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

 /*
  * Copyright (c) 2012-2014,2017-2018,2020-2021 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_LSQ_UNIT_HH__
 #define __CPU_O3_LSQ_UNIT_HH__

 #include <algorithm>
 #include <cstring>
 #include <map>
 #include <memory>
 #include <queue>

 #include "arch/generic/debugfaults.hh"
 #include "arch/generic/vec_reg.hh"
 #include "base/circular_queue.hh"
 #include "config/the_isa.hh"
 #include "cpu/base.hh"
 #include "cpu/inst_seq.hh"
 #include "cpu/o3/comm.hh"
 #include "cpu/o3/cpu.hh"
 #include "cpu/o3/dyn_inst_ptr.hh"
 #include "cpu/o3/lsq.hh"
 #include "cpu/timebuf.hh"
 #include "debug/HtmCpu.hh"
 #include "debug/LSQUnit.hh"
 #include "mem/packet.hh"
 #include "mem/port.hh"

 namespace gem5
 {

 struct BaseO3CPUParams;

 namespace o3
 {

 class IEW;

 /**
  * Class that implements the actual LQ and SQ for each specific
  * thread.  Both are circular queues; load entries are freed upon
  * committing, while store entries are freed once they writeback. The
  * LSQUnit tracks if there are memory ordering violations, and also
  * detects partial load to store forwarding cases (a store only has
  * part of a load's data) that requires the load to wait until the
  * store writes back. In the former case it holds onto the instruction
  * until the dependence unit looks at it, and in the latter it stalls
  * the LSQ until the store writes back. At that point the load is
  * replayed.
  */
 class LSQUnit
 {
   public:
     static constexpr auto MaxDataBytes = MaxVecRegLenInBytes;

     using LSQRequest = LSQ::LSQRequest;
   private:
     class LSQEntry
     {
       private:
         /** The instruction. */
         DynInstPtr _inst;
         /** The request. */
         LSQRequest* _request = nullptr;
         /** The size of the operation. */
         uint32_t _size = 0;
         /** Valid entry. */
         bool _valid = false;

       public:
         ~LSQEntry()
         {
             if (_request != nullptr) {
                 _request->freeLSQEntry();
                 _request = nullptr;
             }
         }

         void
         clear()
         {
             _inst = nullptr;
             if (_request != nullptr) {
                 _request->freeLSQEntry();
             }
             _request = nullptr;
             _valid = false;
             _size = 0;
         }

         void
         set(const DynInstPtr& new_inst)
         {
             assert(!_valid);
             _inst = new_inst;
             _valid = true;
             _size = 0;
         }

         LSQRequest* request() { return _request; }
         void setRequest(LSQRequest* r) { _request = r; }
         bool hasRequest() { return _request != nullptr; }
         /** Member accessors. */
         /** @{ */
         bool valid() const { return _valid; }
         uint32_t& size() { return _size; }
         const uint32_t& size() const { return _size; }
         const DynInstPtr& instruction() const { return _inst; }
         /** @} */
     };

     class SQEntry : public LSQEntry
     {
       private:
         /** The store data. */
         char _data[MaxDataBytes];
         /** Whether or not the store can writeback. */
         bool _canWB = false;
         /** Whether or not the store is committed. */
         bool _committed = false;
         /** Whether or not the store is completed. */
         bool _completed = false;
         /** Does this request write all zeros and thus doesn't
          * have any data attached to it. Used for cache block zero
          * style instructs (ARM DC ZVA; ALPHA WH64)
          */
         bool _isAllZeros = false;

       public:
         static constexpr size_t DataSize = sizeof(_data);
         /** Constructs an empty store queue entry. */
         SQEntry()
         {
             std::memset(_data, 0, DataSize);
         }

         void set(const DynInstPtr& inst) { LSQEntry::set(inst); }

         void
         clear()
         {
             LSQEntry::clear();
             _canWB = _completed = _committed = _isAllZeros = false;
         }

         /** Member accessors. */
         /** @{ */
         bool& canWB() { return _canWB; }
         const bool& canWB() const { return _canWB; }
         bool& completed() { return _completed; }
         const bool& completed() const { return _completed; }
         bool& committed() { return _committed; }
         const bool& committed() const { return _committed; }
         bool& isAllZeros() { return _isAllZeros; }
         const bool& isAllZeros() const { return _isAllZeros; }
         char* data() { return _data; }
         const char* data() const { return _data; }
         /** @} */
     };
     using LQEntry = LSQEntry;

     /** Coverage of one address range with another */
     enum class AddrRangeCoverage
     {
         PartialAddrRangeCoverage, /* Two ranges partly overlap */
         FullAddrRangeCoverage, /* One range fully covers another */
         NoAddrRangeCoverage /* Two ranges are disjoint */
     };

   public:
     using LoadQueue = CircularQueue<LQEntry>;
     using StoreQueue = CircularQueue<SQEntry>;

   public:
     /** Constructs an LSQ unit. init() must be called prior to use. */
     LSQUnit(uint32_t lqEntries, uint32_t sqEntries);

     /** We cannot copy LSQUnit because it has stats for which copy
      * contructor is deleted explicitly. However, STL vector requires
      * a valid copy constructor for the base type at compile time.
      */
     LSQUnit(const LSQUnit &l): stats(nullptr)
     {
         panic("LSQUnit is not copy-able");
     }

     /** Initializes the LSQ unit with the specified number of entries. */
     void init(CPU *cpu_ptr, IEW *iew_ptr, const BaseO3CPUParams &params,
             LSQ *lsq_ptr, unsigned id);

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

     /** Sets the pointer to the dcache port. */
     void setDcachePort(RequestPort *dcache_port);

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

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

     /** Inserts an instruction. */
     void insert(const DynInstPtr &inst);
     /** Inserts a load instruction. */
     void insertLoad(const DynInstPtr &load_inst);
     /** Inserts a store instruction. */
     void insertStore(const DynInstPtr &store_inst);

     /** Check for ordering violations in the LSQ. For a store squash if we
      * ever find a conflicting load. For a load, only squash if we
      * an external snoop invalidate has been seen for that load address
      * @param load_idx index to start checking at
      * @param inst the instruction to check
      */
     Fault checkViolations(typename LoadQueue::iterator& loadIt,
             const DynInstPtr& inst);

     /** Check if an incoming invalidate hits in the lsq on a load
      * that might have issued out of order wrt another load beacuse
      * of the intermediate invalidate.
      */
     void checkSnoop(PacketPtr pkt);

     /** Executes a load instruction. */
     Fault executeLoad(const DynInstPtr &inst);

     Fault executeLoad(int lq_idx) { panic("Not implemented"); return NoFault; }
     /** Executes a store instruction. */
     Fault executeStore(const DynInstPtr &inst);

     /** Commits the head load. */
     void commitLoad();
     /** Commits loads older than a specific sequence number. */
     void commitLoads(InstSeqNum &youngest_inst);

     /** Commits stores older than a specific sequence number. */
     void commitStores(InstSeqNum &youngest_inst);

     /** Writes back stores. */
     void writebackStores();

     /** Completes the data access that has been returned from the
      * memory system. */
     void completeDataAccess(PacketPtr pkt);

     /** Squashes all instructions younger than a specific sequence number. */
     void squash(const InstSeqNum &squashed_num);

     /** Returns if there is a memory ordering violation. Value is reset upon
      * call to getMemDepViolator().
      */
     bool violation() { return memDepViolator; }

     /** Returns the memory ordering violator. */
     DynInstPtr getMemDepViolator();

     /** Returns the number of free LQ entries. */
     unsigned numFreeLoadEntries();

     /** Returns the number of free SQ entries. */
     unsigned numFreeStoreEntries();

     /** Returns the number of loads in the LQ. */
     int numLoads() { return loadQueue.size(); }

     /** Returns the number of stores in the SQ. */
     int numStores() { return storeQueue.size(); }

     // hardware transactional memory
     int numHtmStarts() const { return htmStarts; }
     int numHtmStops() const { return htmStops; }
     void resetHtmStartsStops() { htmStarts = htmStops = 0; }
     uint64_t getLatestHtmUid() const;
     void
     setLastRetiredHtmUid(uint64_t htm_uid)
     {
         assert(htm_uid >= lastRetiredHtmUid);
         lastRetiredHtmUid = htm_uid;
     }

     // Stale translation checks
     void startStaleTranslationFlush();
     bool checkStaleTranslations() const;

     /** Returns if either the LQ or SQ is full. */
     bool isFull() { return lqFull() || sqFull(); }

     /** Returns if both the LQ and SQ are empty. */
     bool isEmpty() const { return lqEmpty() && sqEmpty(); }

     /** Returns if the LQ is full. */
     bool lqFull() { return loadQueue.full(); }

     /** Returns if the SQ is full. */
     bool sqFull() { return storeQueue.full(); }

     /** Returns if the LQ is empty. */
     bool lqEmpty() const { return loadQueue.size() == 0; }

     /** Returns if the SQ is empty. */
     bool sqEmpty() const { return storeQueue.size() == 0; }

     /** Returns the number of instructions in the LSQ. */
     unsigned getCount() { return loadQueue.size() + storeQueue.size(); }

     /** Returns if there are any stores to writeback. */
     bool hasStoresToWB() { return storesToWB; }

     /** Returns the number of stores to writeback. */
     int numStoresToWB() { return storesToWB; }

     /** Returns if the LSQ unit will writeback on this cycle. */
     bool
     willWB()
     {
         return storeWBIt.dereferenceable() &&
                         storeWBIt->valid() &&
                         storeWBIt->canWB() &&
                         !storeWBIt->completed() &&
                         !isStoreBlocked;
     }

     /** Handles doing the retry. */
     void recvRetry();

     unsigned int cacheLineSize();
   private:
     /** Reset the LSQ state */
     void resetState();

     /** Writes back the instruction, sending it to IEW. */
     void writeback(const DynInstPtr &inst, PacketPtr pkt);

     /** Try to finish a previously blocked write back attempt */
     void writebackBlockedStore();

     /** Completes the store at the specified index. */
     void completeStore(typename StoreQueue::iterator store_idx);

     /** Handles completing the send of a store to memory. */
     void storePostSend();

   public:
     /** Attempts to send a packet to the cache.
      * Check if there are ports available. Return true if
      * there are, false if there are not.
      */
     bool trySendPacket(bool isLoad, PacketPtr data_pkt);


     /** Debugging function to dump instructions in the LSQ. */
     void dumpInsts() const;

     /** Schedule event for the cpu. */
     void schedule(Event& ev, Tick when);

     BaseMMU *getMMUPtr();

   private:
     /** Pointer to the CPU. */
     CPU *cpu;

     /** Pointer to the IEW stage. */
     IEW *iewStage;

     /** Pointer to the LSQ. */
     LSQ *lsq;

     /** Pointer to the dcache port.  Used only for sending. */
     RequestPort *dcachePort;

     /** Writeback event, specifically for when stores forward data to loads. */
     class WritebackEvent : public Event
     {
       public:
         /** Constructs a writeback event. */
         WritebackEvent(const DynInstPtr &_inst, PacketPtr pkt,
                 LSQUnit *lsq_ptr);

         /** Processes the writeback event. */
         void process();

         /** Returns the description of this event. */
         const char *description() const;

       private:
         /** Instruction whose results are being written back. */
         DynInstPtr inst;

         /** The packet that would have been sent to memory. */
         PacketPtr pkt;

         /** The pointer to the LSQ unit that issued the store. */
         LSQUnit *lsqPtr;
     };

   public:
     /**
      * Handles writing back and completing the load or store that has
      * returned from memory.
      *
      * @param pkt Response packet from the memory sub-system
      */
     bool recvTimingResp(PacketPtr pkt);

   private:
     /** The LSQUnit thread id. */
     ThreadID lsqID;
   public:
     /** The store queue. */
     StoreQueue storeQueue;

     /** The load queue. */
     LoadQueue loadQueue;

   private:
     /** The number of places to shift addresses in the LSQ before checking
      * for dependency violations
      */
     unsigned depCheckShift;

     /** Should loads be checked for dependency issues */
     bool checkLoads;

     /** The number of store instructions in the SQ waiting to writeback. */
     int storesToWB;

     // hardware transactional memory
     // nesting depth
     int htmStarts;
     int htmStops;
     // sanity checks and debugging
     uint64_t lastRetiredHtmUid;

     /** The index of the first instruction that may be ready to be
      * written back, and has not yet been written back.
      */
     typename StoreQueue::iterator storeWBIt;

     /** Address Mask for a cache block (e.g. ~(cache_block_size-1)) */
     Addr cacheBlockMask;

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

     /** Whether or not the LSQ is stalled. */
     bool stalled;
     /** The store that causes the stall due to partial store to load
      * forwarding.
      */
     InstSeqNum stallingStoreIsn;
     /** The index of the above store. */
     ssize_t stallingLoadIdx;

     /** The packet that needs to be retried. */
     PacketPtr retryPkt;

     /** Whehter or not a store is blocked due to the memory system. */
     bool isStoreBlocked;

     /** Whether or not a store is in flight. */
     bool storeInFlight;

     /** The oldest load that caused a memory ordering violation. */
     DynInstPtr memDepViolator;

     /** Flag for memory model. */
     bool needsTSO;

   protected:
     // Will also need how many read/write ports the Dcache has.  Or keep track
     // of that in stage that is one level up, and only call executeLoad/Store
     // the appropriate number of times.
     struct LSQUnitStats : public statistics::Group
     {
         LSQUnitStats(statistics::Group *parent);

         /** Total number of loads forwaded from LSQ stores. */
         statistics::Scalar forwLoads;

         /** Total number of squashed loads. */
         statistics::Scalar squashedLoads;

         /** Total number of responses from the memory system that are
          * ignored due to the instruction already being squashed. */
         statistics::Scalar ignoredResponses;

         /** Tota number of memory ordering violations. */
         statistics::Scalar memOrderViolation;

         /** Total number of squashed stores. */
         statistics::Scalar squashedStores;

         /** Number of loads that were rescheduled. */
         statistics::Scalar rescheduledLoads;

         /** Number of times the LSQ is blocked due to the cache. */
         statistics::Scalar blockedByCache;

         /** Distribution of cycle latency between the first time a load
          * is issued and its completion */
         statistics::Distribution loadToUse;
     } stats;

   public:
     /** Executes the load at the given index. */
     Fault read(LSQRequest *request, ssize_t load_idx);

     /** Executes the store at the given index. */
     Fault write(LSQRequest *requst, uint8_t *data, ssize_t store_idx);

     /** Returns the index of the head load instruction. */
     int getLoadHead() { return loadQueue.head(); }

     /** Returns the sequence number of the head load instruction. */
     InstSeqNum getLoadHeadSeqNum();

     /** Returns the index of the head store instruction. */
     int getStoreHead() { return storeQueue.head(); }
     /** Returns the sequence number of the head store instruction. */
     InstSeqNum getStoreHeadSeqNum();

     /** Returns whether or not the LSQ unit is stalled. */
     bool isStalled()  { return stalled; }
   public:
     typedef typename CircularQueue<LQEntry>::iterator LQIterator;
     typedef typename CircularQueue<SQEntry>::iterator SQIterator;
 };

 } // namespace o3
 } // namespace gem5

 #endif // __CPU_O3_LSQ_UNIT_HH__
	/*
	* Copyright (c) 2012-2014,2017-2018,2020-2021 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_LSQ_UNIT_HH__
	#define __CPU_O3_LSQ_UNIT_HH__

	#include <algorithm>
	#include <cstring>
	#include <map>
	#include <memory>
	#include <queue>

	#include "arch/generic/debugfaults.hh"
	#include "arch/generic/vec_reg.hh"
	#include "base/circular_queue.hh"
	#include "config/the_isa.hh"
	#include "cpu/base.hh"
	#include "cpu/inst_seq.hh"
	#include "cpu/o3/comm.hh"
	#include "cpu/o3/cpu.hh"
	#include "cpu/o3/dyn_inst_ptr.hh"
	#include "cpu/o3/lsq.hh"
	#include "cpu/timebuf.hh"
	#include "debug/HtmCpu.hh"
	#include "debug/LSQUnit.hh"
	#include "mem/packet.hh"
	#include "mem/port.hh"

	namespace gem5
	{

	struct BaseO3CPUParams;

	namespace o3
	{

	class IEW;

	/**
	* Class that implements the actual LQ and SQ for each specific
	* thread. Both are circular queues; load entries are freed upon
	* committing, while store entries are freed once they writeback. The
	* LSQUnit tracks if there are memory ordering violations, and also
	* detects partial load to store forwarding cases (a store only has
	* part of a load's data) that requires the load to wait until the
	* store writes back. In the former case it holds onto the instruction
	* until the dependence unit looks at it, and in the latter it stalls
	* the LSQ until the store writes back. At that point the load is
	* replayed.
	*/
	class LSQUnit
	{
	public:
	static constexpr auto MaxDataBytes = MaxVecRegLenInBytes;

	using LSQRequest = LSQ::LSQRequest;
	private:
	class LSQEntry
	{
	private:
	/** The instruction. */
	DynInstPtr _inst;
	/** The request. */
	LSQRequest* _request = nullptr;
	/** The size of the operation. */
	uint32_t _size = 0;
	/** Valid entry. */
	bool _valid = false;

	public:
	~LSQEntry()
	{
	if (_request != nullptr) {
	_request->freeLSQEntry();
	_request = nullptr;
	}
	}

	void
	clear()
	{
	_inst = nullptr;
	if (_request != nullptr) {
	_request->freeLSQEntry();
	}
	_request = nullptr;
	_valid = false;
	_size = 0;
	}

	void
	set(const DynInstPtr& new_inst)
	{
	assert(!_valid);
	_inst = new_inst;
	_valid = true;
	_size = 0;
	}

	LSQRequest* request() { return _request; }
	void setRequest(LSQRequest* r) { _request = r; }
	bool hasRequest() { return _request != nullptr; }
	/** Member accessors. */
	/** @{ */
	bool valid() const { return _valid; }
	uint32_t& size() { return _size; }
	const uint32_t& size() const { return _size; }
	const DynInstPtr& instruction() const { return _inst; }
	/** @} */
	};

	class SQEntry : public LSQEntry
	{
	private:
	/** The store data. */
	char _data[MaxDataBytes];
	/** Whether or not the store can writeback. */
	bool _canWB = false;
	/** Whether or not the store is committed. */
	bool _committed = false;
	/** Whether or not the store is completed. */
	bool _completed = false;
	/** Does this request write all zeros and thus doesn't
	* have any data attached to it. Used for cache block zero
	* style instructs (ARM DC ZVA; ALPHA WH64)
	*/
	bool _isAllZeros = false;

	public:
	static constexpr size_t DataSize = sizeof(_data);
	/** Constructs an empty store queue entry. */
	SQEntry()
	{
	std::memset(_data, 0, DataSize);
	}

	void set(const DynInstPtr& inst) { LSQEntry::set(inst); }

	void
	clear()
	{
	LSQEntry::clear();
	_canWB = _completed = _committed = _isAllZeros = false;
	}

	/** Member accessors. */
	/** @{ */
	bool& canWB() { return _canWB; }
	const bool& canWB() const { return _canWB; }
	bool& completed() { return _completed; }
	const bool& completed() const { return _completed; }
	bool& committed() { return _committed; }
	const bool& committed() const { return _committed; }
	bool& isAllZeros() { return _isAllZeros; }
	const bool& isAllZeros() const { return _isAllZeros; }
	char* data() { return _data; }
	const char* data() const { return _data; }
	/** @} */
	};
	using LQEntry = LSQEntry;

	/** Coverage of one address range with another */
	enum class AddrRangeCoverage
	{
	PartialAddrRangeCoverage, /* Two ranges partly overlap */
	FullAddrRangeCoverage, /* One range fully covers another */
	NoAddrRangeCoverage /* Two ranges are disjoint */
	};

	public:
	using LoadQueue = CircularQueue<LQEntry>;
	using StoreQueue = CircularQueue<SQEntry>;

	public:
	/** Constructs an LSQ unit. init() must be called prior to use. */
	LSQUnit(uint32_t lqEntries, uint32_t sqEntries);

	/** We cannot copy LSQUnit because it has stats for which copy
	* contructor is deleted explicitly. However, STL vector requires
	* a valid copy constructor for the base type at compile time.
	*/
	LSQUnit(const LSQUnit &l): stats(nullptr)
	{
	panic("LSQUnit is not copy-able");
	}

	/** Initializes the LSQ unit with the specified number of entries. */
	void init(CPU cpu_ptr, IEW iew_ptr, const BaseO3CPUParams &params,
	LSQ *lsq_ptr, unsigned id);

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

	/** Sets the pointer to the dcache port. */
	void setDcachePort(RequestPort *dcache_port);

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

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

	/** Inserts an instruction. */
	void insert(const DynInstPtr &inst);
	/** Inserts a load instruction. */
	void insertLoad(const DynInstPtr &load_inst);
	/** Inserts a store instruction. */
	void insertStore(const DynInstPtr &store_inst);

	/** Check for ordering violations in the LSQ. For a store squash if we
	* ever find a conflicting load. For a load, only squash if we
	* an external snoop invalidate has been seen for that load address
	* @param load_idx index to start checking at
	* @param inst the instruction to check
	*/
	Fault checkViolations(typename LoadQueue::iterator& loadIt,
	const DynInstPtr& inst);

	/** Check if an incoming invalidate hits in the lsq on a load
	* that might have issued out of order wrt another load beacuse
	* of the intermediate invalidate.
	*/
	void checkSnoop(PacketPtr pkt);

	/** Executes a load instruction. */
	Fault executeLoad(const DynInstPtr &inst);

	Fault executeLoad(int lq_idx) { panic("Not implemented"); return NoFault; }
	/** Executes a store instruction. */
	Fault executeStore(const DynInstPtr &inst);

	/** Commits the head load. */
	void commitLoad();
	/** Commits loads older than a specific sequence number. */
	void commitLoads(InstSeqNum &youngest_inst);

	/** Commits stores older than a specific sequence number. */
	void commitStores(InstSeqNum &youngest_inst);

	/** Writes back stores. */
	void writebackStores();

	/** Completes the data access that has been returned from the
	* memory system. */
	void completeDataAccess(PacketPtr pkt);

	/** Squashes all instructions younger than a specific sequence number. */
	void squash(const InstSeqNum &squashed_num);

	/** Returns if there is a memory ordering violation. Value is reset upon
	* call to getMemDepViolator().
	*/
	bool violation() { return memDepViolator; }

	/** Returns the memory ordering violator. */
	DynInstPtr getMemDepViolator();

	/** Returns the number of free LQ entries. */
	unsigned numFreeLoadEntries();

	/** Returns the number of free SQ entries. */
	unsigned numFreeStoreEntries();

	/** Returns the number of loads in the LQ. */
	int numLoads() { return loadQueue.size(); }

	/** Returns the number of stores in the SQ. */
	int numStores() { return storeQueue.size(); }

	// hardware transactional memory
	int numHtmStarts() const { return htmStarts; }
	int numHtmStops() const { return htmStops; }
	void resetHtmStartsStops() { htmStarts = htmStops = 0; }
	uint64_t getLatestHtmUid() const;
	void
	setLastRetiredHtmUid(uint64_t htm_uid)
	{
	assert(htm_uid >= lastRetiredHtmUid);
	lastRetiredHtmUid = htm_uid;
	}

	// Stale translation checks
	void startStaleTranslationFlush();
	bool checkStaleTranslations() const;

	/** Returns if either the LQ or SQ is full. */
	bool isFull() { return lqFull() \|\| sqFull(); }

	/** Returns if both the LQ and SQ are empty. */
	bool isEmpty() const { return lqEmpty() && sqEmpty(); }

	/** Returns if the LQ is full. */
	bool lqFull() { return loadQueue.full(); }

	/** Returns if the SQ is full. */
	bool sqFull() { return storeQueue.full(); }

	/** Returns if the LQ is empty. */
	bool lqEmpty() const { return loadQueue.size() == 0; }

	/** Returns if the SQ is empty. */
	bool sqEmpty() const { return storeQueue.size() == 0; }

	/** Returns the number of instructions in the LSQ. */
	unsigned getCount() { return loadQueue.size() + storeQueue.size(); }

	/** Returns if there are any stores to writeback. */
	bool hasStoresToWB() { return storesToWB; }

	/** Returns the number of stores to writeback. */
	int numStoresToWB() { return storesToWB; }

	/** Returns if the LSQ unit will writeback on this cycle. */
	bool
	willWB()
	{
	return storeWBIt.dereferenceable() &&
	storeWBIt->valid() &&
	storeWBIt->canWB() &&
	!storeWBIt->completed() &&
	!isStoreBlocked;
	}

	/** Handles doing the retry. */
	void recvRetry();

	unsigned int cacheLineSize();
	private:
	/** Reset the LSQ state */
	void resetState();

	/** Writes back the instruction, sending it to IEW. */
	void writeback(const DynInstPtr &inst, PacketPtr pkt);

	/** Try to finish a previously blocked write back attempt */
	void writebackBlockedStore();

	/** Completes the store at the specified index. */
	void completeStore(typename StoreQueue::iterator store_idx);

	/** Handles completing the send of a store to memory. */
	void storePostSend();

	public:
	/** Attempts to send a packet to the cache.
	* Check if there are ports available. Return true if
	* there are, false if there are not.
	*/
	bool trySendPacket(bool isLoad, PacketPtr data_pkt);


	/** Debugging function to dump instructions in the LSQ. */
	void dumpInsts() const;

	/** Schedule event for the cpu. */
	void schedule(Event& ev, Tick when);

	BaseMMU *getMMUPtr();

	private:
	/** Pointer to the CPU. */
	CPU *cpu;

	/** Pointer to the IEW stage. */
	IEW *iewStage;

	/** Pointer to the LSQ. */
	LSQ *lsq;

	/** Pointer to the dcache port. Used only for sending. */
	RequestPort *dcachePort;

	/** Writeback event, specifically for when stores forward data to loads. */
	class WritebackEvent : public Event
	{
	public:
	/** Constructs a writeback event. */
	WritebackEvent(const DynInstPtr &_inst, PacketPtr pkt,
	LSQUnit *lsq_ptr);

	/** Processes the writeback event. */
	void process();

	/** Returns the description of this event. */
	const char *description() const;

	private:
	/** Instruction whose results are being written back. */
	DynInstPtr inst;

	/** The packet that would have been sent to memory. */
	PacketPtr pkt;

	/** The pointer to the LSQ unit that issued the store. */
	LSQUnit *lsqPtr;
	};

	public:
	/**
	* Handles writing back and completing the load or store that has
	* returned from memory.
	*
	* @param pkt Response packet from the memory sub-system
	*/
	bool recvTimingResp(PacketPtr pkt);

	private:
	/** The LSQUnit thread id. */
	ThreadID lsqID;
	public:
	/** The store queue. */
	StoreQueue storeQueue;

	/** The load queue. */
	LoadQueue loadQueue;

	private:
	/** The number of places to shift addresses in the LSQ before checking
	* for dependency violations
	*/
	unsigned depCheckShift;

	/** Should loads be checked for dependency issues */
	bool checkLoads;

	/** The number of store instructions in the SQ waiting to writeback. */
	int storesToWB;

	// hardware transactional memory
	// nesting depth
	int htmStarts;
	int htmStops;
	// sanity checks and debugging
	uint64_t lastRetiredHtmUid;

	/** The index of the first instruction that may be ready to be
	* written back, and has not yet been written back.
	*/
	typename StoreQueue::iterator storeWBIt;

	/** Address Mask for a cache block (e.g. ~(cache_block_size-1)) */
	Addr cacheBlockMask;

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

	/** Whether or not the LSQ is stalled. */
	bool stalled;
	/** The store that causes the stall due to partial store to load
	* forwarding.
	*/
	InstSeqNum stallingStoreIsn;
	/** The index of the above store. */
	ssize_t stallingLoadIdx;

	/** The packet that needs to be retried. */
	PacketPtr retryPkt;

	/** Whehter or not a store is blocked due to the memory system. */
	bool isStoreBlocked;

	/** Whether or not a store is in flight. */
	bool storeInFlight;

	/** The oldest load that caused a memory ordering violation. */
	DynInstPtr memDepViolator;

	/** Flag for memory model. */
	bool needsTSO;

	protected:
	// Will also need how many read/write ports the Dcache has. Or keep track
	// of that in stage that is one level up, and only call executeLoad/Store
	// the appropriate number of times.
	struct LSQUnitStats : public statistics::Group
	{
	LSQUnitStats(statistics::Group *parent);

	/** Total number of loads forwaded from LSQ stores. */
	statistics::Scalar forwLoads;

	/** Total number of squashed loads. */
	statistics::Scalar squashedLoads;

	/** Total number of responses from the memory system that are
	* ignored due to the instruction already being squashed. */
	statistics::Scalar ignoredResponses;

	/** Tota number of memory ordering violations. */
	statistics::Scalar memOrderViolation;

	/** Total number of squashed stores. */
	statistics::Scalar squashedStores;

	/** Number of loads that were rescheduled. */
	statistics::Scalar rescheduledLoads;

	/** Number of times the LSQ is blocked due to the cache. */
	statistics::Scalar blockedByCache;

	/** Distribution of cycle latency between the first time a load
	* is issued and its completion */
	statistics::Distribution loadToUse;
	} stats;

	public:
	/** Executes the load at the given index. */
	Fault read(LSQRequest *request, ssize_t load_idx);

	/** Executes the store at the given index. */
	Fault write(LSQRequest requst, uint8_t data, ssize_t store_idx);

	/** Returns the index of the head load instruction. */
	int getLoadHead() { return loadQueue.head(); }

	/** Returns the sequence number of the head load instruction. */
	InstSeqNum getLoadHeadSeqNum();

	/** Returns the index of the head store instruction. */
	int getStoreHead() { return storeQueue.head(); }
	/** Returns the sequence number of the head store instruction. */
	InstSeqNum getStoreHeadSeqNum();

	/** Returns whether or not the LSQ unit is stalled. */
	bool isStalled() { return stalled; }
	public:
	typedef typename CircularQueue<LQEntry>::iterator LQIterator;
	typedef typename CircularQueue<SQEntry>::iterator SQIterator;
	};

	} // namespace o3
	} // namespace gem5

	#endif // __CPU_O3_LSQ_UNIT_HH__