feat: 实现对象属性布局缓存结构

crates/oxide_vm/src/lib.rs

@@ -3,6 +3,7 @@
 pub mod coercion;
 pub mod mem;
 pub mod object;
+pub mod shape;
 pub mod value;
 pub mod vm;
 pub use value::JsValue;

crates/oxide_vm/src/shape.rs

@@ -0,0 +1,229 @@
+use std::sync::{Arc, Mutex, OnceLock};
+
+use hashbrown::HashMap;
+
+pub type ShapeId = u32;
+pub type StringIndex = u32;
+
+pub const EMPTY_SHAPE_ID: ShapeId = 1;
+
+#[derive(Debug, Clone)]
+pub struct Shape {
+    pub id: ShapeId,
+    pub property_name: StringIndex,
+    pub property_offset: u8,
+    pub parent: Option<ShapeId>,
+}
+
+struct ShapeStore {
+    shapes: Vec<Option<Arc<Shape>>>,
+    transitions: HashMap<(ShapeId, StringIndex), ShapeId>,
+    next_id: ShapeId,
+}
+
+impl ShapeStore {
+    fn new() -> Self {
+        let mut store = Self {
+            shapes: Vec::with_capacity(256),
+            transitions: HashMap::with_capacity(256),
+            next_id: 1,
+        };
+        store.create_empty_shape();
+        store
+    }
+
+    fn create_empty_shape(&mut self) {
+        let empty = Arc::new(Shape {
+            id: EMPTY_SHAPE_ID,
+            property_name: 0,
+            property_offset: 0,
+            parent: None,
+        });
+        debug_assert_eq!(self.shapes.len(), 0);
+        self.shapes.push(Some(empty));
+        self.next_id = 2;
+    }
+
+    fn get_shape(&self, id: ShapeId) -> Option<Arc<Shape>> {
+        self.shapes.get((id - 1) as usize)?.clone()
+    }
+
+    fn make_shape(&mut self, parent_id: ShapeId, prop_name: StringIndex) -> ShapeId {
+        let key = (parent_id, prop_name);
+        if let Some(&existing) = self.transitions.get(&key) {
+            return existing;
+        }
+
+        let prop_offset = self.compute_offset(parent_id);
+        let new_id = self.next_id;
+        self.next_id += 1;
+
+        let shape = Arc::new(Shape {
+            id: new_id,
+            property_name: prop_name,
+            property_offset: prop_offset,
+            parent: Some(parent_id),
+        });
+
+        while self.shapes.len() < new_id as usize {
+            self.shapes.push(None);
+        }
+        self.shapes[(new_id - 1) as usize] = Some(shape);
+        self.transitions.insert(key, new_id);
+
+        new_id
+    }
+
+    fn compute_offset(&self, shape_id: ShapeId) -> u8 {
+        let mut count = 0u8;
+        let mut cursor = Some(shape_id);
+        while let Some(id) = cursor {
+            match self.get_shape(id) {
+                Some(s) => {
+                    if s.property_name != 0 {
+                        count += 1;
+                    }
+                    cursor = s.parent;
+                }
+                None => break,
+            }
+        }
+        count.min(31)
+    }
+
+    fn lookup_offset(&self, shape_id: ShapeId, prop_name: StringIndex) -> Option<u8> {
+        let mut cursor = Some(shape_id);
+        while let Some(id) = cursor {
+            match self.get_shape(id) {
+                Some(s) => {
+                    if s.property_name == prop_name {
+                        return Some(s.property_offset);
+                    }
+                    cursor = s.parent;
+                }
+                None => return None,
+            }
+        }
+        None
+    }
+
+    fn shape_prop_count(&self, shape_id: ShapeId) -> u8 {
+        let mut count = 0u8;
+        let mut cursor = Some(shape_id);
+        while let Some(id) = cursor {
+            match self.get_shape(id) {
+                Some(s) => {
+                    if s.property_name != 0 {
+                        count += 1;
+                    }
+                    cursor = s.parent;
+                }
+                None => break,
+            }
+        }
+        count
+    }
+}
+
+static SHAPE_STORE: OnceLock<Mutex<ShapeStore>> = OnceLock::new();
+
+fn store() -> &'static Mutex<ShapeStore> {
+    SHAPE_STORE.get_or_init(|| Mutex::new(ShapeStore::new()))
+}
+
+pub fn get_shape(id: ShapeId) -> Option<Arc<Shape>> {
+    store().lock().unwrap().get_shape(id)
+}
+
+pub fn make_shape(parent_id: ShapeId, prop_name: StringIndex) -> ShapeId {
+    store().lock().unwrap().make_shape(parent_id, prop_name)
+}
+
+pub fn lookup_offset(shape_id: ShapeId, prop_name: StringIndex) -> Option<u8> {
+    store().lock().unwrap().lookup_offset(shape_id, prop_name)
+}
+
+pub fn shape_prop_count(shape_id: ShapeId) -> u8 {
+    store().lock().unwrap().shape_prop_count(shape_id)
+}
+
+pub fn init_shape_store() {
+    let _ = store();
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_shape_exists() {
+        let s = get_shape(EMPTY_SHAPE_ID);
+        assert!(s.is_some());
+        let s = s.unwrap();
+        assert_eq!(s.id, EMPTY_SHAPE_ID);
+        assert!(s.parent.is_none());
+    }
+
+    #[test]
+    fn make_shape_creates_new_id() {
+        let key: StringIndex = 1_000_000;
+        let s1 = make_shape(EMPTY_SHAPE_ID, key);
+        assert!(s1 > EMPTY_SHAPE_ID);
+        let shape = get_shape(s1).unwrap();
+        assert_eq!(shape.property_name, key);
+        assert_eq!(shape.parent, Some(EMPTY_SHAPE_ID));
+    }
+
+    #[test]
+    fn hash_cons_returns_same_id() {
+        let key: StringIndex = 1_000_001;
+        let a = make_shape(EMPTY_SHAPE_ID, key);
+        let b = make_shape(EMPTY_SHAPE_ID, key);
+        assert_eq!(a, b);
+    }
+
+    #[test]
+    fn different_props_different_ids() {
+        let a = make_shape(EMPTY_SHAPE_ID, 1_000_002);
+        let b = make_shape(EMPTY_SHAPE_ID, 1_000_003);
+        assert_ne!(a, b);
+    }
+
+    #[test]
+    fn chain_of_three() {
+        let s1 = make_shape(EMPTY_SHAPE_ID, 1_000_010);
+        let s2 = make_shape(s1, 1_000_020);
+        let s3 = make_shape(s2, 1_000_030);
+
+        assert_eq!(shape_prop_count(s3), 3);
+
+        assert_eq!(lookup_offset(s3, 1_000_030), Some(2));
+        assert_eq!(lookup_offset(s3, 1_000_020), Some(1));
+        assert_eq!(lookup_offset(s3, 1_000_010), Some(0));
+        assert_eq!(lookup_offset(s3, 99), None);
+    }
+
+    #[test]
+    fn two_branches_share_ancestor() {
+        let base = make_shape(EMPTY_SHAPE_ID, 1_000_040);
+        let branch_a = make_shape(base, 1_000_050);
+        let branch_b = make_shape(base, 1_000_060);
+        assert_ne!(branch_a, branch_b);
+        let a_shape = get_shape(branch_a).unwrap();
+        let b_shape = get_shape(branch_b).unwrap();
+        assert_eq!(a_shape.parent, Some(base));
+        assert_eq!(b_shape.parent, Some(base));
+    }
+
+    #[test]
+    fn edge_same_structure_different_names() {
+        let s1 = make_shape(EMPTY_SHAPE_ID, 1_000_070);
+        let s2 = make_shape(s1, 1_000_080);
+        let s3 = make_shape(EMPTY_SHAPE_ID, 1_000_090);
+        let s4 = make_shape(s3, 1_000_100);
+        assert_ne!(s1, s3);
+        assert_ne!(s2, s4);
+        assert_eq!(lookup_offset(s2, 1_000_070), Some(0));
+        assert_eq!(lookup_offset(s4, 1_000_090), Some(0));
+    }
+}