runtime/vm/locations.h

// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#ifndef VM_LOCATIONS_H_
#define VM_LOCATIONS_H_

#include "vm/allocation.h"
#include "vm/assembler.h"
#include "vm/bitfield.h"
#include "vm/log.h"

namespace dart {


class BufferFormatter;
class ConstantInstr;
class Definition;
class PairLocation;
class Value;


enum Representation {
  kNoRepresentation,
  kTagged,
  kUntagged,
  kUnboxedDouble,
  kUnboxedInt32,
  kUnboxedUint32,
  kUnboxedMint,
  kUnboxedFloat32x4,
  kUnboxedInt32x4,
  kUnboxedFloat64x2,
  kPairOfTagged,
  kPairOfUnboxedDouble,
  kNumRepresentations
};


// Location objects are used to connect register allocator and code generator.
// Instruction templates used by code generator have a corresponding
// LocationSummary object which specifies expected location for every input
// and output.
// Each location is encoded as a single word: for non-constant locations
// low 4 bits denote location kind, rest is kind specific location payload
// e.g. for REGISTER kind payload is register code (value of the Register
// enumeration), constant locations contain a tagged (low 2 bits are set to 01)
// Object handle.
//
// Locations must satisfy the following invariant: if two locations' encodings
// are bitwise unequal then these two locations are guaranteed to be disjoint.
// Properties like representation belong to the value that is stored in
// the location not to the location itself.
class Location : public ValueObject {
 private:
  enum {
    // Number of bits required to encode Kind value.
    kBitsForKind = 4,
    kBitsForPayload = kWordSize * kBitsPerByte - kBitsForKind,
  };

  static const uword kInvalidLocation = 0;
  static const uword kLocationTagMask = 0x3;

 public:
  // Constant payload can overlap with kind field so Kind values
  // have to be chosen in a way that their last 2 bits are never
  // the same as kConstantTag or kPairLocationTag.
  // Note that two locations with different kinds should never point to
  // the same place. For example kQuadStackSlot location should never intersect
  // with kDoubleStackSlot location.
  enum Kind {
    // This location is invalid.  Payload must be zero.
    kInvalid = 0,

    // Constant value. This location contains a tagged Object handle.
    kConstantTag = 1,

    // This location contains a tagged pointer to a PairLocation.
    kPairLocationTag = 2,

    // Unallocated location represents a location that is not fixed and can be
    // allocated by a register allocator.  Each unallocated location has
    // a policy that specifies what kind of location is suitable. Payload
    // contains register allocation policy.
    kUnallocated = 3,

    // Spill slots allocated by the register allocator.  Payload contains
    // a spill index.
    kStackSlot = 4,  // Word size slot.
    kDoubleStackSlot = 7,  // 64bit stack slot.
    kQuadStackSlot = 11,  // 128bit stack slot.

    // Register location represents a fixed register.  Payload contains
    // register code.
    kRegister = 8,

    // FpuRegister location represents a fixed fpu register.  Payload contains
    // its code.
    kFpuRegister = 12,
  };

  Location() : value_(kInvalidLocation) {
    // Verify that non-tagged location kinds do not interfere with location tags
    // (kConstantTag and kPairLocationTag).
    COMPILE_ASSERT((kInvalid & kLocationTagMask) != kConstantTag);
    COMPILE_ASSERT((kInvalid & kLocationTagMask) != kPairLocationTag);

    COMPILE_ASSERT((kUnallocated & kLocationTagMask) != kConstantTag);
    COMPILE_ASSERT((kUnallocated & kLocationTagMask) != kPairLocationTag);

    COMPILE_ASSERT((kStackSlot & kLocationTagMask) != kConstantTag);
    COMPILE_ASSERT((kStackSlot & kLocationTagMask) != kPairLocationTag);

    COMPILE_ASSERT((kDoubleStackSlot & kLocationTagMask) != kConstantTag);
    COMPILE_ASSERT((kDoubleStackSlot & kLocationTagMask) != kPairLocationTag);

    COMPILE_ASSERT((kQuadStackSlot & kLocationTagMask) != kConstantTag);
    COMPILE_ASSERT((kQuadStackSlot & kLocationTagMask) != kPairLocationTag);

    COMPILE_ASSERT((kRegister & kLocationTagMask) != kConstantTag);
    COMPILE_ASSERT((kRegister & kLocationTagMask) != kPairLocationTag);

    COMPILE_ASSERT((kFpuRegister & kLocationTagMask) != kConstantTag);
    COMPILE_ASSERT((kFpuRegister & kLocationTagMask) != kPairLocationTag);

    // Verify tags and tagmask.
    COMPILE_ASSERT((kConstantTag & kLocationTagMask) == kConstantTag);

    COMPILE_ASSERT((kPairLocationTag & kLocationTagMask) == kPairLocationTag);

    ASSERT(IsInvalid());
  }

  Location(const Location& other) : ValueObject(), value_(other.value_) { }

  Location& operator=(const Location& other) {
    value_ = other.value_;
    return *this;
  }

  bool IsInvalid() const {
    return value_ == kInvalidLocation;
  }

  // Constants.
  bool IsConstant() const {
    return (value_ & kLocationTagMask) == kConstantTag;
  }

  static Location Constant(const ConstantInstr* obj) {
    Location loc(reinterpret_cast<uword>(obj) | kConstantTag);
    ASSERT(obj == loc.constant_instruction());
    return loc;
  }

  ConstantInstr* constant_instruction() const {
    ASSERT(IsConstant());
    return reinterpret_cast<ConstantInstr*>(value_ & ~kLocationTagMask);
  }

  const Object& constant() const;

  bool IsPairLocation() const {
    return (value_ & kLocationTagMask) == kPairLocationTag;
  }

  static Location Pair(Location first, Location second);

  PairLocation* AsPairLocation() const;

  // Unallocated locations.
  enum Policy {
    kAny,
    kPrefersRegister,
    kRequiresRegister,
    kRequiresFpuRegister,
    kWritableRegister,
    kSameAsFirstInput,
  };

  bool IsUnallocated() const {
    return kind() == kUnallocated;
  }

  bool IsRegisterBeneficial() {
    return !Equals(Any());
  }

  static Location UnallocatedLocation(Policy policy) {
    return Location(kUnallocated, PolicyField::encode(policy));
  }

  // Any free register is suitable to replace this unallocated location.
  static Location Any() {
    return UnallocatedLocation(kAny);
  }

  static Location PrefersRegister() {
    return UnallocatedLocation(kPrefersRegister);
  }

  static Location RequiresRegister() {
    return UnallocatedLocation(kRequiresRegister);
  }

  static Location RequiresFpuRegister() {
    return UnallocatedLocation(kRequiresFpuRegister);
  }

  static Location WritableRegister() {
    return UnallocatedLocation(kWritableRegister);
  }

  // The location of the first input to the instruction will be
  // used to replace this unallocated location.
  static Location SameAsFirstInput() {
    return UnallocatedLocation(kSameAsFirstInput);
  }

  // Empty location. Used if there the location should be ignored.
  static Location NoLocation() {
    return Location();
  }

  Policy policy() const {
    ASSERT(IsUnallocated());
    return PolicyField::decode(payload());
  }

  // Register locations.
  static Location RegisterLocation(Register reg) {
    return Location(kRegister, reg);
  }

  bool IsRegister() const {
    return kind() == kRegister;
  }

  Register reg() const {
    ASSERT(IsRegister());
    return static_cast<Register>(payload());
  }

  // FpuRegister locations.
  static Location FpuRegisterLocation(FpuRegister reg) {
    return Location(kFpuRegister, reg);
  }

  bool IsFpuRegister() const {
    return kind() == kFpuRegister;
  }

  FpuRegister fpu_reg() const {
    ASSERT(IsFpuRegister());
    return static_cast<FpuRegister>(payload());
  }

  static bool IsMachineRegisterKind(Kind kind) {
    return (kind == kRegister) || (kind == kFpuRegister);
  }

  static Location MachineRegisterLocation(Kind kind,
                                          intptr_t reg) {
    if (kind == kRegister) {
      return RegisterLocation(static_cast<Register>(reg));
    } else {
      ASSERT(kind == kFpuRegister);
      return FpuRegisterLocation(static_cast<FpuRegister>(reg));
    }
  }

  bool IsMachineRegister() const {
    return IsMachineRegisterKind(kind());
  }

  intptr_t register_code() const {
    ASSERT(IsMachineRegister());
    return static_cast<intptr_t>(payload());
  }

  static uword EncodeStackIndex(intptr_t stack_index) {
    ASSERT((-kStackIndexBias <= stack_index) &&
           (stack_index < kStackIndexBias));
    return static_cast<uword>(kStackIndexBias + stack_index);
  }

  // Spill slots.
  static Location StackSlot(intptr_t stack_index,
                            Register base = FPREG) {
    uword payload = StackSlotBaseField::encode(base)
        | StackIndexField::encode(EncodeStackIndex(stack_index));
    Location loc(kStackSlot, payload);
    // Ensure that sign is preserved.
    ASSERT(loc.stack_index() == stack_index);
    return loc;
  }

  bool IsStackSlot() const {
    return kind() == kStackSlot;
  }

  static Location DoubleStackSlot(intptr_t stack_index) {
    uword payload = StackSlotBaseField::encode(FPREG)
        | StackIndexField::encode(EncodeStackIndex(stack_index));
    Location loc(kDoubleStackSlot, payload);
    // Ensure that sign is preserved.
    ASSERT(loc.stack_index() == stack_index);
    return loc;
  }

  bool IsDoubleStackSlot() const {
    return kind() == kDoubleStackSlot;
  }

  static Location QuadStackSlot(intptr_t stack_index) {
    uword payload = StackSlotBaseField::encode(FPREG)
        | StackIndexField::encode(EncodeStackIndex(stack_index));
    Location loc(kQuadStackSlot, payload);
    // Ensure that sign is preserved.
    ASSERT(loc.stack_index() == stack_index);
    return loc;
  }

  bool IsQuadStackSlot() const {
    return kind() == kQuadStackSlot;
  }

  Register base_reg() const {
    ASSERT(HasStackIndex());
    return StackSlotBaseField::decode(payload());
  }

  intptr_t stack_index() const {
    ASSERT(HasStackIndex());
    // Decode stack index manually to preserve sign.
    return StackIndexField::decode(payload()) - kStackIndexBias;
  }

  bool HasStackIndex() const {
    return IsStackSlot() || IsDoubleStackSlot() || IsQuadStackSlot();
  }

  // Return a memory operand for stack slot locations.
  Address ToStackSlotAddress() const;

  // Returns the offset from the frame pointer for stack slot locations.
  intptr_t ToStackSlotOffset() const;

  // Constants.
  static Location RegisterOrConstant(Value* value);
  static Location RegisterOrSmiConstant(Value* value);
  static Location WritableRegisterOrSmiConstant(Value* value);
  static Location FixedRegisterOrConstant(Value* value, Register reg);
  static Location FixedRegisterOrSmiConstant(Value* value, Register reg);
  static Location AnyOrConstant(Value* value);

  const char* Name() const;
  void PrintTo(BufferFormatter* f) const;
  void Print() const;
  const char* ToCString() const;

  // Compare two locations.
  bool Equals(Location other) const {
    return value_ == other.value_;
  }

  // If current location is constant might return something that
  // is not equal to any Kind.
  Kind kind() const {
    return KindField::decode(value_);
  }

  Location Copy() const;

  Location RemapForSlowPath(Definition* def,
                            intptr_t* cpu_reg_slots,
                            intptr_t* fpu_reg_slots) const;

 private:
  explicit Location(uword value) : value_(value) { }

  Location(Kind kind, uword payload)
      : value_(KindField::encode(kind) | PayloadField::encode(payload)) { }

  uword payload() const {
    return PayloadField::decode(value_);
  }

  typedef BitField<Kind, 0, kBitsForKind> KindField;
  typedef BitField<uword, kBitsForKind, kBitsForPayload> PayloadField;

  // Layout for kUnallocated locations payload.
  typedef BitField<Policy, 0, 3> PolicyField;

  // Layout for stack slots.
  static const intptr_t kBitsForBaseReg = 5;
  static const intptr_t kBitsForStackIndex = kBitsForPayload - kBitsForBaseReg;
  typedef BitField<Register, 0, kBitsForBaseReg> StackSlotBaseField;
  typedef BitField<intptr_t,
                   kBitsForBaseReg,
                   kBitsForStackIndex> StackIndexField;
  COMPILE_ASSERT(1 << kBitsForBaseReg >= kNumberOfCpuRegisters);

  static const intptr_t kStackIndexBias =
      static_cast<intptr_t>(1) << (kBitsForStackIndex - 1);

  // Location either contains kind and payload fields or a tagged handle for
  // a constant locations. Values of enumeration Kind are selected in such a
  // way that none of them can be interpreted as a kConstant tag.
  uword value_;
};


class PairLocation : public ZoneAllocated {
 public:
  PairLocation() {
    for (intptr_t i = 0; i < kPairLength; i++) {
      ASSERT(locations_[i].IsInvalid());
    }
  }

  intptr_t length() const { return kPairLength; }

  Location At(intptr_t i) const {
    ASSERT(i >= 0);
    ASSERT(i < kPairLength);
    return locations_[i];
  }

  void SetAt(intptr_t i, Location loc) {
    ASSERT(i >= 0);
    ASSERT(i < kPairLength);
    locations_[i] = loc;
  }

  Location* SlotAt(intptr_t i) {
    ASSERT(i >= 0);
    ASSERT(i < kPairLength);
    return &locations_[i];
  }

 private:
  static const intptr_t kPairLength = 2;
  Location locations_[kPairLength];
};


template<typename T>
class SmallSet {
 public:
  SmallSet() : data_(0) { }

  explicit SmallSet(intptr_t data) : data_(data) { }

  bool Contains(T value) const { return (data_ & ToMask(value)) != 0; }

  void Add(T value) { data_ |= ToMask(value); }

  void Remove(T value) { data_ &= ~ToMask(value); }

  bool IsEmpty() const { return data_ == 0; }

  intptr_t data() const { return data_; }

 private:
  static intptr_t ToMask(T value) {
    ASSERT(static_cast<intptr_t>(value) < (kWordSize * kBitsPerByte));
    return 1 << static_cast<intptr_t>(value);
  }

  intptr_t data_;
};


class RegisterSet : public ValueObject {
 public:
  RegisterSet()
      : cpu_registers_(),
        untagged_cpu_registers_(),
        fpu_registers_() {
    ASSERT(kNumberOfCpuRegisters <= (kWordSize * kBitsPerByte));
    ASSERT(kNumberOfFpuRegisters <= (kWordSize * kBitsPerByte));
  }


  void Add(Location loc, Representation rep = kTagged) {
    if (loc.IsRegister()) {
      cpu_registers_.Add(loc.reg());
      if (rep != kTagged) {
        // CPU register contains an untagged value.
        MarkUntagged(loc);
      }
    } else if (loc.IsFpuRegister()) {
      fpu_registers_.Add(loc.fpu_reg());
    }
  }

  void Remove(Location loc) {
    if (loc.IsRegister()) {
      cpu_registers_.Remove(loc.reg());
    } else if (loc.IsFpuRegister()) {
      fpu_registers_.Remove(loc.fpu_reg());
    }
  }

  bool Contains(Location loc) {
    if (loc.IsRegister()) {
      return ContainsRegister(loc.reg());
    } else if (loc.IsFpuRegister()) {
      return ContainsFpuRegister(loc.fpu_reg());
    } else {
      UNREACHABLE();
      return false;
    }
  }

  void DebugPrint() {
    for (intptr_t i = 0; i < kNumberOfCpuRegisters; i++) {
      Register r = static_cast<Register>(i);
      if (ContainsRegister(r)) {
        THR_Print("%s %s\n", Assembler::RegisterName(r),
                           IsTagged(r) ? "tagged" : "untagged");
      }
    }

    for (intptr_t i = 0; i < kNumberOfFpuRegisters; i++) {
      FpuRegister r = static_cast<FpuRegister>(i);
      if (ContainsFpuRegister(r)) {
        THR_Print("%s\n", Assembler::FpuRegisterName(r));
      }
    }
  }

  void MarkUntagged(Location loc) {
    ASSERT(loc.IsRegister());
    untagged_cpu_registers_.Add(loc.reg());
  }

  bool HasUntaggedValues() const {
    return !untagged_cpu_registers_.IsEmpty() || !fpu_registers_.IsEmpty();
  }

  bool IsTagged(Register reg) const {
    return !untagged_cpu_registers_.Contains(reg);
  }

  bool ContainsRegister(Register reg) const {
    return cpu_registers_.Contains(reg);
  }

  bool ContainsFpuRegister(FpuRegister fpu_reg) const {
    return fpu_registers_.Contains(fpu_reg);
  }

  intptr_t CpuRegisterCount() const { return RegisterCount(cpu_registers()); }
  intptr_t FpuRegisterCount() const { return RegisterCount(fpu_registers()); }

  static intptr_t RegisterCount(intptr_t registers);
  static bool Contains(intptr_t register_set, intptr_t reg) {
    return (register_set & (1 << reg)) != 0;
  }

  intptr_t cpu_registers() const { return cpu_registers_.data(); }
  intptr_t fpu_registers() const { return fpu_registers_.data(); }

 private:
  SmallSet<Register> cpu_registers_;
  SmallSet<Register> untagged_cpu_registers_;
  SmallSet<FpuRegister> fpu_registers_;

  DISALLOW_COPY_AND_ASSIGN(RegisterSet);
};


// Specification of locations for inputs and output.
class LocationSummary : public ZoneAllocated {
 public:
  enum ContainsCall {
    kNoCall,
    kCall,
    kCallOnSlowPath
  };

  LocationSummary(Zone* zone,
                  intptr_t input_count,
                  intptr_t temp_count,
                  LocationSummary::ContainsCall contains_call);

  intptr_t input_count() const {
    return num_inputs_;
  }

  Location in(intptr_t index) const {
    ASSERT(index >= 0);
    ASSERT(index < num_inputs_);
    return input_locations_[index];
  }

  Location* in_slot(intptr_t index) {
    ASSERT(index >= 0);
    ASSERT(index < num_inputs_);
    return &input_locations_[index];
  }

  void set_in(intptr_t index, Location loc) {
    ASSERT(index >= 0);
    ASSERT(index < num_inputs_);
    ASSERT(!always_calls() || loc.IsMachineRegister());
    input_locations_[index] = loc;
  }

  intptr_t temp_count() const {
    return num_temps_;
  }

  Location temp(intptr_t index) const {
    ASSERT(index >= 0);
    ASSERT(index < num_temps_);
    return temp_locations_[index];
  }

  Location* temp_slot(intptr_t index) {
    ASSERT(index >= 0);
    ASSERT(index < num_temps_);
    return &temp_locations_[index];
  }

  void set_temp(intptr_t index, Location loc) {
    ASSERT(index >= 0);
    ASSERT(index < num_temps_);
    ASSERT(!always_calls() || loc.IsMachineRegister());
    temp_locations_[index] = loc;
  }

  intptr_t output_count() const {
    return 1;
  }

  Location out(intptr_t index) const {
    ASSERT(index == 0);
    return output_location_;
  }

  Location* out_slot(intptr_t index) {
    ASSERT(index == 0);
    return &output_location_;
  }

  void set_out(intptr_t index, Location loc) {
    ASSERT(index == 0);
    ASSERT(!always_calls() ||
           (loc.IsMachineRegister() || loc.IsInvalid() ||
            loc.IsPairLocation()));
    output_location_ = loc;
  }

  BitmapBuilder* stack_bitmap() {
    if (stack_bitmap_ == NULL) {
      stack_bitmap_ = new BitmapBuilder();
    }
    return stack_bitmap_;
  }
  void SetStackBit(intptr_t index) {
    stack_bitmap()->Set(index, true);
  }

  bool always_calls() const {
    return contains_call_ == kCall;
  }

  bool can_call() {
    return contains_call_ != kNoCall;
  }

  bool HasCallOnSlowPath() {
    return can_call() && !always_calls();
  }

  void PrintTo(BufferFormatter* f) const;

  static LocationSummary* Make(Zone* zone,
                               intptr_t input_count,
                               Location out,
                               ContainsCall contains_call);

  RegisterSet* live_registers() {
    return &live_registers_;
  }

#if defined(DEBUG)
  // Debug only verification that ensures that writable registers are correctly
  // preserved on the slow path.
  void DiscoverWritableInputs();
  void CheckWritableInputs();
#endif

 private:
  const intptr_t num_inputs_;
  Location* input_locations_;
  const intptr_t num_temps_;
  Location* temp_locations_;
  Location output_location_;

  BitmapBuilder* stack_bitmap_;

  const ContainsCall contains_call_;
  RegisterSet live_registers_;

#if defined(DEBUG)
  intptr_t writable_inputs_;
#endif
};


}  // namespace dart

#endif  // VM_LOCATIONS_H_