v8/src/register-allocator.h

// Copyright 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
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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#ifndef V8_REGISTER_ALLOCATOR_H_
#define V8_REGISTER_ALLOCATOR_H_

#include "macro-assembler.h"

#if V8_TARGET_ARCH_IA32
#include "ia32/register-allocator-ia32.h"
#elif V8_TARGET_ARCH_X64
#include "x64/register-allocator-x64.h"
#elif V8_TARGET_ARCH_ARM
#include "arm/register-allocator-arm.h"
#else
#error Unsupported target architecture.
#endif

namespace v8 {
namespace internal {


// -------------------------------------------------------------------------
// StaticType
//
// StaticType represent the type of an expression or a word at runtime.
// The types are ordered by knowledge, so that if a value can come about
// in more than one way, and there are different static types inferred
// for the different ways, the types can be combined to a type that we
// are still certain of (possibly just "unknown").

class StaticType BASE_EMBEDDED {
 public:
  StaticType() : static_type_(UNKNOWN_TYPE) {}

  static StaticType unknown() { return StaticType(); }
  static StaticType smi() { return StaticType(SMI_TYPE); }
  static StaticType jsstring() { return StaticType(STRING_TYPE); }
  static StaticType heap_object() { return StaticType(HEAP_OBJECT_TYPE); }

  // Accessors
  bool is_unknown() { return static_type_ == UNKNOWN_TYPE; }
  bool is_smi() { return static_type_ == SMI_TYPE; }
  bool is_heap_object() { return (static_type_ & HEAP_OBJECT_TYPE) != 0; }
  bool is_jsstring() { return static_type_ == STRING_TYPE; }

  bool operator==(StaticType other) const {
    return static_type_ == other.static_type_;
  }

  // Find the best approximating type for a value.
  // The argument must not be NULL.
  static StaticType TypeOf(Object* object) {
    // Remember to make the most specific tests first. A string is also a heap
    // object, so test for string-ness first.
    if (object->IsSmi()) return smi();
    if (object->IsString()) return jsstring();
    if (object->IsHeapObject()) return heap_object();
    return unknown();
  }

  // Merges two static types to a type that combines the knowledge
  // of both. If there is no way to combine (e.g., being a string *and*
  // being a smi), the resulting type is unknown.
  StaticType merge(StaticType other) {
    StaticType x(
        static_cast<StaticTypeEnum>(static_type_ & other.static_type_));
    return x;
  }

 private:
  enum StaticTypeEnum {
    // Numbers are chosen so that least upper bound of the following
    // partial order is implemented by bitwise "and":
    //
    //    string
    //       |
    //    heap-object    smi
    //           \       /
    //            unknown
    //
    UNKNOWN_TYPE     = 0x00,
    SMI_TYPE         = 0x01,
    HEAP_OBJECT_TYPE = 0x02,
    STRING_TYPE      = 0x04 | HEAP_OBJECT_TYPE
  };
  explicit StaticType(StaticTypeEnum static_type) : static_type_(static_type) {}

  // StaticTypeEnum static_type_;
  StaticTypeEnum static_type_;

  friend class FrameElement;
  friend class Result;
};


// -------------------------------------------------------------------------
// Results
//
// Results encapsulate the compile-time values manipulated by the code
// generator.  They can represent registers or constants.

class Result BASE_EMBEDDED {
 public:
  enum Type {
    INVALID,
    REGISTER,
    CONSTANT
  };

  // Construct an invalid result.
  Result() { invalidate(); }

  // Construct a register Result.
  explicit Result(Register reg);

  // Construct a register Result with a known static type.
  Result(Register reg, StaticType static_type);

  // Construct a Result whose value is a compile-time constant.
  explicit Result(Handle<Object> value) {
    value_ = StaticTypeField::encode(StaticType::TypeOf(*value).static_type_)
        | TypeField::encode(CONSTANT)
        | DataField::encode(ConstantList()->length());
    ConstantList()->Add(value);
  }

  // The copy constructor and assignment operators could each create a new
  // register reference.
  Result(const Result& other) {
    other.CopyTo(this);
  }

  Result& operator=(const Result& other) {
    if (this != &other) {
      Unuse();
      other.CopyTo(this);
    }
    return *this;
  }

  inline ~Result();

  // Static indirection table for handles to constants.  If a Result
  // represents a constant, the data contains an index into this table
  // of handles to the actual constants.
  typedef ZoneList<Handle<Object> > ZoneObjectList;

  static ZoneObjectList* ConstantList() {
    static ZoneObjectList list(10);
    return &list;
  }

  // Clear the constants indirection table.
  static void ClearConstantList() {
    ConstantList()->Clear();
  }

  inline void Unuse();

  StaticType static_type() const {
    return StaticType(StaticTypeField::decode(value_));
  }

  void set_static_type(StaticType type) {
    value_ = value_ & ~StaticTypeField::mask();
    value_ = value_ | StaticTypeField::encode(type.static_type_);
  }

  Type type() const { return TypeField::decode(value_); }

  void invalidate() { value_ = TypeField::encode(INVALID); }

  bool is_valid() const { return type() != INVALID; }
  bool is_register() const { return type() == REGISTER; }
  bool is_constant() const { return type() == CONSTANT; }

  Register reg() const {
    ASSERT(is_register());
    uint32_t reg = DataField::decode(value_);
    Register result;
    result.code_ = reg;
    return result;
  }

  Handle<Object> handle() const {
    ASSERT(type() == CONSTANT);
    return ConstantList()->at(DataField::decode(value_));
  }

  // Move this result to an arbitrary register.  The register is not
  // necessarily spilled from the frame or even singly-referenced outside
  // it.
  void ToRegister();

  // Move this result to a specified register.  The register is spilled from
  // the frame, and the register is singly-referenced (by this result)
  // outside the frame.
  void ToRegister(Register reg);

 private:
  uint32_t value_;

  class StaticTypeField: public BitField<StaticType::StaticTypeEnum, 0, 3> {};
  class TypeField: public BitField<Type, 3, 2> {};
  class DataField: public BitField<uint32_t, 5, 32 - 6> {};

  inline void CopyTo(Result* destination) const;

  friend class CodeGeneratorScope;
};


// -------------------------------------------------------------------------
// Register file
//
// The register file tracks reference counts for the processor registers.
// It is used by both the register allocator and the virtual frame.

class RegisterFile BASE_EMBEDDED {
 public:
  RegisterFile() { Reset(); }

  void Reset() {
    for (int i = 0; i < kNumRegisters; i++) {
      ref_counts_[i] = 0;
    }
  }

  // Predicates and accessors for the reference counts.
  bool is_used(int num) {
    ASSERT(0 <= num && num < kNumRegisters);
    return ref_counts_[num] > 0;
  }

  int count(int num) {
    ASSERT(0 <= num && num < kNumRegisters);
    return ref_counts_[num];
  }

  // Record a use of a register by incrementing its reference count.
  void Use(int num) {
    ASSERT(0 <= num && num < kNumRegisters);
    ref_counts_[num]++;
  }

  // Record that a register will no longer be used by decrementing its
  // reference count.
  void Unuse(int num) {
    ASSERT(is_used(num));
    ref_counts_[num]--;
  }

  // Copy the reference counts from this register file to the other.
  void CopyTo(RegisterFile* other) {
    for (int i = 0; i < kNumRegisters; i++) {
      other->ref_counts_[i] = ref_counts_[i];
    }
  }

 private:
  static const int kNumRegisters = RegisterAllocatorConstants::kNumRegisters;

  int ref_counts_[kNumRegisters];

  // Very fast inlined loop to find a free register.  Used in
  // RegisterAllocator::AllocateWithoutSpilling.  Returns
  // kInvalidRegister if no free register found.
  int ScanForFreeRegister() {
    for (int i = 0; i < RegisterAllocatorConstants::kNumRegisters; i++) {
      if (!is_used(i)) return i;
    }
    return RegisterAllocatorConstants::kInvalidRegister;
  }

  friend class RegisterAllocator;
};


// -------------------------------------------------------------------------
// Register allocator
//

class RegisterAllocator BASE_EMBEDDED {
 public:
  static const int kNumRegisters =
      RegisterAllocatorConstants::kNumRegisters;
  static const int kInvalidRegister =
      RegisterAllocatorConstants::kInvalidRegister;

  explicit RegisterAllocator(CodeGenerator* cgen) : cgen_(cgen) {}

  // True if the register is reserved by the code generator, false if it
  // can be freely used by the allocator Defined in the
  // platform-specific XXX-inl.h files..
  static inline bool IsReserved(Register reg);

  // Convert between (unreserved) assembler registers and allocator
  // numbers.  Defined in the platform-specific XXX-inl.h files.
  static inline int ToNumber(Register reg);
  static inline Register ToRegister(int num);

  // Predicates and accessors for the registers' reference counts.
  bool is_used(int num) { return registers_.is_used(num); }
  bool is_used(Register reg) { return registers_.is_used(ToNumber(reg)); }

  int count(int num) { return registers_.count(num); }
  int count(Register reg) { return registers_.count(ToNumber(reg)); }

  // Explicitly record a reference to a register.
  void Use(int num) { registers_.Use(num); }
  void Use(Register reg) { registers_.Use(ToNumber(reg)); }

  // Explicitly record that a register will no longer be used.
  void Unuse(int num) { registers_.Unuse(num); }
  void Unuse(Register reg) { registers_.Unuse(ToNumber(reg)); }

  // Reset the register reference counts to free all non-reserved registers.
  void Reset() { registers_.Reset(); }

  // Initialize the register allocator for entry to a JS function.  On
  // entry, the (non-reserved) registers used by the JS calling
  // convention are referenced and the other (non-reserved) registers
  // are free.
  inline void Initialize();

  // Allocate a free register and return a register result if possible or
  // fail and return an invalid result.
  Result Allocate();

  // Allocate a specific register if possible, spilling it from the
  // current frame if necessary, or else fail and return an invalid
  // result.
  Result Allocate(Register target);

  // Allocate a free register without spilling any from the current
  // frame or fail and return an invalid result.
  Result AllocateWithoutSpilling();

  // Allocate a free byte register without spilling any from the current
  // frame or fail and return an invalid result.
  Result AllocateByteRegisterWithoutSpilling();

  // Copy the internal state to a register file, to be restored later by
  // RestoreFrom.
  void SaveTo(RegisterFile* register_file) {
    registers_.CopyTo(register_file);
  }

  // Restore the internal state.
  void RestoreFrom(RegisterFile* register_file) {
    register_file->CopyTo(&registers_);
  }

 private:
  CodeGenerator* cgen_;
  RegisterFile registers_;
};

} }  // namespace v8::internal

#endif  // V8_REGISTER_ALLOCATOR_H_