runtime/vm/assembler_mips.cc

// 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.

#include "vm/globals.h"
#if defined(TARGET_ARCH_MIPS)

#include "vm/assembler.h"
#include "vm/longjump.h"
#include "vm/runtime_entry.h"
#include "vm/simulator.h"
#include "vm/stack_frame.h"
#include "vm/stub_code.h"

namespace dart {

#if defined(USING_SIMULATOR)
DECLARE_FLAG(bool, trace_sim);
#endif
DEFINE_FLAG(bool, print_stop_message, false, "Print stop message.");
DECLARE_FLAG(bool, inline_alloc);

void Assembler::InitializeMemoryWithBreakpoints(uword data, int length) {
  ASSERT(Utils::IsAligned(data, 4));
  ASSERT(Utils::IsAligned(length, 4));
  const uword end = data + length;
  while (data < end) {
    *reinterpret_cast<int32_t*>(data) = Instr::kBreakPointInstruction;
    data += 4;
  }
}


void Assembler::GetNextPC(Register dest, Register temp) {
  if (temp != kNoRegister) {
    mov(temp, RA);
  }
  EmitRegImmType(REGIMM, R0, BGEZAL, 1);
  mov(dest, RA);
  if (temp != kNoRegister) {
    mov(RA, temp);
  }
}


static bool CanEncodeBranchOffset(int32_t offset) {
  ASSERT(Utils::IsAligned(offset, 4));
  return Utils::IsInt(18, offset);
}


int32_t Assembler::EncodeBranchOffset(int32_t offset, int32_t instr) {
  if (!CanEncodeBranchOffset(offset)) {
    ASSERT(!use_far_branches());
    Isolate::Current()->long_jump_base()->Jump(
        1, Object::branch_offset_error());
  }

  // Properly preserve only the bits supported in the instruction.
  offset >>= 2;
  offset &= kBranchOffsetMask;
  return (instr & ~kBranchOffsetMask) | offset;
}


static int DecodeBranchOffset(int32_t instr) {
  // Sign-extend, left-shift by 2.
  return (((instr & kBranchOffsetMask) << 16) >> 14);
}


static int32_t DecodeLoadImmediate(int32_t ori_instr, int32_t lui_instr) {
  return (((lui_instr & kBranchOffsetMask) << 16) |
           (ori_instr & kBranchOffsetMask));
}


static int32_t EncodeLoadImmediate(int32_t dest, int32_t instr) {
  return ((instr & ~kBranchOffsetMask) | (dest & kBranchOffsetMask));
}


class PatchFarJump : public AssemblerFixup {
 public:
  PatchFarJump() {}

  void Process(const MemoryRegion& region, int position) {
    const int32_t high = region.Load<int32_t>(position);
    const int32_t low = region.Load<int32_t>(position + Instr::kInstrSize);
    const int32_t offset = DecodeLoadImmediate(low, high);
    const int32_t dest = region.start() + offset;

    if ((Instr::At(reinterpret_cast<uword>(&high))->OpcodeField() == LUI) &&
        (Instr::At(reinterpret_cast<uword>(&low))->OpcodeField() == ORI)) {
      // Change the offset to the absolute value.
      const int32_t encoded_low =
          EncodeLoadImmediate(dest & kBranchOffsetMask, low);
      const int32_t encoded_high =
          EncodeLoadImmediate(dest >> 16, high);

      region.Store<int32_t>(position, encoded_high);
      region.Store<int32_t>(position + Instr::kInstrSize, encoded_low);
      return;
    }
    // If the offset loading instructions aren't there, we must have replaced
    // the far branch with a near one, and so these instructions should be NOPs.
    ASSERT((high == Instr::kNopInstruction) && (low == Instr::kNopInstruction));
  }
};


void Assembler::EmitFarJump(int32_t offset, bool link) {
  ASSERT(use_far_branches());
  const uint16_t low = Utils::Low16Bits(offset);
  const uint16_t high = Utils::High16Bits(offset);
  buffer_.EmitFixup(new PatchFarJump());
  lui(TMP, Immediate(high));
  ori(TMP, TMP, Immediate(low));
  if (link) {
    EmitRType(SPECIAL, TMP, R0, RA, 0, JALR);
  } else {
    EmitRType(SPECIAL, TMP, R0, R0, 0, JR);
  }
}


static Opcode OppositeBranchOpcode(Opcode b) {
  switch (b) {
    case BEQ: return BNE;
    case BNE: return BEQ;
    case BGTZ: return BLEZ;
    case BLEZ: return BGTZ;
    case BEQL: return BNEL;
    case BNEL: return BEQL;
    case BGTZL: return BLEZL;
    case BLEZL: return BGTZL;
    default:
      UNREACHABLE();
      break;
  }
  return BNE;
}


void Assembler::EmitFarBranch(Opcode b, Register rs, Register rt,
                              int32_t offset) {
  EmitIType(b, rs, rt, 4);
  nop();
  EmitFarJump(offset, false);
}


static RtRegImm OppositeBranchNoLink(RtRegImm b) {
  switch (b) {
    case BLTZ: return BGEZ;
    case BGEZ: return BLTZ;
    case BLTZAL: return BGEZ;
    case BGEZAL: return BLTZ;
    default:
      UNREACHABLE();
      break;
  }
  return BLTZ;
}


void Assembler::EmitFarRegImmBranch(RtRegImm b, Register rs, int32_t offset) {
  EmitRegImmType(REGIMM, rs, b, 4);
  nop();
  EmitFarJump(offset, (b == BLTZAL) || (b == BGEZAL));
}


void Assembler::EmitFarFpuBranch(bool kind, int32_t offset) {
  const uint32_t b16 = kind ? (1 << 16) : 0;
  Emit(COP1 << kOpcodeShift | COP1_BC << kCop1SubShift | b16 | 4);
  nop();
  EmitFarJump(offset, false);
}


void Assembler::EmitBranch(Opcode b, Register rs, Register rt, Label* label) {
  if (label->IsBound()) {
    // Relative destination from an instruction after the branch.
    const int32_t dest =
        label->Position() - (buffer_.Size() + Instr::kInstrSize);
    if (use_far_branches() && !CanEncodeBranchOffset(dest)) {
      EmitFarBranch(b, rs, rt, label->Position());
    } else {
      const uint16_t dest_off = EncodeBranchOffset(dest, 0);
      EmitIType(b, rs, rt, dest_off);
    }
  } else {
    const int position = buffer_.Size();
    if (use_far_branches()) {
      const uint32_t dest_off = label->position_;
      EmitFarBranch(b, rs, rt, dest_off);
    } else {
      const uint16_t dest_off = EncodeBranchOffset(label->position_, 0);
      EmitIType(b, rs, rt, dest_off);
    }
    label->LinkTo(position);
  }
}


void Assembler::EmitRegImmBranch(RtRegImm b, Register rs, Label* label) {
  if (label->IsBound()) {
    // Relative destination from an instruction after the branch.
    const int32_t dest =
        label->Position() - (buffer_.Size() + Instr::kInstrSize);
    if (use_far_branches() && !CanEncodeBranchOffset(dest)) {
      EmitFarRegImmBranch(b, rs, label->Position());
    } else {
      const uint16_t dest_off = EncodeBranchOffset(dest, 0);
      EmitRegImmType(REGIMM, rs, b, dest_off);
    }
  } else {
    const int position = buffer_.Size();
    if (use_far_branches()) {
      const uint32_t dest_off = label->position_;
      EmitFarRegImmBranch(b, rs, dest_off);
    } else {
      const uint16_t dest_off = EncodeBranchOffset(label->position_, 0);
      EmitRegImmType(REGIMM, rs, b, dest_off);
    }
    label->LinkTo(position);
  }
}


void Assembler::EmitFpuBranch(bool kind, Label *label) {
  const int32_t b16 = kind ? (1 << 16) : 0;  // Bit 16 set for branch on true.
  if (label->IsBound()) {
    // Relative destination from an instruction after the branch.
    const int32_t dest =
        label->Position() - (buffer_.Size() + Instr::kInstrSize);
    if (use_far_branches() && !CanEncodeBranchOffset(dest)) {
      EmitFarFpuBranch(kind, label->Position());
    } else {
      const uint16_t dest_off = EncodeBranchOffset(dest, 0);
      Emit(COP1 << kOpcodeShift |
           COP1_BC << kCop1SubShift |
           b16 |
           dest_off);
    }
  } else {
    const int position = buffer_.Size();
    if (use_far_branches()) {
      const uint32_t dest_off = label->position_;
      EmitFarFpuBranch(kind, dest_off);
    } else {
      const uint16_t dest_off = EncodeBranchOffset(label->position_, 0);
      Emit(COP1 << kOpcodeShift |
           COP1_BC << kCop1SubShift |
           b16 |
           dest_off);
    }
    label->LinkTo(position);
  }
}


static int32_t FlipBranchInstruction(int32_t instr) {
  Instr* i = Instr::At(reinterpret_cast<uword>(&instr));
  if (i->OpcodeField() == REGIMM) {
    RtRegImm b = OppositeBranchNoLink(i->RegImmFnField());
    i->SetRegImmFnField(b);
    return i->InstructionBits();
  } else if (i->OpcodeField() == COP1) {
    return instr ^ (1 << 16);
  }
  Opcode b = OppositeBranchOpcode(i->OpcodeField());
  i->SetOpcodeField(b);
  return i->InstructionBits();
}


void Assembler::Bind(Label* label) {
  ASSERT(!label->IsBound());
  int bound_pc = buffer_.Size();

  while (label->IsLinked()) {
    int32_t position = label->Position();
    int32_t dest = bound_pc - (position + Instr::kInstrSize);

    if (use_far_branches() && !CanEncodeBranchOffset(dest)) {
      // Far branches are enabled and we can't encode the branch offset.

      // Grab the branch instruction. We'll need to flip it later.
      const int32_t branch = buffer_.Load<int32_t>(position);

      // Grab instructions that load the offset.
      const int32_t high =
          buffer_.Load<int32_t>(position + 2 * Instr::kInstrSize);
      const int32_t low =
          buffer_.Load<int32_t>(position + 3 * Instr::kInstrSize);

      // Change from relative to the branch to relative to the assembler buffer.
      dest = buffer_.Size();
      const int32_t encoded_low =
          EncodeLoadImmediate(dest & kBranchOffsetMask, low);
      const int32_t encoded_high =
          EncodeLoadImmediate(dest >> 16, high);

      // Skip the unconditional far jump if the test fails by flipping the
      // sense of the branch instruction.
      buffer_.Store<int32_t>(position, FlipBranchInstruction(branch));
      buffer_.Store<int32_t>(position + 2 * Instr::kInstrSize, encoded_high);
      buffer_.Store<int32_t>(position + 3 * Instr::kInstrSize, encoded_low);
      label->position_ = DecodeLoadImmediate(low, high);
    } else if (use_far_branches() && CanEncodeBranchOffset(dest)) {
      // We assembled a far branch, but we don't need it. Replace with a near
      // branch.

      // Grab the link to the next branch.
      const int32_t high =
          buffer_.Load<int32_t>(position + 2 * Instr::kInstrSize);
      const int32_t low =
          buffer_.Load<int32_t>(position + 3 * Instr::kInstrSize);

      // Grab the original branch instruction.
      int32_t branch = buffer_.Load<int32_t>(position);

      // Clear out the old (far) branch.
      for (int i = 0; i < 5; i++) {
        buffer_.Store<int32_t>(position + i * Instr::kInstrSize,
            Instr::kNopInstruction);
      }

      // Calculate the new offset.
      dest = dest - 4 * Instr::kInstrSize;
      const int32_t encoded = EncodeBranchOffset(dest, branch);
      buffer_.Store<int32_t>(position + 4 * Instr::kInstrSize, encoded);
      label->position_ = DecodeLoadImmediate(low, high);
    } else {
      const int32_t next = buffer_.Load<int32_t>(position);
      const int32_t encoded = EncodeBranchOffset(dest, next);
      buffer_.Store<int32_t>(position, encoded);
      label->position_ = DecodeBranchOffset(next);
    }
  }
  label->BindTo(bound_pc);
  delay_slot_available_ = false;
}


void Assembler::LoadWordFromPoolOffset(Register rd, int32_t offset) {
  ASSERT(rd != PP);
  if (Address::CanHoldOffset(offset)) {
    lw(rd, Address(PP, offset));
  } else {
    const int16_t offset_low = Utils::Low16Bits(offset);  // Signed.
    offset -= offset_low;
    const uint16_t offset_high = Utils::High16Bits(offset);  // Unsigned.
    if (offset_high != 0) {
      lui(rd, Immediate(offset_high));
      addu(rd, rd, PP);
      lw(rd, Address(rd, offset_low));
    } else {
      lw(rd, Address(PP, offset_low));
    }
  }
}


void Assembler::AdduDetectOverflow(Register rd, Register rs, Register rt,
                                   Register ro, Register scratch) {
  ASSERT(rd != ro);
  ASSERT(rd != TMP1);
  ASSERT(ro != TMP1);
  ASSERT(ro != rs);
  ASSERT(ro != rt);

  if ((rs == rt) && (rd == rs)) {
    ASSERT(scratch != kNoRegister);
    ASSERT(scratch != TMP1);
    ASSERT(rd != scratch);
    ASSERT(ro != scratch);
    ASSERT(rs != scratch);
    ASSERT(rt != scratch);
    mov(scratch, rt);
    rt = scratch;
  }

  if (rd == rs) {
    mov(TMP1, rs);  // Preserve rs.
    addu(rd, rs, rt);  // rs is overwritten.
    xor_(TMP1, rd, TMP1);  // Original rs.
    xor_(ro, rd, rt);
    and_(ro, ro, TMP1);
  } else if (rd == rt) {
    mov(TMP1, rt);  // Preserve rt.
    addu(rd, rs, rt);  // rt is overwritten.
    xor_(TMP1, rd, TMP1);  // Original rt.
    xor_(ro, rd, rs);
    and_(ro, ro, TMP1);
  } else {
    addu(rd, rs, rt);
    xor_(ro, rd, rs);
    xor_(TMP1, rd, rt);
    and_(ro, TMP1, ro);
  }
}


void Assembler::SubuDetectOverflow(Register rd, Register rs, Register rt,
                                   Register ro) {
  ASSERT(rd != ro);
  ASSERT(rd != TMP1);
  ASSERT(ro != TMP1);
  ASSERT(ro != rs);
  ASSERT(ro != rt);
  ASSERT(rs != TMP1);
  ASSERT(rt != TMP1);

  // This happens with some crankshaft code. Since Subu works fine if
  // left == right, let's not make that restriction here.
  if (rs == rt) {
    mov(rd, ZR);
    mov(ro, ZR);
    return;
  }

  if (rd == rs) {
    mov(TMP1, rs);  // Preserve left.
    subu(rd, rs, rt);  // Left is overwritten.
    xor_(ro, rd, TMP1);  // scratch is original left.
    xor_(TMP1, TMP1, rs);  // scratch is original left.
    and_(ro, TMP1, ro);
  } else if (rd == rt) {
    mov(TMP1, rt);  // Preserve right.
    subu(rd, rs, rt);  // Right is overwritten.
    xor_(ro, rd, rs);
    xor_(TMP1, rs, TMP1);  // Original right.
    and_(ro, TMP1, ro);
  } else {
    subu(rd, rs, rt);
    xor_(ro, rd, rs);
    xor_(TMP1, rs, rt);
    and_(ro, TMP1, ro);
  }
}


void Assembler::LoadObject(Register rd, const Object& object) {
  // Smis and VM heap objects are never relocated; do not use object pool.
  if (object.IsSmi()) {
    LoadImmediate(rd, reinterpret_cast<int32_t>(object.raw()));
  } else if (object.InVMHeap()) {
    // Make sure that class CallPattern is able to decode this load immediate.
    int32_t object_raw = reinterpret_cast<int32_t>(object.raw());
    const uint16_t object_low = Utils::Low16Bits(object_raw);
    const uint16_t object_high = Utils::High16Bits(object_raw);
    lui(rd, Immediate(object_high));
    ori(rd, rd, Immediate(object_low));
  } else {
    // Make sure that class CallPattern is able to decode this load from the
    // object pool.
    const int32_t offset =
        Array::data_offset() + 4*AddObject(object) - kHeapObjectTag;
    LoadWordFromPoolOffset(rd, offset);
  }
}


int32_t Assembler::AddObject(const Object& obj) {
  ASSERT(obj.IsNotTemporaryScopedHandle());
  ASSERT(obj.IsOld());
  if (object_pool_.IsNull()) {
    // The object pool cannot be used in the vm isolate.
    ASSERT(Isolate::Current() != Dart::vm_isolate());
    object_pool_ = GrowableObjectArray::New(Heap::kOld);
  }
  for (int i = 0; i < object_pool_.Length(); i++) {
    if (object_pool_.At(i) == obj.raw()) {
      return i;
    }
  }
  object_pool_.Add(obj, Heap::kOld);
  return object_pool_.Length() - 1;
}


void Assembler::PushObject(const Object& object) {
  LoadObject(TMP1, object);
  Push(TMP1);
}


void Assembler::CompareObject(Register rd1, Register rd2,
                              Register rn, const Object& object) {
  ASSERT(rn != TMP1);
  ASSERT(rd1 != TMP1);
  ASSERT(rd1 != rd2);
  LoadObject(TMP1, object);
  slt(rd1, rn, TMP1);
  slt(rd2, TMP1, rn);
}


// Preserves object and value registers.
void Assembler::StoreIntoObjectFilterNoSmi(Register object,
                                           Register value,
                                           Label* no_update) {
  COMPILE_ASSERT((kNewObjectAlignmentOffset == kWordSize) &&
                 (kOldObjectAlignmentOffset == 0), young_alignment);

  // Write-barrier triggers if the value is in the new space (has bit set) and
  // the object is in the old space (has bit cleared).
  // To check that, we compute value & ~object and skip the write barrier
  // if the bit is not set. We can't destroy the object.
  nor(TMP1, ZR, object);
  and_(TMP1, value, TMP1);
  andi(CMPRES1, TMP1, Immediate(kNewObjectAlignmentOffset));
  beq(CMPRES1, ZR, no_update);
}


// Preserves object and value registers.
void Assembler::StoreIntoObjectFilter(Register object,
                                      Register value,
                                      Label* no_update) {
  // For the value we are only interested in the new/old bit and the tag bit.
  // And the new bit with the tag bit. The resulting bit will be 0 for a Smi.
  sll(TMP1, value, kObjectAlignmentLog2 - 1);
  and_(TMP1, value, TMP1);
  // And the result with the negated space bit of the object.
  nor(CMPRES1, ZR, object);
  and_(TMP1, TMP1, CMPRES1);
  andi(CMPRES1, TMP1, Immediate(kNewObjectAlignmentOffset));
  beq(CMPRES1, ZR, no_update);
}


void Assembler::StoreIntoObject(Register object,
                                const Address& dest,
                                Register value,
                                bool can_value_be_smi) {
  ASSERT(object != value);
  sw(value, dest);
  Label done;
  if (can_value_be_smi) {
    StoreIntoObjectFilter(object, value, &done);
  } else {
    StoreIntoObjectFilterNoSmi(object, value, &done);
  }
  // A store buffer update is required.
  if (value != T0) {
    // Preserve T0.
    addiu(SP, SP, Immediate(-2 * kWordSize));
    sw(T0, Address(SP, 1 * kWordSize));
  } else {
    addiu(SP, SP, Immediate(-1 * kWordSize));
  }
  sw(RA, Address(SP, 0 * kWordSize));
  if (object != T0) {
    mov(T0, object);
  }
  BranchLink(&StubCode::UpdateStoreBufferLabel());
  lw(RA, Address(SP, 0 * kWordSize));
  if (value != T0) {
    // Restore T0.
    lw(T0, Address(SP, 1 * kWordSize));
    addiu(SP, SP, Immediate(2 * kWordSize));
  } else {
    addiu(SP, SP, Immediate(1 * kWordSize));
  }
  Bind(&done);
}


void Assembler::StoreIntoObjectNoBarrier(Register object,
                                         const Address& dest,
                                         Register value) {
  sw(value, dest);
#if defined(DEBUG)
  Label done;
  StoreIntoObjectFilter(object, value, &done);
  Stop("Store buffer update is required");
  Bind(&done);
#endif  // defined(DEBUG)
  // No store buffer update.
}


void Assembler::StoreIntoObjectNoBarrier(Register object,
                                         const Address& dest,
                                         const Object& value) {
  ASSERT(value.IsSmi() || value.InVMHeap() ||
         (value.IsOld() && value.IsNotTemporaryScopedHandle()));
  // No store buffer update.
  LoadObject(TMP1, value);
  sw(TMP1, dest);
}


void Assembler::LoadClassId(Register result, Register object) {
  ASSERT(RawObject::kClassIdTagBit == 16);
  ASSERT(RawObject::kClassIdTagSize == 16);
  const intptr_t class_id_offset = Object::tags_offset() +
      RawObject::kClassIdTagBit / kBitsPerByte;
  lhu(result, FieldAddress(object, class_id_offset));
}


void Assembler::LoadClassById(Register result, Register class_id) {
  ASSERT(result != class_id);
  lw(result, FieldAddress(CTX, Context::isolate_offset()));
  const intptr_t table_offset_in_isolate =
      Isolate::class_table_offset() + ClassTable::table_offset();
  lw(result, Address(result, table_offset_in_isolate));
  sll(TMP1, class_id, 2);
  addu(result, result, TMP1);
  lw(result, Address(result));
}


void Assembler::LoadClass(Register result, Register object) {
  ASSERT(TMP1 != result);
  LoadClassId(TMP1, object);

  lw(result, FieldAddress(CTX, Context::isolate_offset()));
  const intptr_t table_offset_in_isolate =
      Isolate::class_table_offset() + ClassTable::table_offset();
  lw(result, Address(result, table_offset_in_isolate));
  sll(TMP1, TMP1, 2);
  addu(result, result, TMP1);
  lw(result, Address(result));
}


void Assembler::EnterStubFrame(bool uses_pp) {
  SetPrologueOffset();
  if (uses_pp) {
    addiu(SP, SP, Immediate(-4 * kWordSize));
    sw(ZR, Address(SP, 3 * kWordSize));  // PC marker is 0 in stubs.
    sw(RA, Address(SP, 2 * kWordSize));
    sw(FP, Address(SP, 1 * kWordSize));
    sw(PP, Address(SP, 0 * kWordSize));
    addiu(FP, SP, Immediate(1 * kWordSize));
    // Setup pool pointer for this stub.

    GetNextPC(TMP1);  // TMP1 gets the address of the next instruction.

    const intptr_t object_pool_pc_dist =
        Instructions::HeaderSize() - Instructions::object_pool_offset() +
        CodeSize();

    lw(PP, Address(TMP1, -object_pool_pc_dist));
  } else {
    addiu(SP, SP, Immediate(-3 * kWordSize));
    sw(ZR, Address(SP, 2 * kWordSize));  // PC marker is 0 in stubs.
    sw(RA, Address(SP, 1 * kWordSize));
    sw(FP, Address(SP, 0 * kWordSize));
    mov(FP, SP);
  }
}


void Assembler::LeaveStubFrame(bool uses_pp) {
  if (uses_pp) {
    addiu(SP, FP, Immediate(-1 * kWordSize));
    lw(RA, Address(SP, 2 * kWordSize));
    lw(FP, Address(SP, 1 * kWordSize));
    lw(PP, Address(SP, 0 * kWordSize));
    addiu(SP, SP, Immediate(4 * kWordSize));
  } else {
    mov(SP, FP);
    lw(RA, Address(SP, 1 * kWordSize));
    lw(FP, Address(SP, 0 * kWordSize));
    addiu(SP, SP, Immediate(3 * kWordSize));
  }
}


void Assembler::LeaveStubFrameAndReturn(Register ra, bool uses_pp) {
  if (uses_pp) {
    addiu(SP, FP, Immediate(-1 * kWordSize));
    lw(RA, Address(SP, 2 * kWordSize));
    lw(FP, Address(SP, 1 * kWordSize));
    lw(PP, Address(SP, 0 * kWordSize));
    jr(ra);
    delay_slot()->addiu(SP, SP, Immediate(4 * kWordSize));
  } else {
    mov(SP, FP);
    lw(RA, Address(SP, 1 * kWordSize));
    lw(FP, Address(SP, 0 * kWordSize));
    jr(ra);
    delay_slot()->addiu(SP, SP, Immediate(3 * kWordSize));
  }
}


void Assembler::TryAllocate(const Class& cls,
                            Label* failure,
                            Register instance_reg) {
  ASSERT(failure != NULL);
  if (FLAG_inline_alloc) {
    Heap* heap = Isolate::Current()->heap();
    const intptr_t instance_size = cls.instance_size();
    LoadImmediate(instance_reg, heap->TopAddress());
    lw(instance_reg, Address(instance_reg, 0));
    AddImmediate(instance_reg, instance_size);

    // instance_reg: potential next object start.
    LoadImmediate(TMP, heap->EndAddress());
    lw(TMP, Address(TMP, 0));
    // Fail if heap end unsigned less than or equal to instance_reg.
    BranchUnsignedLessEqual(TMP, instance_reg, failure);

    // Successfully allocated the object, now update top to point to
    // next object start and store the class in the class field of object.
    LoadImmediate(TMP, heap->TopAddress());
    sw(instance_reg, Address(TMP, 0));

    ASSERT(instance_size >= kHeapObjectTag);
    AddImmediate(instance_reg, -instance_size + kHeapObjectTag);

    uword tags = 0;
    tags = RawObject::SizeTag::update(instance_size, tags);
    ASSERT(cls.id() != kIllegalCid);
    tags = RawObject::ClassIdTag::update(cls.id(), tags);
    LoadImmediate(TMP, tags);
    sw(TMP, FieldAddress(instance_reg, Object::tags_offset()));
  } else {
    b(failure);
  }
}


void Assembler::CallRuntime(const RuntimeEntry& entry) {
  entry.Call(this);
}


void Assembler::EnterDartFrame(intptr_t frame_size) {
  const intptr_t offset = CodeSize();

  SetPrologueOffset();

  addiu(SP, SP, Immediate(-4 * kWordSize));
  sw(RA, Address(SP, 2 * kWordSize));
  sw(FP, Address(SP, 1 * kWordSize));
  sw(PP, Address(SP, 0 * kWordSize));

  GetNextPC(TMP1);  // TMP1 gets the address of the next instruction.

  // Calculate the offset of the pool pointer from the PC.
  const intptr_t object_pool_pc_dist =
      Instructions::HeaderSize() - Instructions::object_pool_offset() +
      CodeSize();

  // Save PC in frame for fast identification of corresponding code.
  AddImmediate(TMP1, -offset);
  sw(TMP1, Address(SP, 3 * kWordSize));

  // Set FP to the saved previous FP.
  addiu(FP, SP, Immediate(kWordSize));

  // Load the pool pointer. offset has already been subtracted from TMP1.
  lw(PP, Address(TMP1, -object_pool_pc_dist + offset));

  // Reserve space for locals.
  AddImmediate(SP, -frame_size);
}


// On entry to a function compiled for OSR, the caller's frame pointer, the
// stack locals, and any copied parameters are already in place.  The frame
// pointer is already set up.  The PC marker is not correct for the
// optimized function and there may be extra space for spill slots to
// allocate. We must also set up the pool pointer for the function.
void Assembler::EnterOsrFrame(intptr_t extra_size) {
  Comment("EnterOsrFrame");

  GetNextPC(TMP);  // TMP gets the address of the next instruction.

  // The runtime system assumes that the code marker address is
  // kEntryPointToPcMarkerOffset bytes from the entry.  Since there is no
  // code to set up the frame pointer, etc., the address needs to be adjusted.
  const intptr_t offset = kEntryPointToPcMarkerOffset - CodeSize();
  // Calculate the offset of the pool pointer from the PC.
  const intptr_t object_pool_pc_dist =
      Instructions::HeaderSize() - Instructions::object_pool_offset() +
      CodeSize();

  // Adjust PC by the offset, and store it in the stack frame.
  AddImmediate(TMP, TMP, offset);
  sw(TMP, Address(FP, kPcMarkerSlotFromFp * kWordSize));

  // Restore return address.
  lw(RA, Address(FP, 1 * kWordSize));

  // Load the pool pointer. offset has already been subtracted from temp.
  lw(PP, Address(TMP, -object_pool_pc_dist - offset));

  // Reserve space for locals.
  AddImmediate(SP, -extra_size);
}


void Assembler::LeaveDartFrame() {
  addiu(SP, FP, Immediate(-kWordSize));

  lw(RA, Address(SP, 2 * kWordSize));
  lw(FP, Address(SP, 1 * kWordSize));
  lw(PP, Address(SP, 0 * kWordSize));

  // Adjust SP for PC, RA, FP, PP pushed in EnterDartFrame.
  addiu(SP, SP, Immediate(4 * kWordSize));
}


void Assembler::LeaveDartFrameAndReturn() {
  addiu(SP, FP, Immediate(-kWordSize));

  lw(RA, Address(SP, 2 * kWordSize));
  lw(FP, Address(SP, 1 * kWordSize));
  lw(PP, Address(SP, 0 * kWordSize));

  // Adjust SP for PC, RA, FP, PP pushed in EnterDartFrame, and return.
  Ret();
  delay_slot()->addiu(SP, SP, Immediate(4 * kWordSize));
}


void Assembler::ReserveAlignedFrameSpace(intptr_t frame_space) {
  // Reserve space for arguments and align frame before entering
  // the C++ world.
  AddImmediate(SP, -frame_space);
  if (OS::ActivationFrameAlignment() > 0) {
    LoadImmediate(TMP1, ~(OS::ActivationFrameAlignment() - 1));
    and_(SP, SP, TMP1);
  }
}


void Assembler::EnterCallRuntimeFrame(intptr_t frame_space) {
  const intptr_t kPushedRegistersSize =
      kDartVolatileCpuRegCount * kWordSize +
      2 * kWordSize +  // FP and RA.
      kDartVolatileFpuRegCount * kWordSize;

  SetPrologueOffset();

  TraceSimMsg("EnterCallRuntimeFrame");

  // Save volatile CPU and FPU registers on the stack:
  // -------------
  // FPU Registers
  // CPU Registers
  // RA
  // FP
  // -------------
  // TODO(zra): It may be a problem for walking the stack that FP is below
  //            the saved registers. If it turns out to be a problem in the
  //            future, try pushing RA and FP before the volatile registers.
  addiu(SP, SP, Immediate(-kPushedRegistersSize));
  for (int i = kDartFirstVolatileFpuReg; i <= kDartLastVolatileFpuReg; i++) {
    // These go above the volatile CPU registers.
    const int slot =
        (i - kDartFirstVolatileFpuReg) + kDartVolatileCpuRegCount + 2;
    FRegister reg = static_cast<FRegister>(i);
    swc1(reg, Address(SP, slot * kWordSize));
  }
  for (int i = kDartFirstVolatileCpuReg; i <= kDartLastVolatileCpuReg; i++) {
    // + 2 because FP goes in slot 0.
    const int slot = (i - kDartFirstVolatileCpuReg) + 2;
    Register reg = static_cast<Register>(i);
    sw(reg, Address(SP, slot * kWordSize));
  }
  sw(RA, Address(SP, 1 * kWordSize));
  sw(FP, Address(SP, 0 * kWordSize));
  mov(FP, SP);

  ReserveAlignedFrameSpace(frame_space);
}


void Assembler::LeaveCallRuntimeFrame() {
  const intptr_t kPushedRegistersSize =
      kDartVolatileCpuRegCount * kWordSize +
      2 * kWordSize +  // FP and RA.
      kDartVolatileFpuRegCount * kWordSize;

  TraceSimMsg("LeaveCallRuntimeFrame");

  // SP might have been modified to reserve space for arguments
  // and ensure proper alignment of the stack frame.
  // We need to restore it before restoring registers.
  mov(SP, FP);

  // Restore volatile CPU and FPU registers from the stack.
  lw(FP, Address(SP, 0 * kWordSize));
  lw(RA, Address(SP, 1 * kWordSize));
  for (int i = kDartFirstVolatileCpuReg; i <= kDartLastVolatileCpuReg; i++) {
    // + 2 because FP goes in slot 0.
    const int slot = (i - kDartFirstVolatileCpuReg) + 2;
    Register reg = static_cast<Register>(i);
    lw(reg, Address(SP, slot * kWordSize));
  }
  for (int i = kDartFirstVolatileFpuReg; i <= kDartLastVolatileFpuReg; i++) {
    // These go above the volatile CPU registers.
    const int slot =
        (i - kDartFirstVolatileFpuReg) + kDartVolatileCpuRegCount + 2;
    FRegister reg = static_cast<FRegister>(i);
    lwc1(reg, Address(SP, slot * kWordSize));
  }
  addiu(SP, SP, Immediate(kPushedRegistersSize));
}


int32_t Assembler::AddExternalLabel(const ExternalLabel* label) {
  if (object_pool_.IsNull()) {
    // The object pool cannot be used in the vm isolate.
    ASSERT(Isolate::Current() != Dart::vm_isolate());
    object_pool_ = GrowableObjectArray::New(Heap::kOld);
  }
  const word address = label->address();
  ASSERT(Utils::IsAligned(address, 4));
  // The address is stored in the object array as a RawSmi.
  const Smi& smi = Smi::Handle(Smi::New(address >> kSmiTagShift));
  // Do not reuse an existing entry, since each reference may be patched
  // independently.
  object_pool_.Add(smi, Heap::kOld);
  return object_pool_.Length() - 1;
}


static const char* cpu_reg_names[kNumberOfCpuRegisters] = {
  "zr", "tmp", "v0", "v1", "a0", "a1", "a2", "a3",
  "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7",
  "s0", "s1", "s2", "s3", "s4", "s5", "s6", "s7",
  "t8", "t9", "k0", "k1", "gp", "sp", "fp", "ra",
};


const char* Assembler::RegisterName(Register reg) {
  ASSERT((0 <= reg) && (reg < kNumberOfCpuRegisters));
  return cpu_reg_names[reg];
}


static const char* fpu_reg_names[kNumberOfFpuRegisters] = {
  "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7",
  "d8", "d9", "d10", "d11", "d12", "d13", "d14", "d15",
};


const char* Assembler::FpuRegisterName(FpuRegister reg) {
  ASSERT((0 <= reg) && (reg < kNumberOfFpuRegisters));
  return fpu_reg_names[reg];
}


void Assembler::Stop(const char* message) {
  if (FLAG_print_stop_message) {
    UNIMPLEMENTED();
  }
  Label stop;
  b(&stop);
  Emit(reinterpret_cast<int32_t>(message));
  Bind(&stop);
  break_(Instr::kStopMessageCode);
}


void Assembler::TraceSimMsg(const char* message) {
  // Don't bother adding in the messages unless tracing is enabled, and we are
  // running in the simulator.
#if defined(USING_SIMULATOR)
  if (FLAG_trace_sim) {
    Label msg;
    b(&msg);
    Emit(reinterpret_cast<int32_t>(message));
    Bind(&msg);
    break_(Instr::kMsgMessageCode);
  }
#endif
}

}  // namespace dart

#endif  // defined TARGET_ARCH_MIPS