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diff --git a/js/src/jit/Registers.h b/js/src/jit/Registers.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef jit_Registers_h
+#define jit_Registers_h
+
+#include "mozilla/Array.h"
+
+#include "jit/IonTypes.h"
+#if defined(JS_CODEGEN_X86) || defined(JS_CODEGEN_X64)
+#  include "jit/x86-shared/Architecture-x86-shared.h"
+#elif defined(JS_CODEGEN_ARM)
+#  include "jit/arm/Architecture-arm.h"
+#elif defined(JS_CODEGEN_ARM64)
+#  include "jit/arm64/Architecture-arm64.h"
+#elif defined(JS_CODEGEN_MIPS32)
+#  include "jit/mips32/Architecture-mips32.h"
+#elif defined(JS_CODEGEN_MIPS64)
+#  include "jit/mips64/Architecture-mips64.h"
+#elif defined(JS_CODEGEN_LOONG64)
+#  include "jit/loong64/Architecture-loong64.h"
+#elif defined(JS_CODEGEN_RISCV64)
+#  include "jit/riscv64/Architecture-riscv64.h"
+#elif defined(JS_CODEGEN_WASM32)
+#  include "jit/wasm32/Architecture-wasm32.h"
+#elif defined(JS_CODEGEN_NONE)
+#  include "jit/none/Architecture-none.h"
+#else
+#  error "Unknown architecture!"
+#endif
+
+namespace js {
+namespace jit {
+
+struct Register {
+  using Codes = Registers;
+  using Encoding = Codes::Encoding;
+  using Code = Codes::Code;
+  using SetType = Codes::SetType;
+
+  Encoding reg_;
+  explicit constexpr Register(Encoding e) : reg_(e) {}
+  Register() : reg_(Encoding(Codes::Invalid)) {}
+
+  static Register FromCode(Code i) {
+    MOZ_ASSERT(i < Registers::Total);
+    Register r{Encoding(i)};
+    return r;
+  }
+  static Register FromName(const char* name) {
+    Code code = Registers::FromName(name);
+    Register r{Encoding(code)};
+    return r;
+  }
+  constexpr static Register Invalid() {
+    Register r{Encoding(Codes::Invalid)};
+    return r;
+  }
+  constexpr Code code() const { return Code(reg_); }
+  Encoding encoding() const {
+    MOZ_ASSERT(Code(reg_) < Registers::Total);
+    return reg_;
+  }
+  const char* name() const { return Registers::GetName(code()); }
+  constexpr bool operator==(Register other) const { return reg_ == other.reg_; }
+  constexpr bool operator!=(Register other) const { return reg_ != other.reg_; }
+  bool volatile_() const {
+    return !!((SetType(1) << code()) & Registers::VolatileMask);
+  }
+  bool aliases(const Register& other) const { return reg_ == other.reg_; }
+  uint32_t numAliased() const { return 1; }
+
+  Register aliased(uint32_t aliasIdx) const {
+    MOZ_ASSERT(aliasIdx == 0);
+    return *this;
+  }
+
+  SetType alignedOrDominatedAliasedSet() const { return SetType(1) << code(); }
+
+  static constexpr RegTypeName DefaultType = RegTypeName::GPR;
+
+  template <RegTypeName = DefaultType>
+  static SetType LiveAsIndexableSet(SetType s) {
+    return SetType(0);
+  }
+
+  template <RegTypeName Name = DefaultType>
+  static SetType AllocatableAsIndexableSet(SetType s) {
+    static_assert(Name != RegTypeName::Any, "Allocatable set are not iterable");
+    return SetType(0);
+  }
+
+  static uint32_t SetSize(SetType x) { return Codes::SetSize(x); }
+  static uint32_t FirstBit(SetType x) { return Codes::FirstBit(x); }
+  static uint32_t LastBit(SetType x) { return Codes::LastBit(x); }
+
+  // Returns the offset of |reg| on the stack, assuming all registers in |set|
+  // were pushed in order (e.g. by |PushRegsInMask|). This is computed by
+  // clearing the lower bits (registers that were pushed later).
+  static size_t OffsetOfPushedRegister(SetType set, Register reg) {
+    return sizeof(Codes::RegisterContent) * Codes::SetSize(set >> reg.code());
+  }
+};
+
+// Architectures where the stack pointer is not a plain register with a standard
+// register encoding must define JS_HAS_HIDDEN_SP and HiddenSPEncoding.
+
+#ifdef JS_HAS_HIDDEN_SP
+struct RegisterOrSP {
+  // The register code -- but possibly one that cannot be represented as a bit
+  // position in a 32-bit vector.
+  uint32_t code;
+
+  explicit RegisterOrSP(uint32_t code) : code(code) {}
+  explicit RegisterOrSP(Register r) : code(r.code()) {}
+};
+
+static inline bool IsHiddenSP(RegisterOrSP r) {
+  return r.code == HiddenSPEncoding;
+}
+
+static inline Register AsRegister(RegisterOrSP r) {
+  MOZ_ASSERT(!IsHiddenSP(r));
+  return Register::FromCode(r.code);
+}
+
+static inline Register AsRegister(Register r) { return r; }
+
+inline bool operator==(Register r, RegisterOrSP e) {
+  return r.code() == e.code;
+}
+
+inline bool operator!=(Register r, RegisterOrSP e) { return !(r == e); }
+
+inline bool operator==(RegisterOrSP e, Register r) { return r == e; }
+
+inline bool operator!=(RegisterOrSP e, Register r) { return r != e; }
+
+inline bool operator==(RegisterOrSP lhs, RegisterOrSP rhs) {
+  return lhs.code == rhs.code;
+}
+
+inline bool operator!=(RegisterOrSP lhs, RegisterOrSP rhs) {
+  return !(lhs == rhs);
+}
+#else
+// On platforms where there's nothing special about SP, make RegisterOrSP be
+// just Register, and return false for IsHiddenSP(r) for any r so that we use
+// "normal" code for handling the SP.  This reduces ifdeffery throughout the
+// jit.
+using RegisterOrSP = Register;
+
+static inline bool IsHiddenSP(RegisterOrSP r) { return false; }
+
+static inline Register AsRegister(RegisterOrSP r) { return r; }
+#endif
+
+template <>
+inline Register::SetType Register::LiveAsIndexableSet<RegTypeName::GPR>(
+    SetType set) {
+  return set;
+}
+
+template <>
+inline Register::SetType Register::LiveAsIndexableSet<RegTypeName::Any>(
+    SetType set) {
+  return set;
+}
+
+template <>
+inline Register::SetType Register::AllocatableAsIndexableSet<RegTypeName::GPR>(
+    SetType set) {
+  return set;
+}
+
+#if JS_BITS_PER_WORD == 32
+// Note, some platform code depends on INT64LOW_OFFSET being zero.
+static const uint32_t INT64LOW_OFFSET = 0 * sizeof(int32_t);
+static const uint32_t INT64HIGH_OFFSET = 1 * sizeof(int32_t);
+#endif
+
+struct Register64 {
+#ifdef JS_PUNBOX64
+  Register reg;
+#else
+  Register high;
+  Register low;
+#endif
+
+#ifdef JS_PUNBOX64
+  explicit constexpr Register64(Register r) : reg(r) {}
+  constexpr bool operator==(Register64 other) const { return reg == other.reg; }
+  constexpr bool operator!=(Register64 other) const { return reg != other.reg; }
+  Register scratchReg() { return reg; }
+  static Register64 Invalid() { return Register64(Register::Invalid()); }
+#else
+  constexpr Register64(Register h, Register l) : high(h), low(l) {}
+  constexpr bool operator==(Register64 other) const {
+    return high == other.high && low == other.low;
+  }
+  constexpr bool operator!=(Register64 other) const {
+    return high != other.high || low != other.low;
+  }
+  Register scratchReg() { return high; }
+  static Register64 Invalid() {
+    return Register64(Register::Invalid(), Register::Invalid());
+  }
+#endif
+};
+
+class RegisterDump {
+ public:
+  typedef mozilla::Array<Registers::RegisterContent, Registers::Total> GPRArray;
+  typedef mozilla::Array<FloatRegisters::RegisterContent,
+                         FloatRegisters::TotalPhys>
+      FPUArray;
+
+ protected:  // Silence Clang warning.
+  GPRArray regs_;
+  FPUArray fpregs_;
+
+ public:
+  static size_t offsetOfRegister(Register reg) {
+    return offsetof(RegisterDump, regs_) + reg.code() * sizeof(uintptr_t);
+  }
+  static size_t offsetOfRegister(FloatRegister reg) {
+    return offsetof(RegisterDump, fpregs_) + reg.getRegisterDumpOffsetInBytes();
+  }
+};
+
+// Class for mapping each register to an offset.
+class RegisterOffsets {
+  mozilla::Array<uint32_t, Registers::Total> offsets_;
+
+  // Sentinel value representing an uninitialized offset.
+  static constexpr uint32_t InvalidOffset = UINT32_MAX;
+
+ public:
+  RegisterOffsets() {
+    for (size_t i = 0; i < Registers::Total; i++) {
+      offsets_[i] = InvalidOffset;
+    }
+  }
+
+  RegisterOffsets(const RegisterOffsets&) = delete;
+  void operator=(const RegisterOffsets&) = delete;
+
+  bool hasOffset(Register reg) const {
+    return offsets_[reg.code()] != InvalidOffset;
+  }
+  uint32_t getOffset(Register reg) const {
+    MOZ_ASSERT(hasOffset(reg));
+    return offsets_[reg.code()];
+  }
+  void setOffset(Register reg, size_t offset) {
+    MOZ_ASSERT(offset < InvalidOffset);
+    offsets_[reg.code()] = uint32_t(offset);
+  }
+};
+
+class MacroAssembler;
+
+// Declares a register as owned within the scope of the object.
+// In debug mode, owned register state is tracked within the MacroAssembler,
+// and an assert will fire if ownership is conflicting.
+// In contrast to ARM64's UseScratchRegisterScope, this class has no overhead
+// in non-debug builds.
+template <class RegisterType>
+struct AutoGenericRegisterScope : public RegisterType {
+  // Prevent MacroAssembler templates from creating copies,
+  // which causes the destructor to fire more than once.
+  AutoGenericRegisterScope(const AutoGenericRegisterScope& other) = delete;
+
+#ifdef DEBUG
+  MacroAssembler& masm_;
+  bool released_;
+  explicit AutoGenericRegisterScope(MacroAssembler& masm, RegisterType reg);
+  ~AutoGenericRegisterScope();
+  void release();
+  void reacquire();
+#else
+  constexpr explicit AutoGenericRegisterScope(MacroAssembler& masm,
+                                              RegisterType reg)
+      : RegisterType(reg) {}
+  void release() {}
+  void reacquire() {}
+#endif
+};
+
+using AutoRegisterScope = AutoGenericRegisterScope<Register>;
+using AutoFloatRegisterScope = AutoGenericRegisterScope<FloatRegister>;
+
+}  // namespace jit
+}  // namespace js
+
+#endif /* jit_Registers_h */