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diff --git a/llvm/lib/CodeGen/LiveRangeShrink.cpp b/llvm/lib/CodeGen/LiveRangeShrink.cpp
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+++ b/llvm/lib/CodeGen/LiveRangeShrink.cpp
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+//===- LiveRangeShrink.cpp - Move instructions to shrink live range -------===//
+//
+// 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 pass moves instructions close to the definition of its operands to
+/// shrink live range of the def instruction. The code motion is limited within
+/// the basic block. The moved instruction should have 1 def, and more than one
+/// uses, all of which are the only use of the def.
+///
+///===---------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetRegisterInfo.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <iterator>
+#include <utility>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "lrshrink"
+
+STATISTIC(NumInstrsHoistedToShrinkLiveRange,
+          "Number of insructions hoisted to shrink live range.");
+
+namespace {
+
+class LiveRangeShrink : public MachineFunctionPass {
+public:
+  static char ID;
+
+  LiveRangeShrink() : MachineFunctionPass(ID) {
+    initializeLiveRangeShrinkPass(*PassRegistry::getPassRegistry());
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  StringRef getPassName() const override { return "Live Range Shrink"; }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+
+} // end anonymous namespace
+
+char LiveRangeShrink::ID = 0;
+
+char &llvm::LiveRangeShrinkID = LiveRangeShrink::ID;
+
+INITIALIZE_PASS(LiveRangeShrink, "lrshrink", "Live Range Shrink Pass", false,
+                false)
+
+using InstOrderMap = DenseMap<MachineInstr *, unsigned>;
+
+/// Returns \p New if it's dominated by \p Old, otherwise return \p Old.
+/// \p M maintains a map from instruction to its dominating order that satisfies
+/// M[A] > M[B] guarantees that A is dominated by B.
+/// If \p New is not in \p M, return \p Old. Otherwise if \p Old is null, return
+/// \p New.
+static MachineInstr *FindDominatedInstruction(MachineInstr &New,
+                                              MachineInstr *Old,
+                                              const InstOrderMap &M) {
+  auto NewIter = M.find(&New);
+  if (NewIter == M.end())
+    return Old;
+  if (Old == nullptr)
+    return &New;
+  unsigned OrderOld = M.find(Old)->second;
+  unsigned OrderNew = NewIter->second;
+  if (OrderOld != OrderNew)
+    return OrderOld < OrderNew ? &New : Old;
+  // OrderOld == OrderNew, we need to iterate down from Old to see if it
+  // can reach New, if yes, New is dominated by Old.
+  for (MachineInstr *I = Old->getNextNode(); M.find(I)->second == OrderNew;
+       I = I->getNextNode())
+    if (I == &New)
+      return &New;
+  return Old;
+}
+
+/// Builds Instruction to its dominating order number map \p M by traversing
+/// from instruction \p Start.
+static void BuildInstOrderMap(MachineBasicBlock::iterator Start,
+                              InstOrderMap &M) {
+  M.clear();
+  unsigned i = 0;
+  for (MachineInstr &I : make_range(Start, Start->getParent()->end()))
+    M[&I] = i++;
+}
+
+bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
+  if (skipFunction(MF.getFunction()))
+    return false;
+
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+
+  LLVM_DEBUG(dbgs() << "**** Analysing " << MF.getName() << '\n');
+
+  InstOrderMap IOM;
+  // Map from register to instruction order (value of IOM) where the
+  // register is used last. When moving instructions up, we need to
+  // make sure all its defs (including dead def) will not cross its
+  // last use when moving up.
+  DenseMap<unsigned, std::pair<unsigned, MachineInstr *>> UseMap;
+
+  for (MachineBasicBlock &MBB : MF) {
+    if (MBB.empty())
+      continue;
+    bool SawStore = false;
+    BuildInstOrderMap(MBB.begin(), IOM);
+    UseMap.clear();
+
+    for (MachineBasicBlock::iterator Next = MBB.begin(); Next != MBB.end();) {
+      MachineInstr &MI = *Next;
+      ++Next;
+      if (MI.isPHI() || MI.isDebugInstr())
+        continue;
+      if (MI.mayStore())
+        SawStore = true;
+
+      unsigned CurrentOrder = IOM[&MI];
+      unsigned Barrier = 0;
+      MachineInstr *BarrierMI = nullptr;
+      for (const MachineOperand &MO : MI.operands()) {
+        if (!MO.isReg() || MO.isDebug())
+          continue;
+        if (MO.isUse())
+          UseMap[MO.getReg()] = std::make_pair(CurrentOrder, &MI);
+        else if (MO.isDead() && UseMap.count(MO.getReg()))
+          // Barrier is the last instruction where MO get used. MI should not
+          // be moved above Barrier.
+          if (Barrier < UseMap[MO.getReg()].first) {
+            Barrier = UseMap[MO.getReg()].first;
+            BarrierMI = UseMap[MO.getReg()].second;
+          }
+      }
+
+      if (!MI.isSafeToMove(nullptr, SawStore)) {
+        // If MI has side effects, it should become a barrier for code motion.
+        // IOM is rebuild from the next instruction to prevent later
+        // instructions from being moved before this MI.
+        if (MI.hasUnmodeledSideEffects() && Next != MBB.end()) {
+          BuildInstOrderMap(Next, IOM);
+          SawStore = false;
+        }
+        continue;
+      }
+
+      const MachineOperand *DefMO = nullptr;
+      MachineInstr *Insert = nullptr;
+
+      // Number of live-ranges that will be shortened. We do not count
+      // live-ranges that are defined by a COPY as it could be coalesced later.
+      unsigned NumEligibleUse = 0;
+
+      for (const MachineOperand &MO : MI.operands()) {
+        if (!MO.isReg() || MO.isDead() || MO.isDebug())
+          continue;
+        unsigned Reg = MO.getReg();
+        // Do not move the instruction if it def/uses a physical register,
+        // unless it is a constant physical register or a noreg.
+        if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
+          if (!Reg || MRI.isConstantPhysReg(Reg))
+            continue;
+          Insert = nullptr;
+          break;
+        }
+        if (MO.isDef()) {
+          // Do not move if there is more than one def.
+          if (DefMO) {
+            Insert = nullptr;
+            break;
+          }
+          DefMO = &MO;
+        } else if (MRI.hasOneNonDBGUse(Reg) && MRI.hasOneDef(Reg) && DefMO &&
+                   MRI.getRegClass(DefMO->getReg()) ==
+                       MRI.getRegClass(MO.getReg())) {
+          // The heuristic does not handle different register classes yet
+          // (registers of different sizes, looser/tighter constraints). This
+          // is because it needs more accurate model to handle register
+          // pressure correctly.
+          MachineInstr &DefInstr = *MRI.def_instr_begin(Reg);
+          if (!DefInstr.isCopy())
+            NumEligibleUse++;
+          Insert = FindDominatedInstruction(DefInstr, Insert, IOM);
+        } else {
+          Insert = nullptr;
+          break;
+        }
+      }
+
+      // If Barrier equals IOM[I], traverse forward to find if BarrierMI is
+      // after Insert, if yes, then we should not hoist.
+      for (MachineInstr *I = Insert; I && IOM[I] == Barrier;
+           I = I->getNextNode())
+        if (I == BarrierMI) {
+          Insert = nullptr;
+          break;
+        }
+      // Move the instruction when # of shrunk live range > 1.
+      if (DefMO && Insert && NumEligibleUse > 1 && Barrier <= IOM[Insert]) {
+        MachineBasicBlock::iterator I = std::next(Insert->getIterator());
+        // Skip all the PHI and debug instructions.
+        while (I != MBB.end() && (I->isPHI() || I->isDebugInstr()))
+          I = std::next(I);
+        if (I == MI.getIterator())
+          continue;
+
+        // Update the dominator order to be the same as the insertion point.
+        // We do this to maintain a non-decreasing order without need to update
+        // all instruction orders after the insertion point.
+        unsigned NewOrder = IOM[&*I];
+        IOM[&MI] = NewOrder;
+        NumInstrsHoistedToShrinkLiveRange++;
+
+        // Find MI's debug value following MI.
+        MachineBasicBlock::iterator EndIter = std::next(MI.getIterator());
+        if (MI.getOperand(0).isReg())
+          for (; EndIter != MBB.end() && EndIter->isDebugValue() &&
+                 EndIter->getOperand(0).isReg() &&
+                 EndIter->getOperand(0).getReg() == MI.getOperand(0).getReg();
+               ++EndIter, ++Next)
+            IOM[&*EndIter] = NewOrder;
+        MBB.splice(I, &MBB, MI.getIterator(), EndIter);
+      }
+    }
+  }
+  return false;
+}