src/variables.h

// Copyright 2011 the V8 project authors. All rights reserved.
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#ifndef V8_VARIABLES_H_
#define V8_VARIABLES_H_

#include "zone.h"

namespace v8 {
namespace internal {

// The AST refers to variables via VariableProxies - placeholders for the actual
// variables. Variables themselves are never directly referred to from the AST,
// they are maintained by scopes, and referred to from VariableProxies and Slots
// after binding and variable allocation.

class Variable: public ZoneObject {
 public:
  enum Mode {
    // User declared variables:
    VAR,       // declared via 'var', and 'function' declarations

    CONST,     // declared via 'const' declarations

    LET,       // declared via 'let' declarations

    // Variables introduced by the compiler:
    DYNAMIC,         // always require dynamic lookup (we don't know
                     // the declaration)

    DYNAMIC_GLOBAL,  // requires dynamic lookup, but we know that the
                     // variable is global unless it has been shadowed
                     // by an eval-introduced variable

    DYNAMIC_LOCAL,   // requires dynamic lookup, but we know that the
                     // variable is local and where it is unless it
                     // has been shadowed by an eval-introduced
                     // variable

    INTERNAL,        // like VAR, but not user-visible (may or may not
                     // be in a context)

    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);

  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_scope() const {
    return is_accessed_from_inner_scope_;
  }
  void MarkAsAccessedFromInnerScope() {
    ASSERT(mode_ != TEMPORARY);
    is_accessed_from_inner_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 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;
  }

  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_;
  int index_;

  Variable* local_if_not_shadowed_;

  // Valid as a LHS? (const and this are not valid LHS, for example)
  bool is_valid_LHS_;

  // Usage info.
  bool is_accessed_from_inner_scope_;  // set by variable resolver
  bool is_used_;
};


} }  // namespace v8::internal

#endif  // V8_VARIABLES_H_