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

 /*
  * Copyright (c) 2012 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_DECODE_HH__
 #define __CPU_O3_DECODE_HH__

 #include <queue>

 #include "base/statistics.hh"
 #include "cpu/o3/comm.hh"
 #include "cpu/o3/dyn_inst_ptr.hh"
 #include "cpu/o3/limits.hh"
 #include "cpu/timebuf.hh"

 namespace gem5
 {

 struct O3CPUParams;

 namespace o3
 {

 class CPU;

 /**
  * Decode class handles both single threaded and SMT
  * decode. Its width is specified by the parameters; each cycles it
  * tries to decode that many instructions. Because instructions are
  * actually decoded when the StaticInst is created, this stage does
  * not do much other than check any PC-relative branches.
  */
 class Decode
 {
   public:
     /** Overall decode stage status. Used to determine if the CPU can
      * deschedule itself due to a lack of activity.
      */
     enum DecodeStatus
     {
         Active,
         Inactive
     };

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

   private:
     /** Decode status. */
     DecodeStatus _status;

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

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

     void startupStage();

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

     void resetStage();

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

     /** 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 setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr);

     /** Sets pointer to time buffer coming from fetch. */
     void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);

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

     /** Ticks decode, processing all input signals and decoding as many
      * instructions as possible.
      */
     void tick();

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

     /** Processes instructions from fetch and passes them on to rename.
      * Decoding of instructions actually happens when they are created in
      * fetch, so this function mostly checks if PC-relative branches are
      * correct.
      */
     void decodeInsts(ThreadID tid);

   private:
     /** Inserts a thread's instructions into the skid buffer, to be decoded
      * once decode unblocks.
      */
     void skidInsert(ThreadID tid);

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

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

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

     /** Reads all stall signals from the backwards communication timebuffer. */
     void readStallSignals(ThreadID tid);

     /** Checks all input signals and updates decode's status appropriately. */
     bool checkSignalsAndUpdate(ThreadID tid);

     /** Checks all stall signals, and returns if any are true. */
     bool checkStall(ThreadID tid) const;

     /** Returns if there any instructions from fetch on this cycle. */
     bool fetchInstsValid();

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

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

     /** Squashes if there is a PC-relative branch that was predicted
      * incorrectly. Sends squash information back to fetch.
      */
     void squash(const DynInstPtr &inst, ThreadID tid);

   public:
     /** Squashes due to commit signalling a squash. Changes status to
      * squashing and clears block/unblock signals as needed.
      */
     unsigned squash(ThreadID tid);

   private:
     // Interfaces to objects outside of decode.
     /** CPU interface. */
     CPU *cpu;

     /** Time buffer interface. */
     TimeBuffer<TimeStruct> *timeBuffer;

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

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

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

     /** Wire to write information heading to previous stages. */
     // Might not be the best name as not only fetch will read it.
     TimeBuffer<TimeStruct>::wire toFetch;

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

     /** Wire used to write any information heading to rename. */
     TimeBuffer<DecodeStruct>::wire toRename;

     /** Fetch instruction queue interface. */
     TimeBuffer<FetchStruct> *fetchQueue;

     /** Wire to get fetch's output from fetch queue. */
     TimeBuffer<FetchStruct>::wire fromFetch;

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

     /** Skid buffer between fetch and decode. */
     std::queue<DynInstPtr> skidBuffer[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;

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

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

     /** Rename to decode delay. */
     Cycles renameToDecodeDelay;

     /** IEW to decode delay. */
     Cycles iewToDecodeDelay;

     /** Commit to decode delay. */
     Cycles commitToDecodeDelay;

     /** Fetch to decode delay. */
     Cycles fetchToDecodeDelay;

     /** The width of decode, in instructions. */
     unsigned decodeWidth;

     /** Index of instructions being sent to rename. */
     unsigned toRenameIndex;

     /** number of Active Threads*/
     ThreadID numThreads;

     /** List of active thread ids */
     std::list<ThreadID> *activeThreads;

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

     /** SeqNum of Squashing Branch Delay Instruction (used for MIPS)*/
     Addr bdelayDoneSeqNum[MaxThreads];

     /** Instruction used for squashing branch (used for MIPS)*/
     DynInstPtr squashInst[MaxThreads];

     /** Tells when their is a pending delay slot inst. to send
      *  to rename. If there is, then wait squash after the next
      *  instruction (used for MIPS).
      */
     bool squashAfterDelaySlot[MaxThreads];

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

         /** Stat for total number of idle cycles. */
         statistics::Scalar idleCycles;
         /** Stat for total number of blocked cycles. */
         statistics::Scalar blockedCycles;
         /** Stat for total number of normal running cycles. */
         statistics::Scalar runCycles;
         /** Stat for total number of unblocking cycles. */
         statistics::Scalar unblockCycles;
         /** Stat for total number of squashing cycles. */
         statistics::Scalar squashCycles;
         /** Stat for number of times a branch is resolved at decode. */
         statistics::Scalar branchResolved;
         /** Stat for number of times a branch mispredict is detected. */
         statistics::Scalar branchMispred;
         /** Stat for number of times decode detected a non-control instruction
          * incorrectly predicted as a branch.
          */
         statistics::Scalar controlMispred;
         /** Stat for total number of decoded instructions. */
         statistics::Scalar decodedInsts;
         /** Stat for total number of squashed instructions. */
         statistics::Scalar squashedInsts;
     } stats;
 };

 } // namespace o3
 } // namespace gem5

 #endif // __CPU_O3_DECODE_HH__
	/*
	* Copyright (c) 2012 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_DECODE_HH__
	#define __CPU_O3_DECODE_HH__

	#include <queue>

	#include "base/statistics.hh"
	#include "cpu/o3/comm.hh"
	#include "cpu/o3/dyn_inst_ptr.hh"
	#include "cpu/o3/limits.hh"
	#include "cpu/timebuf.hh"

	namespace gem5
	{

	struct O3CPUParams;

	namespace o3
	{

	class CPU;

	/**
	* Decode class handles both single threaded and SMT
	* decode. Its width is specified by the parameters; each cycles it
	* tries to decode that many instructions. Because instructions are
	* actually decoded when the StaticInst is created, this stage does
	* not do much other than check any PC-relative branches.
	*/
	class Decode
	{
	public:
	/** Overall decode stage status. Used to determine if the CPU can
	* deschedule itself due to a lack of activity.
	*/
	enum DecodeStatus
	{
	Active,
	Inactive
	};

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

	private:
	/** Decode status. */
	DecodeStatus _status;

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

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

	void startupStage();

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

	void resetStage();

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

	/** 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 setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr);

	/** Sets pointer to time buffer coming from fetch. */
	void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);

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

	/** Ticks decode, processing all input signals and decoding as many
	* instructions as possible.
	*/
	void tick();

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

	/** Processes instructions from fetch and passes them on to rename.
	* Decoding of instructions actually happens when they are created in
	* fetch, so this function mostly checks if PC-relative branches are
	* correct.
	*/
	void decodeInsts(ThreadID tid);

	private:
	/** Inserts a thread's instructions into the skid buffer, to be decoded
	* once decode unblocks.
	*/
	void skidInsert(ThreadID tid);

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

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

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

	/** Reads all stall signals from the backwards communication timebuffer. */
	void readStallSignals(ThreadID tid);

	/** Checks all input signals and updates decode's status appropriately. */
	bool checkSignalsAndUpdate(ThreadID tid);

	/** Checks all stall signals, and returns if any are true. */
	bool checkStall(ThreadID tid) const;

	/** Returns if there any instructions from fetch on this cycle. */
	bool fetchInstsValid();

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

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

	/** Squashes if there is a PC-relative branch that was predicted
	* incorrectly. Sends squash information back to fetch.
	*/
	void squash(const DynInstPtr &inst, ThreadID tid);

	public:
	/** Squashes due to commit signalling a squash. Changes status to
	* squashing and clears block/unblock signals as needed.
	*/
	unsigned squash(ThreadID tid);

	private:
	// Interfaces to objects outside of decode.
	/** CPU interface. */
	CPU *cpu;

	/** Time buffer interface. */
	TimeBuffer<TimeStruct> *timeBuffer;

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

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

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

	/** Wire to write information heading to previous stages. */
	// Might not be the best name as not only fetch will read it.
	TimeBuffer<TimeStruct>::wire toFetch;

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

	/** Wire used to write any information heading to rename. */
	TimeBuffer<DecodeStruct>::wire toRename;

	/** Fetch instruction queue interface. */
	TimeBuffer<FetchStruct> *fetchQueue;

	/** Wire to get fetch's output from fetch queue. */
	TimeBuffer<FetchStruct>::wire fromFetch;

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

	/** Skid buffer between fetch and decode. */
	std::queue<DynInstPtr> skidBuffer[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;

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

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

	/** Rename to decode delay. */
	Cycles renameToDecodeDelay;

	/** IEW to decode delay. */
	Cycles iewToDecodeDelay;

	/** Commit to decode delay. */
	Cycles commitToDecodeDelay;

	/** Fetch to decode delay. */
	Cycles fetchToDecodeDelay;

	/** The width of decode, in instructions. */
	unsigned decodeWidth;

	/** Index of instructions being sent to rename. */
	unsigned toRenameIndex;

	/** number of Active Threads*/
	ThreadID numThreads;

	/** List of active thread ids */
	std::list<ThreadID> *activeThreads;

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

	/** SeqNum of Squashing Branch Delay Instruction (used for MIPS)*/
	Addr bdelayDoneSeqNum[MaxThreads];

	/** Instruction used for squashing branch (used for MIPS)*/
	DynInstPtr squashInst[MaxThreads];

	/** Tells when their is a pending delay slot inst. to send
	* to rename. If there is, then wait squash after the next
	* instruction (used for MIPS).
	*/
	bool squashAfterDelaySlot[MaxThreads];

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

	/** Stat for total number of idle cycles. */
	statistics::Scalar idleCycles;
	/** Stat for total number of blocked cycles. */
	statistics::Scalar blockedCycles;
	/** Stat for total number of normal running cycles. */
	statistics::Scalar runCycles;
	/** Stat for total number of unblocking cycles. */
	statistics::Scalar unblockCycles;
	/** Stat for total number of squashing cycles. */
	statistics::Scalar squashCycles;
	/** Stat for number of times a branch is resolved at decode. */
	statistics::Scalar branchResolved;
	/** Stat for number of times a branch mispredict is detected. */
	statistics::Scalar branchMispred;
	/** Stat for number of times decode detected a non-control instruction
	* incorrectly predicted as a branch.
	*/
	statistics::Scalar controlMispred;
	/** Stat for total number of decoded instructions. */
	statistics::Scalar decodedInsts;
	/** Stat for total number of squashed instructions. */
	statistics::Scalar squashedInsts;
	} stats;
	};

	} // namespace o3
	} // namespace gem5

	#endif // __CPU_O3_DECODE_HH__