Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2296 insertions, 0 deletions

diff --git a/js/src/jit/arm/Assembler-arm.h b/js/src/jit/arm/Assembler-arm.h
new file mode 100644
index 0000000000..fdbac15a80
--- /dev/null
+++ b/js/src/jit/arm/Assembler-arm.h
@@ -0,0 +1,2296 @@
+/* -*- 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/. */
+
+#ifndef jit_arm_Assembler_arm_h
+#define jit_arm_Assembler_arm_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/MathAlgorithms.h"
+
+#include <algorithm>
+#include <iterator>
+#include <type_traits>
+
+#include "jit/arm/Architecture-arm.h"
+#include "jit/arm/disasm/Disasm-arm.h"
+#include "jit/CompactBuffer.h"
+#include "jit/JitCode.h"
+#include "jit/shared/Assembler-shared.h"
+#include "jit/shared/Disassembler-shared.h"
+#include "jit/shared/IonAssemblerBufferWithConstantPools.h"
+#include "wasm/WasmTypeDecls.h"
+
+union PoolHintPun;
+
+namespace js {
+namespace jit {
+
+using LiteralDoc = DisassemblerSpew::LiteralDoc;
+using LabelDoc = DisassemblerSpew::LabelDoc;
+
+// NOTE: there are duplicates in this list! Sometimes we want to specifically
+// refer to the link register as a link register (bl lr is much clearer than bl
+// r14). HOWEVER, this register can easily be a gpr when it is not busy holding
+// the return address.
+static constexpr Register r0{Registers::r0};
+static constexpr Register r1{Registers::r1};
+static constexpr Register r2{Registers::r2};
+static constexpr Register r3{Registers::r3};
+static constexpr Register r4{Registers::r4};
+static constexpr Register r5{Registers::r5};
+static constexpr Register r6{Registers::r6};
+static constexpr Register r7{Registers::r7};
+static constexpr Register r8{Registers::r8};
+static constexpr Register r9{Registers::r9};
+static constexpr Register r10{Registers::r10};
+static constexpr Register r11{Registers::r11};
+static constexpr Register r12{Registers::ip};
+static constexpr Register ip{Registers::ip};
+static constexpr Register sp{Registers::sp};
+static constexpr Register r14{Registers::lr};
+static constexpr Register lr{Registers::lr};
+static constexpr Register pc{Registers::pc};
+
+static constexpr Register ScratchRegister{Registers::ip};
+
+// Helper class for ScratchRegister usage. Asserts that only one piece
+// of code thinks it has exclusive ownership of the scratch register.
+struct ScratchRegisterScope : public AutoRegisterScope {
+  explicit ScratchRegisterScope(MacroAssembler& masm)
+      : AutoRegisterScope(masm, ScratchRegister) {}
+};
+
+struct SecondScratchRegisterScope : public AutoRegisterScope {
+  explicit SecondScratchRegisterScope(MacroAssembler& masm);
+};
+
+static constexpr Register OsrFrameReg = r3;
+static constexpr Register CallTempReg0 = r5;
+static constexpr Register CallTempReg1 = r6;
+static constexpr Register CallTempReg2 = r7;
+static constexpr Register CallTempReg3 = r8;
+static constexpr Register CallTempReg4 = r0;
+static constexpr Register CallTempReg5 = r1;
+
+static constexpr Register IntArgReg0 = r0;
+static constexpr Register IntArgReg1 = r1;
+static constexpr Register IntArgReg2 = r2;
+static constexpr Register IntArgReg3 = r3;
+static constexpr Register HeapReg = r10;
+static constexpr Register CallTempNonArgRegs[] = {r5, r6, r7, r8};
+static const uint32_t NumCallTempNonArgRegs = std::size(CallTempNonArgRegs);
+
+// These register assignments for the 64-bit atomic ops are frequently too
+// constraining, but we have no way of expressing looser constraints to the
+// register allocator.
+
+// CompareExchange: Any two odd/even pairs would do for `new` and `out`, and any
+// pair would do for `old`, so long as none of them overlap.
+
+static constexpr Register CmpXchgOldLo = r4;
+static constexpr Register CmpXchgOldHi = r5;
+static constexpr Register64 CmpXchgOld64 =
+    Register64(CmpXchgOldHi, CmpXchgOldLo);
+static constexpr Register CmpXchgNewLo = IntArgReg2;
+static constexpr Register CmpXchgNewHi = IntArgReg3;
+static constexpr Register64 CmpXchgNew64 =
+    Register64(CmpXchgNewHi, CmpXchgNewLo);
+static constexpr Register CmpXchgOutLo = IntArgReg0;
+static constexpr Register CmpXchgOutHi = IntArgReg1;
+static constexpr Register64 CmpXchgOut64 =
+    Register64(CmpXchgOutHi, CmpXchgOutLo);
+
+// Exchange: Any two non-equal odd/even pairs would do for `new` and `out`.
+
+static constexpr Register XchgNewLo = IntArgReg2;
+static constexpr Register XchgNewHi = IntArgReg3;
+static constexpr Register64 XchgNew64 = Register64(XchgNewHi, XchgNewLo);
+static constexpr Register XchgOutLo = IntArgReg0;
+static constexpr Register XchgOutHi = IntArgReg1;
+
+// Atomic rmw operations: Any two odd/even pairs would do for `tmp` and `out`,
+// and any pair would do for `val`, so long as none of them overlap.
+
+static constexpr Register FetchOpValLo = r4;
+static constexpr Register FetchOpValHi = r5;
+static constexpr Register64 FetchOpVal64 =
+    Register64(FetchOpValHi, FetchOpValLo);
+static constexpr Register FetchOpTmpLo = IntArgReg2;
+static constexpr Register FetchOpTmpHi = IntArgReg3;
+static constexpr Register64 FetchOpTmp64 =
+    Register64(FetchOpTmpHi, FetchOpTmpLo);
+static constexpr Register FetchOpOutLo = IntArgReg0;
+static constexpr Register FetchOpOutHi = IntArgReg1;
+static constexpr Register64 FetchOpOut64 =
+    Register64(FetchOpOutHi, FetchOpOutLo);
+
+class ABIArgGenerator {
+  unsigned intRegIndex_;
+  unsigned floatRegIndex_;
+  uint32_t stackOffset_;
+  ABIArg current_;
+
+  // ARM can either use HardFp (use float registers for float arguments), or
+  // SoftFp (use general registers for float arguments) ABI.  We keep this
+  // switch as a runtime switch because wasm always use the HardFp back-end
+  // while the calls to native functions have to use the one provided by the
+  // system.
+  bool useHardFp_;
+
+  ABIArg softNext(MIRType argType);
+  ABIArg hardNext(MIRType argType);
+
+ public:
+  ABIArgGenerator();
+
+  void setUseHardFp(bool useHardFp) {
+    MOZ_ASSERT(intRegIndex_ == 0 && floatRegIndex_ == 0);
+    useHardFp_ = useHardFp;
+  }
+  ABIArg next(MIRType argType);
+  ABIArg& current() { return current_; }
+  uint32_t stackBytesConsumedSoFar() const { return stackOffset_; }
+  void increaseStackOffset(uint32_t bytes) { stackOffset_ += bytes; }
+};
+
+bool IsUnaligned(const wasm::MemoryAccessDesc& access);
+
+// These registers may be volatile or nonvolatile.
+static constexpr Register ABINonArgReg0 = r4;
+static constexpr Register ABINonArgReg1 = r5;
+static constexpr Register ABINonArgReg2 = r6;
+static constexpr Register ABINonArgReg3 = r7;
+
+// This register may be volatile or nonvolatile. Avoid d15 which is the
+// ScratchDoubleReg_.
+static constexpr FloatRegister ABINonArgDoubleReg{FloatRegisters::d8,
+                                                  VFPRegister::Double};
+
+// These registers may be volatile or nonvolatile.
+// Note: these three registers are all guaranteed to be different
+static constexpr Register ABINonArgReturnReg0 = r4;
+static constexpr Register ABINonArgReturnReg1 = r5;
+static constexpr Register ABINonVolatileReg = r6;
+
+// This register is guaranteed to be clobberable during the prologue and
+// epilogue of an ABI call which must preserve both ABI argument, return
+// and non-volatile registers.
+static constexpr Register ABINonArgReturnVolatileReg = lr;
+
+// Instance pointer argument register for WebAssembly functions. This must not
+// alias any other register used for passing function arguments or return
+// values. Preserved by WebAssembly functions.
+static constexpr Register InstanceReg = r9;
+
+// Registers used for wasm table calls. These registers must be disjoint
+// from the ABI argument registers, InstanceReg and each other.
+static constexpr Register WasmTableCallScratchReg0 = ABINonArgReg0;
+static constexpr Register WasmTableCallScratchReg1 = ABINonArgReg1;
+static constexpr Register WasmTableCallSigReg = ABINonArgReg2;
+static constexpr Register WasmTableCallIndexReg = ABINonArgReg3;
+
+// Registers used for ref calls.
+static constexpr Register WasmCallRefCallScratchReg0 = ABINonArgReg0;
+static constexpr Register WasmCallRefCallScratchReg1 = ABINonArgReg1;
+static constexpr Register WasmCallRefReg = ABINonArgReg3;
+
+// Register used as a scratch along the return path in the fast js -> wasm stub
+// code.  This must not overlap ReturnReg, JSReturnOperand, or InstanceReg.
+// It must be a volatile register.
+static constexpr Register WasmJitEntryReturnScratch = r5;
+
+static constexpr Register PreBarrierReg = r1;
+
+static constexpr Register InterpreterPCReg = r9;
+
+static constexpr Register InvalidReg{Registers::invalid_reg};
+static constexpr FloatRegister InvalidFloatReg;
+
+static constexpr Register JSReturnReg_Type = r3;
+static constexpr Register JSReturnReg_Data = r2;
+static constexpr Register StackPointer = sp;
+static constexpr Register FramePointer = r11;
+static constexpr Register ReturnReg = r0;
+static constexpr Register64 ReturnReg64(r1, r0);
+
+// The attribute '__value_in_regs' alters the calling convention of a function
+// so that a structure of up to four elements can be returned via the argument
+// registers rather than being written to memory.
+static constexpr Register ReturnRegVal0 = IntArgReg0;
+static constexpr Register ReturnRegVal1 = IntArgReg1;
+static constexpr Register ReturnRegVal2 = IntArgReg2;
+static constexpr Register ReturnRegVal3 = IntArgReg3;
+
+static constexpr FloatRegister ReturnFloat32Reg = {FloatRegisters::d0,
+                                                   VFPRegister::Single};
+static constexpr FloatRegister ReturnDoubleReg = {FloatRegisters::d0,
+                                                  VFPRegister::Double};
+static constexpr FloatRegister ReturnSimd128Reg = InvalidFloatReg;
+static constexpr FloatRegister ScratchFloat32Reg_ = {FloatRegisters::s30,
+                                                     VFPRegister::Single};
+static constexpr FloatRegister ScratchDoubleReg_ = {FloatRegisters::d15,
+                                                    VFPRegister::Double};
+static constexpr FloatRegister ScratchSimd128Reg = InvalidFloatReg;
+static constexpr FloatRegister ScratchUIntReg = {FloatRegisters::d15,
+                                                 VFPRegister::UInt};
+static constexpr FloatRegister ScratchIntReg = {FloatRegisters::d15,
+                                                VFPRegister::Int};
+
+// Do not reference ScratchFloat32Reg_ directly, use ScratchFloat32Scope
+// instead.
+struct ScratchFloat32Scope : public AutoFloatRegisterScope {
+  explicit ScratchFloat32Scope(MacroAssembler& masm)
+      : AutoFloatRegisterScope(masm, ScratchFloat32Reg_) {}
+};
+
+// Do not reference ScratchDoubleReg_ directly, use ScratchDoubleScope instead.
+struct ScratchDoubleScope : public AutoFloatRegisterScope {
+  explicit ScratchDoubleScope(MacroAssembler& masm)
+      : AutoFloatRegisterScope(masm, ScratchDoubleReg_) {}
+};
+
+// Registers used by RegExpMatcher and RegExpExecMatch stubs (do not use
+// JSReturnOperand).
+static constexpr Register RegExpMatcherRegExpReg = CallTempReg0;
+static constexpr Register RegExpMatcherStringReg = CallTempReg1;
+static constexpr Register RegExpMatcherLastIndexReg = CallTempReg2;
+
+// Registers used by RegExpExecTest stub (do not use ReturnReg).
+static constexpr Register RegExpExecTestRegExpReg = CallTempReg0;
+static constexpr Register RegExpExecTestStringReg = CallTempReg1;
+
+// Registers used by RegExpSearcher stub (do not use ReturnReg).
+static constexpr Register RegExpSearcherRegExpReg = CallTempReg0;
+static constexpr Register RegExpSearcherStringReg = CallTempReg1;
+static constexpr Register RegExpSearcherLastIndexReg = CallTempReg2;
+
+static constexpr FloatRegister d0 = {FloatRegisters::d0, VFPRegister::Double};
+static constexpr FloatRegister d1 = {FloatRegisters::d1, VFPRegister::Double};
+static constexpr FloatRegister d2 = {FloatRegisters::d2, VFPRegister::Double};
+static constexpr FloatRegister d3 = {FloatRegisters::d3, VFPRegister::Double};
+static constexpr FloatRegister d4 = {FloatRegisters::d4, VFPRegister::Double};
+static constexpr FloatRegister d5 = {FloatRegisters::d5, VFPRegister::Double};
+static constexpr FloatRegister d6 = {FloatRegisters::d6, VFPRegister::Double};
+static constexpr FloatRegister d7 = {FloatRegisters::d7, VFPRegister::Double};
+static constexpr FloatRegister d8 = {FloatRegisters::d8, VFPRegister::Double};
+static constexpr FloatRegister d9 = {FloatRegisters::d9, VFPRegister::Double};
+static constexpr FloatRegister d10 = {FloatRegisters::d10, VFPRegister::Double};
+static constexpr FloatRegister d11 = {FloatRegisters::d11, VFPRegister::Double};
+static constexpr FloatRegister d12 = {FloatRegisters::d12, VFPRegister::Double};
+static constexpr FloatRegister d13 = {FloatRegisters::d13, VFPRegister::Double};
+static constexpr FloatRegister d14 = {FloatRegisters::d14, VFPRegister::Double};
+static constexpr FloatRegister d15 = {FloatRegisters::d15, VFPRegister::Double};
+
+// For maximal awesomeness, 8 should be sufficent. ldrd/strd (dual-register
+// load/store) operate in a single cycle when the address they are dealing with
+// is 8 byte aligned. Also, the ARM abi wants the stack to be 8 byte aligned at
+// function boundaries. I'm trying to make sure this is always true.
+static constexpr uint32_t ABIStackAlignment = 8;
+static constexpr uint32_t CodeAlignment = 8;
+static constexpr uint32_t JitStackAlignment = 8;
+
+static constexpr uint32_t JitStackValueAlignment =
+    JitStackAlignment / sizeof(Value);
+static_assert(JitStackAlignment % sizeof(Value) == 0 &&
+                  JitStackValueAlignment >= 1,
+              "Stack alignment should be a non-zero multiple of sizeof(Value)");
+
+static constexpr uint32_t SimdMemoryAlignment = 8;
+
+static_assert(CodeAlignment % SimdMemoryAlignment == 0,
+              "Code alignment should be larger than any of the alignments "
+              "which are used for "
+              "the constant sections of the code buffer.  Thus it should be "
+              "larger than the "
+              "alignment for SIMD constants.");
+
+static_assert(JitStackAlignment % SimdMemoryAlignment == 0,
+              "Stack alignment should be larger than any of the alignments "
+              "which are used for "
+              "spilled values.  Thus it should be larger than the alignment "
+              "for SIMD accesses.");
+
+static const uint32_t WasmStackAlignment = SimdMemoryAlignment;
+static const uint32_t WasmTrapInstructionLength = 4;
+
+// See comments in wasm::GenerateFunctionPrologue.  The difference between these
+// is the size of the largest callable prologue on the platform.
+static constexpr uint32_t WasmCheckedCallEntryOffset = 0u;
+
+static const Scale ScalePointer = TimesFour;
+
+class Instruction;
+class InstBranchImm;
+uint32_t RM(Register r);
+uint32_t RS(Register r);
+uint32_t RD(Register r);
+uint32_t RT(Register r);
+uint32_t RN(Register r);
+
+uint32_t maybeRD(Register r);
+uint32_t maybeRT(Register r);
+uint32_t maybeRN(Register r);
+
+Register toRN(Instruction i);
+Register toRM(Instruction i);
+Register toRD(Instruction i);
+Register toR(Instruction i);
+
+class VFPRegister;
+uint32_t VD(VFPRegister vr);
+uint32_t VN(VFPRegister vr);
+uint32_t VM(VFPRegister vr);
+
+// For being passed into the generic vfp instruction generator when there is an
+// instruction that only takes two registers.
+static constexpr VFPRegister NoVFPRegister(VFPRegister::Double, 0, false, true);
+
+struct ImmTag : public Imm32 {
+  explicit ImmTag(JSValueTag mask) : Imm32(int32_t(mask)) {}
+};
+
+struct ImmType : public ImmTag {
+  explicit ImmType(JSValueType type) : ImmTag(JSVAL_TYPE_TO_TAG(type)) {}
+};
+
+enum Index {
+  Offset = 0 << 21 | 1 << 24,
+  PreIndex = 1 << 21 | 1 << 24,
+  PostIndex = 0 << 21 | 0 << 24
+  // The docs were rather unclear on this. It sounds like
+  // 1 << 21 | 0 << 24 encodes dtrt.
+};
+
+enum IsImmOp2_ { IsImmOp2 = 1 << 25, IsNotImmOp2 = 0 << 25 };
+enum IsImmDTR_ { IsImmDTR = 0 << 25, IsNotImmDTR = 1 << 25 };
+// For the extra memory operations, ldrd, ldrsb, ldrh.
+enum IsImmEDTR_ { IsImmEDTR = 1 << 22, IsNotImmEDTR = 0 << 22 };
+
+enum ShiftType {
+  LSL = 0,   // << 5
+  LSR = 1,   // << 5
+  ASR = 2,   // << 5
+  ROR = 3,   // << 5
+  RRX = ROR  // RRX is encoded as ROR with a 0 offset.
+};
+
+// Modes for STM/LDM. Names are the suffixes applied to the instruction.
+enum DTMMode {
+  A = 0 << 24,  // empty / after
+  B = 1 << 24,  // full / before
+  D = 0 << 23,  // decrement
+  I = 1 << 23,  // increment
+  DA = D | A,
+  DB = D | B,
+  IA = I | A,
+  IB = I | B
+};
+
+enum DTMWriteBack { WriteBack = 1 << 21, NoWriteBack = 0 << 21 };
+
+// Condition code updating mode.
+enum SBit {
+  SetCC = 1 << 20,   // Set condition code.
+  LeaveCC = 0 << 20  // Leave condition code unchanged.
+};
+
+enum LoadStore { IsLoad = 1 << 20, IsStore = 0 << 20 };
+
+// You almost never want to use this directly. Instead, you wantto pass in a
+// signed constant, and let this bit be implicitly set for you. This is however,
+// necessary if we want a negative index.
+enum IsUp_ { IsUp = 1 << 23, IsDown = 0 << 23 };
+enum ALUOp {
+  OpMov = 0xd << 21,
+  OpMvn = 0xf << 21,
+  OpAnd = 0x0 << 21,
+  OpBic = 0xe << 21,
+  OpEor = 0x1 << 21,
+  OpOrr = 0xc << 21,
+  OpAdc = 0x5 << 21,
+  OpAdd = 0x4 << 21,
+  OpSbc = 0x6 << 21,
+  OpSub = 0x2 << 21,
+  OpRsb = 0x3 << 21,
+  OpRsc = 0x7 << 21,
+  OpCmn = 0xb << 21,
+  OpCmp = 0xa << 21,
+  OpTeq = 0x9 << 21,
+  OpTst = 0x8 << 21,
+  OpInvalid = -1
+};
+
+enum MULOp {
+  OpmMul = 0 << 21,
+  OpmMla = 1 << 21,
+  OpmUmaal = 2 << 21,
+  OpmMls = 3 << 21,
+  OpmUmull = 4 << 21,
+  OpmUmlal = 5 << 21,
+  OpmSmull = 6 << 21,
+  OpmSmlal = 7 << 21
+};
+enum BranchTag {
+  OpB = 0x0a000000,
+  OpBMask = 0x0f000000,
+  OpBDestMask = 0x00ffffff,
+  OpBl = 0x0b000000,
+  OpBlx = 0x012fff30,
+  OpBx = 0x012fff10
+};
+
+// Just like ALUOp, but for the vfp instruction set.
+enum VFPOp {
+  OpvMul = 0x2 << 20,
+  OpvAdd = 0x3 << 20,
+  OpvSub = 0x3 << 20 | 0x1 << 6,
+  OpvDiv = 0x8 << 20,
+  OpvMov = 0xB << 20 | 0x1 << 6,
+  OpvAbs = 0xB << 20 | 0x3 << 6,
+  OpvNeg = 0xB << 20 | 0x1 << 6 | 0x1 << 16,
+  OpvSqrt = 0xB << 20 | 0x3 << 6 | 0x1 << 16,
+  OpvCmp = 0xB << 20 | 0x1 << 6 | 0x4 << 16,
+  OpvCmpz = 0xB << 20 | 0x1 << 6 | 0x5 << 16
+};
+
+// Negate the operation, AND negate the immediate that we were passed in.
+ALUOp ALUNeg(ALUOp op, Register dest, Register scratch, Imm32* imm,
+             Register* negDest);
+bool can_dbl(ALUOp op);
+bool condsAreSafe(ALUOp op);
+
+// If there is a variant of op that has a dest (think cmp/sub) return that
+// variant of it.
+ALUOp getDestVariant(ALUOp op);
+
+static constexpr ValueOperand JSReturnOperand{JSReturnReg_Type,
+                                              JSReturnReg_Data};
+static const ValueOperand softfpReturnOperand = ValueOperand(r1, r0);
+
+// All of these classes exist solely to shuffle data into the various operands.
+// For example Operand2 can be an imm8, a register-shifted-by-a-constant or a
+// register-shifted-by-a-register. We represent this in C++ by having a base
+// class Operand2, which just stores the 32 bits of data as they will be encoded
+// in the instruction. You cannot directly create an Operand2 since it is
+// tricky, and not entirely sane to do so. Instead, you create one of its child
+// classes, e.g. Imm8. Imm8's constructor takes a single integer argument. Imm8
+// will verify that its argument can be encoded as an ARM 12 bit imm8, encode it
+// using an Imm8data, and finally call its parent's (Operand2) constructor with
+// the Imm8data. The Operand2 constructor will then call the Imm8data's encode()
+// function to extract the raw bits from it.
+//
+// In the future, we should be able to extract data from the Operand2 by asking
+// it for its component Imm8data structures. The reason this is so horribly
+// round-about is we wanted to have Imm8 and RegisterShiftedRegister inherit
+// directly from Operand2 but have all of them take up only a single word of
+// storage. We also wanted to avoid passing around raw integers at all since
+// they are error prone.
+class Op2Reg;
+class O2RegImmShift;
+class O2RegRegShift;
+
+namespace datastore {
+
+class Reg {
+  // The "second register".
+  uint32_t rm_ : 4;
+  // Do we get another register for shifting.
+  uint32_t rrs_ : 1;
+  uint32_t type_ : 2;
+  // We'd like this to be a more sensible encoding, but that would need to be
+  // a struct and that would not pack :(
+  uint32_t shiftAmount_ : 5;
+
+ protected:
+  // Mark as a protected field to avoid unused private field warnings.
+  uint32_t pad_ : 20;
+
+ public:
+  Reg(uint32_t rm, ShiftType type, uint32_t rsr, uint32_t shiftAmount)
+      : rm_(rm), rrs_(rsr), type_(type), shiftAmount_(shiftAmount), pad_(0) {}
+  explicit Reg(const Op2Reg& op) { memcpy(this, &op, sizeof(*this)); }
+
+  uint32_t shiftAmount() const { return shiftAmount_; }
+
+  uint32_t encode() const {
+    return rm_ | (rrs_ << 4) | (type_ << 5) | (shiftAmount_ << 7);
+  }
+};
+
+// Op2 has a mode labelled "<imm8m>", which is arm's magical immediate encoding.
+// Some instructions actually get 8 bits of data, which is called Imm8Data
+// below. These should have edit distance > 1, but this is how it is for now.
+class Imm8mData {
+  uint32_t data_ : 8;
+  uint32_t rot_ : 4;
+
+ protected:
+  // Mark as a protected field to avoid unused private field warnings.
+  uint32_t buff_ : 19;
+
+ private:
+  // Throw in an extra bit that will be 1 if we can't encode this properly.
+  // if we can encode it properly, a simple "|" will still suffice to meld it
+  // into the instruction.
+  uint32_t invalid_ : 1;
+
+ public:
+  // Default constructor makes an invalid immediate.
+  Imm8mData() : data_(0xff), rot_(0xf), buff_(0), invalid_(true) {}
+
+  Imm8mData(uint32_t data, uint32_t rot)
+      : data_(data), rot_(rot), buff_(0), invalid_(false) {
+    MOZ_ASSERT(data == data_);
+    MOZ_ASSERT(rot == rot_);
+  }
+
+  bool invalid() const { return invalid_; }
+
+  uint32_t encode() const {
+    MOZ_ASSERT(!invalid_);
+    return data_ | (rot_ << 8);
+  };
+};
+
+class Imm8Data {
+  uint32_t imm4L_ : 4;
+
+ protected:
+  // Mark as a protected field to avoid unused private field warnings.
+  uint32_t pad_ : 4;
+
+ private:
+  uint32_t imm4H_ : 4;
+
+ public:
+  explicit Imm8Data(uint32_t imm) : imm4L_(imm & 0xf), imm4H_(imm >> 4) {
+    MOZ_ASSERT(imm <= 0xff);
+  }
+
+  uint32_t encode() const { return imm4L_ | (imm4H_ << 8); };
+};
+
+// VLDR/VSTR take an 8 bit offset, which is implicitly left shifted by 2.
+class Imm8VFPOffData {
+  uint32_t data_;
+
+ public:
+  explicit Imm8VFPOffData(uint32_t imm) : data_(imm) {
+    MOZ_ASSERT((imm & ~(0xff)) == 0);
+  }
+  uint32_t encode() const { return data_; };
+};
+
+// ARM can magically encode 256 very special immediates to be moved into a
+// register.
+struct Imm8VFPImmData {
+  // This structure's members are public and it has no constructor to
+  // initialize them, for a very special reason. Were this structure to
+  // have a constructor, the initialization for DoubleEncoder's internal
+  // table (see below) would require a rather large static constructor on
+  // some of our supported compilers. The known solution to this is to mark
+  // the constructor constexpr, but, again, some of our supported
+  // compilers don't support constexpr! So we are reduced to public
+  // members and eschewing a constructor in hopes that the initialization
+  // of DoubleEncoder's table is correct.
+  uint32_t imm4L : 4;
+  uint32_t imm4H : 4;
+  int32_t isInvalid : 24;
+
+  uint32_t encode() const {
+    // This assert is an attempting at ensuring that we don't create random
+    // instances of this structure and then asking to encode() it.
+    MOZ_ASSERT(isInvalid == 0);
+    return imm4L | (imm4H << 16);
+  };
+};
+
+class Imm12Data {
+  uint32_t data_ : 12;
+
+ public:
+  explicit Imm12Data(uint32_t imm) : data_(imm) { MOZ_ASSERT(data_ == imm); }
+
+  uint32_t encode() const { return data_; }
+};
+
+class RIS {
+  uint32_t shiftAmount_ : 5;
+
+ public:
+  explicit RIS(uint32_t imm) : shiftAmount_(imm) {
+    MOZ_ASSERT(shiftAmount_ == imm);
+  }
+
+  explicit RIS(Reg r) : shiftAmount_(r.shiftAmount()) {}
+
+  uint32_t encode() const { return shiftAmount_; }
+};
+
+class RRS {
+ protected:
+  // Mark as a protected field to avoid unused private field warnings.
+  uint32_t mustZero_ : 1;
+
+ private:
+  // The register that holds the shift amount.
+  uint32_t rs_ : 4;
+
+ public:
+  explicit RRS(uint32_t rs) : rs_(rs) { MOZ_ASSERT(rs_ == rs); }
+
+  uint32_t encode() const { return rs_ << 1; }
+};
+
+}  // namespace datastore
+
+class MacroAssemblerARM;
+class Operand;
+
+class Operand2 {
+  friend class Operand;
+  friend class MacroAssemblerARM;
+  friend class InstALU;
+
+  uint32_t oper_ : 31;
+  uint32_t invalid_ : 1;
+
+ protected:
+  explicit Operand2(datastore::Imm8mData base)
+      : oper_(base.invalid() ? -1 : (base.encode() | uint32_t(IsImmOp2))),
+        invalid_(base.invalid()) {}
+
+  explicit Operand2(datastore::Reg base)
+      : oper_(base.encode() | uint32_t(IsNotImmOp2)), invalid_(false) {}
+
+ private:
+  explicit Operand2(uint32_t blob) : oper_(blob), invalid_(false) {}
+
+ public:
+  bool isO2Reg() const { return !(oper_ & IsImmOp2); }
+
+  Op2Reg toOp2Reg() const;
+
+  bool isImm8() const { return oper_ & IsImmOp2; }
+
+  bool invalid() const { return invalid_; }
+
+  uint32_t encode() const { return oper_; }
+};
+
+class Imm8 : public Operand2 {
+ public:
+  explicit Imm8(uint32_t imm) : Operand2(EncodeImm(imm)) {}
+
+  static datastore::Imm8mData EncodeImm(uint32_t imm) {
+    // RotateLeft below may not be called with a shift of zero.
+    if (imm <= 0xFF) {
+      return datastore::Imm8mData(imm, 0);
+    }
+
+    // An encodable integer has a maximum of 8 contiguous set bits,
+    // with an optional wrapped left rotation to even bit positions.
+    for (int rot = 1; rot < 16; rot++) {
+      uint32_t rotimm = mozilla::RotateLeft(imm, rot * 2);
+      if (rotimm <= 0xFF) {
+        return datastore::Imm8mData(rotimm, rot);
+      }
+    }
+    return datastore::Imm8mData();
+  }
+
+  // Pair template?
+  struct TwoImm8mData {
+    datastore::Imm8mData fst_, snd_;
+
+    TwoImm8mData() = default;
+
+    TwoImm8mData(datastore::Imm8mData fst, datastore::Imm8mData snd)
+        : fst_(fst), snd_(snd) {}
+
+    datastore::Imm8mData fst() const { return fst_; }
+    datastore::Imm8mData snd() const { return snd_; }
+  };
+
+  static TwoImm8mData EncodeTwoImms(uint32_t);
+};
+
+class Op2Reg : public Operand2 {
+ public:
+  explicit Op2Reg(Register rm, ShiftType type, datastore::RIS shiftImm)
+      : Operand2(datastore::Reg(rm.code(), type, 0, shiftImm.encode())) {}
+
+  explicit Op2Reg(Register rm, ShiftType type, datastore::RRS shiftReg)
+      : Operand2(datastore::Reg(rm.code(), type, 1, shiftReg.encode())) {}
+};
+
+static_assert(sizeof(Op2Reg) == sizeof(datastore::Reg),
+              "datastore::Reg(const Op2Reg&) constructor relies on Reg/Op2Reg "
+              "having same size");
+
+class O2RegImmShift : public Op2Reg {
+ public:
+  explicit O2RegImmShift(Register rn, ShiftType type, uint32_t shift)
+      : Op2Reg(rn, type, datastore::RIS(shift)) {}
+};
+
+class O2RegRegShift : public Op2Reg {
+ public:
+  explicit O2RegRegShift(Register rn, ShiftType type, Register rs)
+      : Op2Reg(rn, type, datastore::RRS(rs.code())) {}
+};
+
+O2RegImmShift O2Reg(Register r);
+O2RegImmShift lsl(Register r, int amt);
+O2RegImmShift lsr(Register r, int amt);
+O2RegImmShift asr(Register r, int amt);
+O2RegImmShift rol(Register r, int amt);
+O2RegImmShift ror(Register r, int amt);
+
+O2RegRegShift lsl(Register r, Register amt);
+O2RegRegShift lsr(Register r, Register amt);
+O2RegRegShift asr(Register r, Register amt);
+O2RegRegShift ror(Register r, Register amt);
+
+// An offset from a register to be used for ldr/str. This should include the
+// sign bit, since ARM has "signed-magnitude" offsets. That is it encodes an
+// unsigned offset, then the instruction specifies if the offset is positive or
+// negative. The +/- bit is necessary if the instruction set wants to be able to
+// have a negative register offset e.g. ldr pc, [r1,-r2];
+class DtrOff {
+  uint32_t data_;
+
+ protected:
+  explicit DtrOff(datastore::Imm12Data immdata, IsUp_ iu)
+      : data_(immdata.encode() | uint32_t(IsImmDTR) | uint32_t(iu)) {}
+
+  explicit DtrOff(datastore::Reg reg, IsUp_ iu = IsUp)
+      : data_(reg.encode() | uint32_t(IsNotImmDTR) | iu) {}
+
+ public:
+  uint32_t encode() const { return data_; }
+};
+
+class DtrOffImm : public DtrOff {
+ public:
+  explicit DtrOffImm(int32_t imm)
+      : DtrOff(datastore::Imm12Data(mozilla::Abs(imm)),
+               imm >= 0 ? IsUp : IsDown) {
+    MOZ_ASSERT(mozilla::Abs(imm) < 4096);
+  }
+};
+
+class DtrOffReg : public DtrOff {
+  // These are designed to be called by a constructor of a subclass.
+  // Constructing the necessary RIS/RRS structures is annoying.
+
+ protected:
+  explicit DtrOffReg(Register rn, ShiftType type, datastore::RIS shiftImm,
+                     IsUp_ iu = IsUp)
+      : DtrOff(datastore::Reg(rn.code(), type, 0, shiftImm.encode()), iu) {}
+
+  explicit DtrOffReg(Register rn, ShiftType type, datastore::RRS shiftReg,
+                     IsUp_ iu = IsUp)
+      : DtrOff(datastore::Reg(rn.code(), type, 1, shiftReg.encode()), iu) {}
+};
+
+class DtrRegImmShift : public DtrOffReg {
+ public:
+  explicit DtrRegImmShift(Register rn, ShiftType type, uint32_t shift,
+                          IsUp_ iu = IsUp)
+      : DtrOffReg(rn, type, datastore::RIS(shift), iu) {}
+};
+
+class DtrRegRegShift : public DtrOffReg {
+ public:
+  explicit DtrRegRegShift(Register rn, ShiftType type, Register rs,
+                          IsUp_ iu = IsUp)
+      : DtrOffReg(rn, type, datastore::RRS(rs.code()), iu) {}
+};
+
+// We will frequently want to bundle a register with its offset so that we have
+// an "operand" to a load instruction.
+class DTRAddr {
+  friend class Operand;
+
+  uint32_t data_;
+
+ public:
+  explicit DTRAddr(Register reg, DtrOff dtr)
+      : data_(dtr.encode() | (reg.code() << 16)) {}
+
+  uint32_t encode() const { return data_; }
+
+  Register getBase() const { return Register::FromCode((data_ >> 16) & 0xf); }
+};
+
+// Offsets for the extended data transfer instructions:
+// ldrsh, ldrd, ldrsb, etc.
+class EDtrOff {
+  uint32_t data_;
+
+ protected:
+  explicit EDtrOff(datastore::Imm8Data imm8, IsUp_ iu = IsUp)
+      : data_(imm8.encode() | IsImmEDTR | uint32_t(iu)) {}
+
+  explicit EDtrOff(Register rm, IsUp_ iu = IsUp)
+      : data_(rm.code() | IsNotImmEDTR | iu) {}
+
+ public:
+  uint32_t encode() const { return data_; }
+};
+
+class EDtrOffImm : public EDtrOff {
+ public:
+  explicit EDtrOffImm(int32_t imm)
+      : EDtrOff(datastore::Imm8Data(mozilla::Abs(imm)),
+                (imm >= 0) ? IsUp : IsDown) {
+    MOZ_ASSERT(mozilla::Abs(imm) < 256);
+  }
+};
+
+// This is the most-derived class, since the extended data transfer instructions
+// don't support any sort of modifying the "index" operand.
+class EDtrOffReg : public EDtrOff {
+ public:
+  explicit EDtrOffReg(Register rm) : EDtrOff(rm) {}
+};
+
+class EDtrAddr {
+  uint32_t data_;
+
+ public:
+  explicit EDtrAddr(Register r, EDtrOff off) : data_(RN(r) | off.encode()) {}
+
+  uint32_t encode() const { return data_; }
+#ifdef DEBUG
+  Register maybeOffsetRegister() const {
+    if (data_ & IsImmEDTR) {
+      return InvalidReg;
+    }
+    return Register::FromCode(data_ & 0xf);
+  }
+#endif
+};
+
+class VFPOff {
+  uint32_t data_;
+
+ protected:
+  explicit VFPOff(datastore::Imm8VFPOffData imm, IsUp_ isup)
+      : data_(imm.encode() | uint32_t(isup)) {}
+
+ public:
+  uint32_t encode() const { return data_; }
+};
+
+class VFPOffImm : public VFPOff {
+ public:
+  explicit VFPOffImm(int32_t imm)
+      : VFPOff(datastore::Imm8VFPOffData(mozilla::Abs(imm) / 4),
+               imm < 0 ? IsDown : IsUp) {
+    MOZ_ASSERT(mozilla::Abs(imm) <= 255 * 4);
+  }
+};
+
+class VFPAddr {
+  friend class Operand;
+
+  uint32_t data_;
+
+ public:
+  explicit VFPAddr(Register base, VFPOff off)
+      : data_(RN(base) | off.encode()) {}
+
+  uint32_t encode() const { return data_; }
+};
+
+class VFPImm {
+  uint32_t data_;
+
+ public:
+  explicit VFPImm(uint32_t topWordOfDouble);
+
+  static const VFPImm One;
+
+  uint32_t encode() const { return data_; }
+  bool isValid() const { return data_ != (~0U); }
+};
+
+// A BOffImm is an immediate that is used for branches. Namely, it is the offset
+// that will be encoded in the branch instruction. This is the only sane way of
+// constructing a branch.
+class BOffImm {
+  friend class InstBranchImm;
+
+  uint32_t data_;
+
+ public:
+  explicit BOffImm(int offset) : data_((offset - 8) >> 2 & 0x00ffffff) {
+    MOZ_ASSERT((offset & 0x3) == 0);
+    if (!IsInRange(offset)) {
+      MOZ_CRASH("BOffImm offset out of range");
+    }
+  }
+
+  explicit BOffImm() : data_(INVALID) {}
+
+ private:
+  explicit BOffImm(const Instruction& inst);
+
+ public:
+  static const uint32_t INVALID = 0x00800000;
+
+  uint32_t encode() const { return data_; }
+  int32_t decode() const { return ((int32_t(data_) << 8) >> 6) + 8; }
+
+  static bool IsInRange(int offset) {
+    if ((offset - 8) < -33554432) {
+      return false;
+    }
+    if ((offset - 8) > 33554428) {
+      return false;
+    }
+    return true;
+  }
+
+  bool isInvalid() const { return data_ == INVALID; }
+  Instruction* getDest(Instruction* src) const;
+};
+
+class Imm16 {
+  uint32_t lower_ : 12;
+
+ protected:
+  // Mark as a protected field to avoid unused private field warnings.
+  uint32_t pad_ : 4;
+
+ private:
+  uint32_t upper_ : 4;
+  uint32_t invalid_ : 12;
+
+ public:
+  explicit Imm16();
+  explicit Imm16(uint32_t imm);
+  explicit Imm16(Instruction& inst);
+
+  uint32_t encode() const { return lower_ | (upper_ << 16); }
+  uint32_t decode() const { return lower_ | (upper_ << 12); }
+
+  bool isInvalid() const { return invalid_; }
+};
+
+// I would preffer that these do not exist, since there are essentially no
+// instructions that would ever take more than one of these, however, the MIR
+// wants to only have one type of arguments to functions, so bugger.
+class Operand {
+  // The encoding of registers is the same for OP2, DTR and EDTR yet the type
+  // system doesn't let us express this, so choices must be made.
+ public:
+  enum class Tag : uint8_t { OP2, MEM, FOP };
+
+ private:
+  uint32_t tag_ : 8;
+  uint32_t reg_ : 5;
+  int32_t offset_;
+
+ protected:
+  Operand(Tag tag, uint32_t regCode, int32_t offset)
+      : tag_(static_cast<uint32_t>(tag)), reg_(regCode), offset_(offset) {}
+
+ public:
+  explicit Operand(Register reg) : Operand(Tag::OP2, reg.code(), 0) {}
+
+  explicit Operand(FloatRegister freg) : Operand(Tag::FOP, freg.code(), 0) {}
+
+  explicit Operand(Register base, Imm32 off)
+      : Operand(Tag::MEM, base.code(), off.value) {}
+
+  explicit Operand(Register base, int32_t off)
+      : Operand(Tag::MEM, base.code(), off) {}
+
+  explicit Operand(const Address& addr)
+      : Operand(Tag::MEM, addr.base.code(), addr.offset) {}
+
+ public:
+  Tag tag() const { return static_cast<Tag>(tag_); }
+
+  Operand2 toOp2() const {
+    MOZ_ASSERT(tag() == Tag::OP2);
+    return O2Reg(Register::FromCode(reg_));
+  }
+
+  Register toReg() const {
+    MOZ_ASSERT(tag() == Tag::OP2);
+    return Register::FromCode(reg_);
+  }
+
+  Address toAddress() const {
+    MOZ_ASSERT(tag() == Tag::MEM);
+    return Address(Register::FromCode(reg_), offset_);
+  }
+  int32_t disp() const {
+    MOZ_ASSERT(tag() == Tag::MEM);
+    return offset_;
+  }
+
+  int32_t base() const {
+    MOZ_ASSERT(tag() == Tag::MEM);
+    return reg_;
+  }
+  Register baseReg() const {
+    MOZ_ASSERT(tag() == Tag::MEM);
+    return Register::FromCode(reg_);
+  }
+  DTRAddr toDTRAddr() const {
+    MOZ_ASSERT(tag() == Tag::MEM);
+    return DTRAddr(baseReg(), DtrOffImm(offset_));
+  }
+  VFPAddr toVFPAddr() const {
+    MOZ_ASSERT(tag() == Tag::MEM);
+    return VFPAddr(baseReg(), VFPOffImm(offset_));
+  }
+};
+
+inline Imm32 Imm64::firstHalf() const { return low(); }
+
+inline Imm32 Imm64::secondHalf() const { return hi(); }
+
+class InstructionIterator {
+ private:
+  Instruction* inst_;
+
+ public:
+  explicit InstructionIterator(Instruction* inst) : inst_(inst) {
+    maybeSkipAutomaticInstructions();
+  }
+
+  // Advances to the next intentionally-inserted instruction.
+  Instruction* next();
+
+  // Advances past any automatically-inserted instructions.
+  Instruction* maybeSkipAutomaticInstructions();
+
+  Instruction* cur() const { return inst_; }
+
+ protected:
+  // Advances past the given number of instruction-length bytes.
+  inline void advanceRaw(ptrdiff_t instructions = 1);
+};
+
+class Assembler;
+typedef js::jit::AssemblerBufferWithConstantPools<1024, 4, Instruction,
+                                                  Assembler>
+    ARMBuffer;
+
+class Assembler : public AssemblerShared {
+ public:
+  // ARM conditional constants:
+  enum ARMCondition : uint32_t {
+    EQ = 0x00000000,  // Zero
+    NE = 0x10000000,  // Non-zero
+    CS = 0x20000000,
+    CC = 0x30000000,
+    MI = 0x40000000,
+    PL = 0x50000000,
+    VS = 0x60000000,
+    VC = 0x70000000,
+    HI = 0x80000000,
+    LS = 0x90000000,
+    GE = 0xa0000000,
+    LT = 0xb0000000,
+    GT = 0xc0000000,
+    LE = 0xd0000000,
+    AL = 0xe0000000
+  };
+
+  enum Condition : uint32_t {
+    Equal = EQ,
+    NotEqual = NE,
+    Above = HI,
+    AboveOrEqual = CS,
+    Below = CC,
+    BelowOrEqual = LS,
+    GreaterThan = GT,
+    GreaterThanOrEqual = GE,
+    LessThan = LT,
+    LessThanOrEqual = LE,
+    Overflow = VS,
+    CarrySet = CS,
+    CarryClear = CC,
+    Signed = MI,
+    NotSigned = PL,
+    Zero = EQ,
+    NonZero = NE,
+    Always = AL,
+
+    VFP_NotEqualOrUnordered = NE,
+    VFP_Equal = EQ,
+    VFP_Unordered = VS,
+    VFP_NotUnordered = VC,
+    VFP_GreaterThanOrEqualOrUnordered = CS,
+    VFP_GreaterThanOrEqual = GE,
+    VFP_GreaterThanOrUnordered = HI,
+    VFP_GreaterThan = GT,
+    VFP_LessThanOrEqualOrUnordered = LE,
+    VFP_LessThanOrEqual = LS,
+    VFP_LessThanOrUnordered = LT,
+    VFP_LessThan = CC  // MI is valid too.
+  };
+
+  // Bit set when a DoubleCondition does not map to a single ARM condition.
+  // The macro assembler has to special-case these conditions, or else
+  // ConditionFromDoubleCondition will complain.
+  static const int DoubleConditionBitSpecial = 0x1;
+
+  enum DoubleCondition : uint32_t {
+    // These conditions will only evaluate to true if the comparison is
+    // ordered - i.e. neither operand is NaN.
+    DoubleOrdered = VFP_NotUnordered,
+    DoubleEqual = VFP_Equal,
+    DoubleNotEqual = VFP_NotEqualOrUnordered | DoubleConditionBitSpecial,
+    DoubleGreaterThan = VFP_GreaterThan,
+    DoubleGreaterThanOrEqual = VFP_GreaterThanOrEqual,
+    DoubleLessThan = VFP_LessThan,
+    DoubleLessThanOrEqual = VFP_LessThanOrEqual,
+    // If either operand is NaN, these conditions always evaluate to true.
+    DoubleUnordered = VFP_Unordered,
+    DoubleEqualOrUnordered = VFP_Equal | DoubleConditionBitSpecial,
+    DoubleNotEqualOrUnordered = VFP_NotEqualOrUnordered,
+    DoubleGreaterThanOrUnordered = VFP_GreaterThanOrUnordered,
+    DoubleGreaterThanOrEqualOrUnordered = VFP_GreaterThanOrEqualOrUnordered,
+    DoubleLessThanOrUnordered = VFP_LessThanOrUnordered,
+    DoubleLessThanOrEqualOrUnordered = VFP_LessThanOrEqualOrUnordered
+  };
+
+  Condition getCondition(uint32_t inst) {
+    return (Condition)(0xf0000000 & inst);
+  }
+  static inline Condition ConditionFromDoubleCondition(DoubleCondition cond) {
+    MOZ_ASSERT(!(cond & DoubleConditionBitSpecial));
+    return static_cast<Condition>(cond);
+  }
+
+  enum BarrierOption {
+    BarrierSY = 15,  // Full system barrier
+    BarrierST = 14   // StoreStore barrier
+  };
+
+  // This should be protected, but since CodeGenerator wants to use it, it
+  // needs to go out here :(
+
+  BufferOffset nextOffset() { return m_buffer.nextOffset(); }
+
+ protected:
+  // Shim around AssemblerBufferWithConstantPools::allocEntry.
+  BufferOffset allocLiteralLoadEntry(size_t numInst, unsigned numPoolEntries,
+                                     PoolHintPun& php, uint8_t* data,
+                                     const LiteralDoc& doc = LiteralDoc(),
+                                     ARMBuffer::PoolEntry* pe = nullptr,
+                                     bool loadToPC = false);
+
+  Instruction* editSrc(BufferOffset bo) { return m_buffer.getInst(bo); }
+
+#ifdef JS_DISASM_ARM
+  typedef disasm::EmbeddedVector<char, disasm::ReasonableBufferSize>
+      DisasmBuffer;
+
+  static void disassembleInstruction(const Instruction* i,
+                                     DisasmBuffer& buffer);
+
+  void initDisassembler();
+  void finishDisassembler();
+  void spew(Instruction* i);
+  void spewBranch(Instruction* i, const LabelDoc& target);
+  void spewLiteralLoad(PoolHintPun& php, bool loadToPC, const Instruction* offs,
+                       const LiteralDoc& doc);
+#endif
+
+ public:
+  void resetCounter();
+  static uint32_t NopFill;
+  static uint32_t GetNopFill();
+  static uint32_t AsmPoolMaxOffset;
+  static uint32_t GetPoolMaxOffset();
+
+ protected:
+  // Structure for fixing up pc-relative loads/jumps when a the machine code
+  // gets moved (executable copy, gc, etc.).
+  class RelativePatch {
+    void* target_;
+    RelocationKind kind_;
+
+   public:
+    RelativePatch(void* target, RelocationKind kind)
+        : target_(target), kind_(kind) {}
+    void* target() const { return target_; }
+    RelocationKind kind() const { return kind_; }
+  };
+
+  // TODO: this should actually be a pool-like object. It is currently a big
+  // hack, and probably shouldn't exist.
+  js::Vector<RelativePatch, 8, SystemAllocPolicy> jumps_;
+
+  CompactBufferWriter jumpRelocations_;
+  CompactBufferWriter dataRelocations_;
+
+  ARMBuffer m_buffer;
+
+#ifdef JS_DISASM_ARM
+  DisassemblerSpew spew_;
+#endif
+
+ public:
+  // For the alignment fill use NOP: 0x0320f000 or (Always | InstNOP::NopInst).
+  // For the nopFill use a branch to the next instruction: 0xeaffffff.
+  Assembler()
+      : m_buffer(1, 1, 8, GetPoolMaxOffset(), 8, 0xe320f000, 0xeaffffff,
+                 GetNopFill()),
+        isFinished(false),
+        dtmActive(false),
+        dtmCond(Always) {
+#ifdef JS_DISASM_ARM
+    initDisassembler();
+#endif
+  }
+
+  ~Assembler() {
+#ifdef JS_DISASM_ARM
+    finishDisassembler();
+#endif
+  }
+
+  void setUnlimitedBuffer() { m_buffer.setUnlimited(); }
+
+  static Condition InvertCondition(Condition cond);
+  static Condition UnsignedCondition(Condition cond);
+  static Condition ConditionWithoutEqual(Condition cond);
+
+  static DoubleCondition InvertCondition(DoubleCondition cond);
+
+  void writeDataRelocation(BufferOffset offset, ImmGCPtr ptr) {
+    // Raw GC pointer relocations and Value relocations both end up in
+    // Assembler::TraceDataRelocations.
+    if (ptr.value) {
+      if (gc::IsInsideNursery(ptr.value)) {
+        embedsNurseryPointers_ = true;
+      }
+      dataRelocations_.writeUnsigned(offset.getOffset());
+    }
+  }
+
+  enum RelocBranchStyle { B_MOVWT, B_LDR_BX, B_LDR, B_MOVW_ADD };
+
+  enum RelocStyle { L_MOVWT, L_LDR };
+
+ public:
+  // Given the start of a Control Flow sequence, grab the value that is
+  // finally branched to given the start of a function that loads an address
+  // into a register get the address that ends up in the register.
+  template <class Iter>
+  static const uint32_t* GetCF32Target(Iter* iter);
+
+  static uintptr_t GetPointer(uint8_t*);
+  static const uint32_t* GetPtr32Target(InstructionIterator iter,
+                                        Register* dest = nullptr,
+                                        RelocStyle* rs = nullptr);
+
+  bool oom() const;
+
+  void setPrinter(Sprinter* sp) {
+#ifdef JS_DISASM_ARM
+    spew_.setPrinter(sp);
+#endif
+  }
+
+  Register getStackPointer() const { return StackPointer; }
+
+ private:
+  bool isFinished;
+
+ protected:
+  LabelDoc refLabel(const Label* label) {
+#ifdef JS_DISASM_ARM
+    return spew_.refLabel(label);
+#else
+    return LabelDoc();
+#endif
+  }
+
+ public:
+  void finish();
+  bool appendRawCode(const uint8_t* code, size_t numBytes);
+  bool reserve(size_t size);
+  bool swapBuffer(wasm::Bytes& bytes);
+  void copyJumpRelocationTable(uint8_t* dest);
+  void copyDataRelocationTable(uint8_t* dest);
+
+  // Size of the instruction stream, in bytes, after pools are flushed.
+  size_t size() const;
+  // Size of the jump relocation table, in bytes.
+  size_t jumpRelocationTableBytes() const;
+  size_t dataRelocationTableBytes() const;
+
+  // Size of the data table, in bytes.
+  size_t bytesNeeded() const;
+
+  // Write a single instruction into the instruction stream.  Very hot,
+  // inlined for performance
+  MOZ_ALWAYS_INLINE BufferOffset writeInst(uint32_t x) {
+    MOZ_ASSERT(hasCreator());
+    BufferOffset offs = m_buffer.putInt(x);
+#ifdef JS_DISASM_ARM
+    spew(m_buffer.getInstOrNull(offs));
+#endif
+    return offs;
+  }
+
+  // As above, but also mark the instruction as a branch.  Very hot, inlined
+  // for performance
+  MOZ_ALWAYS_INLINE BufferOffset
+  writeBranchInst(uint32_t x, const LabelDoc& documentation) {
+    BufferOffset offs = m_buffer.putInt(x);
+#ifdef JS_DISASM_ARM
+    spewBranch(m_buffer.getInstOrNull(offs), documentation);
+#endif
+    return offs;
+  }
+
+  // Write a placeholder NOP for a branch into the instruction stream
+  // (in order to adjust assembler addresses and mark it as a branch), it will
+  // be overwritten subsequently.
+  BufferOffset allocBranchInst();
+
+  // A static variant for the cases where we don't want to have an assembler
+  // object.
+  static void WriteInstStatic(uint32_t x, uint32_t* dest);
+
+ public:
+  void writeCodePointer(CodeLabel* label);
+
+  void haltingAlign(int alignment);
+  void nopAlign(int alignment);
+  BufferOffset as_nop();
+  BufferOffset as_alu(Register dest, Register src1, Operand2 op2, ALUOp op,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_mov(Register dest, Operand2 op2, SBit s = LeaveCC,
+                      Condition c = Always);
+  BufferOffset as_mvn(Register dest, Operand2 op2, SBit s = LeaveCC,
+                      Condition c = Always);
+
+  static void as_alu_patch(Register dest, Register src1, Operand2 op2, ALUOp op,
+                           SBit s, Condition c, uint32_t* pos);
+  static void as_mov_patch(Register dest, Operand2 op2, SBit s, Condition c,
+                           uint32_t* pos);
+
+  // Logical operations:
+  BufferOffset as_and(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_bic(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_eor(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_orr(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  // Reverse byte operations:
+  BufferOffset as_rev(Register dest, Register src, Condition c = Always);
+  BufferOffset as_rev16(Register dest, Register src, Condition c = Always);
+  BufferOffset as_revsh(Register dest, Register src, Condition c = Always);
+  // Mathematical operations:
+  BufferOffset as_adc(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_add(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_sbc(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_sub(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_rsb(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_rsc(Register dest, Register src1, Operand2 op2,
+                      SBit s = LeaveCC, Condition c = Always);
+  // Test operations:
+  BufferOffset as_cmn(Register src1, Operand2 op2, Condition c = Always);
+  BufferOffset as_cmp(Register src1, Operand2 op2, Condition c = Always);
+  BufferOffset as_teq(Register src1, Operand2 op2, Condition c = Always);
+  BufferOffset as_tst(Register src1, Operand2 op2, Condition c = Always);
+
+  // Sign extension operations:
+  BufferOffset as_sxtb(Register dest, Register src, int rotate,
+                       Condition c = Always);
+  BufferOffset as_sxth(Register dest, Register src, int rotate,
+                       Condition c = Always);
+  BufferOffset as_uxtb(Register dest, Register src, int rotate,
+                       Condition c = Always);
+  BufferOffset as_uxth(Register dest, Register src, int rotate,
+                       Condition c = Always);
+
+  // Not quite ALU worthy, but useful none the less: These also have the issue
+  // of these being formatted completly differently from the standard ALU
+  // operations.
+  BufferOffset as_movw(Register dest, Imm16 imm, Condition c = Always);
+  BufferOffset as_movt(Register dest, Imm16 imm, Condition c = Always);
+
+  static void as_movw_patch(Register dest, Imm16 imm, Condition c,
+                            Instruction* pos);
+  static void as_movt_patch(Register dest, Imm16 imm, Condition c,
+                            Instruction* pos);
+
+  BufferOffset as_genmul(Register d1, Register d2, Register rm, Register rn,
+                         MULOp op, SBit s, Condition c = Always);
+  BufferOffset as_mul(Register dest, Register src1, Register src2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_mla(Register dest, Register acc, Register src1, Register src2,
+                      SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_umaal(Register dest1, Register dest2, Register src1,
+                        Register src2, Condition c = Always);
+  BufferOffset as_mls(Register dest, Register acc, Register src1, Register src2,
+                      Condition c = Always);
+  BufferOffset as_umull(Register dest1, Register dest2, Register src1,
+                        Register src2, SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_umlal(Register dest1, Register dest2, Register src1,
+                        Register src2, SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_smull(Register dest1, Register dest2, Register src1,
+                        Register src2, SBit s = LeaveCC, Condition c = Always);
+  BufferOffset as_smlal(Register dest1, Register dest2, Register src1,
+                        Register src2, SBit s = LeaveCC, Condition c = Always);
+
+  BufferOffset as_sdiv(Register dest, Register num, Register div,
+                       Condition c = Always);
+  BufferOffset as_udiv(Register dest, Register num, Register div,
+                       Condition c = Always);
+  BufferOffset as_clz(Register dest, Register src, Condition c = Always);
+
+  // Data transfer instructions: ldr, str, ldrb, strb.
+  // Using an int to differentiate between 8 bits and 32 bits is overkill.
+  BufferOffset as_dtr(LoadStore ls, int size, Index mode, Register rt,
+                      DTRAddr addr, Condition c = Always);
+
+  static void as_dtr_patch(LoadStore ls, int size, Index mode, Register rt,
+                           DTRAddr addr, Condition c, uint32_t* dest);
+
+  // Handles all of the other integral data transferring functions:
+  // ldrsb, ldrsh, ldrd, etc. The size is given in bits.
+  BufferOffset as_extdtr(LoadStore ls, int size, bool IsSigned, Index mode,
+                         Register rt, EDtrAddr addr, Condition c = Always);
+
+  BufferOffset as_dtm(LoadStore ls, Register rn, uint32_t mask, DTMMode mode,
+                      DTMWriteBack wb, Condition c = Always);
+
+  // Overwrite a pool entry with new data.
+  static void WritePoolEntry(Instruction* addr, Condition c, uint32_t data);
+
+  // Load a 32 bit immediate from a pool into a register.
+  BufferOffset as_Imm32Pool(Register dest, uint32_t value,
+                            Condition c = Always);
+
+  // Load a 64 bit floating point immediate from a pool into a register.
+  BufferOffset as_FImm64Pool(VFPRegister dest, double value,
+                             Condition c = Always);
+  // Load a 32 bit floating point immediate from a pool into a register.
+  BufferOffset as_FImm32Pool(VFPRegister dest, float value,
+                             Condition c = Always);
+
+  // Atomic instructions: ldrexd, ldrex, ldrexh, ldrexb, strexd, strex, strexh,
+  // strexb.
+  //
+  // The doubleword, halfword, and byte versions are available from ARMv6K
+  // forward.
+  //
+  // The word versions are available from ARMv6 forward and can be used to
+  // implement the halfword and byte versions on older systems.
+
+  // LDREXD rt, rt2, [rn].  Constraint: rt even register, rt2=rt+1.
+  BufferOffset as_ldrexd(Register rt, Register rt2, Register rn,
+                         Condition c = Always);
+
+  // LDREX rt, [rn]
+  BufferOffset as_ldrex(Register rt, Register rn, Condition c = Always);
+  BufferOffset as_ldrexh(Register rt, Register rn, Condition c = Always);
+  BufferOffset as_ldrexb(Register rt, Register rn, Condition c = Always);
+
+  // STREXD rd, rt, rt2, [rn].  Constraint: rt even register, rt2=rt+1.
+  BufferOffset as_strexd(Register rd, Register rt, Register rt2, Register rn,
+                         Condition c = Always);
+
+  // STREX rd, rt, [rn].  Constraint: rd != rn, rd != rt.
+  BufferOffset as_strex(Register rd, Register rt, Register rn,
+                        Condition c = Always);
+  BufferOffset as_strexh(Register rd, Register rt, Register rn,
+                         Condition c = Always);
+  BufferOffset as_strexb(Register rd, Register rt, Register rn,
+                         Condition c = Always);
+
+  // CLREX
+  BufferOffset as_clrex();
+
+  // Memory synchronization.
+  // These are available from ARMv7 forward.
+  BufferOffset as_dmb(BarrierOption option = BarrierSY);
+  BufferOffset as_dsb(BarrierOption option = BarrierSY);
+  BufferOffset as_isb();
+
+  // Memory synchronization for architectures before ARMv7.
+  BufferOffset as_dsb_trap();
+  BufferOffset as_dmb_trap();
+  BufferOffset as_isb_trap();
+
+  // Speculation barrier
+  BufferOffset as_csdb();
+
+  // Control flow stuff:
+
+  // bx can *only* branch to a register never to an immediate.
+  BufferOffset as_bx(Register r, Condition c = Always);
+
+  // Branch can branch to an immediate *or* to a register. Branches to
+  // immediates are pc relative, branches to registers are absolute.
+  BufferOffset as_b(BOffImm off, Condition c, Label* documentation = nullptr);
+
+  BufferOffset as_b(Label* l, Condition c = Always);
+  BufferOffset as_b(BOffImm off, Condition c, BufferOffset inst);
+
+  // blx can go to either an immediate or a register. When blx'ing to a
+  // register, we change processor mode depending on the low bit of the
+  // register when blx'ing to an immediate, we *always* change processor
+  // state.
+  BufferOffset as_blx(Label* l);
+
+  BufferOffset as_blx(Register r, Condition c = Always);
+  BufferOffset as_bl(BOffImm off, Condition c, Label* documentation = nullptr);
+  // bl can only branch+link to an immediate, never to a register it never
+  // changes processor state.
+  BufferOffset as_bl();
+  // bl #imm can have a condition code, blx #imm cannot.
+  // blx reg can be conditional.
+  BufferOffset as_bl(Label* l, Condition c);
+  BufferOffset as_bl(BOffImm off, Condition c, BufferOffset inst);
+
+  BufferOffset as_mrs(Register r, Condition c = Always);
+  BufferOffset as_msr(Register r, Condition c = Always);
+
+  // VFP instructions!
+ private:
+  enum vfp_size { IsDouble = 1 << 8, IsSingle = 0 << 8 };
+
+  BufferOffset writeVFPInst(vfp_size sz, uint32_t blob);
+
+  static void WriteVFPInstStatic(vfp_size sz, uint32_t blob, uint32_t* dest);
+
+  // Unityped variants: all registers hold the same (ieee754 single/double)
+  // notably not included are vcvt; vmov vd, #imm; vmov rt, vn.
+  BufferOffset as_vfp_float(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                            VFPOp op, Condition c = Always);
+
+ public:
+  BufferOffset as_vadd(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                       Condition c = Always);
+  BufferOffset as_vdiv(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                       Condition c = Always);
+  BufferOffset as_vmul(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                       Condition c = Always);
+  BufferOffset as_vnmul(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                        Condition c = Always);
+  BufferOffset as_vnmla(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                        Condition c = Always);
+  BufferOffset as_vnmls(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                        Condition c = Always);
+  BufferOffset as_vneg(VFPRegister vd, VFPRegister vm, Condition c = Always);
+  BufferOffset as_vsqrt(VFPRegister vd, VFPRegister vm, Condition c = Always);
+  BufferOffset as_vabs(VFPRegister vd, VFPRegister vm, Condition c = Always);
+  BufferOffset as_vsub(VFPRegister vd, VFPRegister vn, VFPRegister vm,
+                       Condition c = Always);
+  BufferOffset as_vcmp(VFPRegister vd, VFPRegister vm, Condition c = Always);
+  BufferOffset as_vcmpz(VFPRegister vd, Condition c = Always);
+
+  // Specifically, a move between two same sized-registers.
+  BufferOffset as_vmov(VFPRegister vd, VFPRegister vsrc, Condition c = Always);
+
+  // Transfer between Core and VFP.
+  enum FloatToCore_ { FloatToCore = 1 << 20, CoreToFloat = 0 << 20 };
+
+ private:
+  enum VFPXferSize { WordTransfer = 0x02000010, DoubleTransfer = 0x00400010 };
+
+ public:
+  // 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 as_vxfer(Register vt1, Register vt2, VFPRegister vm,
+                        FloatToCore_ f2c, Condition c = Always, int idx = 0);
+
+  // 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 as_vcvt(VFPRegister vd, VFPRegister vm, bool useFPSCR = false,
+                       Condition c = Always);
+
+  // Hard coded to a 32 bit fixed width result for now.
+  BufferOffset as_vcvtFixed(VFPRegister vd, bool isSigned, uint32_t fixedPoint,
+                            bool toFixed, Condition c = Always);
+
+  // Transfer between VFP and memory.
+  BufferOffset as_vdtr(LoadStore ls, VFPRegister vd, VFPAddr addr,
+                       Condition c = Always /* vfp doesn't have a wb option*/);
+
+  static void as_vdtr_patch(LoadStore ls, VFPRegister vd, VFPAddr addr,
+                            Condition c /* vfp doesn't have a wb option */,
+                            uint32_t* dest);
+
+  // VFP's ldm/stm work differently from the standard arm ones. You can only
+  // transfer a range.
+
+  BufferOffset as_vdtm(LoadStore st, Register rn, VFPRegister vd, int length,
+                       /* also has update conditions */ Condition c = Always);
+
+  // vldr/vstr variants that handle unaligned accesses.  These encode as NEON
+  // single-element instructions and can only be used if NEON is available.
+  // Here, vd must be tagged as a float or double register.
+  BufferOffset as_vldr_unaligned(VFPRegister vd, Register rn);
+  BufferOffset as_vstr_unaligned(VFPRegister vd, Register rn);
+
+  BufferOffset as_vimm(VFPRegister vd, VFPImm imm, Condition c = Always);
+
+  BufferOffset as_vmrs(Register r, Condition c = Always);
+  BufferOffset as_vmsr(Register r, Condition c = Always);
+
+  // Label operations.
+  bool nextLink(BufferOffset b, BufferOffset* next);
+  void bind(Label* label, BufferOffset boff = BufferOffset());
+  uint32_t currentOffset() { return nextOffset().getOffset(); }
+  void retarget(Label* label, Label* target);
+  // I'm going to pretend this doesn't exist for now.
+  void retarget(Label* label, void* target, RelocationKind reloc);
+
+  static void Bind(uint8_t* rawCode, const CodeLabel& label);
+
+  void as_bkpt();
+  BufferOffset as_illegal_trap();
+
+ public:
+  static void TraceJumpRelocations(JSTracer* trc, JitCode* code,
+                                   CompactBufferReader& reader);
+  static void TraceDataRelocations(JSTracer* trc, JitCode* code,
+                                   CompactBufferReader& reader);
+
+  void assertNoGCThings() const {
+#ifdef DEBUG
+    MOZ_ASSERT(dataRelocations_.length() == 0);
+    for (auto& j : jumps_) {
+      MOZ_ASSERT(j.kind() == RelocationKind::HARDCODED);
+    }
+#endif
+  }
+
+  static bool SupportsFloatingPoint() { return HasVFP(); }
+  static bool SupportsUnalignedAccesses() { return HasARMv7(); }
+  // Note, returning false here is technically wrong, but one has to go via the
+  // as_vldr_unaligned and as_vstr_unaligned instructions to get proper behavior
+  // and those are NEON-specific and have to be asked for specifically.
+  static bool SupportsFastUnalignedFPAccesses() { return false; }
+
+  static bool HasRoundInstruction(RoundingMode mode) { return false; }
+
+ protected:
+  void addPendingJump(BufferOffset src, ImmPtr target, RelocationKind kind) {
+    enoughMemory_ &= jumps_.append(RelativePatch(target.value, kind));
+    if (kind == RelocationKind::JITCODE) {
+      jumpRelocations_.writeUnsigned(src.getOffset());
+    }
+  }
+
+ public:
+  // The buffer is about to be linked, make sure any constant pools or excess
+  // bookkeeping has been flushed to the instruction stream.
+  void flush() {
+    MOZ_ASSERT(!isFinished);
+    m_buffer.flushPool();
+    return;
+  }
+
+  void comment(const char* msg) {
+#ifdef JS_DISASM_ARM
+    spew_.spew("; %s", msg);
+#endif
+  }
+
+  // Copy the assembly code to the given buffer, and perform any pending
+  // relocations relying on the target address.
+  void executableCopy(uint8_t* buffer);
+
+  // Actual assembly emitting functions.
+
+  // Since I can't think of a reasonable default for the mode, I'm going to
+  // leave it as a required argument.
+  void startDataTransferM(LoadStore ls, Register rm, DTMMode mode,
+                          DTMWriteBack update = NoWriteBack,
+                          Condition c = Always) {
+    MOZ_ASSERT(!dtmActive);
+    dtmUpdate = update;
+    dtmBase = rm;
+    dtmLoadStore = ls;
+    dtmLastReg = -1;
+    dtmRegBitField = 0;
+    dtmActive = 1;
+    dtmCond = c;
+    dtmMode = mode;
+  }
+
+  void transferReg(Register rn) {
+    MOZ_ASSERT(dtmActive);
+    MOZ_ASSERT(rn.code() > dtmLastReg);
+    dtmRegBitField |= 1 << rn.code();
+    if (dtmLoadStore == IsLoad && rn.code() == 13 && dtmBase.code() == 13) {
+      MOZ_CRASH("ARM Spec says this is invalid");
+    }
+  }
+  void finishDataTransfer() {
+    dtmActive = false;
+    as_dtm(dtmLoadStore, dtmBase, dtmRegBitField, dtmMode, dtmUpdate, dtmCond);
+  }
+
+  void startFloatTransferM(LoadStore ls, Register rm, DTMMode mode,
+                           DTMWriteBack update = NoWriteBack,
+                           Condition c = Always) {
+    MOZ_ASSERT(!dtmActive);
+    dtmActive = true;
+    dtmUpdate = update;
+    dtmLoadStore = ls;
+    dtmBase = rm;
+    dtmCond = c;
+    dtmLastReg = -1;
+    dtmMode = mode;
+    dtmDelta = 0;
+  }
+  void transferFloatReg(VFPRegister rn) {
+    if (dtmLastReg == -1) {
+      vdtmFirstReg = rn.code();
+    } else {
+      if (dtmDelta == 0) {
+        dtmDelta = rn.code() - dtmLastReg;
+        MOZ_ASSERT(dtmDelta == 1 || dtmDelta == -1);
+      }
+      MOZ_ASSERT(dtmLastReg >= 0);
+      MOZ_ASSERT(rn.code() == unsigned(dtmLastReg) + dtmDelta);
+    }
+
+    dtmLastReg = rn.code();
+  }
+  void finishFloatTransfer() {
+    MOZ_ASSERT(dtmActive);
+    dtmActive = false;
+    MOZ_ASSERT(dtmLastReg != -1);
+    dtmDelta = dtmDelta ? dtmDelta : 1;
+    // The operand for the vstr/vldr instruction is the lowest register in the
+    // range.
+    int low = std::min(dtmLastReg, vdtmFirstReg);
+    int high = std::max(dtmLastReg, vdtmFirstReg);
+    // Fencepost problem.
+    int len = high - low + 1;
+    // vdtm can only transfer 16 registers at once.  If we need to transfer
+    // more, then either hoops are necessary, or we need to be updating the
+    // register.
+    MOZ_ASSERT_IF(len > 16, dtmUpdate == WriteBack);
+
+    int adjustLow = dtmLoadStore == IsStore ? 0 : 1;
+    int adjustHigh = dtmLoadStore == IsStore ? -1 : 0;
+    while (len > 0) {
+      // Limit the instruction to 16 registers.
+      int curLen = std::min(len, 16);
+      // If it is a store, we want to start at the high end and move down
+      // (e.g. vpush d16-d31; vpush d0-d15).
+      int curStart = (dtmLoadStore == IsStore) ? high - curLen + 1 : low;
+      as_vdtm(dtmLoadStore, dtmBase,
+              VFPRegister(FloatRegister::FromCode(curStart)), curLen, dtmCond);
+      // Update the bounds.
+      low += adjustLow * curLen;
+      high += adjustHigh * curLen;
+      // Update the length parameter.
+      len -= curLen;
+    }
+  }
+
+ private:
+  int dtmRegBitField;
+  int vdtmFirstReg;
+  int dtmLastReg;
+  int dtmDelta;
+  Register dtmBase;
+  DTMWriteBack dtmUpdate;
+  DTMMode dtmMode;
+  LoadStore dtmLoadStore;
+  bool dtmActive;
+  Condition dtmCond;
+
+ public:
+  enum {
+    PadForAlign8 = (int)0x00,
+    PadForAlign16 = (int)0x0000,
+    PadForAlign32 = (int)0xe12fff7f  // 'bkpt 0xffff'
+  };
+
+  // API for speaking with the IonAssemblerBufferWithConstantPools generate an
+  // initial placeholder instruction that we want to later fix up.
+  static void InsertIndexIntoTag(uint8_t* load, uint32_t index);
+
+  // Take the stub value that was written in before, and write in an actual
+  // load using the index we'd computed previously as well as the address of
+  // the pool start.
+  static void PatchConstantPoolLoad(void* loadAddr, void* constPoolAddr);
+
+  // We're not tracking short-range branches for ARM for now.
+  static void PatchShortRangeBranchToVeneer(ARMBuffer*, unsigned rangeIdx,
+                                            BufferOffset deadline,
+                                            BufferOffset veneer) {
+    MOZ_CRASH();
+  }
+  // END API
+
+  // Move our entire pool into the instruction stream. This is to force an
+  // opportunistic dump of the pool, prefferably when it is more convenient to
+  // do a dump.
+  void flushBuffer();
+  void enterNoPool(size_t maxInst);
+  void leaveNoPool();
+  void enterNoNops();
+  void leaveNoNops();
+
+  static void WritePoolHeader(uint8_t* start, Pool* p, bool isNatural);
+  static void WritePoolGuard(BufferOffset branch, Instruction* inst,
+                             BufferOffset dest);
+
+  static uint32_t PatchWrite_NearCallSize();
+  static uint32_t NopSize() { return 4; }
+  static void PatchWrite_NearCall(CodeLocationLabel start,
+                                  CodeLocationLabel toCall);
+  static void PatchDataWithValueCheck(CodeLocationLabel label,
+                                      PatchedImmPtr newValue,
+                                      PatchedImmPtr expectedValue);
+  static void PatchDataWithValueCheck(CodeLocationLabel label, ImmPtr newValue,
+                                      ImmPtr expectedValue);
+  static void PatchWrite_Imm32(CodeLocationLabel label, Imm32 imm);
+
+  static uint32_t AlignDoubleArg(uint32_t offset) { return (offset + 1) & ~1; }
+  static uint8_t* NextInstruction(uint8_t* instruction,
+                                  uint32_t* count = nullptr);
+
+  // Toggle a jmp or cmp emitted by toggledJump().
+  static void ToggleToJmp(CodeLocationLabel inst_);
+  static void ToggleToCmp(CodeLocationLabel inst_);
+
+  static size_t ToggledCallSize(uint8_t* code);
+  static void ToggleCall(CodeLocationLabel inst_, bool enabled);
+
+  void processCodeLabels(uint8_t* rawCode);
+
+  void verifyHeapAccessDisassembly(uint32_t begin, uint32_t end,
+                                   const Disassembler::HeapAccess& heapAccess) {
+    // Implement this if we implement a disassembler.
+  }
+};  // Assembler
+
+// An Instruction is a structure for both encoding and decoding any and all ARM
+// instructions. Many classes have not been implemented thus far.
+class Instruction {
+  uint32_t data;
+
+ protected:
+  // This is not for defaulting to always, this is for instructions that
+  // cannot be made conditional, and have the usually invalid 4b1111 cond
+  // field.
+  explicit Instruction(uint32_t data_, bool fake = false)
+      : data(data_ | 0xf0000000) {
+    MOZ_ASSERT(fake || ((data_ & 0xf0000000) == 0));
+  }
+  // Standard constructor.
+  Instruction(uint32_t data_, Assembler::Condition c)
+      : data(data_ | (uint32_t)c) {
+    MOZ_ASSERT((data_ & 0xf0000000) == 0);
+  }
+  // You should never create an instruction directly. You should create a more
+  // specific instruction which will eventually call one of these constructors
+  // for you.
+ public:
+  uint32_t encode() const { return data; }
+  // Check if this instruction is really a particular case.
+  template <class C>
+  bool is() const {
+    return C::IsTHIS(*this);
+  }
+
+  // Safely get a more specific variant of this pointer.
+  template <class C>
+  C* as() const {
+    return C::AsTHIS(*this);
+  }
+
+  const Instruction& operator=(Instruction src) {
+    data = src.data;
+    return *this;
+  }
+  // Since almost all instructions have condition codes, the condition code
+  // extractor resides in the base class.
+  Assembler::Condition extractCond() const {
+    MOZ_ASSERT(data >> 28 != 0xf,
+               "The instruction does not have condition code");
+    return (Assembler::Condition)(data & 0xf0000000);
+  }
+
+  // Sometimes, an api wants a uint32_t (or a pointer to it) rather than an
+  // instruction. raw() just coerces this into a pointer to a uint32_t.
+  const uint32_t* raw() const { return &data; }
+  uint32_t size() const { return 4; }
+};  // Instruction
+
+// Make sure that it is the right size.
+static_assert(sizeof(Instruction) == 4);
+
+inline void InstructionIterator::advanceRaw(ptrdiff_t instructions) {
+  inst_ = inst_ + instructions;
+}
+
+// Data Transfer Instructions.
+class InstDTR : public Instruction {
+ public:
+  enum IsByte_ { IsByte = 0x00400000, IsWord = 0x00000000 };
+  static const int IsDTR = 0x04000000;
+  static const int IsDTRMask = 0x0c000000;
+
+  // TODO: Replace the initialization with something that is safer.
+  InstDTR(LoadStore ls, IsByte_ ib, Index mode, Register rt, DTRAddr addr,
+          Assembler::Condition c)
+      : Instruction(std::underlying_type_t<LoadStore>(ls) |
+                        std::underlying_type_t<IsByte_>(ib) |
+                        std::underlying_type_t<Index>(mode) | RT(rt) |
+                        addr.encode() | IsDTR,
+                    c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstDTR* AsTHIS(const Instruction& i);
+};
+static_assert(sizeof(InstDTR) == sizeof(Instruction));
+
+class InstLDR : public InstDTR {
+ public:
+  InstLDR(Index mode, Register rt, DTRAddr addr, Assembler::Condition c)
+      : InstDTR(IsLoad, IsWord, mode, rt, addr, c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstLDR* AsTHIS(const Instruction& i);
+
+  int32_t signedOffset() const {
+    int32_t offset = encode() & 0xfff;
+    if (IsUp_(encode() & IsUp) != IsUp) {
+      return -offset;
+    }
+    return offset;
+  }
+  uint32_t* dest() const {
+    int32_t offset = signedOffset();
+    // When patching the load in PatchConstantPoolLoad, we ensure that the
+    // offset is a multiple of 4, offset by 8 bytes from the actual
+    // location.  Indeed, when the base register is PC, ARM's 3 stages
+    // pipeline design makes it that PC is off by 8 bytes (= 2 *
+    // sizeof(uint32*)) when we actually executed it.
+    MOZ_ASSERT(offset % 4 == 0);
+    offset >>= 2;
+    return (uint32_t*)raw() + offset + 2;
+  }
+};
+static_assert(sizeof(InstDTR) == sizeof(InstLDR));
+
+class InstNOP : public Instruction {
+ public:
+  static const uint32_t NopInst = 0x0320f000;
+
+  InstNOP() : Instruction(NopInst, Assembler::Always) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstNOP* AsTHIS(Instruction& i);
+};
+
+// Branching to a register, or calling a register
+class InstBranchReg : public Instruction {
+ protected:
+  // Don't use BranchTag yourself, use a derived instruction.
+  enum BranchTag { IsBX = 0x012fff10, IsBLX = 0x012fff30 };
+
+  static const uint32_t IsBRegMask = 0x0ffffff0;
+
+  InstBranchReg(BranchTag tag, Register rm, Assembler::Condition c)
+      : Instruction(tag | rm.code(), c) {}
+
+ public:
+  static bool IsTHIS(const Instruction& i);
+  static InstBranchReg* AsTHIS(const Instruction& i);
+
+  // Get the register that is being branched to
+  void extractDest(Register* dest);
+  // Make sure we are branching to a pre-known register
+  bool checkDest(Register dest);
+};
+static_assert(sizeof(InstBranchReg) == sizeof(Instruction));
+
+// Branching to an immediate offset, or calling an immediate offset
+class InstBranchImm : public Instruction {
+ protected:
+  enum BranchTag { IsB = 0x0a000000, IsBL = 0x0b000000 };
+
+  static const uint32_t IsBImmMask = 0x0f000000;
+
+  InstBranchImm(BranchTag tag, BOffImm off, Assembler::Condition c)
+      : Instruction(tag | off.encode(), c) {}
+
+ public:
+  static bool IsTHIS(const Instruction& i);
+  static InstBranchImm* AsTHIS(const Instruction& i);
+
+  void extractImm(BOffImm* dest);
+};
+static_assert(sizeof(InstBranchImm) == sizeof(Instruction));
+
+// Very specific branching instructions.
+class InstBXReg : public InstBranchReg {
+ public:
+  static bool IsTHIS(const Instruction& i);
+  static InstBXReg* AsTHIS(const Instruction& i);
+};
+
+class InstBLXReg : public InstBranchReg {
+ public:
+  InstBLXReg(Register reg, Assembler::Condition c)
+      : InstBranchReg(IsBLX, reg, c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstBLXReg* AsTHIS(const Instruction& i);
+};
+
+class InstBImm : public InstBranchImm {
+ public:
+  InstBImm(BOffImm off, Assembler::Condition c) : InstBranchImm(IsB, off, c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstBImm* AsTHIS(const Instruction& i);
+};
+
+class InstBLImm : public InstBranchImm {
+ public:
+  InstBLImm(BOffImm off, Assembler::Condition c)
+      : InstBranchImm(IsBL, off, c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstBLImm* AsTHIS(const Instruction& i);
+};
+
+// Both movw and movt. The layout of both the immediate and the destination
+// register is the same so the code is being shared.
+class InstMovWT : public Instruction {
+ protected:
+  enum WT { IsW = 0x03000000, IsT = 0x03400000 };
+  static const uint32_t IsWTMask = 0x0ff00000;
+
+  InstMovWT(Register rd, Imm16 imm, WT wt, Assembler::Condition c)
+      : Instruction(RD(rd) | imm.encode() | wt, c) {}
+
+ public:
+  void extractImm(Imm16* dest);
+  void extractDest(Register* dest);
+  bool checkImm(Imm16 dest);
+  bool checkDest(Register dest);
+
+  static bool IsTHIS(Instruction& i);
+  static InstMovWT* AsTHIS(Instruction& i);
+};
+static_assert(sizeof(InstMovWT) == sizeof(Instruction));
+
+class InstMovW : public InstMovWT {
+ public:
+  InstMovW(Register rd, Imm16 imm, Assembler::Condition c)
+      : InstMovWT(rd, imm, IsW, c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstMovW* AsTHIS(const Instruction& i);
+};
+
+class InstMovT : public InstMovWT {
+ public:
+  InstMovT(Register rd, Imm16 imm, Assembler::Condition c)
+      : InstMovWT(rd, imm, IsT, c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstMovT* AsTHIS(const Instruction& i);
+};
+
+class InstALU : public Instruction {
+  static const int32_t ALUMask = 0xc << 24;
+
+ public:
+  InstALU(Register rd, Register rn, Operand2 op2, ALUOp op, SBit s,
+          Assembler::Condition c)
+      : Instruction(maybeRD(rd) | maybeRN(rn) | op2.encode() | op | s, c) {}
+
+  static bool IsTHIS(const Instruction& i);
+  static InstALU* AsTHIS(const Instruction& i);
+
+  void extractOp(ALUOp* ret);
+  bool checkOp(ALUOp op);
+  void extractDest(Register* ret);
+  bool checkDest(Register rd);
+  void extractOp1(Register* ret);
+  bool checkOp1(Register rn);
+  Operand2 extractOp2();
+};
+
+class InstCMP : public InstALU {
+ public:
+  static bool IsTHIS(const Instruction& i);
+  static InstCMP* AsTHIS(const Instruction& i);
+};
+
+class InstMOV : public InstALU {
+ public:
+  static bool IsTHIS(const Instruction& i);
+  static InstMOV* AsTHIS(const Instruction& i);
+};
+
+// Compile-time iterator over instructions, with a safe interface that
+// references not-necessarily-linear Instructions by linear BufferOffset.
+class BufferInstructionIterator
+    : public ARMBuffer::AssemblerBufferInstIterator {
+ public:
+  BufferInstructionIterator(BufferOffset bo, ARMBuffer* buffer)
+      : ARMBuffer::AssemblerBufferInstIterator(bo, buffer) {}
+
+  // Advances the buffer to the next intentionally-inserted instruction.
+  Instruction* next() {
+    advance(cur()->size());
+    maybeSkipAutomaticInstructions();
+    return cur();
+  }
+
+  // Advances the BufferOffset past any automatically-inserted instructions.
+  Instruction* maybeSkipAutomaticInstructions();
+};
+
+static const uint32_t NumIntArgRegs = 4;
+
+// There are 16 *float* registers available for arguments
+// If doubles are used, only half the number of registers are available.
+static const uint32_t NumFloatArgRegs = 16;
+
+static inline bool GetIntArgReg(uint32_t usedIntArgs, uint32_t usedFloatArgs,
+                                Register* out) {
+  if (usedIntArgs >= NumIntArgRegs) {
+    return false;
+  }
+
+  *out = Register::FromCode(usedIntArgs);
+  return true;
+}
+
+// Get a register in which we plan to put a quantity that will be used as an
+// integer argument. This differs from GetIntArgReg in that if we have no more
+// actual argument registers to use we will fall back on using whatever
+// CallTempReg* don't overlap the argument registers, and only fail once those
+// run out too.
+static inline bool GetTempRegForIntArg(uint32_t usedIntArgs,
+                                       uint32_t usedFloatArgs, Register* out) {
+  if (GetIntArgReg(usedIntArgs, usedFloatArgs, out)) {
+    return true;
+  }
+
+  // Unfortunately, we have to assume things about the point at which
+  // GetIntArgReg returns false, because we need to know how many registers it
+  // can allocate.
+  usedIntArgs -= NumIntArgRegs;
+  if (usedIntArgs >= NumCallTempNonArgRegs) {
+    return false;
+  }
+
+  *out = CallTempNonArgRegs[usedIntArgs];
+  return true;
+}
+
+#if defined(JS_CODEGEN_ARM_HARDFP) || defined(JS_SIMULATOR_ARM)
+
+static inline bool GetFloat32ArgReg(uint32_t usedIntArgs,
+                                    uint32_t usedFloatArgs,
+                                    FloatRegister* out) {
+  MOZ_ASSERT(UseHardFpABI());
+  if (usedFloatArgs >= NumFloatArgRegs) {
+    return false;
+  }
+  *out = VFPRegister(usedFloatArgs, VFPRegister::Single);
+  return true;
+}
+static inline bool GetDoubleArgReg(uint32_t usedIntArgs, uint32_t usedFloatArgs,
+                                   FloatRegister* out) {
+  MOZ_ASSERT(UseHardFpABI());
+  MOZ_ASSERT((usedFloatArgs % 2) == 0);
+  if (usedFloatArgs >= NumFloatArgRegs) {
+    return false;
+  }
+  *out = VFPRegister(usedFloatArgs >> 1, VFPRegister::Double);
+  return true;
+}
+
+#endif
+
+class DoubleEncoder {
+  struct DoubleEntry {
+    uint32_t dblTop;
+    datastore::Imm8VFPImmData data;
+  };
+
+  static const DoubleEntry table[256];
+
+ public:
+  bool lookup(uint32_t top, datastore::Imm8VFPImmData* ret) const {
+    for (int i = 0; i < 256; i++) {
+      if (table[i].dblTop == top) {
+        *ret = table[i].data;
+        return true;
+      }
+    }
+    return false;
+  }
+};
+
+// Forbids nop filling for testing purposes. Not nestable.
+class AutoForbidNops {
+ protected:
+  Assembler* masm_;
+
+ public:
+  explicit AutoForbidNops(Assembler* masm) : masm_(masm) {
+    masm_->enterNoNops();
+  }
+  ~AutoForbidNops() { masm_->leaveNoNops(); }
+};
+
+class AutoForbidPoolsAndNops : public AutoForbidNops {
+ public:
+  // The maxInst argument is the maximum number of word sized instructions
+  // that will be allocated within this context. It is used to determine if
+  // the pool needs to be dumped before entering this content. The debug code
+  // checks that no more than maxInst instructions are actually allocated.
+  //
+  // Allocation of pool entries is not supported within this content so the
+  // code can not use large integers or float constants etc.
+  AutoForbidPoolsAndNops(Assembler* masm, size_t maxInst)
+      : AutoForbidNops(masm) {
+    masm_->enterNoPool(maxInst);
+  }
+
+  ~AutoForbidPoolsAndNops() { masm_->leaveNoPool(); }
+};
+
+}  // namespace jit
+}  // namespace js
+
+#endif /* jit_arm_Assembler_arm_h */