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diff --git a/llvm/lib/Target/AArch64/AArch64MIPeepholeOpt.cpp b/llvm/lib/Target/AArch64/AArch64MIPeepholeOpt.cpp
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+++ b/llvm/lib/Target/AArch64/AArch64MIPeepholeOpt.cpp
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+//===- AArch64MIPeepholeOpt.cpp - AArch64 MI peephole optimization pass ---===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs below peephole optimizations on MIR level.
+//
+// 1. MOVi32imm + ANDWrr ==> ANDWri + ANDWri
+//    MOVi64imm + ANDXrr ==> ANDXri + ANDXri
+//
+//    The mov pseudo instruction could be expanded to multiple mov instructions
+//    later. In this case, we could try to split the constant  operand of mov
+//    instruction into two bitmask immediates. It makes two AND instructions
+//    intead of multiple `mov` + `and` instructions.
+//
+// 2. Remove redundant ORRWrs which is generated by zero-extend.
+//
+//    %3:gpr32 = ORRWrs $wzr, %2, 0
+//    %4:gpr64 = SUBREG_TO_REG 0, %3, %subreg.sub_32
+//
+//    If AArch64's 32-bit form of instruction defines the source operand of
+//    ORRWrs, we can remove the ORRWrs because the upper 32 bits of the source
+//    operand are set to zero.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AArch64ExpandImm.h"
+#include "AArch64InstrInfo.h"
+#include "MCTargetDesc/AArch64AddressingModes.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "aarch64-mi-peephole-opt"
+
+namespace {
+
+struct AArch64MIPeepholeOpt : public MachineFunctionPass {
+  static char ID;
+
+  AArch64MIPeepholeOpt() : MachineFunctionPass(ID) {
+    initializeAArch64MIPeepholeOptPass(*PassRegistry::getPassRegistry());
+  }
+
+  const AArch64InstrInfo *TII;
+  MachineLoopInfo *MLI;
+  MachineRegisterInfo *MRI;
+
+  template <typename T>
+  bool visitAND(MachineInstr &MI,
+                SmallSetVector<MachineInstr *, 8> &ToBeRemoved);
+  bool visitORR(MachineInstr &MI,
+                SmallSetVector<MachineInstr *, 8> &ToBeRemoved);
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  StringRef getPassName() const override {
+    return "AArch64 MI Peephole Optimization pass";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<MachineLoopInfo>();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+};
+
+char AArch64MIPeepholeOpt::ID = 0;
+
+} // end anonymous namespace
+
+INITIALIZE_PASS(AArch64MIPeepholeOpt, "aarch64-mi-peephole-opt",
+                "AArch64 MI Peephole Optimization", false, false)
+
+template <typename T>
+static bool splitBitmaskImm(T Imm, unsigned RegSize, T &Imm1Enc, T &Imm2Enc) {
+  T UImm = static_cast<T>(Imm);
+  if (AArch64_AM::isLogicalImmediate(UImm, RegSize))
+    return false;
+
+  // If this immediate can be handled by one instruction, do not split it.
+  SmallVector<AArch64_IMM::ImmInsnModel, 4> Insn;
+  AArch64_IMM::expandMOVImm(UImm, RegSize, Insn);
+  if (Insn.size() == 1)
+    return false;
+
+  // The bitmask immediate consists of consecutive ones.  Let's say there is
+  // constant 0b00000000001000000000010000000000 which does not consist of
+  // consecutive ones. We can split it in to two bitmask immediate like
+  // 0b00000000001111111111110000000000 and 0b11111111111000000000011111111111.
+  // If we do AND with these two bitmask immediate, we can see original one.
+  unsigned LowestBitSet = countTrailingZeros(UImm);
+  unsigned HighestBitSet = Log2_64(UImm);
+
+  // Create a mask which is filled with one from the position of lowest bit set
+  // to the position of highest bit set.
+  T NewImm1 = (static_cast<T>(2) << HighestBitSet) -
+              (static_cast<T>(1) << LowestBitSet);
+  // Create a mask which is filled with one outside the position of lowest bit
+  // set and the position of highest bit set.
+  T NewImm2 = UImm | ~NewImm1;
+
+  // If the split value is not valid bitmask immediate, do not split this
+  // constant.
+  if (!AArch64_AM::isLogicalImmediate(NewImm2, RegSize))
+    return false;
+
+  Imm1Enc = AArch64_AM::encodeLogicalImmediate(NewImm1, RegSize);
+  Imm2Enc = AArch64_AM::encodeLogicalImmediate(NewImm2, RegSize);
+  return true;
+}
+
+template <typename T>
+bool AArch64MIPeepholeOpt::visitAND(
+    MachineInstr &MI, SmallSetVector<MachineInstr *, 8> &ToBeRemoved) {
+  // Try below transformation.
+  //
+  // MOVi32imm + ANDWrr ==> ANDWri + ANDWri
+  // MOVi64imm + ANDXrr ==> ANDXri + ANDXri
+  //
+  // The mov pseudo instruction could be expanded to multiple mov instructions
+  // later. Let's try to split the constant operand of mov instruction into two
+  // bitmask immediates. It makes only two AND instructions intead of multiple
+  // mov + and instructions.
+
+  unsigned RegSize = sizeof(T) * 8;
+  assert((RegSize == 32 || RegSize == 64) &&
+         "Invalid RegSize for AND bitmask peephole optimization");
+
+  // Check whether AND's MBB is in loop and the AND is loop invariant.
+  MachineBasicBlock *MBB = MI.getParent();
+  MachineLoop *L = MLI->getLoopFor(MBB);
+  if (L && !L->isLoopInvariant(MI))
+    return false;
+
+  // Check whether AND's operand is MOV with immediate.
+  MachineInstr *MovMI = MRI->getUniqueVRegDef(MI.getOperand(2).getReg());
+  if (!MovMI)
+    return false;
+
+  MachineInstr *SubregToRegMI = nullptr;
+  // If it is SUBREG_TO_REG, check its operand.
+  if (MovMI->getOpcode() == TargetOpcode::SUBREG_TO_REG) {
+    SubregToRegMI = MovMI;
+    MovMI = MRI->getUniqueVRegDef(MovMI->getOperand(2).getReg());
+    if (!MovMI)
+      return false;
+  }
+
+  if (MovMI->getOpcode() != AArch64::MOVi32imm &&
+      MovMI->getOpcode() != AArch64::MOVi64imm)
+    return false;
+
+  // If the MOV has multiple uses, do not split the immediate because it causes
+  // more instructions.
+  if (!MRI->hasOneUse(MovMI->getOperand(0).getReg()))
+    return false;
+
+  if (SubregToRegMI && !MRI->hasOneUse(SubregToRegMI->getOperand(0).getReg()))
+    return false;
+
+  // Split the bitmask immediate into two.
+  T UImm = static_cast<T>(MovMI->getOperand(1).getImm());
+  // For the 32 bit form of instruction, the upper 32 bits of the destination
+  // register are set to zero. If there is SUBREG_TO_REG, set the upper 32 bits
+  // of UImm to zero.
+  if (SubregToRegMI)
+    UImm &= 0xFFFFFFFF;
+  T Imm1Enc;
+  T Imm2Enc;
+  if (!splitBitmaskImm(UImm, RegSize, Imm1Enc, Imm2Enc))
+    return false;
+
+  // Create new AND MIs.
+  DebugLoc DL = MI.getDebugLoc();
+  const TargetRegisterClass *ANDImmRC =
+      (RegSize == 32) ? &AArch64::GPR32spRegClass : &AArch64::GPR64spRegClass;
+  Register DstReg = MI.getOperand(0).getReg();
+  Register SrcReg = MI.getOperand(1).getReg();
+  Register NewTmpReg = MRI->createVirtualRegister(ANDImmRC);
+  Register NewDstReg = MRI->createVirtualRegister(ANDImmRC);
+  unsigned Opcode = (RegSize == 32) ? AArch64::ANDWri : AArch64::ANDXri;
+
+  MRI->constrainRegClass(NewTmpReg, MRI->getRegClass(SrcReg));
+  BuildMI(*MBB, MI, DL, TII->get(Opcode), NewTmpReg)
+      .addReg(SrcReg)
+      .addImm(Imm1Enc);
+
+  MRI->constrainRegClass(NewDstReg, MRI->getRegClass(DstReg));
+  BuildMI(*MBB, MI, DL, TII->get(Opcode), NewDstReg)
+      .addReg(NewTmpReg)
+      .addImm(Imm2Enc);
+
+  MRI->replaceRegWith(DstReg, NewDstReg);
+  // replaceRegWith changes MI's definition register. Keep it for SSA form until
+  // deleting MI.
+  MI.getOperand(0).setReg(DstReg);
+
+  ToBeRemoved.insert(&MI);
+  if (SubregToRegMI)
+    ToBeRemoved.insert(SubregToRegMI);
+  ToBeRemoved.insert(MovMI);
+
+  return true;
+}
+
+bool AArch64MIPeepholeOpt::visitORR(
+    MachineInstr &MI, SmallSetVector<MachineInstr *, 8> &ToBeRemoved) {
+  // Check this ORR comes from below zero-extend pattern.
+  //
+  // def : Pat<(i64 (zext GPR32:$src)),
+  //           (SUBREG_TO_REG (i32 0), (ORRWrs WZR, GPR32:$src, 0), sub_32)>;
+  if (MI.getOperand(3).getImm() != 0)
+    return false;
+
+  if (MI.getOperand(1).getReg() != AArch64::WZR)
+    return false;
+
+  MachineInstr *SrcMI = MRI->getUniqueVRegDef(MI.getOperand(2).getReg());
+  if (!SrcMI)
+    return false;
+
+  // From https://developer.arm.com/documentation/dui0801/b/BABBGCAC
+  //
+  // When you use the 32-bit form of an instruction, the upper 32 bits of the
+  // source registers are ignored and the upper 32 bits of the destination
+  // register are set to zero.
+  //
+  // If AArch64's 32-bit form of instruction defines the source operand of
+  // zero-extend, we do not need the zero-extend. Let's check the MI's opcode is
+  // real AArch64 instruction and if it is not, do not process the opcode
+  // conservatively.
+  if (SrcMI->getOpcode() <= TargetOpcode::GENERIC_OP_END)
+    return false;
+
+  Register DefReg = MI.getOperand(0).getReg();
+  Register SrcReg = MI.getOperand(2).getReg();
+  MRI->replaceRegWith(DefReg, SrcReg);
+  MRI->clearKillFlags(SrcReg);
+  // replaceRegWith changes MI's definition register. Keep it for SSA form until
+  // deleting MI.
+  MI.getOperand(0).setReg(DefReg);
+  ToBeRemoved.insert(&MI);
+
+  LLVM_DEBUG({ dbgs() << "Removed: " << MI << "\n"; });
+
+  return true;
+}
+
+bool AArch64MIPeepholeOpt::runOnMachineFunction(MachineFunction &MF) {
+  if (skipFunction(MF.getFunction()))
+    return false;
+
+  TII = static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());
+  MLI = &getAnalysis<MachineLoopInfo>();
+  MRI = &MF.getRegInfo();
+
+  if (!MRI->isSSA())
+    return false;
+
+  bool Changed = false;
+  SmallSetVector<MachineInstr *, 8> ToBeRemoved;
+
+  for (MachineBasicBlock &MBB : MF) {
+    for (MachineInstr &MI : MBB) {
+      switch (MI.getOpcode()) {
+      default:
+        break;
+      case AArch64::ANDWrr:
+        Changed = visitAND<uint32_t>(MI, ToBeRemoved);
+        break;
+      case AArch64::ANDXrr:
+        Changed = visitAND<uint64_t>(MI, ToBeRemoved);
+        break;
+      case AArch64::ORRWrs:
+        Changed = visitORR(MI, ToBeRemoved);
+      }
+    }
+  }
+
+  for (MachineInstr *MI : ToBeRemoved)
+    MI->eraseFromParent();
+
+  return Changed;
+}
+
+FunctionPass *llvm::createAArch64MIPeepholeOptPass() {
+  return new AArch64MIPeepholeOpt();
+}