Experimental: introduce factory functions for the FrameElement type....

src/virtual-frame-ia32.h

 // Copyright 2008 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 82 matching lines @@
 
   CodeGenerator* cgen_;
 };
 
 
 // -------------------------------------------------------------------------
 // Virtual frame elements
 //
 // The internal elements of the virtual frames.  There are several kinds of
 // elements:
+//   * Invalid: elements that are uninitialized or not actually part
+//     of the virtual frame.  They should not be read.
 //   * Memory: an element that resides in the actual frame.  Its address is
 //     given by its position in the virtual frame.
 //   * Register: an element that resides in a register.
 //   * Constant: an element whose value is known at compile time.
 
 class FrameElement BASE_EMBEDDED {
  public:
-  enum SyncFlag { SYNCED, NOT_SYNCED };
+  enum SyncFlag {
+    SYNCED,
+    NOT_SYNCED
+  };
 
-  // Construct an in-memory frame element.
+  // The default constructor creates an invalid frame element.
   FrameElement() {
-    type_ = TypeField::encode(MEMORY) | SyncField::encode(SYNCED);
-    // In-memory elements have no useful data.
+    type_ = TypeField::encode(INVALID) | SyncField::encode(NOT_SYNCED);
     data_.reg_ = no_reg;
   }
 
-  // Construct an in-register frame element.
-  FrameElement(Register reg, SyncFlag is_synced) {
-    type_ = TypeField::encode(REGISTER) | SyncField::encode(is_synced);
-    data_.reg_ = reg;
+  // Factory function to construct an in-memory frame element.
+  static FrameElement MemoryElement() {
+    FrameElement result;
+    result.type_ = TypeField::encode(MEMORY) | SyncField::encode(SYNCED);
+    // In-memory elements have no useful data.
+    result.data_.reg_ = no_reg;
+    return result;
   }
 
-  // Construct a frame element whose value is known at compile time.
-  FrameElement(Handle<Object> value, SyncFlag is_synced) {
-    type_ = TypeField::encode(CONSTANT) | SyncField::encode(is_synced);
-    data_.handle_ = value.location();
+  // Factory function to construct an in-register frame element.
+  static FrameElement RegisterElement(Register reg, SyncFlag is_synced) {
+    FrameElement result;
+    result.type_ = TypeField::encode(REGISTER) | SyncField::encode(is_synced);
+    result.data_.reg_ = reg;
+    return result;
+  }
+
+  // Factory function to construct a frame element whose value is known at
+  // compile time.
+  static FrameElement ConstantElement(Handle<Object> value,
+                                      SyncFlag is_synced) {
+    FrameElement result;
+    result.type_ = TypeField::encode(CONSTANT) | SyncField::encode(is_synced);
+    result.data_.handle_ = value.location();
+    return result;
   }
 
   bool is_synced() const { return SyncField::decode(type_) == SYNCED; }
 
   void set_sync() {
     ASSERT(type() != MEMORY);
     type_ = (type_ & ~SyncField::mask()) | SyncField::encode(SYNCED);
   }
 
   void clear_sync() {
     ASSERT(type() != MEMORY);
     type_ = (type_ & ~SyncField::mask()) | SyncField::encode(NOT_SYNCED);
   }
 
   bool is_memory() const { return type() == MEMORY; }
   bool is_register() const { return type() == REGISTER; }
   bool is_constant() const { return type() == CONSTANT; }
 
   Register reg() const {
     ASSERT(type() == REGISTER);
     return data_.reg_;
   }
 
   Handle<Object> handle() const {
     ASSERT(type() == CONSTANT);
     return Handle<Object>(data_.handle_);
   }
 
  private:
-  enum Type { MEMORY, REGISTER, CONSTANT };
+  enum Type {
+    INVALID,
+    MEMORY,
+    REGISTER,
+    CONSTANT
+  };
 
   // BitField is <type, shift, size>.
   class SyncField : public BitField<SyncFlag, 0, 1> {};
   class TypeField : public BitField<Type, 1, 32 - 1> {};
 
   Type type() const { return TypeField::decode(type_); }
 
   // The element's type and a dirty bit.  The dirty bit can be cleared
   // for non-memory elements to indicate that the element agrees with
   // the value in memory in the actual frame.
@@ skipping 322 matching lines @@
   // This is because some new memory-to-register moves are
   // created in order to break cycles of register moves.
   // Used in the implementation of MergeTo().
   void MergeMoveRegistersToRegisters(VirtualFrame *expected);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_VIRTUAL_FRAME_IA32_H_