src/cpu/o3/btb.cc

   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 #include "base/intmath.hh"
  32 #include "base/trace.hh"
  33 #include "cpu/o3/btb.hh"
  34
  35 DefaultBTB::DefaultBTB(unsigned _numEntries,
  36                        unsigned _tagBits,
  37                        unsigned _instShiftAmt)
  38     : numEntries(_numEntries),
  39       tagBits(_tagBits),
  40       instShiftAmt(_instShiftAmt)
  41 {
  42     DPRINTF(Fetch, "BTB: Creating BTB object.\n");
  43
  44     if (!isPowerOf2(numEntries)) {
  45         fatal("BTB entries is not a power of 2!");
  46     }
  47
  48     btb.resize(numEntries);
  49
  50     for (int i = 0; i < numEntries; ++i) {
  51         btb[i].valid = false;
  52     }
  53
  54     idxMask = numEntries - 1;
  55
  56     tagMask = (1 << tagBits) - 1;
  57
  58     tagShiftAmt = instShiftAmt + floorLog2(numEntries);
  59 }
  60
  61 void
  62 DefaultBTB::reset()
  63 {
  64     for (int i = 0; i < numEntries; ++i) {
  65         btb[i].valid = false;
  66     }
  67 }
  68
  69 inline
  70 unsigned
  71 DefaultBTB::getIndex(const Addr &inst_PC)
  72 {
  73     // Need to shift PC over by the word offset.
  74     return (inst_PC >> instShiftAmt) & idxMask;
  75 }
  76
  77 inline
  78 Addr
  79 DefaultBTB::getTag(const Addr &inst_PC)
  80 {
  81     return (inst_PC >> tagShiftAmt) & tagMask;
  82 }
  83
  84 bool
  85 DefaultBTB::valid(const Addr &inst_PC, unsigned tid)
  86 {
  87     unsigned btb_idx = getIndex(inst_PC);
  88
  89     Addr inst_tag = getTag(inst_PC);
  90
  91     assert(btb_idx < numEntries);
  92
  93     if (btb[btb_idx].valid
  94         && inst_tag == btb[btb_idx].tag
  95         && btb[btb_idx].tid == tid) {
  96         return true;
  97     } else {
  98         return false;
  99     }
 100 }
 101
 102 // @todo Create some sort of return struct that has both whether or not the
 103 // address is valid, and also the address.  For now will just use addr = 0 to
 104 // represent invalid entry.
 105 Addr
 106 DefaultBTB::lookup(const Addr &inst_PC, unsigned tid)
 107 {
 108     unsigned btb_idx = getIndex(inst_PC);
 109
 110     Addr inst_tag = getTag(inst_PC);
 111
 112     assert(btb_idx < numEntries);
 113
 114     if (btb[btb_idx].valid
 115         && inst_tag == btb[btb_idx].tag
 116         && btb[btb_idx].tid == tid) {
 117         return btb[btb_idx].target;
 118     } else {
 119         return 0;
 120     }
 121 }
 122
 123 void
 124 DefaultBTB::update(const Addr &inst_PC, const Addr &target, unsigned tid)
 125 {
 126     unsigned btb_idx = getIndex(inst_PC);
 127
 128     assert(btb_idx < numEntries);
 129
 130     btb[btb_idx].tid = tid;
 131     btb[btb_idx].valid = true;
 132     btb[btb_idx].target = target;
 133     btb[btb_idx].tag = getTag(inst_PC);
 134 }