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/*
* Copyright (c) 2004-2006 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Kevin Lim
*/
#include "cpu/pred/2bit_local.hh"
#include "base/intmath.hh"
#include "base/logging.hh"
#include "base/trace.hh"
#include "debug/Fetch.hh"
LocalBP::LocalBP(const LocalBPParams *params)
: BPredUnit(params),
localPredictorSize(params->localPredictorSize),
localCtrBits(params->localCtrBits)
{
if (!isPowerOf2(localPredictorSize)) {
fatal("Invalid local predictor size!\n");
}
localPredictorSets = localPredictorSize / localCtrBits;
if (!isPowerOf2(localPredictorSets)) {
fatal("Invalid number of local predictor sets! Check localCtrBits.\n");
}
// Setup the index mask.
indexMask = localPredictorSets - 1;
DPRINTF(Fetch, "index mask: %#x\n", indexMask);
// Setup the array of counters for the local predictor.
localCtrs.resize(localPredictorSets);
for (unsigned i = 0; i < localPredictorSets; ++i)
localCtrs[i].setBits(localCtrBits);
DPRINTF(Fetch, "local predictor size: %i\n",
localPredictorSize);
DPRINTF(Fetch, "local counter bits: %i\n", localCtrBits);
DPRINTF(Fetch, "instruction shift amount: %i\n",
instShiftAmt);
}
void
LocalBP::reset()
{
for (unsigned i = 0; i < localPredictorSets; ++i) {
localCtrs[i].reset();
}
}
void
LocalBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history)
{
// Place holder for a function that is called to update predictor history when
// a BTB entry is invalid or not found.
}
bool
LocalBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history)
{
bool taken;
uint8_t counter_val;
unsigned local_predictor_idx = getLocalIndex(branch_addr);
DPRINTF(Fetch, "Looking up index %#x\n",
local_predictor_idx);
counter_val = localCtrs[local_predictor_idx].read();
DPRINTF(Fetch, "prediction is %i.\n",
(int)counter_val);
taken = getPrediction(counter_val);
#if 0
// Speculative update.
if (taken) {
DPRINTF(Fetch, "Branch updated as taken.\n");
localCtrs[local_predictor_idx].increment();
} else {
DPRINTF(Fetch, "Branch updated as not taken.\n");
localCtrs[local_predictor_idx].decrement();
}
#endif
return taken;
}
void
LocalBP::update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
bool squashed)
{
assert(bp_history == NULL);
unsigned local_predictor_idx;
// No state to restore, and we do not update on the wrong
// path.
if (squashed) {
return;
}
// Update the local predictor.
local_predictor_idx = getLocalIndex(branch_addr);
DPRINTF(Fetch, "Looking up index %#x\n", local_predictor_idx);
if (taken) {
DPRINTF(Fetch, "Branch updated as taken.\n");
localCtrs[local_predictor_idx].increment();
} else {
DPRINTF(Fetch, "Branch updated as not taken.\n");
localCtrs[local_predictor_idx].decrement();
}
}
inline
bool
LocalBP::getPrediction(uint8_t &count)
{
// Get the MSB of the count
return (count >> (localCtrBits - 1));
}
inline
unsigned
LocalBP::getLocalIndex(Addr &branch_addr)
{
return (branch_addr >> instShiftAmt) & indexMask;
}
void
LocalBP::uncondBranch(ThreadID tid, Addr pc, void *&bp_history)
{
}
LocalBP*
LocalBPParams::create()
{
return new LocalBP(this);
}
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