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diff --git a/llvm/lib/Target/X86/X86MacroFusion.cpp b/llvm/lib/Target/X86/X86MacroFusion.cpp
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+++ b/llvm/lib/Target/X86/X86MacroFusion.cpp
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+//===- X86MacroFusion.cpp - X86 Macro Fusion ------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file This file contains the X86 implementation of the DAG scheduling
+/// mutation to pair instructions back to back.
+//
+//===----------------------------------------------------------------------===//
+
+#include "X86MacroFusion.h"
+#include "X86Subtarget.h"
+#include "llvm/CodeGen/MacroFusion.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+
+using namespace llvm;
+
+namespace {
+
+// The classification for the first instruction.
+enum class FirstInstrKind { Test, Cmp, And, ALU, IncDec, Invalid };
+
+// The classification for the second instruction (jump).
+enum class JumpKind {
+  // JE, JL, JG and variants.
+  ELG,
+  // JA, JB and variants.
+  AB,
+  // JS, JP, JO and variants.
+  SPO,
+  // Not a fusable jump.
+  Invalid,
+};
+
+} // namespace
+
+static FirstInstrKind classifyFirst(const MachineInstr &MI) {
+  switch (MI.getOpcode()) {
+  default:
+    return FirstInstrKind::Invalid;
+  case X86::TEST8rr:
+  case X86::TEST16rr:
+  case X86::TEST32rr:
+  case X86::TEST64rr:
+  case X86::TEST8ri:
+  case X86::TEST16ri:
+  case X86::TEST32ri:
+  case X86::TEST64ri32:
+  case X86::TEST8mr:
+  case X86::TEST16mr:
+  case X86::TEST32mr:
+  case X86::TEST64mr:
+    return FirstInstrKind::Test;
+  case X86::AND16ri:
+  case X86::AND16ri8:
+  case X86::AND16rm:
+  case X86::AND16rr:
+  case X86::AND32ri:
+  case X86::AND32ri8:
+  case X86::AND32rm:
+  case X86::AND32rr:
+  case X86::AND64ri32:
+  case X86::AND64ri8:
+  case X86::AND64rm:
+  case X86::AND64rr:
+  case X86::AND8ri:
+  case X86::AND8rm:
+  case X86::AND8rr:
+    return FirstInstrKind::And;
+  case X86::CMP16ri:
+  case X86::CMP16ri8:
+  case X86::CMP16rm:
+  case X86::CMP16rr:
+  case X86::CMP16mr:
+  case X86::CMP32ri:
+  case X86::CMP32ri8:
+  case X86::CMP32rm:
+  case X86::CMP32rr:
+  case X86::CMP32mr:
+  case X86::CMP64ri32:
+  case X86::CMP64ri8:
+  case X86::CMP64rm:
+  case X86::CMP64rr:
+  case X86::CMP64mr:
+  case X86::CMP8ri:
+  case X86::CMP8rm:
+  case X86::CMP8rr:
+  case X86::CMP8mr:
+    return FirstInstrKind::Cmp;
+  case X86::ADD16ri:
+  case X86::ADD16ri8:
+  case X86::ADD16ri8_DB:
+  case X86::ADD16ri_DB:
+  case X86::ADD16rm:
+  case X86::ADD16rr:
+  case X86::ADD16rr_DB:
+  case X86::ADD32ri:
+  case X86::ADD32ri8:
+  case X86::ADD32ri8_DB:
+  case X86::ADD32ri_DB:
+  case X86::ADD32rm:
+  case X86::ADD32rr:
+  case X86::ADD32rr_DB:
+  case X86::ADD64ri32:
+  case X86::ADD64ri32_DB:
+  case X86::ADD64ri8:
+  case X86::ADD64ri8_DB:
+  case X86::ADD64rm:
+  case X86::ADD64rr:
+  case X86::ADD64rr_DB:
+  case X86::ADD8ri:
+  case X86::ADD8ri_DB:
+  case X86::ADD8rm:
+  case X86::ADD8rr:
+  case X86::ADD8rr_DB:
+  case X86::SUB16ri:
+  case X86::SUB16ri8:
+  case X86::SUB16rm:
+  case X86::SUB16rr:
+  case X86::SUB32ri:
+  case X86::SUB32ri8:
+  case X86::SUB32rm:
+  case X86::SUB32rr:
+  case X86::SUB64ri32:
+  case X86::SUB64ri8:
+  case X86::SUB64rm:
+  case X86::SUB64rr:
+  case X86::SUB8ri:
+  case X86::SUB8rm:
+  case X86::SUB8rr:
+    return FirstInstrKind::ALU;
+  case X86::INC16r:
+  case X86::INC32r:
+  case X86::INC64r:
+  case X86::INC8r:
+  case X86::DEC16r:
+  case X86::DEC32r:
+  case X86::DEC64r:
+  case X86::DEC8r:
+    return FirstInstrKind::IncDec;
+  }
+}
+
+static JumpKind classifySecond(const MachineInstr &MI) {
+  X86::CondCode CC = X86::getCondFromBranch(MI);
+  if (CC == X86::COND_INVALID)
+    return JumpKind::Invalid;
+
+  switch (CC) {
+  default:
+    return JumpKind::Invalid;
+  case X86::COND_E:
+  case X86::COND_NE:
+  case X86::COND_L:
+  case X86::COND_LE:
+  case X86::COND_G:
+  case X86::COND_GE:
+    return JumpKind::ELG;
+  case X86::COND_B:
+  case X86::COND_BE:
+  case X86::COND_A:
+  case X86::COND_AE:
+    return JumpKind::AB;
+  case X86::COND_S:
+  case X86::COND_NS:
+  case X86::COND_P:
+  case X86::COND_NP:
+  case X86::COND_O:
+  case X86::COND_NO:
+    return JumpKind::SPO;
+  }
+}
+
+/// Check if the instr pair, FirstMI and SecondMI, should be fused
+/// together. Given SecondMI, when FirstMI is unspecified, then check if
+/// SecondMI may be part of a fused pair at all.
+static bool shouldScheduleAdjacent(const TargetInstrInfo &TII,
+                                   const TargetSubtargetInfo &TSI,
+                                   const MachineInstr *FirstMI,
+                                   const MachineInstr &SecondMI) {
+  const X86Subtarget &ST = static_cast<const X86Subtarget &>(TSI);
+
+  // Check if this processor supports any kind of fusion.
+  if (!(ST.hasBranchFusion() || ST.hasMacroFusion()))
+    return false;
+
+  const JumpKind BranchKind = classifySecond(SecondMI);
+
+  if (BranchKind == JumpKind::Invalid)
+    return false; // Second cannot be fused with anything.
+
+  if (FirstMI == nullptr)
+    return true; // We're only checking whether Second can be fused at all.
+
+  const FirstInstrKind TestKind = classifyFirst(*FirstMI);
+
+  if (ST.hasBranchFusion()) {
+    // Branch fusion can merge CMP and TEST with all conditional jumps.
+    return (TestKind == FirstInstrKind::Cmp ||
+            TestKind == FirstInstrKind::Test);
+  }
+
+  if (ST.hasMacroFusion()) {
+    // Macro Fusion rules are a bit more complex. See Agner Fog's
+    // Microarchitecture table 9.2 "Instruction Fusion".
+    switch (TestKind) {
+    case FirstInstrKind::Test:
+    case FirstInstrKind::And:
+      return true;
+    case FirstInstrKind::Cmp:
+    case FirstInstrKind::ALU:
+      return BranchKind == JumpKind::ELG || BranchKind == JumpKind::AB;
+    case FirstInstrKind::IncDec:
+      return BranchKind == JumpKind::ELG;
+    case FirstInstrKind::Invalid:
+      return false;
+    }
+  }
+
+  llvm_unreachable("unknown branch fusion type");
+}
+
+namespace llvm {
+
+std::unique_ptr<ScheduleDAGMutation>
+createX86MacroFusionDAGMutation () {
+  return createBranchMacroFusionDAGMutation(shouldScheduleAdjacent);
+}
+
+} // end namespace llvm