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+//=- llvm/CodeGen/GlobalISel/RegBankSelect.h - Reg Bank Selector --*- 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 describes the interface of the MachineFunctionPass
+/// responsible for assigning the generic virtual registers to register bank.
+
+/// By default, the reg bank selector relies on local decisions to
+/// assign the register bank. In other words, it looks at one instruction
+/// at a time to decide where the operand of that instruction should live.
+///
+/// At higher optimization level, we could imagine that the reg bank selector
+/// would use more global analysis and do crazier thing like duplicating
+/// instructions and so on. This is future work.
+///
+/// For now, the pass uses a greedy algorithm to decide where the operand
+/// of an instruction should live. It asks the target which banks may be
+/// used for each operand of the instruction and what is the cost. Then,
+/// it chooses the solution which minimize the cost of the instruction plus
+/// the cost of any move that may be needed to the values into the right
+/// register bank.
+/// In other words, the cost for an instruction on a register bank RegBank
+/// is: Cost of I on RegBank plus the sum of the cost for bringing the
+/// input operands from their current register bank to RegBank.
+/// Thus, the following formula:
+/// cost(I, RegBank) = cost(I.Opcode, RegBank) +
+///    sum(for each arg in I.arguments: costCrossCopy(arg.RegBank, RegBank))
+///
+/// E.g., Let say we are assigning the register bank for the instruction
+/// defining v2.
+/// v0(A_REGBANK) = ...
+/// v1(A_REGBANK) = ...
+/// v2 = G_ADD i32 v0, v1 <-- MI
+///
+/// The target may say it can generate G_ADD i32 on register bank A and B
+/// with a cost of respectively 5 and 1.
+/// Then, let say the cost of a cross register bank copies from A to B is 1.
+/// The reg bank selector would compare the following two costs:
+/// cost(MI, A_REGBANK) = cost(G_ADD, A_REGBANK) + cost(v0.RegBank, A_REGBANK) +
+///    cost(v1.RegBank, A_REGBANK)
+///                     = 5 + cost(A_REGBANK, A_REGBANK) + cost(A_REGBANK,
+///                                                             A_REGBANK)
+///                     = 5 + 0 + 0 = 5
+/// cost(MI, B_REGBANK) = cost(G_ADD, B_REGBANK) + cost(v0.RegBank, B_REGBANK) +
+///    cost(v1.RegBank, B_REGBANK)
+///                     = 1 + cost(A_REGBANK, B_REGBANK) + cost(A_REGBANK,
+///                                                             B_REGBANK)
+///                     = 1 + 1 + 1 = 3
+/// Therefore, in this specific example, the reg bank selector would choose
+/// bank B for MI.
+/// v0(A_REGBANK) = ...
+/// v1(A_REGBANK) = ...
+/// tmp0(B_REGBANK) = COPY v0
+/// tmp1(B_REGBANK) = COPY v1
+/// v2(B_REGBANK) = G_ADD i32 tmp0, tmp1
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_GLOBALISEL_REGBANKSELECT_H
+#define LLVM_CODEGEN_GLOBALISEL_REGBANKSELECT_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
+#include "llvm/CodeGen/GlobalISel/RegisterBankInfo.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
+#include <cassert>
+#include <cstdint>
+#include <memory>
+
+namespace llvm {
+
+class BlockFrequency;
+class MachineBlockFrequencyInfo;
+class MachineBranchProbabilityInfo;
+class MachineOperand;
+class MachineRegisterInfo;
+class Pass;
+class raw_ostream;
+class TargetPassConfig;
+class TargetRegisterInfo;
+
+/// This pass implements the reg bank selector pass used in the GlobalISel
+/// pipeline. At the end of this pass, all register operands have been assigned
+class RegBankSelect : public MachineFunctionPass {
+public:
+  static char ID;
+
+  /// List of the modes supported by the RegBankSelect pass.
+  enum Mode {
+    /// Assign the register banks as fast as possible (default).
+    Fast,
+    /// Greedily minimize the cost of assigning register banks.
+    /// This should produce code of greater quality, but will
+    /// require more compile time.
+    Greedy
+  };
+
+  /// Abstract class used to represent an insertion point in a CFG.
+  /// This class records an insertion point and materializes it on
+  /// demand.
+  /// It allows to reason about the frequency of this insertion point,
+  /// without having to logically materialize it (e.g., on an edge),
+  /// before we actually need to insert something.
+  class InsertPoint {
+  protected:
+    /// Tell if the insert point has already been materialized.
+    bool WasMaterialized = false;
+
+    /// Materialize the insertion point.
+    ///
+    /// If isSplit() is true, this involves actually splitting
+    /// the block or edge.
+    ///
+    /// \post getPointImpl() returns a valid iterator.
+    /// \post getInsertMBBImpl() returns a valid basic block.
+    /// \post isSplit() == false ; no more splitting should be required.
+    virtual void materialize() = 0;
+
+    /// Return the materialized insertion basic block.
+    /// Code will be inserted into that basic block.
+    ///
+    /// \pre ::materialize has been called.
+    virtual MachineBasicBlock &getInsertMBBImpl() = 0;
+
+    /// Return the materialized insertion point.
+    /// Code will be inserted before that point.
+    ///
+    /// \pre ::materialize has been called.
+    virtual MachineBasicBlock::iterator getPointImpl() = 0;
+
+  public:
+    virtual ~InsertPoint() = default;
+
+    /// The first call to this method will cause the splitting to
+    /// happen if need be, then sub sequent calls just return
+    /// the iterator to that point. I.e., no more splitting will
+    /// occur.
+    ///
+    /// \return The iterator that should be used with
+    /// MachineBasicBlock::insert. I.e., additional code happens
+    /// before that point.
+    MachineBasicBlock::iterator getPoint() {
+      if (!WasMaterialized) {
+        WasMaterialized = true;
+        assert(canMaterialize() && "Impossible to materialize this point");
+        materialize();
+      }
+      // When we materialized the point we should have done the splitting.
+      assert(!isSplit() && "Wrong pre-condition");
+      return getPointImpl();
+    }
+
+    /// The first call to this method will cause the splitting to
+    /// happen if need be, then sub sequent calls just return
+    /// the basic block that contains the insertion point.
+    /// I.e., no more splitting will occur.
+    ///
+    /// \return The basic block should be used with
+    /// MachineBasicBlock::insert and ::getPoint. The new code should
+    /// happen before that point.
+    MachineBasicBlock &getInsertMBB() {
+      if (!WasMaterialized) {
+        WasMaterialized = true;
+        assert(canMaterialize() && "Impossible to materialize this point");
+        materialize();
+      }
+      // When we materialized the point we should have done the splitting.
+      assert(!isSplit() && "Wrong pre-condition");
+      return getInsertMBBImpl();
+    }
+
+    /// Insert \p MI in the just before ::getPoint()
+    MachineBasicBlock::iterator insert(MachineInstr &MI) {
+      return getInsertMBB().insert(getPoint(), &MI);
+    }
+
+    /// Does this point involve splitting an edge or block?
+    /// As soon as ::getPoint is called and thus, the point
+    /// materialized, the point will not require splitting anymore,
+    /// i.e., this will return false.
+    virtual bool isSplit() const { return false; }
+
+    /// Frequency of the insertion point.
+    /// \p P is used to access the various analysis that will help to
+    /// get that information, like MachineBlockFrequencyInfo.  If \p P
+    /// does not contain enough enough to return the actual frequency,
+    /// this returns 1.
+    virtual uint64_t frequency(const Pass &P) const { return 1; }
+
+    /// Check whether this insertion point can be materialized.
+    /// As soon as ::getPoint is called and thus, the point materialized
+    /// calling this method does not make sense.
+    virtual bool canMaterialize() const { return false; }
+  };
+
+  /// Insertion point before or after an instruction.
+  class InstrInsertPoint : public InsertPoint {
+  private:
+    /// Insertion point.
+    MachineInstr &Instr;
+
+    /// Does the insertion point is before or after Instr.
+    bool Before;
+
+    void materialize() override;
+
+    MachineBasicBlock::iterator getPointImpl() override {
+      if (Before)
+        return Instr;
+      return Instr.getNextNode() ? *Instr.getNextNode()
+                                 : Instr.getParent()->end();
+    }
+
+    MachineBasicBlock &getInsertMBBImpl() override {
+      return *Instr.getParent();
+    }
+
+  public:
+    /// Create an insertion point before (\p Before=true) or after \p Instr.
+    InstrInsertPoint(MachineInstr &Instr, bool Before = true);
+
+    bool isSplit() const override;
+    uint64_t frequency(const Pass &P) const override;
+
+    // Worst case, we need to slice the basic block, but that is still doable.
+    bool canMaterialize() const override { return true; }
+  };
+
+  /// Insertion point at the beginning or end of a basic block.
+  class MBBInsertPoint : public InsertPoint {
+  private:
+    /// Insertion point.
+    MachineBasicBlock &MBB;
+
+    /// Does the insertion point is at the beginning or end of MBB.
+    bool Beginning;
+
+    void materialize() override { /*Nothing to do to materialize*/
+    }
+
+    MachineBasicBlock::iterator getPointImpl() override {
+      return Beginning ? MBB.begin() : MBB.end();
+    }
+
+    MachineBasicBlock &getInsertMBBImpl() override { return MBB; }
+
+  public:
+    MBBInsertPoint(MachineBasicBlock &MBB, bool Beginning = true)
+        : InsertPoint(), MBB(MBB), Beginning(Beginning) {
+      // If we try to insert before phis, we should use the insertion
+      // points on the incoming edges.
+      assert((!Beginning || MBB.getFirstNonPHI() == MBB.begin()) &&
+             "Invalid beginning point");
+      // If we try to insert after the terminators, we should use the
+      // points on the outcoming edges.
+      assert((Beginning || MBB.getFirstTerminator() == MBB.end()) &&
+             "Invalid end point");
+    }
+
+    bool isSplit() const override { return false; }
+    uint64_t frequency(const Pass &P) const override;
+    bool canMaterialize() const override { return true; };
+  };
+
+  /// Insertion point on an edge.
+  class EdgeInsertPoint : public InsertPoint {
+  private:
+    /// Source of the edge.
+    MachineBasicBlock &Src;
+
+    /// Destination of the edge.
+    /// After the materialization is done, this hold the basic block
+    /// that resulted from the splitting.
+    MachineBasicBlock *DstOrSplit;
+
+    /// P is used to update the analysis passes as applicable.
+    Pass &P;
+
+    void materialize() override;
+
+    MachineBasicBlock::iterator getPointImpl() override {
+      // DstOrSplit should be the Split block at this point.
+      // I.e., it should have one predecessor, Src, and one successor,
+      // the original Dst.
+      assert(DstOrSplit && DstOrSplit->isPredecessor(&Src) &&
+             DstOrSplit->pred_size() == 1 && DstOrSplit->succ_size() == 1 &&
+             "Did not split?!");
+      return DstOrSplit->begin();
+    }
+
+    MachineBasicBlock &getInsertMBBImpl() override { return *DstOrSplit; }
+
+  public:
+    EdgeInsertPoint(MachineBasicBlock &Src, MachineBasicBlock &Dst, Pass &P)
+        : InsertPoint(), Src(Src), DstOrSplit(&Dst), P(P) {}
+
+    bool isSplit() const override {
+      return Src.succ_size() > 1 && DstOrSplit->pred_size() > 1;
+    }
+
+    uint64_t frequency(const Pass &P) const override;
+    bool canMaterialize() const override;
+  };
+
+  /// Struct used to represent the placement of a repairing point for
+  /// a given operand.
+  class RepairingPlacement {
+  public:
+    /// Define the kind of action this repairing needs.
+    enum RepairingKind {
+      /// Nothing to repair, just drop this action.
+      None,
+      /// Reparing code needs to happen before InsertPoints.
+      Insert,
+      /// (Re)assign the register bank of the operand.
+      Reassign,
+      /// Mark this repairing placement as impossible.
+      Impossible
+    };
+
+    /// \name Convenient types for a list of insertion points.
+    /// @{
+    using InsertionPoints = SmallVector<std::unique_ptr<InsertPoint>, 2>;
+    using insertpt_iterator = InsertionPoints::iterator;
+    using const_insertpt_iterator = InsertionPoints::const_iterator;
+    /// @}
+
+  private:
+    /// Kind of repairing.
+    RepairingKind Kind;
+    /// Index of the operand that will be repaired.
+    unsigned OpIdx;
+    /// Are all the insert points materializeable?
+    bool CanMaterialize;
+    /// Is there any of the insert points needing splitting?
+    bool HasSplit = false;
+    /// Insertion point for the repair code.
+    /// The repairing code needs to happen just before these points.
+    InsertionPoints InsertPoints;
+    /// Some insertion points may need to update the liveness and such.
+    Pass &P;
+
+  public:
+    /// Create a repairing placement for the \p OpIdx-th operand of
+    /// \p MI. \p TRI is used to make some checks on the register aliases
+    /// if the machine operand is a physical register. \p P is used to
+    /// to update liveness information and such when materializing the
+    /// points.
+    RepairingPlacement(MachineInstr &MI, unsigned OpIdx,
+                       const TargetRegisterInfo &TRI, Pass &P,
+                       RepairingKind Kind = RepairingKind::Insert);
+
+    /// \name Getters.
+    /// @{
+    RepairingKind getKind() const { return Kind; }
+    unsigned getOpIdx() const { return OpIdx; }
+    bool canMaterialize() const { return CanMaterialize; }
+    bool hasSplit() { return HasSplit; }
+    /// @}
+
+    /// \name Overloaded methods to add an insertion point.
+    /// @{
+    /// Add a MBBInsertionPoint to the list of InsertPoints.
+    void addInsertPoint(MachineBasicBlock &MBB, bool Beginning);
+    /// Add a InstrInsertionPoint to the list of InsertPoints.
+    void addInsertPoint(MachineInstr &MI, bool Before);
+    /// Add an EdgeInsertionPoint (\p Src, \p Dst) to the list of InsertPoints.
+    void addInsertPoint(MachineBasicBlock &Src, MachineBasicBlock &Dst);
+    /// Add an InsertPoint to the list of insert points.
+    /// This method takes the ownership of &\p Point.
+    void addInsertPoint(InsertPoint &Point);
+    /// @}
+
+    /// \name Accessors related to the insertion points.
+    /// @{
+    insertpt_iterator begin() { return InsertPoints.begin(); }
+    insertpt_iterator end() { return InsertPoints.end(); }
+
+    const_insertpt_iterator begin() const { return InsertPoints.begin(); }
+    const_insertpt_iterator end() const { return InsertPoints.end(); }
+
+    unsigned getNumInsertPoints() const { return InsertPoints.size(); }
+    /// @}
+
+    /// Change the type of this repairing placement to \p NewKind.
+    /// It is not possible to switch a repairing placement to the
+    /// RepairingKind::Insert. There is no fundamental problem with
+    /// that, but no uses as well, so do not support it for now.
+    ///
+    /// \pre NewKind != RepairingKind::Insert
+    /// \post getKind() == NewKind
+    void switchTo(RepairingKind NewKind) {
+      assert(NewKind != Kind && "Already of the right Kind");
+      Kind = NewKind;
+      InsertPoints.clear();
+      CanMaterialize = NewKind != RepairingKind::Impossible;
+      HasSplit = false;
+      assert(NewKind != RepairingKind::Insert &&
+             "We would need more MI to switch to Insert");
+    }
+  };
+
+private:
+  /// Helper class used to represent the cost for mapping an instruction.
+  /// When mapping an instruction, we may introduce some repairing code.
+  /// In most cases, the repairing code is local to the instruction,
+  /// thus, we can omit the basic block frequency from the cost.
+  /// However, some alternatives may produce non-local cost, e.g., when
+  /// repairing a phi, and thus we then need to scale the local cost
+  /// to the non-local cost. This class does this for us.
+  /// \note: We could simply always scale the cost. The problem is that
+  /// there are higher chances that we saturate the cost easier and end
+  /// up having the same cost for actually different alternatives.
+  /// Another option would be to use APInt everywhere.
+  class MappingCost {
+  private:
+    /// Cost of the local instructions.
+    /// This cost is free of basic block frequency.
+    uint64_t LocalCost = 0;
+    /// Cost of the non-local instructions.
+    /// This cost should include the frequency of the related blocks.
+    uint64_t NonLocalCost = 0;
+    /// Frequency of the block where the local instructions live.
+    uint64_t LocalFreq;
+
+    MappingCost(uint64_t LocalCost, uint64_t NonLocalCost, uint64_t LocalFreq)
+        : LocalCost(LocalCost), NonLocalCost(NonLocalCost),
+          LocalFreq(LocalFreq) {}
+
+    /// Check if this cost is saturated.
+    bool isSaturated() const;
+
+  public:
+    /// Create a MappingCost assuming that most of the instructions
+    /// will occur in a basic block with \p LocalFreq frequency.
+    MappingCost(const BlockFrequency &LocalFreq);
+
+    /// Add \p Cost to the local cost.
+    /// \return true if this cost is saturated, false otherwise.
+    bool addLocalCost(uint64_t Cost);
+
+    /// Add \p Cost to the non-local cost.
+    /// Non-local cost should reflect the frequency of their placement.
+    /// \return true if this cost is saturated, false otherwise.
+    bool addNonLocalCost(uint64_t Cost);
+
+    /// Saturate the cost to the maximal representable value.
+    void saturate();
+
+    /// Return an instance of MappingCost that represents an
+    /// impossible mapping.
+    static MappingCost ImpossibleCost();
+
+    /// Check if this is less than \p Cost.
+    bool operator<(const MappingCost &Cost) const;
+    /// Check if this is equal to \p Cost.
+    bool operator==(const MappingCost &Cost) const;
+    /// Check if this is not equal to \p Cost.
+    bool operator!=(const MappingCost &Cost) const { return !(*this == Cost); }
+    /// Check if this is greater than \p Cost.
+    bool operator>(const MappingCost &Cost) const {
+      return *this != Cost && Cost < *this;
+    }
+
+    /// Print this on dbgs() stream.
+    void dump() const;
+
+    /// Print this on \p OS;
+    void print(raw_ostream &OS) const;
+
+    /// Overload the stream operator for easy debug printing.
+    friend raw_ostream &operator<<(raw_ostream &OS, const MappingCost &Cost) {
+      Cost.print(OS);
+      return OS;
+    }
+  };
+
+  /// Interface to the target lowering info related
+  /// to register banks.
+  const RegisterBankInfo *RBI = nullptr;
+
+  /// MRI contains all the register class/bank information that this
+  /// pass uses and updates.
+  MachineRegisterInfo *MRI = nullptr;
+
+  /// Information on the register classes for the current function.
+  const TargetRegisterInfo *TRI = nullptr;
+
+  /// Get the frequency of blocks.
+  /// This is required for non-fast mode.
+  MachineBlockFrequencyInfo *MBFI = nullptr;
+
+  /// Get the frequency of the edges.
+  /// This is required for non-fast mode.
+  MachineBranchProbabilityInfo *MBPI = nullptr;
+
+  /// Current optimization remark emitter. Used to report failures.
+  std::unique_ptr<MachineOptimizationRemarkEmitter> MORE;
+
+  /// Helper class used for every code morphing.
+  MachineIRBuilder MIRBuilder;
+
+  /// Optimization mode of the pass.
+  Mode OptMode;
+
+  /// Current target configuration. Controls how the pass handles errors.
+  const TargetPassConfig *TPC;
+
+  /// Assign the register bank of each operand of \p MI.
+  /// \return True on success, false otherwise.
+  bool assignInstr(MachineInstr &MI);
+
+  /// Initialize the field members using \p MF.
+  void init(MachineFunction &MF);
+
+  /// Check if \p Reg is already assigned what is described by \p ValMapping.
+  /// \p OnlyAssign == true means that \p Reg just needs to be assigned a
+  /// register bank.  I.e., no repairing is necessary to have the
+  /// assignment match.
+  bool assignmentMatch(unsigned Reg,
+                       const RegisterBankInfo::ValueMapping &ValMapping,
+                       bool &OnlyAssign) const;
+
+  /// Insert repairing code for \p Reg as specified by \p ValMapping.
+  /// The repairing placement is specified by \p RepairPt.
+  /// \p NewVRegs contains all the registers required to remap \p Reg.
+  /// In other words, the number of registers in NewVRegs must be equal
+  /// to ValMapping.BreakDown.size().
+  ///
+  /// The transformation could be sketched as:
+  /// \code
+  /// ... = op Reg
+  /// \endcode
+  /// Becomes
+  /// \code
+  /// <NewRegs> = COPY or extract Reg
+  /// ... = op Reg
+  /// \endcode
+  ///
+  /// and
+  /// \code
+  /// Reg = op ...
+  /// \endcode
+  /// Becomes
+  /// \code
+  /// Reg = op ...
+  /// Reg = COPY or build_sequence <NewRegs>
+  /// \endcode
+  ///
+  /// \pre NewVRegs.size() == ValMapping.BreakDown.size()
+  ///
+  /// \note The caller is supposed to do the rewriting of op if need be.
+  /// I.e., Reg = op ... => <NewRegs> = NewOp ...
+  ///
+  /// \return True if the repairing worked, false otherwise.
+  bool repairReg(MachineOperand &MO,
+                 const RegisterBankInfo::ValueMapping &ValMapping,
+                 RegBankSelect::RepairingPlacement &RepairPt,
+                 const iterator_range<SmallVectorImpl<unsigned>::const_iterator>
+                     &NewVRegs);
+
+  /// Return the cost of the instruction needed to map \p MO to \p ValMapping.
+  /// The cost is free of basic block frequencies.
+  /// \pre MO.isReg()
+  /// \pre MO is assigned to a register bank.
+  /// \pre ValMapping is a valid mapping for MO.
+  uint64_t
+  getRepairCost(const MachineOperand &MO,
+                const RegisterBankInfo::ValueMapping &ValMapping) const;
+
+  /// Find the best mapping for \p MI from \p PossibleMappings.
+  /// \return a reference on the best mapping in \p PossibleMappings.
+  const RegisterBankInfo::InstructionMapping &
+  findBestMapping(MachineInstr &MI,
+                  RegisterBankInfo::InstructionMappings &PossibleMappings,
+                  SmallVectorImpl<RepairingPlacement> &RepairPts);
+
+  /// Compute the cost of mapping \p MI with \p InstrMapping and
+  /// compute the repairing placement for such mapping in \p
+  /// RepairPts.
+  /// \p BestCost is used to specify when the cost becomes too high
+  /// and thus it is not worth computing the RepairPts.  Moreover if
+  /// \p BestCost == nullptr, the mapping cost is actually not
+  /// computed.
+  MappingCost
+  computeMapping(MachineInstr &MI,
+                 const RegisterBankInfo::InstructionMapping &InstrMapping,
+                 SmallVectorImpl<RepairingPlacement> &RepairPts,
+                 const MappingCost *BestCost = nullptr);
+
+  /// When \p RepairPt involves splitting to repair \p MO for the
+  /// given \p ValMapping, try to change the way we repair such that
+  /// the splitting is not required anymore.
+  ///
+  /// \pre \p RepairPt.hasSplit()
+  /// \pre \p MO == MO.getParent()->getOperand(\p RepairPt.getOpIdx())
+  /// \pre \p ValMapping is the mapping of \p MO for MO.getParent()
+  ///      that implied \p RepairPt.
+  void tryAvoidingSplit(RegBankSelect::RepairingPlacement &RepairPt,
+                        const MachineOperand &MO,
+                        const RegisterBankInfo::ValueMapping &ValMapping) const;
+
+  /// Apply \p Mapping to \p MI. \p RepairPts represents the different
+  /// mapping action that need to happen for the mapping to be
+  /// applied.
+  /// \return True if the mapping was applied sucessfully, false otherwise.
+  bool applyMapping(MachineInstr &MI,
+                    const RegisterBankInfo::InstructionMapping &InstrMapping,
+                    SmallVectorImpl<RepairingPlacement> &RepairPts);
+
+public:
+  /// Create a RegBankSelect pass with the specified \p RunningMode.
+  RegBankSelect(Mode RunningMode = Fast);
+
+  StringRef getPassName() const override { return "RegBankSelect"; }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+  MachineFunctionProperties getRequiredProperties() const override {
+    return MachineFunctionProperties()
+        .set(MachineFunctionProperties::Property::IsSSA)
+        .set(MachineFunctionProperties::Property::Legalized);
+  }
+
+  MachineFunctionProperties getSetProperties() const override {
+    return MachineFunctionProperties().set(
+        MachineFunctionProperties::Property::RegBankSelected);
+  }
+
+  /// Walk through \p MF and assign a register bank to every virtual register
+  /// that are still mapped to nothing.
+  /// The target needs to provide a RegisterBankInfo and in particular
+  /// override RegisterBankInfo::getInstrMapping.
+  ///
+  /// Simplified algo:
+  /// \code
+  ///   RBI = MF.subtarget.getRegBankInfo()
+  ///   MIRBuilder.setMF(MF)
+  ///   for each bb in MF
+  ///     for each inst in bb
+  ///       MIRBuilder.setInstr(inst)
+  ///       MappingCosts = RBI.getMapping(inst);
+  ///       Idx = findIdxOfMinCost(MappingCosts)
+  ///       CurRegBank = MappingCosts[Idx].RegBank
+  ///       MRI.setRegBank(inst.getOperand(0).getReg(), CurRegBank)
+  ///       for each argument in inst
+  ///         if (CurRegBank != argument.RegBank)
+  ///           ArgReg = argument.getReg()
+  ///           Tmp = MRI.createNewVirtual(MRI.getSize(ArgReg), CurRegBank)
+  ///           MIRBuilder.buildInstr(COPY, Tmp, ArgReg)
+  ///           inst.getOperand(argument.getOperandNo()).setReg(Tmp)
+  /// \endcode
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_CODEGEN_GLOBALISEL_REGBANKSELECT_H