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+//===- llvm/CodeGen/DFAPacketizer.h - DFA Packetizer for VLIW ---*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This class implements a deterministic finite automaton (DFA) based
+// packetizing mechanism for VLIW architectures. It provides APIs to
+// determine whether there exists a legal mapping of instructions to
+// functional unit assignments in a packet. The DFA is auto-generated from
+// the target's Schedule.td file.
+//
+// A DFA consists of 3 major elements: states, inputs, and transitions. For
+// the packetizing mechanism, the input is the set of instruction classes for
+// a target. The state models all possible combinations of functional unit
+// consumption for a given set of instructions in a packet. A transition
+// models the addition of an instruction to a packet. In the DFA constructed
+// by this class, if an instruction can be added to a packet, then a valid
+// transition exists from the corresponding state. Invalid transitions
+// indicate that the instruction cannot be added to the current packet.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_DFAPACKETIZER_H
+#define LLVM_CODEGEN_DFAPACKETIZER_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/ScheduleDAGMutation.h"
+#include <cstdint>
+#include <map>
+#include <memory>
+#include <utility>
+#include <vector>
+
+namespace llvm {
+
+class DefaultVLIWScheduler;
+class InstrItineraryData;
+class MachineFunction;
+class MachineInstr;
+class MachineLoopInfo;
+class MCInstrDesc;
+class SUnit;
+class TargetInstrInfo;
+
+// --------------------------------------------------------------------
+// Definitions shared between DFAPacketizer.cpp and DFAPacketizerEmitter.cpp
+
+// DFA_MAX_RESTERMS * DFA_MAX_RESOURCES must fit within sizeof DFAInput.
+// This is verified in DFAPacketizer.cpp:DFAPacketizer::DFAPacketizer.
+//
+// e.g. terms x resource bit combinations that fit in uint32_t:
+//      4 terms x 8  bits = 32 bits
+//      3 terms x 10 bits = 30 bits
+//      2 terms x 16 bits = 32 bits
+//
+// e.g. terms x resource bit combinations that fit in uint64_t:
+//      8 terms x 8  bits = 64 bits
+//      7 terms x 9  bits = 63 bits
+//      6 terms x 10 bits = 60 bits
+//      5 terms x 12 bits = 60 bits
+//      4 terms x 16 bits = 64 bits <--- current
+//      3 terms x 21 bits = 63 bits
+//      2 terms x 32 bits = 64 bits
+//
+#define DFA_MAX_RESTERMS        4   // The max # of AND'ed resource terms.
+#define DFA_MAX_RESOURCES       16  // The max # of resource bits in one term.
+
+using DFAInput = uint64_t;
+using DFAStateInput = int64_t;
+
+#define DFA_TBLTYPE             "int64_t" // For generating DFAStateInputTable.
+// --------------------------------------------------------------------
+
+class DFAPacketizer {
+private:
+  using UnsignPair = std::pair<unsigned, DFAInput>;
+
+  const InstrItineraryData *InstrItins;
+  int CurrentState = 0;
+  const DFAStateInput (*DFAStateInputTable)[2];
+  const unsigned *DFAStateEntryTable;
+
+  // CachedTable is a map from <FromState, Input> to ToState.
+  DenseMap<UnsignPair, unsigned> CachedTable;
+
+  // Read the DFA transition table and update CachedTable.
+  void ReadTable(unsigned state);
+
+public:
+  DFAPacketizer(const InstrItineraryData *I, const DFAStateInput (*SIT)[2],
+                const unsigned *SET);
+
+  // Reset the current state to make all resources available.
+  void clearResources() {
+    CurrentState = 0;
+  }
+
+  // Return the DFAInput for an instruction class.
+  DFAInput getInsnInput(unsigned InsnClass);
+
+  // Return the DFAInput for an instruction class input vector.
+  static DFAInput getInsnInput(const std::vector<unsigned> &InsnClass);
+
+  // Check if the resources occupied by a MCInstrDesc are available in
+  // the current state.
+  bool canReserveResources(const MCInstrDesc *MID);
+
+  // Reserve the resources occupied by a MCInstrDesc and change the current
+  // state to reflect that change.
+  void reserveResources(const MCInstrDesc *MID);
+
+  // Check if the resources occupied by a machine instruction are available
+  // in the current state.
+  bool canReserveResources(MachineInstr &MI);
+
+  // Reserve the resources occupied by a machine instruction and change the
+  // current state to reflect that change.
+  void reserveResources(MachineInstr &MI);
+
+  const InstrItineraryData *getInstrItins() const { return InstrItins; }
+};
+
+// VLIWPacketizerList implements a simple VLIW packetizer using DFA. The
+// packetizer works on machine basic blocks. For each instruction I in BB,
+// the packetizer consults the DFA to see if machine resources are available
+// to execute I. If so, the packetizer checks if I depends on any instruction
+// in the current packet. If no dependency is found, I is added to current
+// packet and the machine resource is marked as taken. If any dependency is
+// found, a target API call is made to prune the dependence.
+class VLIWPacketizerList {
+protected:
+  MachineFunction &MF;
+  const TargetInstrInfo *TII;
+  AliasAnalysis *AA;
+
+  // The VLIW Scheduler.
+  DefaultVLIWScheduler *VLIWScheduler;
+  // Vector of instructions assigned to the current packet.
+  std::vector<MachineInstr*> CurrentPacketMIs;
+  // DFA resource tracker.
+  DFAPacketizer *ResourceTracker;
+  // Map: MI -> SU.
+  std::map<MachineInstr*, SUnit*> MIToSUnit;
+
+public:
+  // The AliasAnalysis parameter can be nullptr.
+  VLIWPacketizerList(MachineFunction &MF, MachineLoopInfo &MLI,
+                     AliasAnalysis *AA);
+
+  virtual ~VLIWPacketizerList();
+
+  // Implement this API in the backend to bundle instructions.
+  void PacketizeMIs(MachineBasicBlock *MBB,
+                    MachineBasicBlock::iterator BeginItr,
+                    MachineBasicBlock::iterator EndItr);
+
+  // Return the ResourceTracker.
+  DFAPacketizer *getResourceTracker() {return ResourceTracker;}
+
+  // addToPacket - Add MI to the current packet.
+  virtual MachineBasicBlock::iterator addToPacket(MachineInstr &MI) {
+    CurrentPacketMIs.push_back(&MI);
+    ResourceTracker->reserveResources(MI);
+    return MI;
+  }
+
+  // End the current packet and reset the state of the packetizer.
+  // Overriding this function allows the target-specific packetizer
+  // to perform custom finalization.
+  virtual void endPacket(MachineBasicBlock *MBB,
+                         MachineBasicBlock::iterator MI);
+
+  // Perform initialization before packetizing an instruction. This
+  // function is supposed to be overrided by the target dependent packetizer.
+  virtual void initPacketizerState() {}
+
+  // Check if the given instruction I should be ignored by the packetizer.
+  virtual bool ignorePseudoInstruction(const MachineInstr &I,
+                                       const MachineBasicBlock *MBB) {
+    return false;
+  }
+
+  // Return true if instruction MI can not be packetized with any other
+  // instruction, which means that MI itself is a packet.
+  virtual bool isSoloInstruction(const MachineInstr &MI) { return true; }
+
+  // Check if the packetizer should try to add the given instruction to
+  // the current packet. One reasons for which it may not be desirable
+  // to include an instruction in the current packet could be that it
+  // would cause a stall.
+  // If this function returns "false", the current packet will be ended,
+  // and the instruction will be added to the next packet.
+  virtual bool shouldAddToPacket(const MachineInstr &MI) { return true; }
+
+  // Check if it is legal to packetize SUI and SUJ together.
+  virtual bool isLegalToPacketizeTogether(SUnit *SUI, SUnit *SUJ) {
+    return false;
+  }
+
+  // Check if it is legal to prune dependece between SUI and SUJ.
+  virtual bool isLegalToPruneDependencies(SUnit *SUI, SUnit *SUJ) {
+    return false;
+  }
+
+  // Add a DAG mutation to be done before the packetization begins.
+  void addMutation(std::unique_ptr<ScheduleDAGMutation> Mutation);
+
+  bool alias(const MachineInstr &MI1, const MachineInstr &MI2,
+             bool UseTBAA = true) const;
+
+private:
+  bool alias(const MachineMemOperand &Op1, const MachineMemOperand &Op2,
+             bool UseTBAA = true) const;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_CODEGEN_DFAPACKETIZER_H