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

 /*
  * Copyright (c) 2010-2012, 2014, 2019 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
  * 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_IEW_HH__
 #define __CPU_O3_IEW_HH__

 #include <queue>
 #include <set>

 #include "base/statistics.hh"
 #include "cpu/o3/comm.hh"
 #include "cpu/o3/dyn_inst_ptr.hh"
 #include "cpu/o3/inst_queue.hh"
 #include "cpu/o3/limits.hh"
 #include "cpu/o3/lsq.hh"
 #include "cpu/o3/scoreboard.hh"
 #include "cpu/timebuf.hh"
 #include "debug/IEW.hh"
 #include "sim/probe/probe.hh"

 namespace gem5
 {

 struct BaseO3CPUParams;

 namespace o3
 {

 class FUPool;

 /**
  * IEW handles both single threaded and SMT IEW
  * (issue/execute/writeback).  It handles the dispatching of
  * instructions to the LSQ/IQ as part of the issue stage, and has the
  * IQ try to issue instructions each cycle. The execute latency is
  * actually tied into the issue latency to allow the IQ to be able to
  * do back-to-back scheduling without having to speculatively schedule
  * instructions. This happens by having the IQ have access to the
  * functional units, and the IQ gets the execution latencies from the
  * FUs when it issues instructions. Instructions reach the execute
  * stage on the last cycle of their execution, which is when the IQ
  * knows to wake up any dependent instructions, allowing back to back
  * scheduling. The execute portion of IEW separates memory
  * instructions from non-memory instructions, either telling the LSQ
  * to execute the instruction, or executing the instruction directly.
  * The writeback portion of IEW completes the instructions by waking
  * up any dependents, and marking the register ready on the
  * scoreboard.
  */
 class IEW
 {
   public:
     /** Overall IEW stage status. Used to determine if the CPU can
      * deschedule itself due to a lack of activity.
      */
     enum Status
     {
         Active,
         Inactive
     };

     /** Status for Issue, Execute, and Writeback stages. */
     enum StageStatus
     {
         Running,
         Blocked,
         Idle,
         StartSquash,
         Squashing,
         Unblocking
     };

   private:
     /** Overall stage status. */
     Status _status;
     /** Dispatch status. */
     StageStatus dispatchStatus[MaxThreads];
     /** Execute status. */
     StageStatus exeStatus;
     /** Writeback status. */
     StageStatus wbStatus;

     /** Probe points. */
     ProbePointArg<DynInstPtr> *ppMispredict;
     ProbePointArg<DynInstPtr> *ppDispatch;
     /** To probe when instruction execution begins. */
     ProbePointArg<DynInstPtr> *ppExecute;
     /** To probe when instruction execution is complete. */
     ProbePointArg<DynInstPtr> *ppToCommit;

   public:
     /** Constructs a IEW with the given parameters. */
     IEW(CPU *_cpu, const BaseO3CPUParams &params);

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

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

     /** Initializes stage; sends back the number of free IQ and LSQ entries. */
     void startupStage();

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

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

     /** Sets time buffer for getting instructions coming from rename. */
     void setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr);

     /** Sets time buffer to pass on instructions to commit. */
     void setIEWQueue(TimeBuffer<IEWStruct> *iq_ptr);

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

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

     /** 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 instructions in IEW for a specific thread. */
     void squash(ThreadID tid);

     /** Wakes all dependents of a completed instruction. */
     void wakeDependents(const DynInstPtr &inst);

     /** Tells memory dependence unit that a memory instruction needs to be
      * rescheduled. It will re-execute once replayMemInst() is called.
      */
     void rescheduleMemInst(const DynInstPtr &inst);

     /** Re-executes all rescheduled memory instructions. */
     void replayMemInst(const DynInstPtr &inst);

     /** Moves memory instruction onto the list of cache blocked instructions */
     void blockMemInst(const DynInstPtr &inst);

     /** Notifies that the cache has become unblocked */
     void cacheUnblocked();

     /** Sends an instruction to commit through the time buffer. */
     void instToCommit(const DynInstPtr &inst);

     /** Inserts unused instructions of a thread into the skid buffer. */
     void skidInsert(ThreadID tid);

     /** Returns the max of the number of entries in all of the skid buffers. */
     int skidCount();

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

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

     /** Resets entries of the IQ and the LSQ. */
     void resetEntries();

     /** Tells the CPU to wakeup if it has descheduled itself due to no
      * activity. Used mainly by the LdWritebackEvent.
      */
     void wakeCPU();

     /** Reports to the CPU that there is activity this cycle. */
     void activityThisCycle();

     /** Tells CPU that the IEW stage is active and running. */
     void activateStage();

     /** Tells CPU that the IEW stage is inactive and idle. */
     void deactivateStage();

     /** Returns if the LSQ has any stores to writeback. */
     bool hasStoresToWB() { return ldstQueue.hasStoresToWB(); }

     /** Returns if the LSQ has any stores to writeback. */
     bool hasStoresToWB(ThreadID tid) { return ldstQueue.hasStoresToWB(tid); }

     /** Check misprediction  */
     void checkMisprediction(const DynInstPtr &inst);

     // hardware transactional memory
     // For debugging purposes, it is useful to keep track of the most recent
     // htmUid that has been committed (architecturally, not transactionally)
     // to ensure that the core and the memory subsystem are observing
     // correct ordering constraints.
     void setLastRetiredHtmUid(ThreadID tid, uint64_t htmUid)
     {
         ldstQueue.setLastRetiredHtmUid(tid, htmUid);
     }

   private:
     /** Sends commit proper information for a squash due to a branch
      * mispredict.
      */
     void squashDueToBranch(const DynInstPtr &inst, ThreadID tid);

     /** Sends commit proper information for a squash due to a memory order
      * violation.
      */
     void squashDueToMemOrder(const DynInstPtr &inst, ThreadID tid);

     /** Sets Dispatch to blocked, and signals back to other stages to block. */
     void block(ThreadID tid);

     /** Unblocks Dispatch if the skid buffer is empty, and signals back to
      * other stages to unblock.
      */
     void unblock(ThreadID tid);

     /** Determines proper actions to take given Dispatch's status. */
     void dispatch(ThreadID tid);

     /** Dispatches instructions to IQ and LSQ. */
     void dispatchInsts(ThreadID tid);

     /** Executes instructions. In the case of memory operations, it informs the
      * LSQ to execute the instructions. Also handles any redirects that occur
      * due to the executed instructions.
      */
     void executeInsts();

     /** Writebacks instructions. In our model, the instruction's execute()
      * function atomically reads registers, executes, and writes registers.
      * Thus this writeback only wakes up dependent instructions, and informs
      * the scoreboard of registers becoming ready.
      */
     void writebackInsts();

     /** Checks if any of the stall conditions are currently true. */
     bool checkStall(ThreadID tid);

     /** Processes inputs and changes state accordingly. */
     void checkSignalsAndUpdate(ThreadID tid);

     /** Removes instructions from rename from a thread's instruction list. */
     void emptyRenameInsts(ThreadID tid);

     /** Sorts instructions coming from rename into lists separated by thread. */
     void sortInsts();

   public:
     /** Ticks IEW stage, causing Dispatch, the IQ, the LSQ, Execute, and
      * Writeback to run for one cycle.
      */
     void tick();

   private:
     /** Updates execution stats based on the instruction. */
     void updateExeInstStats(const DynInstPtr &inst);

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

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

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

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

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

     /** Wire to get rename's output from rename queue. */
     TimeBuffer<RenameStruct>::wire fromRename;

     /** Issue stage queue. */
     TimeBuffer<IssueStruct> issueToExecQueue;

     /** Wire to read information from the issue stage time queue. */
     TimeBuffer<IssueStruct>::wire fromIssue;

     /**
      * IEW stage time buffer.  Holds ROB indices of instructions that
      * can be marked as completed.
      */
     TimeBuffer<IEWStruct> *iewQueue;

     /** Wire to write infromation heading to commit. */
     TimeBuffer<IEWStruct>::wire toCommit;

     /** Queue of all instructions coming from rename this cycle. */
     std::queue<DynInstPtr> insts[MaxThreads];

     /** Skid buffer between rename and IEW. */
     std::queue<DynInstPtr> skidBuffer[MaxThreads];

     /** Scoreboard pointer. */
     Scoreboard* scoreboard;

   private:
     /** CPU pointer. */
     CPU *cpu;

     /** Records if IEW has written to the time buffer this cycle, so that the
      * CPU can deschedule itself if there is no activity.
      */
     bool wroteToTimeBuffer;

     /** Debug function to print instructions that are issued this cycle. */
     void printAvailableInsts();

   public:
     /** Instruction queue. */
     InstructionQueue instQueue;

     /** Load / store queue. */
     LSQ ldstQueue;

     /** Pointer to the functional unit pool. */
     FUPool *fuPool;
     /** Records if the LSQ needs to be updated on the next cycle, so that
      * IEW knows if there will be activity on the next cycle.
      */
     bool updateLSQNextCycle;

   private:
     /** Records if there is a fetch redirect on this cycle for each thread. */
     bool fetchRedirect[MaxThreads];

     /** Records if the queues have been changed (inserted or issued insts),
      * so that IEW knows to broadcast the updated amount of free entries.
      */
     bool updatedQueues;

     /** Commit to IEW delay. */
     Cycles commitToIEWDelay;

     /** Rename to IEW delay. */
     Cycles renameToIEWDelay;

     /**
      * Issue to execute delay. What this actually represents is
      * the amount of time it takes for an instruction to wake up, be
      * scheduled, and sent to a FU for execution.
      */
     Cycles issueToExecuteDelay;

     /** Width of dispatch, in instructions. */
     unsigned dispatchWidth;

     /** Width of issue, in instructions. */
     unsigned issueWidth;

     /** Index into queue of instructions being written back. */
     unsigned wbNumInst;

     /** Cycle number within the queue of instructions being written back.
      * Used in case there are too many instructions writing back at the current
      * cycle and writesbacks need to be scheduled for the future. See comments
      * in instToCommit().
      */
     unsigned wbCycle;

     /** Writeback width. */
     unsigned wbWidth;

     /** Number of active threads. */
     ThreadID numThreads;

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

     /** Maximum size of the skid buffer. */
     unsigned skidBufferMax;


     struct IEWStats : public statistics::Group
     {
         IEWStats(CPU *cpu);

         /** Stat for total number of idle cycles. */
         statistics::Scalar idleCycles;
         /** Stat for total number of squashing cycles. */
         statistics::Scalar squashCycles;
         /** Stat for total number of blocking cycles. */
         statistics::Scalar blockCycles;
         /** Stat for total number of unblocking cycles. */
         statistics::Scalar unblockCycles;
         /** Stat for total number of instructions dispatched. */
         statistics::Scalar dispatchedInsts;
         /** Stat for total number of squashed instructions dispatch skips. */
         statistics::Scalar dispSquashedInsts;
         /** Stat for total number of dispatched load instructions. */
         statistics::Scalar dispLoadInsts;
         /** Stat for total number of dispatched store instructions. */
         statistics::Scalar dispStoreInsts;
         /** Stat for total number of dispatched non speculative insts. */
         statistics::Scalar dispNonSpecInsts;
         /** Stat for number of times the IQ becomes full. */
         statistics::Scalar iqFullEvents;
         /** Stat for number of times the LSQ becomes full. */
         statistics::Scalar lsqFullEvents;
         /** Stat for total number of memory ordering violation events. */
         statistics::Scalar memOrderViolationEvents;
         /** Stat for total number of incorrect predicted taken branches. */
         statistics::Scalar predictedTakenIncorrect;
         /** Stat for total number of incorrect predicted not taken branches. */
         statistics::Scalar predictedNotTakenIncorrect;
         /** Stat for total number of mispredicted branches detected at
          *  execute. */
         statistics::Formula branchMispredicts;

         struct ExecutedInstStats : public statistics::Group
         {
             ExecutedInstStats(CPU *cpu);

             /** Stat for total number of executed instructions. */
             statistics::Scalar numInsts;
             /** Stat for total number of executed load instructions. */
             statistics::Vector numLoadInsts;
             /** Stat for total number of squashed instructions skipped at
              *  execute. */
             statistics::Scalar numSquashedInsts;
             /** Number of executed software prefetches. */
             statistics::Vector numSwp;
             /** Number of executed nops. */
             statistics::Vector numNop;
             /** Number of executed meomory references. */
             statistics::Vector numRefs;
             /** Number of executed branches. */
             statistics::Vector numBranches;
             /** Number of executed store instructions. */
             statistics::Formula numStoreInsts;
             /** Number of instructions executed per cycle. */
             statistics::Formula numRate;
         } executedInstStats;

         /** Number of instructions sent to commit. */
         statistics::Vector instsToCommit;
         /** Number of instructions that writeback. */
         statistics::Vector writebackCount;
         /** Number of instructions that wake consumers. */
         statistics::Vector producerInst;
         /** Number of instructions that wake up from producers. */
         statistics::Vector consumerInst;
         /** Number of instructions per cycle written back. */
         statistics::Formula wbRate;
         /** Average number of woken instructions per writeback. */
         statistics::Formula wbFanout;
     } iewStats;
 };

 } // namespace o3
 } // namespace gem5

 #endif // __CPU_O3_IEW_HH__
	/*
	* Copyright (c) 2010-2012, 2014, 2019 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
	* 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_IEW_HH__
	#define __CPU_O3_IEW_HH__

	#include <queue>
	#include <set>

	#include "base/statistics.hh"
	#include "cpu/o3/comm.hh"
	#include "cpu/o3/dyn_inst_ptr.hh"
	#include "cpu/o3/inst_queue.hh"
	#include "cpu/o3/limits.hh"
	#include "cpu/o3/lsq.hh"
	#include "cpu/o3/scoreboard.hh"
	#include "cpu/timebuf.hh"
	#include "debug/IEW.hh"
	#include "sim/probe/probe.hh"

	namespace gem5
	{

	struct BaseO3CPUParams;

	namespace o3
	{

	class FUPool;

	/**
	* IEW handles both single threaded and SMT IEW
	* (issue/execute/writeback). It handles the dispatching of
	* instructions to the LSQ/IQ as part of the issue stage, and has the
	* IQ try to issue instructions each cycle. The execute latency is
	* actually tied into the issue latency to allow the IQ to be able to
	* do back-to-back scheduling without having to speculatively schedule
	* instructions. This happens by having the IQ have access to the
	* functional units, and the IQ gets the execution latencies from the
	* FUs when it issues instructions. Instructions reach the execute
	* stage on the last cycle of their execution, which is when the IQ
	* knows to wake up any dependent instructions, allowing back to back
	* scheduling. The execute portion of IEW separates memory
	* instructions from non-memory instructions, either telling the LSQ
	* to execute the instruction, or executing the instruction directly.
	* The writeback portion of IEW completes the instructions by waking
	* up any dependents, and marking the register ready on the
	* scoreboard.
	*/
	class IEW
	{
	public:
	/** Overall IEW stage status. Used to determine if the CPU can
	* deschedule itself due to a lack of activity.
	*/
	enum Status
	{
	Active,
	Inactive
	};

	/** Status for Issue, Execute, and Writeback stages. */
	enum StageStatus
	{
	Running,
	Blocked,
	Idle,
	StartSquash,
	Squashing,
	Unblocking
	};

	private:
	/** Overall stage status. */
	Status _status;
	/** Dispatch status. */
	StageStatus dispatchStatus[MaxThreads];
	/** Execute status. */
	StageStatus exeStatus;
	/** Writeback status. */
	StageStatus wbStatus;

	/** Probe points. */
	ProbePointArg<DynInstPtr> *ppMispredict;
	ProbePointArg<DynInstPtr> *ppDispatch;
	/** To probe when instruction execution begins. */
	ProbePointArg<DynInstPtr> *ppExecute;
	/** To probe when instruction execution is complete. */
	ProbePointArg<DynInstPtr> *ppToCommit;

	public:
	/** Constructs a IEW with the given parameters. */
	IEW(CPU *_cpu, const BaseO3CPUParams &params);

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

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

	/** Initializes stage; sends back the number of free IQ and LSQ entries. */
	void startupStage();

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

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

	/** Sets time buffer for getting instructions coming from rename. */
	void setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr);

	/** Sets time buffer to pass on instructions to commit. */
	void setIEWQueue(TimeBuffer<IEWStruct> *iq_ptr);

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

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

	/** 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 instructions in IEW for a specific thread. */
	void squash(ThreadID tid);

	/** Wakes all dependents of a completed instruction. */
	void wakeDependents(const DynInstPtr &inst);

	/** Tells memory dependence unit that a memory instruction needs to be
	* rescheduled. It will re-execute once replayMemInst() is called.
	*/
	void rescheduleMemInst(const DynInstPtr &inst);

	/** Re-executes all rescheduled memory instructions. */
	void replayMemInst(const DynInstPtr &inst);

	/** Moves memory instruction onto the list of cache blocked instructions */
	void blockMemInst(const DynInstPtr &inst);

	/** Notifies that the cache has become unblocked */
	void cacheUnblocked();

	/** Sends an instruction to commit through the time buffer. */
	void instToCommit(const DynInstPtr &inst);

	/** Inserts unused instructions of a thread into the skid buffer. */
	void skidInsert(ThreadID tid);

	/** Returns the max of the number of entries in all of the skid buffers. */
	int skidCount();

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

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

	/** Resets entries of the IQ and the LSQ. */
	void resetEntries();

	/** Tells the CPU to wakeup if it has descheduled itself due to no
	* activity. Used mainly by the LdWritebackEvent.
	*/
	void wakeCPU();

	/** Reports to the CPU that there is activity this cycle. */
	void activityThisCycle();

	/** Tells CPU that the IEW stage is active and running. */
	void activateStage();

	/** Tells CPU that the IEW stage is inactive and idle. */
	void deactivateStage();

	/** Returns if the LSQ has any stores to writeback. */
	bool hasStoresToWB() { return ldstQueue.hasStoresToWB(); }

	/** Returns if the LSQ has any stores to writeback. */
	bool hasStoresToWB(ThreadID tid) { return ldstQueue.hasStoresToWB(tid); }

	/** Check misprediction */
	void checkMisprediction(const DynInstPtr &inst);

	// hardware transactional memory
	// For debugging purposes, it is useful to keep track of the most recent
	// htmUid that has been committed (architecturally, not transactionally)
	// to ensure that the core and the memory subsystem are observing
	// correct ordering constraints.
	void setLastRetiredHtmUid(ThreadID tid, uint64_t htmUid)
	{
	ldstQueue.setLastRetiredHtmUid(tid, htmUid);
	}

	private:
	/** Sends commit proper information for a squash due to a branch
	* mispredict.
	*/
	void squashDueToBranch(const DynInstPtr &inst, ThreadID tid);

	/** Sends commit proper information for a squash due to a memory order
	* violation.
	*/
	void squashDueToMemOrder(const DynInstPtr &inst, ThreadID tid);

	/** Sets Dispatch to blocked, and signals back to other stages to block. */
	void block(ThreadID tid);

	/** Unblocks Dispatch if the skid buffer is empty, and signals back to
	* other stages to unblock.
	*/
	void unblock(ThreadID tid);

	/** Determines proper actions to take given Dispatch's status. */
	void dispatch(ThreadID tid);

	/** Dispatches instructions to IQ and LSQ. */
	void dispatchInsts(ThreadID tid);

	/** Executes instructions. In the case of memory operations, it informs the
	* LSQ to execute the instructions. Also handles any redirects that occur
	* due to the executed instructions.
	*/
	void executeInsts();

	/** Writebacks instructions. In our model, the instruction's execute()
	* function atomically reads registers, executes, and writes registers.
	* Thus this writeback only wakes up dependent instructions, and informs
	* the scoreboard of registers becoming ready.
	*/
	void writebackInsts();

	/** Checks if any of the stall conditions are currently true. */
	bool checkStall(ThreadID tid);

	/** Processes inputs and changes state accordingly. */
	void checkSignalsAndUpdate(ThreadID tid);

	/** Removes instructions from rename from a thread's instruction list. */
	void emptyRenameInsts(ThreadID tid);

	/** Sorts instructions coming from rename into lists separated by thread. */
	void sortInsts();

	public:
	/** Ticks IEW stage, causing Dispatch, the IQ, the LSQ, Execute, and
	* Writeback to run for one cycle.
	*/
	void tick();

	private:
	/** Updates execution stats based on the instruction. */
	void updateExeInstStats(const DynInstPtr &inst);

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

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

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

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

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

	/** Wire to get rename's output from rename queue. */
	TimeBuffer<RenameStruct>::wire fromRename;

	/** Issue stage queue. */
	TimeBuffer<IssueStruct> issueToExecQueue;

	/** Wire to read information from the issue stage time queue. */
	TimeBuffer<IssueStruct>::wire fromIssue;

	/**
	* IEW stage time buffer. Holds ROB indices of instructions that
	* can be marked as completed.
	*/
	TimeBuffer<IEWStruct> *iewQueue;

	/** Wire to write infromation heading to commit. */
	TimeBuffer<IEWStruct>::wire toCommit;

	/** Queue of all instructions coming from rename this cycle. */
	std::queue<DynInstPtr> insts[MaxThreads];

	/** Skid buffer between rename and IEW. */
	std::queue<DynInstPtr> skidBuffer[MaxThreads];

	/** Scoreboard pointer. */
	Scoreboard* scoreboard;

	private:
	/** CPU pointer. */
	CPU *cpu;

	/** Records if IEW has written to the time buffer this cycle, so that the
	* CPU can deschedule itself if there is no activity.
	*/
	bool wroteToTimeBuffer;

	/** Debug function to print instructions that are issued this cycle. */
	void printAvailableInsts();

	public:
	/** Instruction queue. */
	InstructionQueue instQueue;

	/** Load / store queue. */
	LSQ ldstQueue;

	/** Pointer to the functional unit pool. */
	FUPool *fuPool;
	/** Records if the LSQ needs to be updated on the next cycle, so that
	* IEW knows if there will be activity on the next cycle.
	*/
	bool updateLSQNextCycle;

	private:
	/** Records if there is a fetch redirect on this cycle for each thread. */
	bool fetchRedirect[MaxThreads];

	/** Records if the queues have been changed (inserted or issued insts),
	* so that IEW knows to broadcast the updated amount of free entries.
	*/
	bool updatedQueues;

	/** Commit to IEW delay. */
	Cycles commitToIEWDelay;

	/** Rename to IEW delay. */
	Cycles renameToIEWDelay;

	/**
	* Issue to execute delay. What this actually represents is
	* the amount of time it takes for an instruction to wake up, be
	* scheduled, and sent to a FU for execution.
	*/
	Cycles issueToExecuteDelay;

	/** Width of dispatch, in instructions. */
	unsigned dispatchWidth;

	/** Width of issue, in instructions. */
	unsigned issueWidth;

	/** Index into queue of instructions being written back. */
	unsigned wbNumInst;

	/** Cycle number within the queue of instructions being written back.
	* Used in case there are too many instructions writing back at the current
	* cycle and writesbacks need to be scheduled for the future. See comments
	* in instToCommit().
	*/
	unsigned wbCycle;

	/** Writeback width. */
	unsigned wbWidth;

	/** Number of active threads. */
	ThreadID numThreads;

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

	/** Maximum size of the skid buffer. */
	unsigned skidBufferMax;


	struct IEWStats : public statistics::Group
	{
	IEWStats(CPU *cpu);

	/** Stat for total number of idle cycles. */
	statistics::Scalar idleCycles;
	/** Stat for total number of squashing cycles. */
	statistics::Scalar squashCycles;
	/** Stat for total number of blocking cycles. */
	statistics::Scalar blockCycles;
	/** Stat for total number of unblocking cycles. */
	statistics::Scalar unblockCycles;
	/** Stat for total number of instructions dispatched. */
	statistics::Scalar dispatchedInsts;
	/** Stat for total number of squashed instructions dispatch skips. */
	statistics::Scalar dispSquashedInsts;
	/** Stat for total number of dispatched load instructions. */
	statistics::Scalar dispLoadInsts;
	/** Stat for total number of dispatched store instructions. */
	statistics::Scalar dispStoreInsts;
	/** Stat for total number of dispatched non speculative insts. */
	statistics::Scalar dispNonSpecInsts;
	/** Stat for number of times the IQ becomes full. */
	statistics::Scalar iqFullEvents;
	/** Stat for number of times the LSQ becomes full. */
	statistics::Scalar lsqFullEvents;
	/** Stat for total number of memory ordering violation events. */
	statistics::Scalar memOrderViolationEvents;
	/** Stat for total number of incorrect predicted taken branches. */
	statistics::Scalar predictedTakenIncorrect;
	/** Stat for total number of incorrect predicted not taken branches. */
	statistics::Scalar predictedNotTakenIncorrect;
	/** Stat for total number of mispredicted branches detected at
	* execute. */
	statistics::Formula branchMispredicts;

	struct ExecutedInstStats : public statistics::Group
	{
	ExecutedInstStats(CPU *cpu);

	/** Stat for total number of executed instructions. */
	statistics::Scalar numInsts;
	/** Stat for total number of executed load instructions. */
	statistics::Vector numLoadInsts;
	/** Stat for total number of squashed instructions skipped at
	* execute. */
	statistics::Scalar numSquashedInsts;
	/** Number of executed software prefetches. */
	statistics::Vector numSwp;
	/** Number of executed nops. */
	statistics::Vector numNop;
	/** Number of executed meomory references. */
	statistics::Vector numRefs;
	/** Number of executed branches. */
	statistics::Vector numBranches;
	/** Number of executed store instructions. */
	statistics::Formula numStoreInsts;
	/** Number of instructions executed per cycle. */
	statistics::Formula numRate;
	} executedInstStats;

	/** Number of instructions sent to commit. */
	statistics::Vector instsToCommit;
	/** Number of instructions that writeback. */
	statistics::Vector writebackCount;
	/** Number of instructions that wake consumers. */
	statistics::Vector producerInst;
	/** Number of instructions that wake up from producers. */
	statistics::Vector consumerInst;
	/** Number of instructions per cycle written back. */
	statistics::Formula wbRate;
	/** Average number of woken instructions per writeback. */
	statistics::Formula wbFanout;
	} iewStats;
	};

	} // namespace o3
	} // namespace gem5

	#endif // __CPU_O3_IEW_HH__