src/cpu/pred/btb.hh

   1 /*
   2  * Copyright (c) 2004-2005 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #ifndef __CPU_PRED_BTB_HH__
  30 #define __CPU_PRED_BTB_HH__
  31
  32 #include "arch/types.hh"
  33 #include "base/logging.hh"
  34 #include "base/types.hh"
  35 #include "config/the_isa.hh"
  36
  37 class DefaultBTB
  38 {
  39   private:
  40     struct BTBEntry
  41     {
  42         BTBEntry()
  43             : tag(0), target(0), valid(false)
  44         {}
  45
  46         /** The entry's tag. */
  47         Addr tag;
  48
  49         /** The entry's target. */
  50         TheISA::PCState target;
  51
  52         /** The entry's thread id. */
  53         ThreadID tid;
  54
  55         /** Whether or not the entry is valid. */
  56         bool valid;
  57     };
  58
  59   public:
  60     /** Creates a BTB with the given number of entries, number of bits per
  61      *  tag, and instruction offset amount.
  62      *  @param numEntries Number of entries for the BTB.
  63      *  @param tagBits Number of bits for each tag in the BTB.
  64      *  @param instShiftAmt Offset amount for instructions to ignore alignment.
  65      */
  66     DefaultBTB(unsigned numEntries, unsigned tagBits,
  67                unsigned instShiftAmt, unsigned numThreads);
  68
  69     void reset();
  70
  71     /** Looks up an address in the BTB. Must call valid() first on the address.
  72      *  @param inst_PC The address of the branch to look up.
  73      *  @param tid The thread id.
  74      *  @return Returns the target of the branch.
  75      */
  76     TheISA::PCState lookup(Addr instPC, ThreadID tid);
  77
  78     /** Checks if a branch is in the BTB.
  79      *  @param inst_PC The address of the branch to look up.
  80      *  @param tid The thread id.
  81      *  @return Whether or not the branch exists in the BTB.
  82      */
  83     bool valid(Addr instPC, ThreadID tid);
  84
  85     /** Updates the BTB with the target of a branch.
  86      *  @param inst_PC The address of the branch being updated.
  87      *  @param target_PC The target address of the branch.
  88      *  @param tid The thread id.
  89      */
  90     void update(Addr instPC, const TheISA::PCState &targetPC,
  91                 ThreadID tid);
  92
  93   private:
  94     /** Returns the index into the BTB, based on the branch's PC.
  95      *  @param inst_PC The branch to look up.
  96      *  @return Returns the index into the BTB.
  97      */
  98     inline unsigned getIndex(Addr instPC, ThreadID tid);
  99
 100     /** Returns the tag bits of a given address.
 101      *  @param inst_PC The branch's address.
 102      *  @return Returns the tag bits.
 103      */
 104     inline Addr getTag(Addr instPC);
 105
 106     /** The actual BTB. */
 107     std::vector<BTBEntry> btb;
 108
 109     /** The number of entries in the BTB. */
 110     unsigned numEntries;
 111
 112     /** The index mask. */
 113     unsigned idxMask;
 114
 115     /** The number of tag bits per entry. */
 116     unsigned tagBits;
 117
 118     /** The tag mask. */
 119     unsigned tagMask;
 120
 121     /** Number of bits to shift PC when calculating index. */
 122     unsigned instShiftAmt;
 123
 124     /** Number of bits to shift PC when calculating tag. */
 125     unsigned tagShiftAmt;
 126
 127     /** Log2 NumThreads used for hashing threadid */
 128     unsigned log2NumThreads;
 129 };
 130
 131 #endif // __CPU_PRED_BTB_HH__