Remove variable rewrites and the unneccesary Slot class.

src/variables.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 56 matching lines @@
     TEMPORARY        // temporary variables (not user-visible), never
                      // in a context
   };
 
   enum Kind {
     NORMAL,
     THIS,
     ARGUMENTS
   };
 
+  enum Location {
+    // Before and during variable allocation, a variable whose location is
+    // not yet determined.  After allocation, a variable looked up as a
+    // property on the global object (and possibly absent).  name() is the
+    // variable name, index() is invalid.
+    UNALLOCATED,
+
+    // A slot in the parameter section on the stack.  index() is the
+    // parameter index, counting left-to-right.  The reciever is index -1;
+    // the first parameter is index 0.
+    PARAMETER,
+
+    // A slot in the local section on the stack.  index() is the variable
+    // index in the stack frame, starting at 0.
+    LOCAL,
+
+    // An indexed slot in a heap context.  index() is the variable index in
+    // the context object on the heap, starting at 0.  scope() is the
+    // corresponding scope.
+    CONTEXT,
+
+    // A named slot in a heap context.  name() is the variable name in the
+    // context object on the heap, with lookup starting at the current
+    // context.  index() is invalid.
+    LOOKUP
+  };
+
   Variable(Scope* scope,
            Handle<String> name,
            Mode mode,
            bool is_valid_lhs,
            Kind kind);
 
   // Printing support
   static const char* Mode2String(Mode mode);
 
-  // Type testing & conversion.  Global variables are not slots.
-  Property* AsProperty() const;
-  Slot* AsSlot() const;
-
   bool IsValidLeftHandSide() { return is_valid_LHS_; }
 
   // The source code for an eval() call may refer to a variable that is
   // in an outer scope about which we don't know anything (it may not
   // be the global scope). scope() is NULL in that case. Currently the
   // scope is only used to follow the context chain length.
   Scope* scope() const { return scope_; }
 
   Handle<String> name() const { return name_; }
   Mode mode() const { return mode_; }
   bool is_accessed_from_inner_function_scope() const {
     return is_accessed_from_inner_function_scope_;
   }
   void MarkAsAccessedFromInnerFunctionScope() {
     ASSERT(mode_ != TEMPORARY);
     is_accessed_from_inner_function_scope_ = true;
   }
   bool is_used() { return is_used_; }
   void set_is_used(bool flag) { is_used_ = flag; }
 
   bool IsVariable(Handle<String> n) const {
     return !is_this() && name().is_identical_to(n);
   }
 
-  bool IsStackAllocated() const;
-  bool IsParameter() const;  // Includes 'this'.
-  bool IsStackLocal() const;
-  bool IsContextSlot() const;
+  bool IsUnallocated() const { return location_ == UNALLOCATED; }
+  bool IsParameter() const { return location_ == PARAMETER; }
+  bool IsStackLocal() const { return location_ == LOCAL; }
+  bool IsStackAllocated() const { return IsParameter() || IsStackLocal(); }
+  bool IsContextSlot() const { return location_ == CONTEXT; }
+  bool IsLookupSlot() const { return location_ == LOOKUP; }
 
   bool is_dynamic() const {
     return (mode_ == DYNAMIC ||
             mode_ == DYNAMIC_GLOBAL ||
             mode_ == DYNAMIC_LOCAL);
   }
 
   bool is_global() const;
   bool is_this() const { return kind_ == THIS; }
   bool is_arguments() const { return kind_ == ARGUMENTS; }
 
   // True if the variable is named eval and not known to be shadowed.
   bool is_possibly_eval() const {
     return IsVariable(FACTORY->eval_symbol()) &&
         (mode_ == DYNAMIC || mode_ == DYNAMIC_GLOBAL);
   }
 
   Variable* local_if_not_shadowed() const {
     ASSERT(mode_ == DYNAMIC_LOCAL && local_if_not_shadowed_ != NULL);
     return local_if_not_shadowed_;
   }
 
   void set_local_if_not_shadowed(Variable* local) {
     local_if_not_shadowed_ = local;
   }
 
-  Slot* rewrite() const { return rewrite_; }
-  void set_rewrite(Slot* slot) { rewrite_ = slot; }
+  Location location() const { return location_; }
+  int index() const { return index_; }
+
+  void AllocateTo(Location location, int index) {
+    location_ = location;
+    index_ = index;
+  }
 
  private:
   Scope* scope_;
   Handle<String> name_;
   Mode mode_;
   Kind kind_;
+  Location location_;

[fschneider, 2011/09/06 09:34:22]

Suggestion for improvement: Compress these three enums into one 32-bit integer.

+  int index_;
 
   Variable* local_if_not_shadowed_;
 
-  // Code generation.
-  Slot* rewrite_;
-
   // Valid as a LHS? (const and this are not valid LHS, for example)
   bool is_valid_LHS_;
 
   // Usage info.
   bool is_accessed_from_inner_function_scope_;  // set by variable resolver
   bool is_used_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_VARIABLES_H_