CSE2410 Fall 2014 Bounce

// Copyright 2006-2008 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

//       with the distribution.

//     * Neither the name of Google Inc. nor the names of its

//       contributors may be used to endorse or promote products derived

//       from this software without specific prior written permission.

//

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef V8_VARIABLES_H_

#define V8_VARIABLES_H_

#include "zone.h"

namespace v8 { namespace internal {

class UseCount BASE_EMBEDDED {

 public:

  UseCount();

  // Inform the node of a "use". The weight can be used to indicate

  // heavier use, for instance if the variable is accessed inside a loop.

  void RecordRead(int weight);

  void RecordWrite(int weight);

  void RecordAccess(int weight);  // records a read & write

  void RecordUses(UseCount* uses);

  int nreads() const  { return nreads_; }

  int nwrites() const  { return nwrites_; }

  int nuses() const  { return nreads_ + nwrites_; }

  bool is_read() const  { return nreads() > 0; }

  bool is_written() const  { return nwrites() > 0; }

  bool is_used() const  { return nuses() > 0; }

#ifdef DEBUG

  void Print();

#endif

 private:

  int nreads_;

  int nwrites_;

};

// Variables and AST expression nodes can track their "type" to enable

// optimizations and removal of redundant checks when generating code.

class SmiAnalysis {

 public:

  enum Kind {

    UNKNOWN,

    LIKELY_SMI

  };

  SmiAnalysis() : kind_(UNKNOWN) {}

  bool Is(Kind kind) const { return kind_ == kind; }

  bool IsKnown() const { return !Is(UNKNOWN); }

  bool IsUnknown() const { return Is(UNKNOWN); }

  bool IsLikelySmi() const { return Is(LIKELY_SMI); }

  void CopyFrom(SmiAnalysis* other) {

    kind_ = other->kind_;

  }

  static const char* Type2String(SmiAnalysis* type);

  // LIKELY_SMI accessors

  void SetAsLikelySmi() {

    kind_ = LIKELY_SMI;

  }

  void SetAsLikelySmiIfUnknown() {

    if (IsUnknown()) {

      SetAsLikelySmi();

    }

  }

 private:

  Kind kind_;

  DISALLOW_COPY_AND_ASSIGN(SmiAnalysis);

};

// 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

    // 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

  };

  // Printing support

  static const char* Mode2String(Mode mode);

  // Type testing & conversion

  Property* AsProperty();

  Variable* AsVariable();

  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_; }

  // If this assertion fails it means that some code has tried to

  // treat the special this variable as an ordinary variable with

  // the name "this".

  Handle<String> name() const  { return name_; }

  Mode mode() const  { return mode_; }

  bool is_accessed_from_inner_scope() const  {

    return is_accessed_from_inner_scope_;

  }

  UseCount* var_uses()  { return &var_uses_; }

  UseCount* obj_uses()  { return &obj_uses_; }

  bool IsVariable(Handle<String> n) {

    return !is_this() && name().is_identical_to(n);

  }

  bool is_dynamic() const {

    return (mode_ == DYNAMIC ||

            mode_ == DYNAMIC_GLOBAL ||

            mode_ == DYNAMIC_LOCAL);

  }

  bool is_global() const;

  bool is_this() const { return is_this_; }

  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;

  }

  Expression* rewrite() const  { return rewrite_; }

  Slot* slot() const;

  SmiAnalysis* type() { return &type_; }

 private:

  Variable(Scope* scope, Handle<String> name, Mode mode, bool is_valid_LHS,

      bool is_this);

  Scope* scope_;

  Handle<String> name_;

  Mode mode_;

  bool is_valid_LHS_;

  bool is_this_;

  Variable* local_if_not_shadowed_;

  // Usage info.

  bool is_accessed_from_inner_scope_;  // set by variable resolver

  UseCount var_uses_;  // uses of the variable value

  UseCount obj_uses_;  // uses of the object the variable points to

  // Static type information

  SmiAnalysis type_;

  // Code generation.

  // rewrite_ is usually a Slot or a Property, but maybe any expression.

  Expression* rewrite_;

  friend class VariableProxy;

  friend class Scope;

  friend class LocalsMap;

  friend class AstBuildingParser;

};

} }  // namespace v8::internal

#endif  // V8_VARIABLES_H_