749 lines
21 KiB
C++
749 lines
21 KiB
C++
/*
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* Copyright (c) 2004-2006 The Regents of The University of Michigan
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "cpu/o3/decode.hh"
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using namespace std;
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template<class Impl>
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DefaultDecode<Impl>::DefaultDecode(Params *params)
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: renameToDecodeDelay(params->renameToDecodeDelay),
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iewToDecodeDelay(params->iewToDecodeDelay),
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commitToDecodeDelay(params->commitToDecodeDelay),
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fetchToDecodeDelay(params->fetchToDecodeDelay),
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decodeWidth(params->decodeWidth),
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numThreads(params->numberOfThreads)
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{
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_status = Inactive;
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// Setup status, make sure stall signals are clear.
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for (int i = 0; i < numThreads; ++i) {
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decodeStatus[i] = Idle;
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stalls[i].rename = false;
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stalls[i].iew = false;
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stalls[i].commit = false;
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}
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// @todo: Make into a parameter
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skidBufferMax = (fetchToDecodeDelay * params->fetchWidth) + decodeWidth;
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}
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template <class Impl>
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std::string
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DefaultDecode<Impl>::name() const
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{
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return cpu->name() + ".decode";
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}
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template <class Impl>
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void
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DefaultDecode<Impl>::regStats()
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{
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decodeIdleCycles
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.name(name() + ".DECODE:IdleCycles")
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.desc("Number of cycles decode is idle")
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.prereq(decodeIdleCycles);
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decodeBlockedCycles
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.name(name() + ".DECODE:BlockedCycles")
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.desc("Number of cycles decode is blocked")
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.prereq(decodeBlockedCycles);
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decodeRunCycles
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.name(name() + ".DECODE:RunCycles")
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.desc("Number of cycles decode is running")
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.prereq(decodeRunCycles);
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decodeUnblockCycles
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.name(name() + ".DECODE:UnblockCycles")
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.desc("Number of cycles decode is unblocking")
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.prereq(decodeUnblockCycles);
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decodeSquashCycles
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.name(name() + ".DECODE:SquashCycles")
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.desc("Number of cycles decode is squashing")
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.prereq(decodeSquashCycles);
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decodeBranchResolved
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.name(name() + ".DECODE:BranchResolved")
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.desc("Number of times decode resolved a branch")
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.prereq(decodeBranchResolved);
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decodeBranchMispred
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.name(name() + ".DECODE:BranchMispred")
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.desc("Number of times decode detected a branch misprediction")
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.prereq(decodeBranchMispred);
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decodeControlMispred
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.name(name() + ".DECODE:ControlMispred")
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.desc("Number of times decode detected an instruction incorrectly"
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" predicted as a control")
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.prereq(decodeControlMispred);
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decodeDecodedInsts
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.name(name() + ".DECODE:DecodedInsts")
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.desc("Number of instructions handled by decode")
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.prereq(decodeDecodedInsts);
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decodeSquashedInsts
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.name(name() + ".DECODE:SquashedInsts")
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.desc("Number of squashed instructions handled by decode")
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.prereq(decodeSquashedInsts);
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::setCPU(FullCPU *cpu_ptr)
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{
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DPRINTF(Decode, "Setting CPU pointer.\n");
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cpu = cpu_ptr;
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr)
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{
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DPRINTF(Decode, "Setting time buffer pointer.\n");
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timeBuffer = tb_ptr;
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// Setup wire to write information back to fetch.
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toFetch = timeBuffer->getWire(0);
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// Create wires to get information from proper places in time buffer.
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fromRename = timeBuffer->getWire(-renameToDecodeDelay);
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fromIEW = timeBuffer->getWire(-iewToDecodeDelay);
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fromCommit = timeBuffer->getWire(-commitToDecodeDelay);
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr)
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{
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DPRINTF(Decode, "Setting decode queue pointer.\n");
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decodeQueue = dq_ptr;
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// Setup wire to write information to proper place in decode queue.
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toRename = decodeQueue->getWire(0);
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr)
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{
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DPRINTF(Decode, "Setting fetch queue pointer.\n");
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fetchQueue = fq_ptr;
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// Setup wire to read information from fetch queue.
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fromFetch = fetchQueue->getWire(-fetchToDecodeDelay);
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::setActiveThreads(list<unsigned> *at_ptr)
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{
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DPRINTF(Decode, "Setting active threads list pointer.\n");
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activeThreads = at_ptr;
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}
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template <class Impl>
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void
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DefaultDecode<Impl>::switchOut()
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{
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// Decode can immediately switch out.
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cpu->signalSwitched();
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}
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template <class Impl>
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void
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DefaultDecode<Impl>::takeOverFrom()
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{
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_status = Inactive;
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// Be sure to reset state and clear out any old instructions.
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for (int i = 0; i < numThreads; ++i) {
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decodeStatus[i] = Idle;
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stalls[i].rename = false;
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stalls[i].iew = false;
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stalls[i].commit = false;
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while (!insts[i].empty())
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insts[i].pop();
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while (!skidBuffer[i].empty())
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skidBuffer[i].pop();
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branchCount[i] = 0;
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}
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wroteToTimeBuffer = false;
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}
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template<class Impl>
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bool
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DefaultDecode<Impl>::checkStall(unsigned tid) const
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{
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bool ret_val = false;
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if (stalls[tid].rename) {
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DPRINTF(Decode,"[tid:%i]: Stall fom Rename stage detected.\n", tid);
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ret_val = true;
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} else if (stalls[tid].iew) {
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DPRINTF(Decode,"[tid:%i]: Stall fom IEW stage detected.\n", tid);
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ret_val = true;
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} else if (stalls[tid].commit) {
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DPRINTF(Decode,"[tid:%i]: Stall fom Commit stage detected.\n", tid);
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ret_val = true;
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}
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return ret_val;
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}
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template<class Impl>
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inline bool
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DefaultDecode<Impl>::fetchInstsValid()
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{
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return fromFetch->size > 0;
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}
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template<class Impl>
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bool
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DefaultDecode<Impl>::block(unsigned tid)
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{
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DPRINTF(Decode, "[tid:%u]: Blocking.\n", tid);
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// Add the current inputs to the skid buffer so they can be
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// reprocessed when this stage unblocks.
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skidInsert(tid);
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// If the decode status is blocked or unblocking then decode has not yet
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// signalled fetch to unblock. In that case, there is no need to tell
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// fetch to block.
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if (decodeStatus[tid] != Blocked) {
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// Set the status to Blocked.
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decodeStatus[tid] = Blocked;
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if (decodeStatus[tid] != Unblocking) {
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toFetch->decodeBlock[tid] = true;
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wroteToTimeBuffer = true;
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}
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return true;
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}
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return false;
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}
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template<class Impl>
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bool
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DefaultDecode<Impl>::unblock(unsigned tid)
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{
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// Decode is done unblocking only if the skid buffer is empty.
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if (skidBuffer[tid].empty()) {
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DPRINTF(Decode, "[tid:%u]: Done unblocking.\n", tid);
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toFetch->decodeUnblock[tid] = true;
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wroteToTimeBuffer = true;
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decodeStatus[tid] = Running;
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return true;
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}
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DPRINTF(Decode, "[tid:%u]: Currently unblocking.\n", tid);
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return false;
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::squash(DynInstPtr &inst, unsigned tid)
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{
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DPRINTF(Decode, "[tid:%i]: Squashing due to incorrect branch prediction "
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"detected at decode.\n", tid);
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// Send back mispredict information.
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toFetch->decodeInfo[tid].branchMispredict = true;
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toFetch->decodeInfo[tid].doneSeqNum = inst->seqNum;
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toFetch->decodeInfo[tid].predIncorrect = true;
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toFetch->decodeInfo[tid].squash = true;
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toFetch->decodeInfo[tid].nextPC = inst->branchTarget();
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toFetch->decodeInfo[tid].branchTaken =
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inst->readNextPC() != (inst->readPC() + sizeof(TheISA::MachInst));
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// Might have to tell fetch to unblock.
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if (decodeStatus[tid] == Blocked ||
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decodeStatus[tid] == Unblocking) {
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toFetch->decodeUnblock[tid] = 1;
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}
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// Set status to squashing.
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decodeStatus[tid] = Squashing;
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for (int i=0; i<fromFetch->size; i++) {
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if (fromFetch->insts[i]->threadNumber == tid &&
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fromFetch->insts[i]->seqNum > inst->seqNum) {
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fromFetch->insts[i]->setSquashed();
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}
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}
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// Clear the instruction list and skid buffer in case they have any
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// insts in them.
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while (!insts[tid].empty()) {
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insts[tid].pop();
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}
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while (!skidBuffer[tid].empty()) {
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skidBuffer[tid].pop();
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}
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// Squash instructions up until this one
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cpu->removeInstsUntil(inst->seqNum, tid);
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}
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template<class Impl>
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unsigned
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DefaultDecode<Impl>::squash(unsigned tid)
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{
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DPRINTF(Decode, "[tid:%i]: Squashing.\n",tid);
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if (decodeStatus[tid] == Blocked ||
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decodeStatus[tid] == Unblocking) {
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#if !FULL_SYSTEM
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// In syscall emulation, we can have both a block and a squash due
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// to a syscall in the same cycle. This would cause both signals to
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// be high. This shouldn't happen in full system.
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// @todo: Determine if this still happens.
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if (toFetch->decodeBlock[tid]) {
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toFetch->decodeBlock[tid] = 0;
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} else {
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toFetch->decodeUnblock[tid] = 1;
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}
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#else
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toFetch->decodeUnblock[tid] = 1;
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#endif
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}
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// Set status to squashing.
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decodeStatus[tid] = Squashing;
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// Go through incoming instructions from fetch and squash them.
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unsigned squash_count = 0;
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for (int i=0; i<fromFetch->size; i++) {
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if (fromFetch->insts[i]->threadNumber == tid) {
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fromFetch->insts[i]->setSquashed();
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squash_count++;
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}
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}
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// Clear the instruction list and skid buffer in case they have any
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// insts in them.
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while (!insts[tid].empty()) {
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insts[tid].pop();
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}
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while (!skidBuffer[tid].empty()) {
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skidBuffer[tid].pop();
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}
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return squash_count;
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::skidInsert(unsigned tid)
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{
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DynInstPtr inst = NULL;
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while (!insts[tid].empty()) {
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inst = insts[tid].front();
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insts[tid].pop();
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assert(tid == inst->threadNumber);
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DPRINTF(Decode,"Inserting [sn:%lli] PC:%#x into decode skidBuffer %i\n",
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inst->seqNum, inst->readPC(), inst->threadNumber);
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skidBuffer[tid].push(inst);
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}
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// @todo: Eventually need to enforce this by not letting a thread
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// fetch past its skidbuffer
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assert(skidBuffer[tid].size() <= skidBufferMax);
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}
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template<class Impl>
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bool
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DefaultDecode<Impl>::skidsEmpty()
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{
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list<unsigned>::iterator threads = (*activeThreads).begin();
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while (threads != (*activeThreads).end()) {
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if (!skidBuffer[*threads++].empty())
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return false;
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}
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return true;
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::updateStatus()
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{
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bool any_unblocking = false;
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list<unsigned>::iterator threads = (*activeThreads).begin();
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threads = (*activeThreads).begin();
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while (threads != (*activeThreads).end()) {
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unsigned tid = *threads++;
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if (decodeStatus[tid] == Unblocking) {
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any_unblocking = true;
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break;
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}
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}
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// Decode will have activity if it's unblocking.
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if (any_unblocking) {
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if (_status == Inactive) {
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_status = Active;
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DPRINTF(Activity, "Activating stage.\n");
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cpu->activateStage(FullCPU::DecodeIdx);
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}
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} else {
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// If it's not unblocking, then decode will not have any internal
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// activity. Switch it to inactive.
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if (_status == Active) {
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_status = Inactive;
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DPRINTF(Activity, "Deactivating stage.\n");
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cpu->deactivateStage(FullCPU::DecodeIdx);
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}
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}
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}
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template <class Impl>
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void
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DefaultDecode<Impl>::sortInsts()
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{
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int insts_from_fetch = fromFetch->size;
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#ifdef DEBUG
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for (int i=0; i < numThreads; i++)
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assert(insts[i].empty());
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#endif
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for (int i = 0; i < insts_from_fetch; ++i) {
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insts[fromFetch->insts[i]->threadNumber].push(fromFetch->insts[i]);
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}
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}
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template<class Impl>
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void
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DefaultDecode<Impl>::readStallSignals(unsigned tid)
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{
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if (fromRename->renameBlock[tid]) {
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stalls[tid].rename = true;
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}
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if (fromRename->renameUnblock[tid]) {
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assert(stalls[tid].rename);
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stalls[tid].rename = false;
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}
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if (fromIEW->iewBlock[tid]) {
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stalls[tid].iew = true;
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}
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if (fromIEW->iewUnblock[tid]) {
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assert(stalls[tid].iew);
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stalls[tid].iew = false;
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}
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if (fromCommit->commitBlock[tid]) {
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stalls[tid].commit = true;
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}
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if (fromCommit->commitUnblock[tid]) {
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assert(stalls[tid].commit);
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stalls[tid].commit = false;
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}
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}
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template <class Impl>
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bool
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DefaultDecode<Impl>::checkSignalsAndUpdate(unsigned tid)
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{
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// Check if there's a squash signal, squash if there is.
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// Check stall signals, block if necessary.
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// If status was blocked
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// Check if stall conditions have passed
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// if so then go to unblocking
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// If status was Squashing
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// check if squashing is not high. Switch to running this cycle.
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// Update the per thread stall statuses.
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readStallSignals(tid);
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// Check squash signals from commit.
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if (fromCommit->commitInfo[tid].squash) {
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DPRINTF(Decode, "[tid:%u]: Squashing instructions due to squash "
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"from commit.\n", tid);
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squash(tid);
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return true;
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}
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// Check ROB squash signals from commit.
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if (fromCommit->commitInfo[tid].robSquashing) {
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DPRINTF(Decode, "[tid:%]: ROB is still squashing.\n",tid);
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// Continue to squash.
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decodeStatus[tid] = Squashing;
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return true;
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}
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if (checkStall(tid)) {
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return block(tid);
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}
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if (decodeStatus[tid] == Blocked) {
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DPRINTF(Decode, "[tid:%u]: Done blocking, switching to unblocking.\n",
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tid);
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decodeStatus[tid] = Unblocking;
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unblock(tid);
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return true;
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}
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if (decodeStatus[tid] == Squashing) {
|
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// Switch status to running if decode isn't being told to block or
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// squash this cycle.
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DPRINTF(Decode, "[tid:%u]: Done squashing, switching to running.\n",
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tid);
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decodeStatus[tid] = Running;
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return false;
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}
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|
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// If we've reached this point, we have not gotten any signals that
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// cause decode to change its status. Decode remains the same as before.
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return false;
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}
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|
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template<class Impl>
|
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void
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DefaultDecode<Impl>::tick()
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{
|
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wroteToTimeBuffer = false;
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|
|
bool status_change = false;
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|
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toRenameIndex = 0;
|
|
|
|
list<unsigned>::iterator threads = (*activeThreads).begin();
|
|
|
|
sortInsts();
|
|
|
|
//Check stall and squash signals.
|
|
while (threads != (*activeThreads).end()) {
|
|
unsigned tid = *threads++;
|
|
|
|
DPRINTF(Decode,"Processing [tid:%i]\n",tid);
|
|
status_change = checkSignalsAndUpdate(tid) || status_change;
|
|
|
|
decode(status_change, tid);
|
|
}
|
|
|
|
if (status_change) {
|
|
updateStatus();
|
|
}
|
|
|
|
if (wroteToTimeBuffer) {
|
|
DPRINTF(Activity, "Activity this cycle.\n");
|
|
|
|
cpu->activityThisCycle();
|
|
}
|
|
}
|
|
|
|
template<class Impl>
|
|
void
|
|
DefaultDecode<Impl>::decode(bool &status_change, unsigned tid)
|
|
{
|
|
// If status is Running or idle,
|
|
// call decodeInsts()
|
|
// If status is Unblocking,
|
|
// buffer any instructions coming from fetch
|
|
// continue trying to empty skid buffer
|
|
// check if stall conditions have passed
|
|
|
|
if (decodeStatus[tid] == Blocked) {
|
|
++decodeBlockedCycles;
|
|
} else if (decodeStatus[tid] == Squashing) {
|
|
++decodeSquashCycles;
|
|
}
|
|
|
|
// Decode should try to decode as many instructions as its bandwidth
|
|
// will allow, as long as it is not currently blocked.
|
|
if (decodeStatus[tid] == Running ||
|
|
decodeStatus[tid] == Idle) {
|
|
DPRINTF(Decode, "[tid:%u] Not blocked, so attempting to run "
|
|
"stage.\n",tid);
|
|
|
|
decodeInsts(tid);
|
|
} else if (decodeStatus[tid] == Unblocking) {
|
|
// Make sure that the skid buffer has something in it if the
|
|
// status is unblocking.
|
|
assert(!skidsEmpty());
|
|
|
|
// If the status was unblocking, then instructions from the skid
|
|
// buffer were used. Remove those instructions and handle
|
|
// the rest of unblocking.
|
|
decodeInsts(tid);
|
|
|
|
if (fetchInstsValid()) {
|
|
// Add the current inputs to the skid buffer so they can be
|
|
// reprocessed when this stage unblocks.
|
|
skidInsert(tid);
|
|
}
|
|
|
|
status_change = unblock(tid) || status_change;
|
|
}
|
|
}
|
|
|
|
template <class Impl>
|
|
void
|
|
DefaultDecode<Impl>::decodeInsts(unsigned tid)
|
|
{
|
|
// Instructions can come either from the skid buffer or the list of
|
|
// instructions coming from fetch, depending on decode's status.
|
|
int insts_available = decodeStatus[tid] == Unblocking ?
|
|
skidBuffer[tid].size() : insts[tid].size();
|
|
|
|
if (insts_available == 0) {
|
|
DPRINTF(Decode, "[tid:%u] Nothing to do, breaking out"
|
|
" early.\n",tid);
|
|
// Should I change the status to idle?
|
|
++decodeIdleCycles;
|
|
return;
|
|
} else if (decodeStatus[tid] == Unblocking) {
|
|
DPRINTF(Decode, "[tid:%u] Unblocking, removing insts from skid "
|
|
"buffer.\n",tid);
|
|
++decodeUnblockCycles;
|
|
} else if (decodeStatus[tid] == Running) {
|
|
++decodeRunCycles;
|
|
}
|
|
|
|
DynInstPtr inst;
|
|
|
|
std::queue<DynInstPtr>
|
|
&insts_to_decode = decodeStatus[tid] == Unblocking ?
|
|
skidBuffer[tid] : insts[tid];
|
|
|
|
DPRINTF(Decode, "[tid:%u]: Sending instruction to rename.\n",tid);
|
|
|
|
while (insts_available > 0 && toRenameIndex < decodeWidth) {
|
|
assert(!insts_to_decode.empty());
|
|
|
|
inst = insts_to_decode.front();
|
|
|
|
insts_to_decode.pop();
|
|
|
|
DPRINTF(Decode, "[tid:%u]: Processing instruction [sn:%lli] with "
|
|
"PC %#x\n",
|
|
tid, inst->seqNum, inst->readPC());
|
|
|
|
if (inst->isSquashed()) {
|
|
DPRINTF(Decode, "[tid:%u]: Instruction %i with PC %#x is "
|
|
"squashed, skipping.\n",
|
|
tid, inst->seqNum, inst->readPC());
|
|
|
|
++decodeSquashedInsts;
|
|
|
|
--insts_available;
|
|
|
|
continue;
|
|
}
|
|
|
|
// Also check if instructions have no source registers. Mark
|
|
// them as ready to issue at any time. Not sure if this check
|
|
// should exist here or at a later stage; however it doesn't matter
|
|
// too much for function correctness.
|
|
if (inst->numSrcRegs() == 0) {
|
|
inst->setCanIssue();
|
|
}
|
|
|
|
// This current instruction is valid, so add it into the decode
|
|
// queue. The next instruction may not be valid, so check to
|
|
// see if branches were predicted correctly.
|
|
toRename->insts[toRenameIndex] = inst;
|
|
|
|
++(toRename->size);
|
|
++toRenameIndex;
|
|
++decodeDecodedInsts;
|
|
--insts_available;
|
|
|
|
// Ensure that if it was predicted as a branch, it really is a
|
|
// branch.
|
|
if (inst->predTaken() && !inst->isControl()) {
|
|
panic("Instruction predicted as a branch!");
|
|
|
|
++decodeControlMispred;
|
|
|
|
// Might want to set some sort of boolean and just do
|
|
// a check at the end
|
|
squash(inst, inst->threadNumber);
|
|
|
|
break;
|
|
}
|
|
|
|
// Go ahead and compute any PC-relative branches.
|
|
if (inst->isDirectCtrl() && inst->isUncondCtrl()) {
|
|
++decodeBranchResolved;
|
|
|
|
if (inst->branchTarget() != inst->readPredTarg()) {
|
|
++decodeBranchMispred;
|
|
|
|
// Might want to set some sort of boolean and just do
|
|
// a check at the end
|
|
squash(inst, inst->threadNumber);
|
|
inst->setPredTarg(inst->branchTarget());
|
|
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If we didn't process all instructions, then we will need to block
|
|
// and put all those instructions into the skid buffer.
|
|
if (!insts_to_decode.empty()) {
|
|
block(tid);
|
|
}
|
|
|
|
// Record that decode has written to the time buffer for activity
|
|
// tracking.
|
|
if (toRenameIndex) {
|
|
wroteToTimeBuffer = true;
|
|
}
|
|
}
|