Implemented a ContextSlotCache for compiled code.

src/scopeinfo.h

Index: src/scopeinfo.h
===================================================================
--- src/scopeinfo.h	(revision 2226)
+++ src/scopeinfo.h	(working copy)
@@ -163,6 +163,75 @@
 };
 
 
+// Cache for mapping (code, property name) into context slot index.
+// The cache contains both positive and negative results.
+// slot index -1 means the property is absent. 

[Mads Ager (chromium), 2009/06/22 08:00:18]

Capitalize 'Slot'?

+// Cleared at startup and prior to mark sweep collection.
+class ContextSlotCache {
+ public:
+  // Lookup context slot index for (code, name).
+  // If absent, kNotFound is returned.
+  static int Lookup(Code* code,
+                    String* name,
+                    Variable::Mode* mode);
+
+  // Update an element in the cache.
+  static void Update(Code* code,
+                     String* name,
+                     Variable::Mode mode,
+                     int slot_index);
+
+  // Clear the cache.
+  static void Clear();
+
+  static const int kNotFound = -2;
+ private:
+  inline static int Hash(Code* code, String* name);
+
+#ifdef DEBUG
+  // Checks whether an entry is valid.
+  static void Check(Code* code,

[Mads Ager (chromium), 2009/06/22 08:00:18]

Use a more telling name such as 'IsValidEntry'?

+                    String* name,
+                    Variable::Mode mode,
+                    int slot_index);
+#endif
+
+  static const int kLength = 256;
+  struct Key {
+    Code* code;
+    String* name;
+  };
+
+  struct Value {
+    Value(Variable::Mode mode, int index) {
+      ASSERT(ModeField::is_valid(mode));
+      ASSERT(IndexField::is_valid(index));
+      value_ = ModeField::encode(mode) | IndexField::encode(index);
+      ASSERT(mode == this->mode());
+      ASSERT(index == this->index());
+    }
+
+    inline Value(uint32_t value) : value_(value) {}
+
+    uint32_t raw() { return value_; }
+
+    Variable::Mode mode() { return ModeField::decode(value_); }
+
+    int index() { return IndexField::decode(value_); }
+
+    // Bit fields in value_ (type, shift, size). Must be public so the
+    // constants can be embedded in generated code.
+    class ModeField:  public BitField<Variable::Mode, 0, 3> {};
+    class IndexField: public BitField<int,            3, 32-3> {};
+   private:
+    uint32_t value_;
+  };
+
+  static Key keys_[kLength];
+  static uint32_t values_[kLength];
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_SCOPEINFO_H_