src/cpu/minor/scoreboard.hh

   1 /*
   2  * Copyright (c) 2013-2014, 2016-2017 ARM Limited
   3  * All rights reserved
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   9  * licensed hereunder.  You may use the software subject to the license
  10  * terms below provided that you ensure that this notice is replicated
  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Redistribution and use in source and binary forms, with or without
  15  * modification, are permitted provided that the following conditions are
  16  * met: redistributions of source code must retain the above copyright
  17  * notice, this list of conditions and the following disclaimer;
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  19  * notice, this list of conditions and the following disclaimer in the
  20  * documentation and/or other materials provided with the distribution;
  21  * neither the name of the copyright holders nor the names of its
  22  * contributors may be used to endorse or promote products derived from
  23  * this software without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  26  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  35  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  */
  37
  38 /**
  39  * @file
  40  *
  41  *  A simple instruction scoreboard for tracking dependencies in Execute.
  42  */
  43
  44 #ifndef __CPU_MINOR_SCOREBOARD_HH__
  45 #define __CPU_MINOR_SCOREBOARD_HH__
  46
  47 #include "cpu/minor/cpu.hh"
  48 #include "cpu/minor/dyn_inst.hh"
  49 #include "cpu/minor/trace.hh"
  50
  51 namespace Minor
  52 {
  53
  54 /** A scoreboard of register dependencies including, for each register:
  55  *  The number of in-flight instructions which will generate a result for
  56  *  this register */
  57 class Scoreboard : public Named
  58 {
  59   public:
  60     /** The number of registers in the Scoreboard.  These
  61      *  are just the integer, CC and float registers packed
  62      *  together with integer regs in the range [0,NumIntRegs-1],
  63      *  CC regs in the range [NumIntRegs, NumIntRegs+NumCCRegs-1]
  64      *  and float regs in the range
  65      *  [NumIntRegs+NumCCRegs, NumFloatRegs+NumIntRegs+NumCCRegs-1] */
  66     const unsigned numRegs;
  67
  68     /** Type to use when indexing numResults */
  69     typedef unsigned short int Index;
  70
  71     /** Count of the number of in-flight instructions that
  72      *  have results for each register */
  73     std::vector<Index> numResults;
  74
  75     /** Count of the number of results which can't be predicted */
  76     std::vector<Index> numUnpredictableResults;
  77
  78     /** Index of the FU generating this result */
  79     std::vector<int> fuIndices;
  80
  81     /** The estimated cycle number that the result will be presented.
  82      *  This can be offset from to allow forwarding to be simulated as
  83      *  long as instruction completion is *strictly* in order with
  84      *  respect to instructions with unpredictable result timing */
  85     std::vector<Cycles> returnCycle;
  86
  87     /** The execute sequence number of the most recent inst to generate this
  88      *  register value */
  89     std::vector<InstSeqNum> writingInst;
  90
  91   public:
  92     Scoreboard(const std::string &name) :
  93         Named(name),
  94         numRegs(TheISA::NumIntRegs + TheISA::NumCCRegs +
  95             TheISA::NumFloatRegs +
  96             (TheISA::NumVecRegs * TheISA::NumVecElemPerVecReg) +
  97             TheISA::NumVecPredRegs),
  98         numResults(numRegs, 0),
  99         numUnpredictableResults(numRegs, 0),
 100         fuIndices(numRegs, 0),
 101         returnCycle(numRegs, Cycles(0)),
 102         writingInst(numRegs, 0)
 103     { }
 104
 105   public:
 106     /** Sets scoreboard_index to the index into numResults of the
 107      *  given register index.  Returns true if the given register
 108      *  is in the scoreboard and false if it isn't */
 109     bool findIndex(const RegId& reg, Index &scoreboard_index);
 110
 111     /** Mark up an instruction's effects by incrementing
 112      *  numResults counts.  If mark_unpredictable is true, the inst's
 113      *  destination registers are marked as being unpredictable without
 114      *  an estimated retire time */
 115     void markupInstDests(MinorDynInstPtr inst, Cycles retire_time,
 116         ThreadContext *thread_context, bool mark_unpredictable);
 117
 118     /** Clear down the dependencies for this instruction.  clear_unpredictable
 119      *  must match mark_unpredictable for the same inst. */
 120     void clearInstDests(MinorDynInstPtr inst, bool clear_unpredictable);
 121
 122     /** Returns the exec sequence number of the most recent inst on
 123      *  which the given inst depends.  Useful for determining which
 124      *  inst must actually be committed before a dependent inst
 125      *  can call initiateAcc */
 126     InstSeqNum execSeqNumToWaitFor(MinorDynInstPtr inst,
 127         ThreadContext *thread_context);
 128
 129     /** Can this instruction be issued.  Are any of its source registers
 130      *  due to be written by other marked-up instructions in flight */
 131     bool canInstIssue(MinorDynInstPtr inst,
 132         const std::vector<Cycles> *src_reg_relative_latencies,
 133         const std::vector<bool> *cant_forward_from_fu_indices,
 134         Cycles now, ThreadContext *thread_context);
 135
 136     /** MinorTraceIF interface */
 137     void minorTrace() const;
 138 };
 139
 140 }
 141
 142 #endif /* __CPU_MINOR_SCOREBOARD_HH__ */