src/cpu/o3/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 "base/misc.hh"
  35 #include "sim/host.hh"
  36
  37 class DefaultBTB
  38 {
  39   private:
  40     struct BTBEntry
  41     {
  42         BTBEntry()
  43             : tag(0), target(0), valid(false)
  44         {
  45         }
  46
  47         /** The entry's tag. */
  48         Addr tag;
  49
  50         /** The entry's target. */
  51         Addr target;
  52
  53         /** The entry's thread id. */
  54         unsigned tid;
  55
  56         /** Whether or not the entry is valid. */
  57         bool valid;
  58     };
  59
  60   public:
  61     /** Creates a BTB with the given number of entries, number of bits per
  62      *  tag, and instruction offset amount.
  63      *  @param numEntries Number of entries for the BTB.
  64      *  @param tagBits Number of bits for each tag in the BTB.
  65      *  @param instShiftAmt Offset amount for instructions to ignore alignment.
  66      */
  67     DefaultBTB(unsigned numEntries, unsigned tagBits,
  68                unsigned instShiftAmt);
  69
  70     void reset();
  71
  72     /** Looks up an address in the BTB. Must call valid() first on the address.
  73      *  @param inst_PC The address of the branch to look up.
  74      *  @param tid The thread id.
  75      *  @return Returns the target of the branch.
  76      */
  77     Addr lookup(const Addr &inst_PC, unsigned tid);
  78
  79     /** Checks if a branch is in the BTB.
  80      *  @param inst_PC The address of the branch to look up.
  81      *  @param tid The thread id.
  82      *  @return Whether or not the branch exists in the BTB.
  83      */
  84     bool valid(const Addr &inst_PC, unsigned tid);
  85
  86     /** Updates the BTB with the target of a branch.
  87      *  @param inst_PC The address of the branch being updated.
  88      *  @param target_PC The target address of the branch.
  89      *  @param tid The thread id.
  90      */
  91     void update(const Addr &inst_PC, const Addr &target_PC,
  92                 unsigned tid);
  93
  94   private:
  95     /** Returns the index into the BTB, based on the branch's PC.
  96      *  @param inst_PC The branch to look up.
  97      *  @return Returns the index into the BTB.
  98      */
  99     inline unsigned getIndex(const Addr &inst_PC);
 100
 101     /** Returns the tag bits of a given address.
 102      *  @param inst_PC The branch's address.
 103      *  @return Returns the tag bits.
 104      */
 105     inline Addr getTag(const Addr &inst_PC);
 106
 107     /** The actual BTB. */
 108     std::vector<BTBEntry> btb;
 109
 110     /** The number of entries in the BTB. */
 111     unsigned numEntries;
 112
 113     /** The index mask. */
 114     unsigned idxMask;
 115
 116     /** The number of tag bits per entry. */
 117     unsigned tagBits;
 118
 119     /** The tag mask. */
 120     unsigned tagMask;
 121
 122     /** Number of bits to shift PC when calculating index. */
 123     unsigned instShiftAmt;
 124
 125     /** Number of bits to shift PC when calculating tag. */
 126     unsigned tagShiftAmt;
 127 };
 128
 129 #endif // __CPU_O3_BTB_HH__