src/scopeinfo.h

// Copyright 2006-2008 the V8 project authors. All rights reserved.
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#ifndef V8_SCOPEINFO_H_
#define V8_SCOPEINFO_H_

#include "variables.h"
#include "zone-inl.h"

namespace v8 {
namespace internal {

// Scope information represents information about a functions's
// scopes (currently only one, because we don't do any inlining)
// and the allocation of the scope's variables. Scope information
// is stored in a compressed form with Code objects and is used
// at runtime (stack dumps, deoptimization, etc.).
//
// Historical note: In other VMs built by this team, ScopeInfo was
// usually called DebugInfo since the information was used (among
// other things) for on-demand debugging (Self, Smalltalk). However,
// DebugInfo seems misleading, since this information is primarily used
// in debugging-unrelated contexts.

// Forward defined as
// template <class Allocator = FreeStoreAllocationPolicy> class ScopeInfo;
template<class Allocator>
class ScopeInfo BASE_EMBEDDED {
 public:
  // Create a ScopeInfo instance from a scope.
  explicit ScopeInfo(Scope* scope);

  // Create a ScopeInfo instance from a Code object.
  explicit ScopeInfo(Code* code);

  // Write the ScopeInfo data into a Code object, and returns the
  // amount of space that was needed. If no Code object is provided
  // (NULL handle), Serialize() only returns the amount of space needed.
  //
  // This operations requires that the Code object has the correct amount
  // of space for the ScopeInfo data; otherwise the operation fails (fatal
  // error). Any existing scope info in the Code object is simply overwritten.
  int Serialize(Code* code);

  // Garbage collection support for scope info embedded in Code objects.
  // This code is in ScopeInfo because only here we should have to know
  // about the encoding.
  static void IterateScopeInfo(Code* code, ObjectVisitor* v);


  // --------------------------------------------------------------------------
  // Lookup

  Handle<String> function_name() const  { return function_name_; }

  Handle<String> parameter_name(int i) const  { return parameters_[i]; }
  int number_of_parameters() const  { return parameters_.length(); }

  Handle<String> stack_slot_name(int i) const  { return stack_slots_[i]; }
  int number_of_stack_slots() const  { return stack_slots_.length(); }

  Handle<String> context_slot_name(int i) const {
    return context_slots_[i - Context::MIN_CONTEXT_SLOTS];
  }
  int number_of_context_slots() const {
    int l = context_slots_.length();
    return l == 0 ? 0 : l + Context::MIN_CONTEXT_SLOTS;
  }

  Handle<String> LocalName(int i) const;
  int NumberOfLocals() const;

  // --------------------------------------------------------------------------
  // The following functions provide quick access to scope info details
  // for runtime routines w/o the need to explicitly create a ScopeInfo
  // object.
  //
  // ScopeInfo is the only class which should have to know about the
  // encoding of it's information in a Code object, which is why these
  // functions are in this class.

  // Does this scope call eval.
  static bool CallsEval(Code* code);

  // Return the number of stack slots for code.
  static int NumberOfStackSlots(Code* code);

  // Return the number of context slots for code.
  static int NumberOfContextSlots(Code* code);

  // Lookup support for scope info embedded in Code objects. Returns
  // the stack slot index for a given slot name if the slot is
  // present; otherwise returns a value < 0. The name must be a symbol
  // (canonicalized).
  static int StackSlotIndex(Code* code, String* name);

  // Lookup support for scope info embedded in Code objects. Returns the
  // context slot index for a given slot name if the slot is present; otherwise
  // returns a value < 0. The name must be a symbol (canonicalized).
  // If the slot is present and mode != NULL, sets *mode to the corresponding
  // mode for that variable.
  static int ContextSlotIndex(Code* code, String* name, Variable::Mode* mode);

  // Lookup support for scope info embedded in Code objects. Returns the
  // parameter index for a given parameter name if the parameter is present;
  // otherwise returns a value < 0. The name must be a symbol (canonicalized).
  static int ParameterIndex(Code* code, String* name);

  // Lookup support for scope info embedded in Code objects. Returns the
  // function context slot index if the function name is present (named
  // function expressions, only), otherwise returns a value < 0. The name
  // must be a symbol (canonicalized).
  static int FunctionContextSlotIndex(Code* code, String* name);

  // --------------------------------------------------------------------------
  // Debugging support

#ifdef DEBUG
  void Print();
#endif

 private:
  Handle<String> function_name_;
  bool calls_eval_;
  List<Handle<String>, Allocator > parameters_;
  List<Handle<String>, Allocator > stack_slots_;
  List<Handle<String>, Allocator > context_slots_;
  List<Variable::Mode, Allocator > context_modes_;
};

class ZoneScopeInfo: public ScopeInfo<ZoneListAllocationPolicy> {
 public:
  // Create a ZoneScopeInfo instance from a scope.
  explicit ZoneScopeInfo(Scope* scope)
      : ScopeInfo<ZoneListAllocationPolicy>(scope) {}

  // Create a ZoneScopeInfo instance from a Code object.
  explicit ZoneScopeInfo(Code* code)
      :  ScopeInfo<ZoneListAllocationPolicy>(code) {}
};


// Cache for mapping (code, property name) into context slot index.
// The cache contains both positive and negative results.
// Slot index equals -1 means the property is absent.
// Cleared at startup and prior to mark sweep collection.
class ContextSlotCache {
 public:
  // Lookup context slot index for (code, name).
  // If absent, kNotFound is returned.
  static int Lookup(Code* code,
                    String* name,
                    Variable::Mode* mode);

  // Update an element in the cache.
  static void Update(Code* code,
                     String* name,
                     Variable::Mode mode,
                     int slot_index);

  // Clear the cache.
  static void Clear();

  static const int kNotFound = -2;
 private:
  inline static int Hash(Code* code, String* name);

#ifdef DEBUG
  static void ValidateEntry(Code* code,
                            String* name,
                            Variable::Mode mode,
                            int slot_index);
#endif

  static const int kLength = 256;
  struct Key {
    Code* code;
    String* name;
  };

  struct Value {
    Value(Variable::Mode mode, int index) {
      ASSERT(ModeField::is_valid(mode));
      ASSERT(IndexField::is_valid(index));
      value_ = ModeField::encode(mode) | IndexField::encode(index);
      ASSERT(mode == this->mode());
      ASSERT(index == this->index());
    }

    inline Value(uint32_t value) : value_(value) {}

    uint32_t raw() { return value_; }

    Variable::Mode mode() { return ModeField::decode(value_); }

    int index() { return IndexField::decode(value_); }

    // Bit fields in value_ (type, shift, size). Must be public so the
    // constants can be embedded in generated code.
    class ModeField:  public BitField<Variable::Mode, 0, 3> {};
    class IndexField: public BitField<int,            3, 32-3> {};
   private:
    uint32_t value_;
  };

  static Key keys_[kLength];
  static uint32_t values_[kLength];
};


} }  // namespace v8::internal

#endif  // V8_SCOPEINFO_H_