Index: include/llvm/CodeGen/GlobalISel/CSEInfo.h
===================================================================
--- /dev/null
+++ include/llvm/CodeGen/GlobalISel/CSEInfo.h
@@ -0,0 +1,237 @@
+//===- llvm/CodeGen/GlobalISel/CSEInfo.h ------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// Provides analysis for continuously CSEing during GISel passes.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_CODEGEN_GLOBALISEL_CSEINFO_H
+#define LLVM_CODEGEN_GLOBALISEL_CSEINFO_H
+
+#include "llvm/ADT/FoldingSet.h"
+#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
+#include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
+#include "llvm/CodeGen/GlobalISel/Utils.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Allocator.h"
+
+namespace llvm {
+
+/// A class that wraps MachineInstrs and derives from FoldingSetNode in order to
+/// be uniqued in a CSEMap. The tradeoff here is extra memory allocations for
+/// UniqueMachineInstr vs making MachineInstr bigger.
+class UniqueMachineInstr : public FoldingSetNode {
+  friend class GISelCSEInfo;
+  const MachineInstr *MI;
+  explicit UniqueMachineInstr(const MachineInstr *MI) : MI(MI) {}
+
+public:
+  void Profile(FoldingSetNodeID &ID);
+};
+
+// Class representing some configuration that can be done during CSE analysis.
+// Currently it only supports shouldCSE method that each pass can set.
+class CSEConfig {
+public:
+  virtual ~CSEConfig() = default;
+  // Hook for defining which Generic instructions should be CSEd.
+  // GISelCSEInfo currently only calls this hook when dealing with generic
+  // opcodes.
+  virtual bool shouldCSEOpc(unsigned Opc);
+};
+
+// TODO: Find a better place for this.
+// Commonly used for O0 config.
+class CSEConfigConstantOnly : public CSEConfig {
+public:
+  virtual ~CSEConfigConstantOnly() = default;
+  virtual bool shouldCSEOpc(unsigned Opc) override;
+};
+
+/// The CSE Analysis object.
+/// This installs itself as a delegate to the MachineFunction to track
+/// new instructions as well as deletions. It however will not be able to
+/// track instruction mutations. In such cases, recordNewInstruction should be
+/// called (for eg inside MachineIRBuilder::recordInsertion).
+/// Also because of how just the instruction can be inserted without adding any
+/// operands to the instruction, instructions are uniqued and inserted lazily.
+/// CSEInfo should assert when trying to enter an incomplete instruction into
+/// the CSEMap. There is Opcode level granularity on which instructions can be
+/// CSE'd and for now, only Generic instructions are CSEable.
+class GISelCSEInfo : public GISelChangeObserver {
+  // Make it accessible only to CSEMIRBuilder.
+  friend class CSEMIRBuilder;
+
+  BumpPtrAllocator UniqueInstrAllocator;
+  FoldingSet<UniqueMachineInstr> CSEMap;
+  MachineRegisterInfo *MRI = nullptr;
+  MachineFunction *MF = nullptr;
+  std::unique_ptr<CSEConfig> CSEOpt;
+  /// Keep a cache of UniqueInstrs for each MachineInstr. In GISel,
+  /// often instructions are mutated (while their ID has completely changed).
+  /// Whenever mutation happens, invalidate the UniqueMachineInstr for the
+  /// MachineInstr
+  DenseMap<const MachineInstr *, UniqueMachineInstr *> InstrMapping;
+
+  /// Store instructions that are not fully formed in TemporaryInsts.
+  /// Also because CSE insertion happens lazily, we can remove insts from this
+  /// list and avoid inserting and then removing from the CSEMap.
+  GISelWorkList<8> TemporaryInsts;
+
+  // Only used in asserts.
+  DenseMap<unsigned, unsigned> OpcodeHitTable;
+
+  bool isUniqueMachineInstValid(const UniqueMachineInstr &UMI) const;
+
+  void invalidateUniqueMachineInstr(UniqueMachineInstr *UMI);
+
+  UniqueMachineInstr *getNodeIfExists(FoldingSetNodeID &ID,
+                                      MachineBasicBlock *MBB, void *&InsertPos);
+
+  /// Allocate and construct a new UniqueMachineInstr for MI and return.
+  UniqueMachineInstr *getUniqueInstrForMI(const MachineInstr *MI);
+
+  void insertNode(UniqueMachineInstr *UMI, void *InsertPos = nullptr);
+
+  /// Get the MachineInstr(Unique) if it exists already in the CSEMap and the
+  /// same MachineBasicBlock.
+  MachineInstr *getMachineInstrIfExists(FoldingSetNodeID &ID,
+                                        MachineBasicBlock *MBB,
+                                        void *&InsertPos);
+
+  /// Use this method to allocate a new UniqueMachineInstr for MI and insert it
+  /// into the CSEMap. MI should return true for shouldCSE(MI->getOpcode())
+  void insertInstr(MachineInstr *MI, void *InsertPos = nullptr);
+
+public:
+  GISelCSEInfo() = default;
+
+  virtual ~GISelCSEInfo();
+
+  void setMF(MachineFunction &MF);
+
+  /// Records a newly created inst in a list and lazily insert it to the CSEMap.
+  /// Sometimes, this method might be called with a partially constructed
+  /// MachineInstr,
+  //  (right after BuildMI without adding any operands) - and in such cases,
+  //  defer the hashing of the instruction to a later stage.
+  void recordNewInstruction(MachineInstr *MI);
+
+  /// Use this callback to inform CSE about a newly fully created instruction.
+  void handleRecordedInst(MachineInstr *MI);
+
+  /// Use this callback to insert all the recorded instructions. At this point,
+  /// all of these insts need to be fully constructed and should not be missing
+  /// any operands.
+  void handleRecordedInsts();
+
+  /// Remove this inst from the CSE map. If this inst has not been inserted yet,
+  /// it will be removed from the Tempinsts list if it exists.
+  void handleRemoveInst(MachineInstr *MI);
+
+  void releaseMemory();
+
+  void setCSEConfig(std::unique_ptr<CSEConfig> Opt) { CSEOpt = std::move(Opt); }
+
+  bool shouldCSE(unsigned Opc) const;
+
+  void analyze(MachineFunction &MF);
+
+  void countOpcodeHit(unsigned Opc);
+
+  void print();
+
+  // Observer API
+  void erasingInstr(MachineInstr &MI) override;
+  void createdInstr(MachineInstr &MI) override;
+  void changingInstr(MachineInstr &MI) override;
+  void changedInstr(MachineInstr &MI) override;
+};
+
+class TargetRegisterClass;
+class RegisterBank;
+
+// Simple builder class to easily profile properties about MIs.
+class GISelInstProfileBuilder {
+  FoldingSetNodeID &ID;
+  const MachineRegisterInfo &MRI;
+
+public:
+  GISelInstProfileBuilder(FoldingSetNodeID &ID, const MachineRegisterInfo &MRI)
+      : ID(ID), MRI(MRI) {}
+  // Profiling methods.
+  const GISelInstProfileBuilder &addNodeIDOpcode(unsigned Opc) const;
+  const GISelInstProfileBuilder &addNodeIDRegType(const LLT &Ty) const;
+  const GISelInstProfileBuilder &addNodeIDRegType(const unsigned) const;
+
+  const GISelInstProfileBuilder &
+  addNodeIDRegType(const TargetRegisterClass *RC) const;
+  const GISelInstProfileBuilder &addNodeIDRegType(const RegisterBank *RB) const;
+
+  const GISelInstProfileBuilder &addNodeIDRegNum(unsigned Reg) const;
+
+  const GISelInstProfileBuilder &addNodeIDImmediate(int64_t Imm) const;
+  const GISelInstProfileBuilder &
+  addNodeIDMBB(const MachineBasicBlock *MBB) const;
+
+  const GISelInstProfileBuilder &
+  addNodeIDMachineOperand(const MachineOperand &MO) const;
+
+  const GISelInstProfileBuilder &addNodeIDFlag(unsigned Flag) const;
+  const GISelInstProfileBuilder &addNodeID(const MachineInstr *MI) const;
+};
+
+/// Simple wrapper that does the following.
+/// 1) Lazily evaluate the MachineFunction to compute CSEable instructions.
+/// 2) Allows configuration of which instructions are CSEd through CSEConfig
+/// object. Provides a method called get which takes a CSEConfig object.
+class GISelCSEAnalysisWrapper {
+  GISelCSEInfo Info;
+  MachineFunction *MF = nullptr;
+  bool AlreadyComputed = false;
+
+public:
+  /// Takes a CSEConfig object that defines what opcodes get CSEd.
+  /// If CSEConfig is already set, and the CSE Analysis has been preserved,
+  /// it will not use the new CSEOpt(use Recompute to force using the new
+  /// CSEOpt).
+  GISelCSEInfo &get(std::unique_ptr<CSEConfig> CSEOpt, bool ReCompute = false);
+  void setMF(MachineFunction &MFunc) { MF = &MFunc; }
+  void setComputed(bool Computed) { AlreadyComputed = Computed; }
+  void releaseMemory() { Info.releaseMemory(); }
+};
+
+/// The actual analysis pass wrapper.
+class GISelCSEAnalysisWrapperPass : public MachineFunctionPass {
+  GISelCSEAnalysisWrapper Wrapper;
+
+public:
+  static char ID;
+  GISelCSEAnalysisWrapperPass() : MachineFunctionPass(ID) {
+    initializeGISelCSEAnalysisWrapperPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+  const GISelCSEAnalysisWrapper &getCSEWrapper() const { return Wrapper; }
+  GISelCSEAnalysisWrapper &getCSEWrapper() { return Wrapper; }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  void releaseMemory() override {
+    Wrapper.releaseMemory();
+    Wrapper.setComputed(false);
+  }
+};
+
+} // namespace llvm
+
+#endif
Index: include/llvm/CodeGen/GlobalISel/CSEMIRBuilder.h
===================================================================
--- /dev/null
+++ include/llvm/CodeGen/GlobalISel/CSEMIRBuilder.h
@@ -0,0 +1,110 @@
+//===-- llvm/CodeGen/GlobalISel/CSEMIRBuilder.h  --*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file implements a version of MachineIRBuilder which CSEs insts within
+/// a MachineBasicBlock.
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_CODEGEN_GLOBALISEL_CSEMIRBUILDER_H
+#define LLVM_CODEGEN_GLOBALISEL_CSEMIRBUILDER_H
+
+#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
+#include "llvm/CodeGen/GlobalISel/Utils.h"
+
+namespace llvm {
+
+/// Defines a builder that does CSE of MachineInstructions using GISelCSEInfo.
+/// Eg usage.
+///
+///
+/// GISelCSEInfo *Info =
+/// &getAnalysis<GISelCSEAnalysisWrapperPass>().getCSEInfo(); CSEMIRBuilder
+/// CB(Builder.getState()); CB.setCSEInfo(Info); auto A = CB.buildConstant(s32,
+/// 42); auto B = CB.buildConstant(s32, 42); assert(A == B); unsigned CReg =
+/// MRI.createGenericVirtualRegister(s32); auto C = CB.buildConstant(CReg, 42);
+/// assert(C->getOpcode() == TargetOpcode::COPY);
+/// Explicitly passing in a register would materialize a copy if possible.
+/// CSEMIRBuilder also does trivial constant folding for binary ops.
+class CSEMIRBuilder : public MachineIRBuilder {
+
+  /// Returns true if A dominates B (within the same basic block).
+  /// Both iterators must be in the same basic block.
+  //
+  // TODO: Another approach for checking dominance is having two iterators and
+  // making them go towards each other until they meet or reach begin/end. Which
+  // approach is better? Should this even change dynamically? For G_CONSTANTS
+  // most of which will be at the top of the BB, the top down approach would be
+  // a better choice. Does IRTranslator placing constants at the beginning still
+  // make sense? Should this change based on Opcode?
+  bool dominates(MachineBasicBlock::const_iterator A,
+                 MachineBasicBlock::const_iterator B) const;
+
+  /// For given ID, find a machineinstr in the CSE Map. If found, check if it
+  /// dominates the current insertion point and if not, move it just before the
+  /// current insertion point and return it. If not found, return Null
+  /// MachineInstrBuilder.
+  MachineInstrBuilder getDominatingInstrForID(FoldingSetNodeID &ID,
+                                              void *&NodeInsertPos);
+  /// Simple check if we can CSE (we have the CSEInfo) or if this Opcode is
+  /// safe to CSE.
+  bool canPerformCSEForOpc(unsigned Opc) const;
+
+  void profileDstOp(const DstOp &Op, GISelInstProfileBuilder &B) const;
+
+  void profileDstOps(ArrayRef<DstOp> Ops, GISelInstProfileBuilder &B) const {
+    for (const DstOp &Op : Ops)
+      profileDstOp(Op, B);
+  }
+
+  void profileSrcOp(const SrcOp &Op, GISelInstProfileBuilder &B) const;
+
+  void profileSrcOps(ArrayRef<SrcOp> Ops, GISelInstProfileBuilder &B) const {
+    for (const SrcOp &Op : Ops)
+      profileSrcOp(Op, B);
+  }
+
+  void profileMBBOpcode(GISelInstProfileBuilder &B, unsigned Opc) const;
+
+  void profileEverything(unsigned Opc, ArrayRef<DstOp> DstOps,
+                         ArrayRef<SrcOp> SrcOps, Optional<unsigned> Flags,
+                         GISelInstProfileBuilder &B) const;
+
+  // Takes a MachineInstrBuilder and inserts it into the CSEMap using the
+  // NodeInsertPos.
+  MachineInstrBuilder memoizeMI(MachineInstrBuilder MIB, void *NodeInsertPos);
+
+  // If we have can CSE an instruction, but still need to materialize to a VReg,
+  // we emit a copy from the CSE'd inst to the VReg.
+  MachineInstrBuilder generateCopiesIfRequired(ArrayRef<DstOp> DstOps,
+                                               MachineInstrBuilder &MIB);
+
+  // If we have can CSE an instruction, but still need to materialize to a VReg,
+  // check if we can generate copies. It's not possible to return a single MIB,
+  // while emitting copies to multiple vregs.
+  bool checkCopyToDefsPossible(ArrayRef<DstOp> DstOps);
+
+public:
+  // Pull in base class constructors.
+  using MachineIRBuilder::MachineIRBuilder;
+  // Unhide buildInstr
+  MachineInstrBuilder buildInstr(unsigned Opc, ArrayRef<DstOp> DstOps,
+                                 ArrayRef<SrcOp> SrcOps,
+                                 Optional<unsigned> Flag = None) override;
+  // Bring in the other overload from the base class.
+  using MachineIRBuilder::buildConstant;
+
+  MachineInstrBuilder buildConstant(const DstOp &Res,
+                                    const ConstantInt &Val) override;
+
+  // Bring in the other overload from the base class.
+  using MachineIRBuilder::buildFConstant;
+  MachineInstrBuilder buildFConstant(const DstOp &Res,
+                                     const ConstantFP &Val) override;
+};
+} // namespace llvm
+#endif
Index: include/llvm/CodeGen/GlobalISel/Combiner.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/Combiner.h
+++ include/llvm/CodeGen/GlobalISel/Combiner.h
@@ -21,6 +21,7 @@
 namespace llvm {
 class MachineRegisterInfo;
 class CombinerInfo;
+class GISelCSEInfo;
 class TargetPassConfig;
 class MachineFunction;
 
@@ -28,14 +29,17 @@
 public:
   Combiner(CombinerInfo &CombinerInfo, const TargetPassConfig *TPC);
 
-  bool combineMachineInstrs(MachineFunction &MF);
+  /// If CSEInfo is not null, then the Combiner will setup observer for
+  /// CSEInfo and instantiate a CSEMIRBuilder. Pass nullptr if CSE is not
+  /// needed.
+  bool combineMachineInstrs(MachineFunction &MF, GISelCSEInfo *CSEInfo);
 
 protected:
   CombinerInfo &CInfo;
 
   MachineRegisterInfo *MRI = nullptr;
   const TargetPassConfig *TPC;
-  MachineIRBuilder Builder;
+  std::unique_ptr<MachineIRBuilder> Builder;
 };
 
 } // End namespace llvm.
Index: include/llvm/CodeGen/GlobalISel/ConstantFoldingMIRBuilder.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/ConstantFoldingMIRBuilder.h
+++ include/llvm/CodeGen/GlobalISel/ConstantFoldingMIRBuilder.h
@@ -15,57 +15,6 @@
 
 namespace llvm {
 
-static Optional<APInt> ConstantFoldBinOp(unsigned Opcode, const unsigned Op1,
-                                         const unsigned Op2,
-                                         const MachineRegisterInfo &MRI) {
-  auto MaybeOp1Cst = getConstantVRegVal(Op1, MRI);
-  auto MaybeOp2Cst = getConstantVRegVal(Op2, MRI);
-  if (MaybeOp1Cst && MaybeOp2Cst) {
-    LLT Ty = MRI.getType(Op1);
-    APInt C1(Ty.getSizeInBits(), *MaybeOp1Cst, true);
-    APInt C2(Ty.getSizeInBits(), *MaybeOp2Cst, true);
-    switch (Opcode) {
-    default:
-      break;
-    case TargetOpcode::G_ADD:
-      return C1 + C2;
-    case TargetOpcode::G_AND:
-      return C1 & C2;
-    case TargetOpcode::G_ASHR:
-      return C1.ashr(C2);
-    case TargetOpcode::G_LSHR:
-      return C1.lshr(C2);
-    case TargetOpcode::G_MUL:
-      return C1 * C2;
-    case TargetOpcode::G_OR:
-      return C1 | C2;
-    case TargetOpcode::G_SHL:
-      return C1 << C2;
-    case TargetOpcode::G_SUB:
-      return C1 - C2;
-    case TargetOpcode::G_XOR:
-      return C1 ^ C2;
-    case TargetOpcode::G_UDIV:
-      if (!C2.getBoolValue())
-        break;
-      return C1.udiv(C2);
-    case TargetOpcode::G_SDIV:
-      if (!C2.getBoolValue())
-        break;
-      return C1.sdiv(C2);
-    case TargetOpcode::G_UREM:
-      if (!C2.getBoolValue())
-        break;
-      return C1.urem(C2);
-    case TargetOpcode::G_SREM:
-      if (!C2.getBoolValue())
-        break;
-      return C1.srem(C2);
-    }
-  }
-  return None;
-}
-
 /// An MIRBuilder which does trivial constant folding of binary ops.
 /// Calls to buildInstr will also try to constant fold binary ops.
 class ConstantFoldingMIRBuilder : public MachineIRBuilder {
Index: include/llvm/CodeGen/GlobalISel/GISelChangeObserver.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/GISelChangeObserver.h
+++ include/llvm/CodeGen/GlobalISel/GISelChangeObserver.h
@@ -15,6 +15,7 @@
 #define LLVM_CODEGEN_GLOBALISEL_GISELCHANGEOBSERVER_H
 
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/CodeGen/MachineFunction.h"
 
 namespace llvm {
 class MachineInstr;
@@ -32,13 +33,13 @@
   virtual ~GISelChangeObserver() {}
 
   /// An instruction is about to be erased.
-  virtual void erasingInstr(const MachineInstr &MI) = 0;
+  virtual void erasingInstr(MachineInstr &MI) = 0;
   /// An instruction was created and inserted into the function.
-  virtual void createdInstr(const MachineInstr &MI) = 0;
+  virtual void createdInstr(MachineInstr &MI) = 0;
   /// This instruction is about to be mutated in some way.
-  virtual void changingInstr(const MachineInstr &MI) = 0;
+  virtual void changingInstr(MachineInstr &MI) = 0;
   /// This instruction was mutated in some way.
-  virtual void changedInstr(const MachineInstr &MI) = 0;
+  virtual void changedInstr(MachineInstr &MI) = 0;
 
   /// All the instructions using the given register are being changed.
   /// For convenience, finishedChangingAllUsesOfReg() will report the completion
@@ -51,5 +52,60 @@
 
 };
 
+/// Simple wrapper observer that takes several observers, and calls
+/// each one for each event. If there are multiple observers (say CSE,
+/// Legalizer, Combiner), it's sufficient to register this to the machine
+/// function as the delegate.
+class GISelObserverWrapper : public MachineFunction::Delegate,
+                             public GISelChangeObserver {
+  SmallVector<GISelChangeObserver *, 4> Observers;
+
+public:
+  GISelObserverWrapper() = default;
+  GISelObserverWrapper(ArrayRef<GISelChangeObserver *> Obs)
+      : Observers(Obs.begin(), Obs.end()) {}
+  // Adds an observer.
+  void addObserver(GISelChangeObserver *O) { Observers.push_back(O); }
+  // Removes an observer from the list and does nothing if observer is not
+  // present.
+  void removeObserver(GISelChangeObserver *O) {
+    auto It = std::find(Observers.begin(), Observers.end(), O);
+    if (It != Observers.end())
+      Observers.erase(It);
+  }
+  // API for Observer.
+  void erasingInstr(MachineInstr &MI) override {
+    for (auto &O : Observers)
+      O->erasingInstr(MI);
+  }
+  void createdInstr(MachineInstr &MI) override {
+    for (auto &O : Observers)
+      O->createdInstr(MI);
+  }
+  void changingInstr(MachineInstr &MI) override {
+    for (auto &O : Observers)
+      O->changingInstr(MI);
+  }
+  void changedInstr(MachineInstr &MI) override {
+    for (auto &O : Observers)
+      O->changedInstr(MI);
+  }
+  // API for MachineFunction::Delegate
+  void MF_HandleInsertion(MachineInstr &MI) override { createdInstr(MI); }
+  void MF_HandleRemoval(MachineInstr &MI) override { erasingInstr(MI); }
+};
+
+/// A simple RAII based CSEInfo installer.
+/// Use this in a scope to install a delegate to the MachineFunction and reset
+/// it at the end of the scope.
+class RAIIDelegateInstaller {
+  MachineFunction &MF;
+  MachineFunction::Delegate *Delegate;
+
+public:
+  RAIIDelegateInstaller(MachineFunction &MF, MachineFunction::Delegate *Del);
+  ~RAIIDelegateInstaller();
+};
+
 } // namespace llvm
 #endif
Index: include/llvm/CodeGen/GlobalISel/GISelWorkList.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/GISelWorkList.h
+++ include/llvm/CodeGen/GlobalISel/GISelWorkList.h
@@ -18,6 +18,7 @@
 
 namespace llvm {
 
+class MachineInstr;
 class MachineFunction;
 
 // Worklist which mostly works similar to InstCombineWorkList, but on
@@ -25,23 +26,15 @@
 // erasing an element doesn't move all elements over one place - instead just
 // nulls out the element of the vector.
 //
-// This worklist operates on instructions within a particular function. This is
-// important for acquiring the rights to modify/replace instructions a
-// GISelChangeObserver reports as the observer doesn't have the right to make
-// changes to the instructions it sees so we use our access to the
-// MachineFunction to establish that it's ok to add a given instruction to the
-// worklist.
-//
 // FIXME: Does it make sense to factor out common code with the
 // instcombinerWorkList?
 template<unsigned N>
 class GISelWorkList {
-  MachineFunction *MF;
   SmallVector<MachineInstr *, N> Worklist;
   DenseMap<MachineInstr *, unsigned> WorklistMap;
 
 public:
-  GISelWorkList(MachineFunction *MF) : MF(MF) {}
+  GISelWorkList() {}
 
   bool empty() const { return WorklistMap.empty(); }
 
@@ -49,27 +42,8 @@
 
   /// Add the specified instruction to the worklist if it isn't already in it.
   void insert(MachineInstr *I) {
-    // It would be safe to add this instruction to the worklist regardless but
-    // for consistency with the const version, check that the instruction we're
-    // adding would have been accepted if we were given a const pointer instead.
-    insert(const_cast<const MachineInstr *>(I));
-  }
-
-  void insert(const MachineInstr *I) {
-    // Confirm we'd be able to find the non-const pointer we want to schedule if
-    // we wanted to. We have the right to schedule work that may modify any
-    // instruction in MF.
-    assert(I->getParent() && "Expected parent BB");
-    assert(I->getParent()->getParent() && "Expected parent function");
-    assert((!MF || I->getParent()->getParent() == MF) &&
-           "Expected parent function to be current function or not given");
-
-    // But don't actually do the search since we can derive it from the const
-    // pointer.
-    MachineInstr *NonConstI = const_cast<MachineInstr *>(I);
-    if (WorklistMap.try_emplace(NonConstI, Worklist.size()).second) {
-      Worklist.push_back(NonConstI);
-    }
+    if (WorklistMap.try_emplace(I, Worklist.size()).second)
+      Worklist.push_back(I);
   }
 
   /// Remove I from the worklist if it exists.
@@ -83,6 +57,11 @@
     WorklistMap.erase(It);
   }
 
+  void clear() {
+    Worklist.clear();
+    WorklistMap.clear();
+  }
+
   MachineInstr *pop_back_val() {
     MachineInstr *I;
     do {
Index: include/llvm/CodeGen/GlobalISel/IRTranslator.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/IRTranslator.h
+++ include/llvm/CodeGen/GlobalISel/IRTranslator.h
@@ -21,11 +21,11 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
+#include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/Types.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/Support/Allocator.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/Support/Allocator.h"
 #include <memory>
 #include <utility>
 
@@ -444,11 +444,13 @@
   // I.e., compared to regular MIBuilder, this one also inserts the instruction
   // in the current block, it can creates block, etc., basically a kind of
   // IRBuilder, but for Machine IR.
-  MachineIRBuilder CurBuilder;
+  // CSEMIRBuilder CurBuilder;
+  std::unique_ptr<MachineIRBuilder> CurBuilder;
 
   // Builder set to the entry block (just after ABI lowering instructions). Used
   // as a convenient location for Constants.
-  MachineIRBuilder EntryBuilder;
+  // CSEMIRBuilder EntryBuilder;
+  std::unique_ptr<MachineIRBuilder> EntryBuilder;
 
   // The MachineFunction currently being translated.
   MachineFunction *MF;
Index: include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
+++ include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
@@ -49,9 +49,10 @@
     UnableToLegalize,
   };
 
-  LegalizerHelper(MachineFunction &MF, GISelChangeObserver &Observer);
+  LegalizerHelper(MachineFunction &MF, GISelChangeObserver &Observer,
+                  MachineIRBuilder &B);
   LegalizerHelper(MachineFunction &MF, const LegalizerInfo &LI,
-                  GISelChangeObserver &Observer);
+                  GISelChangeObserver &Observer, MachineIRBuilder &B);
 
   /// Replace \p MI by a sequence of legal instructions that can implement the
   /// same operation. Note that this means \p MI may be deleted, so any iterator
@@ -90,7 +91,7 @@
 
   /// Expose MIRBuilder so clients can set their own RecordInsertInstruction
   /// functions
-  MachineIRBuilder MIRBuilder;
+  MachineIRBuilder &MIRBuilder;
 
   /// Expose LegalizerInfo so the clients can re-use.
   const LegalizerInfo &getLegalizerInfo() const { return LI; }
Index: include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h
+++ include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h
@@ -14,6 +14,7 @@
 #ifndef LLVM_CODEGEN_GLOBALISEL_MACHINEIRBUILDER_H
 #define LLVM_CODEGEN_GLOBALISEL_MACHINEIRBUILDER_H
 
+#include "llvm/CodeGen/GlobalISel/CSEInfo.h"
 #include "llvm/CodeGen/GlobalISel/Types.h"
 
 #include "llvm/CodeGen/LowLevelType.h"
@@ -52,6 +53,8 @@
   /// @}
 
   GISelChangeObserver *Observer;
+
+  GISelCSEInfo *CSEInfo;
 };
 
 class DstOp {
@@ -81,8 +84,6 @@
     }
   }
 
-  DstType getType() const { return Ty; }
-
   LLT getLLTTy(const MachineRegisterInfo &MRI) const {
     switch (Ty) {
     case DstType::Ty_RC:
@@ -95,6 +96,20 @@
     llvm_unreachable("Unrecognised DstOp::DstType enum");
   }
 
+  unsigned getReg() const {
+    assert(Ty == DstType::Ty_Reg && "Not a register");
+    return Reg;
+  }
+
+  const TargetRegisterClass *getRegClass() const {
+    switch (Ty) {
+    case DstType::Ty_RC:
+      return RC;
+    default:
+      llvm_unreachable("Not a RC Operand");
+    }
+  }
+
   DstType getDstOpKind() const { return Ty; }
 
 private:
@@ -220,16 +235,25 @@
 
   /// Getter for MRI
   MachineRegisterInfo *getMRI() { return State.MRI; }
+  const MachineRegisterInfo *getMRI() const { return State.MRI; }
 
   /// Getter for the State
   MachineIRBuilderState &getState() { return State; }
 
   /// Getter for the basic block we currently build.
-  MachineBasicBlock &getMBB() {
+  const MachineBasicBlock &getMBB() const {
     assert(State.MBB && "MachineBasicBlock is not set");
     return *State.MBB;
   }
 
+  MachineBasicBlock &getMBB() {
+    return const_cast<MachineBasicBlock &>(
+        const_cast<const MachineIRBuilder *>(this)->getMBB());
+  }
+
+  GISelCSEInfo *getCSEInfo() { return State.CSEInfo; }
+  const GISelCSEInfo *getCSEInfo() const { return State.CSEInfo; }
+
   /// Current insertion point for new instructions.
   MachineBasicBlock::iterator getInsertPt() { return State.II; }
 
@@ -239,10 +263,12 @@
   void setInsertPt(MachineBasicBlock &MBB, MachineBasicBlock::iterator II);
   /// @}
 
+  void setCSEInfo(GISelCSEInfo *Info);
+
   /// \name Setters for the insertion point.
   /// @{
   /// Set the MachineFunction where to build instructions.
-  void setMF(MachineFunction &);
+  void setMF(MachineFunction &MF);
 
   /// Set the insertion point to the  end of \p MBB.
   /// \pre \p MBB must be contained by getMF().
@@ -534,7 +560,8 @@
   ///      type.
   ///
   /// \return The newly created instruction.
-  MachineInstrBuilder buildConstant(const DstOp &Res, const ConstantInt &Val);
+  virtual MachineInstrBuilder buildConstant(const DstOp &Res,
+                                            const ConstantInt &Val);
 
   /// Build and insert \p Res = G_CONSTANT \p Val
   ///
@@ -555,7 +582,8 @@
   /// \pre \p Res must be a generic virtual register with scalar type.
   ///
   /// \return The newly created instruction.
-  MachineInstrBuilder buildFConstant(const DstOp &Res, const ConstantFP &Val);
+  virtual MachineInstrBuilder buildFConstant(const DstOp &Res,
+                                             const ConstantFP &Val);
 
   MachineInstrBuilder buildFConstant(const DstOp &Res, double Val);
 
Index: include/llvm/CodeGen/GlobalISel/Utils.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/Utils.h
+++ include/llvm/CodeGen/GlobalISel/Utils.h
@@ -108,5 +108,8 @@
 /// fallback.
 void getSelectionDAGFallbackAnalysisUsage(AnalysisUsage &AU);
 
+Optional<APInt> ConstantFoldBinOp(unsigned Opcode, const unsigned Op1,
+                                  const unsigned Op2,
+                                  const MachineRegisterInfo &MRI);
 } // End namespace llvm.
 #endif
Index: include/llvm/CodeGen/MachineFunction.h
===================================================================
--- include/llvm/CodeGen/MachineFunction.h
+++ include/llvm/CodeGen/MachineFunction.h
@@ -372,16 +372,18 @@
 
   public:
     virtual ~Delegate() = default;
-    virtual void MF_HandleInsertion(const MachineInstr &MI) = 0;
-    virtual void MF_HandleRemoval(const MachineInstr &MI) = 0;
+    /// Callback after an insertion. This should not modify the MI directly.
+    virtual void MF_HandleInsertion(MachineInstr &MI) = 0;
+    /// Callback before a removal. This should not modify the MI directly.
+    virtual void MF_HandleRemoval(MachineInstr &MI) = 0;
   };
 
 private:
   Delegate *TheDelegate = nullptr;
 
   // Callbacks for insertion and removal.
-  void handleInsertion(const MachineInstr &MI);
-  void handleRemoval(const MachineInstr &MI);
+  void handleInsertion(MachineInstr &MI);
+  void handleRemoval(MachineInstr &MI);
   friend struct ilist_traits<MachineInstr>;
 
 public:
Index: include/llvm/InitializePasses.h
===================================================================
--- include/llvm/InitializePasses.h
+++ include/llvm/InitializePasses.h
@@ -199,6 +199,7 @@
 void initializeLegacyLICMPassPass(PassRegistry&);
 void initializeLegacyLoopSinkPassPass(PassRegistry&);
 void initializeLegalizerPass(PassRegistry&);
+void initializeGISelCSEAnalysisWrapperPassPass(PassRegistry &);
 void initializeLibCallsShrinkWrapLegacyPassPass(PassRegistry&);
 void initializeLintPass(PassRegistry&);
 void initializeLiveDebugValuesPass(PassRegistry&);
Index: include/llvm/Support/LowLevelTypeImpl.h
===================================================================
--- include/llvm/Support/LowLevelTypeImpl.h
+++ include/llvm/Support/LowLevelTypeImpl.h
@@ -147,6 +147,7 @@
   bool operator!=(const LLT &RHS) const { return !(*this == RHS); }
 
   friend struct DenseMapInfo<LLT>;
+  friend class GISelInstProfileBuilder;
 
 private:
   /// LLT is packed into 64 bits as follows:
@@ -231,6 +232,11 @@
             maskAndShift(AddressSpace, PointerVectorAddressSpaceFieldInfo);
     }
   }
+
+  uint64_t getUniqueRAWLLTData() const {
+    return ((uint64_t)RawData) << 2 | ((uint64_t)IsPointer) << 1 |
+           ((uint64_t)IsVector);
+  }
 };
 
 inline raw_ostream& operator<<(raw_ostream &OS, const LLT &Ty) {
@@ -250,8 +256,7 @@
     return Invalid;
   }
   static inline unsigned getHashValue(const LLT &Ty) {
-    uint64_t Val = ((uint64_t)Ty.RawData) << 2 | ((uint64_t)Ty.IsPointer) << 1 |
-                   ((uint64_t)Ty.IsVector);
+    uint64_t Val = Ty.getUniqueRAWLLTData();
     return DenseMapInfo<uint64_t>::getHashValue(Val);
   }
   static bool isEqual(const LLT &LHS, const LLT &RHS) {
Index: lib/CodeGen/GlobalISel/CMakeLists.txt
===================================================================
--- lib/CodeGen/GlobalISel/CMakeLists.txt
+++ lib/CodeGen/GlobalISel/CMakeLists.txt
@@ -1,4 +1,6 @@
 add_llvm_library(LLVMGlobalISel
+        CSEInfo.cpp
+        CSEMIRBuilder.cpp
         CallLowering.cpp
         GlobalISel.cpp
         Combiner.cpp
Index: lib/CodeGen/GlobalISel/CSEInfo.cpp
===================================================================
--- /dev/null
+++ lib/CodeGen/GlobalISel/CSEInfo.cpp
@@ -0,0 +1,370 @@
+//===- CSEInfo.cpp ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//
+//===----------------------------------------------------------------------===//
+#include "llvm/CodeGen/GlobalISel/CSEInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+
+#define DEBUG_TYPE "cseinfo"
+
+using namespace llvm;
+char llvm::GISelCSEAnalysisWrapperPass::ID = 0;
+INITIALIZE_PASS_BEGIN(GISelCSEAnalysisWrapperPass, DEBUG_TYPE,
+                      "Analysis containing CSE Info", false, true)
+INITIALIZE_PASS_END(GISelCSEAnalysisWrapperPass, DEBUG_TYPE,
+                    "Analysis containing CSE Info", false, true)
+
+/// -------- UniqueMachineInstr -------------//
+
+void UniqueMachineInstr::Profile(FoldingSetNodeID &ID) {
+  GISelInstProfileBuilder(ID, MI->getMF()->getRegInfo()).addNodeID(MI);
+}
+/// -----------------------------------------
+
+/// --------- CSEConfig ---------- ///
+bool CSEConfig::shouldCSEOpc(unsigned Opc) {
+  switch (Opc) {
+  default:
+    break;
+  case TargetOpcode::G_ADD:
+  case TargetOpcode::G_AND:
+  case TargetOpcode::G_ASHR:
+  case TargetOpcode::G_LSHR:
+  case TargetOpcode::G_MUL:
+  case TargetOpcode::G_OR:
+  case TargetOpcode::G_SHL:
+  case TargetOpcode::G_SUB:
+  case TargetOpcode::G_XOR:
+  case TargetOpcode::G_UDIV:
+  case TargetOpcode::G_SDIV:
+  case TargetOpcode::G_UREM:
+  case TargetOpcode::G_SREM:
+  case TargetOpcode::G_CONSTANT:
+  case TargetOpcode::G_FCONSTANT:
+  case TargetOpcode::G_ZEXT:
+  case TargetOpcode::G_SEXT:
+  case TargetOpcode::G_ANYEXT:
+  case TargetOpcode::G_UNMERGE_VALUES:
+  case TargetOpcode::G_TRUNC:
+    return true;
+  }
+  return false;
+}
+
+bool CSEConfigConstantOnly::shouldCSEOpc(unsigned Opc) {
+  return Opc == TargetOpcode::G_CONSTANT;
+}
+/// -----------------------------------------
+
+/// -------- GISelCSEInfo -------------//
+void GISelCSEInfo::setMF(MachineFunction &MF) {
+  this->MF = &MF;
+  this->MRI = &MF.getRegInfo();
+}
+
+GISelCSEInfo::~GISelCSEInfo() {}
+
+bool GISelCSEInfo::isUniqueMachineInstValid(
+    const UniqueMachineInstr &UMI) const {
+  // Should we check here and assert that the instruction has been fully
+  // constructed?
+  // FIXME: Any other checks required to be done here? Remove this method if
+  // none.
+  return true;
+}
+
+void GISelCSEInfo::invalidateUniqueMachineInstr(UniqueMachineInstr *UMI) {
+  bool Removed = CSEMap.RemoveNode(UMI);
+  (void)Removed;
+  assert(Removed && "Invalidation called on invalid UMI");
+  // FIXME: Should UMI be deallocated/destroyed?
+}
+
+UniqueMachineInstr *GISelCSEInfo::getNodeIfExists(FoldingSetNodeID &ID,
+                                                  MachineBasicBlock *MBB,
+                                                  void *&InsertPos) {
+  auto *Node = CSEMap.FindNodeOrInsertPos(ID, InsertPos);
+  if (Node) {
+    if (!isUniqueMachineInstValid(*Node)) {
+      invalidateUniqueMachineInstr(Node);
+      return nullptr;
+    }
+
+    if (Node->MI->getParent() != MBB)
+      return nullptr;
+  }
+  return Node;
+}
+
+void GISelCSEInfo::insertNode(UniqueMachineInstr *UMI, void *InsertPos) {
+  handleRecordedInsts();
+  assert(UMI);
+  UniqueMachineInstr *MaybeNewNode = UMI;
+  if (InsertPos)
+    CSEMap.InsertNode(UMI, InsertPos);
+  else
+    MaybeNewNode = CSEMap.GetOrInsertNode(UMI);
+  if (MaybeNewNode != UMI) {
+    // A similar node exists in the folding set. Let's ignore this one.
+    return;
+  }
+  assert(InstrMapping.count(UMI->MI) == 0 &&
+         "This instruction should not be in the map");
+  InstrMapping[UMI->MI] = MaybeNewNode;
+}
+
+UniqueMachineInstr *GISelCSEInfo::getUniqueInstrForMI(const MachineInstr *MI) {
+  assert(shouldCSE(MI->getOpcode()) && "Trying to CSE an unsupported Node");
+  auto *Node = new (UniqueInstrAllocator) UniqueMachineInstr(MI);
+  return Node;
+}
+
+void GISelCSEInfo::insertInstr(MachineInstr *MI, void *InsertPos) {
+  assert(MI);
+  // If it exists in temporary insts, remove it.
+  TemporaryInsts.remove(MI);
+  auto *Node = getUniqueInstrForMI(MI);
+  insertNode(Node, InsertPos);
+}
+
+MachineInstr *GISelCSEInfo::getMachineInstrIfExists(FoldingSetNodeID &ID,
+                                                    MachineBasicBlock *MBB,
+                                                    void *&InsertPos) {
+  handleRecordedInsts();
+  if (auto *Inst = getNodeIfExists(ID, MBB, InsertPos)) {
+    LLVM_DEBUG(dbgs() << "CSEInfo: Found Instr " << *Inst->MI << "\n";);
+    return const_cast<MachineInstr *>(Inst->MI);
+  }
+  return nullptr;
+}
+
+void GISelCSEInfo::countOpcodeHit(unsigned Opc) {
+#ifndef NDEBUG
+  if (OpcodeHitTable.count(Opc))
+    OpcodeHitTable[Opc] += 1;
+  else
+    OpcodeHitTable[Opc] = 1;
+#endif
+  // Else do nothing.
+}
+
+void GISelCSEInfo::recordNewInstruction(MachineInstr *MI) {
+  if (shouldCSE(MI->getOpcode())) {
+    TemporaryInsts.insert(MI);
+    LLVM_DEBUG(dbgs() << "CSEInfo: Recording new MI" << *MI << "\n";);
+  }
+}
+
+void GISelCSEInfo::handleRecordedInst(MachineInstr *MI) {
+  assert(shouldCSE(MI->getOpcode()) && "Invalid instruction for CSE");
+  auto *UMI = InstrMapping.lookup(MI);
+  LLVM_DEBUG(dbgs() << "CSEInfo: Handling recorded MI" << *MI << "\n";);
+  if (UMI) {
+    // Invalidate this MI.
+    invalidateUniqueMachineInstr(UMI);
+    InstrMapping.erase(MI);
+  }
+  /// Now insert the new instruction.
+  if (UMI) {
+    /// We'll reuse the same UniqueMachineInstr to avoid the new
+    /// allocation.
+    *UMI = UniqueMachineInstr(MI);
+    insertNode(UMI, nullptr);
+  } else {
+    /// This is a new instruction. Allocate a new UniqueMachineInstr and
+    /// Insert.
+    insertInstr(MI);
+  }
+}
+
+void GISelCSEInfo::handleRemoveInst(MachineInstr *MI) {
+  if (auto *UMI = InstrMapping.lookup(MI)) {
+    invalidateUniqueMachineInstr(UMI);
+    InstrMapping.erase(MI);
+  }
+  TemporaryInsts.remove(MI);
+}
+
+void GISelCSEInfo::handleRecordedInsts() {
+  while (!TemporaryInsts.empty()) {
+    auto *MI = TemporaryInsts.pop_back_val();
+    handleRecordedInst(MI);
+  }
+}
+
+bool GISelCSEInfo::shouldCSE(unsigned Opc) const {
+  // Only GISel opcodes are CSEable
+  if (!isPreISelGenericOpcode(Opc))
+    return false;
+  assert(CSEOpt.get() && "CSEConfig not set");
+  return CSEOpt->shouldCSEOpc(Opc);
+}
+
+void GISelCSEInfo::erasingInstr(MachineInstr &MI) { handleRemoveInst(&MI); }
+void GISelCSEInfo::createdInstr(MachineInstr &MI) { recordNewInstruction(&MI); }
+void GISelCSEInfo::changingInstr(MachineInstr &MI) {
+  // For now, perform erase, followed by insert.
+  erasingInstr(MI);
+  createdInstr(MI);
+}
+void GISelCSEInfo::changedInstr(MachineInstr &MI) { changingInstr(MI); }
+
+void GISelCSEInfo::analyze(MachineFunction &MF) {
+  setMF(MF);
+  for (auto &MBB : MF) {
+    if (MBB.empty())
+      continue;
+    for (MachineInstr &MI : MBB) {
+      if (!shouldCSE(MI.getOpcode()))
+        continue;
+      LLVM_DEBUG(dbgs() << "CSEInfo::Add MI: " << MI << "\n";);
+      insertInstr(&MI);
+    }
+  }
+}
+
+void GISelCSEInfo::releaseMemory() {
+  // print();
+  CSEMap.clear();
+  InstrMapping.clear();
+  UniqueInstrAllocator.Reset();
+  TemporaryInsts.clear();
+  CSEOpt.reset();
+  MRI = nullptr;
+  MF = nullptr;
+#ifndef NDEBUG
+  OpcodeHitTable.clear();
+#endif
+}
+
+void GISelCSEInfo::print() {
+#ifndef NDEBUG
+  for (auto &It : OpcodeHitTable) {
+    dbgs() << "CSE Count for Opc " << It.first << " : " << It.second << "\n";
+  };
+#endif
+}
+/// -----------------------------------------
+// ---- Profiling methods for FoldingSetNode --- //
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeID(const MachineInstr *MI) const {
+  addNodeIDMBB(MI->getParent());
+  addNodeIDOpcode(MI->getOpcode());
+  for (auto &Op : MI->operands())
+    addNodeIDMachineOperand(Op);
+  addNodeIDFlag(MI->getFlags());
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDOpcode(unsigned Opc) const {
+  ID.AddInteger(Opc);
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDRegType(const LLT &Ty) const {
+  uint64_t Val = Ty.getUniqueRAWLLTData();
+  ID.AddInteger(Val);
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDRegType(const TargetRegisterClass *RC) const {
+  ID.AddPointer(RC);
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDRegType(const RegisterBank *RB) const {
+  ID.AddPointer(RB);
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDImmediate(int64_t Imm) const {
+  ID.AddInteger(Imm);
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDRegNum(unsigned Reg) const {
+  ID.AddInteger(Reg);
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDRegType(const unsigned Reg) const {
+  addNodeIDMachineOperand(MachineOperand::CreateReg(Reg, false));
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDMBB(const MachineBasicBlock *MBB) const {
+  ID.AddPointer(MBB);
+  return *this;
+}
+
+const GISelInstProfileBuilder &
+GISelInstProfileBuilder::addNodeIDFlag(unsigned Flag) const {
+  if (Flag)
+    ID.AddInteger(Flag);
+  return *this;
+}
+
+const GISelInstProfileBuilder &GISelInstProfileBuilder::addNodeIDMachineOperand(
+    const MachineOperand &MO) const {
+  if (MO.isReg()) {
+    unsigned Reg = MO.getReg();
+    if (!MO.isDef())
+      addNodeIDRegNum(Reg);
+    LLT Ty = MRI.getType(Reg);
+    if (Ty.isValid())
+      addNodeIDRegType(Ty);
+    auto *RB = MRI.getRegBankOrNull(Reg);
+    if (RB)
+      addNodeIDRegType(RB);
+    auto *RC = MRI.getRegClassOrNull(Reg);
+    if (RC)
+      addNodeIDRegType(RC);
+    assert(!MO.isImplicit() && "Unhandled case");
+  } else if (MO.isImm())
+    ID.AddInteger(MO.getImm());
+  else if (MO.isCImm())
+    ID.AddPointer(MO.getCImm());
+  else if (MO.isFPImm())
+    ID.AddPointer(MO.getFPImm());
+  else if (MO.isPredicate())
+    ID.AddInteger(MO.getPredicate());
+  else
+    llvm_unreachable("Unhandled operand type");
+  // Handle other types
+  return *this;
+}
+
+GISelCSEInfo &GISelCSEAnalysisWrapper::get(std::unique_ptr<CSEConfig> CSEOpt,
+                                           bool Recompute) {
+  if (!AlreadyComputed || Recompute) {
+    Info.setCSEConfig(std::move(CSEOpt));
+    Info.analyze(*MF);
+    AlreadyComputed = true;
+  }
+  return Info;
+}
+void GISelCSEAnalysisWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesAll();
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+bool GISelCSEAnalysisWrapperPass::runOnMachineFunction(MachineFunction &MF) {
+  releaseMemory();
+  Wrapper.setMF(MF);
+  return false;
+}
Index: lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
===================================================================
--- /dev/null
+++ lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
@@ -0,0 +1,231 @@
+//===-- llvm/CodeGen/GlobalISel/CSEMIRBuilder.cpp - MIBuilder--*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file implements the CSEMIRBuilder class which CSEs as it builds
+/// instructions.
+//===----------------------------------------------------------------------===//
+//
+
+#include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
+#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
+
+using namespace llvm;
+
+bool CSEMIRBuilder::dominates(MachineBasicBlock::const_iterator A,
+                              MachineBasicBlock::const_iterator B) const {
+  auto MBBEnd = getMBB().end();
+  if (B == MBBEnd)
+    return true;
+  assert(A->getParent() == B->getParent() &&
+         "Iterators should be in same block");
+  const MachineBasicBlock *BBA = A->getParent();
+  MachineBasicBlock::const_iterator I = BBA->begin();
+  for (; &*I != A && &*I != B; ++I)
+    ;
+  return &*I == A;
+}
+
+MachineInstrBuilder
+CSEMIRBuilder::getDominatingInstrForID(FoldingSetNodeID &ID,
+                                       void *&NodeInsertPos) {
+  GISelCSEInfo *CSEInfo = getCSEInfo();
+  assert(CSEInfo && "Can't get here without setting CSEInfo");
+  MachineBasicBlock *CurMBB = &getMBB();
+  MachineInstr *MI =
+      CSEInfo->getMachineInstrIfExists(ID, CurMBB, NodeInsertPos);
+  if (MI) {
+    auto CurrPos = getInsertPt();
+    if (!dominates(MI, CurrPos))
+      CurMBB->splice(CurrPos, CurMBB, MI);
+    return MachineInstrBuilder(getMF(), MI);
+  }
+  return MachineInstrBuilder();
+}
+
+bool CSEMIRBuilder::canPerformCSEForOpc(unsigned Opc) const {
+  const GISelCSEInfo *CSEInfo = getCSEInfo();
+  if (!CSEInfo || !CSEInfo->shouldCSE(Opc))
+    return false;
+  return true;
+}
+
+void CSEMIRBuilder::profileDstOp(const DstOp &Op,
+                                 GISelInstProfileBuilder &B) const {
+  switch (Op.getDstOpKind()) {
+  case DstOp::DstType::Ty_RC:
+    B.addNodeIDRegType(Op.getRegClass());
+    break;
+  default:
+    B.addNodeIDRegType(Op.getLLTTy(*getMRI()));
+    break;
+  }
+}
+
+void CSEMIRBuilder::profileSrcOp(const SrcOp &Op,
+                                 GISelInstProfileBuilder &B) const {
+  switch (Op.getSrcOpKind()) {
+  case SrcOp::SrcType::Ty_Predicate:
+    B.addNodeIDImmediate(static_cast<int64_t>(Op.getPredicate()));
+    break;
+  default:
+    B.addNodeIDRegType(Op.getReg());
+    break;
+  }
+}
+
+void CSEMIRBuilder::profileMBBOpcode(GISelInstProfileBuilder &B,
+                                     unsigned Opc) const {
+  // First add the MBB (Local CSE).
+  B.addNodeIDMBB(&getMBB());
+  // Then add the opcode.
+  B.addNodeIDOpcode(Opc);
+}
+
+void CSEMIRBuilder::profileEverything(unsigned Opc, ArrayRef<DstOp> DstOps,
+                                      ArrayRef<SrcOp> SrcOps,
+                                      Optional<unsigned> Flags,
+                                      GISelInstProfileBuilder &B) const {
+
+  profileMBBOpcode(B, Opc);
+  // Then add the DstOps.
+  profileDstOps(DstOps, B);
+  // Then add the SrcOps.
+  profileSrcOps(SrcOps, B);
+  // Add Flags if passed in.
+  if (Flags)
+    B.addNodeIDFlag(*Flags);
+}
+
+MachineInstrBuilder CSEMIRBuilder::memoizeMI(MachineInstrBuilder MIB,
+                                             void *NodeInsertPos) {
+  assert(canPerformCSEForOpc(MIB->getOpcode()) &&
+         "Attempting to CSE illegal op");
+  MachineInstr *MIBInstr = MIB;
+  getCSEInfo()->insertInstr(MIBInstr, NodeInsertPos);
+  return MIB;
+}
+
+bool CSEMIRBuilder::checkCopyToDefsPossible(ArrayRef<DstOp> DstOps) {
+  if (DstOps.size() == 1)
+    return true; // always possible to emit copy to just 1 vreg.
+
+  return std::all_of(DstOps.begin(), DstOps.end(), [](const DstOp &Op) {
+    DstOp::DstType DT = Op.getDstOpKind();
+    return DT == DstOp::DstType::Ty_LLT || DT == DstOp::DstType::Ty_RC;
+  });
+}
+
+MachineInstrBuilder
+CSEMIRBuilder::generateCopiesIfRequired(ArrayRef<DstOp> DstOps,
+                                        MachineInstrBuilder &MIB) {
+  assert(checkCopyToDefsPossible(DstOps) &&
+         "Impossible return a single MIB with copies to multiple defs");
+  if (DstOps.size() == 1) {
+    const DstOp &Op = DstOps[0];
+    if (Op.getDstOpKind() == DstOp::DstType::Ty_Reg)
+      return buildCopy(Op.getReg(), MIB->getOperand(0).getReg());
+  }
+  return MIB;
+}
+
+MachineInstrBuilder CSEMIRBuilder::buildInstr(unsigned Opc,
+                                              ArrayRef<DstOp> DstOps,
+                                              ArrayRef<SrcOp> SrcOps,
+                                              Optional<unsigned> Flag) {
+  switch (Opc) {
+  default:
+    break;
+  case TargetOpcode::G_ADD:
+  case TargetOpcode::G_AND:
+  case TargetOpcode::G_ASHR:
+  case TargetOpcode::G_LSHR:
+  case TargetOpcode::G_MUL:
+  case TargetOpcode::G_OR:
+  case TargetOpcode::G_SHL:
+  case TargetOpcode::G_SUB:
+  case TargetOpcode::G_XOR:
+  case TargetOpcode::G_UDIV:
+  case TargetOpcode::G_SDIV:
+  case TargetOpcode::G_UREM:
+  case TargetOpcode::G_SREM: {
+    // Try to constant fold these.
+    assert(SrcOps.size() == 2 && "Invalid sources");
+    assert(DstOps.size() == 1 && "Invalid dsts");
+    if (Optional<APInt> Cst = ConstantFoldBinOp(Opc, SrcOps[0].getReg(),
+                                                SrcOps[1].getReg(), *getMRI()))
+      return buildConstant(DstOps[0], Cst->getSExtValue());
+    break;
+  }
+  }
+  bool CanCopy = checkCopyToDefsPossible(DstOps);
+  if (!canPerformCSEForOpc(Opc))
+    return MachineIRBuilder::buildInstr(Opc, DstOps, SrcOps, Flag);
+  // If we can CSE this instruction, but involves generating copies to multiple
+  // regs, give up. This frequently happens to UNMERGEs.
+  if (!CanCopy) {
+    auto MIB = MachineIRBuilder::buildInstr(Opc, DstOps, SrcOps, Flag);
+    // CSEInfo would have tracked this instruction. Remove it from the temporary
+    // insts.
+    getCSEInfo()->handleRemoveInst(&*MIB);
+    return MIB;
+  }
+  FoldingSetNodeID ID;
+  GISelInstProfileBuilder ProfBuilder(ID, *getMRI());
+  void *InsertPos = nullptr;
+  profileEverything(Opc, DstOps, SrcOps, Flag, ProfBuilder);
+  MachineInstrBuilder MIB = getDominatingInstrForID(ID, InsertPos);
+  if (MIB) {
+    // Handle generating copies here.
+    return generateCopiesIfRequired(DstOps, MIB);
+  }
+  // This instruction does not exist in the CSEInfo. Build it and CSE it.
+  MachineInstrBuilder NewMIB =
+      MachineIRBuilder::buildInstr(Opc, DstOps, SrcOps, Flag);
+  return memoizeMI(NewMIB, InsertPos);
+}
+
+MachineInstrBuilder CSEMIRBuilder::buildConstant(const DstOp &Res,
+                                                 const ConstantInt &Val) {
+  constexpr unsigned Opc = TargetOpcode::G_CONSTANT;
+  if (!canPerformCSEForOpc(Opc))
+    return MachineIRBuilder::buildConstant(Res, Val);
+  FoldingSetNodeID ID;
+  GISelInstProfileBuilder ProfBuilder(ID, *getMRI());
+  void *InsertPos = nullptr;
+  profileMBBOpcode(ProfBuilder, Opc);
+  profileDstOp(Res, ProfBuilder);
+  ProfBuilder.addNodeIDMachineOperand(MachineOperand::CreateCImm(&Val));
+  MachineInstrBuilder MIB = getDominatingInstrForID(ID, InsertPos);
+  if (MIB) {
+    // Handle generating copies here.
+    return generateCopiesIfRequired({Res}, MIB);
+  }
+  MachineInstrBuilder NewMIB = MachineIRBuilder::buildConstant(Res, Val);
+  return memoizeMI(NewMIB, InsertPos);
+}
+
+MachineInstrBuilder CSEMIRBuilder::buildFConstant(const DstOp &Res,
+                                                  const ConstantFP &Val) {
+  constexpr unsigned Opc = TargetOpcode::G_FCONSTANT;
+  if (!canPerformCSEForOpc(Opc))
+    return MachineIRBuilder::buildFConstant(Res, Val);
+  FoldingSetNodeID ID;
+  GISelInstProfileBuilder ProfBuilder(ID, *getMRI());
+  void *InsertPos = nullptr;
+  profileMBBOpcode(ProfBuilder, Opc);
+  profileDstOp(Res, ProfBuilder);
+  ProfBuilder.addNodeIDMachineOperand(MachineOperand::CreateFPImm(&Val));
+  MachineInstrBuilder MIB = getDominatingInstrForID(ID, InsertPos);
+  if (MIB) {
+    // Handle generating copies here.
+    return generateCopiesIfRequired({Res}, MIB);
+  }
+  MachineInstrBuilder NewMIB = MachineIRBuilder::buildFConstant(Res, Val);
+  return memoizeMI(NewMIB, InsertPos);
+}
Index: lib/CodeGen/GlobalISel/Combiner.cpp
===================================================================
--- lib/CodeGen/GlobalISel/Combiner.cpp
+++ lib/CodeGen/GlobalISel/Combiner.cpp
@@ -13,7 +13,9 @@
 
 #include "llvm/CodeGen/GlobalISel/Combiner.h"
 #include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/CodeGen/GlobalISel/CSEInfo.h"
 #include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
+#include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
@@ -35,38 +37,33 @@
 /// instruction creation will schedule that instruction for a future visit.
 /// Other Combiner implementations may require more complex behaviour from
 /// their GISelChangeObserver subclass.
-class WorkListMaintainer : public GISelChangeObserver,
-                           public MachineFunction::Delegate {
+class WorkListMaintainer : public GISelChangeObserver {
   using WorkListTy = GISelWorkList<512>;
-  MachineFunction &MF;
   WorkListTy &WorkList;
   /// The instructions that have been created but we want to report once they
   /// have their operands. This is only maintained if debug output is requested.
   SmallPtrSet<const MachineInstr *, 4> CreatedInstrs;
 
 public:
-  WorkListMaintainer(MachineFunction &MF, WorkListTy &WorkList)
-      : GISelChangeObserver(), MF(MF), WorkList(WorkList) {
-    MF.setDelegate(this);
-  }
+  WorkListMaintainer(WorkListTy &WorkList)
+      : GISelChangeObserver(), WorkList(WorkList) {}
   virtual ~WorkListMaintainer() {
-    MF.resetDelegate(this);
   }
 
-  void erasingInstr(const MachineInstr &MI) override {
+  void erasingInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << "Erased: " << MI << "\n");
     WorkList.remove(&MI);
   }
-  void createdInstr(const MachineInstr &MI) override {
+  void createdInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << "Creating: " << MI << "\n");
     WorkList.insert(&MI);
     LLVM_DEBUG(CreatedInstrs.insert(&MI));
   }
-  void changingInstr(const MachineInstr &MI) override {
+  void changingInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << "Changing: " << MI << "\n");
     WorkList.insert(&MI);
   }
-  void changedInstr(const MachineInstr &MI) override {
+  void changedInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << "Changed: " << MI << "\n");
     WorkList.insert(&MI);
   }
@@ -79,13 +76,6 @@
     });
     LLVM_DEBUG(CreatedInstrs.clear());
   }
-
-  void MF_HandleInsertion(const MachineInstr &MI) override {
-    createdInstr(MI);
-  }
-  void MF_HandleRemoval(const MachineInstr &MI) override {
-    erasingInstr(MI);
-  }
 };
 }
 
@@ -94,15 +84,20 @@
   (void)this->TPC; // FIXME: Remove when used.
 }
 
-bool Combiner::combineMachineInstrs(MachineFunction &MF) {
+bool Combiner::combineMachineInstrs(MachineFunction &MF,
+                                    GISelCSEInfo *CSEInfo) {
   // If the ISel pipeline failed, do not bother running this pass.
   // FIXME: Should this be here or in individual combiner passes.
   if (MF.getProperties().hasProperty(
           MachineFunctionProperties::Property::FailedISel))
     return false;
 
+  Builder =
+      CSEInfo ? make_unique<CSEMIRBuilder>() : make_unique<MachineIRBuilder>();
   MRI = &MF.getRegInfo();
-  Builder.setMF(MF);
+  Builder->setMF(MF);
+  if (CSEInfo)
+    Builder->setCSEInfo(CSEInfo);
 
   LLVM_DEBUG(dbgs() << "Generic MI Combiner for: " << MF.getName() << '\n');
 
@@ -110,14 +105,19 @@
 
   bool MFChanged = false;
   bool Changed;
+  MachineIRBuilder &B = *Builder.get();
 
   do {
     // Collect all instructions. Do a post order traversal for basic blocks and
     // insert with list bottom up, so while we pop_back_val, we'll traverse top
     // down RPOT.
     Changed = false;
-    GISelWorkList<512> WorkList(&MF);
-    WorkListMaintainer Observer(MF, WorkList);
+    GISelWorkList<512> WorkList;
+    WorkListMaintainer Observer(WorkList);
+    GISelObserverWrapper WrapperObserver(&Observer);
+    if (CSEInfo)
+      WrapperObserver.addObserver(CSEInfo);
+    RAIIDelegateInstaller DelInstall(MF, &WrapperObserver);
     for (MachineBasicBlock *MBB : post_order(&MF)) {
       if (MBB->empty())
         continue;
@@ -137,7 +137,7 @@
     while (!WorkList.empty()) {
       MachineInstr *CurrInst = WorkList.pop_back_val();
       LLVM_DEBUG(dbgs() << "\nTry combining " << *CurrInst;);
-      Changed |= CInfo.combine(Observer, *CurrInst, Builder);
+      Changed |= CInfo.combine(WrapperObserver, *CurrInst, B);
       Observer.reportFullyCreatedInstrs();
     }
     MFChanged |= Changed;
Index: lib/CodeGen/GlobalISel/GISelChangeObserver.cpp
===================================================================
--- lib/CodeGen/GlobalISel/GISelChangeObserver.cpp
+++ lib/CodeGen/GlobalISel/GISelChangeObserver.cpp
@@ -29,3 +29,12 @@
     changedInstr(*ChangedMI);
 }
 
+RAIIDelegateInstaller::RAIIDelegateInstaller(MachineFunction &MF,
+                                             MachineFunction::Delegate *Del)
+    : MF(MF), Delegate(Del) {
+  // Register this as the delegate for handling insertions and deletions of
+  // instructions.
+  MF.setDelegate(Del);
+}
+
+RAIIDelegateInstaller::~RAIIDelegateInstaller() { MF.resetDelegate(Delegate); }
Index: lib/CodeGen/GlobalISel/IRTranslator.cpp
===================================================================
--- lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -19,6 +19,7 @@
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/GlobalISel/CallLowering.h"
+#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
 #include "llvm/CodeGen/LowLevelType.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
@@ -75,11 +76,16 @@
 
 using namespace llvm;
 
+static cl::opt<bool>
+    EnableCSEInIRTranslator("enable-cse-in-irtranslator",
+                            cl::desc("Should enable CSE in irtranslator"),
+                            cl::Optional, cl::init(false));
 char IRTranslator::ID = 0;
 
 INITIALIZE_PASS_BEGIN(IRTranslator, DEBUG_TYPE, "IRTranslator LLVM IR -> MI",
                 false, false)
 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
+INITIALIZE_PASS_DEPENDENCY(GISelCSEAnalysisWrapperPass)
 INITIALIZE_PASS_END(IRTranslator, DEBUG_TYPE, "IRTranslator LLVM IR -> MI",
                 false, false)
 
@@ -108,18 +114,21 @@
 namespace {
 /// Verify that every instruction created has the same DILocation as the
 /// instruction being translated.
-class DILocationVerifier : MachineFunction::Delegate {
-  MachineFunction &MF;
+class DILocationVerifier : public GISelChangeObserver {
   const Instruction *CurrInst = nullptr;
 
 public:
-  DILocationVerifier(MachineFunction &MF) : MF(MF) { MF.setDelegate(this); }
-  ~DILocationVerifier() { MF.resetDelegate(this); }
+  DILocationVerifier() = default;
+  ~DILocationVerifier() = default;
 
   const Instruction *getCurrentInst() const { return CurrInst; }
   void setCurrentInst(const Instruction *Inst) { CurrInst = Inst; }
 
-  void MF_HandleInsertion(const MachineInstr &MI) override {
+  void erasingInstr(MachineInstr &MI) override {}
+  void changingInstr(MachineInstr &MI) override {}
+  void changedInstr(MachineInstr &MI) override {}
+
+  void createdInstr(MachineInstr &MI) override {
     assert(getCurrentInst() && "Inserted instruction without a current MI");
 
     // Only print the check message if we're actually checking it.
@@ -130,7 +139,6 @@
     assert(CurrInst->getDebugLoc() == MI.getDebugLoc() &&
            "Line info was not transferred to all instructions");
   }
-  void MF_HandleRemoval(const MachineInstr &MI) override {}
 };
 } // namespace
 #endif // ifndef NDEBUG
@@ -139,6 +147,7 @@
 void IRTranslator::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<StackProtector>();
   AU.addRequired<TargetPassConfig>();
+  AU.addRequired<GISelCSEAnalysisWrapperPass>();
   getSelectionDAGFallbackAnalysisUsage(AU);
   MachineFunctionPass::getAnalysisUsage(AU);
 }
@@ -1553,12 +1562,14 @@
 
 void IRTranslator::finishPendingPhis() {
 #ifndef NDEBUG
-  DILocationVerifier Verifier(*MF);
+  DILocationVerifier Verifier;
+  GISelObserverWrapper WrapperObserver(&Verifier);
+  RAIIDelegateInstaller DelInstall(*MF, &WrapperObserver);
 #endif // ifndef NDEBUG
   for (auto &Phi : PendingPHIs) {
     const PHINode *PI = Phi.first;
     ArrayRef<MachineInstr *> ComponentPHIs = Phi.second;
-    EntryBuilder.setDebugLoc(PI->getDebugLoc());
+    EntryBuilder->setDebugLoc(PI->getDebugLoc());
 #ifndef NDEBUG
     Verifier.setCurrentInst(PI);
 #endif // ifndef NDEBUG
@@ -1599,11 +1610,12 @@
 }
 
 bool IRTranslator::translate(const Instruction &Inst) {
-  CurBuilder.setDebugLoc(Inst.getDebugLoc());
-  EntryBuilder.setDebugLoc(Inst.getDebugLoc());
+  CurBuilder->setDebugLoc(Inst.getDebugLoc());
+  EntryBuilder->setDebugLoc(Inst.getDebugLoc());
   switch(Inst.getOpcode()) {
-#define HANDLE_INST(NUM, OPCODE, CLASS) \
-    case Instruction::OPCODE: return translate##OPCODE(Inst, CurBuilder);
+#define HANDLE_INST(NUM, OPCODE, CLASS)                                        \
+  case Instruction::OPCODE:                                                    \
+    return translate##OPCODE(Inst, *CurBuilder.get());
 #include "llvm/IR/Instruction.def"
   default:
     return false;
@@ -1612,11 +1624,11 @@
 
 bool IRTranslator::translate(const Constant &C, unsigned Reg) {
   if (auto CI = dyn_cast<ConstantInt>(&C))
-    EntryBuilder.buildConstant(Reg, *CI);
+    EntryBuilder->buildConstant(Reg, *CI);
   else if (auto CF = dyn_cast<ConstantFP>(&C))
-    EntryBuilder.buildFConstant(Reg, *CF);
+    EntryBuilder->buildFConstant(Reg, *CF);
   else if (isa<UndefValue>(C))
-    EntryBuilder.buildUndef(Reg);
+    EntryBuilder->buildUndef(Reg);
   else if (isa<ConstantPointerNull>(C)) {
     // As we are trying to build a constant val of 0 into a pointer,
     // insert a cast to make them correct with respect to types.
@@ -1624,9 +1636,9 @@
     auto *ZeroTy = Type::getIntNTy(C.getContext(), NullSize);
     auto *ZeroVal = ConstantInt::get(ZeroTy, 0);
     unsigned ZeroReg = getOrCreateVReg(*ZeroVal);
-    EntryBuilder.buildCast(Reg, ZeroReg);
+    EntryBuilder->buildCast(Reg, ZeroReg);
   } else if (auto GV = dyn_cast<GlobalValue>(&C))
-    EntryBuilder.buildGlobalValue(Reg, GV);
+    EntryBuilder->buildGlobalValue(Reg, GV);
   else if (auto CAZ = dyn_cast<ConstantAggregateZero>(&C)) {
     if (!CAZ->getType()->isVectorTy())
       return false;
@@ -1638,7 +1650,7 @@
       Constant &Elt = *CAZ->getElementValue(i);
       Ops.push_back(getOrCreateVReg(Elt));
     }
-    EntryBuilder.buildBuildVector(Reg, Ops);
+    EntryBuilder->buildBuildVector(Reg, Ops);
   } else if (auto CV = dyn_cast<ConstantDataVector>(&C)) {
     // Return the scalar if it is a <1 x Ty> vector.
     if (CV->getNumElements() == 1)
@@ -1648,11 +1660,12 @@
       Constant &Elt = *CV->getElementAsConstant(i);
       Ops.push_back(getOrCreateVReg(Elt));
     }
-    EntryBuilder.buildBuildVector(Reg, Ops);
+    EntryBuilder->buildBuildVector(Reg, Ops);
   } else if (auto CE = dyn_cast<ConstantExpr>(&C)) {
     switch(CE->getOpcode()) {
-#define HANDLE_INST(NUM, OPCODE, CLASS)                         \
-      case Instruction::OPCODE: return translate##OPCODE(*CE, EntryBuilder);
+#define HANDLE_INST(NUM, OPCODE, CLASS)                                        \
+  case Instruction::OPCODE:                                                    \
+    return translate##OPCODE(*CE, *EntryBuilder.get());
 #include "llvm/IR/Instruction.def"
     default:
       return false;
@@ -1664,9 +1677,9 @@
     for (unsigned i = 0; i < CV->getNumOperands(); ++i) {
       Ops.push_back(getOrCreateVReg(*CV->getOperand(i)));
     }
-    EntryBuilder.buildBuildVector(Reg, Ops);
+    EntryBuilder->buildBuildVector(Reg, Ops);
   } else if (auto *BA = dyn_cast<BlockAddress>(&C)) {
-    EntryBuilder.buildBlockAddress(Reg, BA);
+    EntryBuilder->buildBlockAddress(Reg, BA);
   } else
     return false;
 
@@ -1683,8 +1696,8 @@
   // MachineIRBuilder::DebugLoc can outlive the DILocation it holds. Clear it
   // to avoid accessing free’d memory (in runOnMachineFunction) and to avoid
   // destroying it twice (in ~IRTranslator() and ~LLVMContext())
-  EntryBuilder = MachineIRBuilder();
-  CurBuilder = MachineIRBuilder();
+  EntryBuilder.reset();
+  CurBuilder.reset();
 }
 
 bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
@@ -1692,12 +1705,30 @@
   const Function &F = MF->getFunction();
   if (F.empty())
     return false;
+  GISelCSEAnalysisWrapper &Wrapper =
+      getAnalysis<GISelCSEAnalysisWrapperPass>().getCSEWrapper();
+  // Set the CSEConfig and run the analysis.
+  GISelCSEInfo *CSEInfo = nullptr;
+  TPC = &getAnalysis<TargetPassConfig>();
+  bool IsO0 = TPC->getOptLevel() == CodeGenOpt::Level::None;
+  // Disable CSE for O0.
+  bool EnableCSE = !IsO0 && EnableCSEInIRTranslator;
+  if (EnableCSE) {
+    EntryBuilder = make_unique<CSEMIRBuilder>(CurMF);
+    std::unique_ptr<CSEConfig> Config = make_unique<CSEConfig>();
+    CSEInfo = &Wrapper.get(std::move(Config));
+    EntryBuilder->setCSEInfo(CSEInfo);
+    CurBuilder = make_unique<CSEMIRBuilder>(CurMF);
+    CurBuilder->setCSEInfo(CSEInfo);
+  } else {
+    EntryBuilder = make_unique<MachineIRBuilder>();
+    CurBuilder = make_unique<MachineIRBuilder>();
+  }
   CLI = MF->getSubtarget().getCallLowering();
-  CurBuilder.setMF(*MF);
-  EntryBuilder.setMF(*MF);
+  CurBuilder->setMF(*MF);
+  EntryBuilder->setMF(*MF);
   MRI = &MF->getRegInfo();
   DL = &F.getParent()->getDataLayout();
-  TPC = &getAnalysis<TargetPassConfig>();
   ORE = llvm::make_unique<OptimizationRemarkEmitter>(&F);
 
   assert(PendingPHIs.empty() && "stale PHIs");
@@ -1716,7 +1747,7 @@
   // Setup a separate basic-block for the arguments and constants
   MachineBasicBlock *EntryBB = MF->CreateMachineBasicBlock();
   MF->push_back(EntryBB);
-  EntryBuilder.setMBB(*EntryBB);
+  EntryBuilder->setMBB(*EntryBB);
 
   // Create all blocks, in IR order, to preserve the layout.
   for (const BasicBlock &BB: F) {
@@ -1753,7 +1784,7 @@
     }
   }
 
-  if (!CLI->lowerFormalArguments(EntryBuilder, F, VRegArgs)) {
+  if (!CLI->lowerFormalArguments(*EntryBuilder.get(), F, VRegArgs)) {
     OptimizationRemarkMissed R("gisel-irtranslator", "GISelFailure",
                                F.getSubprogram(), &F.getEntryBlock());
     R << "unable to lower arguments: " << ore::NV("Prototype", F.getType());
@@ -1770,22 +1801,27 @@
       assert(VRegs.empty() && "VRegs already populated?");
       VRegs.push_back(VArg);
     } else {
-      unpackRegs(*ArgIt, VArg, EntryBuilder);
+      unpackRegs(*ArgIt, VArg, *EntryBuilder.get());
     }
     ArgIt++;
   }
 
   // Need to visit defs before uses when translating instructions.
+  GISelObserverWrapper WrapperObserver;
+  if (EnableCSE && CSEInfo)
+    WrapperObserver.addObserver(CSEInfo);
   {
     ReversePostOrderTraversal<const Function *> RPOT(&F);
 #ifndef NDEBUG
-    DILocationVerifier Verifier(*MF);
+    DILocationVerifier Verifier;
+    WrapperObserver.addObserver(&Verifier);
 #endif // ifndef NDEBUG
+    RAIIDelegateInstaller DelInstall(*MF, &WrapperObserver);
     for (const BasicBlock *BB : RPOT) {
       MachineBasicBlock &MBB = getMBB(*BB);
       // Set the insertion point of all the following translations to
       // the end of this basic block.
-      CurBuilder.setMBB(MBB);
+      CurBuilder->setMBB(MBB);
 
       for (const Instruction &Inst : *BB) {
 #ifndef NDEBUG
@@ -1810,6 +1846,9 @@
         return false;
       }
     }
+#ifndef NDEBUG
+    WrapperObserver.removeObserver(&Verifier);
+#endif
   }
 
   finishPendingPhis();
Index: lib/CodeGen/GlobalISel/Legalizer.cpp
===================================================================
--- lib/CodeGen/GlobalISel/Legalizer.cpp
+++ lib/CodeGen/GlobalISel/Legalizer.cpp
@@ -16,6 +16,8 @@
 #include "llvm/CodeGen/GlobalISel/Legalizer.h"
 #include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/SetVector.h"
+#include "llvm/CodeGen/GlobalISel/CSEInfo.h"
+#include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
 #include "llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h"
@@ -33,11 +35,17 @@
 
 using namespace llvm;
 
+static cl::opt<bool>
+    EnableCSEInLegalizer("enable-cse-in-legalizer",
+                         cl::desc("Should enable CSE in Legalizer"),
+                         cl::Optional, cl::init(false));
+
 char Legalizer::ID = 0;
 INITIALIZE_PASS_BEGIN(Legalizer, DEBUG_TYPE,
                       "Legalize the Machine IR a function's Machine IR", false,
                       false)
 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
+INITIALIZE_PASS_DEPENDENCY(GISelCSEAnalysisWrapperPass)
 INITIALIZE_PASS_END(Legalizer, DEBUG_TYPE,
                     "Legalize the Machine IR a function's Machine IR", false,
                     false)
@@ -48,6 +56,8 @@
 
 void Legalizer::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<TargetPassConfig>();
+  AU.addRequired<GISelCSEAnalysisWrapperPass>();
+  AU.addPreserved<GISelCSEAnalysisWrapperPass>();
   getSelectionDAGFallbackAnalysisUsage(AU);
   MachineFunctionPass::getAnalysisUsage(AU);
 }
@@ -82,7 +92,7 @@
   LegalizerWorkListManager(InstListTy &Insts, ArtifactListTy &Arts)
       : InstList(Insts), ArtifactList(Arts) {}
 
-  void createdInstr(const MachineInstr &MI) override {
+  void createdInstr(MachineInstr &MI) override {
     // Only legalize pre-isel generic instructions.
     // Legalization process could generate Target specific pseudo
     // instructions with generic types. Don't record them
@@ -95,17 +105,17 @@
     LLVM_DEBUG(dbgs() << ".. .. New MI: " << MI);
   }
 
-  void erasingInstr(const MachineInstr &MI) override {
+  void erasingInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << ".. .. Erasing: " << MI);
     InstList.remove(&MI);
     ArtifactList.remove(&MI);
   }
 
-  void changingInstr(const MachineInstr &MI) override {
+  void changingInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << ".. .. Changing MI: " << MI);
   }
 
-  void changedInstr(const MachineInstr &MI) override {
+  void changedInstr(MachineInstr &MI) override {
     // When insts change, we want to revisit them to legalize them again.
     // We'll consider them the same as created.
     LLVM_DEBUG(dbgs() << ".. .. Changed MI: " << MI);
@@ -122,14 +132,16 @@
   LLVM_DEBUG(dbgs() << "Legalize Machine IR for: " << MF.getName() << '\n');
   init(MF);
   const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
+  GISelCSEAnalysisWrapper &Wrapper =
+      getAnalysis<GISelCSEAnalysisWrapperPass>().getCSEWrapper();
   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
 
   const size_t NumBlocks = MF.size();
   MachineRegisterInfo &MRI = MF.getRegInfo();
 
   // Populate Insts
-  InstListTy InstList(&MF);
-  ArtifactListTy ArtifactList(&MF);
+  InstListTy InstList;
+  ArtifactListTy ArtifactList;
   ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
   // Perform legalization bottom up so we can DCE as we legalize.
   // Traverse BB in RPOT and within each basic block, add insts top down,
@@ -148,12 +160,34 @@
         InstList.insert(&MI);
     }
   }
+  std::unique_ptr<MachineIRBuilder> MIRBuilder;
+  GISelCSEInfo *CSEInfo = nullptr;
+  bool IsO0 = TPC.getOptLevel() == CodeGenOpt::Level::None;
+  // Disable CSE for O0.
+  bool EnableCSE = !IsO0 && EnableCSEInLegalizer;
+  if (EnableCSE) {
+    MIRBuilder = make_unique<CSEMIRBuilder>();
+    std::unique_ptr<CSEConfig> Config = make_unique<CSEConfig>();
+    CSEInfo = &Wrapper.get(std::move(Config));
+    MIRBuilder->setCSEInfo(CSEInfo);
+  } else
+    MIRBuilder = make_unique<MachineIRBuilder>();
+  // This observer keeps the worklist updated.
   LegalizerWorkListManager WorkListObserver(InstList, ArtifactList);
-  LegalizerHelper Helper(MF, WorkListObserver);
+  // We want both WorkListObserver as well as CSEInfo to observe all changes.
+  // Use the wrapper observer.
+  GISelObserverWrapper WrapperObserver(&WorkListObserver);
+  if (EnableCSE && CSEInfo)
+    WrapperObserver.addObserver(CSEInfo);
+  // Now install the observer as the delegate to MF.
+  // This will keep all the observers notified about new insertions/deletions.
+  RAIIDelegateInstaller DelInstall(MF, &WrapperObserver);
+  LegalizerHelper Helper(MF, WrapperObserver, *MIRBuilder.get());
   const LegalizerInfo &LInfo(Helper.getLegalizerInfo());
-  LegalizationArtifactCombiner ArtCombiner(Helper.MIRBuilder, MF.getRegInfo(), LInfo);
-  auto RemoveDeadInstFromLists = [&WorkListObserver](MachineInstr *DeadMI) {
-    WorkListObserver.erasingInstr(*DeadMI);
+  LegalizationArtifactCombiner ArtCombiner(*MIRBuilder.get(), MF.getRegInfo(),
+                                           LInfo);
+  auto RemoveDeadInstFromLists = [&WrapperObserver](MachineInstr *DeadMI) {
+    WrapperObserver.erasingInstr(*DeadMI);
   };
   bool Changed = false;
   do {
Index: lib/CodeGen/GlobalISel/LegalizerHelper.cpp
===================================================================
--- lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -31,16 +31,18 @@
 using namespace LegalizeActions;
 
 LegalizerHelper::LegalizerHelper(MachineFunction &MF,
-                                 GISelChangeObserver &Observer)
-    : MRI(MF.getRegInfo()), LI(*MF.getSubtarget().getLegalizerInfo()),
-      Observer(Observer) {
+                                 GISelChangeObserver &Observer,
+                                 MachineIRBuilder &Builder)
+    : MIRBuilder(Builder), MRI(MF.getRegInfo()),
+      LI(*MF.getSubtarget().getLegalizerInfo()), Observer(Observer) {
   MIRBuilder.setMF(MF);
   MIRBuilder.setChangeObserver(Observer);
 }
 
 LegalizerHelper::LegalizerHelper(MachineFunction &MF, const LegalizerInfo &LI,
-                                 GISelChangeObserver &Observer)
-    : MRI(MF.getRegInfo()), LI(LI), Observer(Observer) {
+                                 GISelChangeObserver &Observer,
+                                 MachineIRBuilder &B)
+    : MIRBuilder(B), MRI(MF.getRegInfo()), LI(LI), Observer(Observer) {
   MIRBuilder.setMF(MF);
   MIRBuilder.setChangeObserver(Observer);
 }
Index: lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
===================================================================
--- lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
+++ lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
@@ -46,6 +46,8 @@
   State.II = MI.getIterator();
 }
 
+void MachineIRBuilder::setCSEInfo(GISelCSEInfo *Info) { State.CSEInfo = Info; }
+
 void MachineIRBuilder::setInsertPt(MachineBasicBlock &MBB,
                                    MachineBasicBlock::iterator II) {
   assert(MBB.getParent() == &getMF() &&
Index: lib/CodeGen/GlobalISel/Utils.cpp
===================================================================
--- lib/CodeGen/GlobalISel/Utils.cpp
+++ lib/CodeGen/GlobalISel/Utils.cpp
@@ -235,6 +235,57 @@
   return APF;
 }
 
+Optional<APInt> llvm::ConstantFoldBinOp(unsigned Opcode, const unsigned Op1,
+                                        const unsigned Op2,
+                                        const MachineRegisterInfo &MRI) {
+  auto MaybeOp1Cst = getConstantVRegVal(Op1, MRI);
+  auto MaybeOp2Cst = getConstantVRegVal(Op2, MRI);
+  if (MaybeOp1Cst && MaybeOp2Cst) {
+    LLT Ty = MRI.getType(Op1);
+    APInt C1(Ty.getSizeInBits(), *MaybeOp1Cst, true);
+    APInt C2(Ty.getSizeInBits(), *MaybeOp2Cst, true);
+    switch (Opcode) {
+    default:
+      break;
+    case TargetOpcode::G_ADD:
+      return C1 + C2;
+    case TargetOpcode::G_AND:
+      return C1 & C2;
+    case TargetOpcode::G_ASHR:
+      return C1.ashr(C2);
+    case TargetOpcode::G_LSHR:
+      return C1.lshr(C2);
+    case TargetOpcode::G_MUL:
+      return C1 * C2;
+    case TargetOpcode::G_OR:
+      return C1 | C2;
+    case TargetOpcode::G_SHL:
+      return C1 << C2;
+    case TargetOpcode::G_SUB:
+      return C1 - C2;
+    case TargetOpcode::G_XOR:
+      return C1 ^ C2;
+    case TargetOpcode::G_UDIV:
+      if (!C2.getBoolValue())
+        break;
+      return C1.udiv(C2);
+    case TargetOpcode::G_SDIV:
+      if (!C2.getBoolValue())
+        break;
+      return C1.sdiv(C2);
+    case TargetOpcode::G_UREM:
+      if (!C2.getBoolValue())
+        break;
+      return C1.urem(C2);
+    case TargetOpcode::G_SREM:
+      if (!C2.getBoolValue())
+        break;
+      return C1.srem(C2);
+    }
+  }
+  return None;
+}
+
 void llvm::getSelectionDAGFallbackAnalysisUsage(AnalysisUsage &AU) {
   AU.addPreserved<StackProtector>();
 }
Index: lib/CodeGen/MachineFunction.cpp
===================================================================
--- lib/CodeGen/MachineFunction.cpp
+++ lib/CodeGen/MachineFunction.cpp
@@ -139,12 +139,12 @@
   init();
 }
 
-void MachineFunction::handleInsertion(const MachineInstr &MI) {
+void MachineFunction::handleInsertion(MachineInstr &MI) {
   if (TheDelegate)
     TheDelegate->MF_HandleInsertion(MI);
 }
 
-void MachineFunction::handleRemoval(const MachineInstr &MI) {
+void MachineFunction::handleRemoval(MachineInstr &MI) {
   if (TheDelegate)
     TheDelegate->MF_HandleRemoval(MI);
 }
Index: lib/Target/AArch64/AArch64PreLegalizerCombiner.cpp
===================================================================
--- lib/Target/AArch64/AArch64PreLegalizerCombiner.cpp
+++ lib/Target/AArch64/AArch64PreLegalizerCombiner.cpp
@@ -88,7 +88,7 @@
   auto *TPC = &getAnalysis<TargetPassConfig>();
   AArch64PreLegalizerCombinerInfo PCInfo;
   Combiner C(PCInfo, TPC);
-  return C.combineMachineInstrs(MF);
+  return C.combineMachineInstrs(MF, /*CSEInfo*/ nullptr);
 }
 
 char AArch64PreLegalizerCombiner::ID = 0;
Index: lib/Target/Mips/MipsPreLegalizerCombiner.cpp
===================================================================
--- lib/Target/Mips/MipsPreLegalizerCombiner.cpp
+++ lib/Target/Mips/MipsPreLegalizerCombiner.cpp
@@ -73,7 +73,7 @@
   auto *TPC = &getAnalysis<TargetPassConfig>();
   MipsPreLegalizerCombinerInfo PCInfo;
   Combiner C(PCInfo, TPC);
-  return C.combineMachineInstrs(MF);
+  return C.combineMachineInstrs(MF, nullptr);
 }
 
 char MipsPreLegalizerCombiner::ID = 0;
Index: test/CodeGen/AArch64/GlobalISel/call-translator-cse.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/GlobalISel/call-translator-cse.ll
@@ -0,0 +1,34 @@
+; RUN: llc -mtriple=aarch64-linux-gnu -O1 -stop-after=irtranslator -enable-cse-in-irtranslator=1 -global-isel -verify-machineinstrs %s -o - 2>&1 | FileCheck %s
+
+; CHECK-LABEL: name: test_split_struct
+; CHECK: [[ADDR:%[0-9]+]]:_(p0) = COPY $x0
+; CHECK: [[LO:%[0-9]+]]:_(s64) = G_LOAD %0(p0) :: (load 8 from %ir.ptr)
+; CHECK: [[CST:%[0-9]+]]:_(s64) = G_CONSTANT i64 8
+; CHECK: [[GEP:%[0-9]+]]:_(p0) = G_GEP [[ADDR]], [[CST]](s64)
+; CHECK: [[HI:%[0-9]+]]:_(s64) = G_LOAD [[GEP]](p0) :: (load 8 from %ir.ptr + 8)
+
+; CHECK: [[IMPDEF:%[0-9]+]]:_(s128) = G_IMPLICIT_DEF
+; CHECK: [[INS1:%[0-9]+]]:_(s128) = G_INSERT [[IMPDEF]], [[LO]](s64), 0
+; CHECK: [[INS2:%[0-9]+]]:_(s128) = G_INSERT [[INS1]], [[HI]](s64), 64
+; CHECK: [[EXTLO:%[0-9]+]]:_(s64) = G_EXTRACT [[INS2]](s128), 0
+; CHECK: [[EXTHI:%[0-9]+]]:_(s64) = G_EXTRACT [[INS2]](s128), 64
+
+; CHECK: [[SP:%[0-9]+]]:_(p0) = COPY $sp
+; CHECK: [[CST2:%[0-9]+]]:_(s64) = G_CONSTANT i64 0
+; CHECK: [[GEP2:%[0-9]+]]:_(p0) = G_GEP [[SP]], [[CST2]](s64)
+; CHECK: G_STORE [[EXTLO]](s64), [[GEP2]](p0) :: (store 8 into stack, align 0)
+; CHECK: [[SP:%[0-9]+]]:_(p0) = COPY $sp
+; CHECK: [[CST3:%[0-9]+]]:_(s64) = COPY [[CST]]
+; CHECK: [[GEP3:%[0-9]+]]:_(p0) = G_GEP [[SP]], [[CST3]](s64)
+; CHECK: G_STORE [[EXTHI]](s64), [[GEP3]](p0) :: (store 8 into stack + 8, align 0)
+define void @test_split_struct([2 x i64]* %ptr) {
+  %struct = load [2 x i64], [2 x i64]* %ptr
+  call void @take_split_struct([2 x i64]* null, i64 1, i64 2, i64 3,
+                               i64 4, i64 5, i64 6,
+                               [2 x i64] %struct)
+  ret void
+}
+
+declare void @take_split_struct([2 x i64]* %ptr, i64, i64, i64,
+                               i64, i64, i64,
+                               [2 x i64] %in) ;
Index: test/CodeGen/AArch64/GlobalISel/gisel-commandline-option.ll
===================================================================
--- test/CodeGen/AArch64/GlobalISel/gisel-commandline-option.ll
+++ test/CodeGen/AArch64/GlobalISel/gisel-commandline-option.ll
@@ -45,6 +45,7 @@
 ; VERIFY-NEXT:   Verify generated machine code
 ; ENABLED-NEXT:  PreLegalizerCombiner
 ; VERIFY-NEXT:   Verify generated machine code
+; ENABLED-NEXT:  Analysis containing CSE Info
 ; ENABLED-NEXT:  Legalizer
 ; VERIFY-NEXT:   Verify generated machine code
 ; ENABLED-NEXT:  RegBankSelect
Index: test/CodeGen/AArch64/GlobalISel/legalize-ext-cse.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/GlobalISel/legalize-ext-cse.mir
@@ -0,0 +1,21 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=aarch64 -run-pass=legalizer %s -o - -enable-cse-in-legalizer=1 -O1 | FileCheck %s
+---
+name:            test_cse_in_legalizer
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: test_cse_in_legalizer
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[COPY]](s64)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[TRUNC]], [[C]]
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[AND]](s32)
+    ; CHECK: $w0 = COPY [[COPY1]](s32)
+    ; CHECK: $w0 = COPY [[AND]](s32)
+    %0:_(s64) = COPY $x0
+    %1:_(s8) = G_TRUNC %0(s64)
+    %19:_(s32) = G_ZEXT %1(s8)
+    $w0 = COPY %19(s32)
+    %2:_(s8) = G_TRUNC %0(s64)
+    %20:_(s32) = G_ZEXT %2(s8)
+    $w0 = COPY %20(s32)
Index: test/CodeGen/AArch64/O0-pipeline.ll
===================================================================
--- test/CodeGen/AArch64/O0-pipeline.ll
+++ test/CodeGen/AArch64/O0-pipeline.ll
@@ -32,8 +32,10 @@
 ; CHECK-NEXT:       Safe Stack instrumentation pass
 ; CHECK-NEXT:       Insert stack protectors
 ; CHECK-NEXT:       Module Verifier
+; CHECK-NEXT:       Analysis containing CSE Info
 ; CHECK-NEXT:       IRTranslator
 ; CHECK-NEXT:       AArch64PreLegalizerCombiner
+; CHECK-NEXT:       Analysis containing CSE Info
 ; CHECK-NEXT:       Legalizer
 ; CHECK-NEXT:       RegBankSelect
 ; CHECK-NEXT:       Localizer
Index: unittests/CodeGen/GlobalISel/CMakeLists.txt
===================================================================
--- unittests/CodeGen/GlobalISel/CMakeLists.txt
+++ unittests/CodeGen/GlobalISel/CMakeLists.txt
@@ -13,4 +13,5 @@
         LegalizerInfoTest.cpp
         PatternMatchTest.cpp
         LegalizerHelperTest.cpp
+        CSETest.cpp
         )
Index: unittests/CodeGen/GlobalISel/CSETest.cpp
===================================================================
--- /dev/null
+++ unittests/CodeGen/GlobalISel/CSETest.cpp
@@ -0,0 +1,87 @@
+//===- CSETest.cpp -----------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "GISelMITest.h"
+#include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
+
+namespace {
+
+TEST_F(GISelMITest, TestCSE) {
+  if (!TM)
+    return;
+
+  LLT s16{LLT::scalar(16)};
+  LLT s32{LLT::scalar(32)};
+  auto MIBInput = B.buildInstr(TargetOpcode::G_TRUNC, {s16}, {Copies[0]});
+  auto MIBInput1 = B.buildInstr(TargetOpcode::G_TRUNC, {s16}, {Copies[1]});
+  auto MIBAdd = B.buildInstr(TargetOpcode::G_ADD, {s16}, {MIBInput, MIBInput});
+  GISelCSEInfo CSEInfo;
+  CSEInfo.setCSEConfig(make_unique<CSEConfig>());
+  CSEInfo.analyze(*MF);
+  B.setCSEInfo(&CSEInfo);
+  CSEMIRBuilder CSEB(B.getState());
+  CSEB.setInsertPt(*EntryMBB, EntryMBB->begin());
+  unsigned AddReg = MRI->createGenericVirtualRegister(s16);
+  auto MIBAddCopy =
+      CSEB.buildInstr(TargetOpcode::G_ADD, {AddReg}, {MIBInput, MIBInput});
+  ASSERT_EQ(MIBAddCopy->getOpcode(), TargetOpcode::COPY);
+  auto MIBAdd2 =
+      CSEB.buildInstr(TargetOpcode::G_ADD, {s16}, {MIBInput, MIBInput});
+  ASSERT_TRUE(&*MIBAdd == &*MIBAdd2);
+  auto MIBAdd4 =
+      CSEB.buildInstr(TargetOpcode::G_ADD, {s16}, {MIBInput, MIBInput});
+  ASSERT_TRUE(&*MIBAdd == &*MIBAdd4);
+  auto MIBAdd5 =
+      CSEB.buildInstr(TargetOpcode::G_ADD, {s16}, {MIBInput, MIBInput1});
+  ASSERT_TRUE(&*MIBAdd != &*MIBAdd5);
+
+  // Try building G_CONSTANTS.
+  auto MIBCst = CSEB.buildConstant(s32, 0);
+  auto MIBCst1 = CSEB.buildConstant(s32, 0);
+  ASSERT_TRUE(&*MIBCst == &*MIBCst1);
+  // Try the CFing of BinaryOps.
+  auto MIBCF1 = CSEB.buildInstr(TargetOpcode::G_ADD, {s32}, {MIBCst, MIBCst});
+  ASSERT_TRUE(&*MIBCF1 == &*MIBCst);
+
+  // Try out building FCONSTANTs.
+  auto MIBFP0 = CSEB.buildFConstant(s32, 1.0);
+  auto MIBFP0_1 = CSEB.buildFConstant(s32, 1.0);
+  ASSERT_TRUE(&*MIBFP0 == &*MIBFP0_1);
+  CSEInfo.print();
+
+  // Check G_UNMERGE_VALUES
+  auto MIBUnmerge = CSEB.buildUnmerge({s32, s32}, Copies[0]);
+  auto MIBUnmerge2 = CSEB.buildUnmerge({s32, s32}, Copies[0]);
+  ASSERT_TRUE(&*MIBUnmerge == &*MIBUnmerge2);
+}
+
+TEST_F(GISelMITest, TestCSEConstantConfig) {
+  if (!TM)
+    return;
+
+  LLT s16{LLT::scalar(16)};
+  auto MIBInput = B.buildInstr(TargetOpcode::G_TRUNC, {s16}, {Copies[0]});
+  auto MIBAdd = B.buildInstr(TargetOpcode::G_ADD, {s16}, {MIBInput, MIBInput});
+  auto MIBZero = B.buildConstant(s16, 0);
+  GISelCSEInfo CSEInfo;
+  CSEInfo.setCSEConfig(make_unique<CSEConfigConstantOnly>());
+  CSEInfo.analyze(*MF);
+  B.setCSEInfo(&CSEInfo);
+  CSEMIRBuilder CSEB(B.getState());
+  CSEB.setInsertPt(*EntryMBB, EntryMBB->begin());
+  auto MIBAdd1 =
+      CSEB.buildInstr(TargetOpcode::G_ADD, {s16}, {MIBInput, MIBInput});
+  // We should CSE constants only. Adds should not be CSEd.
+  ASSERT_TRUE(MIBAdd1->getOpcode() != TargetOpcode::COPY);
+  ASSERT_TRUE(&*MIBAdd1 != &*MIBAdd);
+  // We should CSE constant.
+  auto MIBZeroTmp = CSEB.buildConstant(s16, 0);
+  ASSERT_TRUE(&*MIBZero == &*MIBZeroTmp);
+}
+} // namespace
Index: unittests/CodeGen/GlobalISel/GISelMITest.h
===================================================================
--- unittests/CodeGen/GlobalISel/GISelMITest.h
+++ unittests/CodeGen/GlobalISel/GISelMITest.h
@@ -1,4 +1,4 @@
-//===- LegalizerHelperTest.h
+//===- GISelMITest.h
 //-----------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
@@ -7,6 +7,8 @@
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef LLVM_UNITTEST_CODEGEN_GLOBALISEL_GISELMI_H
+#define LLVM_UNITTEST_CODEGEN_GLOBALISEL_GISELMI_H
 
 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
 #include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
@@ -32,7 +34,7 @@
 using namespace llvm;
 using namespace MIPatternMatch;
 
-void initLLVM() {
+static inline void initLLVM() {
   InitializeAllTargets();
   InitializeAllTargetMCs();
   InitializeAllAsmPrinters();
@@ -45,7 +47,7 @@
 
 /// Create a TargetMachine. As we lack a dedicated always available target for
 /// unittests, we go for "AArch64".
-std::unique_ptr<LLVMTargetMachine> createTargetMachine() {
+static std::unique_ptr<LLVMTargetMachine> createTargetMachine() {
   Triple TargetTriple("aarch64--");
   std::string Error;
   const Target *T = TargetRegistry::lookupTarget("", TargetTriple, Error);
@@ -53,15 +55,16 @@
     return nullptr;
 
   TargetOptions Options;
-  return std::unique_ptr<LLVMTargetMachine>(static_cast<LLVMTargetMachine*>(
-      T->createTargetMachine("AArch64", "", "", Options, None, None,
-                             CodeGenOpt::Aggressive)));
+  return std::unique_ptr<LLVMTargetMachine>(
+      static_cast<LLVMTargetMachine *>(T->createTargetMachine(
+          "AArch64", "", "", Options, None, None, CodeGenOpt::Aggressive)));
 }
 
-std::unique_ptr<Module> parseMIR(LLVMContext &Context,
-                                 std::unique_ptr<MIRParser> &MIR,
-                                 const TargetMachine &TM, StringRef MIRCode,
-                                 const char *FuncName, MachineModuleInfo &MMI) {
+static std::unique_ptr<Module> parseMIR(LLVMContext &Context,
+                                        std::unique_ptr<MIRParser> &MIR,
+                                        const TargetMachine &TM,
+                                        StringRef MIRCode, const char *FuncName,
+                                        MachineModuleInfo &MMI) {
   SMDiagnostic Diagnostic;
   std::unique_ptr<MemoryBuffer> MBuffer = MemoryBuffer::getMemBuffer(MIRCode);
   MIR = createMIRParser(std::move(MBuffer), Context);
@@ -80,7 +83,7 @@
   return M;
 }
 
-std::pair<std::unique_ptr<Module>, std::unique_ptr<MachineModuleInfo>>
+static std::pair<std::unique_ptr<Module>, std::unique_ptr<MachineModuleInfo>>
 createDummyModule(LLVMContext &Context, const LLVMTargetMachine &TM,
                   StringRef MIRFunc) {
   SmallString<512> S;
@@ -123,9 +126,9 @@
     }
 }
 
-class LegalizerHelperTest : public ::testing::Test {
+class GISelMITest : public ::testing::Test {
 protected:
-  LegalizerHelperTest() : ::testing::Test() {
+  GISelMITest() : ::testing::Test() {
     TM = createTargetMachine();
     if (!TM)
       return;
@@ -168,8 +171,8 @@
     }                                                                          \
   };
 
-static bool CheckMachineFunction(const MachineFunction &MF,
-                                 StringRef CheckStr) {
+static inline bool CheckMachineFunction(const MachineFunction &MF,
+                                        StringRef CheckStr) {
   SmallString<512> Msg;
   raw_svector_ostream OS(Msg);
   MF.print(OS);
@@ -190,3 +193,4 @@
   SM.AddNewSourceBuffer(std::move(OutputBuf), SMLoc());
   return FC.CheckInput(SM, OutBuffer, CheckStrings);
 }
+#endif
Index: unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
===================================================================
--- unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
+++ unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
@@ -1,4 +1,5 @@
-//===- PatternMatchTest.cpp -----------------------------------------------===//
+//===- LegalizerHelperTest.cpp
+//-----------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -7,21 +8,21 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "LegalizerHelperTest.h"
+#include "GISelMITest.h"
 
 namespace {
 
 class DummyGISelObserver : public GISelChangeObserver {
 public:
-  void changingInstr(const MachineInstr &MI) override {}
-  void changedInstr(const MachineInstr &MI) override {}
-  void createdInstr(const MachineInstr &MI) override {}
-  void erasingInstr(const MachineInstr &MI) override {}
+  void changingInstr(MachineInstr &MI) override {}
+  void changedInstr(MachineInstr &MI) override {}
+  void createdInstr(MachineInstr &MI) override {}
+  void erasingInstr(MachineInstr &MI) override {}
 };
 
 // Test CTTZ expansion when CTTZ_ZERO_UNDEF is legal or custom,
 // in which case it becomes CTTZ_ZERO_UNDEF with select.
-TEST_F(LegalizerHelperTest, LowerBitCountingCTTZ0) {
+TEST_F(GISelMITest, LowerBitCountingCTTZ0) {
   if (!TM)
     return;
 
@@ -33,7 +34,7 @@
       B.buildInstr(TargetOpcode::G_CTTZ, {LLT::scalar(64)}, {Copies[0]});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   // Perform Legalization
   ASSERT_TRUE(Helper.lower(*MIBCTTZ, 0, LLT::scalar(64)) ==
               LegalizerHelper::LegalizeResult::Legalized);
@@ -51,7 +52,7 @@
 }
 
 // CTTZ expansion in terms of CTLZ
-TEST_F(LegalizerHelperTest, LowerBitCountingCTTZ1) {
+TEST_F(GISelMITest, LowerBitCountingCTTZ1) {
   if (!TM)
     return;
 
@@ -63,7 +64,7 @@
       B.buildInstr(TargetOpcode::G_CTTZ, {LLT::scalar(64)}, {Copies[0]});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   // Perform Legalization
   ASSERT_TRUE(Helper.lower(*MIBCTTZ, 0, LLT::scalar(64)) ==
               LegalizerHelper::LegalizeResult::Legalized);
@@ -83,7 +84,7 @@
 }
 
 // CTTZ expansion in terms of CTPOP
-TEST_F(LegalizerHelperTest, LowerBitCountingCTTZ2) {
+TEST_F(GISelMITest, LowerBitCountingCTTZ2) {
   if (!TM)
     return;
 
@@ -95,7 +96,7 @@
       B.buildInstr(TargetOpcode::G_CTTZ, {LLT::scalar(64)}, {Copies[0]});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.lower(*MIBCTTZ, 0, LLT::scalar(64)) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -112,7 +113,7 @@
 }
 
 // CTTZ_ZERO_UNDEF expansion in terms of CTTZ
-TEST_F(LegalizerHelperTest, LowerBitCountingCTTZ3) {
+TEST_F(GISelMITest, LowerBitCountingCTTZ3) {
   if (!TM)
     return;
 
@@ -124,7 +125,7 @@
                               {LLT::scalar(64)}, {Copies[0]});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.lower(*MIBCTTZ, 0, LLT::scalar(64)) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -137,7 +138,7 @@
 }
 
 // CTLZ expansion in terms of CTLZ_ZERO_UNDEF
-TEST_F(LegalizerHelperTest, LowerBitCountingCTLZ0) {
+TEST_F(GISelMITest, LowerBitCountingCTLZ0) {
   if (!TM)
     return;
 
@@ -149,7 +150,7 @@
       B.buildInstr(TargetOpcode::G_CTLZ, {LLT::scalar(64)}, {Copies[0]});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.lower(*MIBCTLZ, 0, LLT::scalar(64)) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -166,7 +167,7 @@
 }
 
 // CTLZ expansion in terms of CTLZ_ZERO_UNDEF if the latter is a libcall
-TEST_F(LegalizerHelperTest, LowerBitCountingCTLZLibcall) {
+TEST_F(GISelMITest, LowerBitCountingCTLZLibcall) {
   if (!TM)
     return;
 
@@ -178,7 +179,7 @@
       B.buildInstr(TargetOpcode::G_CTLZ, {LLT::scalar(64)}, {Copies[0]});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.lower(*MIBCTLZ, 0, LLT::scalar(64)) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -195,7 +196,7 @@
 }
 
 // CTLZ expansion
-TEST_F(LegalizerHelperTest, LowerBitCountingCTLZ1) {
+TEST_F(GISelMITest, LowerBitCountingCTLZ1) {
   if (!TM)
     return;
 
@@ -209,7 +210,7 @@
   auto MIBCTLZ = B.buildInstr(TargetOpcode::G_CTLZ, {s8}, {MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.lower(*MIBCTLZ, 0, s8) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -234,7 +235,7 @@
 }
 
 // CTLZ widening.
-TEST_F(LegalizerHelperTest, WidenBitCountingCTLZ) {
+TEST_F(GISelMITest, WidenBitCountingCTLZ) {
   if (!TM)
     return;
 
@@ -249,7 +250,7 @@
   auto MIBCTLZ = B.buildInstr(TargetOpcode::G_CTLZ, {s8}, {MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.widenScalar(*MIBCTLZ, 0, s16) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -267,7 +268,7 @@
 }
 
 // CTLZ_ZERO_UNDEF widening.
-TEST_F(LegalizerHelperTest, WidenBitCountingCTLZZeroUndef) {
+TEST_F(GISelMITest, WidenBitCountingCTLZZeroUndef) {
   if (!TM)
     return;
 
@@ -283,7 +284,7 @@
       B.buildInstr(TargetOpcode::G_CTLZ_ZERO_UNDEF, {s8}, {MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.widenScalar(*MIBCTLZ_ZU, 0, s16) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -301,7 +302,7 @@
 }
 
 // CTPOP widening.
-TEST_F(LegalizerHelperTest, WidenBitCountingCTPOP) {
+TEST_F(GISelMITest, WidenBitCountingCTPOP) {
   if (!TM)
     return;
 
@@ -316,7 +317,7 @@
   auto MIBCTPOP = B.buildInstr(TargetOpcode::G_CTPOP, {s8}, {MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.widenScalar(*MIBCTPOP, 0, s16) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -332,7 +333,7 @@
 }
 
 // CTTZ_ZERO_UNDEF widening.
-TEST_F(LegalizerHelperTest, WidenBitCountingCTTZ_ZERO_UNDEF) {
+TEST_F(GISelMITest, WidenBitCountingCTTZ_ZERO_UNDEF) {
   if (!TM)
     return;
 
@@ -348,7 +349,7 @@
       B.buildInstr(TargetOpcode::G_CTTZ_ZERO_UNDEF, {s8}, {MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.widenScalar(*MIBCTTZ_ZERO_UNDEF, 0, s16) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -364,7 +365,7 @@
 }
 
 // CTTZ widening.
-TEST_F(LegalizerHelperTest, WidenBitCountingCTTZ) {
+TEST_F(GISelMITest, WidenBitCountingCTTZ) {
   if (!TM)
     return;
 
@@ -379,7 +380,7 @@
   auto MIBCTTZ = B.buildInstr(TargetOpcode::G_CTTZ, {s8}, {MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.widenScalar(*MIBCTTZ, 0, s16) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -396,7 +397,7 @@
   ASSERT_TRUE(CheckMachineFunction(*MF, CheckStr));
 }
 // UADDO widening.
-TEST_F(LegalizerHelperTest, WidenUADDO) {
+TEST_F(GISelMITest, WidenUADDO) {
   if (!TM)
     return;
 
@@ -413,7 +414,7 @@
       B.buildInstr(TargetOpcode::G_UADDO, {s8, CarryReg}, {MIBTrunc, MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.widenScalar(*MIBUAddO, 0, s16) ==
               LegalizerHelper::LegalizeResult::Legalized);
 
@@ -433,7 +434,7 @@
 }
 
 // USUBO widening.
-TEST_F(LegalizerHelperTest, WidenUSUBO) {
+TEST_F(GISelMITest, WidenUSUBO) {
   if (!TM)
     return;
 
@@ -450,7 +451,7 @@
       B.buildInstr(TargetOpcode::G_USUBO, {s8, CarryReg}, {MIBTrunc, MIBTrunc});
   AInfo Info(MF->getSubtarget());
   DummyGISelObserver Observer;
-  LegalizerHelper Helper(*MF, Info, Observer);
+  LegalizerHelper Helper(*MF, Info, Observer, B);
   ASSERT_TRUE(Helper.widenScalar(*MIBUSUBO, 0, s16) ==
               LegalizerHelper::LegalizeResult::Legalized);