scopes.cc.svn-base

Google浏览器V8内核代码

           scope_calls_eval_ || scope_inside_with_)) {
        // We must look up the variable at runtime, and we don't
        // know anything else.
        var = NonLocal(proxy->name());

      } else {
        // We must have a global variable.
        ASSERT(global_scope != NULL);
        var = new Variable(global_scope, proxy->name(),
                           Variable::DYNAMIC, true, false);
        // Ideally we simply rewrite these variables into property
        // accesses. Unfortunately, we cannot do this here at the
        // moment because then we can't differentiate between
        // global variable ('x') and global property ('this.x') access.
        // If 'x' doesn't exist, the former leads to an error, while the
        // latter returns undefined. Sigh...
        // var->rewrite_ = new Property(new Literal(env_->global()),
        //                              new Literal(proxy->name()));
      }
    }
  }

  proxy->BindTo(var);
}


void Scope::ResolveVariablesRecursively(Scope* global_scope) {
  ASSERT(global_scope == NULL || global_scope->is_global_scope());

  // Resolve unresolved variables for this scope.
  for (int i = 0; i < unresolved_.length(); i++) {
    ResolveVariable(global_scope, unresolved_[i]);
  }

  // Resolve unresolved variables for inner scopes.
  for (int i = 0; i < inner_scopes_.length(); i++) {
    inner_scopes_[i]->ResolveVariablesRecursively(global_scope);
  }
}


bool Scope::PropagateScopeInfo(bool outer_scope_calls_eval) {
  if (outer_scope_calls_eval) {
    outer_scope_calls_eval_ = true;
  }

  bool b = scope_calls_eval_ || outer_scope_calls_eval_;
  for (int i = 0; i < inner_scopes_.length(); i++) {
    Scope* inner_scope = inner_scopes_[i];
    if (inner_scope->PropagateScopeInfo(b)) {
      inner_scope_calls_eval_ = true;
    }
    if (inner_scope->force_eager_compilation_) {
      force_eager_compilation_ = true;
    }
  }

  return scope_calls_eval_ || inner_scope_calls_eval_;
}


bool Scope::MustAllocate(Variable* var) {
  // Give var a read/write use if there is a chance it might be
  // accessed via an eval() call, or if it is a global variable.
  // This is only possible if the variable has a visible name.
  if ((var->is_this() || var->name()->length() > 0) &&
      (var->is_accessed_from_inner_scope_ ||
       scope_calls_eval_ || inner_scope_calls_eval_ ||
       scope_contains_with_ || var->is_global())) {
    var->var_uses()->RecordAccess(1);
  }
  return var->var_uses()->is_used();
}


bool Scope::MustAllocateInContext(Variable* var) {
  // If var is accessed from an inner scope, or if there is a
  // possibility that it might be accessed from the current or
  // an inner scope (through an eval() call), it must be allocated
  // in the context.
  // Exceptions: Global variables and temporary variables must
  // never be allocated in the (FixedArray part of the) context.
  return
    var->mode() != Variable::TEMPORARY &&
    (var->is_accessed_from_inner_scope_ ||
     scope_calls_eval_ || inner_scope_calls_eval_ ||
     scope_contains_with_ || var->is_global());
}


bool Scope::HasArgumentsParameter() {
  for (int i = 0; i < params_.length(); i++) {
    if (params_[i]->name().is_identical_to(Factory::arguments_symbol()))
      return true;
  }
  return false;
}


void Scope::AllocateStackSlot(Variable* var) {
  var->rewrite_ = new Slot(var, Slot::LOCAL, num_stack_slots_++);
}


void Scope::AllocateHeapSlot(Variable* var) {
  var->rewrite_ = new Slot(var, Slot::CONTEXT, num_heap_slots_++);
}


void Scope::AllocateParameterLocals() {
  ASSERT(is_function_scope());
  Variable* arguments = Lookup(Factory::arguments_symbol());
  ASSERT(arguments != NULL);  // functions have 'arguments' declared implicitly
  if (MustAllocate(arguments) && !HasArgumentsParameter()) {
    // 'arguments' is used. Unless there is also a parameter called
    // 'arguments', we must be conservative and access all parameters via
    // the arguments object: The i'th parameter is rewritten into
    // '.arguments[i]' (*). If we have a parameter named 'arguments', a
    // (new) value is always assigned to it via the function
    // invocation. Then 'arguments' denotes that specific parameter value
    // and cannot be used to access the parameters, which is why we don't
    // need to rewrite in that case.
    //
    // (*) Instead of having a parameter called 'arguments', we may have an
    // assignment to 'arguments' in the function body, at some arbitrary
    // point in time (possibly through an 'eval()' call!). After that
    // assignment any re-write of parameters would be invalid (was bug
    // 881452). Thus, we introduce a shadow '.arguments'
    // variable which also points to the arguments object. For rewrites we
    // use '.arguments' which remains valid even if we assign to
    // 'arguments'. To summarize: If we need to rewrite, we allocate an
    // 'arguments' object dynamically upon function invocation. The compiler
    // introduces 2 local variables 'arguments' and '.arguments', both of
    // which originally point to the arguments object that was
    // allocated. All parameters are rewritten into property accesses via
    // the '.arguments' variable. Thus, any changes to properties of
    // 'arguments' are reflected in the variables and vice versa. If the
    // 'arguments' variable is changed, '.arguments' still points to the
    // correct arguments object and the rewrites still work.

    // We are using 'arguments'. Tell the code generator that is needs to
    // allocate the arguments object by setting 'arguments_'.
    arguments_ = new VariableProxy(Factory::arguments_symbol(), false, false);
    arguments_->BindTo(arguments);

    // We also need the '.arguments' shadow variable. Declare it and create
    // and bind the corresponding proxy. It's ok to declare it only now
    // because it's a local variable that is allocated after the parameters
    // have been allocated.
    //
    // Note: This is "almost" at temporary variable but we cannot use
    // NewTemporary() because the mode needs to be INTERNAL since this
    // variable may be allocated in the heap-allocated context (temporaries
    // are never allocated in the context).
    Variable* arguments_shadow =
        new Variable(this, Factory::arguments_shadow_symbol(),
                     Variable::INTERNAL, true, false);
    arguments_shadow_ =
        new VariableProxy(Factory::arguments_shadow_symbol(), false, false);
    arguments_shadow_->BindTo(arguments_shadow);
    temps_.Add(arguments_shadow);

    // Allocate the parameters by rewriting them into '.arguments[i]' accesses.
    for (int i = 0; i < params_.length(); i++) {
      Variable* var = params_[i];
      ASSERT(var->scope() == this);
      if (MustAllocate(var)) {
        if (MustAllocateInContext(var)) {
          // It is ok to set this only now, because arguments is a local
          // variable that is allocated after the parameters have been
          // allocated.
          arguments_shadow->is_accessed_from_inner_scope_ = true;
        }
        var->rewrite_ =
          new Property(arguments_shadow_,
                       new Literal(Handle<Object>(Smi::FromInt(i))),
                       RelocInfo::kNoPosition);
        arguments_shadow->var_uses()->RecordUses(var->var_uses());
      }
    }

  } else {
    // The arguments object is not used, so we can access parameters directly.
    // The same parameter may occur multiple times in the parameters_ list.
    // If it does, and if it is not copied into the context object, it must
    // receive the highest parameter index for that parameter; thus iteration
    // order is relevant!
    for (int i = 0; i < params_.length(); i++) {
      Variable* var = params_[i];
      ASSERT(var->scope() == this);
      if (MustAllocate(var)) {
        if (MustAllocateInContext(var)) {
          ASSERT(var->rewrite_ == NULL ||
                 (var->slot() != NULL && var->slot()->type() == Slot::CONTEXT));
          if (var->rewrite_ == NULL) {
            // Only set the heap allocation if the parameter has not
            // been allocated yet.
            AllocateHeapSlot(var);
          }
        } else {
          ASSERT(var->rewrite_ == NULL ||
                 (var->slot() != NULL &&
                  var->slot()->type() == Slot::PARAMETER));
          // Set the parameter index always, even if the parameter
          // was seen before! (We need to access the actual parameter
          // supplied for the last occurrence of a multiply declared
          // parameter.)
          var->rewrite_ = new Slot(var, Slot::PARAMETER, i);
        }
      }
    }
  }
}


void Scope::AllocateNonParameterLocal(Variable* var) {
  ASSERT(var->scope() == this);
  ASSERT(var->rewrite_ == NULL ||
         (!var->IsVariable(Factory::result_symbol())) ||
         (var->slot() == NULL || var->slot()->type() != Slot::LOCAL));
  if (MustAllocate(var) && var->rewrite_ == NULL) {
    if (MustAllocateInContext(var)) {
      AllocateHeapSlot(var);
    } else {
      AllocateStackSlot(var);
    }
  }
}


void Scope::AllocateNonParameterLocals() {
  // Each variable occurs exactly once in the locals_ list; all
  // variables that have no rewrite yet are non-parameter locals.

  // Sort them according to use such that the locals with more uses
  // get allocated first.
  if (FLAG_usage_computation) {
    // This is currently not implemented.
  }

  for (int i = 0; i < temps_.length(); i++) {
    AllocateNonParameterLocal(temps_[i]);
  }

  for (LocalsMap::Entry* p = locals_.Start(); p != NULL; p = locals_.Next(p)) {
    Variable* var = reinterpret_cast<Variable*>(p->value);
    AllocateNonParameterLocal(var);
  }

  // Note: For now, function_ must be allocated at the very end.  If
  // it gets allocated in the context, it must be the last slot in the
  // context, because of the current ScopeInfo implementation (see
  // ScopeInfo::ScopeInfo(FunctionScope* scope) constructor).
  if (function_ != NULL) {
    AllocateNonParameterLocal(function_);
  }
}


void Scope::AllocateVariablesRecursively() {
  // The number of slots required for variables.
  num_stack_slots_ = 0;
  num_heap_slots_ = Context::MIN_CONTEXT_SLOTS;

  // Allocate variables for inner scopes.
  for (int i = 0; i < inner_scopes_.length(); i++) {
    inner_scopes_[i]->AllocateVariablesRecursively();
  }

  // Allocate variables for this scope.
  // Parameters must be allocated first, if any.
  if (is_function_scope()) AllocateParameterLocals();
  AllocateNonParameterLocals();

  // Allocate context if necessary.
  bool must_have_local_context = false;
  if (scope_calls_eval_ || scope_contains_with_) {
    // The context for the eval() call or 'with' statement in this scope.
    // Unless we are in the global or an eval scope, we need a local
    // context even if we didn't statically allocate any locals in it,
    // and the compiler will access the context variable. If we are
    // not in an inner scope, the scope is provided from the outside.
    must_have_local_context = is_function_scope();
  }

  // If we didn't allocate any locals in the local context, then we only
  // need the minimal number of slots if we must have a local context.
  if (num_heap_slots_ == Context::MIN_CONTEXT_SLOTS &&
      !must_have_local_context) {
    num_heap_slots_ = 0;
  }

  // Allocation done.
  ASSERT(num_heap_slots_ == 0 || num_heap_slots_ >= Context::MIN_CONTEXT_SLOTS);
}

} }  // namespace v8::internal