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/*
* Copyright (c) 2014 ARM Limited
* 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: Mitch Hayenga
*/
#include "cpu/pred/simple_indirect.hh"
#include "base/intmath.hh"
#include "debug/Indirect.hh"
SimpleIndirectPredictor::SimpleIndirectPredictor(
const SimpleIndirectPredictorParams * params)
: IndirectPredictor(params),
hashGHR(params->indirectHashGHR),
hashTargets(params->indirectHashTargets),
numSets(params->indirectSets),
numWays(params->indirectWays),
tagBits(params->indirectTagSize),
pathLength(params->indirectPathLength),
instShift(params->instShiftAmt),
ghrNumBits(params->indirectGHRBits),
ghrMask((1 << params->indirectGHRBits)-1)
{
if (!isPowerOf2(numSets)) {
panic("Indirect predictor requires power of 2 number of sets");
}
threadInfo.resize(params->numThreads);
targetCache.resize(numSets);
for (unsigned i = 0; i < numSets; i++) {
targetCache[i].resize(numWays);
}
fatal_if(ghrNumBits > (sizeof(ThreadInfo::ghr)*8), "ghr_size is too big");
}
void
SimpleIndirectPredictor::genIndirectInfo(ThreadID tid,
void* & indirect_history)
{
// record the GHR as it was before this prediction
// It will be used to recover the history in case this prediction is
// wrong or belongs to bad path
indirect_history = new unsigned(threadInfo[tid].ghr);
}
void
SimpleIndirectPredictor::updateDirectionInfo(
ThreadID tid, bool actually_taken)
{
threadInfo[tid].ghr <<= 1;
threadInfo[tid].ghr |= actually_taken;
threadInfo[tid].ghr &= ghrMask;
}
void
SimpleIndirectPredictor::changeDirectionPrediction(ThreadID tid,
void * indirect_history, bool actually_taken)
{
unsigned * previousGhr = static_cast<unsigned *>(indirect_history);
threadInfo[tid].ghr = ((*previousGhr) << 1) + actually_taken;
threadInfo[tid].ghr &= ghrMask;
}
bool
SimpleIndirectPredictor::lookup(Addr br_addr, TheISA::PCState& target,
ThreadID tid)
{
Addr set_index = getSetIndex(br_addr, threadInfo[tid].ghr, tid);
Addr tag = getTag(br_addr);
assert(set_index < numSets);
DPRINTF(Indirect, "Looking up %x (set:%d)\n", br_addr, set_index);
const auto &iset = targetCache[set_index];
for (auto way = iset.begin(); way != iset.end(); ++way) {
if (way->tag == tag) {
DPRINTF(Indirect, "Hit %x (target:%s)\n", br_addr, way->target);
target = way->target;
return true;
}
}
DPRINTF(Indirect, "Miss %x\n", br_addr);
return false;
}
void
SimpleIndirectPredictor::recordIndirect(Addr br_addr, Addr tgt_addr,
InstSeqNum seq_num, ThreadID tid)
{
DPRINTF(Indirect, "Recording %x seq:%d\n", br_addr, seq_num);
HistoryEntry entry(br_addr, tgt_addr, seq_num);
threadInfo[tid].pathHist.push_back(entry);
}
void
SimpleIndirectPredictor::commit(InstSeqNum seq_num, ThreadID tid,
void * indirect_history)
{
DPRINTF(Indirect, "Committing seq:%d\n", seq_num);
ThreadInfo &t_info = threadInfo[tid];
// we do not need to recover the GHR, so delete the information
unsigned * previousGhr = static_cast<unsigned *>(indirect_history);
delete previousGhr;
if (t_info.pathHist.empty()) return;
if (t_info.headHistEntry < t_info.pathHist.size() &&
t_info.pathHist[t_info.headHistEntry].seqNum <= seq_num) {
if (t_info.headHistEntry >= pathLength) {
t_info.pathHist.pop_front();
} else {
++t_info.headHistEntry;
}
}
}
void
SimpleIndirectPredictor::squash(InstSeqNum seq_num, ThreadID tid)
{
DPRINTF(Indirect, "Squashing seq:%d\n", seq_num);
ThreadInfo &t_info = threadInfo[tid];
auto squash_itr = t_info.pathHist.begin();
while (squash_itr != t_info.pathHist.end()) {
if (squash_itr->seqNum > seq_num) {
break;
}
++squash_itr;
}
if (squash_itr != t_info.pathHist.end()) {
DPRINTF(Indirect, "Squashing series starting with sn:%d\n",
squash_itr->seqNum);
}
t_info.pathHist.erase(squash_itr, t_info.pathHist.end());
}
void
SimpleIndirectPredictor::deleteIndirectInfo(ThreadID tid,
void * indirect_history)
{
unsigned * previousGhr = static_cast<unsigned *>(indirect_history);
threadInfo[tid].ghr = *previousGhr;
delete previousGhr;
}
void
SimpleIndirectPredictor::recordTarget(
InstSeqNum seq_num, void * indirect_history, const TheISA::PCState& target,
ThreadID tid)
{
ThreadInfo &t_info = threadInfo[tid];
unsigned * ghr = static_cast<unsigned *>(indirect_history);
// Should have just squashed so this branch should be the oldest
auto hist_entry = *(t_info.pathHist.rbegin());
// Temporarily pop it off the history so we can calculate the set
t_info.pathHist.pop_back();
Addr set_index = getSetIndex(hist_entry.pcAddr, *ghr, tid);
Addr tag = getTag(hist_entry.pcAddr);
hist_entry.targetAddr = target.instAddr();
t_info.pathHist.push_back(hist_entry);
assert(set_index < numSets);
auto &iset = targetCache[set_index];
for (auto way = iset.begin(); way != iset.end(); ++way) {
if (way->tag == tag) {
DPRINTF(Indirect, "Updating Target (seq: %d br:%x set:%d target:"
"%s)\n", seq_num, hist_entry.pcAddr, set_index, target);
way->target = target;
return;
}
}
DPRINTF(Indirect, "Allocating Target (seq: %d br:%x set:%d target:%s)\n",
seq_num, hist_entry.pcAddr, set_index, target);
// Did not find entry, random replacement
auto &way = iset[rand() % numWays];
way.tag = tag;
way.target = target;
}
inline Addr
SimpleIndirectPredictor::getSetIndex(Addr br_addr, unsigned ghr, ThreadID tid)
{
ThreadInfo &t_info = threadInfo[tid];
Addr hash = br_addr >> instShift;
if (hashGHR) {
hash ^= ghr;
}
if (hashTargets) {
unsigned hash_shift = floorLog2(numSets) / pathLength;
for (int i = t_info.pathHist.size()-1, p = 0;
i >= 0 && p < pathLength; i--, p++) {
hash ^= (t_info.pathHist[i].targetAddr >>
(instShift + p*hash_shift));
}
}
return hash & (numSets-1);
}
inline Addr
SimpleIndirectPredictor::getTag(Addr br_addr)
{
return (br_addr >> instShift) & ((0x1<<tagBits)-1);
}
SimpleIndirectPredictor *
SimpleIndirectPredictorParams::create()
{
return new SimpleIndirectPredictor(this);
}
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