[PowerPC] Expand ISEL instruction into if-then-else sequence.

Generally, the ISEL is expanded into if-then-else sequence, in some
cases (like when the destination register is the same with the true
or false value register), it may just be expanded into just the if
or else sequence.

llvm-svn: 292154

8 files changed, 467 insertions, 14 deletions

diff --git a/llvm/lib/Target/PowerPC/CMakeLists.txt b/llvm/lib/Target/PowerPC/CMakeLists.txt
index 4842c3b7a65..7ca4c199900 100644
--- a/llvm/lib/Target/PowerPC/CMakeLists.txt
+++ b/llvm/lib/Target/PowerPC/CMakeLists.txt
@@ -40,6 +40,7 @@ add_llvm_target(PowerPCCodeGen
   PPCVSXCopy.cpp
   PPCVSXFMAMutate.cpp
   PPCVSXSwapRemoval.cpp
+  PPCExpandISEL.cpp
   )
 
 add_subdirectory(AsmParser)
diff --git a/llvm/lib/Target/PowerPC/PPC.h b/llvm/lib/Target/PowerPC/PPC.h
index e01f49dce81..38ae62b2675 100644
--- a/llvm/lib/Target/PowerPC/PPC.h
+++ b/llvm/lib/Target/PowerPC/PPC.h
@@ -45,11 +45,13 @@ namespace llvm {
   FunctionPass *createPPCISelDag(PPCTargetMachine &TM);
   FunctionPass *createPPCTLSDynamicCallPass();
   FunctionPass *createPPCBoolRetToIntPass();
+  FunctionPass *createPPCExpandISELPass();
   void LowerPPCMachineInstrToMCInst(const MachineInstr *MI, MCInst &OutMI,
                                     AsmPrinter &AP, bool isDarwin);
 
   void initializePPCVSXFMAMutatePass(PassRegistry&);
   void initializePPCBoolRetToIntPass(PassRegistry&);
+  void initializePPCExpandISELPass(PassRegistry &);
   extern char &PPCVSXFMAMutateID;
 
   namespace PPCII {
diff --git a/llvm/lib/Target/PowerPC/PPCExpandISEL.cpp b/llvm/lib/Target/PowerPC/PPCExpandISEL.cpp
new file mode 100644
index 00000000000..accb84a8094
--- /dev/null
+++ b/llvm/lib/Target/PowerPC/PPCExpandISEL.cpp
@@ -0,0 +1,456 @@
+//===------------- PPCExpandISEL.cpp - Expand ISEL instruction ------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// A pass that expands the ISEL instruction into an if-then-else sequence.
+// This pass must be run post-RA since all operands must be physical registers.
+//
+//===----------------------------------------------------------------------===//
+
+#include "PPC.h"
+#include "PPCInstrInfo.h"
+#include "PPCSubtarget.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/LivePhysRegs.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "ppc-expand-isel"
+
+STATISTIC(NumExpanded, "Number of ISEL instructions expanded");
+STATISTIC(NumRemoved, "Number of ISEL instructions removed");
+STATISTIC(NumFolded, "Number of ISEL instructions folded");
+
+// If -ppc-gen-isel=false is set, we will disable generating the ISEL
+// instruction on all PPC targets. Otherwise, if the user set option
+// -misel or the platform supports ISEL by default, still generate the
+// ISEL instruction, else expand it.
+static cl::opt<bool>
+    GenerateISEL("ppc-gen-isel",
+                 cl::desc("Enable generating the ISEL instruction."),
+                 cl::init(true), cl::Hidden);
+
+class PPCExpandISEL : public MachineFunctionPass {
+  DebugLoc dl;
+  MachineFunction *MF;
+  const TargetInstrInfo *TII;
+  bool IsTrueBlockRequired;
+  bool IsFalseBlockRequired;
+  MachineBasicBlock *TrueBlock;
+  MachineBasicBlock *FalseBlock;
+  MachineBasicBlock *NewSuccessor;
+  MachineBasicBlock::iterator TrueBlockI;
+  MachineBasicBlock::iterator FalseBlockI;
+
+  typedef SmallVector<MachineInstr *, 4> BlockISELList;
+  typedef SmallDenseMap<int, BlockISELList> ISELInstructionList;
+
+  // A map of MBB numbers to their lists of contained ISEL instructions.
+  ISELInstructionList ISELInstructions;
+
+  /// Initialize the object.
+  void initialize(MachineFunction &MFParam);
+
+  void handleSpecialCases(BlockISELList &BIL, MachineBasicBlock *MBB);
+  void reorganizeBlockLayout(BlockISELList &BIL, MachineBasicBlock *MBB);
+  void populateBlocks(BlockISELList &BIL);
+  void expandMergeableISELs(BlockISELList &BIL);
+  void expandAndMergeISELs();
+
+  bool canMerge(MachineInstr *PrevPushedMI, MachineInstr *MI);
+
+  ///  Is this instruction an ISEL or ISEL8?
+  static bool isISEL(const MachineInstr &MI) {
+    return (MI.getOpcode() == PPC::ISEL || MI.getOpcode() == PPC::ISEL8);
+  }
+
+  ///  Is this instruction an ISEL8?
+  static bool isISEL8(const MachineInstr &MI) {
+    return (MI.getOpcode() == PPC::ISEL8);
+  }
+
+  /// Are the two operands using the same register?
+  bool useSameRegister(const MachineOperand &Op1, const MachineOperand &Op2) {
+    return (Op1.getReg() == Op2.getReg());
+  }
+
+  ///
+  ///  Collect all ISEL instructions from the current function.
+  ///
+  /// Walk the current function and collect all the ISEL instructions that are
+  /// found. The instructions are placed in the ISELInstructions vector.
+  ///
+  /// \return true if any ISEL instructions were found, false otherwise
+  ///
+  bool collectISELInstructions();
+
+public:
+  static char ID;
+  PPCExpandISEL() : MachineFunctionPass(ID) {
+    initializePPCExpandISELPass(*PassRegistry::getPassRegistry());
+  }
+
+  ///
+  ///  Determine whether to generate the ISEL instruction or expand it.
+  ///
+  /// Expand ISEL instruction into if-then-else sequence when one of
+  /// the following two conditions hold:
+  /// (1) -ppc-gen-isel=false
+  /// (2) hasISEL() return false
+  /// Otherwise, still generate ISEL instruction.
+  /// The -ppc-gen-isel option is set to true by default. Which means the ISEL
+  /// instruction is still generated by default on targets that support them.
+  ///
+  /// \return true if ISEL should be expanded into if-then-else code sequence;
+  ///         false if ISEL instruction should be generated, i.e. not expaned.
+  ///
+  static bool isExpandISELEnabled(const MachineFunction &MF);
+
+#ifndef NDEBUG
+  void DumpISELInstructions() const;
+#endif
+
+  bool runOnMachineFunction(MachineFunction &MF) override {
+    if (!isExpandISELEnabled(MF))
+      return false;
+
+    DEBUG(dbgs() << "Function: "; MF.dump(); dbgs() << "\n");
+    initialize(MF);
+
+    if (!collectISELInstructions()) {
+      DEBUG(dbgs() << "No ISEL instructions in this function\n");
+      return false;
+    }
+
+#ifndef NDEBUG
+    DumpISELInstructions();
+#endif
+
+    expandAndMergeISELs();
+
+    return true;
+  }
+};
+
+void PPCExpandISEL::initialize(MachineFunction &MFParam) {
+  MF = &MFParam;
+  TII = MF->getSubtarget().getInstrInfo();
+  ISELInstructions.clear();
+}
+
+bool PPCExpandISEL::isExpandISELEnabled(const MachineFunction &MF) {
+  return !GenerateISEL || !MF.getSubtarget<PPCSubtarget>().hasISEL();
+}
+
+bool PPCExpandISEL::collectISELInstructions() {
+  for (MachineBasicBlock &MBB : *MF) {
+    BlockISELList thisBlockISELs;
+    for (MachineInstr &MI : MBB)
+      if (isISEL(MI))
+        thisBlockISELs.push_back(&MI);
+    if (!thisBlockISELs.empty())
+      ISELInstructions.insert(std::make_pair(MBB.getNumber(), thisBlockISELs));
+  }
+  return !ISELInstructions.empty();
+}
+
+#ifndef NDEBUG
+void PPCExpandISEL::DumpISELInstructions() const {
+  for (const auto &I : ISELInstructions) {
+    DEBUG(dbgs() << "BB#" << I.first << ":\n");
+    for (const auto &VI : I.second)
+      DEBUG(dbgs() << "    "; VI->print(dbgs()));
+  }
+}
+#endif
+
+/// Contiguous ISELs that have the same condition can be merged.
+bool PPCExpandISEL::canMerge(MachineInstr *PrevPushedMI, MachineInstr *MI) {
+  // Same Condition Register?
+  if (!useSameRegister(PrevPushedMI->getOperand(3), MI->getOperand(3)))
+    return false;
+
+  MachineBasicBlock::iterator PrevPushedMBBI = *PrevPushedMI;
+  MachineBasicBlock::iterator MBBI = *MI;
+  return (std::prev(MBBI) == PrevPushedMBBI); // Contiguous ISELs?
+}
+
+void PPCExpandISEL::expandAndMergeISELs() {
+  for (auto &BlockList : ISELInstructions) {
+    DEBUG(dbgs() << "Expanding ISEL instructions in BB#" << BlockList.first
+                 << "\n");
+
+    BlockISELList &CurrentISELList = BlockList.second;
+    auto I = CurrentISELList.begin();
+    auto E = CurrentISELList.end();
+
+    while (I != E) {
+      BlockISELList SubISELList;
+
+      SubISELList.push_back(*I++);
+
+      // Collect the ISELs that can be merged together.
+      while (I != E && canMerge(SubISELList.back(), *I))
+        SubISELList.push_back(*I++);
+
+      expandMergeableISELs(SubISELList);
+    }
+  }
+}
+
+void PPCExpandISEL::handleSpecialCases(BlockISELList &BIL,
+                                       MachineBasicBlock *MBB) {
+  IsTrueBlockRequired = false;
+  IsFalseBlockRequired = false;
+
+  auto MI = BIL.begin();
+  while (MI != BIL.end()) {
+    assert(isISEL(**MI) && "Expecting an ISEL instruction");
+    DEBUG(dbgs() << "ISEL: " << **MI << "\n");
+
+    MachineOperand &Dest = (*MI)->getOperand(0);
+    MachineOperand &TrueValue = (*MI)->getOperand(1);
+    MachineOperand &FalseValue = (*MI)->getOperand(2);
+
+    // If at least one of the ISEL instructions satisfy the following
+    // condition, we need the True Block:
+    // The Dest Register and True Value Register are not the same
+    // Similarly, if at least one of the ISEL instructions satisfy the
+    // following condition, we need the False Block:
+    // The Dest Register and False Value Register are not the same.
+
+    bool IsADDIInstRequired = !useSameRegister(Dest, TrueValue);
+    bool IsORIInstRequired = !useSameRegister(Dest, FalseValue);
+
+    // Special case 1, all registers used by ISEL are the same one.
+    if (!IsADDIInstRequired && !IsORIInstRequired) {
+      DEBUG(dbgs() << "Remove redudant ISEL instruction.");
+      NumRemoved++;
+      (*MI)->eraseFromParent();
+      // Setting MI to the erase result keeps the iterator valid and increased.
+      MI = BIL.erase(MI);
+      continue;
+    }
+
+    // Special case 2, the two input registers used by ISEL are the same.
+    // Note 1: We favor merging ISEL expansions over folding a single one. If
+    // the passed list has multiple merge-able ISEL's, we won't fold any.
+    // Note 2: There is no need to test for PPC::R0/PPC::X0 because PPC::ZERO/
+    // PPC::ZERO8 will be used for the first operand if the value is meant to
+    // be zero. In this case, the useSameRegister method will return false,
+    // thereby preventing this ISEL from being folded.
+
+    if (useSameRegister(TrueValue, FalseValue) && (BIL.size() == 1)) {
+      DEBUG(dbgs() << "Fold the ISEL instruction to an unconditonal copy.");
+      NumFolded++;
+      BuildMI(*MBB, (*MI), dl, TII->get(isISEL8(**MI) ? PPC::ADDI8 : PPC::ADDI))
+          .add(Dest)
+          .add(TrueValue)
+          .add(MachineOperand::CreateImm(0));
+      (*MI)->eraseFromParent();
+      // Setting MI to the erase result keeps the iterator valid and increased.
+      MI = BIL.erase(MI);
+      continue;
+    }
+
+    IsTrueBlockRequired |= IsADDIInstRequired;
+    IsFalseBlockRequired |= IsORIInstRequired;
+    MI++;
+  }
+}
+
+void PPCExpandISEL::reorganizeBlockLayout(BlockISELList &BIL,
+                                          MachineBasicBlock *MBB) {
+  if (BIL.empty())
+    return;
+
+  assert((IsTrueBlockRequired || IsFalseBlockRequired) &&
+         "Should have been handled by special cases earlier!");
+
+  MachineBasicBlock *Successor = nullptr;
+  const BasicBlock *LLVM_BB = MBB->getBasicBlock();
+  MachineBasicBlock::iterator MBBI = (*BIL.back());
+  NewSuccessor = (MBBI != MBB->getLastNonDebugInstr() || !MBB->canFallThrough())
+                     // Another BB is needed to move the instructions that
+                     // follow this ISEL.  If the ISEL is the last instruction
+                     // in a block that can't fall through, we also need a block
+                     // to branch to.
+                     ? MF->CreateMachineBasicBlock(LLVM_BB)
+                     : nullptr;
+
+  MachineFunction::iterator It = MBB->getIterator();
+  ++It; // Point to the successor block of MBB.
+
+  // If NewSuccessor is NULL then the last ISEL in this group is the last
+  // non-debug instruction in this block. Find the fall-through successor
+  // of this block to use when updating the CFG below.
+  if (!NewSuccessor) {
+    for (auto &Succ : MBB->successors()) {
+      if (MBB->isLayoutSuccessor(Succ)) {
+        Successor = Succ;
+        break;
+      }
+    }
+  } else
+    Successor = NewSuccessor;
+
+  // The FalseBlock and TrueBlock are inserted after the MBB block but before
+  // its successor.
+  // Note this need to be done *after* the above setting the Successor code.
+  if (IsFalseBlockRequired) {
+    FalseBlock = MF->CreateMachineBasicBlock(LLVM_BB);
+    MF->insert(It, FalseBlock);
+  }
+
+  if (IsTrueBlockRequired) {
+    TrueBlock = MF->CreateMachineBasicBlock(LLVM_BB);
+    MF->insert(It, TrueBlock);
+  }
+
+  if (NewSuccessor) {
+    MF->insert(It, NewSuccessor);
+
+    // Transfer the rest of this block into the new successor block.
+    NewSuccessor->splice(NewSuccessor->end(), MBB,
+                         std::next(MachineBasicBlock::iterator(BIL.back())),
+                         MBB->end());
+    NewSuccessor->transferSuccessorsAndUpdatePHIs(MBB);
+
+    // Copy the original liveIns of MBB to NewSuccessor.
+    for (auto &LI : MBB->liveins())
+      NewSuccessor->addLiveIn(LI);
+
+    // After splitting the NewSuccessor block, Regs defined but not killed
+    // in MBB should be treated as liveins of NewSuccessor.
+    // Note: Cannot use stepBackward instead since we are using the Reg
+    // liveness state at the end of MBB (liveOut of MBB) as the liveIn for
+    // NewSuccessor. Otherwise, will cause cyclic dependence.
+    LivePhysRegs LPR(MF->getSubtarget<PPCSubtarget>().getRegisterInfo());
+    SmallVector<std::pair<unsigned, const MachineOperand *>, 2> Clobbers;
+    for (MachineInstr &MI : *MBB)
+      LPR.stepForward(MI, Clobbers);
+    for (auto &LI : LPR)
+      NewSuccessor->addLiveIn(LI);
+  } else {
+    // Remove successor from MBB.
+    MBB->removeSuccessor(Successor);
+  }
+
+  // Note that this needs to be done *after* transfering the successors from MBB
+  // to the NewSuccessor block, otherwise these blocks will also be transferred
+  // as successors!
+  MBB->addSuccessor(IsTrueBlockRequired ? TrueBlock : Successor);
+  MBB->addSuccessor(IsFalseBlockRequired ? FalseBlock : Successor);
+
+  if (IsTrueBlockRequired) {
+    TrueBlockI = TrueBlock->begin();
+    TrueBlock->addSuccessor(Successor);
+  }
+
+  if (IsFalseBlockRequired) {
+    FalseBlockI = FalseBlock->begin();
+    FalseBlock->addSuccessor(Successor);
+  }
+
+  // Conditional branch to the TrueBlock or Successor
+  BuildMI(*MBB, BIL.back(), dl, TII->get(PPC::BC))
+      .add(BIL.back()->getOperand(3))
+      .addMBB(IsTrueBlockRequired ? TrueBlock : Successor);
+
+  // Jump over the true block to the new successor if the condition is false.
+  BuildMI(*(IsFalseBlockRequired ? FalseBlock : MBB),
+          (IsFalseBlockRequired ? FalseBlockI : BIL.back()), dl,
+          TII->get(PPC::B))
+      .addMBB(Successor);
+
+  if (IsFalseBlockRequired)
+    FalseBlockI = FalseBlock->begin(); // get the position of PPC::B
+}
+
+void PPCExpandISEL::populateBlocks(BlockISELList &BIL) {
+  for (auto &MI : BIL) {
+    assert(isISEL(*MI) && "Expecting an ISEL instruction");
+
+    MachineOperand &Dest = MI->getOperand(0);       // location to store to
+    MachineOperand &TrueValue = MI->getOperand(1);  // Value to store if
+                                                       // condition is true
+    MachineOperand &FalseValue = MI->getOperand(2); // Value to store if
+                                                       // condition is false
+    MachineOperand &ConditionRegister = MI->getOperand(3); // Condition
+
+    DEBUG(dbgs() << "Dest: " << Dest << "\n");
+    DEBUG(dbgs() << "TrueValue: " << TrueValue << "\n");
+    DEBUG(dbgs() << "FalseValue: " << FalseValue << "\n");
+    DEBUG(dbgs() << "ConditionRegister: " << ConditionRegister << "\n");
+
+
+    // If the Dest Register and True Value Register are not the same one, we
+    // need the True Block.
+    bool IsADDIInstRequired = !useSameRegister(Dest, TrueValue);
+    bool IsORIInstRequired = !useSameRegister(Dest, FalseValue);
+
+    if (IsADDIInstRequired) {
+      // Copy the result into the destination if the condition is true.
+      BuildMI(*TrueBlock, TrueBlockI, dl,
+              TII->get(isISEL8(*MI) ? PPC::ADDI8 : PPC::ADDI))
+          .add(Dest)
+          .add(TrueValue)
+          .add(MachineOperand::CreateImm(0));
+
+      // Add the LiveIn registers required by true block.
+      TrueBlock->addLiveIn(TrueValue.getReg());
+    }
+
+    if (IsORIInstRequired) {
+      // Add the LiveIn registers required by false block.
+      FalseBlock->addLiveIn(FalseValue.getReg());
+    }
+
+    if (NewSuccessor) {
+      // Add the LiveIn registers required by NewSuccessor block.
+      NewSuccessor->addLiveIn(Dest.getReg());
+      NewSuccessor->addLiveIn(TrueValue.getReg());
+      NewSuccessor->addLiveIn(FalseValue.getReg());
+      NewSuccessor->addLiveIn(ConditionRegister.getReg());
+    }
+
+    // Copy the value into the destination if the condition is false.
+    if (IsORIInstRequired)
+      BuildMI(*FalseBlock, FalseBlockI, dl,
+              TII->get(isISEL8(*MI) ? PPC::ORI8 : PPC::ORI))
+          .add(Dest)
+          .add(FalseValue)
+          .add(MachineOperand::CreateImm(0));
+
+    MI->eraseFromParent(); // Remove the ISEL instruction.
+
+    NumExpanded++;
+  }
+}
+
+void PPCExpandISEL::expandMergeableISELs(BlockISELList &BIL) {
+  // At this stage all the ISELs of BIL are in the same MBB.
+  MachineBasicBlock *MBB = BIL.back()->getParent();
+
+  handleSpecialCases(BIL, MBB);
+  reorganizeBlockLayout(BIL, MBB);
+  populateBlocks(BIL);
+}
+
+INITIALIZE_PASS(PPCExpandISEL, DEBUG_TYPE, "PowerPC Expand ISEL Generation",
+                false, false)
+char PPCExpandISEL::ID = 0;
+
+FunctionPass *llvm::createPPCExpandISELPass() { return new PPCExpandISEL(); }
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 805d9b9ea6b..5b540b1ab6f 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -3536,10 +3536,6 @@ void PPCDAGToDAGISel::PostprocessISelDAG() {
 // be folded with the isel so that we don't need to materialize a register
 // containing zero.
 bool PPCDAGToDAGISel::AllUsersSelectZero(SDNode *N) {
-  // If we're not using isel, then this does not matter.
-  if (!PPCSubTarget->hasISEL())
-    return false;
-
   for (SDNode::use_iterator UI = N->use_begin(), UE = N->use_end();
        UI != UE; ++UI) {
     SDNode *User = *UI;
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 1224d4f6f49..53e7dd1cb0f 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -9305,10 +9305,9 @@ PPCTargetLowering::EmitInstrWithCustomInserter(MachineInstr &MI,
 
   MachineFunction *F = BB->getParent();
 
-  if (Subtarget.hasISEL() &&
-      (MI.getOpcode() == PPC::SELECT_CC_I4 ||
+  if (MI.getOpcode() == PPC::SELECT_CC_I4 ||
        MI.getOpcode() == PPC::SELECT_CC_I8 ||
-       MI.getOpcode() == PPC::SELECT_I4 || MI.getOpcode() == PPC::SELECT_I8)) {
+       MI.getOpcode() == PPC::SELECT_I4 || MI.getOpcode() == PPC::SELECT_I8) {
     SmallVector<MachineOperand, 2> Cond;
     if (MI.getOpcode() == PPC::SELECT_CC_I4 ||
         MI.getOpcode() == PPC::SELECT_CC_I8)
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index 51c86dd2170..315911db4e3 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -696,9 +696,6 @@ bool PPCInstrInfo::canInsertSelect(const MachineBasicBlock &MBB,
                 ArrayRef<MachineOperand> Cond,
                 unsigned TrueReg, unsigned FalseReg,
                 int &CondCycles, int &TrueCycles, int &FalseCycles) const {
-  if (!Subtarget.hasISEL())
-    return false;
-
   if (Cond.size() != 2)
     return false;
 
@@ -740,9 +737,6 @@ void PPCInstrInfo::insertSelect(MachineBasicBlock &MBB,
   assert(Cond.size() == 2 &&
          "PPC branch conditions have two components!");
 
-  assert(Subtarget.hasISEL() &&
-         "Cannot insert select on target without ISEL support");
-
   // Get the register classes.
   MachineRegisterInfo &MRI = MBB.getParent()->getRegInfo();
   const TargetRegisterClass *RC =
diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.h b/llvm/lib/Target/PowerPC/PPCSubtarget.h
index 7fd907990ce..48d6365d3e7 100644
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.h
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.h
@@ -298,7 +298,9 @@ public:
   bool isSVR4ABI() const { return !isDarwinABI(); }
   bool isELFv2ABI() const;
 
-  bool enableEarlyIfConversion() const override { return hasISEL(); }
+  /// Originally, this function return hasISEL(). Now we always enable it,
+  /// but may expand the ISEL instruction later.
+  bool enableEarlyIfConversion() const override { return true; }
 
   // Scheduling customization.
   bool enableMachineScheduler() const override;
diff --git a/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp b/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
index c7b74bc6a53..5d68f32ccc5 100644
--- a/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
+++ b/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
@@ -92,6 +92,7 @@ extern "C" void LLVMInitializePowerPCTarget() {
 
   PassRegistry &PR = *PassRegistry::getPassRegistry();
   initializePPCBoolRetToIntPass(PR);
+  initializePPCExpandISELPass(PR);
 }
 
 /// Return the datalayout string of a subtarget.
@@ -430,6 +431,8 @@ void PPCPassConfig::addPreSched2() {
 }
 
 void PPCPassConfig::addPreEmitPass() {
+  addPass(createPPCExpandISELPass());
+
   if (getOptLevel() != CodeGenOpt::None)
     addPass(createPPCEarlyReturnPass(), false);
   // Must run branch selection immediately preceding the asm printer.