src/cpu/o3/rename.hh - public/gem5 - Git at Google

 /*
  * Copyright (c) 2012, 2017 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
  * not be construed as granting a license to any other intellectual
  * property including but not limited to intellectual property relating
  * to a hardware implementation of the functionality of the software
  * licensed hereunder.  You may use the software subject to the license
  * terms below provided that you ensure that this notice is replicated
  * unmodified and in its entirety in all distributions of the software,
  * modified or unmodified, in source code or in binary form.
  *
  * Copyright (c) 2004-2006 The Regents of The University of Michigan
  * Copyright (c) 2013 Advanced Micro Devices, Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met: redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer;
  * redistributions in binary form must reproduce the above copyright
  * notice, this list of conditions and the following disclaimer in the
  * documentation and/or other materials provided with the distribution;
  * neither the name of the copyright holders nor the names of its
  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #ifndef __CPU_O3_RENAME_HH__
 #define __CPU_O3_RENAME_HH__

 #include <list>
 #include <utility>

 #include "base/statistics.hh"
 #include "cpu/o3/comm.hh"
 #include "cpu/o3/commit.hh"
 #include "cpu/o3/dyn_inst_ptr.hh"
 #include "cpu/o3/free_list.hh"
 #include "cpu/o3/iew.hh"
 #include "cpu/o3/limits.hh"
 #include "cpu/timebuf.hh"
 #include "sim/probe/probe.hh"

 namespace gem5
 {

 struct O3CPUParams;

 namespace o3
 {

 /**
  * Rename handles both single threaded and SMT rename. Its
  * width is specified by the parameters; each cycle it tries to rename
  * that many instructions. It holds onto the rename history of all
  * instructions with destination registers, storing the
  * arch. register, the new physical register, and the old physical
  * register, to allow for undoing of mappings if squashing happens, or
  * freeing up registers upon commit. Rename handles blocking if the
  * ROB, IQ, or LSQ is going to be full. Rename also handles barriers,
  * and does so by stalling on the instruction until the ROB is empty
  * and there are no instructions in flight to the ROB.
  */
 class Rename
 {
   public:
     // A deque is used to queue the instructions. Barrier insts must
     // be added to the front of the queue, which is the only reason for
     // using a deque instead of a queue. (Most other stages use a
     // queue)
     typedef std::deque<DynInstPtr> InstQueue;

   public:
     /** Overall rename status. Used to determine if the CPU can
      * deschedule itself due to a lack of activity.
      */
     enum RenameStatus
     {
         Active,
         Inactive
     };

     /** Individual thread status. */
     enum ThreadStatus
     {
         Running,
         Idle,
         StartSquash,
         Squashing,
         Blocked,
         Unblocking,
         SerializeStall
     };

   private:
     /** Rename status. */
     RenameStatus _status;

     /** Per-thread status. */
     ThreadStatus renameStatus[MaxThreads];

     /** Probe points. */
     typedef std::pair<InstSeqNum, PhysRegIdPtr> SeqNumRegPair;
     /** To probe when register renaming for an instruction is complete */
     ProbePointArg<DynInstPtr> *ppRename;
     /**
      * To probe when an instruction is squashed and the register mapping
      * for it needs to be undone
      */
     ProbePointArg<SeqNumRegPair> *ppSquashInRename;

   public:
     /** Rename constructor. */
     Rename(CPU *_cpu, const O3CPUParams &params);

     /** Returns the name of rename. */
     std::string name() const;

     /** Registers probes. */
     void regProbePoints();

     /** Sets the main backwards communication time buffer pointer. */
     void setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr);

     /** Sets pointer to time buffer used to communicate to the next stage. */
     void setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr);

     /** Sets pointer to time buffer coming from decode. */
     void setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr);

     /** Sets pointer to IEW stage. Used only for initialization. */
     void setIEWStage(IEW *iew_stage) { iew_ptr = iew_stage; }

     /** Sets pointer to commit stage. Used only for initialization. */
     void
     setCommitStage(Commit *commit_stage)
     {
         commit_ptr = commit_stage;
     }

   private:
     /** Pointer to IEW stage. Used only for initialization. */
     IEW *iew_ptr;

     /** Pointer to commit stage. Used only for initialization. */
     Commit *commit_ptr;

   public:
     /** Initializes variables for the stage. */
     void startupStage();

     /** Clear all thread-specific states */
     void clearStates(ThreadID tid);

     /** Sets pointer to list of active threads. */
     void setActiveThreads(std::list<ThreadID> *at_ptr);

     /** Sets pointer to rename maps (per-thread structures). */
     void setRenameMap(UnifiedRenameMap rm_ptr[MaxThreads]);

     /** Sets pointer to the free list. */
     void setFreeList(UnifiedFreeList *fl_ptr);

     /** Sets pointer to the scoreboard. */
     void setScoreboard(Scoreboard *_scoreboard);

     /** Perform sanity checks after a drain. */
     void drainSanityCheck() const;

     /** Has the stage drained? */
     bool isDrained() const;

     /** Takes over from another CPU's thread. */
     void takeOverFrom();

     /** Squashes all instructions in a thread. */
     void squash(const InstSeqNum &squash_seq_num, ThreadID tid);

     /** Ticks rename, which processes all input signals and attempts to rename
      * as many instructions as possible.
      */
     void tick();

     /** Debugging function used to dump history buffer of renamings. */
     void dumpHistory();

   private:
     /** Reset this pipeline stage */
     void resetStage();

     /** Determines what to do based on rename's current status.
      * @param status_change rename() sets this variable if there was a status
      * change (ie switching from blocking to unblocking).
      * @param tid Thread id to rename instructions from.
      */
     void rename(bool &status_change, ThreadID tid);

     /** Renames instructions for the given thread. Also handles serializing
      * instructions.
      */
     void renameInsts(ThreadID tid);

     /** Inserts unused instructions from a given thread into the skid buffer,
      * to be renamed once rename unblocks.
      */
     void skidInsert(ThreadID tid);

     /** Separates instructions from decode into individual lists of instructions
      * sorted by thread.
      */
     void sortInsts();

     /** Returns if all of the skid buffers are empty. */
     bool skidsEmpty();

     /** Updates overall rename status based on all of the threads' statuses. */
     void updateStatus();

     /** Switches rename to blocking, and signals back that rename has become
      * blocked.
      * @return Returns true if there is a status change.
      */
     bool block(ThreadID tid);

     /** Switches rename to unblocking if the skid buffer is empty, and signals
      * back that rename has unblocked.
      * @return Returns true if there is a status change.
      */
     bool unblock(ThreadID tid);

     /** Executes actual squash, removing squashed instructions. */
     void doSquash(const InstSeqNum &squash_seq_num, ThreadID tid);

     /** Removes a committed instruction's rename history. */
     void removeFromHistory(InstSeqNum inst_seq_num, ThreadID tid);

     /** Renames the source registers of an instruction. */
     void renameSrcRegs(const DynInstPtr &inst, ThreadID tid);

     /** Renames the destination registers of an instruction. */
     void renameDestRegs(const DynInstPtr &inst, ThreadID tid);

     /** Calculates the number of free ROB entries for a specific thread. */
     int calcFreeROBEntries(ThreadID tid);

     /** Calculates the number of free IQ entries for a specific thread. */
     int calcFreeIQEntries(ThreadID tid);

     /** Calculates the number of free LQ entries for a specific thread. */
     int calcFreeLQEntries(ThreadID tid);

     /** Calculates the number of free SQ entries for a specific thread. */
     int calcFreeSQEntries(ThreadID tid);

     /** Returns the number of valid instructions coming from decode. */
     unsigned validInsts();

     /** Reads signals telling rename to block/unblock. */
     void readStallSignals(ThreadID tid);

     /** Checks if any stages are telling rename to block. */
     bool checkStall(ThreadID tid);

     /** Gets the number of free entries for a specific thread. */
     void readFreeEntries(ThreadID tid);

     /** Checks the signals and updates the status. */
     bool checkSignalsAndUpdate(ThreadID tid);

     /** Either serializes on the next instruction available in the InstQueue,
      * or records that it must serialize on the next instruction to enter
      * rename.
      * @param inst_list The list of younger, unprocessed instructions for the
      * thread that has the serializeAfter instruction.
      * @param tid The thread id.
      */
     void serializeAfter(InstQueue &inst_list, ThreadID tid);

     /** Holds the information for each destination register rename. It holds
      * the instruction's sequence number, the arch register, the old physical
      * register for that arch. register, and the new physical register.
      */
     struct RenameHistory
     {
         RenameHistory(InstSeqNum _instSeqNum, const RegId& _archReg,
                       PhysRegIdPtr _newPhysReg,
                       PhysRegIdPtr _prevPhysReg)
             : instSeqNum(_instSeqNum), archReg(_archReg),
               newPhysReg(_newPhysReg), prevPhysReg(_prevPhysReg)
         {
         }

         /** The sequence number of the instruction that renamed. */
         InstSeqNum instSeqNum;
         /** The architectural register index that was renamed. */
         RegId archReg;
         /** The new physical register that the arch. register is renamed to. */
         PhysRegIdPtr newPhysReg;
         /** The old physical register that the arch. register was renamed to.
          */
         PhysRegIdPtr prevPhysReg;
     };

     /** A per-thread list of all destination register renames, used to either
      * undo rename mappings or free old physical registers.
      */
     std::list<RenameHistory> historyBuffer[MaxThreads];

     /** Pointer to CPU. */
     CPU *cpu;

     /** Pointer to main time buffer used for backwards communication. */
     TimeBuffer<TimeStruct> *timeBuffer;

     /** Wire to get IEW's output from backwards time buffer. */
     TimeBuffer<TimeStruct>::wire fromIEW;

     /** Wire to get commit's output from backwards time buffer. */
     TimeBuffer<TimeStruct>::wire fromCommit;

     /** Wire to write infromation heading to previous stages. */
     TimeBuffer<TimeStruct>::wire toDecode;

     /** Rename instruction queue. */
     TimeBuffer<RenameStruct> *renameQueue;

     /** Wire to write any information heading to IEW. */
     TimeBuffer<RenameStruct>::wire toIEW;

     /** Decode instruction queue interface. */
     TimeBuffer<DecodeStruct> *decodeQueue;

     /** Wire to get decode's output from decode queue. */
     TimeBuffer<DecodeStruct>::wire fromDecode;

     /** Queue of all instructions coming from decode this cycle. */
     InstQueue insts[MaxThreads];

     /** Skid buffer between rename and decode. */
     InstQueue skidBuffer[MaxThreads];

     /** Rename map interface. */
     UnifiedRenameMap *renameMap[MaxThreads];

     /** Free list interface. */
     UnifiedFreeList *freeList;

     /** Pointer to the list of active threads. */
     std::list<ThreadID> *activeThreads;

     /** Pointer to the scoreboard. */
     Scoreboard *scoreboard;

     /** Count of instructions in progress that have been sent off to the IQ
      * and ROB, but are not yet included in their occupancy counts.
      */
     int instsInProgress[MaxThreads];

     /** Count of Load instructions in progress that have been sent off to the
      * IQ and ROB, but are not yet included in their occupancy counts.
      */
     int loadsInProgress[MaxThreads];

     /** Count of Store instructions in progress that have been sent off to the
      * IQ and ROB, but are not yet included in their occupancy counts.
      */
     int storesInProgress[MaxThreads];

     /** Variable that tracks if decode has written to the time buffer this
      * cycle. Used to tell CPU if there is activity this cycle.
      */
     bool wroteToTimeBuffer;

     /** Structures whose free entries impact the amount of instructions that
      * can be renamed.
      */
     struct FreeEntries
     {
         unsigned iqEntries;
         unsigned robEntries;
         unsigned lqEntries;
         unsigned sqEntries;
     };

     /** Per-thread tracking of the number of free entries of back-end
      * structures.
      */
     FreeEntries freeEntries[MaxThreads];

     /** Records if the ROB is empty. In SMT mode the ROB may be dynamically
      * partitioned between threads, so the ROB must tell rename when it is
      * empty.
      */
     bool emptyROB[MaxThreads];

     /** Source of possible stalls. */
     struct Stalls
     {
         bool iew;
         bool commit;
     };

     /** Tracks which stages are telling decode to stall. */
     Stalls stalls[MaxThreads];

     /** The serialize instruction that rename has stalled on. */
     DynInstPtr serializeInst[MaxThreads];

     /** Records if rename needs to serialize on the next instruction for any
      * thread.
      */
     bool serializeOnNextInst[MaxThreads];

     /** Delay between iew and rename, in ticks. */
     int iewToRenameDelay;

     /** Delay between decode and rename, in ticks. */
     int decodeToRenameDelay;

     /** Delay between commit and rename, in ticks. */
     unsigned commitToRenameDelay;

     /** Rename width, in instructions. */
     unsigned renameWidth;

     /** The index of the instruction in the time buffer to IEW that rename is
      * currently using.
      */
     unsigned toIEWIndex;

     /** Whether or not rename needs to block this cycle. */
     bool blockThisCycle;

     /** Whether or not rename needs to resume a serialize instruction
      * after squashing. */
     bool resumeSerialize;

     /** Whether or not rename needs to resume clearing out the skidbuffer
      * after squashing. */
     bool resumeUnblocking;

     /** The number of threads active in rename. */
     ThreadID numThreads;

     /** The maximum skid buffer size. */
     unsigned skidBufferMax;

     /** Enum to record the source of a structure full stall.  Can come from
      * either ROB, IQ, LSQ, and it is priortized in that order.
      */
     enum FullSource
     {
         ROB,
         IQ,
         LQ,
         SQ,
         NONE
     };

     /** Function used to increment the stat that corresponds to the source of
      * the stall.
      */
     void incrFullStat(const FullSource &source);

     struct RenameStats : public statistics::Group
     {
         RenameStats(statistics::Group *parent);

         /** Stat for total number of cycles spent squashing. */
         statistics::Scalar squashCycles;
         /** Stat for total number of cycles spent idle. */
         statistics::Scalar idleCycles;
         /** Stat for total number of cycles spent blocking. */
         statistics::Scalar blockCycles;
         /** Stat for total number of cycles spent stalling for a serializing
          *  inst. */
         statistics::Scalar serializeStallCycles;
         /** Stat for total number of cycles spent running normally. */
         statistics::Scalar runCycles;
         /** Stat for total number of cycles spent unblocking. */
         statistics::Scalar unblockCycles;
         /** Stat for total number of renamed instructions. */
         statistics::Scalar renamedInsts;
         /** Stat for total number of squashed instructions that rename
          * discards. */
         statistics::Scalar squashedInsts;
         /** Stat for total number of times that the ROB starts a stall in
          * rename. */
         statistics::Scalar ROBFullEvents;
         /** Stat for total number of times that the IQ starts a stall in
          *  rename. */
         statistics::Scalar IQFullEvents;
         /** Stat for total number of times that the LQ starts a stall in
          *  rename. */
         statistics::Scalar LQFullEvents;
         /** Stat for total number of times that the SQ starts a stall in
          *  rename. */
         statistics::Scalar SQFullEvents;
         /** Stat for total number of times that rename runs out of free
          *  registers to use to rename. */
         statistics::Scalar fullRegistersEvents;
         /** Stat for total number of renamed destination registers. */
         statistics::Scalar renamedOperands;
         /** Stat for total number of source register rename lookups. */
         statistics::Scalar lookups;
         statistics::Scalar intLookups;
         statistics::Scalar fpLookups;
         statistics::Scalar vecLookups;
         statistics::Scalar vecPredLookups;
         /** Stat for total number of committed renaming mappings. */
         statistics::Scalar committedMaps;
         /** Stat for total number of mappings that were undone due to a
          *  squash. */
         statistics::Scalar undoneMaps;
         /** Number of serialize instructions handled. */
         statistics::Scalar serializing;
         /** Number of instructions marked as temporarily serializing. */
         statistics::Scalar tempSerializing;
         /** Number of instructions inserted into skid buffers. */
         statistics::Scalar skidInsts;
     } stats;
 };

 } // namespace o3
 } // namespace gem5

 #endif // __CPU_O3_RENAME_HH__
	/*
	* Copyright (c) 2012, 2017 ARM Limited
	* All rights reserved
	*
	* The license below extends only to copyright in the software and shall
	* not be construed as granting a license to any other intellectual
	* property including but not limited to intellectual property relating
	* to a hardware implementation of the functionality of the software
	* licensed hereunder. You may use the software subject to the license
	* terms below provided that you ensure that this notice is replicated
	* unmodified and in its entirety in all distributions of the software,
	* modified or unmodified, in source code or in binary form.
	*
	* Copyright (c) 2004-2006 The Regents of The University of Michigan
	* Copyright (c) 2013 Advanced Micro Devices, Inc.
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions are
	* met: redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer;
	* redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution;
	* neither the name of the copyright holders nor the names of its
	* contributors may be used to endorse or promote products derived from
	* this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#ifndef __CPU_O3_RENAME_HH__
	#define __CPU_O3_RENAME_HH__

	#include <list>
	#include <utility>

	#include "base/statistics.hh"
	#include "cpu/o3/comm.hh"
	#include "cpu/o3/commit.hh"
	#include "cpu/o3/dyn_inst_ptr.hh"
	#include "cpu/o3/free_list.hh"
	#include "cpu/o3/iew.hh"
	#include "cpu/o3/limits.hh"
	#include "cpu/timebuf.hh"
	#include "sim/probe/probe.hh"

	namespace gem5
	{

	struct O3CPUParams;

	namespace o3
	{

	/**
	* Rename handles both single threaded and SMT rename. Its
	* width is specified by the parameters; each cycle it tries to rename
	* that many instructions. It holds onto the rename history of all
	* instructions with destination registers, storing the
	* arch. register, the new physical register, and the old physical
	* register, to allow for undoing of mappings if squashing happens, or
	* freeing up registers upon commit. Rename handles blocking if the
	* ROB, IQ, or LSQ is going to be full. Rename also handles barriers,
	* and does so by stalling on the instruction until the ROB is empty
	* and there are no instructions in flight to the ROB.
	*/
	class Rename
	{
	public:
	// A deque is used to queue the instructions. Barrier insts must
	// be added to the front of the queue, which is the only reason for
	// using a deque instead of a queue. (Most other stages use a
	// queue)
	typedef std::deque<DynInstPtr> InstQueue;

	public:
	/** Overall rename status. Used to determine if the CPU can
	* deschedule itself due to a lack of activity.
	*/
	enum RenameStatus
	{
	Active,
	Inactive
	};

	/** Individual thread status. */
	enum ThreadStatus
	{
	Running,
	Idle,
	StartSquash,
	Squashing,
	Blocked,
	Unblocking,
	SerializeStall
	};

	private:
	/** Rename status. */
	RenameStatus _status;

	/** Per-thread status. */
	ThreadStatus renameStatus[MaxThreads];

	/** Probe points. */
	typedef std::pair<InstSeqNum, PhysRegIdPtr> SeqNumRegPair;
	/** To probe when register renaming for an instruction is complete */
	ProbePointArg<DynInstPtr> *ppRename;
	/**
	* To probe when an instruction is squashed and the register mapping
	* for it needs to be undone
	*/
	ProbePointArg<SeqNumRegPair> *ppSquashInRename;

	public:
	/** Rename constructor. */
	Rename(CPU *_cpu, const O3CPUParams &params);

	/** Returns the name of rename. */
	std::string name() const;

	/** Registers probes. */
	void regProbePoints();

	/** Sets the main backwards communication time buffer pointer. */
	void setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr);

	/** Sets pointer to time buffer used to communicate to the next stage. */
	void setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr);

	/** Sets pointer to time buffer coming from decode. */
	void setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr);

	/** Sets pointer to IEW stage. Used only for initialization. */
	void setIEWStage(IEW *iew_stage) { iew_ptr = iew_stage; }

	/** Sets pointer to commit stage. Used only for initialization. */
	void
	setCommitStage(Commit *commit_stage)
	{
	commit_ptr = commit_stage;
	}

	private:
	/** Pointer to IEW stage. Used only for initialization. */
	IEW *iew_ptr;

	/** Pointer to commit stage. Used only for initialization. */
	Commit *commit_ptr;

	public:
	/** Initializes variables for the stage. */
	void startupStage();

	/** Clear all thread-specific states */
	void clearStates(ThreadID tid);

	/** Sets pointer to list of active threads. */
	void setActiveThreads(std::list<ThreadID> *at_ptr);

	/** Sets pointer to rename maps (per-thread structures). */
	void setRenameMap(UnifiedRenameMap rm_ptr[MaxThreads]);

	/** Sets pointer to the free list. */
	void setFreeList(UnifiedFreeList *fl_ptr);

	/** Sets pointer to the scoreboard. */
	void setScoreboard(Scoreboard *_scoreboard);

	/** Perform sanity checks after a drain. */
	void drainSanityCheck() const;

	/** Has the stage drained? */
	bool isDrained() const;

	/** Takes over from another CPU's thread. */
	void takeOverFrom();

	/** Squashes all instructions in a thread. */
	void squash(const InstSeqNum &squash_seq_num, ThreadID tid);

	/** Ticks rename, which processes all input signals and attempts to rename
	* as many instructions as possible.
	*/
	void tick();

	/** Debugging function used to dump history buffer of renamings. */
	void dumpHistory();

	private:
	/** Reset this pipeline stage */
	void resetStage();

	/** Determines what to do based on rename's current status.
	* @param status_change rename() sets this variable if there was a status
	* change (ie switching from blocking to unblocking).
	* @param tid Thread id to rename instructions from.
	*/
	void rename(bool &status_change, ThreadID tid);

	/** Renames instructions for the given thread. Also handles serializing
	* instructions.
	*/
	void renameInsts(ThreadID tid);

	/** Inserts unused instructions from a given thread into the skid buffer,
	* to be renamed once rename unblocks.
	*/
	void skidInsert(ThreadID tid);

	/** Separates instructions from decode into individual lists of instructions
	* sorted by thread.
	*/
	void sortInsts();

	/** Returns if all of the skid buffers are empty. */
	bool skidsEmpty();

	/** Updates overall rename status based on all of the threads' statuses. */
	void updateStatus();

	/** Switches rename to blocking, and signals back that rename has become
	* blocked.
	* @return Returns true if there is a status change.
	*/
	bool block(ThreadID tid);

	/** Switches rename to unblocking if the skid buffer is empty, and signals
	* back that rename has unblocked.
	* @return Returns true if there is a status change.
	*/
	bool unblock(ThreadID tid);

	/** Executes actual squash, removing squashed instructions. */
	void doSquash(const InstSeqNum &squash_seq_num, ThreadID tid);

	/** Removes a committed instruction's rename history. */
	void removeFromHistory(InstSeqNum inst_seq_num, ThreadID tid);

	/** Renames the source registers of an instruction. */
	void renameSrcRegs(const DynInstPtr &inst, ThreadID tid);

	/** Renames the destination registers of an instruction. */
	void renameDestRegs(const DynInstPtr &inst, ThreadID tid);

	/** Calculates the number of free ROB entries for a specific thread. */
	int calcFreeROBEntries(ThreadID tid);

	/** Calculates the number of free IQ entries for a specific thread. */
	int calcFreeIQEntries(ThreadID tid);

	/** Calculates the number of free LQ entries for a specific thread. */
	int calcFreeLQEntries(ThreadID tid);

	/** Calculates the number of free SQ entries for a specific thread. */
	int calcFreeSQEntries(ThreadID tid);

	/** Returns the number of valid instructions coming from decode. */
	unsigned validInsts();

	/** Reads signals telling rename to block/unblock. */
	void readStallSignals(ThreadID tid);

	/** Checks if any stages are telling rename to block. */
	bool checkStall(ThreadID tid);

	/** Gets the number of free entries for a specific thread. */
	void readFreeEntries(ThreadID tid);

	/** Checks the signals and updates the status. */
	bool checkSignalsAndUpdate(ThreadID tid);

	/** Either serializes on the next instruction available in the InstQueue,
	* or records that it must serialize on the next instruction to enter
	* rename.
	* @param inst_list The list of younger, unprocessed instructions for the
	* thread that has the serializeAfter instruction.
	* @param tid The thread id.
	*/
	void serializeAfter(InstQueue &inst_list, ThreadID tid);

	/** Holds the information for each destination register rename. It holds
	* the instruction's sequence number, the arch register, the old physical
	* register for that arch. register, and the new physical register.
	*/
	struct RenameHistory
	{
	RenameHistory(InstSeqNum _instSeqNum, const RegId& _archReg,
	PhysRegIdPtr _newPhysReg,
	PhysRegIdPtr _prevPhysReg)
	: instSeqNum(_instSeqNum), archReg(_archReg),
	newPhysReg(_newPhysReg), prevPhysReg(_prevPhysReg)
	{
	}

	/** The sequence number of the instruction that renamed. */
	InstSeqNum instSeqNum;
	/** The architectural register index that was renamed. */
	RegId archReg;
	/** The new physical register that the arch. register is renamed to. */
	PhysRegIdPtr newPhysReg;
	/** The old physical register that the arch. register was renamed to.
	*/
	PhysRegIdPtr prevPhysReg;
	};

	/** A per-thread list of all destination register renames, used to either
	* undo rename mappings or free old physical registers.
	*/
	std::list<RenameHistory> historyBuffer[MaxThreads];

	/** Pointer to CPU. */
	CPU *cpu;

	/** Pointer to main time buffer used for backwards communication. */
	TimeBuffer<TimeStruct> *timeBuffer;

	/** Wire to get IEW's output from backwards time buffer. */
	TimeBuffer<TimeStruct>::wire fromIEW;

	/** Wire to get commit's output from backwards time buffer. */
	TimeBuffer<TimeStruct>::wire fromCommit;

	/** Wire to write infromation heading to previous stages. */
	TimeBuffer<TimeStruct>::wire toDecode;

	/** Rename instruction queue. */
	TimeBuffer<RenameStruct> *renameQueue;

	/** Wire to write any information heading to IEW. */
	TimeBuffer<RenameStruct>::wire toIEW;

	/** Decode instruction queue interface. */
	TimeBuffer<DecodeStruct> *decodeQueue;

	/** Wire to get decode's output from decode queue. */
	TimeBuffer<DecodeStruct>::wire fromDecode;

	/** Queue of all instructions coming from decode this cycle. */
	InstQueue insts[MaxThreads];

	/** Skid buffer between rename and decode. */
	InstQueue skidBuffer[MaxThreads];

	/** Rename map interface. */
	UnifiedRenameMap *renameMap[MaxThreads];

	/** Free list interface. */
	UnifiedFreeList *freeList;

	/** Pointer to the list of active threads. */
	std::list<ThreadID> *activeThreads;

	/** Pointer to the scoreboard. */
	Scoreboard *scoreboard;

	/** Count of instructions in progress that have been sent off to the IQ
	* and ROB, but are not yet included in their occupancy counts.
	*/
	int instsInProgress[MaxThreads];

	/** Count of Load instructions in progress that have been sent off to the
	* IQ and ROB, but are not yet included in their occupancy counts.
	*/
	int loadsInProgress[MaxThreads];

	/** Count of Store instructions in progress that have been sent off to the
	* IQ and ROB, but are not yet included in their occupancy counts.
	*/
	int storesInProgress[MaxThreads];

	/** Variable that tracks if decode has written to the time buffer this
	* cycle. Used to tell CPU if there is activity this cycle.
	*/
	bool wroteToTimeBuffer;

	/** Structures whose free entries impact the amount of instructions that
	* can be renamed.
	*/
	struct FreeEntries
	{
	unsigned iqEntries;
	unsigned robEntries;
	unsigned lqEntries;
	unsigned sqEntries;
	};

	/** Per-thread tracking of the number of free entries of back-end
	* structures.
	*/
	FreeEntries freeEntries[MaxThreads];

	/** Records if the ROB is empty. In SMT mode the ROB may be dynamically
	* partitioned between threads, so the ROB must tell rename when it is
	* empty.
	*/
	bool emptyROB[MaxThreads];

	/** Source of possible stalls. */
	struct Stalls
	{
	bool iew;
	bool commit;
	};

	/** Tracks which stages are telling decode to stall. */
	Stalls stalls[MaxThreads];

	/** The serialize instruction that rename has stalled on. */
	DynInstPtr serializeInst[MaxThreads];

	/** Records if rename needs to serialize on the next instruction for any
	* thread.
	*/
	bool serializeOnNextInst[MaxThreads];

	/** Delay between iew and rename, in ticks. */
	int iewToRenameDelay;

	/** Delay between decode and rename, in ticks. */
	int decodeToRenameDelay;

	/** Delay between commit and rename, in ticks. */
	unsigned commitToRenameDelay;

	/** Rename width, in instructions. */
	unsigned renameWidth;

	/** The index of the instruction in the time buffer to IEW that rename is
	* currently using.
	*/
	unsigned toIEWIndex;

	/** Whether or not rename needs to block this cycle. */
	bool blockThisCycle;

	/** Whether or not rename needs to resume a serialize instruction
	* after squashing. */
	bool resumeSerialize;

	/** Whether or not rename needs to resume clearing out the skidbuffer
	* after squashing. */
	bool resumeUnblocking;

	/** The number of threads active in rename. */
	ThreadID numThreads;

	/** The maximum skid buffer size. */
	unsigned skidBufferMax;

	/** Enum to record the source of a structure full stall. Can come from
	* either ROB, IQ, LSQ, and it is priortized in that order.
	*/
	enum FullSource
	{
	ROB,
	IQ,
	LQ,
	SQ,
	NONE
	};

	/** Function used to increment the stat that corresponds to the source of
	* the stall.
	*/
	void incrFullStat(const FullSource &source);

	struct RenameStats : public statistics::Group
	{
	RenameStats(statistics::Group *parent);

	/** Stat for total number of cycles spent squashing. */
	statistics::Scalar squashCycles;
	/** Stat for total number of cycles spent idle. */
	statistics::Scalar idleCycles;
	/** Stat for total number of cycles spent blocking. */
	statistics::Scalar blockCycles;
	/** Stat for total number of cycles spent stalling for a serializing
	* inst. */
	statistics::Scalar serializeStallCycles;
	/** Stat for total number of cycles spent running normally. */
	statistics::Scalar runCycles;
	/** Stat for total number of cycles spent unblocking. */
	statistics::Scalar unblockCycles;
	/** Stat for total number of renamed instructions. */
	statistics::Scalar renamedInsts;
	/** Stat for total number of squashed instructions that rename
	* discards. */
	statistics::Scalar squashedInsts;
	/** Stat for total number of times that the ROB starts a stall in
	* rename. */
	statistics::Scalar ROBFullEvents;
	/** Stat for total number of times that the IQ starts a stall in
	* rename. */
	statistics::Scalar IQFullEvents;
	/** Stat for total number of times that the LQ starts a stall in
	* rename. */
	statistics::Scalar LQFullEvents;
	/** Stat for total number of times that the SQ starts a stall in
	* rename. */
	statistics::Scalar SQFullEvents;
	/** Stat for total number of times that rename runs out of free
	* registers to use to rename. */
	statistics::Scalar fullRegistersEvents;
	/** Stat for total number of renamed destination registers. */
	statistics::Scalar renamedOperands;
	/** Stat for total number of source register rename lookups. */
	statistics::Scalar lookups;
	statistics::Scalar intLookups;
	statistics::Scalar fpLookups;
	statistics::Scalar vecLookups;
	statistics::Scalar vecPredLookups;
	/** Stat for total number of committed renaming mappings. */
	statistics::Scalar committedMaps;
	/** Stat for total number of mappings that were undone due to a
	* squash. */
	statistics::Scalar undoneMaps;
	/** Number of serialize instructions handled. */
	statistics::Scalar serializing;
	/** Number of instructions marked as temporarily serializing. */
	statistics::Scalar tempSerializing;
	/** Number of instructions inserted into skid buffers. */
	statistics::Scalar skidInsts;
	} stats;
	};

	} // namespace o3
	} // namespace gem5

	#endif // __CPU_O3_RENAME_HH__