Squeeze the layout of variable proxy nodes.

Around 200MB less peak memory usage in the bug mentioned below.

BUG=417697
LOG=y
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/629983002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24413 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ast.cc

@@ -62,12 +62,12 @@ bool Expression::IsUndefinedLiteral(Isolate* isolate) const {
 VariableProxy::VariableProxy(Zone* zone, Variable* var, int position,
                              IdGen* id_gen)
     : Expression(zone, position, id_gen),
-      name_(var->raw_name()),
-      var_(NULL),  // Will be set by the call to BindTo.
+      raw_name_(var->raw_name()),
+      interface_(var->interface()),
+      variable_feedback_slot_(kInvalidFeedbackSlot),
       is_this_(var->is_this()),
       is_assigned_(false),
-      interface_(var->interface()),
-      variable_feedback_slot_(kInvalidFeedbackSlot) {
+      is_resolved_(false) {
   BindTo(var);
 }
 
@@ -75,25 +75,24 @@ VariableProxy::VariableProxy(Zone* zone, Variable* var, int position,
 VariableProxy::VariableProxy(Zone* zone, const AstRawString* name, bool is_this,
                              Interface* interface, int position, IdGen* id_gen)
     : Expression(zone, position, id_gen),
-      name_(name),
-      var_(NULL),
+      raw_name_(name),
+      interface_(interface),
+      variable_feedback_slot_(kInvalidFeedbackSlot),
       is_this_(is_this),
       is_assigned_(false),
-      interface_(interface),
-      variable_feedback_slot_(kInvalidFeedbackSlot) {}
+      is_resolved_(false) {}
 
 
 void VariableProxy::BindTo(Variable* var) {
-  DCHECK(var_ == NULL);  // must be bound only once
-  DCHECK(var != NULL);  // must bind
   DCHECK(!FLAG_harmony_modules || interface_->IsUnified(var->interface()));
-  DCHECK((is_this() && var->is_this()) || name_ == var->raw_name());
+  DCHECK((is_this() && var->is_this()) || raw_name() == var->raw_name());
   // Ideally CONST-ness should match. However, this is very hard to achieve
   // because we don't know the exact semantics of conflicting (const and
   // non-const) multiple variable declarations, const vars introduced via
   // eval() etc.  Const-ness and variable declarations are a complete mess
   // in JS. Sigh...
-  var_ = var;
+  set_var(var);
+  set_is_resolved();
   var->set_is_used();
 }
 

src/ast.h

@@ -1636,20 +1636,36 @@ class VariableProxy FINAL : public Expression {
   DECLARE_NODE_TYPE(VariableProxy)
 
   virtual bool IsValidReferenceExpression() const OVERRIDE {
-    return var_ == NULL ? true : var_->IsValidReference();
+    return !is_resolved() || var()->IsValidReference();
   }
 
-  bool IsArguments() const { return var_ != NULL && var_->is_arguments(); }
+  bool IsArguments() const { return is_resolved() && var()->is_arguments(); }
+
+  Handle<String> name() const { return raw_name()->string(); }
+  const AstRawString* raw_name() const {
+    return is_resolved() ? var_->raw_name() : raw_name_;
+  }
+
+  Variable* var() const {
+    DCHECK(is_resolved());
+    return var_;
+  }
+  void set_var(Variable* v) {
+    DCHECK(!is_resolved());
+    DCHECK_NOT_NULL(v);
+    var_ = v;
+  }
 
-  Handle<String> name() const { return name_->string(); }
-  const AstRawString* raw_name() const { return name_; }
-  Variable* var() const { return var_; }
   bool is_this() const { return is_this_; }
-  Interface* interface() const { return interface_; }
 
   bool is_assigned() const { return is_assigned_; }
   void set_is_assigned() { is_assigned_ = true; }
 
+  bool is_resolved() const { return is_resolved_; }
+  void set_is_resolved() { is_resolved_ = true; }
+
+  Interface* interface() const { return interface_; }
+
   // Bind this proxy to the variable var. Interfaces must match.
   void BindTo(Variable* var);
 
@@ -1666,12 +1682,15 @@ class VariableProxy FINAL : public Expression {
   VariableProxy(Zone* zone, const AstRawString* name, bool is_this,
                 Interface* interface, int position, IdGen* id_gen);
 
-  const AstRawString* name_;
-  Variable* var_;  // resolved variable, or NULL
-  bool is_this_;
-  bool is_assigned_;
+  union {
+    const AstRawString* raw_name_;  // if !is_resolved_
+    Variable* var_;                 // if is_resolved_
+  };
   Interface* interface_;
   int variable_feedback_slot_;
+  bool is_this_ : 1;
+  bool is_assigned_ : 1;
+  bool is_resolved_ : 1;
 };
 
 

src/parser.cc

@@ -2259,7 +2259,7 @@ Block* Parser::ParseVariableDeclarations(
     }
 
     // Record the end position of the initializer.
-    if (proxy->var() != NULL) {
+    if (proxy->is_resolved()) {
       proxy->var()->set_initializer_position(position());
     }
 

src/rewriter.cc

@@ -253,9 +253,8 @@ bool Rewriter::Rewrite(CompilationInfo* info) {
       // the end position of the function generated for executing the eval code
       // coincides with the end of the with scope which is the position of '1'.
       int pos = function->end_position();
-      VariableProxy* result_proxy = processor.factory()->NewVariableProxy(
-          result->raw_name(), false, result->interface(), pos);
-      result_proxy->BindTo(result);
+      VariableProxy* result_proxy =
+          processor.factory()->NewVariableProxy(result, pos);
       Statement* result_statement =
           processor.factory()->NewReturnStatement(result_proxy, pos);
       body->Add(result_statement, info->zone());

src/scopes.cc

@@ -1031,7 +1031,7 @@ bool Scope::ResolveVariable(CompilationInfo* info,
 
   // If the proxy is already resolved there's nothing to do
   // (functions and consts may be resolved by the parser).
-  if (proxy->var() != NULL) return true;
+  if (proxy->is_resolved()) return true;
 
   // Otherwise, try to resolve the variable.
   BindingKind binding_kind;