path: root/js/src/jit/arm/Assembler-arm.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "jit/arm/Assembler-arm.h"

#include "mozilla/DebugOnly.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/Maybe.h"
#include "mozilla/Sprintf.h"

#include <type_traits>

#include "gc/Marking.h"
#include "jit/arm/disasm/Disasm-arm.h"
#include "jit/arm/MacroAssembler-arm.h"
#include "jit/AutoWritableJitCode.h"
#include "jit/ExecutableAllocator.h"
#include "jit/MacroAssembler.h"
#include "vm/Realm.h"

using namespace js;
using namespace js::jit;

using mozilla::CountLeadingZeroes32;
using mozilla::DebugOnly;

using LabelDoc = DisassemblerSpew::LabelDoc;
using LiteralDoc = DisassemblerSpew::LiteralDoc;

void dbg_break() {}

// The ABIArgGenerator is used for making system ABI calls and for inter-wasm
// calls. The system ABI can either be SoftFp or HardFp, and inter-wasm calls
// are always HardFp calls. The initialization defaults to HardFp, and the ABI
// choice is made before any system ABI calls with the method "setUseHardFp".
ABIArgGenerator::ABIArgGenerator()
    : intRegIndex_(0),
      floatRegIndex_(0),
      stackOffset_(0),
      current_(),
      useHardFp_(true) {}

// See the "Parameter Passing" section of the "Procedure Call Standard for the
// ARM Architecture" documentation.
ABIArg ABIArgGenerator::softNext(MIRType type) {
  switch (type) {
    case MIRType::Int32:
    case MIRType::Pointer:
    case MIRType::RefOrNull:
    case MIRType::StackResults:
      if (intRegIndex_ == NumIntArgRegs) {
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint32_t);
        break;
      }
      current_ = ABIArg(Register::FromCode(intRegIndex_));
      intRegIndex_++;
      break;
    case MIRType::Int64:
      // Make sure to use an even register index. Increase to next even number
      // when odd.
      intRegIndex_ = (intRegIndex_ + 1) & ~1;
      if (intRegIndex_ == NumIntArgRegs) {
        // Align the stack on 8 bytes.
        static const uint32_t align = sizeof(uint64_t) - 1;
        stackOffset_ = (stackOffset_ + align) & ~align;
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint64_t);
        break;
      }
      current_ = ABIArg(Register::FromCode(intRegIndex_),
                        Register::FromCode(intRegIndex_ + 1));
      intRegIndex_ += 2;
      break;
    case MIRType::Float32:
      if (intRegIndex_ == NumIntArgRegs) {
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint32_t);
        break;
      }
      current_ = ABIArg(Register::FromCode(intRegIndex_));
      intRegIndex_++;
      break;
    case MIRType::Double:
      // Make sure to use an even register index. Increase to next even number
      // when odd.
      intRegIndex_ = (intRegIndex_ + 1) & ~1;
      if (intRegIndex_ == NumIntArgRegs) {
        // Align the stack on 8 bytes.
        static const uint32_t align = sizeof(double) - 1;
        stackOffset_ = (stackOffset_ + align) & ~align;
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(double);
        break;
      }
      current_ = ABIArg(Register::FromCode(intRegIndex_),
                        Register::FromCode(intRegIndex_ + 1));
      intRegIndex_ += 2;
      break;
    default:
      MOZ_CRASH("Unexpected argument type");
  }

  return current_;
}

ABIArg ABIArgGenerator::hardNext(MIRType type) {
  switch (type) {
    case MIRType::Int32:
    case MIRType::Pointer:
    case MIRType::RefOrNull:
    case MIRType::StackResults:
      if (intRegIndex_ == NumIntArgRegs) {
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint32_t);
        break;
      }
      current_ = ABIArg(Register::FromCode(intRegIndex_));
      intRegIndex_++;
      break;
    case MIRType::Int64:
      // Make sure to use an even register index. Increase to next even number
      // when odd.
      intRegIndex_ = (intRegIndex_ + 1) & ~1;
      if (intRegIndex_ == NumIntArgRegs) {
        // Align the stack on 8 bytes.
        static const uint32_t align = sizeof(uint64_t) - 1;
        stackOffset_ = (stackOffset_ + align) & ~align;
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint64_t);
        break;
      }
      current_ = ABIArg(Register::FromCode(intRegIndex_),
                        Register::FromCode(intRegIndex_ + 1));
      intRegIndex_ += 2;
      break;
    case MIRType::Float32:
      if (floatRegIndex_ == NumFloatArgRegs) {
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint32_t);
        break;
      }
      current_ = ABIArg(VFPRegister(floatRegIndex_, VFPRegister::Single));
      floatRegIndex_++;
      break;
    case MIRType::Double:
      // Double register are composed of 2 float registers, thus we have to
      // skip any float register which cannot be used in a pair of float
      // registers in which a double value can be stored.
      floatRegIndex_ = (floatRegIndex_ + 1) & ~1;
      if (floatRegIndex_ == NumFloatArgRegs) {
        static const uint32_t align = sizeof(double) - 1;
        stackOffset_ = (stackOffset_ + align) & ~align;
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint64_t);
        break;
      }
      current_ = ABIArg(VFPRegister(floatRegIndex_ >> 1, VFPRegister::Double));
      floatRegIndex_ += 2;
      break;
    default:
      MOZ_CRASH("Unexpected argument type");
  }

  return current_;
}

ABIArg ABIArgGenerator::next(MIRType type) {
  if (useHardFp_) {
    return hardNext(type);
  }
  return softNext(type);
}

bool js::jit::IsUnaligned(const wasm::MemoryAccessDesc& access) {
  if (!access.align()) {
    return false;
  }

  if (access.type() == Scalar::Float64 && access.align() >= 4) {
    return false;
  }

  return access.align() < access.byteSize();
}

// Encode a standard register when it is being used as src1, the dest, and an
// extra register. These should never be called with an InvalidReg.
uint32_t js::jit::RT(Register r) {
  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return r.code() << 12;
}

uint32_t js::jit::RN(Register r) {
  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return r.code() << 16;
}

uint32_t js::jit::RD(Register r) {
  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return r.code() << 12;
}

uint32_t js::jit::RM(Register r) {
  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return r.code() << 8;
}

// Encode a standard register when it is being used as src1, the dest, and an
// extra register. For these, an InvalidReg is used to indicate a optional
// register that has been omitted.
uint32_t js::jit::maybeRT(Register r) {
  if (r == InvalidReg) {
    return 0;
  }

  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return r.code() << 12;
}

uint32_t js::jit::maybeRN(Register r) {
  if (r == InvalidReg) {
    return 0;
  }

  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return r.code() << 16;
}

uint32_t js::jit::maybeRD(Register r) {
  if (r == InvalidReg) {
    return 0;
  }

  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return r.code() << 12;
}

Register js::jit::toRD(Instruction i) {
  return Register::FromCode((i.encode() >> 12) & 0xf);
}
Register js::jit::toR(Instruction i) {
  return Register::FromCode(i.encode() & 0xf);
}

Register js::jit::toRM(Instruction i) {
  return Register::FromCode((i.encode() >> 8) & 0xf);
}

Register js::jit::toRN(Instruction i) {
  return Register::FromCode((i.encode() >> 16) & 0xf);
}

uint32_t js::jit::VD(VFPRegister vr) {
  if (vr.isMissing()) {
    return 0;
  }

  // Bits 15,14,13,12, 22.
  VFPRegister::VFPRegIndexSplit s = vr.encode();
  return s.bit << 22 | s.block << 12;
}
uint32_t js::jit::VN(VFPRegister vr) {
  if (vr.isMissing()) {
    return 0;
  }

  // Bits 19,18,17,16, 7.
  VFPRegister::VFPRegIndexSplit s = vr.encode();
  return s.bit << 7 | s.block << 16;
}
uint32_t js::jit::VM(VFPRegister vr) {
  if (vr.isMissing()) {
    return 0;
  }

  // Bits 5, 3,2,1,0.
  VFPRegister::VFPRegIndexSplit s = vr.encode();
  return s.bit << 5 | s.block;
}

VFPRegister::VFPRegIndexSplit jit::VFPRegister::encode() {
  MOZ_ASSERT(!_isInvalid);

  switch (kind) {
    case Double:
      return VFPRegIndexSplit(code_ & 0xf, code_ >> 4);
    case Single:
      return VFPRegIndexSplit(code_ >> 1, code_ & 1);
    default:
      // VFP register treated as an integer, NOT a gpr.
      return VFPRegIndexSplit(code_ >> 1, code_ & 1);
  }
}

bool InstDTR::IsTHIS(const Instruction& i) {
  return (i.encode() & IsDTRMask) == (uint32_t)IsDTR;
}

InstDTR* InstDTR::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstDTR*)&i;
  }
  return nullptr;
}

bool InstLDR::IsTHIS(const Instruction& i) {
  return (i.encode() & IsDTRMask) == (uint32_t)IsDTR;
}

InstLDR* InstLDR::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstLDR*)&i;
  }
  return nullptr;
}

InstNOP* InstNOP::AsTHIS(Instruction& i) {
  if (IsTHIS(i)) {
    return (InstNOP*)&i;
  }
  return nullptr;
}

bool InstNOP::IsTHIS(const Instruction& i) {
  return (i.encode() & 0x0fffffff) == NopInst;
}

bool InstBranchReg::IsTHIS(const Instruction& i) {
  return InstBXReg::IsTHIS(i) || InstBLXReg::IsTHIS(i);
}

InstBranchReg* InstBranchReg::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstBranchReg*)&i;
  }
  return nullptr;
}
void InstBranchReg::extractDest(Register* dest) { *dest = toR(*this); }
bool InstBranchReg::checkDest(Register dest) { return dest == toR(*this); }

bool InstBranchImm::IsTHIS(const Instruction& i) {
  return InstBImm::IsTHIS(i) || InstBLImm::IsTHIS(i);
}

InstBranchImm* InstBranchImm::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstBranchImm*)&i;
  }
  return nullptr;
}

void InstBranchImm::extractImm(BOffImm* dest) { *dest = BOffImm(*this); }

bool InstBXReg::IsTHIS(const Instruction& i) {
  return (i.encode() & IsBRegMask) == IsBX;
}

InstBXReg* InstBXReg::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstBXReg*)&i;
  }
  return nullptr;
}

bool InstBLXReg::IsTHIS(const Instruction& i) {
  return (i.encode() & IsBRegMask) == IsBLX;
}
InstBLXReg* InstBLXReg::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstBLXReg*)&i;
  }
  return nullptr;
}

bool InstBImm::IsTHIS(const Instruction& i) {
  return (i.encode() & IsBImmMask) == IsB;
}
InstBImm* InstBImm::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstBImm*)&i;
  }
  return nullptr;
}

bool InstBLImm::IsTHIS(const Instruction& i) {
  return (i.encode() & IsBImmMask) == IsBL;
}
InstBLImm* InstBLImm::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstBLImm*)&i;
  }
  return nullptr;
}

bool InstMovWT::IsTHIS(Instruction& i) {
  return InstMovW::IsTHIS(i) || InstMovT::IsTHIS(i);
}
InstMovWT* InstMovWT::AsTHIS(Instruction& i) {
  if (IsTHIS(i)) {
    return (InstMovWT*)&i;
  }
  return nullptr;
}

void InstMovWT::extractImm(Imm16* imm) { *imm = Imm16(*this); }
bool InstMovWT::checkImm(Imm16 imm) {
  return imm.decode() == Imm16(*this).decode();
}

void InstMovWT::extractDest(Register* dest) { *dest = toRD(*this); }
bool InstMovWT::checkDest(Register dest) { return dest == toRD(*this); }

bool InstMovW::IsTHIS(const Instruction& i) {
  return (i.encode() & IsWTMask) == IsW;
}

InstMovW* InstMovW::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstMovW*)&i;
  }
  return nullptr;
}
InstMovT* InstMovT::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstMovT*)&i;
  }
  return nullptr;
}

bool InstMovT::IsTHIS(const Instruction& i) {
  return (i.encode() & IsWTMask) == IsT;
}

InstALU* InstALU::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstALU*)&i;
  }
  return nullptr;
}
bool InstALU::IsTHIS(const Instruction& i) {
  return (i.encode() & ALUMask) == 0;
}
void InstALU::extractOp(ALUOp* ret) { *ret = ALUOp(encode() & (0xf << 21)); }
bool InstALU::checkOp(ALUOp op) {
  ALUOp mine;
  extractOp(&mine);
  return mine == op;
}
void InstALU::extractDest(Register* ret) { *ret = toRD(*this); }
bool InstALU::checkDest(Register rd) { return rd == toRD(*this); }
void InstALU::extractOp1(Register* ret) { *ret = toRN(*this); }
bool InstALU::checkOp1(Register rn) { return rn == toRN(*this); }
Operand2 InstALU::extractOp2() { return Operand2(encode()); }

InstCMP* InstCMP::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstCMP*)&i;
  }
  return nullptr;
}

bool InstCMP::IsTHIS(const Instruction& i) {
  return InstALU::IsTHIS(i) && InstALU::AsTHIS(i)->checkDest(r0) &&
         InstALU::AsTHIS(i)->checkOp(OpCmp);
}

InstMOV* InstMOV::AsTHIS(const Instruction& i) {
  if (IsTHIS(i)) {
    return (InstMOV*)&i;
  }
  return nullptr;
}

bool InstMOV::IsTHIS(const Instruction& i) {
  return InstALU::IsTHIS(i) && InstALU::AsTHIS(i)->checkOp1(r0) &&
         InstALU::AsTHIS(i)->checkOp(OpMov);
}

Op2Reg Operand2::toOp2Reg() const { return *(Op2Reg*)this; }

Imm16::Imm16(Instruction& inst)
    : lower_(inst.encode() & 0xfff),
      upper_(inst.encode() >> 16),
      invalid_(0xfff) {}

Imm16::Imm16(uint32_t imm)
    : lower_(imm & 0xfff), pad_(0), upper_((imm >> 12) & 0xf), invalid_(0) {
  MOZ_ASSERT(decode() == imm);
}

Imm16::Imm16() : invalid_(0xfff) {}

void Assembler::finish() {
  flush();
  MOZ_ASSERT(!isFinished);
  isFinished = true;
}

bool Assembler::appendRawCode(const uint8_t* code, size_t numBytes) {
  flush();
  return m_buffer.appendRawCode(code, numBytes);
}

bool Assembler::reserve(size_t size) {
  // This buffer uses fixed-size chunks so there's no point in reserving
  // now vs. on-demand.
  return !oom();
}

bool Assembler::swapBuffer(wasm::Bytes& bytes) {
  // For now, specialize to the one use case. As long as wasm::Bytes is a
  // Vector, not a linked-list of chunks, there's not much we can do other
  // than copy.
  MOZ_ASSERT(bytes.empty());
  if (!bytes.resize(bytesNeeded())) {
    return false;
  }
  m_buffer.executableCopy(bytes.begin());
  return true;
}

void Assembler::executableCopy(uint8_t* buffer) {
  MOZ_ASSERT(isFinished);
  m_buffer.executableCopy(buffer);
}

class RelocationIterator {
  CompactBufferReader reader_;
  // Offset in bytes.
  uint32_t offset_;

 public:
  explicit RelocationIterator(CompactBufferReader& reader) : reader_(reader) {}

  bool read() {
    if (!reader_.more()) {
      return false;
    }
    offset_ = reader_.readUnsigned();
    return true;
  }

  uint32_t offset() const { return offset_; }
};

template <class Iter>
const uint32_t* Assembler::GetCF32Target(Iter* iter) {
  Instruction* inst1 = iter->cur();

  if (inst1->is<InstBranchImm>()) {
    // See if we have a simple case, b #offset.
    BOffImm imm;
    InstBranchImm* jumpB = inst1->as<InstBranchImm>();
    jumpB->extractImm(&imm);
    return imm.getDest(inst1)->raw();
  }

  if (inst1->is<InstMovW>()) {
    // See if we have the complex case:
    //  movw r_temp, #imm1
    //  movt r_temp, #imm2
    //  bx r_temp
    // OR
    //  movw r_temp, #imm1
    //  movt r_temp, #imm2
    //  str pc, [sp]
    //  bx r_temp

    Imm16 targ_bot;
    Imm16 targ_top;
    Register temp;

    // Extract both the temp register and the bottom immediate.
    InstMovW* bottom = inst1->as<InstMovW>();
    bottom->extractImm(&targ_bot);
    bottom->extractDest(&temp);

    // Extract the top part of the immediate.
    Instruction* inst2 = iter->next();
    MOZ_ASSERT(inst2->is<InstMovT>());
    InstMovT* top = inst2->as<InstMovT>();
    top->extractImm(&targ_top);

    // Make sure they are being loaded into the same register.
    MOZ_ASSERT(top->checkDest(temp));

    // Make sure we're branching to the same register.
#ifdef DEBUG
    // A toggled call sometimes has a NOP instead of a branch for the third
    // instruction. No way to assert that it's valid in that situation.
    Instruction* inst3 = iter->next();
    if (!inst3->is<InstNOP>()) {
      InstBranchReg* realBranch = nullptr;
      if (inst3->is<InstBranchReg>()) {
        realBranch = inst3->as<InstBranchReg>();
      } else {
        Instruction* inst4 = iter->next();
        realBranch = inst4->as<InstBranchReg>();
      }
      MOZ_ASSERT(realBranch->checkDest(temp));
    }
#endif

    uint32_t* dest = (uint32_t*)(targ_bot.decode() | (targ_top.decode() << 16));
    return dest;
  }

  if (inst1->is<InstLDR>()) {
    return *(uint32_t**)inst1->as<InstLDR>()->dest();
  }

  MOZ_CRASH("unsupported branch relocation");
}

uintptr_t Assembler::GetPointer(uint8_t* instPtr) {
  InstructionIterator iter((Instruction*)instPtr);
  uintptr_t ret = (uintptr_t)GetPtr32Target(iter, nullptr, nullptr);
  return ret;
}

const uint32_t* Assembler::GetPtr32Target(InstructionIterator start,
                                          Register* dest, RelocStyle* style) {
  Instruction* load1 = start.cur();
  Instruction* load2 = start.next();

  if (load1->is<InstMovW>() && load2->is<InstMovT>()) {
    if (style) {
      *style = L_MOVWT;
    }

    // See if we have the complex case:
    //  movw r_temp, #imm1
    //  movt r_temp, #imm2

    Imm16 targ_bot;
    Imm16 targ_top;
    Register temp;

    // Extract both the temp register and the bottom immediate.
    InstMovW* bottom = load1->as<InstMovW>();
    bottom->extractImm(&targ_bot);
    bottom->extractDest(&temp);

    // Extract the top part of the immediate.
    InstMovT* top = load2->as<InstMovT>();
    top->extractImm(&targ_top);

    // Make sure they are being loaded into the same register.
    MOZ_ASSERT(top->checkDest(temp));

    if (dest) {
      *dest = temp;
    }

    uint32_t* value =
        (uint32_t*)(targ_bot.decode() | (targ_top.decode() << 16));
    return value;
  }

  if (load1->is<InstLDR>()) {
    if (style) {
      *style = L_LDR;
    }
    if (dest) {
      *dest = toRD(*load1);
    }
    return *(uint32_t**)load1->as<InstLDR>()->dest();
  }

  MOZ_CRASH("unsupported relocation");
}

static JitCode* CodeFromJump(InstructionIterator* jump) {
  uint8_t* target = (uint8_t*)Assembler::GetCF32Target(jump);
  return JitCode::FromExecutable(target);
}

void Assembler::TraceJumpRelocations(JSTracer* trc, JitCode* code,
                                     CompactBufferReader& reader) {
  RelocationIterator iter(reader);
  while (iter.read()) {
    InstructionIterator institer((Instruction*)(code->raw() + iter.offset()));
    JitCode* child = CodeFromJump(&institer);
    TraceManuallyBarrieredEdge(trc, &child, "rel32");
  }
}

static void TraceOneDataRelocation(JSTracer* trc,
                                   mozilla::Maybe<AutoWritableJitCode>& awjc,
                                   JitCode* code, InstructionIterator iter) {
  Register dest;
  Assembler::RelocStyle rs;
  const void* prior = Assembler::GetPtr32Target(iter, &dest, &rs);
  void* ptr = const_cast<void*>(prior);

  // No barrier needed since these are constants.
  TraceManuallyBarrieredGenericPointerEdge(
      trc, reinterpret_cast<gc::Cell**>(&ptr), "jit-masm-ptr");

  if (ptr != prior) {
    if (awjc.isNothing()) {
      awjc.emplace(code);
    }

    MacroAssemblerARM::ma_mov_patch(Imm32(int32_t(ptr)), dest,
                                    Assembler::Always, rs, iter);
  }
}

/* static */
void Assembler::TraceDataRelocations(JSTracer* trc, JitCode* code,
                                     CompactBufferReader& reader) {
  mozilla::Maybe<AutoWritableJitCode> awjc;
  while (reader.more()) {
    size_t offset = reader.readUnsigned();
    InstructionIterator iter((Instruction*)(code->raw() + offset));
    TraceOneDataRelocation(trc, awjc, code, iter);
  }
}

void Assembler::copyJumpRelocationTable(uint8_t* dest) {
  if (jumpRelocations_.length()) {
    memcpy(dest, jumpRelocations_.buffer(), jumpRelocations_.length());
  }
}

void Assembler::copyDataRelocationTable(uint8_t* dest) {
  if (dataRelocations_.length()) {
    memcpy(dest, dataRelocations_.buffer(), dataRelocations_.length());
  }
}

void Assembler::processCodeLabels(uint8_t* rawCode) {
  for (const CodeLabel& label : codeLabels_) {
    Bind(rawCode, label);
  }
}

void Assembler::writeCodePointer(CodeLabel* label) {
  m_buffer.assertNoPoolAndNoNops();
  BufferOffset off = writeInst(-1);
  label->patchAt()->bind(off.getOffset());
}

void Assembler::Bind(uint8_t* rawCode, const CodeLabel& label) {
  size_t offset = label.patchAt().offset();
  size_t target = label.target().offset();
  *reinterpret_cast<const void**>(rawCode + offset) = rawCode + target;
}

Assembler::Condition Assembler::InvertCondition(Condition cond) {
  const uint32_t ConditionInversionBit = 0x10000000;
  return Condition(ConditionInversionBit ^ cond);
}

Assembler::Condition Assembler::UnsignedCondition(Condition cond) {
  switch (cond) {
    case Zero:
    case NonZero:
      return cond;
    case LessThan:
    case Below:
      return Below;
    case LessThanOrEqual:
    case BelowOrEqual:
      return BelowOrEqual;
    case GreaterThan:
    case Above:
      return Above;
    case AboveOrEqual:
    case GreaterThanOrEqual:
      return AboveOrEqual;
    default:
      MOZ_CRASH("unexpected condition");
  }
}

Assembler::Condition Assembler::ConditionWithoutEqual(Condition cond) {
  switch (cond) {
    case LessThan:
    case LessThanOrEqual:
      return LessThan;
    case Below:
    case BelowOrEqual:
      return Below;
    case GreaterThan:
    case GreaterThanOrEqual:
      return GreaterThan;
    case Above:
    case AboveOrEqual:
      return Above;
    default:
      MOZ_CRASH("unexpected condition");
  }
}

Assembler::DoubleCondition Assembler::InvertCondition(DoubleCondition cond) {
  const uint32_t ConditionInversionBit = 0x10000000;
  return DoubleCondition(ConditionInversionBit ^ cond);
}

Imm8::TwoImm8mData Imm8::EncodeTwoImms(uint32_t imm) {
  // In the ideal case, we are looking for a number that (in binary) looks
  // like:
  //   0b((00)*)n_1((00)*)n_2((00)*)
  //      left  n1   mid  n2
  //   where both n_1 and n_2 fit into 8 bits.
  // Since this is being done with rotates, we also need to handle the case
  // that one of these numbers is in fact split between the left and right
  // sides, in which case the constant will look like:
  //   0bn_1a((00)*)n_2((00)*)n_1b
  //     n1a  mid  n2   rgh    n1b
  // Also remember, values are rotated by multiples of two, and left, mid or
  // right can have length zero.
  uint32_t imm1, imm2;
  int left = CountLeadingZeroes32(imm) & 0x1E;
  uint32_t no_n1 = imm & ~(0xff << (24 - left));

  // Not technically needed: this case only happens if we can encode as a
  // single imm8m. There is a perfectly reasonable encoding in this case, but
  // we shouldn't encourage people to do things like this.
  if (no_n1 == 0) {
    return TwoImm8mData();
  }

  int mid = CountLeadingZeroes32(no_n1) & 0x1E;
  uint32_t no_n2 =
      no_n1 & ~((0xff << ((24 - mid) & 0x1f)) | 0xff >> ((8 + mid) & 0x1f));

  if (no_n2 == 0) {
    // We hit the easy case, no wraparound.
    // Note: a single constant *may* look like this.
    int imm1shift = left + 8;
    int imm2shift = mid + 8;
    imm1 = (imm >> (32 - imm1shift)) & 0xff;
    if (imm2shift >= 32) {
      imm2shift = 0;
      // This assert does not always hold, in fact, this would lead to
      // some incredibly subtle bugs.
      // assert((imm & 0xff) == no_n1);
      imm2 = no_n1;
    } else {
      imm2 = ((imm >> (32 - imm2shift)) | (imm << imm2shift)) & 0xff;
      MOZ_ASSERT(((no_n1 >> (32 - imm2shift)) | (no_n1 << imm2shift)) == imm2);
    }
    MOZ_ASSERT((imm1shift & 0x1) == 0);
    MOZ_ASSERT((imm2shift & 0x1) == 0);
    return TwoImm8mData(datastore::Imm8mData(imm1, imm1shift >> 1),
                        datastore::Imm8mData(imm2, imm2shift >> 1));
  }

  // Either it wraps, or it does not fit. If we initially chopped off more
  // than 8 bits, then it won't fit.
  if (left >= 8) {
    return TwoImm8mData();
  }

  int right = 32 - (CountLeadingZeroes32(no_n2) & 30);
  // All remaining set bits *must* fit into the lower 8 bits.
  // The right == 8 case should be handled by the previous case.
  if (right > 8) {
    return TwoImm8mData();
  }

  // Make sure the initial bits that we removed for no_n1 fit into the
  // 8-(32-right) leftmost bits.
  if (((imm & (0xff << (24 - left))) << (8 - right)) != 0) {
    // BUT we may have removed more bits than we needed to for no_n1
    // 0x04104001 e.g. we can encode 0x104 with a single op, then 0x04000001
    // with a second, but we try to encode 0x0410000 and find that we need a
    // second op for 0x4000, and 0x1 cannot be included in the encoding of
    // 0x04100000.
    no_n1 = imm & ~((0xff >> (8 - right)) | (0xff << (24 + right)));
    mid = CountLeadingZeroes32(no_n1) & 30;
    no_n2 = no_n1 & ~((0xff << ((24 - mid) & 31)) | 0xff >> ((8 + mid) & 31));
    if (no_n2 != 0) {
      return TwoImm8mData();
    }
  }

  // Now assemble all of this information into a two coherent constants it is
  // a rotate right from the lower 8 bits.
  int imm1shift = 8 - right;
  imm1 = 0xff & ((imm << imm1shift) | (imm >> (32 - imm1shift)));
  MOZ_ASSERT((imm1shift & ~0x1e) == 0);
  // left + 8 + mid is the position of the leftmost bit of n_2.
  // We needed to rotate 0x000000ab right by 8 in order to get 0xab000000,
  // then shift again by the leftmost bit in order to get the constant that we
  // care about.
  int imm2shift = mid + 8;
  imm2 = ((imm >> (32 - imm2shift)) | (imm << imm2shift)) & 0xff;
  MOZ_ASSERT((imm1shift & 0x1) == 0);
  MOZ_ASSERT((imm2shift & 0x1) == 0);
  return TwoImm8mData(datastore::Imm8mData(imm1, imm1shift >> 1),
                      datastore::Imm8mData(imm2, imm2shift >> 1));
}

ALUOp jit::ALUNeg(ALUOp op, Register dest, Register scratch, Imm32* imm,
                  Register* negDest) {
  // Find an alternate ALUOp to get the job done, and use a different imm.
  *negDest = dest;
  switch (op) {
    case OpMov:
      *imm = Imm32(~imm->value);
      return OpMvn;
    case OpMvn:
      *imm = Imm32(~imm->value);
      return OpMov;
    case OpAnd:
      *imm = Imm32(~imm->value);
      return OpBic;
    case OpBic:
      *imm = Imm32(~imm->value);
      return OpAnd;
    case OpAdd:
      *imm = Imm32(-imm->value);
      return OpSub;
    case OpSub:
      *imm = Imm32(-imm->value);
      return OpAdd;
    case OpCmp:
      *imm = Imm32(-imm->value);
      return OpCmn;
    case OpCmn:
      *imm = Imm32(-imm->value);
      return OpCmp;
    case OpTst:
      MOZ_ASSERT(dest == InvalidReg);
      *imm = Imm32(~imm->value);
      *negDest = scratch;
      return OpBic;
      // orr has orn on thumb2 only.
    default:
      return OpInvalid;
  }
}

bool jit::can_dbl(ALUOp op) {
  // Some instructions can't be processed as two separate instructions such as
  // and, and possibly add (when we're setting ccodes). There is also some
  // hilarity with *reading* condition codes. For example, adc dest, src1,
  // 0xfff; (add with carry) can be split up into adc dest, src1, 0xf00; add
  // dest, dest, 0xff, since "reading" the condition code increments the
  // result by one conditionally, that only needs to be done on one of the two
  // instructions.
  switch (op) {
    case OpBic:
    case OpAdd:
    case OpSub:
    case OpEor:
    case OpOrr:
      return true;
    default:
      return false;
  }
}

bool jit::condsAreSafe(ALUOp op) {
  // Even when we are setting condition codes, sometimes we can get away with
  // splitting an operation into two. For example, if our immediate is
  // 0x00ff00ff, and the operation is eors we can split this in half, since x
  // ^ 0x00ff0000 ^ 0x000000ff should set all of its condition codes exactly
  // the same as x ^ 0x00ff00ff. However, if the operation were adds, we
  // cannot split this in half. If the source on the add is 0xfff00ff0, the
  // result sholud be 0xef10ef, but do we set the overflow bit or not?
  // Depending on which half is performed first (0x00ff0000 or 0x000000ff) the
  // V bit will be set differently, and *not* updating the V bit would be
  // wrong. Theoretically, the following should work:
  //  adds r0, r1, 0x00ff0000;
  //  addsvs r0, r1, 0x000000ff;
  //  addvc r0, r1, 0x000000ff;
  // But this is 3 instructions, and at that point, we might as well use
  // something else.
  switch (op) {
    case OpBic:
    case OpOrr:
    case OpEor:
      return true;
    default:
      return false;
  }
}

ALUOp jit::getDestVariant(ALUOp op) {
  // All of the compare operations are dest-less variants of a standard
  // operation. Given the dest-less variant, return the dest-ful variant.
  switch (op) {
    case OpCmp:
      return OpSub;
    case OpCmn:
      return OpAdd;
    case OpTst:
      return OpAnd;
    case OpTeq:
      return OpEor;
    default:
      return op;
  }
}

O2RegImmShift jit::O2Reg(Register r) { return O2RegImmShift(r, LSL, 0); }

O2RegImmShift jit::lsl(Register r, int amt) {
  MOZ_ASSERT(0 <= amt && amt <= 31);
  return O2RegImmShift(r, LSL, amt);
}

O2RegImmShift jit::lsr(Register r, int amt) {
  MOZ_ASSERT(1 <= amt && amt <= 32);
  return O2RegImmShift(r, LSR, amt);
}

O2RegImmShift jit::ror(Register r, int amt) {
  MOZ_ASSERT(1 <= amt && amt <= 31);
  return O2RegImmShift(r, ROR, amt);
}
O2RegImmShift jit::rol(Register r, int amt) {
  MOZ_ASSERT(1 <= amt && amt <= 31);
  return O2RegImmShift(r, ROR, 32 - amt);
}

O2RegImmShift jit::asr(Register r, int amt) {
  MOZ_ASSERT(1 <= amt && amt <= 32);
  return O2RegImmShift(r, ASR, amt);
}

O2RegRegShift jit::lsl(Register r, Register amt) {
  return O2RegRegShift(r, LSL, amt);
}

O2RegRegShift jit::lsr(Register r, Register amt) {
  return O2RegRegShift(r, LSR, amt);
}

O2RegRegShift jit::ror(Register r, Register amt) {
  return O2RegRegShift(r, ROR, amt);
}

O2RegRegShift jit::asr(Register r, Register amt) {
  return O2RegRegShift(r, ASR, amt);
}

static js::jit::DoubleEncoder doubleEncoder;

/* static */
const js::jit::VFPImm js::jit::VFPImm::One(0x3FF00000);

js::jit::VFPImm::VFPImm(uint32_t top) {
  data_ = -1;
  datastore::Imm8VFPImmData tmp;
  if (doubleEncoder.lookup(top, &tmp)) {
    data_ = tmp.encode();
  }
}

BOffImm::BOffImm(const Instruction& inst) : data_(inst.encode() & 0x00ffffff) {}

Instruction* BOffImm::getDest(Instruction* src) const {
  // TODO: It is probably worthwhile to verify that src is actually a branch.
  // NOTE: This does not explicitly shift the offset of the destination left by
  // 2, since it is indexing into an array of instruction sized objects.
  return &src[((int32_t(data_) << 8) >> 8) + 2];
}

const js::jit::DoubleEncoder::DoubleEntry js::jit::DoubleEncoder::table[256] = {
#include "jit/arm/DoubleEntryTable.tbl"
};

// VFPRegister implementation
VFPRegister VFPRegister::doubleOverlay(unsigned int which) const {
  MOZ_ASSERT(!_isInvalid);
  MOZ_ASSERT(which == 0);
  if (kind != Double) {
    return VFPRegister(code_ >> 1, Double);
  }
  return *this;
}
VFPRegister VFPRegister::singleOverlay(unsigned int which) const {
  MOZ_ASSERT(!_isInvalid);
  if (kind == Double) {
    // There are no corresponding float registers for d16-d31.
    MOZ_ASSERT(code_ < 16);
    MOZ_ASSERT(which < 2);
    return VFPRegister((code_ << 1) + which, Single);
  }
  MOZ_ASSERT(which == 0);
  return VFPRegister(code_, Single);
}

static_assert(
    FloatRegisters::TotalDouble <= 16,
    "We assume that every Double register also has an Integer personality");

VFPRegister VFPRegister::sintOverlay(unsigned int which) const {
  MOZ_ASSERT(!_isInvalid);
  if (kind == Double) {
    // There are no corresponding float registers for d16-d31.
    MOZ_ASSERT(code_ < 16);
    MOZ_ASSERT(which < 2);
    return VFPRegister((code_ << 1) + which, Int);
  }
  MOZ_ASSERT(which == 0);
  return VFPRegister(code_, Int);
}
VFPRegister VFPRegister::uintOverlay(unsigned int which) const {
  MOZ_ASSERT(!_isInvalid);
  if (kind == Double) {
    // There are no corresponding float registers for d16-d31.
    MOZ_ASSERT(code_ < 16);
    MOZ_ASSERT(which < 2);
    return VFPRegister((code_ << 1) + which, UInt);
  }
  MOZ_ASSERT(which == 0);
  return VFPRegister(code_, UInt);
}

bool Assembler::oom() const {
  return AssemblerShared::oom() || m_buffer.oom() || jumpRelocations_.oom() ||
         dataRelocations_.oom();
}

// Size of the instruction stream, in bytes. Including pools. This function
// expects all pools that need to be placed have been placed. If they haven't
// then we need to go an flush the pools :(
size_t Assembler::size() const { return m_buffer.size(); }
// Size of the relocation table, in bytes.
size_t Assembler::jumpRelocationTableBytes() const {
  return jumpRelocations_.length();
}
size_t Assembler::dataRelocationTableBytes() const {
  return dataRelocations_.length();
}

// Size of the data table, in bytes.
size_t Assembler::bytesNeeded() const {
  return size() + jumpRelocationTableBytes() + dataRelocationTableBytes();
}

// Allocate memory for a branch instruction, it will be overwritten
// subsequently and should not be disassembled.

BufferOffset Assembler::allocBranchInst() {
  return m_buffer.putInt(Always | InstNOP::NopInst);
}

void Assembler::WriteInstStatic(uint32_t x, uint32_t* dest) {
  MOZ_ASSERT(dest != nullptr);
  *dest = x;
}

void Assembler::haltingAlign(int alignment) {
  // HLT with payload 0xBAAD
  m_buffer.align(alignment, 0xE1000070 | (0xBAA << 8) | 0xD);
}

void Assembler::nopAlign(int alignment) { m_buffer.align(alignment); }

BufferOffset Assembler::as_nop() { return writeInst(0xe320f000); }

static uint32_t EncodeAlu(Register dest, Register src1, Operand2 op2, ALUOp op,
                          SBit s, Assembler::Condition c) {
  return (int)op | (int)s | (int)c | op2.encode() |
         ((dest == InvalidReg) ? 0 : RD(dest)) |
         ((src1 == InvalidReg) ? 0 : RN(src1));
}

BufferOffset Assembler::as_alu(Register dest, Register src1, Operand2 op2,
                               ALUOp op, SBit s, Condition c) {
  return writeInst(EncodeAlu(dest, src1, op2, op, s, c));
}

BufferOffset Assembler::as_mov(Register dest, Operand2 op2, SBit s,
                               Condition c) {
  return as_alu(dest, InvalidReg, op2, OpMov, s, c);
}

/* static */
void Assembler::as_alu_patch(Register dest, Register src1, Operand2 op2,
                             ALUOp op, SBit s, Condition c, uint32_t* pos) {
  WriteInstStatic(EncodeAlu(dest, src1, op2, op, s, c), pos);
}

/* static */
void Assembler::as_mov_patch(Register dest, Operand2 op2, SBit s, Condition c,
                             uint32_t* pos) {
  as_alu_patch(dest, InvalidReg, op2, OpMov, s, c, pos);
}

BufferOffset Assembler::as_mvn(Register dest, Operand2 op2, SBit s,
                               Condition c) {
  return as_alu(dest, InvalidReg, op2, OpMvn, s, c);
}

// Logical operations.
BufferOffset Assembler::as_and(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpAnd, s, c);
}
BufferOffset Assembler::as_bic(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpBic, s, c);
}
BufferOffset Assembler::as_eor(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpEor, s, c);
}
BufferOffset Assembler::as_orr(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpOrr, s, c);
}

// Reverse byte operations.
BufferOffset Assembler::as_rev(Register dest, Register src, Condition c) {
  return writeInst((int)c | 0b0000'0110'1011'1111'0000'1111'0011'0000 |
                   RD(dest) | src.code());
}
BufferOffset Assembler::as_rev16(Register dest, Register src, Condition c) {
  return writeInst((int)c | 0b0000'0110'1011'1111'0000'1111'1011'0000 |
                   RD(dest) | src.code());
}
BufferOffset Assembler::as_revsh(Register dest, Register src, Condition c) {
  return writeInst((int)c | 0b0000'0110'1111'1111'0000'1111'1011'0000 |
                   RD(dest) | src.code());
}

// Mathematical operations.
BufferOffset Assembler::as_adc(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpAdc, s, c);
}
BufferOffset Assembler::as_add(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpAdd, s, c);
}
BufferOffset Assembler::as_sbc(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpSbc, s, c);
}
BufferOffset Assembler::as_sub(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpSub, s, c);
}
BufferOffset Assembler::as_rsb(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpRsb, s, c);
}
BufferOffset Assembler::as_rsc(Register dest, Register src1, Operand2 op2,
                               SBit s, Condition c) {
  return as_alu(dest, src1, op2, OpRsc, s, c);
}

// Test operations.
BufferOffset Assembler::as_cmn(Register src1, Operand2 op2, Condition c) {
  return as_alu(InvalidReg, src1, op2, OpCmn, SetCC, c);
}
BufferOffset Assembler::as_cmp(Register src1, Operand2 op2, Condition c) {
  return as_alu(InvalidReg, src1, op2, OpCmp, SetCC, c);
}
BufferOffset Assembler::as_teq(Register src1, Operand2 op2, Condition c) {
  return as_alu(InvalidReg, src1, op2, OpTeq, SetCC, c);
}
BufferOffset Assembler::as_tst(Register src1, Operand2 op2, Condition c) {
  return as_alu(InvalidReg, src1, op2, OpTst, SetCC, c);
}

static constexpr Register NoAddend{Registers::pc};

static const int SignExtend = 0x06000070;

enum SignExtend {
  SxSxtb = 10 << 20,
  SxSxth = 11 << 20,
  SxUxtb = 14 << 20,
  SxUxth = 15 << 20
};

// Sign extension operations.
BufferOffset Assembler::as_sxtb(Register dest, Register src, int rotate,
                                Condition c) {
  return writeInst((int)c | SignExtend | SxSxtb | RN(NoAddend) | RD(dest) |
                   ((rotate & 3) << 10) | src.code());
}
BufferOffset Assembler::as_sxth(Register dest, Register src, int rotate,
                                Condition c) {
  return writeInst((int)c | SignExtend | SxSxth | RN(NoAddend) | RD(dest) |
                   ((rotate & 3) << 10) | src.code());
}
BufferOffset Assembler::as_uxtb(Register dest, Register src, int rotate,
                                Condition c) {
  return writeInst((int)c | SignExtend | SxUxtb | RN(NoAddend) | RD(dest) |
                   ((rotate & 3) << 10) | src.code());
}
BufferOffset Assembler::as_uxth(Register dest, Register src, int rotate,
                                Condition c) {
  return writeInst((int)c | SignExtend | SxUxth | RN(NoAddend) | RD(dest) |
                   ((rotate & 3) << 10) | src.code());
}

static uint32_t EncodeMovW(Register dest, Imm16 imm, Assembler::Condition c) {
  MOZ_ASSERT(HasMOVWT());
  return 0x03000000 | c | imm.encode() | RD(dest);
}

static uint32_t EncodeMovT(Register dest, Imm16 imm, Assembler::Condition c) {
  MOZ_ASSERT(HasMOVWT());
  return 0x03400000 | c | imm.encode() | RD(dest);
}

// Not quite ALU worthy, but these are useful none the less. These also have
// the isue of these being formatted completly differently from the standard ALU
// operations.
BufferOffset Assembler::as_movw(Register dest, Imm16 imm, Condition c) {
  return writeInst(EncodeMovW(dest, imm, c));
}

/* static */
void Assembler::as_movw_patch(Register dest, Imm16 imm, Condition c,
                              Instruction* pos) {
  WriteInstStatic(EncodeMovW(dest, imm, c), (uint32_t*)pos);
}

BufferOffset Assembler::as_movt(Register dest, Imm16 imm, Condition c) {
  return writeInst(EncodeMovT(dest, imm, c));
}

/* static */
void Assembler::as_movt_patch(Register dest, Imm16 imm, Condition c,
                              Instruction* pos) {
  WriteInstStatic(EncodeMovT(dest, imm, c), (uint32_t*)pos);
}

static const int mull_tag = 0x90;

BufferOffset Assembler::as_genmul(Register dhi, Register dlo, Register rm,
                                  Register rn, MULOp op, SBit s, Condition c) {
  return writeInst(RN(dhi) | maybeRD(dlo) | RM(rm) | rn.code() | op | s | c |
                   mull_tag);
}
BufferOffset Assembler::as_mul(Register dest, Register src1, Register src2,
                               SBit s, Condition c) {
  return as_genmul(dest, InvalidReg, src1, src2, OpmMul, s, c);
}
BufferOffset Assembler::as_mla(Register dest, Register acc, Register src1,
                               Register src2, SBit s, Condition c) {
  return as_genmul(dest, acc, src1, src2, OpmMla, s, c);
}
BufferOffset Assembler::as_umaal(Register destHI, Register destLO,
                                 Register src1, Register src2, Condition c) {
  return as_genmul(destHI, destLO, src1, src2, OpmUmaal, LeaveCC, c);
}
BufferOffset Assembler::as_mls(Register dest, Register acc, Register src1,
                               Register src2, Condition c) {
  return as_genmul(dest, acc, src1, src2, OpmMls, LeaveCC, c);
}

BufferOffset Assembler::as_umull(Register destHI, Register destLO,
                                 Register src1, Register src2, SBit s,
                                 Condition c) {
  return as_genmul(destHI, destLO, src1, src2, OpmUmull, s, c);
}

BufferOffset Assembler::as_umlal(Register destHI, Register destLO,
                                 Register src1, Register src2, SBit s,
                                 Condition c) {
  return as_genmul(destHI, destLO, src1, src2, OpmUmlal, s, c);
}

BufferOffset Assembler::as_smull(Register destHI, Register destLO,
                                 Register src1, Register src2, SBit s,
                                 Condition c) {
  return as_genmul(destHI, destLO, src1, src2, OpmSmull, s, c);
}

BufferOffset Assembler::as_smlal(Register destHI, Register destLO,
                                 Register src1, Register src2, SBit s,
                                 Condition c) {
  return as_genmul(destHI, destLO, src1, src2, OpmSmlal, s, c);
}

BufferOffset Assembler::as_sdiv(Register rd, Register rn, Register rm,
                                Condition c) {
  return writeInst(0x0710f010 | c | RN(rd) | RM(rm) | rn.code());
}

BufferOffset Assembler::as_udiv(Register rd, Register rn, Register rm,
                                Condition c) {
  return writeInst(0x0730f010 | c | RN(rd) | RM(rm) | rn.code());
}

BufferOffset Assembler::as_clz(Register dest, Register src, Condition c) {
  MOZ_ASSERT(src != pc && dest != pc);
  return writeInst(RD(dest) | src.code() | c | 0x016f0f10);
}

// Data transfer instructions: ldr, str, ldrb, strb. Using an int to
// differentiate between 8 bits and 32 bits is overkill, but meh.

static uint32_t EncodeDtr(LoadStore ls, int size, Index mode, Register rt,
                          DTRAddr addr, Assembler::Condition c) {
  MOZ_ASSERT(mode == Offset || (rt != addr.getBase() && pc != addr.getBase()));
  MOZ_ASSERT(size == 32 || size == 8);
  return 0x04000000 | ls | (size == 8 ? 0x00400000 : 0) | mode | c | RT(rt) |
         addr.encode();
}

BufferOffset Assembler::as_dtr(LoadStore ls, int size, Index mode, Register rt,
                               DTRAddr addr, Condition c) {
  return writeInst(EncodeDtr(ls, size, mode, rt, addr, c));
}

/* static */
void Assembler::as_dtr_patch(LoadStore ls, int size, Index mode, Register rt,
                             DTRAddr addr, Condition c, uint32_t* dest) {
  WriteInstStatic(EncodeDtr(ls, size, mode, rt, addr, c), dest);
}

class PoolHintData {
 public:
  enum LoadType {
    // Set 0 to bogus, since that is the value most likely to be
    // accidentally left somewhere.
    PoolBOGUS = 0,
    PoolDTR = 1,
    PoolBranch = 2,
    PoolVDTR = 3
  };

 private:
  uint32_t index_ : 16;
  uint32_t cond_ : 4;
  uint32_t loadType_ : 2;
  uint32_t destReg_ : 5;
  uint32_t destType_ : 1;
  uint32_t ONES : 4;

  static const uint32_t ExpectedOnes = 0xfu;

 public:
  void init(uint32_t index, Assembler::Condition cond, LoadType lt,
            Register destReg) {
    index_ = index;
    MOZ_ASSERT(index_ == index);
    cond_ = cond >> 28;
    MOZ_ASSERT(cond_ == cond >> 28);
    loadType_ = lt;
    ONES = ExpectedOnes;
    destReg_ = destReg.code();
    destType_ = 0;
  }
  void init(uint32_t index, Assembler::Condition cond, LoadType lt,
            const VFPRegister& destReg) {
    MOZ_ASSERT(destReg.isFloat());
    index_ = index;
    MOZ_ASSERT(index_ == index);
    cond_ = cond >> 28;
    MOZ_ASSERT(cond_ == cond >> 28);
    loadType_ = lt;
    ONES = ExpectedOnes;
    destReg_ = destReg.id();
    destType_ = destReg.isDouble();
  }
  Assembler::Condition getCond() const {
    return Assembler::Condition(cond_ << 28);
  }

  Register getReg() const { return Register::FromCode(destReg_); }
  VFPRegister getVFPReg() const {
    VFPRegister r = VFPRegister(
        destReg_, destType_ ? VFPRegister::Double : VFPRegister::Single);
    return r;
  }

  int32_t getIndex() const { return index_; }
  void setIndex(uint32_t index) {
    MOZ_ASSERT(ONES == ExpectedOnes && loadType_ != PoolBOGUS);
    index_ = index;
    MOZ_ASSERT(index_ == index);
  }

  LoadType getLoadType() const {
    // If this *was* a PoolBranch, but the branch has already been bound
    // then this isn't going to look like a real poolhintdata, but we still
    // want to lie about it so everyone knows it *used* to be a branch.
    if (ONES != ExpectedOnes) {
      return PoolHintData::PoolBranch;
    }
    return static_cast<LoadType>(loadType_);
  }

  bool isValidPoolHint() const {
    // Most instructions cannot have a condition that is 0xf. Notable
    // exceptions are blx and the entire NEON instruction set. For the
    // purposes of pool loads, and possibly patched branches, the possible
    // instructions are ldr and b, neither of which can have a condition
    // code of 0xf.
    return ONES == ExpectedOnes;
  }
};

union PoolHintPun {
  PoolHintData phd;
  uint32_t raw;
};

// Handles all of the other integral data transferring functions: ldrsb, ldrsh,
// ldrd, etc. The size is given in bits.
BufferOffset Assembler::as_extdtr(LoadStore ls, int size, bool IsSigned,
                                  Index mode, Register rt, EDtrAddr addr,
                                  Condition c) {
  int extra_bits2 = 0;
  int extra_bits1 = 0;
  switch (size) {
    case 8:
      MOZ_ASSERT(IsSigned);
      MOZ_ASSERT(ls != IsStore);
      extra_bits1 = 0x1;
      extra_bits2 = 0x2;
      break;
    case 16:
      // 'case 32' doesn't need to be handled, it is handled by the default
      // ldr/str.
      extra_bits2 = 0x01;
      extra_bits1 = (ls == IsStore) ? 0 : 1;
      if (IsSigned) {
        MOZ_ASSERT(ls != IsStore);
        extra_bits2 |= 0x2;
      }
      break;
    case 64:
      extra_bits2 = (ls == IsStore) ? 0x3 : 0x2;
      extra_bits1 = 0;
      break;
    default:
      MOZ_CRASH("unexpected size in as_extdtr");
  }
  return writeInst(extra_bits2 << 5 | extra_bits1 << 20 | 0x90 | addr.encode() |
                   RT(rt) | mode | c);
}

BufferOffset Assembler::as_dtm(LoadStore ls, Register rn, uint32_t mask,
                               DTMMode mode, DTMWriteBack wb, Condition c) {
  return writeInst(0x08000000 | RN(rn) | ls | mode | mask | c | wb);
}

BufferOffset Assembler::allocLiteralLoadEntry(
    size_t numInst, unsigned numPoolEntries, PoolHintPun& php, uint8_t* data,
    const LiteralDoc& doc, ARMBuffer::PoolEntry* pe, bool loadToPC) {
  uint8_t* inst = (uint8_t*)&php.raw;

  MOZ_ASSERT(inst);
  MOZ_ASSERT(numInst == 1);  // Or fix the disassembly

  BufferOffset offs =
      m_buffer.allocEntry(numInst, numPoolEntries, inst, data, pe);
  propagateOOM(offs.assigned());
#ifdef JS_DISASM_ARM
  Instruction* instruction = m_buffer.getInstOrNull(offs);
  if (instruction) {
    spewLiteralLoad(php, loadToPC, instruction, doc);
  }
#endif
  return offs;
}

// This is also used for instructions that might be resolved into branches,
// or might not.  If dest==pc then it is effectively a branch.

BufferOffset Assembler::as_Imm32Pool(Register dest, uint32_t value,
                                     Condition c) {
  PoolHintPun php;
  php.phd.init(0, c, PoolHintData::PoolDTR, dest);
  BufferOffset offs = allocLiteralLoadEntry(
      1, 1, php, (uint8_t*)&value, LiteralDoc(value), nullptr, dest == pc);
  return offs;
}

/* static */
void Assembler::WritePoolEntry(Instruction* addr, Condition c, uint32_t data) {
  MOZ_ASSERT(addr->is<InstLDR>());
  *addr->as<InstLDR>()->dest() = data;
  MOZ_ASSERT(addr->extractCond() == c);
}

BufferOffset Assembler::as_FImm64Pool(VFPRegister dest, double d, Condition c) {
  MOZ_ASSERT(dest.isDouble());
  PoolHintPun php;
  php.phd.init(0, c, PoolHintData::PoolVDTR, dest);
  return allocLiteralLoadEntry(1, 2, php, (uint8_t*)&d, LiteralDoc(d));
}

BufferOffset Assembler::as_FImm32Pool(VFPRegister dest, float f, Condition c) {
  // Insert floats into the double pool as they have the same limitations on
  // immediate offset. This wastes 4 bytes padding per float. An alternative
  // would be to have a separate pool for floats.
  MOZ_ASSERT(dest.isSingle());
  PoolHintPun php;
  php.phd.init(0, c, PoolHintData::PoolVDTR, dest);
  return allocLiteralLoadEntry(1, 1, php, (uint8_t*)&f, LiteralDoc(f));
}

// Pool callbacks stuff:
void Assembler::InsertIndexIntoTag(uint8_t* load_, uint32_t index) {
  uint32_t* load = (uint32_t*)load_;
  PoolHintPun php;
  php.raw = *load;
  php.phd.setIndex(index);
  *load = php.raw;
}

// patchConstantPoolLoad takes the address of the instruction that wants to be
// patched, and the address of the start of the constant pool, and figures
// things out from there.
void Assembler::PatchConstantPoolLoad(void* loadAddr, void* constPoolAddr) {
  PoolHintData data = *(PoolHintData*)loadAddr;
  uint32_t* instAddr = (uint32_t*)loadAddr;
  int offset = (char*)constPoolAddr - (char*)loadAddr;
  switch (data.getLoadType()) {
    case PoolHintData::PoolBOGUS:
      MOZ_CRASH("bogus load type!");
    case PoolHintData::PoolDTR:
      Assembler::as_dtr_patch(
          IsLoad, 32, Offset, data.getReg(),
          DTRAddr(pc, DtrOffImm(offset + 4 * data.getIndex() - 8)),
          data.getCond(), instAddr);
      break;
    case PoolHintData::PoolBranch:
      // Either this used to be a poolBranch, and the label was already bound,
      // so it was replaced with a real branch, or this may happen in the
      // future. If this is going to happen in the future, then the actual
      // bits that are written here don't matter (except the condition code,
      // since that is always preserved across patchings) but if it does not
      // get bound later, then we want to make sure this is a load from the
      // pool entry (and the pool entry should be nullptr so it will crash).
      if (data.isValidPoolHint()) {
        Assembler::as_dtr_patch(
            IsLoad, 32, Offset, pc,
            DTRAddr(pc, DtrOffImm(offset + 4 * data.getIndex() - 8)),
            data.getCond(), instAddr);
      }
      break;
    case PoolHintData::PoolVDTR: {
      VFPRegister dest = data.getVFPReg();
      int32_t imm = offset + (data.getIndex() * 4) - 8;
      MOZ_ASSERT(-1024 < imm && imm < 1024);
      Assembler::as_vdtr_patch(IsLoad, dest, VFPAddr(pc, VFPOffImm(imm)),
                               data.getCond(), instAddr);
      break;
    }
  }
}

// Atomic instruction stuff:

BufferOffset Assembler::as_ldrexd(Register rt, Register rt2, Register rn,
                                  Condition c) {
  MOZ_ASSERT(!(rt.code() & 1) && rt2.code() == rt.code() + 1);
  MOZ_ASSERT(rt.code() != 14 && rn.code() != 15);
  return writeInst(0x01b00f9f | (int)c | RT(rt) | RN(rn));
}

BufferOffset Assembler::as_ldrex(Register rt, Register rn, Condition c) {
  MOZ_ASSERT(rt.code() != 15 && rn.code() != 15);
  return writeInst(0x01900f9f | (int)c | RT(rt) | RN(rn));
}

BufferOffset Assembler::as_ldrexh(Register rt, Register rn, Condition c) {
  MOZ_ASSERT(rt.code() != 15 && rn.code() != 15);
  return writeInst(0x01f00f9f | (int)c | RT(rt) | RN(rn));
}

BufferOffset Assembler::as_ldrexb(Register rt, Register rn, Condition c) {
  MOZ_ASSERT(rt.code() != 15 && rn.code() != 15);
  return writeInst(0x01d00f9f | (int)c | RT(rt) | RN(rn));
}

BufferOffset Assembler::as_strexd(Register rd, Register rt, Register rt2,
                                  Register rn, Condition c) {
  MOZ_ASSERT(!(rt.code() & 1) && rt2.code() == rt.code() + 1);
  MOZ_ASSERT(rt.code() != 14 && rn.code() != 15 && rd.code() != 15);
  MOZ_ASSERT(rd != rn && rd != rt && rd != rt2);
  return writeInst(0x01a00f90 | (int)c | RD(rd) | RN(rn) | rt.code());
}

BufferOffset Assembler::as_strex(Register rd, Register rt, Register rn,
                                 Condition c) {
  MOZ_ASSERT(rd != rn && rd != rt);  // True restriction on Cortex-A7 (RPi2)
  return writeInst(0x01800f90 | (int)c | RD(rd) | RN(rn) | rt.code());
}

BufferOffset Assembler::as_strexh(Register rd, Register rt, Register rn,
                                  Condition c) {
  MOZ_ASSERT(rd != rn && rd != rt);  // True restriction on Cortex-A7 (RPi2)
  return writeInst(0x01e00f90 | (int)c | RD(rd) | RN(rn) | rt.code());
}

BufferOffset Assembler::as_strexb(Register rd, Register rt, Register rn,
                                  Condition c) {
  MOZ_ASSERT(rd != rn && rd != rt);  // True restriction on Cortex-A7 (RPi2)
  return writeInst(0x01c00f90 | (int)c | RD(rd) | RN(rn) | rt.code());
}

BufferOffset Assembler::as_clrex() { return writeInst(0xf57ff01f); }

// Memory barrier stuff:

BufferOffset Assembler::as_dmb(BarrierOption option) {
  return writeInst(0xf57ff050U | (int)option);
}
BufferOffset Assembler::as_dsb(BarrierOption option) {
  return writeInst(0xf57ff040U | (int)option);
}
BufferOffset Assembler::as_isb() {
  return writeInst(0xf57ff06fU);  // option == SY
}
BufferOffset Assembler::as_dsb_trap() {
  // DSB is "mcr 15, 0, r0, c7, c10, 4".
  // See eg https://bugs.kde.org/show_bug.cgi?id=228060.
  // ARMv7 manual, "VMSA CP15 c7 register summary".
  // Flagged as "legacy" starting with ARMv8, may be disabled on chip, see
  // ARMv8 manual E2.7.3 and G3.18.16.
  return writeInst(0xee070f9a);
}
BufferOffset Assembler::as_dmb_trap() {
  // DMB is "mcr 15, 0, r0, c7, c10, 5".
  // ARMv7 manual, "VMSA CP15 c7 register summary".
  // Flagged as "legacy" starting with ARMv8, may be disabled on chip, see
  // ARMv8 manual E2.7.3 and G3.18.16.
  return writeInst(0xee070fba);
}
BufferOffset Assembler::as_isb_trap() {
  // ISB is "mcr 15, 0, r0, c7, c5, 4".
  // ARMv7 manual, "VMSA CP15 c7 register summary".
  // Flagged as "legacy" starting with ARMv8, may be disabled on chip, see
  // ARMv8 manual E2.7.3 and G3.18.16.
  return writeInst(0xee070f94);
}

BufferOffset Assembler::as_csdb() {
  // NOP (see as_nop) on architectures where this instruction is not defined.
  //
  // https://developer.arm.com/-/media/developer/pdf/Cache_Speculation_Side-channels_22Feb18.pdf
  // CSDB A32: 1110_0011_0010_0000_1111_0000_0001_0100
  return writeInst(0xe320f000 | 0x14);
}

// Control flow stuff:

// bx can *only* branch to a register, never to an immediate.
BufferOffset Assembler::as_bx(Register r, Condition c) {
  BufferOffset ret = writeInst(((int)c) | OpBx | r.code());
  return ret;
}

void Assembler::WritePoolGuard(BufferOffset branch, Instruction* dest,
                               BufferOffset afterPool) {
  BOffImm off = afterPool.diffB<BOffImm>(branch);
  if (off.isInvalid()) {
    MOZ_CRASH("BOffImm invalid");
  }
  *dest = InstBImm(off, Always);
}

// Branch can branch to an immediate *or* to a register.
// Branches to immediates are pc relative, branches to registers are absolute.
BufferOffset Assembler::as_b(BOffImm off, Condition c, Label* documentation) {
  return writeBranchInst(((int)c) | OpB | off.encode(),
                         refLabel(documentation));
}

BufferOffset Assembler::as_b(Label* l, Condition c) {
  if (l->bound()) {
    // Note only one instruction is emitted here, the NOP is overwritten.
    BufferOffset ret = allocBranchInst();
    if (oom()) {
      return BufferOffset();
    }

    BOffImm offset = BufferOffset(l).diffB<BOffImm>(ret);
    MOZ_RELEASE_ASSERT(!offset.isInvalid(),
                       "Buffer size limit should prevent this");
    as_b(offset, c, ret);
#ifdef JS_DISASM_ARM
    spewBranch(m_buffer.getInstOrNull(ret), refLabel(l));
#endif
    return ret;
  }

  if (oom()) {
    return BufferOffset();
  }

  BufferOffset ret;
  if (l->used()) {
    int32_t old = l->offset();
    MOZ_RELEASE_ASSERT(BOffImm::IsInRange(old),
                       "Buffer size limit should prevent this");
    ret = as_b(BOffImm(old), c, l);
  } else {
    BOffImm inv;
    ret = as_b(inv, c, l);
  }

  if (oom()) {
    return BufferOffset();
  }

  l->use(ret.getOffset());
  return ret;
}

BufferOffset Assembler::as_b(BOffImm off, Condition c, BufferOffset inst) {
  // JS_DISASM_ARM NOTE: Can't disassemble here, because numerous callers use
  // this to patchup old code.  Must disassemble in caller where it makes sense.
  // Not many callers.
  *editSrc(inst) = InstBImm(off, c);
  return inst;
}

// blx can go to either an immediate or a register.
// When blx'ing to a register, we change processor state depending on the low
// bit of the register when blx'ing to an immediate, we *always* change
// processor state.

BufferOffset Assembler::as_blx(Register r, Condition c) {
  return writeInst(((int)c) | OpBlx | r.code());
}

// bl can only branch to an pc-relative immediate offset
// It cannot change the processor state.
BufferOffset Assembler::as_bl(BOffImm off, Condition c, Label* documentation) {
  return writeBranchInst(((int)c) | OpBl | off.encode(),
                         refLabel(documentation));
}

BufferOffset Assembler::as_bl(Label* l, Condition c) {
  if (l->bound()) {
    // Note only one instruction is emitted here, the NOP is overwritten.
    BufferOffset ret = allocBranchInst();
    if (oom()) {
      return BufferOffset();
    }

    BOffImm offset = BufferOffset(l).diffB<BOffImm>(ret);
    MOZ_RELEASE_ASSERT(!offset.isInvalid(),
                       "Buffer size limit should prevent this");

    as_bl(offset, c, ret);
#ifdef JS_DISASM_ARM
    spewBranch(m_buffer.getInstOrNull(ret), refLabel(l));
#endif
    return ret;
  }

  if (oom()) {
    return BufferOffset();
  }

  BufferOffset ret;
  // See if the list was empty.
  if (l->used()) {
    int32_t old = l->offset();
    MOZ_RELEASE_ASSERT(BOffImm::IsInRange(old),
                       "Buffer size limit should prevent this");
    ret = as_bl(BOffImm(old), c, l);
  } else {
    BOffImm inv;
    ret = as_bl(inv, c, l);
  }

  if (oom()) {
    return BufferOffset();
  }

  l->use(ret.getOffset());
  return ret;
}

BufferOffset Assembler::as_bl(BOffImm off, Condition c, BufferOffset inst) {
  *editSrc(inst) = InstBLImm(off, c);
  return inst;
}

BufferOffset Assembler::as_mrs(Register r, Condition c) {
  return writeInst(0x010f0000 | int(c) | RD(r));
}

BufferOffset Assembler::as_msr(Register r, Condition c) {
  // Hardcode the 'mask' field to 0b11 for now. It is bits 18 and 19, which
  // are the two high bits of the 'c' in this constant.
  MOZ_ASSERT((r.code() & ~0xf) == 0);
  return writeInst(0x012cf000 | int(c) | r.code());
}

// VFP instructions!
enum vfp_tags { VfpTag = 0x0C000A00, VfpArith = 0x02000000 };

BufferOffset Assembler::writeVFPInst(vfp_size sz, uint32_t blob) {
  MOZ_ASSERT((sz & blob) == 0);
  MOZ_ASSERT((VfpTag & blob) == 0);
  return writeInst(VfpTag | std::underlying_type_t<vfp_size>(sz) | blob);
}

/* static */
void Assembler::WriteVFPInstStatic(vfp_size sz, uint32_t blob, uint32_t* dest) {
  MOZ_ASSERT((sz & blob) == 0);
  MOZ_ASSERT((VfpTag & blob) == 0);
  WriteInstStatic(VfpTag | std::underlying_type_t<vfp_size>(sz) | blob, dest);
}

// Unityped variants: all registers hold the same (ieee754 single/double)
// notably not included are vcvt; vmov vd, #imm; vmov rt, vn.
BufferOffset Assembler::as_vfp_float(VFPRegister vd, VFPRegister vn,
                                     VFPRegister vm, VFPOp op, Condition c) {
  // Make sure we believe that all of our operands are the same kind.
  MOZ_ASSERT_IF(!vn.isMissing(), vd.equiv(vn));
  MOZ_ASSERT_IF(!vm.isMissing(), vd.equiv(vm));
  vfp_size sz = vd.isDouble() ? IsDouble : IsSingle;
  return writeVFPInst(sz, VD(vd) | VN(vn) | VM(vm) | op | VfpArith | c);
}

BufferOffset Assembler::as_vadd(VFPRegister vd, VFPRegister vn, VFPRegister vm,
                                Condition c) {
  return as_vfp_float(vd, vn, vm, OpvAdd, c);
}

BufferOffset Assembler::as_vdiv(VFPRegister vd, VFPRegister vn, VFPRegister vm,
                                Condition c) {
  return as_vfp_float(vd, vn, vm, OpvDiv, c);
}

BufferOffset Assembler::as_vmul(VFPRegister vd, VFPRegister vn, VFPRegister vm,
                                Condition c) {
  return as_vfp_float(vd, vn, vm, OpvMul, c);
}

BufferOffset Assembler::as_vnmul(VFPRegister vd, VFPRegister vn, VFPRegister vm,
                                 Condition c) {
  return as_vfp_float(vd, vn, vm, OpvMul, c);
}

BufferOffset Assembler::as_vnmla(VFPRegister vd, VFPRegister vn, VFPRegister vm,
                                 Condition c) {
  MOZ_CRASH("Feature NYI");
}

BufferOffset Assembler::as_vnmls(VFPRegister vd, VFPRegister vn, VFPRegister vm,
                                 Condition c) {
  MOZ_CRASH("Feature NYI");
}

BufferOffset Assembler::as_vneg(VFPRegister vd, VFPRegister vm, Condition c) {
  return as_vfp_float(vd, NoVFPRegister, vm, OpvNeg, c);
}

BufferOffset Assembler::as_vsqrt(VFPRegister vd, VFPRegister vm, Condition c) {
  return as_vfp_float(vd, NoVFPRegister, vm, OpvSqrt, c);
}

BufferOffset Assembler::as_vabs(VFPRegister vd, VFPRegister vm, Condition c) {
  return as_vfp_float(vd, NoVFPRegister, vm, OpvAbs, c);
}

BufferOffset Assembler::as_vsub(VFPRegister vd, VFPRegister vn, VFPRegister vm,
                                Condition c) {
  return as_vfp_float(vd, vn, vm, OpvSub, c);
}

BufferOffset Assembler::as_vcmp(VFPRegister vd, VFPRegister vm, Condition c) {
  return as_vfp_float(vd, NoVFPRegister, vm, OpvCmp, c);
}

BufferOffset Assembler::as_vcmpz(VFPRegister vd, Condition c) {
  return as_vfp_float(vd, NoVFPRegister, NoVFPRegister, OpvCmpz, c);
}

// Specifically, a move between two same sized-registers.
BufferOffset Assembler::as_vmov(VFPRegister vd, VFPRegister vsrc, Condition c) {
  return as_vfp_float(vd, NoVFPRegister, vsrc, OpvMov, c);
}

// Transfer between Core and VFP.

// Unlike the next function, moving between the core registers and vfp registers
// can't be *that* properly typed. Namely, since I don't want to munge the type
// VFPRegister to also include core registers. Thus, the core and vfp registers
// are passed in based on their type, and src/dest is determined by the
// float2core.

BufferOffset Assembler::as_vxfer(Register vt1, Register vt2, VFPRegister vm,
                                 FloatToCore_ f2c, Condition c, int idx) {
  vfp_size sz = IsSingle;
  if (vm.isDouble()) {
    // Technically, this can be done with a vmov à la ARM ARM under vmov
    // however, that requires at least an extra bit saying if the operation
    // should be performed on the lower or upper half of the double. Moving
    // a single to/from 2N/2N+1 isn't equivalent, since there are 32 single
    // registers, and 32 double registers so there is no way to encode the
    // last 16 double registers.
    sz = IsDouble;
    MOZ_ASSERT(idx == 0 || idx == 1);
    // If we are transferring a single half of the double then it must be
    // moving a VFP reg to a core reg.
    MOZ_ASSERT_IF(vt2 == InvalidReg, f2c == FloatToCore);
    idx = idx << 21;
  } else {
    MOZ_ASSERT(idx == 0);
  }

  if (vt2 == InvalidReg) {
    return writeVFPInst(sz, WordTransfer |
                                std::underlying_type_t<FloatToCore_>(f2c) |
                                std::underlying_type_t<Condition>(c) | RT(vt1) |
                                maybeRN(vt2) | VN(vm) | idx);
  }

  // We are doing a 64 bit transfer.
  return writeVFPInst(sz, DoubleTransfer |
                              std::underlying_type_t<FloatToCore_>(f2c) |
                              std::underlying_type_t<Condition>(c) | RT(vt1) |
                              maybeRN(vt2) | VM(vm) | idx);
}

enum vcvt_destFloatness { VcvtToInteger = 1 << 18, VcvtToFloat = 0 << 18 };
enum vcvt_toZero {
  VcvtToZero =
      1 << 7,  // Use the default rounding mode, which rounds truncates.
  VcvtToFPSCR = 0 << 7  // Use whatever rounding mode the fpscr specifies.
};
enum vcvt_Signedness {
  VcvtToSigned = 1 << 16,
  VcvtToUnsigned = 0 << 16,
  VcvtFromSigned = 1 << 7,
  VcvtFromUnsigned = 0 << 7
};

// Our encoding actually allows just the src and the dest (and their types) to
// uniquely specify the encoding that we are going to use.
BufferOffset Assembler::as_vcvt(VFPRegister vd, VFPRegister vm, bool useFPSCR,
                                Condition c) {
  // Unlike other cases, the source and dest types cannot be the same.
  MOZ_ASSERT(!vd.equiv(vm));
  vfp_size sz = IsDouble;
  if (vd.isFloat() && vm.isFloat()) {
    // Doing a float -> float conversion.
    if (vm.isSingle()) {
      sz = IsSingle;
    }
    return writeVFPInst(sz, c | 0x02B700C0 | VM(vm) | VD(vd));
  }

  // At least one of the registers should be a float.
  vcvt_destFloatness destFloat;
  vcvt_Signedness opSign;
  vcvt_toZero doToZero = VcvtToFPSCR;
  MOZ_ASSERT(vd.isFloat() || vm.isFloat());
  if (vd.isSingle() || vm.isSingle()) {
    sz = IsSingle;
  }

  if (vd.isFloat()) {
    destFloat = VcvtToFloat;
    opSign = (vm.isSInt()) ? VcvtFromSigned : VcvtFromUnsigned;
  } else {
    destFloat = VcvtToInteger;
    opSign = (vd.isSInt()) ? VcvtToSigned : VcvtToUnsigned;
    doToZero = useFPSCR ? VcvtToFPSCR : VcvtToZero;
  }
  return writeVFPInst(
      sz, c | 0x02B80040 | VD(vd) | VM(vm) | destFloat | opSign | doToZero);
}

BufferOffset Assembler::as_vcvtFixed(VFPRegister vd, bool isSigned,
                                     uint32_t fixedPoint, bool toFixed,
                                     Condition c) {
  MOZ_ASSERT(vd.isFloat());
  uint32_t sx = 0x1;
  vfp_size sf = vd.isDouble() ? IsDouble : IsSingle;
  int32_t imm5 = fixedPoint;
  imm5 = (sx ? 32 : 16) - imm5;
  MOZ_ASSERT(imm5 >= 0);
  imm5 = imm5 >> 1 | (imm5 & 1) << 5;
  return writeVFPInst(sf, 0x02BA0040 | VD(vd) | toFixed << 18 | sx << 7 |
                              (!isSigned) << 16 | imm5 | c);
}

// Transfer between VFP and memory.
static uint32_t EncodeVdtr(LoadStore ls, VFPRegister vd, VFPAddr addr,
                           Assembler::Condition c) {
  return ls | 0x01000000 | addr.encode() | VD(vd) | c;
}

BufferOffset Assembler::as_vdtr(
    LoadStore ls, VFPRegister vd, VFPAddr addr,
    Condition c /* vfp doesn't have a wb option */) {
  vfp_size sz = vd.isDouble() ? IsDouble : IsSingle;
  return writeVFPInst(sz, EncodeVdtr(ls, vd, addr, c));
}

/* static */
void Assembler::as_vdtr_patch(LoadStore ls, VFPRegister vd, VFPAddr addr,
                              Condition c, uint32_t* dest) {
  vfp_size sz = vd.isDouble() ? IsDouble : IsSingle;
  WriteVFPInstStatic(sz, EncodeVdtr(ls, vd, addr, c), dest);
}

// VFP's ldm/stm work differently from the standard arm ones. You can only
// transfer a range.

BufferOffset Assembler::as_vdtm(LoadStore st, Register rn, VFPRegister vd,
                                int length,
                                /* also has update conditions */ Condition c) {
  MOZ_ASSERT(length <= 16 && length >= 0);
  vfp_size sz = vd.isDouble() ? IsDouble : IsSingle;

  if (vd.isDouble()) {
    length *= 2;
  }

  return writeVFPInst(sz, dtmLoadStore | RN(rn) | VD(vd) | length | dtmMode |
                              dtmUpdate | dtmCond);
}

BufferOffset Assembler::as_vldr_unaligned(VFPRegister vd, Register rn) {
  MOZ_ASSERT(HasNEON());
  if (vd.isDouble()) {
    // vld1 (multiple single elements) with align=0, size=3, numregs=1
    return writeInst(0xF42007CF | RN(rn) | VD(vd));
  }
  // vld1 (single element to single lane) with index=0, size=2
  MOZ_ASSERT(vd.isFloat());
  MOZ_ASSERT((vd.code() & 1) == 0);
  return writeInst(0xF4A0080F | RN(rn) | VD(vd.asDouble()));
}

BufferOffset Assembler::as_vstr_unaligned(VFPRegister vd, Register rn) {
  MOZ_ASSERT(HasNEON());
  if (vd.isDouble()) {
    // vst1 (multiple single elements) with align=0, size=3, numregs=1
    return writeInst(0xF40007CF | RN(rn) | VD(vd));
  }
  // vst1 (single element from one lane) with index=0, size=2
  MOZ_ASSERT(vd.isFloat());
  MOZ_ASSERT((vd.code() & 1) == 0);
  return writeInst(0xF480080F | RN(rn) | VD(vd.asDouble()));
}

BufferOffset Assembler::as_vimm(VFPRegister vd, VFPImm imm, Condition c) {
  MOZ_ASSERT(imm.isValid());
  vfp_size sz = vd.isDouble() ? IsDouble : IsSingle;
  return writeVFPInst(sz, c | imm.encode() | VD(vd) | 0x02B00000);
}

BufferOffset Assembler::as_vmrs(Register r, Condition c) {
  return writeInst(c | 0x0ef10a10 | RT(r));
}

BufferOffset Assembler::as_vmsr(Register r, Condition c) {
  return writeInst(c | 0x0ee10a10 | RT(r));
}

bool Assembler::nextLink(BufferOffset b, BufferOffset* next) {
  Instruction branch = *editSrc(b);
  MOZ_ASSERT(branch.is<InstBranchImm>());

  BOffImm destOff;
  branch.as<InstBranchImm>()->extractImm(&destOff);
  if (destOff.isInvalid()) {
    return false;
  }

  // Propagate the next link back to the caller, by constructing a new
  // BufferOffset into the space they provided.
  new (next) BufferOffset(destOff.decode());
  return true;
}

void Assembler::bind(Label* label, BufferOffset boff) {
#ifdef JS_DISASM_ARM
  spew_.spewBind(label);
#endif
  if (oom()) {
    // Ensure we always bind the label. This matches what we do on
    // x86/x64 and silences the assert in ~Label.
    label->bind(0);
    return;
  }

  if (label->used()) {
    bool more;
    // If our caller didn't give us an explicit target to bind to then we
    // want to bind to the location of the next instruction.
    BufferOffset dest = boff.assigned() ? boff : nextOffset();
    BufferOffset b(label);
    do {
      BufferOffset next;
      more = nextLink(b, &next);
      Instruction branch = *editSrc(b);
      Condition c = branch.extractCond();
      BOffImm offset = dest.diffB<BOffImm>(b);
      MOZ_RELEASE_ASSERT(!offset.isInvalid(),
                         "Buffer size limit should prevent this");
      if (branch.is<InstBImm>()) {
        as_b(offset, c, b);
      } else if (branch.is<InstBLImm>()) {
        as_bl(offset, c, b);
      } else {
        MOZ_CRASH("crazy fixup!");
      }
      b = next;
    } while (more);
  }
  label->bind(nextOffset().getOffset());
  MOZ_ASSERT(!oom());
}

void Assembler::retarget(Label* label, Label* target) {
#ifdef JS_DISASM_ARM
  spew_.spewRetarget(label, target);
#endif
  if (label->used() && !oom()) {
    if (target->bound()) {
      bind(label, BufferOffset(target));
    } else if (target->used()) {
      // The target is not bound but used. Prepend label's branch list
      // onto target's.
      BufferOffset labelBranchOffset(label);
      BufferOffset next;

      // Find the head of the use chain for label.
      while (nextLink(labelBranchOffset, &next)) {
        labelBranchOffset = next;
      }

      // Then patch the head of label's use chain to the tail of target's
      // use chain, prepending the entire use chain of target.
      Instruction branch = *editSrc(labelBranchOffset);
      Condition c = branch.extractCond();
      int32_t prev = target->offset();
      target->use(label->offset());
      if (branch.is<InstBImm>()) {
        as_b(BOffImm(prev), c, labelBranchOffset);
      } else if (branch.is<InstBLImm>()) {
        as_bl(BOffImm(prev), c, labelBranchOffset);
      } else {
        MOZ_CRASH("crazy fixup!");
      }
    } else {
      // The target is unbound and unused. We can just take the head of
      // the list hanging off of label, and dump that into target.
      target->use(label->offset());
    }
  }
  label->reset();
}

static int stopBKPT = -1;
void Assembler::as_bkpt() {
  // This is a count of how many times a breakpoint instruction has been
  // generated. It is embedded into the instruction for debugging
  // purposes. Gdb will print "bkpt xxx" when you attempt to dissassemble a
  // breakpoint with the number xxx embedded into it. If this breakpoint is
  // being hit, then you can run (in gdb):
  //  >b dbg_break
  //  >b main
  //  >commands
  //  >set stopBKPT = xxx
  //  >c
  //  >end
  // which will set a breakpoint on the function dbg_break above set a
  // scripted breakpoint on main that will set the (otherwise unmodified)
  // value to the number of the breakpoint, so dbg_break will actuall be
  // called and finally, when you run the executable, execution will halt when
  // that breakpoint is generated.
  static int hit = 0;
  if (stopBKPT == hit) {
    dbg_break();
  }
  writeInst(0xe1200070 | (hit & 0xf) | ((hit & 0xfff0) << 4));
  hit++;
}

BufferOffset Assembler::as_illegal_trap() {
  // Encoding of the permanently-undefined 'udf' instruction, with the imm16
  // set to 0.
  return writeInst(0xe7f000f0);
}

void Assembler::flushBuffer() { m_buffer.flushPool(); }

void Assembler::enterNoPool(size_t maxInst) { m_buffer.enterNoPool(maxInst); }

void Assembler::leaveNoPool() { m_buffer.leaveNoPool(); }

void Assembler::enterNoNops() { m_buffer.enterNoNops(); }

void Assembler::leaveNoNops() { m_buffer.leaveNoNops(); }

struct PoolHeader : Instruction {
  struct Header {
    // The size should take into account the pool header.
    // The size is in units of Instruction (4 bytes), not byte.
    uint32_t size : 15;
    uint32_t isNatural : 1;
    uint32_t ONES : 16;

    Header(int size_, bool isNatural_)
        : size(size_), isNatural(isNatural_), ONES(0xffff) {}

    explicit Header(const Instruction* i) {
      static_assert(sizeof(Header) == sizeof(uint32_t));
      memcpy(this, i, sizeof(Header));
      MOZ_ASSERT(ONES == 0xffff);
    }

    uint32_t raw() const {
      static_assert(sizeof(Header) == sizeof(uint32_t));
      uint32_t dest;
      memcpy(&dest, this, sizeof(Header));
      return dest;
    }
  };

  PoolHeader(int size_, bool isNatural_)
      : Instruction(Header(size_, isNatural_).raw(), true) {}

  uint32_t size() const {
    Header tmp(this);
    return tmp.size;
  }
  uint32_t isNatural() const {
    Header tmp(this);
    return tmp.isNatural;
  }

  static bool IsTHIS(const Instruction& i) {
    return (*i.raw() & 0xffff0000) == 0xffff0000;
  }
  static const PoolHeader* AsTHIS(const Instruction& i) {
    if (!IsTHIS(i)) {
      return nullptr;
    }
    return static_cast<const PoolHeader*>(&i);
  }
};

void Assembler::WritePoolHeader(uint8_t* start, Pool* p, bool isNatural) {
  static_assert(sizeof(PoolHeader) == 4,
                "PoolHandler must have the correct size.");
  uint8_t* pool = start + 4;
  // Go through the usual rigmarole to get the size of the pool.
  pool += p->getPoolSize();
  uint32_t size = pool - start;
  MOZ_ASSERT((size & 3) == 0);
  size = size >> 2;
  MOZ_ASSERT(size < (1 << 15));
  PoolHeader header(size, isNatural);
  *(PoolHeader*)start = header;
}

// The size of an arbitrary 32-bit call in the instruction stream. On ARM this
// sequence is |pc = ldr pc - 4; imm32| given that we never reach the imm32.
uint32_t Assembler::PatchWrite_NearCallSize() { return sizeof(uint32_t); }

void Assembler::PatchWrite_NearCall(CodeLocationLabel start,
                                    CodeLocationLabel toCall) {
  Instruction* inst = (Instruction*)start.raw();
  // Overwrite whatever instruction used to be here with a call. Since the
  // destination is in the same function, it will be within range of the
  // 24 << 2 byte bl instruction.
  uint8_t* dest = toCall.raw();
  new (inst) InstBLImm(BOffImm(dest - (uint8_t*)inst), Always);
}

void Assembler::PatchDataWithValueCheck(CodeLocationLabel label,
                                        PatchedImmPtr newValue,
                                        PatchedImmPtr expectedValue) {
  Instruction* ptr = reinterpret_cast<Instruction*>(label.raw());

  Register dest;
  Assembler::RelocStyle rs;

  {
    InstructionIterator iter(ptr);
    DebugOnly<const uint32_t*> val = GetPtr32Target(iter, &dest, &rs);
    MOZ_ASSERT(uint32_t((const uint32_t*)val) == uint32_t(expectedValue.value));
  }

  // Patch over actual instructions.
  {
    InstructionIterator iter(ptr);
    MacroAssembler::ma_mov_patch(Imm32(int32_t(newValue.value)), dest, Always,
                                 rs, iter);
  }
}

void Assembler::PatchDataWithValueCheck(CodeLocationLabel label,
                                        ImmPtr newValue, ImmPtr expectedValue) {
  PatchDataWithValueCheck(label, PatchedImmPtr(newValue.value),
                          PatchedImmPtr(expectedValue.value));
}

// This just stomps over memory with 32 bits of raw data. Its purpose is to
// overwrite the call of JITed code with 32 bits worth of an offset. This will
// is only meant to function on code that has been invalidated, so it should be
// totally safe. Since that instruction will never be executed again, a ICache
// flush should not be necessary
void Assembler::PatchWrite_Imm32(CodeLocationLabel label, Imm32 imm) {
  // Raw is going to be the return address.
  uint32_t* raw = (uint32_t*)label.raw();
  // Overwrite the 4 bytes before the return address, which will end up being
  // the call instruction.
  *(raw - 1) = imm.value;
}

uint8_t* Assembler::NextInstruction(uint8_t* inst_, uint32_t* count) {
  if (count != nullptr) {
    *count += sizeof(Instruction);
  }

  InstructionIterator iter(reinterpret_cast<Instruction*>(inst_));
  return reinterpret_cast<uint8_t*>(iter.next());
}

static bool InstIsGuard(Instruction* inst, const PoolHeader** ph) {
  Assembler::Condition c = inst->extractCond();
  if (c != Assembler::Always) {
    return false;
  }
  if (!(inst->is<InstBXReg>() || inst->is<InstBImm>())) {
    return false;
  }
  // See if the next instruction is a pool header.
  *ph = (inst + 1)->as<const PoolHeader>();
  return *ph != nullptr;
}

static bool InstIsGuard(BufferInstructionIterator& iter,
                        const PoolHeader** ph) {
  Instruction* inst = iter.cur();
  Assembler::Condition c = inst->extractCond();
  if (c != Assembler::Always) {
    return false;
  }
  if (!(inst->is<InstBXReg>() || inst->is<InstBImm>())) {
    return false;
  }
  // See if the next instruction is a pool header.
  *ph = iter.peek()->as<const PoolHeader>();
  return *ph != nullptr;
}

template <class T>
static bool InstIsBNop(const T& iter) {
  // In some special situations, it is necessary to insert a NOP into the
  // instruction stream that nobody knows about, since nobody should know
  // about it, make sure it gets skipped when Instruction::next() is called.
  // this generates a very specific nop, namely a branch to the next
  // instruction.
  const Instruction* cur = iter.cur();
  Assembler::Condition c = cur->extractCond();
  if (c != Assembler::Always) {
    return false;
  }
  if (!cur->is<InstBImm>()) {
    return false;
  }
  InstBImm* b = cur->as<InstBImm>();
  BOffImm offset;
  b->extractImm(&offset);
  return offset.decode() == 4;
}

Instruction* InstructionIterator::maybeSkipAutomaticInstructions() {
  // If the current instruction was automatically-inserted, skip past it.
  const PoolHeader* ph;

  // Loop until an intentionally-placed instruction is found.
  while (true) {
    if (InstIsGuard(cur(), &ph)) {
      // Don't skip a natural guard.
      if (ph->isNatural()) {
        return cur();
      }
      advanceRaw(1 + ph->size());
    } else if (InstIsBNop<InstructionIterator>(*this)) {
      advanceRaw(1);
    } else {
      return cur();
    }
  }
}

Instruction* BufferInstructionIterator::maybeSkipAutomaticInstructions() {
  const PoolHeader* ph;
  // If this is a guard, and the next instruction is a header, always work
  // around the pool. If it isn't a guard, then start looking ahead.
  if (InstIsGuard(*this, &ph)) {
    // Don't skip a natural guard.
    if (ph->isNatural()) {
      return cur();
    }
    advance(sizeof(Instruction) * ph->size());
    return next();
  }
  if (InstIsBNop<BufferInstructionIterator>(*this)) {
    return next();
  }
  return cur();
}

// Cases to be handled:
// 1) no pools or branches in sight => return this+1
// 2) branch to next instruction => return this+2, because a nop needed to be
//    inserted into the stream.
// 3) this+1 is an artificial guard for a pool => return first instruction
//    after the pool
// 4) this+1 is a natural guard => return the branch
// 5) this is a branch, right before a pool => return first instruction after
//    the pool
// in assembly form:
// 1) add r0, r0, r0 <= this
//    add r1, r1, r1 <= returned value
//    add r2, r2, r2
//
// 2) add r0, r0, r0 <= this
//    b foo
//    foo:
//    add r2, r2, r2 <= returned value
//
// 3) add r0, r0, r0 <= this
//    b after_pool;
//    .word 0xffff0002  # bit 15 being 0 indicates that the branch was not
//                      # requested by the assembler
//    0xdeadbeef        # the 2 indicates that there is 1 pool entry, and the
//                      # pool header
//    add r4, r4, r4 <= returned value
// 4) add r0, r0, r0 <= this
//    b after_pool  <= returned value
//    .word 0xffff8002  # bit 15 being 1 indicates that the branch was
//                      # requested by the assembler
//    0xdeadbeef
//    add r4, r4, r4
// 5) b after_pool  <= this
//    .word 0xffff8002  # bit 15 has no bearing on the returned value
//    0xdeadbeef
//    add r4, r4, r4  <= returned value

Instruction* InstructionIterator::next() {
  const PoolHeader* ph;

  // If the current instruction is followed by a pool header,
  // move past the current instruction and the pool.
  if (InstIsGuard(cur(), &ph)) {
    advanceRaw(1 + ph->size());
    return maybeSkipAutomaticInstructions();
  }

  // The next instruction is then known to not be a PoolHeader.
  advanceRaw(1);
  return maybeSkipAutomaticInstructions();
}

void Assembler::ToggleToJmp(CodeLocationLabel inst_) {
  uint32_t* ptr = (uint32_t*)inst_.raw();

  DebugOnly<Instruction*> inst = (Instruction*)inst_.raw();
  MOZ_ASSERT(inst->is<InstCMP>());

  // Zero bits 20-27, then set 24-27 to be correct for a branch.
  // 20-23 will be party of the B's immediate, and should be 0.
  *ptr = (*ptr & ~(0xff << 20)) | (0xa0 << 20);
}

void Assembler::ToggleToCmp(CodeLocationLabel inst_) {
  uint32_t* ptr = (uint32_t*)inst_.raw();

  DebugOnly<Instruction*> inst = (Instruction*)inst_.raw();
  MOZ_ASSERT(inst->is<InstBImm>());

  // Ensure that this masking operation doesn't affect the offset of the
  // branch instruction when it gets toggled back.
  MOZ_ASSERT((*ptr & (0xf << 20)) == 0);

  // Also make sure that the CMP is valid. Part of having a valid CMP is that
  // all of the bits describing the destination in most ALU instructions are
  // all unset (looks like it is encoding r0).
  MOZ_ASSERT(toRD(*inst) == r0);

  // Zero out bits 20-27, then set them to be correct for a compare.
  *ptr = (*ptr & ~(0xff << 20)) | (0x35 << 20);
}

void Assembler::ToggleCall(CodeLocationLabel inst_, bool enabled) {
  InstructionIterator iter(reinterpret_cast<Instruction*>(inst_.raw()));
  MOZ_ASSERT(iter.cur()->is<InstMovW>() || iter.cur()->is<InstLDR>());

  if (iter.cur()->is<InstMovW>()) {
    // If it looks like the start of a movw/movt sequence, then make sure we
    // have all of it (and advance the iterator past the full sequence).
    iter.next();
    MOZ_ASSERT(iter.cur()->is<InstMovT>());
  }

  iter.next();
  MOZ_ASSERT(iter.cur()->is<InstNOP>() || iter.cur()->is<InstBLXReg>());

  if (enabled == iter.cur()->is<InstBLXReg>()) {
    // Nothing to do.
    return;
  }

  Instruction* inst = iter.cur();

  if (enabled) {
    *inst = InstBLXReg(ScratchRegister, Always);
  } else {
    *inst = InstNOP();
  }
}

size_t Assembler::ToggledCallSize(uint8_t* code) {
  InstructionIterator iter(reinterpret_cast<Instruction*>(code));
  MOZ_ASSERT(iter.cur()->is<InstMovW>() || iter.cur()->is<InstLDR>());

  if (iter.cur()->is<InstMovW>()) {
    // If it looks like the start of a movw/movt sequence, then make sure we
    // have all of it (and advance the iterator past the full sequence).
    iter.next();
    MOZ_ASSERT(iter.cur()->is<InstMovT>());
  }

  iter.next();
  MOZ_ASSERT(iter.cur()->is<InstNOP>() || iter.cur()->is<InstBLXReg>());
  return uintptr_t(iter.cur()) + 4 - uintptr_t(code);
}

uint32_t Assembler::NopFill = 0;

uint32_t Assembler::GetNopFill() {
  static bool isSet = false;
  if (!isSet) {
    char* fillStr = getenv("ARM_ASM_NOP_FILL");
    uint32_t fill;
    if (fillStr && sscanf(fillStr, "%u", &fill) == 1) {
      NopFill = fill;
    }
    if (NopFill > 8) {
      MOZ_CRASH("Nop fill > 8 is not supported");
    }
    isSet = true;
  }
  return NopFill;
}

uint32_t Assembler::AsmPoolMaxOffset = 1024;

uint32_t Assembler::GetPoolMaxOffset() {
  static bool isSet = false;
  if (!isSet) {
    char* poolMaxOffsetStr = getenv("ASM_POOL_MAX_OFFSET");
    uint32_t poolMaxOffset;
    if (poolMaxOffsetStr &&
        sscanf(poolMaxOffsetStr, "%u", &poolMaxOffset) == 1) {
      AsmPoolMaxOffset = poolMaxOffset;
    }
    isSet = true;
  }
  return AsmPoolMaxOffset;
}

SecondScratchRegisterScope::SecondScratchRegisterScope(MacroAssembler& masm)
    : AutoRegisterScope(masm, masm.getSecondScratchReg()) {}

#ifdef JS_DISASM_ARM

/* static */
void Assembler::disassembleInstruction(const Instruction* i,
                                       DisasmBuffer& buffer) {
  disasm::NameConverter converter;
  disasm::Disassembler dasm(converter);
  uint8_t* loc = reinterpret_cast<uint8_t*>(const_cast<uint32_t*>(i->raw()));
  dasm.InstructionDecode(buffer, loc);
}

void Assembler::initDisassembler() {
  // The line is normally laid out like this:
  //
  // xxxxxxxx        ldr r, op   ; comment
  //
  // where xx...x is the instruction bit pattern.
  //
  // Labels are laid out by themselves to line up with the instructions above
  // and below:
  //
  //            nnnn:
  //
  // Branch targets are normally on the same line as the branch instruction,
  // but when they cannot be they will be on a line by themselves, indented
  // significantly:
  //
  //                     -> label

  spew_.setLabelIndent("          ");             // 10
  spew_.setTargetIndent("                    ");  // 20
}

void Assembler::finishDisassembler() { spew_.spewOrphans(); }

// Labels are named as they are encountered by adding names to a
// table, using the Label address as the key.  This is made tricky by
// the (memory for) Label objects being reused, but reused label
// objects are recognizable from being marked as not used or not
// bound.  See spew_.refLabel().
//
// In a number of cases there is no information about the target, and
// we just end up printing "patchable constant load to PC".  This is
// true especially for jumps to bailout handlers (which have no
// names).  See allocLiteralLoadEntry() and its callers.  In some cases
// (loop back edges) some information about the intended target may be
// propagated from higher levels, and if so it's printed here.

void Assembler::spew(Instruction* i) {
  if (spew_.isDisabled() || !i) {
    return;
  }

  DisasmBuffer buffer;
  disassembleInstruction(i, buffer);
  spew_.spew("%s", buffer.start());
}

// If a target label is known, always print that and do not attempt to
// disassemble the branch operands, as they will often be encoding
// metainformation (pointers for a chain of jump instructions), and
// not actual branch targets.

void Assembler::spewBranch(Instruction* i, const LabelDoc& target) {
  if (spew_.isDisabled() || !i) {
    return;
  }

  DisasmBuffer buffer;
  disassembleInstruction(i, buffer);

  char labelBuf[128];
  labelBuf[0] = 0;

  bool haveTarget = target.valid;
  if (!haveTarget) {
    SprintfLiteral(labelBuf, "  -> (link-time target)");
  }

  if (InstBranchImm::IsTHIS(*i)) {
    InstBranchImm* bimm = InstBranchImm::AsTHIS(*i);
    BOffImm destOff;
    bimm->extractImm(&destOff);
    if (destOff.isInvalid() || haveTarget) {
      // The target information in the instruction is likely garbage, so remove
      // it. The target label will in any case be printed if we have it.
      //
      // The format of the instruction disassembly is [0-9a-f]{8}\s+\S+\s+.*,
      // where the \S+ string is the opcode.  Strip everything after the opcode,
      // and attach the label if we have it.
      int i;
      for (i = 8; i < buffer.length() && buffer[i] == ' '; i++) {
      }
      for (; i < buffer.length() && buffer[i] != ' '; i++) {
      }
      buffer[i] = 0;
      if (haveTarget) {
        SprintfLiteral(labelBuf, "  -> %d%s", target.doc,
                       !target.bound ? "f" : "");
        haveTarget = false;
      }
    }
  }
  spew_.spew("%s%s", buffer.start(), labelBuf);

  if (haveTarget) {
    spew_.spewRef(target);
  }
}

void Assembler::spewLiteralLoad(PoolHintPun& php, bool loadToPC,
                                const Instruction* i, const LiteralDoc& doc) {
  if (spew_.isDisabled()) {
    return;
  }

  char litbuf[2048];
  spew_.formatLiteral(doc, litbuf, sizeof(litbuf));

  // See patchConstantPoolLoad, above.  We assemble the instruction into a
  // buffer with a zero offset, as documentation, but the offset will be
  // patched later.

  uint32_t inst;
  PoolHintData& data = php.phd;
  switch (php.phd.getLoadType()) {
    case PoolHintData::PoolDTR:
      Assembler::as_dtr_patch(IsLoad, 32, Offset, data.getReg(),
                              DTRAddr(pc, DtrOffImm(0)), data.getCond(), &inst);
      break;
    case PoolHintData::PoolBranch:
      if (data.isValidPoolHint()) {
        Assembler::as_dtr_patch(IsLoad, 32, Offset, pc,
                                DTRAddr(pc, DtrOffImm(0)), data.getCond(),
                                &inst);
      }
      break;
    case PoolHintData::PoolVDTR:
      Assembler::as_vdtr_patch(IsLoad, data.getVFPReg(),
                               VFPAddr(pc, VFPOffImm(0)), data.getCond(),
                               &inst);
      break;

    default:
      MOZ_CRASH();
  }

  DisasmBuffer buffer;
  disasm::NameConverter converter;
  disasm::Disassembler dasm(converter);
  dasm.InstructionDecode(buffer, reinterpret_cast<uint8_t*>(&inst));
  spew_.spew("%s    ; .const %s", buffer.start(), litbuf);
}

#endif  // JS_DISASM_ARM