CallFrame 尺寸钉：constructed_this 的判别位并入尾部 bool 组后，
+    /// 帧固定 104 字节（Option 包装时代为 112 字节）。
+    #[test]
+    fn call_frame_size_pinned() {
+        assert_eq!(std::mem::size_of::<CallFrame>(), 104);
+    }
+}
+
 /// 一次 `for-in` 迭代的游标：已收集的 key 列表与当前下标。
 ///
 /// 体是堆上 `Box`：迭代器表与挂起状态盒各独占持有体，出表/状态盒释放时

crates/oxide_vm/src/vm/gc_hooks.rs

@@ -74,7 +74,14 @@ impl Vm {
             f(RootGroup::Frames, frame.saved_new_target);
             f(RootGroup::Frames, frame.callee);
             f(RootGroup::Frames, frame.arguments_obj);
-            f(RootGroup::Frames, frame.constructed_this.unwrap_or(JsValue::undefined()));
+            f(
+                RootGroup::Frames,
+                if frame.has_constructed_this {
+                    frame.constructed_this
+                } else {
+                    JsValue::undefined()
+                },
+            );
         }
         for &v in &self.save_stack {
             f(RootGroup::SaveStack, v);

crates/oxide_vm/src/vm_dispatch_ctrl.rs

@@ -819,7 +819,11 @@ impl Vm {
         if let Some(frame) = self.frames.pop() {
             self.cell_stack.pop();
             let construct_result_reg = frame.construct_result_reg;
-            let constructed_this = frame.constructed_this;
+            let constructed_this = if frame.has_constructed_this {
+                Some(frame.constructed_this)
+            } else {
+                None
+            };
             let is_derived_constructor = frame.is_derived_constructor;
             let super_called = frame.super_called;
             let continuation = frame.continuation;

crates/oxide_vm/src/vm_dispatch_misc.rs

@@ -1646,7 +1646,7 @@ mod tests {
         // NEW 帧契约：构造结果寄存器与 constructed_this 随帧携带
         assert_eq!(frame.construct_result_reg, Some(0), "构造结果写回 regs[0]");
         assert!(
-            frame.constructed_this.is_some_and(|v| v.is_object()),
+            frame.has_constructed_this && frame.constructed_this.is_object(),
             "基类构造路径 constructed_this 应为新对象"
         );
         assert!(!frame.is_derived_constructor, "普通函数非 derived 构造器");

crates/oxide_vm/src/vm_support/tests.rs

@@ -852,7 +852,8 @@ fn reset_clears_runtime_state_like_rerun() {
         arguments_obj: JsValue::undefined(),
         construct_result_reg: None,
         strict: false,
-        constructed_this: None,
+        constructed_this: JsValue::undefined(),
+        has_constructed_this: false,
         is_derived_constructor: false,
         super_called: false,
         continuation: crate::vm::FrameContinuation::None,