Adding upstream version 110.0.1.upstream/110.0.1upstream

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

1 files changed, 7195 insertions, 0 deletions

diff --git a/js/src/jit/MIR.cpp b/js/src/jit/MIR.cpp
new file mode 100644
index 0000000000..a403b4ff83
--- /dev/null
+++ b/js/src/jit/MIR.cpp
@@ -0,0 +1,7195 @@
+/* -*- 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/MIR.h"
+
+#include "mozilla/CheckedInt.h"
+#include "mozilla/EndianUtils.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/ScopeExit.h"
+
+#include <array>
+#include <utility>
+
+#include "jslibmath.h"
+#include "jsmath.h"
+#include "jsnum.h"
+
+#include "builtin/RegExp.h"
+#include "jit/AtomicOperations.h"
+#include "jit/CompileInfo.h"
+#include "jit/KnownClass.h"
+#include "jit/MIRGraph.h"
+#include "jit/RangeAnalysis.h"
+#include "jit/VMFunctions.h"
+#include "js/Conversions.h"
+#include "js/experimental/JitInfo.h"  // JSJitInfo, JSTypedMethodJitInfo
+#include "js/ScalarType.h"            // js::Scalar::Type
+#include "util/Text.h"
+#include "util/Unicode.h"
+#include "vm/Iteration.h"    // js::NativeIterator
+#include "vm/PlainObject.h"  // js::PlainObject
+#include "vm/Uint8Clamped.h"
+#include "wasm/WasmCode.h"
+
+#include "vm/JSAtom-inl.h"
+#include "wasm/WasmInstance-inl.h"
+
+using namespace js;
+using namespace js::jit;
+
+using JS::ToInt32;
+
+using mozilla::CheckedInt;
+using mozilla::DebugOnly;
+using mozilla::IsFloat32Representable;
+using mozilla::IsNaN;
+using mozilla::IsPowerOfTwo;
+using mozilla::Maybe;
+using mozilla::NumbersAreIdentical;
+
+NON_GC_POINTER_TYPE_ASSERTIONS_GENERATED
+
+#ifdef DEBUG
+size_t MUse::index() const { return consumer()->indexOf(this); }
+#endif
+
+template <size_t Op>
+static void ConvertDefinitionToDouble(TempAllocator& alloc, MDefinition* def,
+                                      MInstruction* consumer) {
+  MInstruction* replace = MToDouble::New(alloc, def);
+  consumer->replaceOperand(Op, replace);
+  consumer->block()->insertBefore(consumer, replace);
+}
+
+template <size_t Arity, size_t Index>
+static void ConvertOperandToDouble(MAryInstruction<Arity>* def,
+                                   TempAllocator& alloc) {
+  static_assert(Index < Arity);
+  auto* operand = def->getOperand(Index);
+  if (operand->type() == MIRType::Float32) {
+    ConvertDefinitionToDouble<Index>(alloc, operand, def);
+  }
+}
+
+template <size_t Arity, size_t... ISeq>
+static void ConvertOperandsToDouble(MAryInstruction<Arity>* def,
+                                    TempAllocator& alloc,
+                                    std::index_sequence<ISeq...>) {
+  (ConvertOperandToDouble<Arity, ISeq>(def, alloc), ...);
+}
+
+template <size_t Arity>
+static void ConvertOperandsToDouble(MAryInstruction<Arity>* def,
+                                    TempAllocator& alloc) {
+  ConvertOperandsToDouble<Arity>(def, alloc, std::make_index_sequence<Arity>{});
+}
+
+template <size_t Arity, size_t... ISeq>
+static bool AllOperandsCanProduceFloat32(MAryInstruction<Arity>* def,
+                                         std::index_sequence<ISeq...>) {
+  return (def->getOperand(ISeq)->canProduceFloat32() && ...);
+}
+
+template <size_t Arity>
+static bool AllOperandsCanProduceFloat32(MAryInstruction<Arity>* def) {
+  return AllOperandsCanProduceFloat32<Arity>(def,
+                                             std::make_index_sequence<Arity>{});
+}
+
+static bool CheckUsesAreFloat32Consumers(const MInstruction* ins) {
+  if (ins->isImplicitlyUsed()) {
+    return false;
+  }
+  bool allConsumerUses = true;
+  for (MUseDefIterator use(ins); allConsumerUses && use; use++) {
+    allConsumerUses &= use.def()->canConsumeFloat32(use.use());
+  }
+  return allConsumerUses;
+}
+
+#ifdef JS_JITSPEW
+static const char* OpcodeName(MDefinition::Opcode op) {
+  static const char* const names[] = {
+#  define NAME(x) #x,
+      MIR_OPCODE_LIST(NAME)
+#  undef NAME
+  };
+  return names[unsigned(op)];
+}
+
+void MDefinition::PrintOpcodeName(GenericPrinter& out, Opcode op) {
+  const char* name = OpcodeName(op);
+  size_t len = strlen(name);
+  for (size_t i = 0; i < len; i++) {
+    out.printf("%c", unicode::ToLowerCase(name[i]));
+  }
+}
+
+uint32_t js::jit::GetMBasicBlockId(const MBasicBlock* block) {
+  return block->id();
+}
+#endif
+
+static MConstant* EvaluateInt64ConstantOperands(TempAllocator& alloc,
+                                                MBinaryInstruction* ins) {
+  MDefinition* left = ins->getOperand(0);
+  MDefinition* right = ins->getOperand(1);
+
+  if (!left->isConstant() || !right->isConstant()) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(left->type() == MIRType::Int64);
+  MOZ_ASSERT(right->type() == MIRType::Int64);
+
+  int64_t lhs = left->toConstant()->toInt64();
+  int64_t rhs = right->toConstant()->toInt64();
+  int64_t ret;
+
+  switch (ins->op()) {
+    case MDefinition::Opcode::BitAnd:
+      ret = lhs & rhs;
+      break;
+    case MDefinition::Opcode::BitOr:
+      ret = lhs | rhs;
+      break;
+    case MDefinition::Opcode::BitXor:
+      ret = lhs ^ rhs;
+      break;
+    case MDefinition::Opcode::Lsh:
+      ret = lhs << (rhs & 0x3F);
+      break;
+    case MDefinition::Opcode::Rsh:
+      ret = lhs >> (rhs & 0x3F);
+      break;
+    case MDefinition::Opcode::Ursh:
+      ret = uint64_t(lhs) >> (uint64_t(rhs) & 0x3F);
+      break;
+    case MDefinition::Opcode::Add:
+      ret = lhs + rhs;
+      break;
+    case MDefinition::Opcode::Sub:
+      ret = lhs - rhs;
+      break;
+    case MDefinition::Opcode::Mul:
+      ret = lhs * rhs;
+      break;
+    case MDefinition::Opcode::Div:
+      if (rhs == 0) {
+        // Division by zero will trap at runtime.
+        return nullptr;
+      }
+      if (ins->toDiv()->isUnsigned()) {
+        ret = int64_t(uint64_t(lhs) / uint64_t(rhs));
+      } else if (lhs == INT64_MIN || rhs == -1) {
+        // Overflow will trap at runtime.
+        return nullptr;
+      } else {
+        ret = lhs / rhs;
+      }
+      break;
+    case MDefinition::Opcode::Mod:
+      if (rhs == 0) {
+        // Division by zero will trap at runtime.
+        return nullptr;
+      }
+      if (!ins->toMod()->isUnsigned() && (lhs < 0 || rhs < 0)) {
+        // Handle all negative values at runtime, for simplicity.
+        return nullptr;
+      }
+      ret = int64_t(uint64_t(lhs) % uint64_t(rhs));
+      break;
+    default:
+      MOZ_CRASH("NYI");
+  }
+
+  return MConstant::NewInt64(alloc, ret);
+}
+
+static MConstant* EvaluateConstantOperands(TempAllocator& alloc,
+                                           MBinaryInstruction* ins,
+                                           bool* ptypeChange = nullptr) {
+  MDefinition* left = ins->getOperand(0);
+  MDefinition* right = ins->getOperand(1);
+
+  MOZ_ASSERT(IsTypeRepresentableAsDouble(left->type()));
+  MOZ_ASSERT(IsTypeRepresentableAsDouble(right->type()));
+
+  if (!left->isConstant() || !right->isConstant()) {
+    return nullptr;
+  }
+
+  MConstant* lhs = left->toConstant();
+  MConstant* rhs = right->toConstant();
+  double ret = JS::GenericNaN();
+
+  switch (ins->op()) {
+    case MDefinition::Opcode::BitAnd:
+      ret = double(lhs->toInt32() & rhs->toInt32());
+      break;
+    case MDefinition::Opcode::BitOr:
+      ret = double(lhs->toInt32() | rhs->toInt32());
+      break;
+    case MDefinition::Opcode::BitXor:
+      ret = double(lhs->toInt32() ^ rhs->toInt32());
+      break;
+    case MDefinition::Opcode::Lsh:
+      ret = double(uint32_t(lhs->toInt32()) << (rhs->toInt32() & 0x1F));
+      break;
+    case MDefinition::Opcode::Rsh:
+      ret = double(lhs->toInt32() >> (rhs->toInt32() & 0x1F));
+      break;
+    case MDefinition::Opcode::Ursh:
+      ret = double(uint32_t(lhs->toInt32()) >> (rhs->toInt32() & 0x1F));
+      break;
+    case MDefinition::Opcode::Add:
+      ret = lhs->numberToDouble() + rhs->numberToDouble();
+      break;
+    case MDefinition::Opcode::Sub:
+      ret = lhs->numberToDouble() - rhs->numberToDouble();
+      break;
+    case MDefinition::Opcode::Mul:
+      ret = lhs->numberToDouble() * rhs->numberToDouble();
+      break;
+    case MDefinition::Opcode::Div:
+      if (ins->toDiv()->isUnsigned()) {
+        if (rhs->isInt32(0)) {
+          if (ins->toDiv()->trapOnError()) {
+            return nullptr;
+          }
+          ret = 0.0;
+        } else {
+          ret = double(uint32_t(lhs->toInt32()) / uint32_t(rhs->toInt32()));
+        }
+      } else {
+        ret = NumberDiv(lhs->numberToDouble(), rhs->numberToDouble());
+      }
+      break;
+    case MDefinition::Opcode::Mod:
+      if (ins->toMod()->isUnsigned()) {
+        if (rhs->isInt32(0)) {
+          if (ins->toMod()->trapOnError()) {
+            return nullptr;
+          }
+          ret = 0.0;
+        } else {
+          ret = double(uint32_t(lhs->toInt32()) % uint32_t(rhs->toInt32()));
+        }
+      } else {
+        ret = NumberMod(lhs->numberToDouble(), rhs->numberToDouble());
+      }
+      break;
+    default:
+      MOZ_CRASH("NYI");
+  }
+
+  if (ins->type() == MIRType::Float32) {
+    return MConstant::NewFloat32(alloc, float(ret));
+  }
+  if (ins->type() == MIRType::Double) {
+    return MConstant::New(alloc, DoubleValue(ret));
+  }
+
+  Value retVal;
+  retVal.setNumber(JS::CanonicalizeNaN(ret));
+
+  // If this was an int32 operation but the result isn't an int32 (for
+  // example, a division where the numerator isn't evenly divisible by the
+  // denominator), decline folding.
+  MOZ_ASSERT(ins->type() == MIRType::Int32);
+  if (!retVal.isInt32()) {
+    if (ptypeChange) {
+      *ptypeChange = true;
+    }
+    return nullptr;
+  }
+
+  return MConstant::New(alloc, retVal);
+}
+
+static MMul* EvaluateExactReciprocal(TempAllocator& alloc, MDiv* ins) {
+  // we should fold only when it is a floating point operation
+  if (!IsFloatingPointType(ins->type())) {
+    return nullptr;
+  }
+
+  MDefinition* left = ins->getOperand(0);
+  MDefinition* right = ins->getOperand(1);
+
+  if (!right->isConstant()) {
+    return nullptr;
+  }
+
+  int32_t num;
+  if (!mozilla::NumberIsInt32(right->toConstant()->numberToDouble(), &num)) {
+    return nullptr;
+  }
+
+  // check if rhs is a power of two
+  if (mozilla::Abs(num) & (mozilla::Abs(num) - 1)) {
+    return nullptr;
+  }
+
+  Value ret;
+  ret.setDouble(1.0 / double(num));
+
+  MConstant* foldedRhs;
+  if (ins->type() == MIRType::Float32) {
+    foldedRhs = MConstant::NewFloat32(alloc, ret.toDouble());
+  } else {
+    foldedRhs = MConstant::New(alloc, ret);
+  }
+
+  MOZ_ASSERT(foldedRhs->type() == ins->type());
+  ins->block()->insertBefore(ins, foldedRhs);
+
+  MMul* mul = MMul::New(alloc, left, foldedRhs, ins->type());
+  mul->setMustPreserveNaN(ins->mustPreserveNaN());
+  return mul;
+}
+
+#ifdef JS_JITSPEW
+const char* MDefinition::opName() const { return OpcodeName(op()); }
+
+void MDefinition::printName(GenericPrinter& out) const {
+  PrintOpcodeName(out, op());
+  out.printf("%u", id());
+}
+#endif
+
+HashNumber MDefinition::valueHash() const {
+  HashNumber out = HashNumber(op());
+  for (size_t i = 0, e = numOperands(); i < e; i++) {
+    out = addU32ToHash(out, getOperand(i)->id());
+  }
+  if (MDefinition* dep = dependency()) {
+    out = addU32ToHash(out, dep->id());
+  }
+  return out;
+}
+
+HashNumber MNullaryInstruction::valueHash() const {
+  HashNumber hash = HashNumber(op());
+  if (MDefinition* dep = dependency()) {
+    hash = addU32ToHash(hash, dep->id());
+  }
+  MOZ_ASSERT(hash == MDefinition::valueHash());
+  return hash;
+}
+
+HashNumber MUnaryInstruction::valueHash() const {
+  HashNumber hash = HashNumber(op());
+  hash = addU32ToHash(hash, getOperand(0)->id());
+  if (MDefinition* dep = dependency()) {
+    hash = addU32ToHash(hash, dep->id());
+  }
+  MOZ_ASSERT(hash == MDefinition::valueHash());
+  return hash;
+}
+
+HashNumber MBinaryInstruction::valueHash() const {
+  HashNumber hash = HashNumber(op());
+  hash = addU32ToHash(hash, getOperand(0)->id());
+  hash = addU32ToHash(hash, getOperand(1)->id());
+  if (MDefinition* dep = dependency()) {
+    hash = addU32ToHash(hash, dep->id());
+  }
+  MOZ_ASSERT(hash == MDefinition::valueHash());
+  return hash;
+}
+
+HashNumber MTernaryInstruction::valueHash() const {
+  HashNumber hash = HashNumber(op());
+  hash = addU32ToHash(hash, getOperand(0)->id());
+  hash = addU32ToHash(hash, getOperand(1)->id());
+  hash = addU32ToHash(hash, getOperand(2)->id());
+  if (MDefinition* dep = dependency()) {
+    hash = addU32ToHash(hash, dep->id());
+  }
+  MOZ_ASSERT(hash == MDefinition::valueHash());
+  return hash;
+}
+
+HashNumber MQuaternaryInstruction::valueHash() const {
+  HashNumber hash = HashNumber(op());
+  hash = addU32ToHash(hash, getOperand(0)->id());
+  hash = addU32ToHash(hash, getOperand(1)->id());
+  hash = addU32ToHash(hash, getOperand(2)->id());
+  hash = addU32ToHash(hash, getOperand(3)->id());
+  if (MDefinition* dep = dependency()) {
+    hash = addU32ToHash(hash, dep->id());
+  }
+  MOZ_ASSERT(hash == MDefinition::valueHash());
+  return hash;
+}
+
+const MDefinition* MDefinition::skipObjectGuards() const {
+  const MDefinition* result = this;
+  // These instructions don't modify the object and just guard specific
+  // properties.
+  while (true) {
+    if (result->isGuardShape()) {
+      result = result->toGuardShape()->object();
+      continue;
+    }
+    if (result->isGuardNullProto()) {
+      result = result->toGuardNullProto()->object();
+      continue;
+    }
+    if (result->isGuardProto()) {
+      result = result->toGuardProto()->object();
+      continue;
+    }
+
+    break;
+  }
+
+  return result;
+}
+
+bool MDefinition::congruentIfOperandsEqual(const MDefinition* ins) const {
+  if (op() != ins->op()) {
+    return false;
+  }
+
+  if (type() != ins->type()) {
+    return false;
+  }
+
+  if (isEffectful() || ins->isEffectful()) {
+    return false;
+  }
+
+  if (numOperands() != ins->numOperands()) {
+    return false;
+  }
+
+  for (size_t i = 0, e = numOperands(); i < e; i++) {
+    if (getOperand(i) != ins->getOperand(i)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+MDefinition* MDefinition::foldsTo(TempAllocator& alloc) {
+  // In the default case, there are no constants to fold.
+  return this;
+}
+
+bool MDefinition::mightBeMagicType() const {
+  if (IsMagicType(type())) {
+    return true;
+  }
+
+  if (MIRType::Value != type()) {
+    return false;
+  }
+
+  return true;
+}
+
+bool MDefinition::definitelyType(std::initializer_list<MIRType> types) const {
+#ifdef DEBUG
+  // Only support specialized, non-magic types.
+  auto isSpecializedNonMagic = [](MIRType type) {
+    return type <= MIRType::Object;
+  };
+#endif
+
+  MOZ_ASSERT(types.size() > 0);
+  MOZ_ASSERT(std::all_of(types.begin(), types.end(), isSpecializedNonMagic));
+
+  if (type() == MIRType::Value) {
+    return false;
+  }
+
+  return std::find(types.begin(), types.end(), type()) != types.end();
+}
+
+MDefinition* MInstruction::foldsToStore(TempAllocator& alloc) {
+  if (!dependency()) {
+    return nullptr;
+  }
+
+  MDefinition* store = dependency();
+  if (mightAlias(store) != AliasType::MustAlias) {
+    return nullptr;
+  }
+
+  if (!store->block()->dominates(block())) {
+    return nullptr;
+  }
+
+  MDefinition* value;
+  switch (store->op()) {
+    case Opcode::StoreFixedSlot:
+      value = store->toStoreFixedSlot()->value();
+      break;
+    case Opcode::StoreDynamicSlot:
+      value = store->toStoreDynamicSlot()->value();
+      break;
+    case Opcode::StoreElement:
+      value = store->toStoreElement()->value();
+      break;
+    default:
+      MOZ_CRASH("unknown store");
+  }
+
+  // If the type are matching then we return the value which is used as
+  // argument of the store.
+  if (value->type() != type()) {
+    // If we expect to read a type which is more generic than the type seen
+    // by the store, then we box the value used by the store.
+    if (type() != MIRType::Value) {
+      return nullptr;
+    }
+
+    MOZ_ASSERT(value->type() < MIRType::Value);
+    MBox* box = MBox::New(alloc, value);
+    value = box;
+  }
+
+  return value;
+}
+
+void MDefinition::analyzeEdgeCasesForward() {}
+
+void MDefinition::analyzeEdgeCasesBackward() {}
+
+void MInstruction::setResumePoint(MResumePoint* resumePoint) {
+  MOZ_ASSERT(!resumePoint_);
+  resumePoint_ = resumePoint;
+  resumePoint_->setInstruction(this);
+}
+
+void MInstruction::stealResumePoint(MInstruction* other) {
+  MResumePoint* resumePoint = other->resumePoint_;
+  other->resumePoint_ = nullptr;
+
+  resumePoint->resetInstruction();
+  setResumePoint(resumePoint);
+}
+
+void MInstruction::moveResumePointAsEntry() {
+  MOZ_ASSERT(isNop());
+  block()->clearEntryResumePoint();
+  block()->setEntryResumePoint(resumePoint_);
+  resumePoint_->resetInstruction();
+  resumePoint_ = nullptr;
+}
+
+void MInstruction::clearResumePoint() {
+  resumePoint_->resetInstruction();
+  block()->discardPreAllocatedResumePoint(resumePoint_);
+  resumePoint_ = nullptr;
+}
+
+MDefinition* MTest::foldsDoubleNegation(TempAllocator& alloc) {
+  MDefinition* op = getOperand(0);
+
+  if (op->isNot()) {
+    // If the operand of the Not is itself a Not, they cancel out.
+    MDefinition* opop = op->getOperand(0);
+    if (opop->isNot()) {
+      return MTest::New(alloc, opop->toNot()->input(), ifTrue(), ifFalse());
+    }
+    return MTest::New(alloc, op->toNot()->input(), ifFalse(), ifTrue());
+  }
+  return nullptr;
+}
+
+MDefinition* MTest::foldsConstant(TempAllocator& alloc) {
+  MDefinition* op = getOperand(0);
+  if (MConstant* opConst = op->maybeConstantValue()) {
+    bool b;
+    if (opConst->valueToBoolean(&b)) {
+      return MGoto::New(alloc, b ? ifTrue() : ifFalse());
+    }
+  }
+  return nullptr;
+}
+
+MDefinition* MTest::foldsTypes(TempAllocator& alloc) {
+  MDefinition* op = getOperand(0);
+
+  switch (op->type()) {
+    case MIRType::Undefined:
+    case MIRType::Null:
+      return MGoto::New(alloc, ifFalse());
+    case MIRType::Symbol:
+      return MGoto::New(alloc, ifTrue());
+    default:
+      break;
+  }
+  return nullptr;
+}
+
+class UsesIterator {
+  MDefinition* def_;
+
+ public:
+  explicit UsesIterator(MDefinition* def) : def_(def) {}
+  auto begin() const { return def_->usesBegin(); }
+  auto end() const { return def_->usesEnd(); }
+};
+
+static bool AllInstructionsDeadIfUnused(MBasicBlock* block) {
+  for (auto* ins : *block) {
+    // Skip trivial instructions.
+    if (ins->isNop() || ins->isGoto()) {
+      continue;
+    }
+
+    // All uses must be within the current block.
+    for (auto* use : UsesIterator(ins)) {
+      if (use->consumer()->block() != block) {
+        return false;
+      }
+    }
+
+    // All instructions within this block must be dead if unused.
+    if (!DeadIfUnused(ins)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+MDefinition* MTest::foldsNeedlessControlFlow(TempAllocator& alloc) {
+  // All instructions within both successors need be dead if unused.
+  if (!AllInstructionsDeadIfUnused(ifTrue()) ||
+      !AllInstructionsDeadIfUnused(ifFalse())) {
+    return nullptr;
+  }
+
+  // Both successors must have the same target successor.
+  if (ifTrue()->numSuccessors() != 1 || ifFalse()->numSuccessors() != 1) {
+    return nullptr;
+  }
+  if (ifTrue()->getSuccessor(0) != ifFalse()->getSuccessor(0)) {
+    return nullptr;
+  }
+
+  // The target successor's phis must be redundant. Redundant phis should have
+  // been removed in an earlier pass, so only check if any phis are present,
+  // which is a stronger condition.
+  if (ifTrue()->successorWithPhis()) {
+    return nullptr;
+  }
+
+  return MGoto::New(alloc, ifTrue());
+}
+
+MDefinition* MTest::foldsTo(TempAllocator& alloc) {
+  if (MDefinition* def = foldsDoubleNegation(alloc)) {
+    return def;
+  }
+
+  if (MDefinition* def = foldsConstant(alloc)) {
+    return def;
+  }
+
+  if (MDefinition* def = foldsTypes(alloc)) {
+    return def;
+  }
+
+  if (MDefinition* def = foldsNeedlessControlFlow(alloc)) {
+    return def;
+  }
+
+  return this;
+}
+
+AliasSet MThrow::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+AliasSet MNewArrayDynamicLength::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+AliasSet MNewTypedArrayDynamicLength::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+#ifdef JS_JITSPEW
+void MDefinition::printOpcode(GenericPrinter& out) const {
+  PrintOpcodeName(out, op());
+  for (size_t j = 0, e = numOperands(); j < e; j++) {
+    out.printf(" ");
+    if (getUseFor(j)->hasProducer()) {
+      getOperand(j)->printName(out);
+      out.printf(":%s", StringFromMIRType(getOperand(j)->type()));
+    } else {
+      out.printf("(null)");
+    }
+  }
+}
+
+void MDefinition::dump(GenericPrinter& out) const {
+  printName(out);
+  out.printf(":%s", StringFromMIRType(type()));
+  out.printf(" = ");
+  printOpcode(out);
+  out.printf("\n");
+
+  if (isInstruction()) {
+    if (MResumePoint* resume = toInstruction()->resumePoint()) {
+      resume->dump(out);
+    }
+  }
+}
+
+void MDefinition::dump() const {
+  Fprinter out(stderr);
+  dump(out);
+  out.finish();
+}
+
+void MDefinition::dumpLocation(GenericPrinter& out) const {
+  MResumePoint* rp = nullptr;
+  const char* linkWord = nullptr;
+  if (isInstruction() && toInstruction()->resumePoint()) {
+    rp = toInstruction()->resumePoint();
+    linkWord = "at";
+  } else {
+    rp = block()->entryResumePoint();
+    linkWord = "after";
+  }
+
+  while (rp) {
+    JSScript* script = rp->block()->info().script();
+    uint32_t lineno = PCToLineNumber(rp->block()->info().script(), rp->pc());
+    out.printf("  %s %s:%u\n", linkWord, script->filename(), lineno);
+    rp = rp->caller();
+    linkWord = "in";
+  }
+}
+
+void MDefinition::dumpLocation() const {
+  Fprinter out(stderr);
+  dumpLocation(out);
+  out.finish();
+}
+#endif
+
+#ifdef DEBUG
+bool MDefinition::trackedSiteMatchesBlock(const BytecodeSite* site) const {
+  return site == block()->trackedSite();
+}
+#endif
+
+#if defined(DEBUG) || defined(JS_JITSPEW)
+size_t MDefinition::useCount() const {
+  size_t count = 0;
+  for (MUseIterator i(uses_.begin()); i != uses_.end(); i++) {
+    count++;
+  }
+  return count;
+}
+
+size_t MDefinition::defUseCount() const {
+  size_t count = 0;
+  for (MUseIterator i(uses_.begin()); i != uses_.end(); i++) {
+    if ((*i)->consumer()->isDefinition()) {
+      count++;
+    }
+  }
+  return count;
+}
+#endif
+
+bool MDefinition::hasOneUse() const {
+  MUseIterator i(uses_.begin());
+  if (i == uses_.end()) {
+    return false;
+  }
+  i++;
+  return i == uses_.end();
+}
+
+bool MDefinition::hasOneDefUse() const {
+  bool hasOneDefUse = false;
+  for (MUseIterator i(uses_.begin()); i != uses_.end(); i++) {
+    if (!(*i)->consumer()->isDefinition()) {
+      continue;
+    }
+
+    // We already have a definition use. So 1+
+    if (hasOneDefUse) {
+      return false;
+    }
+
+    // We saw one definition. Loop to test if there is another.
+    hasOneDefUse = true;
+  }
+
+  return hasOneDefUse;
+}
+
+bool MDefinition::hasDefUses() const {
+  for (MUseIterator i(uses_.begin()); i != uses_.end(); i++) {
+    if ((*i)->consumer()->isDefinition()) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool MDefinition::hasLiveDefUses() const {
+  for (MUseIterator i(uses_.begin()); i != uses_.end(); i++) {
+    MNode* ins = (*i)->consumer();
+    if (ins->isDefinition()) {
+      if (!ins->toDefinition()->isRecoveredOnBailout()) {
+        return true;
+      }
+    } else {
+      MOZ_ASSERT(ins->isResumePoint());
+      if (!ins->toResumePoint()->isRecoverableOperand(*i)) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+MDefinition* MDefinition::maybeSingleDefUse() const {
+  MUseDefIterator use(this);
+  if (!use) {
+    // No def-uses.
+    return nullptr;
+  }
+
+  MDefinition* useDef = use.def();
+
+  use++;
+  if (use) {
+    // More than one def-use.
+    return nullptr;
+  }
+
+  return useDef;
+}
+
+MDefinition* MDefinition::maybeMostRecentlyAddedDefUse() const {
+  MUseDefIterator use(this);
+  if (!use) {
+    // No def-uses.
+    return nullptr;
+  }
+
+  MDefinition* mostRecentUse = use.def();
+
+#ifdef DEBUG
+  // This function relies on addUse adding new uses to the front of the list.
+  // Check this invariant by asserting the next few uses are 'older'. Skip this
+  // for phis because setBackedge can add a new use for a loop phi even if the
+  // loop body has a use with an id greater than the loop phi's id.
+  if (!mostRecentUse->isPhi()) {
+    static constexpr size_t NumUsesToCheck = 3;
+    use++;
+    for (size_t i = 0; use && i < NumUsesToCheck; i++, use++) {
+      MOZ_ASSERT(use.def()->id() <= mostRecentUse->id());
+    }
+  }
+#endif
+
+  return mostRecentUse;
+}
+
+void MDefinition::replaceAllUsesWith(MDefinition* dom) {
+  for (size_t i = 0, e = numOperands(); i < e; ++i) {
+    getOperand(i)->setImplicitlyUsedUnchecked();
+  }
+
+  justReplaceAllUsesWith(dom);
+}
+
+void MDefinition::justReplaceAllUsesWith(MDefinition* dom) {
+  MOZ_ASSERT(dom != nullptr);
+  MOZ_ASSERT(dom != this);
+
+  // Carry over the fact the value has uses which are no longer inspectable
+  // with the graph.
+  if (isImplicitlyUsed()) {
+    dom->setImplicitlyUsedUnchecked();
+  }
+
+  for (MUseIterator i(usesBegin()), e(usesEnd()); i != e; ++i) {
+    i->setProducerUnchecked(dom);
+  }
+  dom->uses_.takeElements(uses_);
+}
+
+bool MDefinition::optimizeOutAllUses(TempAllocator& alloc) {
+  for (MUseIterator i(usesBegin()), e(usesEnd()); i != e;) {
+    MUse* use = *i++;
+    MConstant* constant = use->consumer()->block()->optimizedOutConstant(alloc);
+    if (!alloc.ensureBallast()) {
+      return false;
+    }
+
+    // Update the resume point operand to use the optimized-out constant.
+    use->setProducerUnchecked(constant);
+    constant->addUseUnchecked(use);
+  }
+
+  // Remove dangling pointers.
+  this->uses_.clear();
+  return true;
+}
+
+void MDefinition::replaceAllLiveUsesWith(MDefinition* dom) {
+  for (MUseIterator i(usesBegin()), e(usesEnd()); i != e;) {
+    MUse* use = *i++;
+    MNode* consumer = use->consumer();
+    if (consumer->isResumePoint()) {
+      continue;
+    }
+    if (consumer->isDefinition() &&
+        consumer->toDefinition()->isRecoveredOnBailout()) {
+      continue;
+    }
+
+    // Update the operand to use the dominating definition.
+    use->replaceProducer(dom);
+  }
+}
+
+MConstant* MConstant::New(TempAllocator& alloc, const Value& v) {
+  return new (alloc) MConstant(alloc, v);
+}
+
+MConstant* MConstant::New(TempAllocator::Fallible alloc, const Value& v) {
+  return new (alloc) MConstant(alloc.alloc, v);
+}
+
+MConstant* MConstant::NewFloat32(TempAllocator& alloc, double d) {
+  MOZ_ASSERT(IsNaN(d) || d == double(float(d)));
+  return new (alloc) MConstant(float(d));
+}
+
+MConstant* MConstant::NewInt64(TempAllocator& alloc, int64_t i) {
+  return new (alloc) MConstant(MIRType::Int64, i);
+}
+
+MConstant* MConstant::NewIntPtr(TempAllocator& alloc, intptr_t i) {
+  return new (alloc) MConstant(MIRType::IntPtr, i);
+}
+
+MConstant* MConstant::New(TempAllocator& alloc, const Value& v, MIRType type) {
+  if (type == MIRType::Float32) {
+    return NewFloat32(alloc, v.toNumber());
+  }
+  MConstant* res = New(alloc, v);
+  MOZ_ASSERT(res->type() == type);
+  return res;
+}
+
+MConstant* MConstant::NewObject(TempAllocator& alloc, JSObject* v) {
+  return new (alloc) MConstant(v);
+}
+
+MConstant* MConstant::NewShape(TempAllocator& alloc, Shape* s) {
+  return new (alloc) MConstant(s);
+}
+
+static MIRType MIRTypeFromValue(const js::Value& vp) {
+  if (vp.isDouble()) {
+    return MIRType::Double;
+  }
+  if (vp.isMagic()) {
+    switch (vp.whyMagic()) {
+      case JS_OPTIMIZED_OUT:
+        return MIRType::MagicOptimizedOut;
+      case JS_ELEMENTS_HOLE:
+        return MIRType::MagicHole;
+      case JS_IS_CONSTRUCTING:
+        return MIRType::MagicIsConstructing;
+      case JS_UNINITIALIZED_LEXICAL:
+        return MIRType::MagicUninitializedLexical;
+      default:
+        MOZ_ASSERT_UNREACHABLE("Unexpected magic constant");
+    }
+  }
+  return MIRTypeFromValueType(vp.extractNonDoubleType());
+}
+
+MConstant::MConstant(TempAllocator& alloc, const js::Value& vp)
+    : MNullaryInstruction(classOpcode) {
+  setResultType(MIRTypeFromValue(vp));
+
+  MOZ_ASSERT(payload_.asBits == 0);
+
+  switch (type()) {
+    case MIRType::Undefined:
+    case MIRType::Null:
+      break;
+    case MIRType::Boolean:
+      payload_.b = vp.toBoolean();
+      break;
+    case MIRType::Int32:
+      payload_.i32 = vp.toInt32();
+      break;
+    case MIRType::Double:
+      payload_.d = vp.toDouble();
+      break;
+    case MIRType::String:
+      MOZ_ASSERT(!IsInsideNursery(vp.toString()));
+      MOZ_ASSERT(vp.toString()->isLinear());
+      payload_.str = vp.toString();
+      break;
+    case MIRType::Symbol:
+      payload_.sym = vp.toSymbol();
+      break;
+    case MIRType::BigInt:
+      MOZ_ASSERT(!IsInsideNursery(vp.toBigInt()));
+      payload_.bi = vp.toBigInt();
+      break;
+    case MIRType::Object:
+      MOZ_ASSERT(!IsInsideNursery(&vp.toObject()));
+      payload_.obj = &vp.toObject();
+      break;
+    case MIRType::MagicOptimizedOut:
+    case MIRType::MagicHole:
+    case MIRType::MagicIsConstructing:
+    case MIRType::MagicUninitializedLexical:
+      break;
+    default:
+      MOZ_CRASH("Unexpected type");
+  }
+
+  setMovable();
+}
+
+MConstant::MConstant(JSObject* obj) : MNullaryInstruction(classOpcode) {
+  MOZ_ASSERT(!IsInsideNursery(obj));
+  setResultType(MIRType::Object);
+  payload_.obj = obj;
+  setMovable();
+}
+
+MConstant::MConstant(Shape* shape) : MNullaryInstruction(classOpcode) {
+  setResultType(MIRType::Shape);
+  payload_.shape = shape;
+  setMovable();
+}
+
+MConstant::MConstant(float f) : MNullaryInstruction(classOpcode) {
+  setResultType(MIRType::Float32);
+  payload_.f = f;
+  setMovable();
+}
+
+MConstant::MConstant(MIRType type, int64_t i)
+    : MNullaryInstruction(classOpcode) {
+  MOZ_ASSERT(type == MIRType::Int64 || type == MIRType::IntPtr);
+  setResultType(type);
+  if (type == MIRType::Int64) {
+    payload_.i64 = i;
+  } else {
+    payload_.iptr = i;
+  }
+  setMovable();
+}
+
+#ifdef DEBUG
+void MConstant::assertInitializedPayload() const {
+  // valueHash() and equals() expect the unused payload bits to be
+  // initialized to zero. Assert this in debug builds.
+
+  switch (type()) {
+    case MIRType::Int32:
+    case MIRType::Float32:
+#  if MOZ_LITTLE_ENDIAN()
+      MOZ_ASSERT((payload_.asBits >> 32) == 0);
+#  else
+      MOZ_ASSERT((payload_.asBits << 32) == 0);
+#  endif
+      break;
+    case MIRType::Boolean:
+#  if MOZ_LITTLE_ENDIAN()
+      MOZ_ASSERT((payload_.asBits >> 1) == 0);
+#  else
+      MOZ_ASSERT((payload_.asBits & ~(1ULL << 56)) == 0);
+#  endif
+      break;
+    case MIRType::Double:
+    case MIRType::Int64:
+      break;
+    case MIRType::String:
+    case MIRType::Object:
+    case MIRType::Symbol:
+    case MIRType::BigInt:
+    case MIRType::IntPtr:
+    case MIRType::Shape:
+#  if MOZ_LITTLE_ENDIAN()
+      MOZ_ASSERT_IF(JS_BITS_PER_WORD == 32, (payload_.asBits >> 32) == 0);
+#  else
+      MOZ_ASSERT_IF(JS_BITS_PER_WORD == 32, (payload_.asBits << 32) == 0);
+#  endif
+      break;
+    default:
+      MOZ_ASSERT(IsNullOrUndefined(type()) || IsMagicType(type()));
+      MOZ_ASSERT(payload_.asBits == 0);
+      break;
+  }
+}
+#endif
+
+static HashNumber ConstantValueHash(MIRType type, uint64_t payload) {
+  // Build a 64-bit value holding both the payload and the type.
+  static const size_t TypeBits = 8;
+  static const size_t TypeShift = 64 - TypeBits;
+  MOZ_ASSERT(uintptr_t(type) <= (1 << TypeBits) - 1);
+  uint64_t bits = (uint64_t(type) << TypeShift) ^ payload;
+
+  // Fold all 64 bits into the 32-bit result. It's tempting to just discard
+  // half of the bits, as this is just a hash, however there are many common
+  // patterns of values where only the low or the high bits vary, so
+  // discarding either side would lead to excessive hash collisions.
+  return (HashNumber)bits ^ (HashNumber)(bits >> 32);
+}
+
+HashNumber MConstant::valueHash() const {
+  static_assert(sizeof(Payload) == sizeof(uint64_t),
+                "Code below assumes payload fits in 64 bits");
+
+  assertInitializedPayload();
+  return ConstantValueHash(type(), payload_.asBits);
+}
+
+// We will in theory get some extra collisions here, but dealing with those
+// should be cheaper than doing the skipObjectGuards for the receiver object.
+HashNumber MConstantProto::valueHash() const {
+  return protoObject()->valueHash();
+}
+
+bool MConstant::congruentTo(const MDefinition* ins) const {
+  return ins->isConstant() && equals(ins->toConstant());
+}
+
+#ifdef JS_JITSPEW
+void MConstant::printOpcode(GenericPrinter& out) const {
+  PrintOpcodeName(out, op());
+  out.printf(" ");
+  switch (type()) {
+    case MIRType::Undefined:
+      out.printf("undefined");
+      break;
+    case MIRType::Null:
+      out.printf("null");
+      break;
+    case MIRType::Boolean:
+      out.printf(toBoolean() ? "true" : "false");
+      break;
+    case MIRType::Int32:
+      out.printf("0x%x", uint32_t(toInt32()));
+      break;
+    case MIRType::Int64:
+      out.printf("0x%" PRIx64, uint64_t(toInt64()));
+      break;
+    case MIRType::IntPtr:
+      out.printf("0x%" PRIxPTR, uintptr_t(toIntPtr()));
+      break;
+    case MIRType::Double:
+      out.printf("%.16g", toDouble());
+      break;
+    case MIRType::Float32: {
+      float val = toFloat32();
+      out.printf("%.16g", val);
+      break;
+    }
+    case MIRType::Object:
+      if (toObject().is<JSFunction>()) {
+        JSFunction* fun = &toObject().as<JSFunction>();
+        if (fun->displayAtom()) {
+          out.put("function ");
+          EscapedStringPrinter(out, fun->displayAtom(), 0);
+        } else {
+          out.put("unnamed function");
+        }
+        if (fun->hasBaseScript()) {
+          BaseScript* script = fun->baseScript();
+          out.printf(" (%s:%u)", script->filename() ? script->filename() : "",
+                     script->lineno());
+        }
+        out.printf(" at %p", (void*)fun);
+        break;
+      }
+      out.printf("object %p (%s)", (void*)&toObject(),
+                 toObject().getClass()->name);
+      break;
+    case MIRType::Symbol:
+      out.printf("symbol at %p", (void*)toSymbol());
+      break;
+    case MIRType::BigInt:
+      out.printf("BigInt at %p", (void*)toBigInt());
+      break;
+    case MIRType::String:
+      out.printf("string %p", (void*)toString());
+      break;
+    case MIRType::Shape:
+      out.printf("shape at %p", (void*)toShape());
+      break;
+    case MIRType::MagicHole:
+      out.printf("magic hole");
+      break;
+    case MIRType::MagicIsConstructing:
+      out.printf("magic is-constructing");
+      break;
+    case MIRType::MagicOptimizedOut:
+      out.printf("magic optimized-out");
+      break;
+    case MIRType::MagicUninitializedLexical:
+      out.printf("magic uninitialized-lexical");
+      break;
+    default:
+      MOZ_CRASH("unexpected type");
+  }
+}
+#endif
+
+bool MConstant::canProduceFloat32() const {
+  if (!isTypeRepresentableAsDouble()) {
+    return false;
+  }
+
+  if (type() == MIRType::Int32) {
+    return IsFloat32Representable(static_cast<double>(toInt32()));
+  }
+  if (type() == MIRType::Double) {
+    return IsFloat32Representable(toDouble());
+  }
+  MOZ_ASSERT(type() == MIRType::Float32);
+  return true;
+}
+
+Value MConstant::toJSValue() const {
+  // Wasm has types like int64 that cannot be stored as js::Value. It also
+  // doesn't want the NaN canonicalization enforced by js::Value.
+  MOZ_ASSERT(!IsCompilingWasm());
+
+  switch (type()) {
+    case MIRType::Undefined:
+      return UndefinedValue();
+    case MIRType::Null:
+      return NullValue();
+    case MIRType::Boolean:
+      return BooleanValue(toBoolean());
+    case MIRType::Int32:
+      return Int32Value(toInt32());
+    case MIRType::Double:
+      return DoubleValue(toDouble());
+    case MIRType::Float32:
+      return Float32Value(toFloat32());
+    case MIRType::String:
+      return StringValue(toString());
+    case MIRType::Symbol:
+      return SymbolValue(toSymbol());
+    case MIRType::BigInt:
+      return BigIntValue(toBigInt());
+    case MIRType::Object:
+      return ObjectValue(toObject());
+    case MIRType::Shape:
+      return PrivateGCThingValue(toShape());
+    case MIRType::MagicOptimizedOut:
+      return MagicValue(JS_OPTIMIZED_OUT);
+    case MIRType::MagicHole:
+      return MagicValue(JS_ELEMENTS_HOLE);
+    case MIRType::MagicIsConstructing:
+      return MagicValue(JS_IS_CONSTRUCTING);
+    case MIRType::MagicUninitializedLexical:
+      return MagicValue(JS_UNINITIALIZED_LEXICAL);
+    default:
+      MOZ_CRASH("Unexpected type");
+  }
+}
+
+bool MConstant::valueToBoolean(bool* res) const {
+  switch (type()) {
+    case MIRType::Boolean:
+      *res = toBoolean();
+      return true;
+    case MIRType::Int32:
+      *res = toInt32() != 0;
+      return true;
+    case MIRType::Int64:
+      *res = toInt64() != 0;
+      return true;
+    case MIRType::Double:
+      *res = !mozilla::IsNaN(toDouble()) && toDouble() != 0.0;
+      return true;
+    case MIRType::Float32:
+      *res = !mozilla::IsNaN(toFloat32()) && toFloat32() != 0.0f;
+      return true;
+    case MIRType::Null:
+    case MIRType::Undefined:
+      *res = false;
+      return true;
+    case MIRType::Symbol:
+      *res = true;
+      return true;
+    case MIRType::BigInt:
+      *res = !toBigInt()->isZero();
+      return true;
+    case MIRType::String:
+      *res = toString()->length() != 0;
+      return true;
+    case MIRType::Object:
+      // TODO(Warp): Lazy groups have been removed.
+      // We have to call EmulatesUndefined but that reads obj->group->clasp
+      // and so it's racy when the object has a lazy group. The main callers
+      // of this (MTest, MNot) already know how to fold the object case, so
+      // just give up.
+      return false;
+    default:
+      MOZ_ASSERT(IsMagicType(type()));
+      return false;
+  }
+}
+
+HashNumber MWasmFloatConstant::valueHash() const {
+#ifdef ENABLE_WASM_SIMD
+  return ConstantValueHash(type(), u.bits_[0] ^ u.bits_[1]);
+#else
+  return ConstantValueHash(type(), u.bits_[0]);
+#endif
+}
+
+bool MWasmFloatConstant::congruentTo(const MDefinition* ins) const {
+  return ins->isWasmFloatConstant() && type() == ins->type() &&
+#ifdef ENABLE_WASM_SIMD
+         u.bits_[1] == ins->toWasmFloatConstant()->u.bits_[1] &&
+#endif
+         u.bits_[0] == ins->toWasmFloatConstant()->u.bits_[0];
+}
+
+HashNumber MWasmNullConstant::valueHash() const {
+  return ConstantValueHash(MIRType::RefOrNull, 0);
+}
+
+#ifdef JS_JITSPEW
+void MControlInstruction::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  for (size_t j = 0; j < numSuccessors(); j++) {
+    if (getSuccessor(j)) {
+      out.printf(" block%u", getSuccessor(j)->id());
+    } else {
+      out.printf(" (null-to-be-patched)");
+    }
+  }
+}
+
+void MCompare::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" %s", CodeName(jsop()));
+}
+
+void MTypeOfIs::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" %s", CodeName(jsop()));
+
+  const char* name = "";
+  switch (jstype()) {
+    case JSTYPE_UNDEFINED:
+      name = "undefined";
+      break;
+    case JSTYPE_OBJECT:
+      name = "object";
+      break;
+    case JSTYPE_FUNCTION:
+      name = "function";
+      break;
+    case JSTYPE_STRING:
+      name = "string";
+      break;
+    case JSTYPE_NUMBER:
+      name = "number";
+      break;
+    case JSTYPE_BOOLEAN:
+      name = "boolean";
+      break;
+    case JSTYPE_SYMBOL:
+      name = "symbol";
+      break;
+    case JSTYPE_BIGINT:
+      name = "bigint";
+      break;
+#  ifdef ENABLE_RECORD_TUPLE
+    case JSTYPE_RECORD:
+    case JSTYPE_TUPLE:
+#  endif
+    case JSTYPE_LIMIT:
+      MOZ_CRASH("Unexpected type");
+  }
+  out.printf(" '%s'", name);
+}
+
+void MLoadUnboxedScalar::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" %s", Scalar::name(storageType()));
+}
+
+void MLoadDataViewElement::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" %s", Scalar::name(storageType()));
+}
+
+void MAssertRange::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.put(" ");
+  assertedRange()->dump(out);
+}
+
+void MNearbyInt::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  const char* roundingModeStr = nullptr;
+  switch (roundingMode_) {
+    case RoundingMode::Up:
+      roundingModeStr = "(up)";
+      break;
+    case RoundingMode::Down:
+      roundingModeStr = "(down)";
+      break;
+    case RoundingMode::NearestTiesToEven:
+      roundingModeStr = "(nearest ties even)";
+      break;
+    case RoundingMode::TowardsZero:
+      roundingModeStr = "(towards zero)";
+      break;
+  }
+  out.printf(" %s", roundingModeStr);
+}
+#endif
+
+AliasSet MRandom::getAliasSet() const { return AliasSet::Store(AliasSet::RNG); }
+
+MDefinition* MSign::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+  if (!input->isConstant() ||
+      !input->toConstant()->isTypeRepresentableAsDouble()) {
+    return this;
+  }
+
+  double in = input->toConstant()->numberToDouble();
+  double out = js::math_sign_impl(in);
+
+  if (type() == MIRType::Int32) {
+    // Decline folding if this is an int32 operation, but the result type
+    // isn't an int32.
+    Value outValue = NumberValue(out);
+    if (!outValue.isInt32()) {
+      return this;
+    }
+
+    return MConstant::New(alloc, outValue);
+  }
+
+  return MConstant::New(alloc, DoubleValue(out));
+}
+
+const char* MMathFunction::FunctionName(UnaryMathFunction function) {
+  return GetUnaryMathFunctionName(function);
+}
+
+#ifdef JS_JITSPEW
+void MMathFunction::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" %s", FunctionName(function()));
+}
+#endif
+
+MDefinition* MMathFunction::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+  if (!input->isConstant() ||
+      !input->toConstant()->isTypeRepresentableAsDouble()) {
+    return this;
+  }
+
+  UnaryMathFunctionType funPtr = GetUnaryMathFunctionPtr(function());
+
+  double in = input->toConstant()->numberToDouble();
+
+  // The function pointer call can't GC.
+  JS::AutoSuppressGCAnalysis nogc;
+  double out = funPtr(in);
+
+  if (input->type() == MIRType::Float32) {
+    return MConstant::NewFloat32(alloc, out);
+  }
+  return MConstant::New(alloc, DoubleValue(out));
+}
+
+MDefinition* MAtomicIsLockFree::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+  if (!input->isConstant() || input->type() != MIRType::Int32) {
+    return this;
+  }
+
+  int32_t i = input->toConstant()->toInt32();
+  return MConstant::New(alloc, BooleanValue(AtomicOperations::isLockfreeJS(i)));
+}
+
+// Define |THIS_SLOT| as part of this translation unit, as it is used to
+// specialized the parameterized |New| function calls introduced by
+// TRIVIAL_NEW_WRAPPERS.
+const int32_t MParameter::THIS_SLOT;
+
+#ifdef JS_JITSPEW
+void MParameter::printOpcode(GenericPrinter& out) const {
+  PrintOpcodeName(out, op());
+  if (index() == THIS_SLOT) {
+    out.printf(" THIS_SLOT");
+  } else {
+    out.printf(" %d", index());
+  }
+}
+#endif
+
+HashNumber MParameter::valueHash() const {
+  HashNumber hash = MDefinition::valueHash();
+  hash = addU32ToHash(hash, index_);
+  return hash;
+}
+
+bool MParameter::congruentTo(const MDefinition* ins) const {
+  if (!ins->isParameter()) {
+    return false;
+  }
+
+  return ins->toParameter()->index() == index_;
+}
+
+WrappedFunction::WrappedFunction(JSFunction* nativeFun, uint16_t nargs,
+                                 FunctionFlags flags)
+    : nativeFun_(nativeFun), nargs_(nargs), flags_(flags) {
+  MOZ_ASSERT_IF(nativeFun, isNativeWithoutJitEntry());
+
+#ifdef DEBUG
+  // If we are not running off-main thread we can assert that the
+  // metadata is consistent.
+  if (!CanUseExtraThreads() && nativeFun) {
+    MOZ_ASSERT(nativeFun->nargs() == nargs);
+
+    MOZ_ASSERT(nativeFun->isNativeWithoutJitEntry() ==
+               isNativeWithoutJitEntry());
+    MOZ_ASSERT(nativeFun->hasJitEntry() == hasJitEntry());
+    MOZ_ASSERT(nativeFun->isConstructor() == isConstructor());
+    MOZ_ASSERT(nativeFun->isClassConstructor() == isClassConstructor());
+  }
+#endif
+}
+
+MCall* MCall::New(TempAllocator& alloc, WrappedFunction* target, size_t maxArgc,
+                  size_t numActualArgs, bool construct, bool ignoresReturnValue,
+                  bool isDOMCall, mozilla::Maybe<DOMObjectKind> objectKind) {
+  MOZ_ASSERT(isDOMCall == objectKind.isSome());
+  MOZ_ASSERT(maxArgc >= numActualArgs);
+  MCall* ins;
+  if (isDOMCall) {
+    MOZ_ASSERT(!construct);
+    ins = new (alloc) MCallDOMNative(target, numActualArgs, *objectKind);
+  } else {
+    ins =
+        new (alloc) MCall(target, numActualArgs, construct, ignoresReturnValue);
+  }
+  if (!ins->init(alloc, maxArgc + NumNonArgumentOperands)) {
+    return nullptr;
+  }
+  return ins;
+}
+
+AliasSet MCallDOMNative::getAliasSet() const {
+  const JSJitInfo* jitInfo = getJitInfo();
+
+  // If we don't know anything about the types of our arguments, we have to
+  // assume that type-coercions can have side-effects, so we need to alias
+  // everything.
+  if (jitInfo->aliasSet() == JSJitInfo::AliasEverything ||
+      !jitInfo->isTypedMethodJitInfo()) {
+    return AliasSet::Store(AliasSet::Any);
+  }
+
+  uint32_t argIndex = 0;
+  const JSTypedMethodJitInfo* methodInfo =
+      reinterpret_cast<const JSTypedMethodJitInfo*>(jitInfo);
+  for (const JSJitInfo::ArgType* argType = methodInfo->argTypes;
+       *argType != JSJitInfo::ArgTypeListEnd; ++argType, ++argIndex) {
+    if (argIndex >= numActualArgs()) {
+      // Passing through undefined can't have side-effects
+      continue;
+    }
+    // getArg(0) is "this", so skip it
+    MDefinition* arg = getArg(argIndex + 1);
+    MIRType actualType = arg->type();
+    // The only way to reliably avoid side-effects given the information we
+    // have here is if we're passing in a known primitive value to an
+    // argument that expects a primitive value.
+    //
+    // XXXbz maybe we need to communicate better information.  For example,
+    // a sequence argument will sort of unavoidably have side effects, while
+    // a typed array argument won't have any, but both are claimed to be
+    // JSJitInfo::Object.  But if we do that, we need to watch out for our
+    // movability/DCE-ability bits: if we have an arg type that can reliably
+    // throw an exception on conversion, that might not affect our alias set
+    // per se, but it should prevent us being moved or DCE-ed, unless we
+    // know the incoming things match that arg type and won't throw.
+    //
+    if ((actualType == MIRType::Value || actualType == MIRType::Object) ||
+        (*argType & JSJitInfo::Object)) {
+      return AliasSet::Store(AliasSet::Any);
+    }
+  }
+
+  // We checked all the args, and they check out.  So we only alias DOM
+  // mutations or alias nothing, depending on the alias set in the jitinfo.
+  if (jitInfo->aliasSet() == JSJitInfo::AliasNone) {
+    return AliasSet::None();
+  }
+
+  MOZ_ASSERT(jitInfo->aliasSet() == JSJitInfo::AliasDOMSets);
+  return AliasSet::Load(AliasSet::DOMProperty);
+}
+
+void MCallDOMNative::computeMovable() {
+  // We are movable if the jitinfo says we can be and if we're also not
+  // effectful.  The jitinfo can't check for the latter, since it depends on
+  // the types of our arguments.
+  const JSJitInfo* jitInfo = getJitInfo();
+
+  MOZ_ASSERT_IF(jitInfo->isMovable,
+                jitInfo->aliasSet() != JSJitInfo::AliasEverything);
+
+  if (jitInfo->isMovable && !isEffectful()) {
+    setMovable();
+  }
+}
+
+bool MCallDOMNative::congruentTo(const MDefinition* ins) const {
+  if (!isMovable()) {
+    return false;
+  }
+
+  if (!ins->isCall()) {
+    return false;
+  }
+
+  const MCall* call = ins->toCall();
+
+  if (!call->isCallDOMNative()) {
+    return false;
+  }
+
+  if (getSingleTarget() != call->getSingleTarget()) {
+    return false;
+  }
+
+  if (isConstructing() != call->isConstructing()) {
+    return false;
+  }
+
+  if (numActualArgs() != call->numActualArgs()) {
+    return false;
+  }
+
+  if (!congruentIfOperandsEqual(call)) {
+    return false;
+  }
+
+  // The other call had better be movable at this point!
+  MOZ_ASSERT(call->isMovable());
+
+  return true;
+}
+
+const JSJitInfo* MCallDOMNative::getJitInfo() const {
+  MOZ_ASSERT(getSingleTarget()->hasJitInfo());
+  return getSingleTarget()->jitInfo();
+}
+
+MDefinition* MStringLength::foldsTo(TempAllocator& alloc) {
+  if (string()->isConstant()) {
+    JSString* str = string()->toConstant()->toString();
+    return MConstant::New(alloc, Int32Value(str->length()));
+  }
+
+  // MFromCharCode returns a one-element string.
+  if (string()->isFromCharCode()) {
+    return MConstant::New(alloc, Int32Value(1));
+  }
+
+  return this;
+}
+
+MDefinition* MConcat::foldsTo(TempAllocator& alloc) {
+  if (lhs()->isConstant() && lhs()->toConstant()->toString()->empty()) {
+    return rhs();
+  }
+
+  if (rhs()->isConstant() && rhs()->toConstant()->toString()->empty()) {
+    return lhs();
+  }
+
+  return this;
+}
+
+MDefinition* MCharCodeAt::foldsTo(TempAllocator& alloc) {
+  MDefinition* string = this->string();
+  if (!string->isConstant() && !string->isFromCharCode()) {
+    return this;
+  }
+
+  MDefinition* index = this->index();
+  if (index->isSpectreMaskIndex()) {
+    index = index->toSpectreMaskIndex()->index();
+  }
+  if (!index->isConstant()) {
+    return this;
+  }
+  int32_t idx = index->toConstant()->toInt32();
+
+  // Handle the pattern |s[idx].charCodeAt(0)|.
+  if (string->isFromCharCode()) {
+    if (idx != 0) {
+      return this;
+    }
+
+    // Simplify |CharCodeAt(FromCharCode(CharCodeAt(s, idx)), 0)| to just
+    // |CharCodeAt(s, idx)|.
+    auto* charCode = string->toFromCharCode()->code();
+    if (!charCode->isCharCodeAt()) {
+      return this;
+    }
+
+    return charCode;
+  }
+
+  JSLinearString* str = &string->toConstant()->toString()->asLinear();
+  if (idx < 0 || uint32_t(idx) >= str->length()) {
+    return this;
+  }
+
+  char16_t ch = str->latin1OrTwoByteChar(idx);
+  return MConstant::New(alloc, Int32Value(ch));
+}
+
+template <size_t Arity>
+[[nodiscard]] static bool EnsureFloatInputOrConvert(
+    MAryInstruction<Arity>* owner, TempAllocator& alloc) {
+  MOZ_ASSERT(!IsFloatingPointType(owner->type()),
+             "Floating point types must check consumers");
+
+  if (AllOperandsCanProduceFloat32(owner)) {
+    return true;
+  }
+  ConvertOperandsToDouble(owner, alloc);
+  return false;
+}
+
+template <size_t Arity>
+[[nodiscard]] static bool EnsureFloatConsumersAndInputOrConvert(
+    MAryInstruction<Arity>* owner, TempAllocator& alloc) {
+  MOZ_ASSERT(IsFloatingPointType(owner->type()),
+             "Integer types don't need to check consumers");
+
+  if (AllOperandsCanProduceFloat32(owner) &&
+      CheckUsesAreFloat32Consumers(owner)) {
+    return true;
+  }
+  ConvertOperandsToDouble(owner, alloc);
+  return false;
+}
+
+void MFloor::trySpecializeFloat32(TempAllocator& alloc) {
+  MOZ_ASSERT(type() == MIRType::Int32);
+  if (EnsureFloatInputOrConvert(this, alloc)) {
+    specialization_ = MIRType::Float32;
+  }
+}
+
+void MCeil::trySpecializeFloat32(TempAllocator& alloc) {
+  MOZ_ASSERT(type() == MIRType::Int32);
+  if (EnsureFloatInputOrConvert(this, alloc)) {
+    specialization_ = MIRType::Float32;
+  }
+}
+
+void MRound::trySpecializeFloat32(TempAllocator& alloc) {
+  MOZ_ASSERT(type() == MIRType::Int32);
+  if (EnsureFloatInputOrConvert(this, alloc)) {
+    specialization_ = MIRType::Float32;
+  }
+}
+
+void MTrunc::trySpecializeFloat32(TempAllocator& alloc) {
+  MOZ_ASSERT(type() == MIRType::Int32);
+  if (EnsureFloatInputOrConvert(this, alloc)) {
+    specialization_ = MIRType::Float32;
+  }
+}
+
+void MNearbyInt::trySpecializeFloat32(TempAllocator& alloc) {
+  if (EnsureFloatConsumersAndInputOrConvert(this, alloc)) {
+    specialization_ = MIRType::Float32;
+    setResultType(MIRType::Float32);
+  }
+}
+
+MGoto* MGoto::New(TempAllocator& alloc, MBasicBlock* target) {
+  return new (alloc) MGoto(target);
+}
+
+MGoto* MGoto::New(TempAllocator::Fallible alloc, MBasicBlock* target) {
+  MOZ_ASSERT(target);
+  return new (alloc) MGoto(target);
+}
+
+MGoto* MGoto::New(TempAllocator& alloc) { return new (alloc) MGoto(nullptr); }
+
+#ifdef JS_JITSPEW
+void MUnbox::printOpcode(GenericPrinter& out) const {
+  PrintOpcodeName(out, op());
+  out.printf(" ");
+  getOperand(0)->printName(out);
+  out.printf(" ");
+
+  switch (type()) {
+    case MIRType::Int32:
+      out.printf("to Int32");
+      break;
+    case MIRType::Double:
+      out.printf("to Double");
+      break;
+    case MIRType::Boolean:
+      out.printf("to Boolean");
+      break;
+    case MIRType::String:
+      out.printf("to String");
+      break;
+    case MIRType::Symbol:
+      out.printf("to Symbol");
+      break;
+    case MIRType::BigInt:
+      out.printf("to BigInt");
+      break;
+    case MIRType::Object:
+      out.printf("to Object");
+      break;
+    default:
+      break;
+  }
+
+  switch (mode()) {
+    case Fallible:
+      out.printf(" (fallible)");
+      break;
+    case Infallible:
+      out.printf(" (infallible)");
+      break;
+    default:
+      break;
+  }
+}
+#endif
+
+MDefinition* MUnbox::foldsTo(TempAllocator& alloc) {
+  if (input()->isBox()) {
+    MDefinition* unboxed = input()->toBox()->input();
+
+    // Fold MUnbox(MBox(x)) => x if types match.
+    if (unboxed->type() == type()) {
+      if (fallible()) {
+        unboxed->setImplicitlyUsedUnchecked();
+      }
+      return unboxed;
+    }
+
+    // Fold MUnbox(MBox(x)) => MToDouble(x) if possible.
+    if (type() == MIRType::Double &&
+        IsTypeRepresentableAsDouble(unboxed->type())) {
+      if (unboxed->isConstant()) {
+        return MConstant::New(
+            alloc, DoubleValue(unboxed->toConstant()->numberToDouble()));
+      }
+
+      return MToDouble::New(alloc, unboxed);
+    }
+
+    // MUnbox<Int32>(MBox<Double>(x)) will always fail, even if x can be
+    // represented as an Int32. Fold to avoid unnecessary bailouts.
+    if (type() == MIRType::Int32 && unboxed->type() == MIRType::Double) {
+      auto* folded = MToNumberInt32::New(alloc, unboxed,
+                                         IntConversionInputKind::NumbersOnly);
+      folded->setGuard();
+      return folded;
+    }
+  }
+
+  return this;
+}
+
+#ifdef DEBUG
+void MPhi::assertLoopPhi() const {
+  // getLoopPredecessorOperand and getLoopBackedgeOperand rely on these
+  // predecessors being at known indices.
+  if (block()->numPredecessors() == 2) {
+    MBasicBlock* pred = block()->getPredecessor(0);
+    MBasicBlock* back = block()->getPredecessor(1);
+    MOZ_ASSERT(pred == block()->loopPredecessor());
+    MOZ_ASSERT(pred->successorWithPhis() == block());
+    MOZ_ASSERT(pred->positionInPhiSuccessor() == 0);
+    MOZ_ASSERT(back == block()->backedge());
+    MOZ_ASSERT(back->successorWithPhis() == block());
+    MOZ_ASSERT(back->positionInPhiSuccessor() == 1);
+  } else {
+    // After we remove fake loop predecessors for loop headers that
+    // are only reachable via OSR, the only predecessor is the
+    // loop backedge.
+    MOZ_ASSERT(block()->numPredecessors() == 1);
+    MOZ_ASSERT(block()->graph().osrBlock());
+    MOZ_ASSERT(!block()->graph().canBuildDominators());
+    MBasicBlock* back = block()->getPredecessor(0);
+    MOZ_ASSERT(back == block()->backedge());
+    MOZ_ASSERT(back->successorWithPhis() == block());
+    MOZ_ASSERT(back->positionInPhiSuccessor() == 0);
+  }
+}
+#endif
+
+MDefinition* MPhi::getLoopPredecessorOperand() const {
+  // This should not be called after removing fake loop predecessors.
+  MOZ_ASSERT(block()->numPredecessors() == 2);
+  assertLoopPhi();
+  return getOperand(0);
+}
+
+MDefinition* MPhi::getLoopBackedgeOperand() const {
+  assertLoopPhi();
+  uint32_t idx = block()->numPredecessors() == 2 ? 1 : 0;
+  return getOperand(idx);
+}
+
+void MPhi::removeOperand(size_t index) {
+  MOZ_ASSERT(index < numOperands());
+  MOZ_ASSERT(getUseFor(index)->index() == index);
+  MOZ_ASSERT(getUseFor(index)->consumer() == this);
+
+  // If we have phi(..., a, b, c, d, ..., z) and we plan
+  // on removing a, then first shift downward so that we have
+  // phi(..., b, c, d, ..., z, z):
+  MUse* p = inputs_.begin() + index;
+  MUse* e = inputs_.end();
+  p->producer()->removeUse(p);
+  for (; p < e - 1; ++p) {
+    MDefinition* producer = (p + 1)->producer();
+    p->setProducerUnchecked(producer);
+    producer->replaceUse(p + 1, p);
+  }
+
+  // truncate the inputs_ list:
+  inputs_.popBack();
+}
+
+void MPhi::removeAllOperands() {
+  for (MUse& p : inputs_) {
+    p.producer()->removeUse(&p);
+  }
+  inputs_.clear();
+}
+
+MDefinition* MPhi::foldsTernary(TempAllocator& alloc) {
+  /* Look if this MPhi is a ternary construct.
+   * This is a very loose term as it actually only checks for
+   *
+   *      MTest X
+   *       /  \
+   *    ...    ...
+   *       \  /
+   *     MPhi X Y
+   *
+   * Which we will simply call:
+   * x ? x : y or x ? y : x
+   */
+
+  if (numOperands() != 2) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(block()->numPredecessors() == 2);
+
+  MBasicBlock* pred = block()->immediateDominator();
+  if (!pred || !pred->lastIns()->isTest()) {
+    return nullptr;
+  }
+
+  MTest* test = pred->lastIns()->toTest();
+
+  // True branch may only dominate one edge of MPhi.
+  if (test->ifTrue()->dominates(block()->getPredecessor(0)) ==
+      test->ifTrue()->dominates(block()->getPredecessor(1))) {
+    return nullptr;
+  }
+
+  // False branch may only dominate one edge of MPhi.
+  if (test->ifFalse()->dominates(block()->getPredecessor(0)) ==
+      test->ifFalse()->dominates(block()->getPredecessor(1))) {
+    return nullptr;
+  }
+
+  // True and false branch must dominate different edges of MPhi.
+  if (test->ifTrue()->dominates(block()->getPredecessor(0)) ==
+      test->ifFalse()->dominates(block()->getPredecessor(0))) {
+    return nullptr;
+  }
+
+  // We found a ternary construct.
+  bool firstIsTrueBranch =
+      test->ifTrue()->dominates(block()->getPredecessor(0));
+  MDefinition* trueDef = firstIsTrueBranch ? getOperand(0) : getOperand(1);
+  MDefinition* falseDef = firstIsTrueBranch ? getOperand(1) : getOperand(0);
+
+  // Accept either
+  // testArg ? testArg : constant or
+  // testArg ? constant : testArg
+  if (!trueDef->isConstant() && !falseDef->isConstant()) {
+    return nullptr;
+  }
+
+  MConstant* c =
+      trueDef->isConstant() ? trueDef->toConstant() : falseDef->toConstant();
+  MDefinition* testArg = (trueDef == c) ? falseDef : trueDef;
+  if (testArg != test->input()) {
+    return nullptr;
+  }
+
+  // This check should be a tautology, except that the constant might be the
+  // result of the removal of a branch.  In such case the domination scope of
+  // the block which is holding the constant might be incomplete. This
+  // condition is used to prevent doing this optimization based on incomplete
+  // information.
+  //
+  // As GVN removed a branch, it will update the dominations rules before
+  // trying to fold this MPhi again. Thus, this condition does not inhibit
+  // this optimization.
+  MBasicBlock* truePred = block()->getPredecessor(firstIsTrueBranch ? 0 : 1);
+  MBasicBlock* falsePred = block()->getPredecessor(firstIsTrueBranch ? 1 : 0);
+  if (!trueDef->block()->dominates(truePred) ||
+      !falseDef->block()->dominates(falsePred)) {
+    return nullptr;
+  }
+
+  // If testArg is an int32 type we can:
+  // - fold testArg ? testArg : 0 to testArg
+  // - fold testArg ? 0 : testArg to 0
+  if (testArg->type() == MIRType::Int32 && c->numberToDouble() == 0) {
+    testArg->setGuardRangeBailoutsUnchecked();
+
+    // When folding to the constant we need to hoist it.
+    if (trueDef == c && !c->block()->dominates(block())) {
+      c->block()->moveBefore(pred->lastIns(), c);
+    }
+    return trueDef;
+  }
+
+  // If testArg is an double type we can:
+  // - fold testArg ? testArg : 0.0 to MNaNToZero(testArg)
+  if (testArg->type() == MIRType::Double &&
+      mozilla::IsPositiveZero(c->numberToDouble()) && c != trueDef) {
+    MNaNToZero* replace = MNaNToZero::New(alloc, testArg);
+    test->block()->insertBefore(test, replace);
+    return replace;
+  }
+
+  // If testArg is a string type we can:
+  // - fold testArg ? testArg : "" to testArg
+  // - fold testArg ? "" : testArg to ""
+  if (testArg->type() == MIRType::String &&
+      c->toString() == GetJitContext()->runtime->emptyString()) {
+    // When folding to the constant we need to hoist it.
+    if (trueDef == c && !c->block()->dominates(block())) {
+      c->block()->moveBefore(pred->lastIns(), c);
+    }
+    return trueDef;
+  }
+
+  return nullptr;
+}
+
+MDefinition* MPhi::operandIfRedundant() {
+  if (inputs_.length() == 0) {
+    return nullptr;
+  }
+
+  // If this phi is redundant (e.g., phi(a,a) or b=phi(a,this)),
+  // returns the operand that it will always be equal to (a, in
+  // those two cases).
+  MDefinition* first = getOperand(0);
+  for (size_t i = 1, e = numOperands(); i < e; i++) {
+    MDefinition* op = getOperand(i);
+    if (op != first && op != this) {
+      return nullptr;
+    }
+  }
+  return first;
+}
+
+MDefinition* MPhi::foldsTo(TempAllocator& alloc) {
+  if (MDefinition* def = operandIfRedundant()) {
+    return def;
+  }
+
+  if (MDefinition* def = foldsTernary(alloc)) {
+    return def;
+  }
+
+  return this;
+}
+
+bool MPhi::congruentTo(const MDefinition* ins) const {
+  if (!ins->isPhi()) {
+    return false;
+  }
+
+  // Phis in different blocks may have different control conditions.
+  // For example, these phis:
+  //
+  //   if (p)
+  //     goto a
+  //   a:
+  //     t = phi(x, y)
+  //
+  //   if (q)
+  //     goto b
+  //   b:
+  //     s = phi(x, y)
+  //
+  // have identical operands, but they are not equvalent because t is
+  // effectively p?x:y and s is effectively q?x:y.
+  //
+  // For now, consider phis in different blocks incongruent.
+  if (ins->block() != block()) {
+    return false;
+  }
+
+  return congruentIfOperandsEqual(ins);
+}
+
+bool MPhi::updateForReplacement(MDefinition* def) {
+  // This function is called to fix the current Phi flags using it as a
+  // replacement of the other Phi instruction |def|.
+  //
+  // When dealing with usage analysis, any Use will replace all other values,
+  // such as Unused and Unknown. Unless both are Unused, the merge would be
+  // Unknown.
+  MPhi* other = def->toPhi();
+  if (usageAnalysis_ == PhiUsage::Used ||
+      other->usageAnalysis_ == PhiUsage::Used) {
+    usageAnalysis_ = PhiUsage::Used;
+  } else if (usageAnalysis_ != other->usageAnalysis_) {
+    //    this == unused && other == unknown
+    // or this == unknown && other == unused
+    usageAnalysis_ = PhiUsage::Unknown;
+  } else {
+    //    this == unused && other == unused
+    // or this == unknown && other = unknown
+    MOZ_ASSERT(usageAnalysis_ == PhiUsage::Unused ||
+               usageAnalysis_ == PhiUsage::Unknown);
+    MOZ_ASSERT(usageAnalysis_ == other->usageAnalysis_);
+  }
+  return true;
+}
+
+/* static */
+bool MPhi::markIteratorPhis(const PhiVector& iterators) {
+  // Find and mark phis that must transitively hold an iterator live.
+
+  Vector<MPhi*, 8, SystemAllocPolicy> worklist;
+
+  for (MPhi* iter : iterators) {
+    if (!iter->isInWorklist()) {
+      if (!worklist.append(iter)) {
+        return false;
+      }
+      iter->setInWorklist();
+    }
+  }
+
+  while (!worklist.empty()) {
+    MPhi* phi = worklist.popCopy();
+    phi->setNotInWorklist();
+
+    phi->setIterator();
+    phi->setImplicitlyUsedUnchecked();
+
+    for (MUseDefIterator iter(phi); iter; iter++) {
+      MDefinition* use = iter.def();
+      if (!use->isInWorklist() && use->isPhi() && !use->toPhi()->isIterator()) {
+        if (!worklist.append(use->toPhi())) {
+          return false;
+        }
+        use->setInWorklist();
+      }
+    }
+  }
+
+  return true;
+}
+
+bool MPhi::typeIncludes(MDefinition* def) {
+  MOZ_ASSERT(!IsMagicType(def->type()));
+
+  if (def->type() == MIRType::Int32 && this->type() == MIRType::Double) {
+    return true;
+  }
+
+  if (def->type() == MIRType::Value) {
+    // This phi must be able to be any value.
+    return this->type() == MIRType::Value;
+  }
+
+  return this->mightBeType(def->type());
+}
+
+void MCall::addArg(size_t argnum, MDefinition* arg) {
+  // The operand vector is initialized in reverse order by WarpBuilder.
+  // It cannot be checked for consistency until all arguments are added.
+  // FixedList doesn't initialize its elements, so do an unchecked init.
+  initOperand(argnum + NumNonArgumentOperands, arg);
+}
+
+static inline bool IsConstant(MDefinition* def, double v) {
+  if (!def->isConstant()) {
+    return false;
+  }
+
+  return NumbersAreIdentical(def->toConstant()->numberToDouble(), v);
+}
+
+MDefinition* MBinaryBitwiseInstruction::foldsTo(TempAllocator& alloc) {
+  // Identity operations are removed (for int32 only) in foldUnnecessaryBitop.
+
+  if (type() == MIRType::Int32) {
+    if (MDefinition* folded = EvaluateConstantOperands(alloc, this)) {
+      return folded;
+    }
+  } else if (type() == MIRType::Int64) {
+    if (MDefinition* folded = EvaluateInt64ConstantOperands(alloc, this)) {
+      return folded;
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MBinaryBitwiseInstruction::foldUnnecessaryBitop() {
+  // It's probably OK to perform this optimization only for int32, as it will
+  // have the greatest effect for asm.js code that is compiled with the JS
+  // pipeline, and that code will not see int64 values.
+
+  if (type() != MIRType::Int32) {
+    return this;
+  }
+
+  // Fold unsigned shift right operator when the second operand is zero and
+  // the only use is an unsigned modulo. Thus, the expression
+  // |(x >>> 0) % y| becomes |x % y|.
+  if (isUrsh() && IsUint32Type(this)) {
+    MDefinition* defUse = maybeSingleDefUse();
+    if (defUse && defUse->isMod() && defUse->toMod()->isUnsigned()) {
+      return getOperand(0);
+    }
+  }
+
+  // Eliminate bitwise operations that are no-ops when used on integer
+  // inputs, such as (x | 0).
+
+  MDefinition* lhs = getOperand(0);
+  MDefinition* rhs = getOperand(1);
+
+  if (IsConstant(lhs, 0)) {
+    return foldIfZero(0);
+  }
+
+  if (IsConstant(rhs, 0)) {
+    return foldIfZero(1);
+  }
+
+  if (IsConstant(lhs, -1)) {
+    return foldIfNegOne(0);
+  }
+
+  if (IsConstant(rhs, -1)) {
+    return foldIfNegOne(1);
+  }
+
+  if (lhs == rhs) {
+    return foldIfEqual();
+  }
+
+  if (maskMatchesRightRange) {
+    MOZ_ASSERT(lhs->isConstant());
+    MOZ_ASSERT(lhs->type() == MIRType::Int32);
+    return foldIfAllBitsSet(0);
+  }
+
+  if (maskMatchesLeftRange) {
+    MOZ_ASSERT(rhs->isConstant());
+    MOZ_ASSERT(rhs->type() == MIRType::Int32);
+    return foldIfAllBitsSet(1);
+  }
+
+  return this;
+}
+
+static inline bool CanProduceNegativeZero(MDefinition* def) {
+  // Test if this instruction can produce negative zero even when bailing out
+  // and changing types.
+  switch (def->op()) {
+    case MDefinition::Opcode::Constant:
+      if (def->type() == MIRType::Double &&
+          def->toConstant()->toDouble() == -0.0) {
+        return true;
+      }
+      [[fallthrough]];
+    case MDefinition::Opcode::BitAnd:
+    case MDefinition::Opcode::BitOr:
+    case MDefinition::Opcode::BitXor:
+    case MDefinition::Opcode::BitNot:
+    case MDefinition::Opcode::Lsh:
+    case MDefinition::Opcode::Rsh:
+      return false;
+    default:
+      return true;
+  }
+}
+
+static inline bool NeedNegativeZeroCheck(MDefinition* def) {
+  if (def->isGuard() || def->isGuardRangeBailouts()) {
+    return true;
+  }
+
+  // Test if all uses have the same semantics for -0 and 0
+  for (MUseIterator use = def->usesBegin(); use != def->usesEnd(); use++) {
+    if (use->consumer()->isResumePoint()) {
+      return true;
+    }
+
+    MDefinition* use_def = use->consumer()->toDefinition();
+    switch (use_def->op()) {
+      case MDefinition::Opcode::Add: {
+        // If add is truncating -0 and 0 are observed as the same.
+        if (use_def->toAdd()->isTruncated()) {
+          break;
+        }
+
+        // x + y gives -0, when both x and y are -0
+
+        // Figure out the order in which the addition's operands will
+        // execute. EdgeCaseAnalysis::analyzeLate has renumbered the MIR
+        // definitions for us so that this just requires comparing ids.
+        MDefinition* first = use_def->toAdd()->lhs();
+        MDefinition* second = use_def->toAdd()->rhs();
+        if (first->id() > second->id()) {
+          std::swap(first, second);
+        }
+        // Negative zero checks can be removed on the first executed
+        // operand only if it is guaranteed the second executed operand
+        // will produce a value other than -0. While the second is
+        // typed as an int32, a bailout taken between execution of the
+        // operands may change that type and cause a -0 to flow to the
+        // second.
+        //
+        // There is no way to test whether there are any bailouts
+        // between execution of the operands, so remove negative
+        // zero checks from the first only if the second's type is
+        // independent from type changes that may occur after bailing.
+        if (def == first && CanProduceNegativeZero(second)) {
+          return true;
+        }
+
+        // The negative zero check can always be removed on the second
+        // executed operand; by the time this executes the first will have
+        // been evaluated as int32 and the addition's result cannot be -0.
+        break;
+      }
+      case MDefinition::Opcode::Sub: {
+        // If sub is truncating -0 and 0 are observed as the same
+        if (use_def->toSub()->isTruncated()) {
+          break;
+        }
+
+        // x + y gives -0, when x is -0 and y is 0
+
+        // We can remove the negative zero check on the rhs, only if we
+        // are sure the lhs isn't negative zero.
+
+        // The lhs is typed as integer (i.e. not -0.0), but it can bailout
+        // and change type. This should be fine if the lhs is executed
+        // first. However if the rhs is executed first, the lhs can bail,
+        // change type and become -0.0 while the rhs has already been
+        // optimized to not make a difference between zero and negative zero.
+        MDefinition* lhs = use_def->toSub()->lhs();
+        MDefinition* rhs = use_def->toSub()->rhs();
+        if (rhs->id() < lhs->id() && CanProduceNegativeZero(lhs)) {
+          return true;
+        }
+
+        [[fallthrough]];
+      }
+      case MDefinition::Opcode::StoreElement:
+      case MDefinition::Opcode::StoreHoleValueElement:
+      case MDefinition::Opcode::LoadElement:
+      case MDefinition::Opcode::LoadElementHole:
+      case MDefinition::Opcode::LoadUnboxedScalar:
+      case MDefinition::Opcode::LoadDataViewElement:
+      case MDefinition::Opcode::LoadTypedArrayElementHole:
+      case MDefinition::Opcode::CharCodeAt:
+      case MDefinition::Opcode::Mod:
+      case MDefinition::Opcode::InArray:
+        // Only allowed to remove check when definition is the second operand
+        if (use_def->getOperand(0) == def) {
+          return true;
+        }
+        for (size_t i = 2, e = use_def->numOperands(); i < e; i++) {
+          if (use_def->getOperand(i) == def) {
+            return true;
+          }
+        }
+        break;
+      case MDefinition::Opcode::BoundsCheck:
+        // Only allowed to remove check when definition is the first operand
+        if (use_def->toBoundsCheck()->getOperand(1) == def) {
+          return true;
+        }
+        break;
+      case MDefinition::Opcode::ToString:
+      case MDefinition::Opcode::FromCharCode:
+      case MDefinition::Opcode::FromCodePoint:
+      case MDefinition::Opcode::TableSwitch:
+      case MDefinition::Opcode::Compare:
+      case MDefinition::Opcode::BitAnd:
+      case MDefinition::Opcode::BitOr:
+      case MDefinition::Opcode::BitXor:
+      case MDefinition::Opcode::Abs:
+      case MDefinition::Opcode::TruncateToInt32:
+        // Always allowed to remove check. No matter which operand.
+        break;
+      case MDefinition::Opcode::StoreElementHole:
+      case MDefinition::Opcode::StoreTypedArrayElementHole:
+      case MDefinition::Opcode::PostWriteElementBarrier:
+        // Only allowed to remove check when definition is the third operand.
+        for (size_t i = 0, e = use_def->numOperands(); i < e; i++) {
+          if (i == 2) {
+            continue;
+          }
+          if (use_def->getOperand(i) == def) {
+            return true;
+          }
+        }
+        break;
+      default:
+        return true;
+    }
+  }
+  return false;
+}
+
+#ifdef JS_JITSPEW
+void MBinaryArithInstruction::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+
+  switch (type()) {
+    case MIRType::Int32:
+      if (isDiv()) {
+        out.printf(" [%s]", toDiv()->isUnsigned() ? "uint32" : "int32");
+      } else if (isMod()) {
+        out.printf(" [%s]", toMod()->isUnsigned() ? "uint32" : "int32");
+      } else {
+        out.printf(" [int32]");
+      }
+      break;
+    case MIRType::Int64:
+      if (isDiv()) {
+        out.printf(" [%s]", toDiv()->isUnsigned() ? "uint64" : "int64");
+      } else if (isMod()) {
+        out.printf(" [%s]", toMod()->isUnsigned() ? "uint64" : "int64");
+      } else {
+        out.printf(" [int64]");
+      }
+      break;
+    case MIRType::Float32:
+      out.printf(" [float]");
+      break;
+    case MIRType::Double:
+      out.printf(" [double]");
+      break;
+    default:
+      break;
+  }
+}
+#endif
+
+MDefinition* MRsh::foldsTo(TempAllocator& alloc) {
+  MDefinition* f = MBinaryBitwiseInstruction::foldsTo(alloc);
+
+  if (f != this) {
+    return f;
+  }
+
+  MDefinition* lhs = getOperand(0);
+  MDefinition* rhs = getOperand(1);
+
+  // It's probably OK to perform this optimization only for int32, as it will
+  // have the greatest effect for asm.js code that is compiled with the JS
+  // pipeline, and that code will not see int64 values.
+
+  if (!lhs->isLsh() || !rhs->isConstant() || rhs->type() != MIRType::Int32) {
+    return this;
+  }
+
+  if (!lhs->getOperand(1)->isConstant() ||
+      lhs->getOperand(1)->type() != MIRType::Int32) {
+    return this;
+  }
+
+  uint32_t shift = rhs->toConstant()->toInt32();
+  uint32_t shift_lhs = lhs->getOperand(1)->toConstant()->toInt32();
+  if (shift != shift_lhs) {
+    return this;
+  }
+
+  switch (shift) {
+    case 16:
+      return MSignExtendInt32::New(alloc, lhs->getOperand(0),
+                                   MSignExtendInt32::Half);
+    case 24:
+      return MSignExtendInt32::New(alloc, lhs->getOperand(0),
+                                   MSignExtendInt32::Byte);
+  }
+
+  return this;
+}
+
+MDefinition* MBinaryArithInstruction::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(IsNumberType(type()));
+
+  MDefinition* lhs = getOperand(0);
+  MDefinition* rhs = getOperand(1);
+
+  if (type() == MIRType::Int64) {
+    MOZ_ASSERT(!isTruncated());
+
+    if (MConstant* folded = EvaluateInt64ConstantOperands(alloc, this)) {
+      if (!folded->block()) {
+        block()->insertBefore(this, folded);
+      }
+      return folded;
+    }
+    if (isSub() || isDiv() || isMod()) {
+      return this;
+    }
+    if (rhs->isConstant() &&
+        rhs->toConstant()->toInt64() == int64_t(getIdentity())) {
+      return lhs;
+    }
+    if (lhs->isConstant() &&
+        lhs->toConstant()->toInt64() == int64_t(getIdentity())) {
+      return rhs;
+    }
+    return this;
+  }
+
+  if (MConstant* folded = EvaluateConstantOperands(alloc, this)) {
+    if (isTruncated()) {
+      if (!folded->block()) {
+        block()->insertBefore(this, folded);
+      }
+      if (folded->type() != MIRType::Int32) {
+        return MTruncateToInt32::New(alloc, folded);
+      }
+    }
+    return folded;
+  }
+
+  if (mustPreserveNaN_) {
+    return this;
+  }
+
+  // 0 + -0 = 0. So we can't remove addition
+  if (isAdd() && type() != MIRType::Int32) {
+    return this;
+  }
+
+  if (IsConstant(rhs, getIdentity())) {
+    if (isTruncated()) {
+      return MTruncateToInt32::New(alloc, lhs);
+    }
+    return lhs;
+  }
+
+  // subtraction isn't commutative. So we can't remove subtraction when lhs
+  // equals 0
+  if (isSub()) {
+    return this;
+  }
+
+  if (IsConstant(lhs, getIdentity())) {
+    if (isTruncated()) {
+      return MTruncateToInt32::New(alloc, rhs);
+    }
+    return rhs;  // id op x => x
+  }
+
+  return this;
+}
+
+void MBinaryArithInstruction::trySpecializeFloat32(TempAllocator& alloc) {
+  MOZ_ASSERT(IsNumberType(type()));
+
+  // Do not use Float32 if we can use int32.
+  if (type() == MIRType::Int32) {
+    return;
+  }
+
+  if (EnsureFloatConsumersAndInputOrConvert(this, alloc)) {
+    setResultType(MIRType::Float32);
+  }
+}
+
+void MMinMax::trySpecializeFloat32(TempAllocator& alloc) {
+  if (type() == MIRType::Int32) {
+    return;
+  }
+
+  MDefinition* left = lhs();
+  MDefinition* right = rhs();
+
+  if ((left->canProduceFloat32() ||
+       (left->isMinMax() && left->type() == MIRType::Float32)) &&
+      (right->canProduceFloat32() ||
+       (right->isMinMax() && right->type() == MIRType::Float32))) {
+    setResultType(MIRType::Float32);
+  } else {
+    ConvertOperandsToDouble(this, alloc);
+  }
+}
+
+MDefinition* MMinMax::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(lhs()->type() == type());
+  MOZ_ASSERT(rhs()->type() == type());
+
+  if (lhs() == rhs()) {
+    return lhs();
+  }
+
+  // Fold min/max operations with same inputs.
+  if (lhs()->isMinMax() || rhs()->isMinMax()) {
+    auto* other = lhs()->isMinMax() ? lhs()->toMinMax() : rhs()->toMinMax();
+    auto* operand = lhs()->isMinMax() ? rhs() : lhs();
+
+    if (operand == other->lhs() || operand == other->rhs()) {
+      if (isMax() == other->isMax()) {
+        // min(x, min(x, y)) = min(x, y)
+        // max(x, max(x, y)) = max(x, y)
+        return other;
+      }
+      if (!IsFloatingPointType(type())) {
+        // When neither value is NaN:
+        // max(x, min(x, y)) = x
+        // min(x, max(x, y)) = x
+
+        // Ensure that any bailouts that we depend on to guarantee that |y| is
+        // Int32 are not removed.
+        auto* otherOp = operand == other->lhs() ? other->rhs() : other->lhs();
+        otherOp->setGuardRangeBailoutsUnchecked();
+
+        return operand;
+      }
+    }
+  }
+
+  if (!lhs()->isConstant() && !rhs()->isConstant()) {
+    return this;
+  }
+
+  auto foldConstants = [&alloc](MDefinition* lhs, MDefinition* rhs,
+                                bool isMax) -> MConstant* {
+    MOZ_ASSERT(lhs->type() == rhs->type());
+    MOZ_ASSERT(lhs->toConstant()->isTypeRepresentableAsDouble());
+    MOZ_ASSERT(rhs->toConstant()->isTypeRepresentableAsDouble());
+
+    double lnum = lhs->toConstant()->numberToDouble();
+    double rnum = rhs->toConstant()->numberToDouble();
+
+    double result;
+    if (isMax) {
+      result = js::math_max_impl(lnum, rnum);
+    } else {
+      result = js::math_min_impl(lnum, rnum);
+    }
+
+    // The folded MConstant should maintain the same MIRType with the original
+    // inputs.
+    if (lhs->type() == MIRType::Int32) {
+      int32_t cast;
+      if (mozilla::NumberEqualsInt32(result, &cast)) {
+        return MConstant::New(alloc, Int32Value(cast));
+      }
+      return nullptr;
+    }
+    if (lhs->type() == MIRType::Float32) {
+      return MConstant::NewFloat32(alloc, result);
+    }
+    MOZ_ASSERT(lhs->type() == MIRType::Double);
+    return MConstant::New(alloc, DoubleValue(result));
+  };
+
+  // Directly apply math utility to compare the rhs() and lhs() when
+  // they are both constants.
+  if (lhs()->isConstant() && rhs()->isConstant()) {
+    if (!lhs()->toConstant()->isTypeRepresentableAsDouble() ||
+        !rhs()->toConstant()->isTypeRepresentableAsDouble()) {
+      return this;
+    }
+
+    if (auto* folded = foldConstants(lhs(), rhs(), isMax())) {
+      return folded;
+    }
+  }
+
+  MDefinition* operand = lhs()->isConstant() ? rhs() : lhs();
+  MConstant* constant =
+      lhs()->isConstant() ? lhs()->toConstant() : rhs()->toConstant();
+
+  if (operand->isToDouble() &&
+      operand->getOperand(0)->type() == MIRType::Int32) {
+    // min(int32, cte >= INT32_MAX) = int32
+    if (!isMax() && constant->isTypeRepresentableAsDouble() &&
+        constant->numberToDouble() >= INT32_MAX) {
+      MLimitedTruncate* limit = MLimitedTruncate::New(
+          alloc, operand->getOperand(0), TruncateKind::NoTruncate);
+      block()->insertBefore(this, limit);
+      MToDouble* toDouble = MToDouble::New(alloc, limit);
+      return toDouble;
+    }
+
+    // max(int32, cte <= INT32_MIN) = int32
+    if (isMax() && constant->isTypeRepresentableAsDouble() &&
+        constant->numberToDouble() <= INT32_MIN) {
+      MLimitedTruncate* limit = MLimitedTruncate::New(
+          alloc, operand->getOperand(0), TruncateKind::NoTruncate);
+      block()->insertBefore(this, limit);
+      MToDouble* toDouble = MToDouble::New(alloc, limit);
+      return toDouble;
+    }
+  }
+
+  auto foldLength = [](MDefinition* operand, MConstant* constant,
+                       bool isMax) -> MDefinition* {
+    if ((operand->isArrayLength() || operand->isArrayBufferViewLength() ||
+         operand->isArgumentsLength() || operand->isStringLength()) &&
+        constant->type() == MIRType::Int32) {
+      // (Array|ArrayBufferView|Arguments|String)Length is always >= 0.
+      // max(array.length, cte <= 0) = array.length
+      // min(array.length, cte <= 0) = cte
+      if (constant->toInt32() <= 0) {
+        return isMax ? operand : constant;
+      }
+    }
+    return nullptr;
+  };
+
+  if (auto* folded = foldLength(operand, constant, isMax())) {
+    return folded;
+  }
+
+  // Attempt to fold nested min/max operations which are produced by
+  // self-hosted built-in functions.
+  if (operand->isMinMax()) {
+    auto* other = operand->toMinMax();
+    MOZ_ASSERT(other->lhs()->type() == type());
+    MOZ_ASSERT(other->rhs()->type() == type());
+
+    MConstant* otherConstant = nullptr;
+    MDefinition* otherOperand = nullptr;
+    if (other->lhs()->isConstant()) {
+      otherConstant = other->lhs()->toConstant();
+      otherOperand = other->rhs();
+    } else if (other->rhs()->isConstant()) {
+      otherConstant = other->rhs()->toConstant();
+      otherOperand = other->lhs();
+    }
+
+    if (otherConstant && constant->isTypeRepresentableAsDouble() &&
+        otherConstant->isTypeRepresentableAsDouble()) {
+      if (isMax() == other->isMax()) {
+        // Fold min(x, min(y, z)) to min(min(x, y), z) with constant min(x, y).
+        // Fold max(x, max(y, z)) to max(max(x, y), z) with constant max(x, y).
+        if (auto* left = foldConstants(constant, otherConstant, isMax())) {
+          block()->insertBefore(this, left);
+          return MMinMax::New(alloc, left, otherOperand, type(), isMax());
+        }
+      } else {
+        // Fold min(x, max(y, z)) to max(min(x, y), min(x, z)).
+        // Fold max(x, min(y, z)) to min(max(x, y), max(x, z)).
+        //
+        // But only do this when min(x, z) can also be simplified.
+        if (auto* right = foldLength(otherOperand, constant, isMax())) {
+          if (auto* left = foldConstants(constant, otherConstant, isMax())) {
+            block()->insertBefore(this, left);
+            return MMinMax::New(alloc, left, right, type(), !isMax());
+          }
+        }
+      }
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MPow::foldsConstant(TempAllocator& alloc) {
+  // Both `x` and `p` in `x^p` must be constants in order to precompute.
+  if (!input()->isConstant() || !power()->isConstant()) {
+    return nullptr;
+  }
+  if (!power()->toConstant()->isTypeRepresentableAsDouble()) {
+    return nullptr;
+  }
+  if (!input()->toConstant()->isTypeRepresentableAsDouble()) {
+    return nullptr;
+  }
+
+  double x = input()->toConstant()->numberToDouble();
+  double p = power()->toConstant()->numberToDouble();
+  double result = js::ecmaPow(x, p);
+  if (type() == MIRType::Int32) {
+    int32_t cast;
+    if (!mozilla::NumberIsInt32(result, &cast)) {
+      // Reject folding if the result isn't an int32, because we'll bail anyway.
+      return nullptr;
+    }
+    return MConstant::New(alloc, Int32Value(cast));
+  }
+  return MConstant::New(alloc, DoubleValue(result));
+}
+
+MDefinition* MPow::foldsConstantPower(TempAllocator& alloc) {
+  // If `p` in `x^p` isn't constant, we can't apply these folds.
+  if (!power()->isConstant()) {
+    return nullptr;
+  }
+  if (!power()->toConstant()->isTypeRepresentableAsDouble()) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(type() == MIRType::Double || type() == MIRType::Int32);
+
+  // NOTE: The optimizations must match the optimizations used in |js::ecmaPow|
+  // resp. |js::powi| to avoid differential testing issues.
+
+  double pow = power()->toConstant()->numberToDouble();
+
+  // Math.pow(x, 0.5) is a sqrt with edge-case detection.
+  if (pow == 0.5) {
+    MOZ_ASSERT(type() == MIRType::Double);
+    return MPowHalf::New(alloc, input());
+  }
+
+  // Math.pow(x, -0.5) == 1 / Math.pow(x, 0.5), even for edge cases.
+  if (pow == -0.5) {
+    MOZ_ASSERT(type() == MIRType::Double);
+    MPowHalf* half = MPowHalf::New(alloc, input());
+    block()->insertBefore(this, half);
+    MConstant* one = MConstant::New(alloc, DoubleValue(1.0));
+    block()->insertBefore(this, one);
+    return MDiv::New(alloc, one, half, MIRType::Double);
+  }
+
+  // Math.pow(x, 1) == x.
+  if (pow == 1.0) {
+    return input();
+  }
+
+  auto multiply = [this, &alloc](MDefinition* lhs, MDefinition* rhs) {
+    MMul* mul = MMul::New(alloc, lhs, rhs, type());
+    mul->setBailoutKind(bailoutKind());
+
+    // Multiplying the same number can't yield negative zero.
+    mul->setCanBeNegativeZero(lhs != rhs && canBeNegativeZero());
+    return mul;
+  };
+
+  // Math.pow(x, 2) == x*x.
+  if (pow == 2.0) {
+    return multiply(input(), input());
+  }
+
+  // Math.pow(x, 3) == x*x*x.
+  if (pow == 3.0) {
+    MMul* mul1 = multiply(input(), input());
+    block()->insertBefore(this, mul1);
+    return multiply(input(), mul1);
+  }
+
+  // Math.pow(x, 4) == y*y, where y = x*x.
+  if (pow == 4.0) {
+    MMul* y = multiply(input(), input());
+    block()->insertBefore(this, y);
+    return multiply(y, y);
+  }
+
+  // No optimization
+  return nullptr;
+}
+
+MDefinition* MPow::foldsTo(TempAllocator& alloc) {
+  if (MDefinition* def = foldsConstant(alloc)) {
+    return def;
+  }
+  if (MDefinition* def = foldsConstantPower(alloc)) {
+    return def;
+  }
+  return this;
+}
+
+MDefinition* MInt32ToIntPtr::foldsTo(TempAllocator& alloc) {
+  MDefinition* def = input();
+  if (def->isConstant()) {
+    int32_t i = def->toConstant()->toInt32();
+    return MConstant::NewIntPtr(alloc, intptr_t(i));
+  }
+
+  if (def->isNonNegativeIntPtrToInt32()) {
+    return def->toNonNegativeIntPtrToInt32()->input();
+  }
+
+  return this;
+}
+
+bool MAbs::fallible() const {
+  return !implicitTruncate_ && (!range() || !range()->hasInt32Bounds());
+}
+
+void MAbs::trySpecializeFloat32(TempAllocator& alloc) {
+  // Do not use Float32 if we can use int32.
+  if (input()->type() == MIRType::Int32) {
+    return;
+  }
+
+  if (EnsureFloatConsumersAndInputOrConvert(this, alloc)) {
+    setResultType(MIRType::Float32);
+  }
+}
+
+MDefinition* MDiv::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(IsNumberType(type()));
+
+  if (type() == MIRType::Int64) {
+    if (MDefinition* folded = EvaluateInt64ConstantOperands(alloc, this)) {
+      return folded;
+    }
+    return this;
+  }
+
+  if (MDefinition* folded = EvaluateConstantOperands(alloc, this)) {
+    return folded;
+  }
+
+  if (MDefinition* folded = EvaluateExactReciprocal(alloc, this)) {
+    return folded;
+  }
+
+  return this;
+}
+
+void MDiv::analyzeEdgeCasesForward() {
+  // This is only meaningful when doing integer division.
+  if (type() != MIRType::Int32) {
+    return;
+  }
+
+  MOZ_ASSERT(lhs()->type() == MIRType::Int32);
+  MOZ_ASSERT(rhs()->type() == MIRType::Int32);
+
+  // Try removing divide by zero check
+  if (rhs()->isConstant() && !rhs()->toConstant()->isInt32(0)) {
+    canBeDivideByZero_ = false;
+  }
+
+  // If lhs is a constant int != INT32_MIN, then
+  // negative overflow check can be skipped.
+  if (lhs()->isConstant() && !lhs()->toConstant()->isInt32(INT32_MIN)) {
+    canBeNegativeOverflow_ = false;
+  }
+
+  // If rhs is a constant int != -1, likewise.
+  if (rhs()->isConstant() && !rhs()->toConstant()->isInt32(-1)) {
+    canBeNegativeOverflow_ = false;
+  }
+
+  // If lhs is != 0, then negative zero check can be skipped.
+  if (lhs()->isConstant() && !lhs()->toConstant()->isInt32(0)) {
+    setCanBeNegativeZero(false);
+  }
+
+  // If rhs is >= 0, likewise.
+  if (rhs()->isConstant() && rhs()->type() == MIRType::Int32) {
+    if (rhs()->toConstant()->toInt32() >= 0) {
+      setCanBeNegativeZero(false);
+    }
+  }
+}
+
+void MDiv::analyzeEdgeCasesBackward() {
+  if (canBeNegativeZero() && !NeedNegativeZeroCheck(this)) {
+    setCanBeNegativeZero(false);
+  }
+}
+
+bool MDiv::fallible() const { return !isTruncated(); }
+
+MDefinition* MMod::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(IsNumberType(type()));
+
+  if (type() == MIRType::Int64) {
+    if (MDefinition* folded = EvaluateInt64ConstantOperands(alloc, this)) {
+      return folded;
+    }
+  } else {
+    if (MDefinition* folded = EvaluateConstantOperands(alloc, this)) {
+      return folded;
+    }
+  }
+  return this;
+}
+
+void MMod::analyzeEdgeCasesForward() {
+  // These optimizations make sense only for integer division
+  if (type() != MIRType::Int32) {
+    return;
+  }
+
+  if (rhs()->isConstant() && !rhs()->toConstant()->isInt32(0)) {
+    canBeDivideByZero_ = false;
+  }
+
+  if (rhs()->isConstant()) {
+    int32_t n = rhs()->toConstant()->toInt32();
+    if (n > 0 && !IsPowerOfTwo(uint32_t(n))) {
+      canBePowerOfTwoDivisor_ = false;
+    }
+  }
+}
+
+bool MMod::fallible() const {
+  return !isTruncated() &&
+         (isUnsigned() || canBeDivideByZero() || canBeNegativeDividend());
+}
+
+void MMathFunction::trySpecializeFloat32(TempAllocator& alloc) {
+  if (EnsureFloatConsumersAndInputOrConvert(this, alloc)) {
+    setResultType(MIRType::Float32);
+    specialization_ = MIRType::Float32;
+  }
+}
+
+bool MMathFunction::isFloat32Commutative() const {
+  switch (function_) {
+    case UnaryMathFunction::Floor:
+    case UnaryMathFunction::Ceil:
+    case UnaryMathFunction::Round:
+    case UnaryMathFunction::Trunc:
+      return true;
+    default:
+      return false;
+  }
+}
+
+MHypot* MHypot::New(TempAllocator& alloc, const MDefinitionVector& vector) {
+  uint32_t length = vector.length();
+  MHypot* hypot = new (alloc) MHypot;
+  if (!hypot->init(alloc, length)) {
+    return nullptr;
+  }
+
+  for (uint32_t i = 0; i < length; ++i) {
+    hypot->initOperand(i, vector[i]);
+  }
+  return hypot;
+}
+
+bool MAdd::fallible() const {
+  // the add is fallible if range analysis does not say that it is finite, AND
+  // either the truncation analysis shows that there are non-truncated uses.
+  if (truncateKind() >= TruncateKind::IndirectTruncate) {
+    return false;
+  }
+  if (range() && range()->hasInt32Bounds()) {
+    return false;
+  }
+  return true;
+}
+
+bool MSub::fallible() const {
+  // see comment in MAdd::fallible()
+  if (truncateKind() >= TruncateKind::IndirectTruncate) {
+    return false;
+  }
+  if (range() && range()->hasInt32Bounds()) {
+    return false;
+  }
+  return true;
+}
+
+MDefinition* MSub::foldsTo(TempAllocator& alloc) {
+  MDefinition* out = MBinaryArithInstruction::foldsTo(alloc);
+  if (out != this) {
+    return out;
+  }
+
+  if (type() != MIRType::Int32) {
+    return this;
+  }
+
+  // Optimize X - X to 0. This optimization is only valid for Int32
+  // values. Subtracting a floating point value from itself returns
+  // NaN when the operand is either Infinity or NaN.
+  if (lhs() == rhs()) {
+    // Ensure that any bailouts that we depend on to guarantee that X
+    // is Int32 are not removed.
+    lhs()->setGuardRangeBailoutsUnchecked();
+    return MConstant::New(alloc, Int32Value(0));
+  }
+
+  return this;
+}
+
+MDefinition* MMul::foldsTo(TempAllocator& alloc) {
+  MDefinition* out = MBinaryArithInstruction::foldsTo(alloc);
+  if (out != this) {
+    return out;
+  }
+
+  if (type() != MIRType::Int32) {
+    return this;
+  }
+
+  if (lhs() == rhs()) {
+    setCanBeNegativeZero(false);
+  }
+
+  return this;
+}
+
+void MMul::analyzeEdgeCasesForward() {
+  // Try to remove the check for negative zero
+  // This only makes sense when using the integer multiplication
+  if (type() != MIRType::Int32) {
+    return;
+  }
+
+  // If lhs is > 0, no need for negative zero check.
+  if (lhs()->isConstant() && lhs()->type() == MIRType::Int32) {
+    if (lhs()->toConstant()->toInt32() > 0) {
+      setCanBeNegativeZero(false);
+    }
+  }
+
+  // If rhs is > 0, likewise.
+  if (rhs()->isConstant() && rhs()->type() == MIRType::Int32) {
+    if (rhs()->toConstant()->toInt32() > 0) {
+      setCanBeNegativeZero(false);
+    }
+  }
+}
+
+void MMul::analyzeEdgeCasesBackward() {
+  if (canBeNegativeZero() && !NeedNegativeZeroCheck(this)) {
+    setCanBeNegativeZero(false);
+  }
+}
+
+bool MMul::updateForReplacement(MDefinition* ins_) {
+  MMul* ins = ins_->toMul();
+  bool negativeZero = canBeNegativeZero() || ins->canBeNegativeZero();
+  setCanBeNegativeZero(negativeZero);
+  // Remove the imul annotation when merging imul and normal multiplication.
+  if (mode_ == Integer && ins->mode() != Integer) {
+    mode_ = Normal;
+  }
+  return true;
+}
+
+bool MMul::canOverflow() const {
+  if (isTruncated()) {
+    return false;
+  }
+  return !range() || !range()->hasInt32Bounds();
+}
+
+bool MUrsh::fallible() const {
+  if (bailoutsDisabled()) {
+    return false;
+  }
+  return !range() || !range()->hasInt32Bounds();
+}
+
+MIRType MCompare::inputType() {
+  switch (compareType_) {
+    case Compare_Undefined:
+      return MIRType::Undefined;
+    case Compare_Null:
+      return MIRType::Null;
+    case Compare_UInt32:
+    case Compare_Int32:
+      return MIRType::Int32;
+    case Compare_UIntPtr:
+      return MIRType::IntPtr;
+    case Compare_Double:
+      return MIRType::Double;
+    case Compare_Float32:
+      return MIRType::Float32;
+    case Compare_String:
+      return MIRType::String;
+    case Compare_Symbol:
+      return MIRType::Symbol;
+    case Compare_Object:
+      return MIRType::Object;
+    case Compare_BigInt:
+    case Compare_BigInt_Int32:
+    case Compare_BigInt_Double:
+    case Compare_BigInt_String:
+      return MIRType::BigInt;
+    default:
+      MOZ_CRASH("No known conversion");
+  }
+}
+
+static inline bool MustBeUInt32(MDefinition* def, MDefinition** pwrapped) {
+  if (def->isUrsh()) {
+    *pwrapped = def->toUrsh()->lhs();
+    MDefinition* rhs = def->toUrsh()->rhs();
+    return def->toUrsh()->bailoutsDisabled() && rhs->maybeConstantValue() &&
+           rhs->maybeConstantValue()->isInt32(0);
+  }
+
+  if (MConstant* defConst = def->maybeConstantValue()) {
+    *pwrapped = defConst;
+    return defConst->type() == MIRType::Int32 && defConst->toInt32() >= 0;
+  }
+
+  *pwrapped = nullptr;  // silence GCC warning
+  return false;
+}
+
+/* static */
+bool MBinaryInstruction::unsignedOperands(MDefinition* left,
+                                          MDefinition* right) {
+  MDefinition* replace;
+  if (!MustBeUInt32(left, &replace)) {
+    return false;
+  }
+  if (replace->type() != MIRType::Int32) {
+    return false;
+  }
+  if (!MustBeUInt32(right, &replace)) {
+    return false;
+  }
+  if (replace->type() != MIRType::Int32) {
+    return false;
+  }
+  return true;
+}
+
+bool MBinaryInstruction::unsignedOperands() {
+  return unsignedOperands(getOperand(0), getOperand(1));
+}
+
+void MBinaryInstruction::replaceWithUnsignedOperands() {
+  MOZ_ASSERT(unsignedOperands());
+
+  for (size_t i = 0; i < numOperands(); i++) {
+    MDefinition* replace;
+    MustBeUInt32(getOperand(i), &replace);
+    if (replace == getOperand(i)) {
+      continue;
+    }
+
+    getOperand(i)->setImplicitlyUsedUnchecked();
+    replaceOperand(i, replace);
+  }
+}
+
+MDefinition* MBitNot::foldsTo(TempAllocator& alloc) {
+  if (type() == MIRType::Int64) {
+    return this;
+  }
+  MOZ_ASSERT(type() == MIRType::Int32);
+
+  MDefinition* input = getOperand(0);
+
+  if (input->isConstant()) {
+    js::Value v = Int32Value(~(input->toConstant()->toInt32()));
+    return MConstant::New(alloc, v);
+  }
+
+  if (input->isBitNot()) {
+    MOZ_ASSERT(input->toBitNot()->type() == MIRType::Int32);
+    MOZ_ASSERT(input->toBitNot()->getOperand(0)->type() == MIRType::Int32);
+    return MTruncateToInt32::New(alloc,
+                                 input->toBitNot()->input());  // ~~x => x | 0
+  }
+
+  return this;
+}
+
+static void AssertKnownClass(TempAllocator& alloc, MInstruction* ins,
+                             MDefinition* obj) {
+#ifdef DEBUG
+  const JSClass* clasp = GetObjectKnownJSClass(obj);
+  MOZ_ASSERT(clasp);
+
+  auto* assert = MAssertClass::New(alloc, obj, clasp);
+  ins->block()->insertBefore(ins, assert);
+#endif
+}
+
+MDefinition* MBoxNonStrictThis::foldsTo(TempAllocator& alloc) {
+  MDefinition* in = input();
+  if (in->isBox()) {
+    in = in->toBox()->input();
+  }
+
+  if (in->type() == MIRType::Object) {
+    return in;
+  }
+
+  return this;
+}
+
+AliasSet MLoadArgumentsObjectArg::getAliasSet() const {
+  return AliasSet::Load(AliasSet::Any);
+}
+
+AliasSet MLoadArgumentsObjectArgHole::getAliasSet() const {
+  return AliasSet::Load(AliasSet::Any);
+}
+
+AliasSet MInArgumentsObjectArg::getAliasSet() const {
+  // Loads |arguments.length|, but not the actual element, so we can use the
+  // same alias-set as MArgumentsObjectLength.
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+AliasSet MArgumentsObjectLength::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+bool MGuardArgumentsObjectFlags::congruentTo(const MDefinition* ins) const {
+  if (!ins->isGuardArgumentsObjectFlags() ||
+      ins->toGuardArgumentsObjectFlags()->flags() != flags()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MGuardArgumentsObjectFlags::getAliasSet() const {
+  // The flags are packed with the length in a fixed private slot.
+  return AliasSet::Load(AliasSet::FixedSlot);
+}
+
+MDefinition* MReturnFromCtor::foldsTo(TempAllocator& alloc) {
+  MDefinition* rval = value();
+  if (rval->isBox()) {
+    rval = rval->toBox()->input();
+  }
+
+  if (rval->type() == MIRType::Object) {
+    return rval;
+  }
+
+  if (rval->type() != MIRType::Value) {
+    return object();
+  }
+
+  return this;
+}
+
+MDefinition* MTypeOf::foldsTo(TempAllocator& alloc) {
+  MDefinition* unboxed = input();
+  if (unboxed->isBox()) {
+    unboxed = unboxed->toBox()->input();
+  }
+
+  JSType type;
+  switch (unboxed->type()) {
+    case MIRType::Double:
+    case MIRType::Float32:
+    case MIRType::Int32:
+      type = JSTYPE_NUMBER;
+      break;
+    case MIRType::String:
+      type = JSTYPE_STRING;
+      break;
+    case MIRType::Symbol:
+      type = JSTYPE_SYMBOL;
+      break;
+    case MIRType::BigInt:
+      type = JSTYPE_BIGINT;
+      break;
+    case MIRType::Null:
+      type = JSTYPE_OBJECT;
+      break;
+    case MIRType::Undefined:
+      type = JSTYPE_UNDEFINED;
+      break;
+    case MIRType::Boolean:
+      type = JSTYPE_BOOLEAN;
+      break;
+    case MIRType::Object: {
+      KnownClass known = GetObjectKnownClass(unboxed);
+      if (known != KnownClass::None) {
+        if (known == KnownClass::Function) {
+          type = JSTYPE_FUNCTION;
+        } else {
+          type = JSTYPE_OBJECT;
+        }
+
+        AssertKnownClass(alloc, this, unboxed);
+        break;
+      }
+      [[fallthrough]];
+    }
+    default:
+      return this;
+  }
+
+  return MConstant::New(alloc, Int32Value(static_cast<int32_t>(type)));
+}
+
+MDefinition* MTypeOfName::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(input()->type() == MIRType::Int32);
+
+  if (!input()->isConstant()) {
+    return this;
+  }
+
+  static_assert(JSTYPE_UNDEFINED == 0);
+
+  int32_t type = input()->toConstant()->toInt32();
+  MOZ_ASSERT(JSTYPE_UNDEFINED <= type && type < JSTYPE_LIMIT);
+
+  JSString* name =
+      TypeName(static_cast<JSType>(type), GetJitContext()->runtime->names());
+  return MConstant::New(alloc, StringValue(name));
+}
+
+MUrsh* MUrsh::NewWasm(TempAllocator& alloc, MDefinition* left,
+                      MDefinition* right, MIRType type) {
+  MUrsh* ins = new (alloc) MUrsh(left, right, type);
+
+  // Since Ion has no UInt32 type, we use Int32 and we have a special
+  // exception to the type rules: we can return values in
+  // (INT32_MIN,UINT32_MAX] and still claim that we have an Int32 type
+  // without bailing out. This is necessary because Ion has no UInt32
+  // type and we can't have bailouts in wasm code.
+  ins->bailoutsDisabled_ = true;
+
+  return ins;
+}
+
+MResumePoint* MResumePoint::New(TempAllocator& alloc, MBasicBlock* block,
+                                jsbytecode* pc, ResumeMode mode) {
+  MResumePoint* resume = new (alloc) MResumePoint(block, pc, mode);
+  if (!resume->init(alloc)) {
+    block->discardPreAllocatedResumePoint(resume);
+    return nullptr;
+  }
+  resume->inherit(block);
+  return resume;
+}
+
+MResumePoint::MResumePoint(MBasicBlock* block, jsbytecode* pc, ResumeMode mode)
+    : MNode(block, Kind::ResumePoint),
+      pc_(pc),
+      instruction_(nullptr),
+      mode_(mode) {
+  block->addResumePoint(this);
+}
+
+bool MResumePoint::init(TempAllocator& alloc) {
+  return operands_.init(alloc, block()->stackDepth());
+}
+
+MResumePoint* MResumePoint::caller() const {
+  return block()->callerResumePoint();
+}
+
+void MResumePoint::inherit(MBasicBlock* block) {
+  // FixedList doesn't initialize its elements, so do unchecked inits.
+  for (size_t i = 0; i < stackDepth(); i++) {
+    initOperand(i, block->getSlot(i));
+  }
+}
+
+void MResumePoint::addStore(TempAllocator& alloc, MDefinition* store,
+                            const MResumePoint* cache) {
+  MOZ_ASSERT(block()->outerResumePoint() != this);
+  MOZ_ASSERT_IF(cache, !cache->stores_.empty());
+
+  if (cache && cache->stores_.begin()->operand == store) {
+    // If the last resume point had the same side-effect stack, then we can
+    // reuse the current side effect without cloning it. This is a simple
+    // way to share common context by making a spaghetti stack.
+    if (++cache->stores_.begin() == stores_.begin()) {
+      stores_.copy(cache->stores_);
+      return;
+    }
+  }
+
+  // Ensure that the store would not be deleted by DCE.
+  MOZ_ASSERT(store->isEffectful());
+
+  MStoreToRecover* top = new (alloc) MStoreToRecover(store);
+  stores_.push(top);
+}
+
+#ifdef JS_JITSPEW
+void MResumePoint::dump(GenericPrinter& out) const {
+  out.printf("resumepoint mode=");
+
+  switch (mode()) {
+    case ResumeMode::ResumeAt:
+      if (instruction_) {
+        out.printf("ResumeAt(%u)", instruction_->id());
+      } else {
+        out.printf("ResumeAt");
+      }
+      break;
+    default:
+      out.put(ResumeModeToString(mode()));
+      break;
+  }
+
+  if (MResumePoint* c = caller()) {
+    out.printf(" (caller in block%u)", c->block()->id());
+  }
+
+  for (size_t i = 0; i < numOperands(); i++) {
+    out.printf(" ");
+    if (operands_[i].hasProducer()) {
+      getOperand(i)->printName(out);
+    } else {
+      out.printf("(null)");
+    }
+  }
+  out.printf("\n");
+}
+
+void MResumePoint::dump() const {
+  Fprinter out(stderr);
+  dump(out);
+  out.finish();
+}
+#endif
+
+bool MResumePoint::isObservableOperand(MUse* u) const {
+  return isObservableOperand(indexOf(u));
+}
+
+bool MResumePoint::isObservableOperand(size_t index) const {
+  return block()->info().isObservableSlot(index);
+}
+
+bool MResumePoint::isRecoverableOperand(MUse* u) const {
+  return block()->info().isRecoverableOperand(indexOf(u));
+}
+
+MDefinition* MTruncateBigIntToInt64::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+
+  if (input->isBox()) {
+    input = input->getOperand(0);
+  }
+
+  // If the operand converts an I64 to BigInt, drop both conversions.
+  if (input->isInt64ToBigInt()) {
+    return input->getOperand(0);
+  }
+
+  // Fold this operation if the input operand is constant.
+  if (input->isConstant()) {
+    return MConstant::NewInt64(
+        alloc, BigInt::toInt64(input->toConstant()->toBigInt()));
+  }
+
+  return this;
+}
+
+MDefinition* MToInt64::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+
+  if (input->isBox()) {
+    input = input->getOperand(0);
+  }
+
+  // Unwrap MInt64ToBigInt: MToInt64(MInt64ToBigInt(int64)) = int64.
+  if (input->isInt64ToBigInt()) {
+    return input->getOperand(0);
+  }
+
+  // When the input is an Int64 already, just return it.
+  if (input->type() == MIRType::Int64) {
+    return input;
+  }
+
+  // Fold this operation if the input operand is constant.
+  if (input->isConstant()) {
+    switch (input->type()) {
+      case MIRType::Boolean:
+        return MConstant::NewInt64(alloc, input->toConstant()->toBoolean());
+      default:
+        break;
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MToNumberInt32::foldsTo(TempAllocator& alloc) {
+  // Fold this operation if the input operand is constant.
+  if (MConstant* cst = input()->maybeConstantValue()) {
+    switch (cst->type()) {
+      case MIRType::Null:
+        if (conversion() == IntConversionInputKind::Any) {
+          return MConstant::New(alloc, Int32Value(0));
+        }
+        break;
+      case MIRType::Boolean:
+        if (conversion() == IntConversionInputKind::Any ||
+            conversion() == IntConversionInputKind::NumbersOrBoolsOnly) {
+          return MConstant::New(alloc, Int32Value(cst->toBoolean()));
+        }
+        break;
+      case MIRType::Int32:
+        return MConstant::New(alloc, Int32Value(cst->toInt32()));
+      case MIRType::Float32:
+      case MIRType::Double:
+        int32_t ival;
+        // Only the value within the range of Int32 can be substituted as
+        // constant.
+        if (mozilla::NumberIsInt32(cst->numberToDouble(), &ival)) {
+          return MConstant::New(alloc, Int32Value(ival));
+        }
+        break;
+      default:
+        break;
+    }
+  }
+
+  MDefinition* input = getOperand(0);
+  if (input->isBox()) {
+    input = input->toBox()->input();
+  }
+
+  // Do not fold the TruncateToInt32 node when the input is uint32 (e.g. ursh
+  // with a zero constant. Consider the test jit-test/tests/ion/bug1247880.js,
+  // where the relevant code is: |(imul(1, x >>> 0) % 2)|. The imul operator
+  // is folded to a MTruncateToInt32 node, which will result in this MIR:
+  // MMod(MTruncateToInt32(MUrsh(x, MConstant(0))), MConstant(2)). Note that
+  // the MUrsh node's type is int32 (since uint32 is not implemented), and
+  // that would fold the MTruncateToInt32 node. This will make the modulo
+  // unsigned, while is should have been signed.
+  if (input->type() == MIRType::Int32 && !IsUint32Type(input)) {
+    return input;
+  }
+
+  return this;
+}
+
+MDefinition* MToIntegerInt32::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+
+  // Fold this operation if the input operand is constant.
+  if (input->isConstant()) {
+    switch (input->type()) {
+      case MIRType::Undefined:
+      case MIRType::Null:
+        return MConstant::New(alloc, Int32Value(0));
+      case MIRType::Boolean:
+        return MConstant::New(alloc,
+                              Int32Value(input->toConstant()->toBoolean()));
+      case MIRType::Int32:
+        return MConstant::New(alloc,
+                              Int32Value(input->toConstant()->toInt32()));
+      case MIRType::Float32:
+      case MIRType::Double: {
+        double result = JS::ToInteger(input->toConstant()->numberToDouble());
+        int32_t ival;
+        // Only the value within the range of Int32 can be substituted as
+        // constant.
+        if (mozilla::NumberEqualsInt32(result, &ival)) {
+          return MConstant::New(alloc, Int32Value(ival));
+        }
+        break;
+      }
+      default:
+        break;
+    }
+  }
+
+  // See the comment in |MToNumberInt32::foldsTo|.
+  if (input->type() == MIRType::Int32 && !IsUint32Type(input)) {
+    return input;
+  }
+
+  return this;
+}
+
+void MToNumberInt32::analyzeEdgeCasesBackward() {
+  if (!NeedNegativeZeroCheck(this)) {
+    setNeedsNegativeZeroCheck(false);
+  }
+}
+
+MDefinition* MTruncateToInt32::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+  if (input->isBox()) {
+    input = input->getOperand(0);
+  }
+
+  // Do not fold the TruncateToInt32 node when the input is uint32 (e.g. ursh
+  // with a zero constant. Consider the test jit-test/tests/ion/bug1247880.js,
+  // where the relevant code is: |(imul(1, x >>> 0) % 2)|. The imul operator
+  // is folded to a MTruncateToInt32 node, which will result in this MIR:
+  // MMod(MTruncateToInt32(MUrsh(x, MConstant(0))), MConstant(2)). Note that
+  // the MUrsh node's type is int32 (since uint32 is not implemented), and
+  // that would fold the MTruncateToInt32 node. This will make the modulo
+  // unsigned, while is should have been signed.
+  if (input->type() == MIRType::Int32 && !IsUint32Type(input)) {
+    return input;
+  }
+
+  if (input->type() == MIRType::Double && input->isConstant()) {
+    int32_t ret = ToInt32(input->toConstant()->toDouble());
+    return MConstant::New(alloc, Int32Value(ret));
+  }
+
+  return this;
+}
+
+MDefinition* MWasmTruncateToInt32::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+  if (input->type() == MIRType::Int32) {
+    return input;
+  }
+
+  if (input->type() == MIRType::Double && input->isConstant()) {
+    double d = input->toConstant()->toDouble();
+    if (IsNaN(d)) {
+      return this;
+    }
+
+    if (!isUnsigned() && d <= double(INT32_MAX) && d >= double(INT32_MIN)) {
+      return MConstant::New(alloc, Int32Value(ToInt32(d)));
+    }
+
+    if (isUnsigned() && d <= double(UINT32_MAX) && d >= 0) {
+      return MConstant::New(alloc, Int32Value(ToInt32(d)));
+    }
+  }
+
+  if (input->type() == MIRType::Float32 && input->isConstant()) {
+    double f = double(input->toConstant()->toFloat32());
+    if (IsNaN(f)) {
+      return this;
+    }
+
+    if (!isUnsigned() && f <= double(INT32_MAX) && f >= double(INT32_MIN)) {
+      return MConstant::New(alloc, Int32Value(ToInt32(f)));
+    }
+
+    if (isUnsigned() && f <= double(UINT32_MAX) && f >= 0) {
+      return MConstant::New(alloc, Int32Value(ToInt32(f)));
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MWrapInt64ToInt32::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = this->input();
+  if (input->isConstant()) {
+    uint64_t c = input->toConstant()->toInt64();
+    int32_t output = bottomHalf() ? int32_t(c) : int32_t(c >> 32);
+    return MConstant::New(alloc, Int32Value(output));
+  }
+
+  return this;
+}
+
+MDefinition* MExtendInt32ToInt64::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = this->input();
+  if (input->isConstant()) {
+    int32_t c = input->toConstant()->toInt32();
+    int64_t res = isUnsigned() ? int64_t(uint32_t(c)) : int64_t(c);
+    return MConstant::NewInt64(alloc, res);
+  }
+
+  return this;
+}
+
+MDefinition* MSignExtendInt32::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = this->input();
+  if (input->isConstant()) {
+    int32_t c = input->toConstant()->toInt32();
+    int32_t res;
+    switch (mode_) {
+      case Byte:
+        res = int32_t(int8_t(c & 0xFF));
+        break;
+      case Half:
+        res = int32_t(int16_t(c & 0xFFFF));
+        break;
+    }
+    return MConstant::New(alloc, Int32Value(res));
+  }
+
+  return this;
+}
+
+MDefinition* MSignExtendInt64::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = this->input();
+  if (input->isConstant()) {
+    int64_t c = input->toConstant()->toInt64();
+    int64_t res;
+    switch (mode_) {
+      case Byte:
+        res = int64_t(int8_t(c & 0xFF));
+        break;
+      case Half:
+        res = int64_t(int16_t(c & 0xFFFF));
+        break;
+      case Word:
+        res = int64_t(int32_t(c & 0xFFFFFFFFU));
+        break;
+    }
+    return MConstant::NewInt64(alloc, res);
+  }
+
+  return this;
+}
+
+MDefinition* MToDouble::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+  if (input->isBox()) {
+    input = input->getOperand(0);
+  }
+
+  if (input->type() == MIRType::Double) {
+    return input;
+  }
+
+  if (input->isConstant() &&
+      input->toConstant()->isTypeRepresentableAsDouble()) {
+    return MConstant::New(alloc,
+                          DoubleValue(input->toConstant()->numberToDouble()));
+  }
+
+  return this;
+}
+
+MDefinition* MToFloat32::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = getOperand(0);
+  if (input->isBox()) {
+    input = input->getOperand(0);
+  }
+
+  if (input->type() == MIRType::Float32) {
+    return input;
+  }
+
+  // If x is a Float32, Float32(Double(x)) == x
+  if (!mustPreserveNaN_ && input->isToDouble() &&
+      input->toToDouble()->input()->type() == MIRType::Float32) {
+    return input->toToDouble()->input();
+  }
+
+  if (input->isConstant() &&
+      input->toConstant()->isTypeRepresentableAsDouble()) {
+    return MConstant::NewFloat32(alloc,
+                                 float(input->toConstant()->numberToDouble()));
+  }
+
+  // Fold ToFloat32(ToDouble(int32)) to ToFloat32(int32).
+  if (input->isToDouble() &&
+      input->toToDouble()->input()->type() == MIRType::Int32) {
+    return MToFloat32::New(alloc, input->toToDouble()->input());
+  }
+
+  return this;
+}
+
+MDefinition* MToString::foldsTo(TempAllocator& alloc) {
+  MDefinition* in = input();
+  if (in->isBox()) {
+    in = in->getOperand(0);
+  }
+
+  if (in->type() == MIRType::String) {
+    return in;
+  }
+  return this;
+}
+
+MDefinition* MClampToUint8::foldsTo(TempAllocator& alloc) {
+  if (MConstant* inputConst = input()->maybeConstantValue()) {
+    if (inputConst->isTypeRepresentableAsDouble()) {
+      int32_t clamped = ClampDoubleToUint8(inputConst->numberToDouble());
+      return MConstant::New(alloc, Int32Value(clamped));
+    }
+  }
+  return this;
+}
+
+bool MCompare::tryFoldEqualOperands(bool* result) {
+  if (lhs() != rhs()) {
+    return false;
+  }
+
+  // Intuitively somebody would think that if lhs === rhs,
+  // then we can just return true. (Or false for !==)
+  // However NaN !== NaN is true! So we spend some time trying
+  // to eliminate this case.
+
+  if (!IsStrictEqualityOp(jsop())) {
+    return false;
+  }
+
+  MOZ_ASSERT(
+      compareType_ == Compare_Undefined || compareType_ == Compare_Null ||
+      compareType_ == Compare_Int32 || compareType_ == Compare_UInt32 ||
+      compareType_ == Compare_UInt64 || compareType_ == Compare_Double ||
+      compareType_ == Compare_Float32 || compareType_ == Compare_UIntPtr ||
+      compareType_ == Compare_String || compareType_ == Compare_Object ||
+      compareType_ == Compare_Symbol || compareType_ == Compare_BigInt ||
+      compareType_ == Compare_BigInt_Int32 ||
+      compareType_ == Compare_BigInt_Double ||
+      compareType_ == Compare_BigInt_String);
+
+  if (isDoubleComparison() || isFloat32Comparison()) {
+    if (!operandsAreNeverNaN()) {
+      return false;
+    }
+  }
+
+  lhs()->setGuardRangeBailoutsUnchecked();
+
+  *result = (jsop() == JSOp::StrictEq);
+  return true;
+}
+
+static JSType TypeOfName(JSLinearString* str) {
+  static constexpr std::array types = {
+      JSTYPE_UNDEFINED, JSTYPE_OBJECT,  JSTYPE_FUNCTION, JSTYPE_STRING,
+      JSTYPE_NUMBER,    JSTYPE_BOOLEAN, JSTYPE_SYMBOL,   JSTYPE_BIGINT,
+#ifdef ENABLE_RECORD_TUPLE
+      JSTYPE_RECORD,    JSTYPE_TUPLE,
+#endif
+  };
+  static_assert(types.size() == JSTYPE_LIMIT);
+
+  const JSAtomState& names = GetJitContext()->runtime->names();
+  for (auto type : types) {
+    if (EqualStrings(str, TypeName(type, names))) {
+      return type;
+    }
+  }
+  return JSTYPE_LIMIT;
+}
+
+static mozilla::Maybe<std::pair<MTypeOfName*, JSType>> IsTypeOfCompare(
+    MCompare* ins) {
+  if (!IsEqualityOp(ins->jsop())) {
+    return mozilla::Nothing();
+  }
+  if (ins->compareType() != MCompare::Compare_String) {
+    return mozilla::Nothing();
+  }
+
+  auto* lhs = ins->lhs();
+  auto* rhs = ins->rhs();
+
+  MOZ_ASSERT(ins->type() == MIRType::Boolean);
+  MOZ_ASSERT(lhs->type() == MIRType::String);
+  MOZ_ASSERT(rhs->type() == MIRType::String);
+
+  if (!lhs->isTypeOfName() && !rhs->isTypeOfName()) {
+    return mozilla::Nothing();
+  }
+  if (!lhs->isConstant() && !rhs->isConstant()) {
+    return mozilla::Nothing();
+  }
+
+  auto* typeOfName =
+      lhs->isTypeOfName() ? lhs->toTypeOfName() : rhs->toTypeOfName();
+  MOZ_ASSERT(typeOfName->input()->isTypeOf());
+
+  auto* constant = lhs->isConstant() ? lhs->toConstant() : rhs->toConstant();
+
+  JSType type = TypeOfName(&constant->toString()->asLinear());
+  return mozilla::Some(std::pair(typeOfName, type));
+}
+
+bool MCompare::tryFoldTypeOf(bool* result) {
+  auto typeOfPair = IsTypeOfCompare(this);
+  if (!typeOfPair) {
+    return false;
+  }
+  auto [typeOfName, type] = *typeOfPair;
+  auto* typeOf = typeOfName->input()->toTypeOf();
+
+  switch (type) {
+    case JSTYPE_BOOLEAN:
+      if (!typeOf->input()->mightBeType(MIRType::Boolean)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_NUMBER:
+      if (!typeOf->input()->mightBeType(MIRType::Int32) &&
+          !typeOf->input()->mightBeType(MIRType::Float32) &&
+          !typeOf->input()->mightBeType(MIRType::Double)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_STRING:
+      if (!typeOf->input()->mightBeType(MIRType::String)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_SYMBOL:
+      if (!typeOf->input()->mightBeType(MIRType::Symbol)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_BIGINT:
+      if (!typeOf->input()->mightBeType(MIRType::BigInt)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_OBJECT:
+      if (!typeOf->input()->mightBeType(MIRType::Object) &&
+          !typeOf->input()->mightBeType(MIRType::Null)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_UNDEFINED:
+      if (!typeOf->input()->mightBeType(MIRType::Object) &&
+          !typeOf->input()->mightBeType(MIRType::Undefined)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_FUNCTION:
+      if (!typeOf->input()->mightBeType(MIRType::Object)) {
+        *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+        return true;
+      }
+      break;
+    case JSTYPE_LIMIT:
+      *result = (jsop() == JSOp::StrictNe || jsop() == JSOp::Ne);
+      return true;
+#ifdef ENABLE_RECORD_TUPLE
+    case JSTYPE_RECORD:
+    case JSTYPE_TUPLE:
+      MOZ_CRASH("Records and Tuples are not supported yet.");
+#endif
+  }
+
+  return false;
+}
+
+bool MCompare::tryFold(bool* result) {
+  JSOp op = jsop();
+
+  if (tryFoldEqualOperands(result)) {
+    return true;
+  }
+
+  if (tryFoldTypeOf(result)) {
+    return true;
+  }
+
+  if (compareType_ == Compare_Null || compareType_ == Compare_Undefined) {
+    // The LHS is the value we want to test against null or undefined.
+    if (IsStrictEqualityOp(op)) {
+      if (lhs()->type() == inputType()) {
+        *result = (op == JSOp::StrictEq);
+        return true;
+      }
+      if (!lhs()->mightBeType(inputType())) {
+        *result = (op == JSOp::StrictNe);
+        return true;
+      }
+    } else {
+      MOZ_ASSERT(IsLooseEqualityOp(op));
+      if (IsNullOrUndefined(lhs()->type())) {
+        *result = (op == JSOp::Eq);
+        return true;
+      }
+      if (!lhs()->mightBeType(MIRType::Null) &&
+          !lhs()->mightBeType(MIRType::Undefined) &&
+          !lhs()->mightBeType(MIRType::Object)) {
+        *result = (op == JSOp::Ne);
+        return true;
+      }
+    }
+    return false;
+  }
+
+  return false;
+}
+
+template <typename T>
+static bool FoldComparison(JSOp op, T left, T right) {
+  switch (op) {
+    case JSOp::Lt:
+      return left < right;
+    case JSOp::Le:
+      return left <= right;
+    case JSOp::Gt:
+      return left > right;
+    case JSOp::Ge:
+      return left >= right;
+    case JSOp::StrictEq:
+    case JSOp::Eq:
+      return left == right;
+    case JSOp::StrictNe:
+    case JSOp::Ne:
+      return left != right;
+    default:
+      MOZ_CRASH("Unexpected op.");
+  }
+}
+
+bool MCompare::evaluateConstantOperands(TempAllocator& alloc, bool* result) {
+  if (type() != MIRType::Boolean && type() != MIRType::Int32) {
+    return false;
+  }
+
+  MDefinition* left = getOperand(0);
+  MDefinition* right = getOperand(1);
+
+  if (compareType() == Compare_Double) {
+    // Optimize "MCompare MConstant (MToDouble SomethingInInt32Range).
+    // In most cases the MToDouble was added, because the constant is
+    // a double.
+    // e.g. v < 9007199254740991, where v is an int32 is always true.
+    if (!lhs()->isConstant() && !rhs()->isConstant()) {
+      return false;
+    }
+
+    MDefinition* operand = left->isConstant() ? right : left;
+    MConstant* constant =
+        left->isConstant() ? left->toConstant() : right->toConstant();
+    MOZ_ASSERT(constant->type() == MIRType::Double);
+    double cte = constant->toDouble();
+
+    if (operand->isToDouble() &&
+        operand->getOperand(0)->type() == MIRType::Int32) {
+      bool replaced = false;
+      switch (jsop_) {
+        case JSOp::Lt:
+          if (cte > INT32_MAX || cte < INT32_MIN) {
+            *result = !((constant == lhs()) ^ (cte < INT32_MIN));
+            replaced = true;
+          }
+          break;
+        case JSOp::Le:
+          if (constant == lhs()) {
+            if (cte > INT32_MAX || cte <= INT32_MIN) {
+              *result = (cte <= INT32_MIN);
+              replaced = true;
+            }
+          } else {
+            if (cte >= INT32_MAX || cte < INT32_MIN) {
+              *result = (cte >= INT32_MIN);
+              replaced = true;
+            }
+          }
+          break;
+        case JSOp::Gt:
+          if (cte > INT32_MAX || cte < INT32_MIN) {
+            *result = !((constant == rhs()) ^ (cte < INT32_MIN));
+            replaced = true;
+          }
+          break;
+        case JSOp::Ge:
+          if (constant == lhs()) {
+            if (cte >= INT32_MAX || cte < INT32_MIN) {
+              *result = (cte >= INT32_MAX);
+              replaced = true;
+            }
+          } else {
+            if (cte > INT32_MAX || cte <= INT32_MIN) {
+              *result = (cte <= INT32_MIN);
+              replaced = true;
+            }
+          }
+          break;
+        case JSOp::StrictEq:  // Fall through.
+        case JSOp::Eq:
+          if (cte > INT32_MAX || cte < INT32_MIN) {
+            *result = false;
+            replaced = true;
+          }
+          break;
+        case JSOp::StrictNe:  // Fall through.
+        case JSOp::Ne:
+          if (cte > INT32_MAX || cte < INT32_MIN) {
+            *result = true;
+            replaced = true;
+          }
+          break;
+        default:
+          MOZ_CRASH("Unexpected op.");
+      }
+      if (replaced) {
+        MLimitedTruncate* limit = MLimitedTruncate::New(
+            alloc, operand->getOperand(0), TruncateKind::NoTruncate);
+        limit->setGuardUnchecked();
+        block()->insertBefore(this, limit);
+        return true;
+      }
+    }
+  }
+
+  if (!left->isConstant() || !right->isConstant()) {
+    return false;
+  }
+
+  MConstant* lhs = left->toConstant();
+  MConstant* rhs = right->toConstant();
+
+  // Fold away some String equality comparisons.
+  if (lhs->type() == MIRType::String && rhs->type() == MIRType::String) {
+    int32_t comp = 0;  // Default to equal.
+    if (left != right) {
+      comp = CompareStrings(&lhs->toString()->asLinear(),
+                            &rhs->toString()->asLinear());
+    }
+    *result = FoldComparison(jsop_, comp, 0);
+    return true;
+  }
+
+  if (compareType_ == Compare_UInt32) {
+    *result = FoldComparison(jsop_, uint32_t(lhs->toInt32()),
+                             uint32_t(rhs->toInt32()));
+    return true;
+  }
+
+  if (compareType_ == Compare_Int64) {
+    *result = FoldComparison(jsop_, lhs->toInt64(), rhs->toInt64());
+    return true;
+  }
+
+  if (compareType_ == Compare_UInt64) {
+    *result = FoldComparison(jsop_, uint64_t(lhs->toInt64()),
+                             uint64_t(rhs->toInt64()));
+    return true;
+  }
+
+  if (lhs->isTypeRepresentableAsDouble() &&
+      rhs->isTypeRepresentableAsDouble()) {
+    *result =
+        FoldComparison(jsop_, lhs->numberToDouble(), rhs->numberToDouble());
+    return true;
+  }
+
+  return false;
+}
+
+MDefinition* MCompare::tryFoldTypeOf(TempAllocator& alloc) {
+  auto typeOfPair = IsTypeOfCompare(this);
+  if (!typeOfPair) {
+    return this;
+  }
+  auto [typeOfName, type] = *typeOfPair;
+  auto* typeOf = typeOfName->input()->toTypeOf();
+
+  auto* input = typeOf->input();
+  MOZ_ASSERT(input->type() == MIRType::Value ||
+             input->type() == MIRType::Object);
+
+  // Constant typeof folding handles the other cases.
+  MOZ_ASSERT_IF(input->type() == MIRType::Object, type == JSTYPE_UNDEFINED ||
+                                                      type == JSTYPE_OBJECT ||
+                                                      type == JSTYPE_FUNCTION);
+
+  MOZ_ASSERT(type != JSTYPE_LIMIT, "unknown typeof strings folded earlier");
+
+  // If there's only a single use, assume this |typeof| is used in a simple
+  // comparison context.
+  //
+  // if (typeof thing === "number") { ... }
+  //
+  // It'll be compiled into something similar to:
+  //
+  // if (IsNumber(thing)) { ... }
+  //
+  // This heuristic can go wrong when repeated |typeof| are used in consecutive
+  // if-statements.
+  //
+  // if (typeof thing === "number") { ... }
+  // else if (typeof thing === "string") { ... }
+  // ... repeated for all possible types
+  //
+  // In that case it'd more efficient to emit MTypeOf compared to MTypeOfIs. We
+  // don't yet handle that case, because it'd require a separate optimization
+  // pass to correctly detect it.
+  if (typeOfName->hasOneUse()) {
+    return MTypeOfIs::New(alloc, input, jsop(), type);
+  }
+
+  MConstant* cst = MConstant::New(alloc, Int32Value(type));
+  block()->insertBefore(this, cst);
+
+  return MCompare::New(alloc, typeOf, cst, jsop(), MCompare::Compare_Int32);
+}
+
+MDefinition* MCompare::tryFoldCharCompare(TempAllocator& alloc) {
+  if (compareType() != Compare_String) {
+    return this;
+  }
+
+  MDefinition* left = lhs();
+  MOZ_ASSERT(left->type() == MIRType::String);
+
+  MDefinition* right = rhs();
+  MOZ_ASSERT(right->type() == MIRType::String);
+
+  // |str[i]| is compiled as |MFromCharCode(MCharCodeAt(str, i))|.
+  auto isCharAccess = [](MDefinition* ins) {
+    return ins->isFromCharCode() &&
+           ins->toFromCharCode()->input()->isCharCodeAt();
+  };
+
+  if (left->isConstant() || right->isConstant()) {
+    // Try to optimize |MConstant(string) <compare> (MFromCharCode MCharCodeAt)|
+    // as |MConstant(charcode) <compare> MCharCodeAt|.
+    MConstant* constant;
+    MDefinition* operand;
+    if (left->isConstant()) {
+      constant = left->toConstant();
+      operand = right;
+    } else {
+      constant = right->toConstant();
+      operand = left;
+    }
+
+    if (constant->toString()->length() != 1 || !isCharAccess(operand)) {
+      return this;
+    }
+
+    char16_t charCode = constant->toString()->asLinear().latin1OrTwoByteChar(0);
+    MConstant* charCodeConst = MConstant::New(alloc, Int32Value(charCode));
+    block()->insertBefore(this, charCodeConst);
+
+    MDefinition* charCodeAt = operand->toFromCharCode()->input();
+
+    if (left->isConstant()) {
+      left = charCodeConst;
+      right = charCodeAt;
+    } else {
+      left = charCodeAt;
+      right = charCodeConst;
+    }
+  } else if (isCharAccess(left) && isCharAccess(right)) {
+    // Try to optimize |(MFromCharCode MCharCodeAt) <compare> (MFromCharCode
+    // MCharCodeAt)| as |MCharCodeAt <compare> MCharCodeAt|.
+
+    left = left->toFromCharCode()->input();
+    right = right->toFromCharCode()->input();
+  } else {
+    return this;
+  }
+
+  return MCompare::New(alloc, left, right, jsop(), MCompare::Compare_Int32);
+}
+
+MDefinition* MCompare::tryFoldStringCompare(TempAllocator& alloc) {
+  if (compareType() != Compare_String) {
+    return this;
+  }
+
+  MDefinition* left = lhs();
+  MOZ_ASSERT(left->type() == MIRType::String);
+
+  MDefinition* right = rhs();
+  MOZ_ASSERT(right->type() == MIRType::String);
+
+  if (!left->isConstant() && !right->isConstant()) {
+    return this;
+  }
+
+  // Try to optimize |string <compare> MConstant("")| as |MStringLength(string)
+  // <compare> MConstant(0)|.
+
+  MConstant* constant =
+      left->isConstant() ? left->toConstant() : right->toConstant();
+  if (!constant->toString()->empty()) {
+    return this;
+  }
+
+  MDefinition* operand = left->isConstant() ? right : left;
+
+  auto* strLength = MStringLength::New(alloc, operand);
+  block()->insertBefore(this, strLength);
+
+  auto* zero = MConstant::New(alloc, Int32Value(0));
+  block()->insertBefore(this, zero);
+
+  if (left->isConstant()) {
+    left = zero;
+    right = strLength;
+  } else {
+    left = strLength;
+    right = zero;
+  }
+
+  return MCompare::New(alloc, left, right, jsop(), MCompare::Compare_Int32);
+}
+
+MDefinition* MCompare::tryFoldStringSubstring(TempAllocator& alloc) {
+  if (compareType() != Compare_String) {
+    return this;
+  }
+  if (!IsEqualityOp(jsop())) {
+    return this;
+  }
+
+  auto* left = lhs();
+  MOZ_ASSERT(left->type() == MIRType::String);
+
+  auto* right = rhs();
+  MOZ_ASSERT(right->type() == MIRType::String);
+
+  // One operand must be a constant string.
+  if (!left->isConstant() && !right->isConstant()) {
+    return this;
+  }
+
+  // The constant string must be non-empty.
+  auto* constant =
+      left->isConstant() ? left->toConstant() : right->toConstant();
+  if (constant->toString()->empty()) {
+    return this;
+  }
+
+  // The other operand must be a substring operation.
+  auto* operand = left->isConstant() ? right : left;
+  if (!operand->isSubstr()) {
+    return this;
+  }
+
+  // We want to match this pattern:
+  // Substr(string, Constant(0), Min(Constant(length), StringLength(string)))
+  auto* substr = operand->toSubstr();
+
+  auto isConstantZero = [](auto* def) {
+    return def->isConstant() && def->toConstant()->isInt32(0);
+  };
+
+  if (!isConstantZero(substr->begin())) {
+    return this;
+  }
+
+  auto* length = substr->length();
+  if (length->isBitOr()) {
+    // Unnecessary bit-ops haven't yet been removed.
+    auto* bitOr = length->toBitOr();
+    if (isConstantZero(bitOr->lhs())) {
+      length = bitOr->rhs();
+    } else if (isConstantZero(bitOr->rhs())) {
+      length = bitOr->lhs();
+    }
+  }
+  if (!length->isMinMax() || length->toMinMax()->isMax()) {
+    return this;
+  }
+
+  auto* min = length->toMinMax();
+  if (!min->lhs()->isConstant() && !min->rhs()->isConstant()) {
+    return this;
+  }
+
+  auto* minConstant = min->lhs()->isConstant() ? min->lhs()->toConstant()
+                                               : min->rhs()->toConstant();
+
+  auto* minOperand = min->lhs()->isConstant() ? min->rhs() : min->lhs();
+  if (!minOperand->isStringLength() ||
+      minOperand->toStringLength()->string() != substr->string()) {
+    return this;
+  }
+
+  static_assert(JSString::MAX_LENGTH < INT32_MAX,
+                "string length can be casted to int32_t");
+
+  // Ensure the string length matches the substring's length.
+  if (!minConstant->isInt32(int32_t(constant->toString()->length()))) {
+    return this;
+  }
+
+  // Now fold code like |str.substring(0, 2) == "aa"| to |str.startsWith("aa")|.
+
+  auto* startsWith = MStringStartsWith::New(alloc, substr->string(), constant);
+  if (jsop() == JSOp::Eq || jsop() == JSOp::StrictEq) {
+    return startsWith;
+  }
+
+  // Invert for inequality.
+  MOZ_ASSERT(jsop() == JSOp::Ne || jsop() == JSOp::StrictNe);
+
+  block()->insertBefore(this, startsWith);
+  return MNot::New(alloc, startsWith);
+}
+
+MDefinition* MCompare::tryFoldStringIndexOf(TempAllocator& alloc) {
+  if (compareType() != Compare_Int32) {
+    return this;
+  }
+  if (!IsEqualityOp(jsop())) {
+    return this;
+  }
+
+  auto* left = lhs();
+  MOZ_ASSERT(left->type() == MIRType::Int32);
+
+  auto* right = rhs();
+  MOZ_ASSERT(right->type() == MIRType::Int32);
+
+  // One operand must be a constant integer.
+  if (!left->isConstant() && !right->isConstant()) {
+    return this;
+  }
+
+  // The constant must be zero.
+  auto* constant =
+      left->isConstant() ? left->toConstant() : right->toConstant();
+  if (!constant->isInt32(0)) {
+    return this;
+  }
+
+  // The other operand must be an indexOf operation.
+  auto* operand = left->isConstant() ? right : left;
+  if (!operand->isStringIndexOf()) {
+    return this;
+  }
+
+  // Fold |str.indexOf(searchStr) == 0| to |str.startsWith(searchStr)|.
+
+  auto* indexOf = operand->toStringIndexOf();
+  auto* startsWith =
+      MStringStartsWith::New(alloc, indexOf->string(), indexOf->searchString());
+  if (jsop() == JSOp::Eq || jsop() == JSOp::StrictEq) {
+    return startsWith;
+  }
+
+  // Invert for inequality.
+  MOZ_ASSERT(jsop() == JSOp::Ne || jsop() == JSOp::StrictNe);
+
+  block()->insertBefore(this, startsWith);
+  return MNot::New(alloc, startsWith);
+}
+
+MDefinition* MCompare::foldsTo(TempAllocator& alloc) {
+  bool result;
+
+  if (tryFold(&result) || evaluateConstantOperands(alloc, &result)) {
+    if (type() == MIRType::Int32) {
+      return MConstant::New(alloc, Int32Value(result));
+    }
+
+    MOZ_ASSERT(type() == MIRType::Boolean);
+    return MConstant::New(alloc, BooleanValue(result));
+  }
+
+  if (MDefinition* folded = tryFoldTypeOf(alloc); folded != this) {
+    return folded;
+  }
+
+  if (MDefinition* folded = tryFoldCharCompare(alloc); folded != this) {
+    return folded;
+  }
+
+  if (MDefinition* folded = tryFoldStringCompare(alloc); folded != this) {
+    return folded;
+  }
+
+  if (MDefinition* folded = tryFoldStringSubstring(alloc); folded != this) {
+    return folded;
+  }
+
+  if (MDefinition* folded = tryFoldStringIndexOf(alloc); folded != this) {
+    return folded;
+  }
+
+  return this;
+}
+
+void MCompare::trySpecializeFloat32(TempAllocator& alloc) {
+  if (AllOperandsCanProduceFloat32(this) && compareType_ == Compare_Double) {
+    compareType_ = Compare_Float32;
+  } else {
+    ConvertOperandsToDouble(this, alloc);
+  }
+}
+
+MDefinition* MNot::foldsTo(TempAllocator& alloc) {
+  // Fold if the input is constant
+  if (MConstant* inputConst = input()->maybeConstantValue()) {
+    bool b;
+    if (inputConst->valueToBoolean(&b)) {
+      if (type() == MIRType::Int32 || type() == MIRType::Int64) {
+        return MConstant::New(alloc, Int32Value(!b));
+      }
+      return MConstant::New(alloc, BooleanValue(!b));
+    }
+  }
+
+  // If the operand of the Not is itself a Not, they cancel out. But we can't
+  // always convert Not(Not(x)) to x because that may loose the conversion to
+  // boolean. We can simplify Not(Not(Not(x))) to Not(x) though.
+  MDefinition* op = getOperand(0);
+  if (op->isNot()) {
+    MDefinition* opop = op->getOperand(0);
+    if (opop->isNot()) {
+      return opop;
+    }
+  }
+
+  // Not of an undefined or null value is always true
+  if (input()->type() == MIRType::Undefined ||
+      input()->type() == MIRType::Null) {
+    return MConstant::New(alloc, BooleanValue(true));
+  }
+
+  // Not of a symbol is always false.
+  if (input()->type() == MIRType::Symbol) {
+    return MConstant::New(alloc, BooleanValue(false));
+  }
+
+  return this;
+}
+
+void MNot::trySpecializeFloat32(TempAllocator& alloc) {
+  (void)EnsureFloatInputOrConvert(this, alloc);
+}
+
+#ifdef JS_JITSPEW
+void MBeta::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+
+  out.printf(" ");
+  comparison_->dump(out);
+}
+#endif
+
+AliasSet MCreateThis::getAliasSet() const {
+  return AliasSet::Load(AliasSet::Any);
+}
+
+bool MGetArgumentsObjectArg::congruentTo(const MDefinition* ins) const {
+  if (!ins->isGetArgumentsObjectArg()) {
+    return false;
+  }
+  if (ins->toGetArgumentsObjectArg()->argno() != argno()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MGetArgumentsObjectArg::getAliasSet() const {
+  return AliasSet::Load(AliasSet::Any);
+}
+
+AliasSet MSetArgumentsObjectArg::getAliasSet() const {
+  return AliasSet::Store(AliasSet::Any);
+}
+
+MObjectState::MObjectState(MObjectState* state)
+    : MVariadicInstruction(classOpcode),
+      numSlots_(state->numSlots_),
+      numFixedSlots_(state->numFixedSlots_) {
+  // This instruction is only used as a summary for bailout paths.
+  setResultType(MIRType::Object);
+  setRecoveredOnBailout();
+}
+
+MObjectState::MObjectState(JSObject* templateObject)
+    : MObjectState(templateObject->as<NativeObject>().shape()) {}
+
+MObjectState::MObjectState(const Shape* shape)
+    : MVariadicInstruction(classOpcode) {
+  // This instruction is only used as a summary for bailout paths.
+  setResultType(MIRType::Object);
+  setRecoveredOnBailout();
+
+  numSlots_ = shape->asShared().slotSpan();
+  numFixedSlots_ = shape->asShared().numFixedSlots();
+}
+
+/* static */
+JSObject* MObjectState::templateObjectOf(MDefinition* obj) {
+  // MNewPlainObject uses a shape constant, not an object.
+  MOZ_ASSERT(!obj->isNewPlainObject());
+
+  if (obj->isNewObject()) {
+    return obj->toNewObject()->templateObject();
+  } else if (obj->isNewCallObject()) {
+    return obj->toNewCallObject()->templateObject();
+  } else if (obj->isNewIterator()) {
+    return obj->toNewIterator()->templateObject();
+  }
+
+  MOZ_CRASH("unreachable");
+}
+
+bool MObjectState::init(TempAllocator& alloc, MDefinition* obj) {
+  if (!MVariadicInstruction::init(alloc, numSlots() + 1)) {
+    return false;
+  }
+  // +1, for the Object.
+  initOperand(0, obj);
+  return true;
+}
+
+void MObjectState::initFromTemplateObject(TempAllocator& alloc,
+                                          MDefinition* undefinedVal) {
+  if (object()->isNewPlainObject()) {
+    MOZ_ASSERT(object()->toNewPlainObject()->shape()->asShared().slotSpan() ==
+               numSlots());
+    for (size_t i = 0; i < numSlots(); i++) {
+      initSlot(i, undefinedVal);
+    }
+    return;
+  }
+
+  JSObject* templateObject = templateObjectOf(object());
+
+  // Initialize all the slots of the object state with the value contained in
+  // the template object. This is needed to account values which are baked in
+  // the template objects and not visible in IonMonkey, such as the
+  // uninitialized-lexical magic value of call objects.
+
+  MOZ_ASSERT(templateObject->is<NativeObject>());
+  NativeObject& nativeObject = templateObject->as<NativeObject>();
+  MOZ_ASSERT(nativeObject.slotSpan() == numSlots());
+
+  for (size_t i = 0; i < numSlots(); i++) {
+    Value val = nativeObject.getSlot(i);
+    MDefinition* def = undefinedVal;
+    if (!val.isUndefined()) {
+      MConstant* ins = MConstant::New(alloc, val);
+      block()->insertBefore(this, ins);
+      def = ins;
+    }
+    initSlot(i, def);
+  }
+}
+
+MObjectState* MObjectState::New(TempAllocator& alloc, MDefinition* obj) {
+  MObjectState* res;
+  if (obj->isNewPlainObject()) {
+    const Shape* shape = obj->toNewPlainObject()->shape();
+    res = new (alloc) MObjectState(shape);
+  } else {
+    JSObject* templateObject = templateObjectOf(obj);
+    MOZ_ASSERT(templateObject, "Unexpected object creation.");
+    res = new (alloc) MObjectState(templateObject);
+  }
+
+  if (!res || !res->init(alloc, obj)) {
+    return nullptr;
+  }
+  return res;
+}
+
+MObjectState* MObjectState::Copy(TempAllocator& alloc, MObjectState* state) {
+  MObjectState* res = new (alloc) MObjectState(state);
+  if (!res || !res->init(alloc, state->object())) {
+    return nullptr;
+  }
+  for (size_t i = 0; i < res->numSlots(); i++) {
+    res->initSlot(i, state->getSlot(i));
+  }
+  return res;
+}
+
+MArrayState::MArrayState(MDefinition* arr) : MVariadicInstruction(classOpcode) {
+  // This instruction is only used as a summary for bailout paths.
+  setResultType(MIRType::Object);
+  setRecoveredOnBailout();
+  if (arr->isNewArrayObject()) {
+    numElements_ = arr->toNewArrayObject()->length();
+  } else {
+    numElements_ = arr->toNewArray()->length();
+  }
+}
+
+bool MArrayState::init(TempAllocator& alloc, MDefinition* obj,
+                       MDefinition* len) {
+  if (!MVariadicInstruction::init(alloc, numElements() + 2)) {
+    return false;
+  }
+  // +1, for the Array object.
+  initOperand(0, obj);
+  // +1, for the length value of the array.
+  initOperand(1, len);
+  return true;
+}
+
+void MArrayState::initFromTemplateObject(TempAllocator& alloc,
+                                         MDefinition* undefinedVal) {
+  for (size_t i = 0; i < numElements(); i++) {
+    initElement(i, undefinedVal);
+  }
+}
+
+MArrayState* MArrayState::New(TempAllocator& alloc, MDefinition* arr,
+                              MDefinition* initLength) {
+  MArrayState* res = new (alloc) MArrayState(arr);
+  if (!res || !res->init(alloc, arr, initLength)) {
+    return nullptr;
+  }
+  return res;
+}
+
+MArrayState* MArrayState::Copy(TempAllocator& alloc, MArrayState* state) {
+  MDefinition* arr = state->array();
+  MDefinition* len = state->initializedLength();
+  MArrayState* res = new (alloc) MArrayState(arr);
+  if (!res || !res->init(alloc, arr, len)) {
+    return nullptr;
+  }
+  for (size_t i = 0; i < res->numElements(); i++) {
+    res->initElement(i, state->getElement(i));
+  }
+  return res;
+}
+
+MNewArray::MNewArray(uint32_t length, MConstant* templateConst,
+                     gc::InitialHeap initialHeap, bool vmCall)
+    : MUnaryInstruction(classOpcode, templateConst),
+      length_(length),
+      initialHeap_(initialHeap),
+      vmCall_(vmCall) {
+  setResultType(MIRType::Object);
+}
+
+MDefinition::AliasType MLoadFixedSlot::mightAlias(
+    const MDefinition* def) const {
+  if (def->isStoreFixedSlot()) {
+    const MStoreFixedSlot* store = def->toStoreFixedSlot();
+    if (store->slot() != slot()) {
+      return AliasType::NoAlias;
+    }
+    if (store->object() != object()) {
+      return AliasType::MayAlias;
+    }
+    return AliasType::MustAlias;
+  }
+  return AliasType::MayAlias;
+}
+
+MDefinition* MLoadFixedSlot::foldsTo(TempAllocator& alloc) {
+  if (MDefinition* def = foldsToStore(alloc)) {
+    return def;
+  }
+
+  return this;
+}
+
+MDefinition::AliasType MLoadFixedSlotAndUnbox::mightAlias(
+    const MDefinition* def) const {
+  if (def->isStoreFixedSlot()) {
+    const MStoreFixedSlot* store = def->toStoreFixedSlot();
+    if (store->slot() != slot()) {
+      return AliasType::NoAlias;
+    }
+    if (store->object() != object()) {
+      return AliasType::MayAlias;
+    }
+    return AliasType::MustAlias;
+  }
+  return AliasType::MayAlias;
+}
+
+MDefinition* MLoadFixedSlotAndUnbox::foldsTo(TempAllocator& alloc) {
+  if (MDefinition* def = foldsToStore(alloc)) {
+    return def;
+  }
+
+  return this;
+}
+
+MDefinition* MWasmExtendU32Index::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = this->input();
+  if (input->isConstant()) {
+    return MConstant::NewInt64(
+        alloc, int64_t(uint32_t(input->toConstant()->toInt32())));
+  }
+
+  return this;
+}
+
+MDefinition* MWasmWrapU32Index::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = this->input();
+  if (input->isConstant()) {
+    return MConstant::New(
+        alloc, Int32Value(int32_t(uint32_t(input->toConstant()->toInt64()))));
+  }
+
+  return this;
+}
+
+// Some helpers for folding wasm and/or/xor on int32/64 values.  Rather than
+// duplicating these for 32 and 64-bit values, all folding is done on 64-bit
+// values and masked for the 32-bit case.
+
+const uint64_t Low32Mask = uint64_t(0xFFFFFFFFULL);
+
+// Routines to check and disassemble values.
+
+static bool IsIntegralConstant(const MDefinition* def) {
+  return def->isConstant() &&
+         (def->type() == MIRType::Int32 || def->type() == MIRType::Int64);
+}
+
+static uint64_t GetIntegralConstant(const MDefinition* def) {
+  if (def->type() == MIRType::Int32) {
+    return uint64_t(def->toConstant()->toInt32()) & Low32Mask;
+  }
+  return uint64_t(def->toConstant()->toInt64());
+}
+
+static bool IsIntegralConstantZero(const MDefinition* def) {
+  return IsIntegralConstant(def) && GetIntegralConstant(def) == 0;
+}
+
+static bool IsIntegralConstantOnes(const MDefinition* def) {
+  uint64_t ones = def->type() == MIRType::Int32 ? Low32Mask : ~uint64_t(0);
+  return IsIntegralConstant(def) && GetIntegralConstant(def) == ones;
+}
+
+// Routines to create values.
+static MDefinition* ToIntegralConstant(TempAllocator& alloc, MIRType ty,
+                                       uint64_t val) {
+  switch (ty) {
+    case MIRType::Int32:
+      return MConstant::New(alloc,
+                            Int32Value(int32_t(uint32_t(val & Low32Mask))));
+    case MIRType::Int64:
+      return MConstant::NewInt64(alloc, int64_t(val));
+    default:
+      MOZ_CRASH();
+  }
+}
+
+static MDefinition* ZeroOfType(TempAllocator& alloc, MIRType ty) {
+  return ToIntegralConstant(alloc, ty, 0);
+}
+
+static MDefinition* OnesOfType(TempAllocator& alloc, MIRType ty) {
+  return ToIntegralConstant(alloc, ty, ~uint64_t(0));
+}
+
+MDefinition* MWasmBinaryBitwise::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(op() == Opcode::WasmBinaryBitwise);
+  MOZ_ASSERT(type() == MIRType::Int32 || type() == MIRType::Int64);
+
+  MDefinition* argL = getOperand(0);
+  MDefinition* argR = getOperand(1);
+  MOZ_ASSERT(argL->type() == type() && argR->type() == type());
+
+  // The args are the same (SSA name)
+  if (argL == argR) {
+    switch (subOpcode()) {
+      case SubOpcode::And:
+      case SubOpcode::Or:
+        return argL;
+      case SubOpcode::Xor:
+        return ZeroOfType(alloc, type());
+      default:
+        MOZ_CRASH();
+    }
+  }
+
+  // Both args constant
+  if (IsIntegralConstant(argL) && IsIntegralConstant(argR)) {
+    uint64_t valL = GetIntegralConstant(argL);
+    uint64_t valR = GetIntegralConstant(argR);
+    uint64_t val = valL;
+    switch (subOpcode()) {
+      case SubOpcode::And:
+        val &= valR;
+        break;
+      case SubOpcode::Or:
+        val |= valR;
+        break;
+      case SubOpcode::Xor:
+        val ^= valR;
+        break;
+      default:
+        MOZ_CRASH();
+    }
+    return ToIntegralConstant(alloc, type(), val);
+  }
+
+  // Left arg is zero
+  if (IsIntegralConstantZero(argL)) {
+    switch (subOpcode()) {
+      case SubOpcode::And:
+        return ZeroOfType(alloc, type());
+      case SubOpcode::Or:
+      case SubOpcode::Xor:
+        return argR;
+      default:
+        MOZ_CRASH();
+    }
+  }
+
+  // Right arg is zero
+  if (IsIntegralConstantZero(argR)) {
+    switch (subOpcode()) {
+      case SubOpcode::And:
+        return ZeroOfType(alloc, type());
+      case SubOpcode::Or:
+      case SubOpcode::Xor:
+        return argL;
+      default:
+        MOZ_CRASH();
+    }
+  }
+
+  // Left arg is ones
+  if (IsIntegralConstantOnes(argL)) {
+    switch (subOpcode()) {
+      case SubOpcode::And:
+        return argR;
+      case SubOpcode::Or:
+        return OnesOfType(alloc, type());
+      case SubOpcode::Xor:
+        return MBitNot::New(alloc, argR);
+      default:
+        MOZ_CRASH();
+    }
+  }
+
+  // Right arg is ones
+  if (IsIntegralConstantOnes(argR)) {
+    switch (subOpcode()) {
+      case SubOpcode::And:
+        return argL;
+      case SubOpcode::Or:
+        return OnesOfType(alloc, type());
+      case SubOpcode::Xor:
+        return MBitNot::New(alloc, argL);
+      default:
+        MOZ_CRASH();
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MWasmAddOffset::foldsTo(TempAllocator& alloc) {
+  MDefinition* baseArg = base();
+  if (!baseArg->isConstant()) {
+    return this;
+  }
+
+  if (baseArg->type() == MIRType::Int32) {
+    CheckedInt<uint32_t> ptr = baseArg->toConstant()->toInt32();
+    ptr += offset();
+    if (!ptr.isValid()) {
+      return this;
+    }
+    return MConstant::New(alloc, Int32Value(ptr.value()));
+  }
+
+  MOZ_ASSERT(baseArg->type() == MIRType::Int64);
+  CheckedInt<uint64_t> ptr = baseArg->toConstant()->toInt64();
+  ptr += offset();
+  if (!ptr.isValid()) {
+    return this;
+  }
+  return MConstant::NewInt64(alloc, ptr.value());
+}
+
+bool MWasmAlignmentCheck::congruentTo(const MDefinition* ins) const {
+  if (!ins->isWasmAlignmentCheck()) {
+    return false;
+  }
+  const MWasmAlignmentCheck* check = ins->toWasmAlignmentCheck();
+  return byteSize_ == check->byteSize() && congruentIfOperandsEqual(check);
+}
+
+MDefinition::AliasType MAsmJSLoadHeap::mightAlias(
+    const MDefinition* def) const {
+  if (def->isAsmJSStoreHeap()) {
+    const MAsmJSStoreHeap* store = def->toAsmJSStoreHeap();
+    if (store->accessType() != accessType()) {
+      return AliasType::MayAlias;
+    }
+    if (!base()->isConstant() || !store->base()->isConstant()) {
+      return AliasType::MayAlias;
+    }
+    const MConstant* otherBase = store->base()->toConstant();
+    if (base()->toConstant()->equals(otherBase)) {
+      return AliasType::MayAlias;
+    }
+    return AliasType::NoAlias;
+  }
+  return AliasType::MayAlias;
+}
+
+bool MAsmJSLoadHeap::congruentTo(const MDefinition* ins) const {
+  if (!ins->isAsmJSLoadHeap()) {
+    return false;
+  }
+  const MAsmJSLoadHeap* load = ins->toAsmJSLoadHeap();
+  return load->accessType() == accessType() && congruentIfOperandsEqual(load);
+}
+
+MDefinition::AliasType MWasmLoadGlobalVar::mightAlias(
+    const MDefinition* def) const {
+  if (def->isWasmStoreGlobalVar()) {
+    const MWasmStoreGlobalVar* store = def->toWasmStoreGlobalVar();
+    return store->globalDataOffset() == globalDataOffset_ ? AliasType::MayAlias
+                                                          : AliasType::NoAlias;
+  }
+
+  return AliasType::MayAlias;
+}
+
+MDefinition::AliasType MWasmLoadGlobalCell::mightAlias(
+    const MDefinition* def) const {
+  if (def->isWasmStoreGlobalCell()) {
+    // No globals of different type can alias.  See bug 1467415 comment 3.
+    if (type() != def->toWasmStoreGlobalCell()->value()->type()) {
+      return AliasType::NoAlias;
+    }
+
+    // We could do better here.  We're dealing with two indirect globals.
+    // If at at least one of them is created in this module, then they
+    // can't alias -- in other words they can only alias if they are both
+    // imported.  That would require having a flag on globals to indicate
+    // which are imported.  See bug 1467415 comment 3, 4th rule.
+  }
+
+  return AliasType::MayAlias;
+}
+
+HashNumber MWasmLoadGlobalVar::valueHash() const {
+  // Same comment as in MWasmLoadGlobalVar::congruentTo() applies here.
+  HashNumber hash = MDefinition::valueHash();
+  hash = addU32ToHash(hash, globalDataOffset_);
+  return hash;
+}
+
+bool MWasmLoadGlobalVar::congruentTo(const MDefinition* ins) const {
+  if (!ins->isWasmLoadGlobalVar()) {
+    return false;
+  }
+
+  const MWasmLoadGlobalVar* other = ins->toWasmLoadGlobalVar();
+
+  // We don't need to consider the isConstant_ markings here, because
+  // equivalence of offsets implies equivalence of constness.
+  bool sameOffsets = globalDataOffset_ == other->globalDataOffset_;
+  MOZ_ASSERT_IF(sameOffsets, isConstant_ == other->isConstant_);
+
+  // We omit checking congruence of the operands.  There is only one
+  // operand, the instance pointer, and it only ever has one value within the
+  // domain of optimization.  If that should ever change then operand
+  // congruence checking should be reinstated.
+  return sameOffsets /* && congruentIfOperandsEqual(other) */;
+}
+
+MDefinition* MWasmLoadGlobalVar::foldsTo(TempAllocator& alloc) {
+  if (!dependency() || !dependency()->isWasmStoreGlobalVar()) {
+    return this;
+  }
+
+  MWasmStoreGlobalVar* store = dependency()->toWasmStoreGlobalVar();
+  if (!store->block()->dominates(block())) {
+    return this;
+  }
+
+  if (store->globalDataOffset() != globalDataOffset()) {
+    return this;
+  }
+
+  if (store->value()->type() != type()) {
+    return this;
+  }
+
+  return store->value();
+}
+
+bool MWasmLoadGlobalCell::congruentTo(const MDefinition* ins) const {
+  if (!ins->isWasmLoadGlobalCell()) {
+    return false;
+  }
+  const MWasmLoadGlobalCell* other = ins->toWasmLoadGlobalCell();
+  return congruentIfOperandsEqual(other);
+}
+
+#ifdef ENABLE_WASM_SIMD
+MDefinition* MWasmTernarySimd128::foldsTo(TempAllocator& alloc) {
+  if (simdOp() == wasm::SimdOp::V128Bitselect) {
+    if (v2()->op() == MDefinition::Opcode::WasmFloatConstant) {
+      int8_t shuffle[16];
+      if (specializeBitselectConstantMaskAsShuffle(shuffle)) {
+        return BuildWasmShuffleSimd128(alloc, shuffle, v0(), v1());
+      }
+    } else if (canRelaxBitselect()) {
+      return MWasmTernarySimd128::New(alloc, v0(), v1(), v2(),
+                                      wasm::SimdOp::I8x16RelaxedLaneSelect);
+    }
+  }
+  return this;
+}
+
+inline static bool MatchSpecificShift(MDefinition* instr,
+                                      wasm::SimdOp simdShiftOp,
+                                      int shiftValue) {
+  return instr->isWasmShiftSimd128() &&
+         instr->toWasmShiftSimd128()->simdOp() == simdShiftOp &&
+         instr->toWasmShiftSimd128()->rhs()->isConstant() &&
+         instr->toWasmShiftSimd128()->rhs()->toConstant()->toInt32() ==
+             shiftValue;
+}
+
+// Matches MIR subtree that represents PMADDUBSW instruction generated by
+// emscripten. The a and b parameters return subtrees that correspond
+// operands of the instruction, if match is found.
+static bool MatchPmaddubswSequence(MWasmBinarySimd128* lhs,
+                                   MWasmBinarySimd128* rhs, MDefinition** a,
+                                   MDefinition** b) {
+  MOZ_ASSERT(lhs->simdOp() == wasm::SimdOp::I16x8Mul &&
+             rhs->simdOp() == wasm::SimdOp::I16x8Mul);
+  // The emscripten/LLVM produced the following sequence for _mm_maddubs_epi16:
+  //
+  //  return _mm_adds_epi16(
+  //    _mm_mullo_epi16(
+  //      _mm_and_si128(__a, _mm_set1_epi16(0x00FF)),
+  //      _mm_srai_epi16(_mm_slli_epi16(__b, 8), 8)),
+  //    _mm_mullo_epi16(_mm_srli_epi16(__a, 8), _mm_srai_epi16(__b, 8)));
+  //
+  //  This will roughly correspond the following MIR:
+  //    MWasmBinarySimd128[I16x8AddSatS]
+  //      |-- lhs: MWasmBinarySimd128[I16x8Mul]                      (lhs)
+  //      |     |-- lhs: MWasmBinarySimd128WithConstant[V128And]     (op0)
+  //      |     |     |-- lhs: a
+  //      |     |      -- rhs: SimdConstant::SplatX8(0x00FF)
+  //      |      -- rhs: MWasmShiftSimd128[I16x8ShrS]                (op1)
+  //      |           |-- lhs: MWasmShiftSimd128[I16x8Shl]
+  //      |           |     |-- lhs: b
+  //      |           |      -- rhs: MConstant[8]
+  //      |            -- rhs: MConstant[8]
+  //       -- rhs: MWasmBinarySimd128[I16x8Mul]                      (rhs)
+  //            |-- lhs: MWasmShiftSimd128[I16x8ShrU]                (op2)
+  //            |     |-- lhs: a
+  //            |     |-- rhs: MConstant[8]
+  //             -- rhs: MWasmShiftSimd128[I16x8ShrS]                (op3)
+  //                  |-- lhs: b
+  //                   -- rhs: MConstant[8]
+
+  // The I16x8AddSatS and I16x8Mul are commutative, so their operands
+  // may be swapped. Rearrange op0, op1, op2, op3 to be in the order
+  // noted above.
+  MDefinition *op0 = lhs->lhs(), *op1 = lhs->rhs(), *op2 = rhs->lhs(),
+              *op3 = rhs->rhs();
+  if (op1->isWasmBinarySimd128WithConstant()) {
+    // Move MWasmBinarySimd128WithConstant[V128And] as first operand in lhs.
+    std::swap(op0, op1);
+  } else if (op3->isWasmBinarySimd128WithConstant()) {
+    // Move MWasmBinarySimd128WithConstant[V128And] as first operand in rhs.
+    std::swap(op2, op3);
+  }
+  if (op2->isWasmBinarySimd128WithConstant()) {
+    // The lhs and rhs are swapped.
+    // Make MWasmBinarySimd128WithConstant[V128And] to be op0.
+    std::swap(op0, op2);
+    std::swap(op1, op3);
+  }
+  if (op2->isWasmShiftSimd128() &&
+      op2->toWasmShiftSimd128()->simdOp() == wasm::SimdOp::I16x8ShrS) {
+    // The op2 and op3 appears to be in wrong order, swap.
+    std::swap(op2, op3);
+  }
+
+  // Check all instructions SIMD code and constant values for assigned
+  // names op0, op1, op2, op3 (see diagram above).
+  const uint16_t const00FF[8] = {255, 255, 255, 255, 255, 255, 255, 255};
+  if (!op0->isWasmBinarySimd128WithConstant() ||
+      op0->toWasmBinarySimd128WithConstant()->simdOp() !=
+          wasm::SimdOp::V128And ||
+      memcmp(op0->toWasmBinarySimd128WithConstant()->rhs().bytes(), const00FF,
+             16) != 0 ||
+      !MatchSpecificShift(op1, wasm::SimdOp::I16x8ShrS, 8) ||
+      !MatchSpecificShift(op2, wasm::SimdOp::I16x8ShrU, 8) ||
+      !MatchSpecificShift(op3, wasm::SimdOp::I16x8ShrS, 8) ||
+      !MatchSpecificShift(op1->toWasmShiftSimd128()->lhs(),
+                          wasm::SimdOp::I16x8Shl, 8)) {
+    return false;
+  }
+
+  // Check if the instructions arguments that are subtrees match the
+  // a and b assignments. May depend on GVN behavior.
+  MDefinition* maybeA = op0->toWasmBinarySimd128WithConstant()->lhs();
+  MDefinition* maybeB = op3->toWasmShiftSimd128()->lhs();
+  if (maybeA != op2->toWasmShiftSimd128()->lhs() ||
+      maybeB != op1->toWasmShiftSimd128()->lhs()->toWasmShiftSimd128()->lhs()) {
+    return false;
+  }
+
+  *a = maybeA;
+  *b = maybeB;
+  return true;
+}
+
+MDefinition* MWasmBinarySimd128::foldsTo(TempAllocator& alloc) {
+  if (simdOp() == wasm::SimdOp::I8x16Swizzle && rhs()->isWasmFloatConstant()) {
+    // Specialize swizzle(v, constant) as shuffle(mask, v, zero) to trigger all
+    // our shuffle optimizations.  We don't report this rewriting as the report
+    // will be overwritten by the subsequent shuffle analysis.
+    int8_t shuffleMask[16];
+    memcpy(shuffleMask, rhs()->toWasmFloatConstant()->toSimd128().bytes(), 16);
+    for (int i = 0; i < 16; i++) {
+      // Out-of-bounds lanes reference the zero vector; in many cases, the zero
+      // vector is removed by subsequent optimizations.
+      if (shuffleMask[i] < 0 || shuffleMask[i] > 15) {
+        shuffleMask[i] = 16;
+      }
+    }
+    MWasmFloatConstant* zero =
+        MWasmFloatConstant::NewSimd128(alloc, SimdConstant::SplatX4(0));
+    if (!zero) {
+      return nullptr;
+    }
+    block()->insertBefore(this, zero);
+    return BuildWasmShuffleSimd128(alloc, shuffleMask, lhs(), zero);
+  }
+
+  // Specialize var OP const / const OP var when possible.
+  //
+  // As the LIR layer can't directly handle v128 constants as part of its normal
+  // machinery we specialize some nodes here if they have single-use v128
+  // constant arguments.  The purpose is to generate code that inlines the
+  // constant in the instruction stream, using either a rip-relative load+op or
+  // quickly-synthesized constant in a scratch on x64.  There is a general
+  // assumption here that that is better than generating the constant into an
+  // allocatable register, since that register value could not be reused. (This
+  // ignores the possibility that the constant load could be hoisted).
+
+  if (lhs()->isWasmFloatConstant() != rhs()->isWasmFloatConstant() &&
+      specializeForConstantRhs()) {
+    if (isCommutative() && lhs()->isWasmFloatConstant() && lhs()->hasOneUse()) {
+      return MWasmBinarySimd128WithConstant::New(
+          alloc, rhs(), lhs()->toWasmFloatConstant()->toSimd128(), simdOp());
+    }
+
+    if (rhs()->isWasmFloatConstant() && rhs()->hasOneUse()) {
+      return MWasmBinarySimd128WithConstant::New(
+          alloc, lhs(), rhs()->toWasmFloatConstant()->toSimd128(), simdOp());
+    }
+  }
+
+  // Check special encoding for PMADDUBSW.
+  if (canPmaddubsw() && simdOp() == wasm::SimdOp::I16x8AddSatS &&
+      lhs()->isWasmBinarySimd128() && rhs()->isWasmBinarySimd128() &&
+      lhs()->toWasmBinarySimd128()->simdOp() == wasm::SimdOp::I16x8Mul &&
+      rhs()->toWasmBinarySimd128()->simdOp() == wasm::SimdOp::I16x8Mul) {
+    MDefinition *a, *b;
+    if (MatchPmaddubswSequence(lhs()->toWasmBinarySimd128(),
+                               rhs()->toWasmBinarySimd128(), &a, &b)) {
+      return MWasmBinarySimd128::New(alloc, a, b, /* commutative = */ false,
+                                     wasm::SimdOp::MozPMADDUBSW);
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MWasmScalarToSimd128::foldsTo(TempAllocator& alloc) {
+#  ifdef DEBUG
+  auto logging = mozilla::MakeScopeExit([&] {
+    js::wasm::ReportSimdAnalysis("scalar-to-simd128 -> constant folded");
+  });
+#  endif
+  if (input()->isConstant()) {
+    MConstant* c = input()->toConstant();
+    switch (simdOp()) {
+      case wasm::SimdOp::I8x16Splat:
+        return MWasmFloatConstant::NewSimd128(
+            alloc, SimdConstant::SplatX16(c->toInt32()));
+      case wasm::SimdOp::I16x8Splat:
+        return MWasmFloatConstant::NewSimd128(
+            alloc, SimdConstant::SplatX8(c->toInt32()));
+      case wasm::SimdOp::I32x4Splat:
+        return MWasmFloatConstant::NewSimd128(
+            alloc, SimdConstant::SplatX4(c->toInt32()));
+      case wasm::SimdOp::I64x2Splat:
+        return MWasmFloatConstant::NewSimd128(
+            alloc, SimdConstant::SplatX2(c->toInt64()));
+      default:
+#  ifdef DEBUG
+        logging.release();
+#  endif
+        return this;
+    }
+  }
+  if (input()->isWasmFloatConstant()) {
+    MWasmFloatConstant* c = input()->toWasmFloatConstant();
+    switch (simdOp()) {
+      case wasm::SimdOp::F32x4Splat:
+        return MWasmFloatConstant::NewSimd128(
+            alloc, SimdConstant::SplatX4(c->toFloat32()));
+      case wasm::SimdOp::F64x2Splat:
+        return MWasmFloatConstant::NewSimd128(
+            alloc, SimdConstant::SplatX2(c->toDouble()));
+      default:
+#  ifdef DEBUG
+        logging.release();
+#  endif
+        return this;
+    }
+  }
+#  ifdef DEBUG
+  logging.release();
+#  endif
+  return this;
+}
+
+template <typename T>
+static bool AllTrue(const T& v) {
+  constexpr size_t count = sizeof(T) / sizeof(*v);
+  static_assert(count == 16 || count == 8 || count == 4 || count == 2);
+  bool result = true;
+  for (unsigned i = 0; i < count; i++) {
+    result = result && v[i] != 0;
+  }
+  return result;
+}
+
+template <typename T>
+static int32_t Bitmask(const T& v) {
+  constexpr size_t count = sizeof(T) / sizeof(*v);
+  constexpr size_t shift = 8 * sizeof(*v) - 1;
+  static_assert(shift == 7 || shift == 15 || shift == 31 || shift == 63);
+  int32_t result = 0;
+  for (unsigned i = 0; i < count; i++) {
+    result = result | int32_t(((v[i] >> shift) & 1) << i);
+  }
+  return result;
+}
+
+MDefinition* MWasmReduceSimd128::foldsTo(TempAllocator& alloc) {
+#  ifdef DEBUG
+  auto logging = mozilla::MakeScopeExit([&] {
+    js::wasm::ReportSimdAnalysis("simd128-to-scalar -> constant folded");
+  });
+#  endif
+  if (input()->isWasmFloatConstant()) {
+    SimdConstant c = input()->toWasmFloatConstant()->toSimd128();
+    int32_t i32Result = 0;
+    switch (simdOp()) {
+      case wasm::SimdOp::V128AnyTrue:
+        i32Result = !c.isZeroBits();
+        break;
+      case wasm::SimdOp::I8x16AllTrue:
+        i32Result = AllTrue(
+            SimdConstant::CreateSimd128((int8_t*)c.bytes()).asInt8x16());
+        break;
+      case wasm::SimdOp::I8x16Bitmask:
+        i32Result = Bitmask(
+            SimdConstant::CreateSimd128((int8_t*)c.bytes()).asInt8x16());
+        break;
+      case wasm::SimdOp::I16x8AllTrue:
+        i32Result = AllTrue(
+            SimdConstant::CreateSimd128((int16_t*)c.bytes()).asInt16x8());
+        break;
+      case wasm::SimdOp::I16x8Bitmask:
+        i32Result = Bitmask(
+            SimdConstant::CreateSimd128((int16_t*)c.bytes()).asInt16x8());
+        break;
+      case wasm::SimdOp::I32x4AllTrue:
+        i32Result = AllTrue(
+            SimdConstant::CreateSimd128((int32_t*)c.bytes()).asInt32x4());
+        break;
+      case wasm::SimdOp::I32x4Bitmask:
+        i32Result = Bitmask(
+            SimdConstant::CreateSimd128((int32_t*)c.bytes()).asInt32x4());
+        break;
+      case wasm::SimdOp::I64x2AllTrue:
+        i32Result = AllTrue(
+            SimdConstant::CreateSimd128((int64_t*)c.bytes()).asInt64x2());
+        break;
+      case wasm::SimdOp::I64x2Bitmask:
+        i32Result = Bitmask(
+            SimdConstant::CreateSimd128((int64_t*)c.bytes()).asInt64x2());
+        break;
+      case wasm::SimdOp::I8x16ExtractLaneS:
+        i32Result =
+            SimdConstant::CreateSimd128((int8_t*)c.bytes()).asInt8x16()[imm()];
+        break;
+      case wasm::SimdOp::I8x16ExtractLaneU:
+        i32Result = int32_t(SimdConstant::CreateSimd128((int8_t*)c.bytes())
+                                .asInt8x16()[imm()]) &
+                    0xFF;
+        break;
+      case wasm::SimdOp::I16x8ExtractLaneS:
+        i32Result =
+            SimdConstant::CreateSimd128((int16_t*)c.bytes()).asInt16x8()[imm()];
+        break;
+      case wasm::SimdOp::I16x8ExtractLaneU:
+        i32Result = int32_t(SimdConstant::CreateSimd128((int16_t*)c.bytes())
+                                .asInt16x8()[imm()]) &
+                    0xFFFF;
+        break;
+      case wasm::SimdOp::I32x4ExtractLane:
+        i32Result =
+            SimdConstant::CreateSimd128((int32_t*)c.bytes()).asInt32x4()[imm()];
+        break;
+      case wasm::SimdOp::I64x2ExtractLane:
+        return MConstant::NewInt64(
+            alloc, SimdConstant::CreateSimd128((int64_t*)c.bytes())
+                       .asInt64x2()[imm()]);
+      case wasm::SimdOp::F32x4ExtractLane:
+        return MWasmFloatConstant::NewFloat32(
+            alloc, SimdConstant::CreateSimd128((float*)c.bytes())
+                       .asFloat32x4()[imm()]);
+      case wasm::SimdOp::F64x2ExtractLane:
+        return MWasmFloatConstant::NewDouble(
+            alloc, SimdConstant::CreateSimd128((double*)c.bytes())
+                       .asFloat64x2()[imm()]);
+      default:
+#  ifdef DEBUG
+        logging.release();
+#  endif
+        return this;
+    }
+    return MConstant::New(alloc, Int32Value(i32Result), MIRType::Int32);
+  }
+#  ifdef DEBUG
+  logging.release();
+#  endif
+  return this;
+}
+#endif  // ENABLE_WASM_SIMD
+
+MDefinition::AliasType MLoadDynamicSlot::mightAlias(
+    const MDefinition* def) const {
+  if (def->isStoreDynamicSlot()) {
+    const MStoreDynamicSlot* store = def->toStoreDynamicSlot();
+    if (store->slot() != slot()) {
+      return AliasType::NoAlias;
+    }
+
+    if (store->slots() != slots()) {
+      return AliasType::MayAlias;
+    }
+
+    return AliasType::MustAlias;
+  }
+  return AliasType::MayAlias;
+}
+
+HashNumber MLoadDynamicSlot::valueHash() const {
+  HashNumber hash = MDefinition::valueHash();
+  hash = addU32ToHash(hash, slot_);
+  return hash;
+}
+
+MDefinition* MLoadDynamicSlot::foldsTo(TempAllocator& alloc) {
+  if (MDefinition* def = foldsToStore(alloc)) {
+    return def;
+  }
+
+  return this;
+}
+
+#ifdef JS_JITSPEW
+void MLoadDynamicSlot::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" (slot %u)", slot());
+}
+
+void MLoadDynamicSlotAndUnbox::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" (slot %zu)", slot());
+}
+
+void MStoreDynamicSlot::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" (slot %u)", slot());
+}
+
+void MLoadFixedSlot::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" (slot %zu)", slot());
+}
+
+void MLoadFixedSlotAndUnbox::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" (slot %zu)", slot());
+}
+
+void MStoreFixedSlot::printOpcode(GenericPrinter& out) const {
+  MDefinition::printOpcode(out);
+  out.printf(" (slot %zu)", slot());
+}
+#endif
+
+MDefinition* MGuardFunctionScript::foldsTo(TempAllocator& alloc) {
+  MDefinition* in = input();
+  if (in->isLambda() &&
+      in->toLambda()->templateFunction()->baseScript() == expected()) {
+    return in;
+  }
+  return this;
+}
+
+MDefinition* MFunctionEnvironment::foldsTo(TempAllocator& alloc) {
+  if (input()->isLambda()) {
+    return input()->toLambda()->environmentChain();
+  }
+  if (input()->isFunctionWithProto()) {
+    return input()->toFunctionWithProto()->environmentChain();
+  }
+  return this;
+}
+
+static bool AddIsANonZeroAdditionOf(MAdd* add, MDefinition* ins) {
+  if (add->lhs() != ins && add->rhs() != ins) {
+    return false;
+  }
+  MDefinition* other = (add->lhs() == ins) ? add->rhs() : add->lhs();
+  if (!IsNumberType(other->type())) {
+    return false;
+  }
+  if (!other->isConstant()) {
+    return false;
+  }
+  if (other->toConstant()->numberToDouble() == 0) {
+    return false;
+  }
+  return true;
+}
+
+// Skip over instructions that usually appear between the actual index
+// value being used and the MLoadElement.
+// They don't modify the index value in a meaningful way.
+static MDefinition* SkipUninterestingInstructions(MDefinition* ins) {
+  // Drop the MToNumberInt32 added by the TypePolicy for double and float
+  // values.
+  if (ins->isToNumberInt32()) {
+    return SkipUninterestingInstructions(ins->toToNumberInt32()->input());
+  }
+
+  // Ignore the bounds check, which don't modify the index.
+  if (ins->isBoundsCheck()) {
+    return SkipUninterestingInstructions(ins->toBoundsCheck()->index());
+  }
+
+  // Masking the index for Spectre-mitigation is not observable.
+  if (ins->isSpectreMaskIndex()) {
+    return SkipUninterestingInstructions(ins->toSpectreMaskIndex()->index());
+  }
+
+  return ins;
+}
+
+static bool DefinitelyDifferentValue(MDefinition* ins1, MDefinition* ins2) {
+  ins1 = SkipUninterestingInstructions(ins1);
+  ins2 = SkipUninterestingInstructions(ins2);
+
+  if (ins1 == ins2) {
+    return false;
+  }
+
+  // For constants check they are not equal.
+  if (ins1->isConstant() && ins2->isConstant()) {
+    MConstant* cst1 = ins1->toConstant();
+    MConstant* cst2 = ins2->toConstant();
+
+    if (!cst1->isTypeRepresentableAsDouble() ||
+        !cst2->isTypeRepresentableAsDouble()) {
+      return false;
+    }
+
+    // Be conservative and only allow values that fit into int32.
+    int32_t n1, n2;
+    if (!mozilla::NumberIsInt32(cst1->numberToDouble(), &n1) ||
+        !mozilla::NumberIsInt32(cst2->numberToDouble(), &n2)) {
+      return false;
+    }
+
+    return n1 != n2;
+  }
+
+  // Check if "ins1 = ins2 + cte", which would make both instructions
+  // have different values.
+  if (ins1->isAdd()) {
+    if (AddIsANonZeroAdditionOf(ins1->toAdd(), ins2)) {
+      return true;
+    }
+  }
+  if (ins2->isAdd()) {
+    if (AddIsANonZeroAdditionOf(ins2->toAdd(), ins1)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+MDefinition::AliasType MLoadElement::mightAlias(const MDefinition* def) const {
+  if (def->isStoreElement()) {
+    const MStoreElement* store = def->toStoreElement();
+    if (store->index() != index()) {
+      if (DefinitelyDifferentValue(store->index(), index())) {
+        return AliasType::NoAlias;
+      }
+      return AliasType::MayAlias;
+    }
+
+    if (store->elements() != elements()) {
+      return AliasType::MayAlias;
+    }
+
+    return AliasType::MustAlias;
+  }
+  return AliasType::MayAlias;
+}
+
+MDefinition* MLoadElement::foldsTo(TempAllocator& alloc) {
+  if (MDefinition* def = foldsToStore(alloc)) {
+    return def;
+  }
+
+  return this;
+}
+
+MDefinition* MWasmUnsignedToDouble::foldsTo(TempAllocator& alloc) {
+  if (input()->isConstant()) {
+    return MConstant::New(
+        alloc, DoubleValue(uint32_t(input()->toConstant()->toInt32())));
+  }
+
+  return this;
+}
+
+MDefinition* MWasmUnsignedToFloat32::foldsTo(TempAllocator& alloc) {
+  if (input()->isConstant()) {
+    double dval = double(uint32_t(input()->toConstant()->toInt32()));
+    if (IsFloat32Representable(dval)) {
+      return MConstant::NewFloat32(alloc, float(dval));
+    }
+  }
+
+  return this;
+}
+
+MWasmCallCatchable* MWasmCallCatchable::New(TempAllocator& alloc,
+                                            const wasm::CallSiteDesc& desc,
+                                            const wasm::CalleeDesc& callee,
+                                            const Args& args,
+                                            uint32_t stackArgAreaSizeUnaligned,
+                                            const MWasmCallTryDesc& tryDesc,
+                                            MDefinition* tableIndexOrRef) {
+  MOZ_ASSERT(tryDesc.inTry);
+
+  MWasmCallCatchable* call = new (alloc) MWasmCallCatchable(
+      desc, callee, stackArgAreaSizeUnaligned, tryDesc.tryNoteIndex);
+
+  call->setSuccessor(FallthroughBranchIndex, tryDesc.fallthroughBlock);
+  call->setSuccessor(PrePadBranchIndex, tryDesc.prePadBlock);
+
+  MOZ_ASSERT_IF(callee.isTable() || callee.isFuncRef(), tableIndexOrRef);
+  if (!call->initWithArgs(alloc, call, args, tableIndexOrRef)) {
+    return nullptr;
+  }
+
+  return call;
+}
+
+MWasmCallUncatchable* MWasmCallUncatchable::New(
+    TempAllocator& alloc, const wasm::CallSiteDesc& desc,
+    const wasm::CalleeDesc& callee, const Args& args,
+    uint32_t stackArgAreaSizeUnaligned, MDefinition* tableIndexOrRef) {
+  MWasmCallUncatchable* call =
+      new (alloc) MWasmCallUncatchable(desc, callee, stackArgAreaSizeUnaligned);
+
+  MOZ_ASSERT_IF(callee.isTable() || callee.isFuncRef(), tableIndexOrRef);
+  if (!call->initWithArgs(alloc, call, args, tableIndexOrRef)) {
+    return nullptr;
+  }
+
+  return call;
+}
+
+MWasmCallUncatchable* MWasmCallUncatchable::NewBuiltinInstanceMethodCall(
+    TempAllocator& alloc, const wasm::CallSiteDesc& desc,
+    const wasm::SymbolicAddress builtin, wasm::FailureMode failureMode,
+    const ABIArg& instanceArg, const Args& args,
+    uint32_t stackArgAreaSizeUnaligned) {
+  auto callee = wasm::CalleeDesc::builtinInstanceMethod(builtin);
+  MWasmCallUncatchable* call = MWasmCallUncatchable::New(
+      alloc, desc, callee, args, stackArgAreaSizeUnaligned, nullptr);
+  if (!call) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(instanceArg != ABIArg());
+  call->instanceArg_ = instanceArg;
+  call->builtinMethodFailureMode_ = failureMode;
+  return call;
+}
+
+void MSqrt::trySpecializeFloat32(TempAllocator& alloc) {
+  if (EnsureFloatConsumersAndInputOrConvert(this, alloc)) {
+    setResultType(MIRType::Float32);
+    specialization_ = MIRType::Float32;
+  }
+}
+
+MDefinition* MClz::foldsTo(TempAllocator& alloc) {
+  if (num()->isConstant()) {
+    MConstant* c = num()->toConstant();
+    if (type() == MIRType::Int32) {
+      int32_t n = c->toInt32();
+      if (n == 0) {
+        return MConstant::New(alloc, Int32Value(32));
+      }
+      return MConstant::New(alloc,
+                            Int32Value(mozilla::CountLeadingZeroes32(n)));
+    }
+    int64_t n = c->toInt64();
+    if (n == 0) {
+      return MConstant::NewInt64(alloc, int64_t(64));
+    }
+    return MConstant::NewInt64(alloc,
+                               int64_t(mozilla::CountLeadingZeroes64(n)));
+  }
+
+  return this;
+}
+
+MDefinition* MCtz::foldsTo(TempAllocator& alloc) {
+  if (num()->isConstant()) {
+    MConstant* c = num()->toConstant();
+    if (type() == MIRType::Int32) {
+      int32_t n = num()->toConstant()->toInt32();
+      if (n == 0) {
+        return MConstant::New(alloc, Int32Value(32));
+      }
+      return MConstant::New(alloc,
+                            Int32Value(mozilla::CountTrailingZeroes32(n)));
+    }
+    int64_t n = c->toInt64();
+    if (n == 0) {
+      return MConstant::NewInt64(alloc, int64_t(64));
+    }
+    return MConstant::NewInt64(alloc,
+                               int64_t(mozilla::CountTrailingZeroes64(n)));
+  }
+
+  return this;
+}
+
+MDefinition* MPopcnt::foldsTo(TempAllocator& alloc) {
+  if (num()->isConstant()) {
+    MConstant* c = num()->toConstant();
+    if (type() == MIRType::Int32) {
+      int32_t n = num()->toConstant()->toInt32();
+      return MConstant::New(alloc, Int32Value(mozilla::CountPopulation32(n)));
+    }
+    int64_t n = c->toInt64();
+    return MConstant::NewInt64(alloc, int64_t(mozilla::CountPopulation64(n)));
+  }
+
+  return this;
+}
+
+MDefinition* MBoundsCheck::foldsTo(TempAllocator& alloc) {
+  if (type() == MIRType::Int32 && index()->isConstant() &&
+      length()->isConstant()) {
+    uint32_t len = length()->toConstant()->toInt32();
+    uint32_t idx = index()->toConstant()->toInt32();
+    if (idx + uint32_t(minimum()) < len && idx + uint32_t(maximum()) < len) {
+      return index();
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MTableSwitch::foldsTo(TempAllocator& alloc) {
+  MDefinition* op = getOperand(0);
+
+  // If we only have one successor, convert to a plain goto to the only
+  // successor. TableSwitch indices are numeric; other types will always go to
+  // the only successor.
+  if (numSuccessors() == 1 ||
+      (op->type() != MIRType::Value && !IsNumberType(op->type()))) {
+    return MGoto::New(alloc, getDefault());
+  }
+
+  if (MConstant* opConst = op->maybeConstantValue()) {
+    if (op->type() == MIRType::Int32) {
+      int32_t i = opConst->toInt32() - low_;
+      MBasicBlock* target;
+      if (size_t(i) < numCases()) {
+        target = getCase(size_t(i));
+      } else {
+        target = getDefault();
+      }
+      MOZ_ASSERT(target);
+      return MGoto::New(alloc, target);
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MArrayJoin::foldsTo(TempAllocator& alloc) {
+  MDefinition* arr = array();
+
+  if (!arr->isStringSplit()) {
+    return this;
+  }
+
+  setRecoveredOnBailout();
+  if (arr->hasLiveDefUses()) {
+    setNotRecoveredOnBailout();
+    return this;
+  }
+
+  // The MStringSplit won't generate any code.
+  arr->setRecoveredOnBailout();
+
+  // We're replacing foo.split(bar).join(baz) by
+  // foo.replace(bar, baz).  MStringSplit could be recovered by
+  // a bailout.  As we are removing its last use, and its result
+  // could be captured by a resume point, this MStringSplit will
+  // be executed on the bailout path.
+  MDefinition* string = arr->toStringSplit()->string();
+  MDefinition* pattern = arr->toStringSplit()->separator();
+  MDefinition* replacement = sep();
+
+  MStringReplace* substr =
+      MStringReplace::New(alloc, string, pattern, replacement);
+  substr->setFlatReplacement();
+  return substr;
+}
+
+MDefinition* MGetFirstDollarIndex::foldsTo(TempAllocator& alloc) {
+  MDefinition* strArg = str();
+  if (!strArg->isConstant()) {
+    return this;
+  }
+
+  JSLinearString* str = &strArg->toConstant()->toString()->asLinear();
+  int32_t index = GetFirstDollarIndexRawFlat(str);
+  return MConstant::New(alloc, Int32Value(index));
+}
+
+AliasSet MThrowRuntimeLexicalError::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+AliasSet MSlots::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+MDefinition::AliasType MSlots::mightAlias(const MDefinition* store) const {
+  // ArrayPush only modifies object elements, but not object slots.
+  if (store->isArrayPush()) {
+    return AliasType::NoAlias;
+  }
+  return MInstruction::mightAlias(store);
+}
+
+AliasSet MElements::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MInitializedLength::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MSetInitializedLength::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ObjectFields);
+}
+
+AliasSet MArrayLength::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MSetArrayLength::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ObjectFields);
+}
+
+AliasSet MFunctionLength::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+AliasSet MFunctionName::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+AliasSet MArrayBufferByteLength::getAliasSet() const {
+  return AliasSet::Load(AliasSet::FixedSlot);
+}
+
+AliasSet MArrayBufferViewLength::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ArrayBufferViewLengthOrOffset);
+}
+
+AliasSet MArrayBufferViewByteOffset::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ArrayBufferViewLengthOrOffset);
+}
+
+AliasSet MArrayBufferViewElements::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MGuardHasAttachedArrayBuffer::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot);
+}
+
+AliasSet MArrayPush::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ObjectFields | AliasSet::Element);
+}
+
+MDefinition* MGuardNumberToIntPtrIndex::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = this->input();
+
+  if (input->isToDouble() && input->getOperand(0)->type() == MIRType::Int32) {
+    return MInt32ToIntPtr::New(alloc, input->getOperand(0));
+  }
+
+  if (!input->isConstant()) {
+    return this;
+  }
+
+  // Fold constant double representable as intptr to intptr.
+  int64_t ival;
+  if (!mozilla::NumberEqualsInt64(input->toConstant()->toDouble(), &ival)) {
+    // If not representable as an int64, this access is equal to an OOB access.
+    // So replace it with a known int64/intptr value which also produces an OOB
+    // access. If we don't support OOB accesses we have to bail out.
+    if (!supportOOB()) {
+      return this;
+    }
+    ival = -1;
+  }
+
+  if (ival < INTPTR_MIN || ival > INTPTR_MAX) {
+    return this;
+  }
+
+  return MConstant::NewIntPtr(alloc, intptr_t(ival));
+}
+
+MDefinition* MIsObject::foldsTo(TempAllocator& alloc) {
+  if (!object()->isBox()) {
+    return this;
+  }
+
+  MDefinition* unboxed = object()->getOperand(0);
+  if (unboxed->type() == MIRType::Object) {
+    return MConstant::New(alloc, BooleanValue(true));
+  }
+
+  return this;
+}
+
+MDefinition* MIsNullOrUndefined::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = value();
+  if (input->isBox()) {
+    input = input->toBox()->input();
+  }
+
+  if (input->definitelyType({MIRType::Null, MIRType::Undefined})) {
+    return MConstant::New(alloc, BooleanValue(true));
+  }
+
+  if (!input->mightBeType(MIRType::Null) &&
+      !input->mightBeType(MIRType::Undefined)) {
+    return MConstant::New(alloc, BooleanValue(false));
+  }
+
+  return this;
+}
+
+AliasSet MHomeObjectSuperBase::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+MDefinition* MGuardValue::foldsTo(TempAllocator& alloc) {
+  if (MConstant* cst = value()->maybeConstantValue()) {
+    if (cst->toJSValue() == expected()) {
+      return value();
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MGuardNullOrUndefined::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = value();
+  if (input->isBox()) {
+    input = input->toBox()->input();
+  }
+
+  if (input->definitelyType({MIRType::Null, MIRType::Undefined})) {
+    return value();
+  }
+
+  return this;
+}
+
+MDefinition* MGuardIsNotObject::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = value();
+  if (input->isBox()) {
+    input = input->toBox()->input();
+  }
+
+  if (!input->mightBeType(MIRType::Object)) {
+    return value();
+  }
+
+  return this;
+}
+
+MDefinition* MGuardObjectIdentity::foldsTo(TempAllocator& alloc) {
+  if (object()->isConstant() && expected()->isConstant()) {
+    JSObject* obj = &object()->toConstant()->toObject();
+    JSObject* other = &expected()->toConstant()->toObject();
+    if (!bailOnEquality()) {
+      if (obj == other) {
+        return object();
+      }
+    } else {
+      if (obj != other) {
+        return object();
+      }
+    }
+  }
+
+  if (!bailOnEquality() && object()->isNurseryObject() &&
+      expected()->isNurseryObject()) {
+    uint32_t objIndex = object()->toNurseryObject()->nurseryIndex();
+    uint32_t otherIndex = expected()->toNurseryObject()->nurseryIndex();
+    if (objIndex == otherIndex) {
+      return object();
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MGuardSpecificFunction::foldsTo(TempAllocator& alloc) {
+  if (function()->isConstant() && expected()->isConstant()) {
+    JSObject* fun = &function()->toConstant()->toObject();
+    JSObject* other = &expected()->toConstant()->toObject();
+    if (fun == other) {
+      return function();
+    }
+  }
+
+  if (function()->isNurseryObject() && expected()->isNurseryObject()) {
+    uint32_t funIndex = function()->toNurseryObject()->nurseryIndex();
+    uint32_t otherIndex = expected()->toNurseryObject()->nurseryIndex();
+    if (funIndex == otherIndex) {
+      return function();
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MGuardSpecificAtom::foldsTo(TempAllocator& alloc) {
+  if (str()->isConstant()) {
+    JSString* s = str()->toConstant()->toString();
+    if (s->isAtom()) {
+      JSAtom* cstAtom = &s->asAtom();
+      if (cstAtom == atom()) {
+        return str();
+      }
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MGuardSpecificSymbol::foldsTo(TempAllocator& alloc) {
+  if (symbol()->isConstant()) {
+    if (symbol()->toConstant()->toSymbol() == expected()) {
+      return symbol();
+    }
+  }
+
+  return this;
+}
+
+MDefinition* MGuardSpecificInt32::foldsTo(TempAllocator& alloc) {
+  if (num()->isConstant() && num()->toConstant()->isInt32(expected())) {
+    return num();
+  }
+  return this;
+}
+
+bool MCallBindVar::congruentTo(const MDefinition* ins) const {
+  if (!ins->isCallBindVar()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+bool MGuardShape::congruentTo(const MDefinition* ins) const {
+  if (!ins->isGuardShape()) {
+    return false;
+  }
+  if (shape() != ins->toGuardShape()->shape()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MGuardShape::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+MDefinition::AliasType MGuardShape::mightAlias(const MDefinition* store) const {
+  // These instructions only modify object elements, but not the shape.
+  if (store->isStoreElementHole() || store->isArrayPush()) {
+    return AliasType::NoAlias;
+  }
+  if (object()->isConstantProto()) {
+    const MDefinition* receiverObject =
+        object()->toConstantProto()->getReceiverObject();
+    switch (store->op()) {
+      case MDefinition::Opcode::StoreFixedSlot:
+        if (store->toStoreFixedSlot()->object()->skipObjectGuards() ==
+            receiverObject) {
+          return AliasType::NoAlias;
+        }
+        break;
+      case MDefinition::Opcode::StoreDynamicSlot:
+        if (store->toStoreDynamicSlot()
+                ->slots()
+                ->toSlots()
+                ->object()
+                ->skipObjectGuards() == receiverObject) {
+          return AliasType::NoAlias;
+        }
+        break;
+      case MDefinition::Opcode::AddAndStoreSlot:
+        if (store->toAddAndStoreSlot()->object()->skipObjectGuards() ==
+            receiverObject) {
+          return AliasType::NoAlias;
+        }
+        break;
+      case MDefinition::Opcode::AllocateAndStoreSlot:
+        if (store->toAllocateAndStoreSlot()->object()->skipObjectGuards() ==
+            receiverObject) {
+          return AliasType::NoAlias;
+        }
+        break;
+      case MDefinition::Opcode::MegamorphicStoreSlot:
+        if (store->toMegamorphicStoreSlot()->object()->skipObjectGuards() ==
+            receiverObject) {
+          return AliasType::NoAlias;
+        }
+        break;
+      default:
+        break;
+    }
+  }
+  return MInstruction::mightAlias(store);
+}
+
+AliasSet MGuardMultipleShapes::getAliasSet() const {
+  // Note: This instruction loads the elements of the ListObject used to
+  // store the list of shapes, but that object is internal and not exposed
+  // to script, so it doesn't have to be in the alias set.
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+MDefinition* MGuardIsNotProxy::foldsTo(TempAllocator& alloc) {
+  KnownClass known = GetObjectKnownClass(object());
+  if (known == KnownClass::None) {
+    return this;
+  }
+
+  MOZ_ASSERT(!GetObjectKnownJSClass(object())->isProxyObject());
+  AssertKnownClass(alloc, this, object());
+  return object();
+}
+
+AliasSet MMegamorphicLoadSlotByValue::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+MDefinition* MMegamorphicLoadSlotByValue::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = idVal();
+  if (input->isBox()) {
+    input = input->toBox()->input();
+  }
+
+  MDefinition* result = this;
+
+  if (input->isConstant()) {
+    MConstant* constant = input->toConstant();
+    if (constant->type() == MIRType::Symbol) {
+      PropertyKey id = PropertyKey::Symbol(constant->toSymbol());
+      result = MMegamorphicLoadSlot::New(alloc, object(), id);
+    }
+
+    if (constant->type() == MIRType::String) {
+      JSString* str = constant->toString();
+      if (str->isAtom() && !str->asAtom().isIndex()) {
+        PropertyKey id = PropertyKey::NonIntAtom(str);
+        result = MMegamorphicLoadSlot::New(alloc, object(), id);
+      }
+    }
+  }
+
+  if (result != this) {
+    result->setDependency(dependency());
+  }
+
+  return result;
+}
+
+bool MMegamorphicLoadSlot::congruentTo(const MDefinition* ins) const {
+  if (!ins->isMegamorphicLoadSlot()) {
+    return false;
+  }
+  if (ins->toMegamorphicLoadSlot()->name() != name()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MMegamorphicLoadSlot::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+bool MMegamorphicStoreSlot::congruentTo(const MDefinition* ins) const {
+  if (!ins->isMegamorphicStoreSlot()) {
+    return false;
+  }
+  if (ins->toMegamorphicStoreSlot()->name() != name()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MMegamorphicStoreSlot::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                         AliasSet::DynamicSlot);
+}
+
+bool MMegamorphicHasProp::congruentTo(const MDefinition* ins) const {
+  if (!ins->isMegamorphicHasProp()) {
+    return false;
+  }
+  if (ins->toMegamorphicHasProp()->hasOwn() != hasOwn()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MMegamorphicHasProp::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+bool MNurseryObject::congruentTo(const MDefinition* ins) const {
+  if (!ins->isNurseryObject()) {
+    return false;
+  }
+  return nurseryIndex() == ins->toNurseryObject()->nurseryIndex();
+}
+
+AliasSet MGuardFunctionIsNonBuiltinCtor::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+bool MGuardFunctionKind::congruentTo(const MDefinition* ins) const {
+  if (!ins->isGuardFunctionKind()) {
+    return false;
+  }
+  if (expected() != ins->toGuardFunctionKind()->expected()) {
+    return false;
+  }
+  if (bailOnEquality() != ins->toGuardFunctionKind()->bailOnEquality()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MGuardFunctionKind::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+bool MGuardFunctionScript::congruentTo(const MDefinition* ins) const {
+  if (!ins->isGuardFunctionScript()) {
+    return false;
+  }
+  if (expected() != ins->toGuardFunctionScript()->expected()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MGuardFunctionScript::getAliasSet() const {
+  // A JSFunction's BaseScript pointer is immutable. Relazification of
+  // self-hosted functions is an exception to this, but we don't use this
+  // guard for self-hosted functions.
+  MOZ_ASSERT(!flags_.isSelfHostedOrIntrinsic());
+  return AliasSet::None();
+}
+
+bool MGuardSpecificAtom::congruentTo(const MDefinition* ins) const {
+  if (!ins->isGuardSpecificAtom()) {
+    return false;
+  }
+  if (atom() != ins->toGuardSpecificAtom()->atom()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+MDefinition* MGuardStringToIndex::foldsTo(TempAllocator& alloc) {
+  if (!string()->isConstant()) {
+    return this;
+  }
+
+  JSString* str = string()->toConstant()->toString();
+
+  int32_t index = GetIndexFromString(str);
+  if (index < 0) {
+    return this;
+  }
+
+  return MConstant::New(alloc, Int32Value(index));
+}
+
+MDefinition* MGuardStringToInt32::foldsTo(TempAllocator& alloc) {
+  if (!string()->isConstant()) {
+    return this;
+  }
+
+  JSLinearString* str = &string()->toConstant()->toString()->asLinear();
+  double number = LinearStringToNumber(str);
+
+  int32_t n;
+  if (!mozilla::NumberIsInt32(number, &n)) {
+    return this;
+  }
+
+  return MConstant::New(alloc, Int32Value(n));
+}
+
+MDefinition* MGuardStringToDouble::foldsTo(TempAllocator& alloc) {
+  if (!string()->isConstant()) {
+    return this;
+  }
+
+  JSLinearString* str = &string()->toConstant()->toString()->asLinear();
+  double number = LinearStringToNumber(str);
+  return MConstant::New(alloc, DoubleValue(number));
+}
+
+AliasSet MGuardNoDenseElements::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MAllocateAndStoreSlot::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ObjectFields | AliasSet::DynamicSlot);
+}
+
+AliasSet MLoadDOMExpandoValue::getAliasSet() const {
+  return AliasSet::Load(AliasSet::DOMProxyExpando);
+}
+
+AliasSet MLoadDOMExpandoValueIgnoreGeneration::getAliasSet() const {
+  return AliasSet::Load(AliasSet::DOMProxyExpando);
+}
+
+bool MGuardDOMExpandoMissingOrGuardShape::congruentTo(
+    const MDefinition* ins) const {
+  if (!ins->isGuardDOMExpandoMissingOrGuardShape()) {
+    return false;
+  }
+  if (shape() != ins->toGuardDOMExpandoMissingOrGuardShape()->shape()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MGuardDOMExpandoMissingOrGuardShape::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+MDefinition* MGuardToClass::foldsTo(TempAllocator& alloc) {
+  const JSClass* clasp = GetObjectKnownJSClass(object());
+  if (!clasp || getClass() != clasp) {
+    return this;
+  }
+
+  AssertKnownClass(alloc, this, object());
+  return object();
+}
+
+MDefinition* MGuardToFunction::foldsTo(TempAllocator& alloc) {
+  if (GetObjectKnownClass(object()) != KnownClass::Function) {
+    return this;
+  }
+
+  AssertKnownClass(alloc, this, object());
+  return object();
+}
+
+MDefinition* MHasClass::foldsTo(TempAllocator& alloc) {
+  const JSClass* clasp = GetObjectKnownJSClass(object());
+  if (!clasp) {
+    return this;
+  }
+
+  AssertKnownClass(alloc, this, object());
+  return MConstant::New(alloc, BooleanValue(getClass() == clasp));
+}
+
+MDefinition* MIsCallable::foldsTo(TempAllocator& alloc) {
+  if (input()->type() != MIRType::Object) {
+    return this;
+  }
+
+  KnownClass known = GetObjectKnownClass(input());
+  if (known == KnownClass::None) {
+    return this;
+  }
+
+  AssertKnownClass(alloc, this, input());
+  return MConstant::New(alloc, BooleanValue(known == KnownClass::Function));
+}
+
+MDefinition* MIsArray::foldsTo(TempAllocator& alloc) {
+  if (input()->type() != MIRType::Object) {
+    return this;
+  }
+
+  KnownClass known = GetObjectKnownClass(input());
+  if (known == KnownClass::None) {
+    return this;
+  }
+
+  AssertKnownClass(alloc, this, input());
+  return MConstant::New(alloc, BooleanValue(known == KnownClass::Array));
+}
+
+AliasSet MObjectClassToString::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::FixedSlot |
+                        AliasSet::DynamicSlot);
+}
+
+MDefinition* MGuardIsNotArrayBufferMaybeShared::foldsTo(TempAllocator& alloc) {
+  switch (GetObjectKnownClass(object())) {
+    case KnownClass::PlainObject:
+    case KnownClass::Array:
+    case KnownClass::Function:
+    case KnownClass::RegExp:
+    case KnownClass::ArrayIterator:
+    case KnownClass::StringIterator:
+    case KnownClass::RegExpStringIterator: {
+      AssertKnownClass(alloc, this, object());
+      return object();
+    }
+    case KnownClass::None:
+      break;
+  }
+
+  return this;
+}
+
+MDefinition* MCheckIsObj::foldsTo(TempAllocator& alloc) {
+  if (!input()->isBox()) {
+    return this;
+  }
+
+  MDefinition* unboxed = input()->getOperand(0);
+  if (unboxed->type() == MIRType::Object) {
+    return unboxed;
+  }
+
+  return this;
+}
+
+static bool IsBoxedObject(MDefinition* def) {
+  MOZ_ASSERT(def->type() == MIRType::Value);
+
+  if (def->isBox()) {
+    return def->toBox()->input()->type() == MIRType::Object;
+  }
+
+  // Construct calls are always returning a boxed object.
+  //
+  // TODO: We should consider encoding this directly in the graph instead of
+  // having to special case it here.
+  if (def->isCall()) {
+    return def->toCall()->isConstructing();
+  }
+  if (def->isConstructArray()) {
+    return true;
+  }
+  if (def->isConstructArgs()) {
+    return true;
+  }
+
+  return false;
+}
+
+MDefinition* MCheckReturn::foldsTo(TempAllocator& alloc) {
+  auto* returnVal = returnValue();
+  if (!returnVal->isBox()) {
+    return this;
+  }
+
+  auto* unboxedReturnVal = returnVal->toBox()->input();
+  if (unboxedReturnVal->type() == MIRType::Object) {
+    return returnVal;
+  }
+
+  if (unboxedReturnVal->type() != MIRType::Undefined) {
+    return this;
+  }
+
+  auto* thisVal = thisValue();
+  if (IsBoxedObject(thisVal)) {
+    return thisVal;
+  }
+
+  return this;
+}
+
+MDefinition* MCheckThis::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = thisValue();
+  if (!input->isBox()) {
+    return this;
+  }
+
+  MDefinition* unboxed = input->getOperand(0);
+  if (unboxed->mightBeMagicType()) {
+    return this;
+  }
+
+  return input;
+}
+
+MDefinition* MCheckThisReinit::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = thisValue();
+  if (!input->isBox()) {
+    return this;
+  }
+
+  MDefinition* unboxed = input->getOperand(0);
+  if (unboxed->type() != MIRType::MagicUninitializedLexical) {
+    return this;
+  }
+
+  return input;
+}
+
+MDefinition* MCheckObjCoercible::foldsTo(TempAllocator& alloc) {
+  MDefinition* input = checkValue();
+  if (!input->isBox()) {
+    return this;
+  }
+
+  MDefinition* unboxed = input->getOperand(0);
+  if (unboxed->mightBeType(MIRType::Null) ||
+      unboxed->mightBeType(MIRType::Undefined)) {
+    return this;
+  }
+
+  return input;
+}
+
+AliasSet MCheckObjCoercible::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+AliasSet MCheckReturn::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+AliasSet MCheckThis::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+AliasSet MCheckThisReinit::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ExceptionState);
+}
+
+AliasSet MIsPackedArray::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MGuardArrayIsPacked::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MSuperFunction::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MInitHomeObject::getAliasSet() const {
+  return AliasSet::Store(AliasSet::ObjectFields);
+}
+
+AliasSet MLoadWrapperTarget::getAliasSet() const {
+  return AliasSet::Load(AliasSet::Any);
+}
+
+AliasSet MGuardHasGetterSetter::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+bool MGuardHasGetterSetter::congruentTo(const MDefinition* ins) const {
+  if (!ins->isGuardHasGetterSetter()) {
+    return false;
+  }
+  if (ins->toGuardHasGetterSetter()->propId() != propId()) {
+    return false;
+  }
+  if (ins->toGuardHasGetterSetter()->getterSetter() != getterSetter()) {
+    return false;
+  }
+  return congruentIfOperandsEqual(ins);
+}
+
+AliasSet MGuardIsExtensible::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MGuardIndexIsNotDenseElement::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields | AliasSet::Element);
+}
+
+AliasSet MGuardIndexIsValidUpdateOrAdd::getAliasSet() const {
+  return AliasSet::Load(AliasSet::ObjectFields);
+}
+
+AliasSet MCallObjectHasSparseElement::getAliasSet() const {
+  return AliasSet::Load(AliasSet::Element | AliasSet::ObjectFields |
+                        AliasSet::FixedSlot | AliasSet::DynamicSlot);
+}
+
+MDefinition* MGuardInt32IsNonNegative::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(index()->type() == MIRType::Int32);
+
+  MDefinition* input = index();
+  if (!input->isConstant() || input->toConstant()->toInt32() < 0) {
+    return this;
+  }
+  return input;
+}
+
+MDefinition* MGuardInt32Range::foldsTo(TempAllocator& alloc) {
+  MOZ_ASSERT(input()->type() == MIRType::Int32);
+  MOZ_ASSERT(minimum() <= maximum());
+
+  MDefinition* in = input();
+  if (!in->isConstant()) {
+    return this;
+  }
+  int32_t cst = in->toConstant()->toInt32();
+  if (cst < minimum() || cst > maximum()) {
+    return this;
+  }
+  return in;
+}
+
+MDefinition* MGuardNonGCThing::foldsTo(TempAllocator& alloc) {
+  if (!input()->isBox()) {
+    return this;
+  }
+
+  MDefinition* unboxed = input()->getOperand(0);
+  if (!IsNonGCThing(unboxed->type())) {
+    return this;
+  }
+  return input();
+}
+
+AliasSet MSetObjectHasNonBigInt::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MSetObjectHasBigInt::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MSetObjectHasValue::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MSetObjectHasValueVMCall::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MSetObjectSize::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectHasNonBigInt::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectHasBigInt::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectHasValue::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectHasValueVMCall::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectGetNonBigInt::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectGetBigInt::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectGetValue::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectGetValueVMCall::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+AliasSet MMapObjectSize::getAliasSet() const {
+  return AliasSet::Load(AliasSet::MapOrSetHashTable);
+}
+
+MIonToWasmCall* MIonToWasmCall::New(TempAllocator& alloc,
+                                    WasmInstanceObject* instanceObj,
+                                    const wasm::FuncExport& funcExport) {
+  const wasm::FuncType& funcType =
+      instanceObj->instance().metadata().getFuncExportType(funcExport);
+  const wasm::ValTypeVector& results = funcType.results();
+  MIRType resultType = MIRType::Value;
+  // At the JS boundary some wasm types must be represented as a Value, and in
+  // addition a void return requires an Undefined value.
+  if (results.length() > 0 && !results[0].isEncodedAsJSValueOnEscape()) {
+    MOZ_ASSERT(results.length() == 1,
+               "multiple returns not implemented for inlined Wasm calls");
+    resultType = results[0].toMIRType();
+  }
+
+  auto* ins = new (alloc) MIonToWasmCall(instanceObj, resultType, funcExport);
+  if (!ins->init(alloc, funcType.args().length())) {
+    return nullptr;
+  }
+  return ins;
+}
+
+#ifdef DEBUG
+bool MIonToWasmCall::isConsistentFloat32Use(MUse* use) const {
+  const wasm::FuncType& funcType =
+      instance()->metadata().getFuncExportType(funcExport_);
+  return funcType.args()[use->index()].kind() == wasm::ValType::F32;
+}
+#endif
+
+MCreateInlinedArgumentsObject* MCreateInlinedArgumentsObject::New(
+    TempAllocator& alloc, MDefinition* callObj, MDefinition* callee,
+    MDefinitionVector& args, ArgumentsObject* templateObj) {
+  MCreateInlinedArgumentsObject* ins =
+      new (alloc) MCreateInlinedArgumentsObject(templateObj);
+
+  uint32_t argc = args.length();
+  MOZ_ASSERT(argc <= ArgumentsObject::MaxInlinedArgs);
+
+  if (!ins->init(alloc, argc + NumNonArgumentOperands)) {
+    return nullptr;
+  }
+
+  ins->initOperand(0, callObj);
+  ins->initOperand(1, callee);
+  for (uint32_t i = 0; i < argc; i++) {
+    ins->initOperand(i + NumNonArgumentOperands, args[i]);
+  }
+
+  return ins;
+}
+
+MGetInlinedArgument* MGetInlinedArgument::New(
+    TempAllocator& alloc, MDefinition* index,
+    MCreateInlinedArgumentsObject* args) {
+  MGetInlinedArgument* ins = new (alloc) MGetInlinedArgument();
+
+  uint32_t argc = args->numActuals();
+  MOZ_ASSERT(argc <= ArgumentsObject::MaxInlinedArgs);
+
+  if (!ins->init(alloc, argc + NumNonArgumentOperands)) {
+    return nullptr;
+  }
+
+  ins->initOperand(0, index);
+  for (uint32_t i = 0; i < argc; i++) {
+    ins->initOperand(i + NumNonArgumentOperands, args->getArg(i));
+  }
+
+  return ins;
+}
+
+MDefinition* MGetInlinedArgument::foldsTo(TempAllocator& alloc) {
+  MDefinition* indexDef = SkipUninterestingInstructions(index());
+  if (!indexDef->isConstant() || indexDef->type() != MIRType::Int32) {
+    return this;
+  }
+
+  int32_t indexConst = indexDef->toConstant()->toInt32();
+  if (indexConst < 0 || uint32_t(indexConst) >= numActuals()) {
+    return this;
+  }
+
+  MDefinition* arg = getArg(indexConst);
+  if (arg->type() != MIRType::Value) {
+    arg = MBox::New(alloc, arg);
+  }
+
+  return arg;
+}
+
+MGetInlinedArgumentHole* MGetInlinedArgumentHole::New(
+    TempAllocator& alloc, MDefinition* index,
+    MCreateInlinedArgumentsObject* args) {
+  auto* ins = new (alloc) MGetInlinedArgumentHole();
+
+  uint32_t argc = args->numActuals();
+  MOZ_ASSERT(argc <= ArgumentsObject::MaxInlinedArgs);
+
+  if (!ins->init(alloc, argc + NumNonArgumentOperands)) {
+    return nullptr;
+  }
+
+  ins->initOperand(0, index);
+  for (uint32_t i = 0; i < argc; i++) {
+    ins->initOperand(i + NumNonArgumentOperands, args->getArg(i));
+  }
+
+  return ins;
+}
+
+MDefinition* MGetInlinedArgumentHole::foldsTo(TempAllocator& alloc) {
+  MDefinition* indexDef = SkipUninterestingInstructions(index());
+  if (!indexDef->isConstant() || indexDef->type() != MIRType::Int32) {
+    return this;
+  }
+
+  int32_t indexConst = indexDef->toConstant()->toInt32();
+  if (indexConst < 0) {
+    return this;
+  }
+
+  MDefinition* arg;
+  if (uint32_t(indexConst) < numActuals()) {
+    arg = getArg(indexConst);
+
+    if (arg->type() != MIRType::Value) {
+      arg = MBox::New(alloc, arg);
+    }
+  } else {
+    auto* undefined = MConstant::New(alloc, UndefinedValue());
+    block()->insertBefore(this, undefined);
+
+    arg = MBox::New(alloc, undefined);
+  }
+
+  return arg;
+}
+
+MInlineArgumentsSlice* MInlineArgumentsSlice::New(
+    TempAllocator& alloc, MDefinition* begin, MDefinition* count,
+    MCreateInlinedArgumentsObject* args, JSObject* templateObj,
+    gc::InitialHeap initialHeap) {
+  auto* ins = new (alloc) MInlineArgumentsSlice(templateObj, initialHeap);
+
+  uint32_t argc = args->numActuals();
+  MOZ_ASSERT(argc <= ArgumentsObject::MaxInlinedArgs);
+
+  if (!ins->init(alloc, argc + NumNonArgumentOperands)) {
+    return nullptr;
+  }
+
+  ins->initOperand(0, begin);
+  ins->initOperand(1, count);
+  for (uint32_t i = 0; i < argc; i++) {
+    ins->initOperand(i + NumNonArgumentOperands, args->getArg(i));
+  }
+
+  return ins;
+}
+
+MDefinition* MNormalizeSliceTerm::foldsTo(TempAllocator& alloc) {
+  auto* length = this->length();
+  if (!length->isConstant() && !length->isArgumentsLength()) {
+    return this;
+  }
+
+  if (length->isConstant()) {
+    int32_t lengthConst = length->toConstant()->toInt32();
+    MOZ_ASSERT(lengthConst >= 0);
+
+    // Result is always zero when |length| is zero.
+    if (lengthConst == 0) {
+      return length;
+    }
+
+    auto* value = this->value();
+    if (value->isConstant()) {
+      int32_t valueConst = value->toConstant()->toInt32();
+
+      int32_t normalized;
+      if (valueConst < 0) {
+        normalized = std::max(valueConst + lengthConst, 0);
+      } else {
+        normalized = std::min(valueConst, lengthConst);
+      }
+
+      if (normalized == valueConst) {
+        return value;
+      }
+      if (normalized == lengthConst) {
+        return length;
+      }
+      return MConstant::New(alloc, Int32Value(normalized));
+    }
+
+    return this;
+  }
+
+  auto* value = this->value();
+  if (value->isConstant()) {
+    int32_t valueConst = value->toConstant()->toInt32();
+
+    // Minimum of |value| and |length|.
+    if (valueConst > 0) {
+      bool isMax = false;
+      return MMinMax::New(alloc, value, length, MIRType::Int32, isMax);
+    }
+
+    // Maximum of |value + length| and zero.
+    if (valueConst < 0) {
+      // Safe to truncate because |length| is never negative.
+      auto* add = MAdd::New(alloc, value, length, TruncateKind::Truncate);
+      block()->insertBefore(this, add);
+
+      auto* zero = MConstant::New(alloc, Int32Value(0));
+      block()->insertBefore(this, zero);
+
+      bool isMax = true;
+      return MMinMax::New(alloc, add, zero, MIRType::Int32, isMax);
+    }
+
+    // Directly return the value when it's zero.
+    return value;
+  }
+
+  // Normalizing MArgumentsLength is a no-op.
+  if (value->isArgumentsLength()) {
+    return value;
+  }
+
+  return this;
+}
+
+bool MWasmShiftSimd128::congruentTo(const MDefinition* ins) const {
+  return ins->toWasmShiftSimd128()->simdOp() == simdOp_ &&
+         congruentIfOperandsEqual(ins);
+}
+
+bool MWasmShuffleSimd128::congruentTo(const MDefinition* ins) const {
+  return ins->toWasmShuffleSimd128()->shuffle().equals(&shuffle_) &&
+         congruentIfOperandsEqual(ins);
+}
+
+bool MWasmUnarySimd128::congruentTo(const MDefinition* ins) const {
+  return ins->toWasmUnarySimd128()->simdOp() == simdOp_ &&
+         congruentIfOperandsEqual(ins);
+}
+
+#ifdef ENABLE_WASM_SIMD
+MWasmShuffleSimd128* jit::BuildWasmShuffleSimd128(TempAllocator& alloc,
+                                                  const int8_t* control,
+                                                  MDefinition* lhs,
+                                                  MDefinition* rhs) {
+  SimdShuffle s =
+      AnalyzeSimdShuffle(SimdConstant::CreateX16(control), lhs, rhs);
+  switch (s.opd) {
+    case SimdShuffle::Operand::LEFT:
+      // When SimdShuffle::Operand is LEFT the right operand is not used,
+      // lose reference to rhs.
+      rhs = lhs;
+      break;
+    case SimdShuffle::Operand::RIGHT:
+      // When SimdShuffle::Operand is RIGHT the left operand is not used,
+      // lose reference to lhs.
+      lhs = rhs;
+      break;
+    default:
+      break;
+  }
+  return MWasmShuffleSimd128::New(alloc, lhs, rhs, s);
+}
+#endif  // ENABLE_WASM_SIMD