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  * Authors: Kevin Lim
  29  */
  30
  31 #ifndef __CPU_O3_BTB_HH__
  32 #define __CPU_O3_BTB_HH__
  33
  34 #include "arch/types.hh"
  35 #include "base/misc.hh"
  36 #include "base/types.hh"
  37 #include "config/the_isa.hh"
  38
  39 class DefaultBTB
  40 {
  41   private:
  42     struct BTBEntry
  43     {
  44         BTBEntry()
  45             : tag(0), target(0), valid(false)
  46         {}
  47
  48         /** The entry's tag. */
  49         Addr tag;
  50
  51         /** The entry's target. */
  52         TheISA::PCState target;
  53
  54         /** The entry's thread id. */
  55         ThreadID tid;
  56
  57         /** Whether or not the entry is valid. */
  58         bool valid;
  59     };
  60
  61   public:
  62     /** Creates a BTB with the given number of entries, number of bits per
  63      *  tag, and instruction offset amount.
  64      *  @param numEntries Number of entries for the BTB.
  65      *  @param tagBits Number of bits for each tag in the BTB.
  66      *  @param instShiftAmt Offset amount for instructions to ignore alignment.
  67      */
  68     DefaultBTB(unsigned numEntries, unsigned tagBits,
  69                unsigned instShiftAmt);
  70
  71     void reset();
  72
  73     /** Looks up an address in the BTB. Must call valid() first on the address.
  74      *  @param inst_PC The address of the branch to look up.
  75      *  @param tid The thread id.
  76      *  @return Returns the target of the branch.
  77      */
  78     TheISA::PCState lookup(Addr instPC, ThreadID tid);
  79
  80     /** Checks if a branch is in the BTB.
  81      *  @param inst_PC The address of the branch to look up.
  82      *  @param tid The thread id.
  83      *  @return Whether or not the branch exists in the BTB.
  84      */
  85     bool valid(Addr instPC, ThreadID tid);
  86
  87     /** Updates the BTB with the target of a branch.
  88      *  @param inst_PC The address of the branch being updated.
  89      *  @param target_PC The target address of the branch.
  90      *  @param tid The thread id.
  91      */
  92     void update(Addr instPC, const TheISA::PCState &targetPC,
  93                 ThreadID tid);
  94
  95   private:
  96     /** Returns the index into the BTB, based on the branch's PC.
  97      *  @param inst_PC The branch to look up.
  98      *  @return Returns the index into the BTB.
  99      */
 100     inline unsigned getIndex(Addr instPC);
 101
 102     /** Returns the tag bits of a given address.
 103      *  @param inst_PC The branch's address.
 104      *  @return Returns the tag bits.
 105      */
 106     inline Addr getTag(Addr instPC);
 107
 108     /** The actual BTB. */
 109     std::vector<BTBEntry> btb;
 110
 111     /** The number of entries in the BTB. */
 112     unsigned numEntries;
 113
 114     /** The index mask. */
 115     unsigned idxMask;
 116
 117     /** The number of tag bits per entry. */
 118     unsigned tagBits;
 119
 120     /** The tag mask. */
 121     unsigned tagMask;
 122
 123     /** Number of bits to shift PC when calculating index. */
 124     unsigned instShiftAmt;
 125
 126     /** Number of bits to shift PC when calculating tag. */
 127     unsigned tagShiftAmt;
 128 };
 129
 130 #endif // __CPU_O3_BTB_HH__