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Diffstat (limited to 'src/cpu/o3/decode_impl.hh')
| -rw-r--r-- | src/cpu/o3/decode_impl.hh | 741 |
1 files changed, 741 insertions, 0 deletions
diff --git a/src/cpu/o3/decode_impl.hh b/src/cpu/o3/decode_impl.hh new file mode 100644 index 000000000..2ed7ec6fc --- /dev/null +++ b/src/cpu/o3/decode_impl.hh @@ -0,0 +1,741 @@ +/* + * 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. + */ + +#include "cpu/o3/decode.hh" + +using namespace std; + +template<class Impl> +DefaultDecode<Impl>::DefaultDecode(Params *params) + : renameToDecodeDelay(params->renameToDecodeDelay), + iewToDecodeDelay(params->iewToDecodeDelay), + commitToDecodeDelay(params->commitToDecodeDelay), + fetchToDecodeDelay(params->fetchToDecodeDelay), + decodeWidth(params->decodeWidth), + numThreads(params->numberOfThreads) +{ + _status = Inactive; + + for (int i = 0; i < numThreads; ++i) { + decodeStatus[i] = Idle; + + stalls[i].rename = false; + stalls[i].iew = false; + stalls[i].commit = false; + } + + // @todo: Make into a parameter + skidBufferMax = (fetchToDecodeDelay * params->fetchWidth) + decodeWidth; +} + +template <class Impl> +std::string +DefaultDecode<Impl>::name() const +{ + return cpu->name() + ".decode"; +} + +template <class Impl> +void +DefaultDecode<Impl>::regStats() +{ + decodeIdleCycles + .name(name() + ".DECODE:IdleCycles") + .desc("Number of cycles decode is idle") + .prereq(decodeIdleCycles); + decodeBlockedCycles + .name(name() + ".DECODE:BlockedCycles") + .desc("Number of cycles decode is blocked") + .prereq(decodeBlockedCycles); + decodeRunCycles + .name(name() + ".DECODE:RunCycles") + .desc("Number of cycles decode is running") + .prereq(decodeRunCycles); + decodeUnblockCycles + .name(name() + ".DECODE:UnblockCycles") + .desc("Number of cycles decode is unblocking") + .prereq(decodeUnblockCycles); + decodeSquashCycles + .name(name() + ".DECODE:SquashCycles") + .desc("Number of cycles decode is squashing") + .prereq(decodeSquashCycles); + decodeBranchResolved + .name(name() + ".DECODE:BranchResolved") + .desc("Number of times decode resolved a branch") + .prereq(decodeBranchResolved); + decodeBranchMispred + .name(name() + ".DECODE:BranchMispred") + .desc("Number of times decode detected a branch misprediction") + .prereq(decodeBranchMispred); + decodeControlMispred + .name(name() + ".DECODE:ControlMispred") + .desc("Number of times decode detected an instruction incorrectly" + " predicted as a control") + .prereq(decodeControlMispred); + decodeDecodedInsts + .name(name() + ".DECODE:DecodedInsts") + .desc("Number of instructions handled by decode") + .prereq(decodeDecodedInsts); + decodeSquashedInsts + .name(name() + ".DECODE:SquashedInsts") + .desc("Number of squashed instructions handled by decode") + .prereq(decodeSquashedInsts); +} + +template<class Impl> +void +DefaultDecode<Impl>::setCPU(FullCPU *cpu_ptr) +{ + DPRINTF(Decode, "Setting CPU pointer.\n"); + cpu = cpu_ptr; +} + +template<class Impl> +void +DefaultDecode<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr) +{ + DPRINTF(Decode, "Setting time buffer pointer.\n"); + timeBuffer = tb_ptr; + + // Setup wire to write information back to fetch. + toFetch = timeBuffer->getWire(0); + + // Create wires to get information from proper places in time buffer. + fromRename = timeBuffer->getWire(-renameToDecodeDelay); + fromIEW = timeBuffer->getWire(-iewToDecodeDelay); + fromCommit = timeBuffer->getWire(-commitToDecodeDelay); +} + +template<class Impl> +void +DefaultDecode<Impl>::setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr) +{ + DPRINTF(Decode, "Setting decode queue pointer.\n"); + decodeQueue = dq_ptr; + + // Setup wire to write information to proper place in decode queue. + toRename = decodeQueue->getWire(0); +} + +template<class Impl> +void +DefaultDecode<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr) +{ + DPRINTF(Decode, "Setting fetch queue pointer.\n"); + fetchQueue = fq_ptr; + + // Setup wire to read information from fetch queue. + fromFetch = fetchQueue->getWire(-fetchToDecodeDelay); +} + +template<class Impl> +void +DefaultDecode<Impl>::setActiveThreads(list<unsigned> *at_ptr) +{ + DPRINTF(Decode, "Setting active threads list pointer.\n"); + activeThreads = at_ptr; +} + +template <class Impl> +void +DefaultDecode<Impl>::switchOut() +{ + cpu->signalSwitched(); +} + +template <class Impl> +void +DefaultDecode<Impl>::takeOverFrom() +{ + _status = Inactive; + + for (int i = 0; i < numThreads; ++i) { + decodeStatus[i] = Idle; + + stalls[i].rename = false; + stalls[i].iew = false; + stalls[i].commit = false; + while (!insts[i].empty()) + insts[i].pop(); + while (!skidBuffer[i].empty()) + skidBuffer[i].pop(); + branchCount[i] = 0; + } + wroteToTimeBuffer = false; +} + +template<class Impl> +bool +DefaultDecode<Impl>::checkStall(unsigned tid) const +{ + bool ret_val = false; + + if (stalls[tid].rename) { + DPRINTF(Decode,"[tid:%i]: Stall fom Rename stage detected.\n", tid); + ret_val = true; + } else if (stalls[tid].iew) { + DPRINTF(Decode,"[tid:%i]: Stall fom IEW stage detected.\n", tid); + ret_val = true; + } else if (stalls[tid].commit) { + DPRINTF(Decode,"[tid:%i]: Stall fom Commit stage detected.\n", tid); + ret_val = true; + } + + return ret_val; +} + +template<class Impl> +inline bool +DefaultDecode<Impl>::fetchInstsValid() +{ + return fromFetch->size > 0; +} + +template<class Impl> +bool +DefaultDecode<Impl>::block(unsigned tid) +{ + DPRINTF(Decode, "[tid:%u]: Blocking.\n", tid); + + // If the decode status is blocked or unblocking then decode has not yet + // signalled fetch to unblock. In that case, there is no need to tell + // fetch to block. + if (decodeStatus[tid] != Blocked && + decodeStatus[tid] != Unblocking) { + toFetch->decodeBlock[tid] = true; + wroteToTimeBuffer = true; + } + + // Add the current inputs to the skid buffer so they can be + // reprocessed when this stage unblocks. + skidInsert(tid); + + if (decodeStatus[tid] != Blocked) { + // Set the status to Blocked. + decodeStatus[tid] = Blocked; + return true; + } + + return false; +} + +template<class Impl> +bool +DefaultDecode<Impl>::unblock(unsigned tid) +{ + // Decode is done unblocking only if the skid buffer is empty. + if (skidBuffer[tid].empty()) { + DPRINTF(Decode, "[tid:%u]: Done unblocking.\n", tid); + toFetch->decodeUnblock[tid] = true; + wroteToTimeBuffer = true; + + decodeStatus[tid] = Running; + return true; + } + + DPRINTF(Decode, "[tid:%u]: Currently unblocking.\n", tid); + + return false; +} + +template<class Impl> +void +DefaultDecode<Impl>::squash(DynInstPtr &inst, unsigned tid) +{ + DPRINTF(Decode, "[tid:%i]: Squashing due to incorrect branch prediction " + "detected at decode.\n", tid); + + toFetch->decodeInfo[tid].branchMispredict = true; + toFetch->decodeInfo[tid].doneSeqNum = inst->seqNum; + toFetch->decodeInfo[tid].predIncorrect = true; + toFetch->decodeInfo[tid].squash = true; + toFetch->decodeInfo[tid].nextPC = inst->readNextPC(); + toFetch->decodeInfo[tid].branchTaken = true; + + if (decodeStatus[tid] == Blocked || + decodeStatus[tid] == Unblocking) { + toFetch->decodeUnblock[tid] = 1; + } + + // Set status to squashing. + decodeStatus[tid] = Squashing; + + for (int i=0; i<fromFetch->size; i++) { + if (fromFetch->insts[i]->threadNumber == tid && + fromFetch->insts[i]->seqNum > inst->seqNum) { + fromFetch->insts[i]->squashed = true; + } + } + + while (!insts[tid].empty()) { + insts[tid].pop(); + } + + // Clear the skid buffer in case it has any data in it. + while (!skidBuffer[tid].empty()) { + skidBuffer[tid].pop(); + } + + // Squash instructions up until this one + cpu->removeInstsUntil(inst->seqNum, tid); +} + +template<class Impl> +unsigned +DefaultDecode<Impl>::squash(unsigned tid) +{ + DPRINTF(Decode, "[tid:%i]: Squashing.\n",tid); + + if (decodeStatus[tid] == Blocked || + decodeStatus[tid] == Unblocking) { +#if !FULL_SYSTEM + // In syscall emulation, we can have both a block and a squash due + // to a syscall in the same cycle. This would cause both signals to + // be high. This shouldn't happen in full system. + // @todo: Determine if this still happens. + if (toFetch->decodeBlock[tid]) { + toFetch->decodeBlock[tid] = 0; + } else { + toFetch->decodeUnblock[tid] = 1; + } +#else + toFetch->decodeUnblock[tid] = 1; +#endif + } + + // Set status to squashing. + decodeStatus[tid] = Squashing; + + // Go through incoming instructions from fetch and squash them. + unsigned squash_count = 0; + + for (int i=0; i<fromFetch->size; i++) { + if (fromFetch->insts[i]->threadNumber == tid) { + fromFetch->insts[i]->squashed = true; + squash_count++; + } + } + + while (!insts[tid].empty()) { + insts[tid].pop(); + } + + // Clear the skid buffer in case it has any data in it. + while (!skidBuffer[tid].empty()) { + skidBuffer[tid].pop(); + } + + return squash_count; +} + +template<class Impl> +void +DefaultDecode<Impl>::skidInsert(unsigned tid) +{ + DynInstPtr inst = NULL; + + while (!insts[tid].empty()) { + inst = insts[tid].front(); + + insts[tid].pop(); + + assert(tid == inst->threadNumber); + + DPRINTF(Decode,"Inserting [sn:%lli] PC:%#x into decode skidBuffer %i\n", + inst->seqNum, inst->readPC(), inst->threadNumber); + + skidBuffer[tid].push(inst); + } + + // @todo: Eventually need to enforce this by not letting a thread + // fetch past its skidbuffer + assert(skidBuffer[tid].size() <= skidBufferMax); +} + +template<class Impl> +bool +DefaultDecode<Impl>::skidsEmpty() +{ + list<unsigned>::iterator threads = (*activeThreads).begin(); + + while (threads != (*activeThreads).end()) { + if (!skidBuffer[*threads++].empty()) + return false; + } + + return true; +} + +template<class Impl> +void +DefaultDecode<Impl>::updateStatus() +{ + bool any_unblocking = false; + + list<unsigned>::iterator threads = (*activeThreads).begin(); + + threads = (*activeThreads).begin(); + + while (threads != (*activeThreads).end()) { + unsigned tid = *threads++; + + if (decodeStatus[tid] == Unblocking) { + any_unblocking = true; + break; + } + } + + // Decode will have activity if it's unblocking. + if (any_unblocking) { + if (_status == Inactive) { + _status = Active; + + DPRINTF(Activity, "Activating stage.\n"); + + cpu->activateStage(FullCPU::DecodeIdx); + } + } else { + // If it's not unblocking, then decode will not have any internal + // activity. Switch it to inactive. + if (_status == Active) { + _status = Inactive; + DPRINTF(Activity, "Deactivating stage.\n"); + + cpu->deactivateStage(FullCPU::DecodeIdx); + } + } +} + +template <class Impl> +void +DefaultDecode<Impl>::sortInsts() +{ + int insts_from_fetch = fromFetch->size; +#ifdef DEBUG + for (int i=0; i < numThreads; i++) + assert(insts[i].empty()); +#endif + for (int i = 0; i < insts_from_fetch; ++i) { + insts[fromFetch->insts[i]->threadNumber].push(fromFetch->insts[i]); + } +} + +template<class Impl> +void +DefaultDecode<Impl>::readStallSignals(unsigned tid) +{ + if (fromRename->renameBlock[tid]) { + stalls[tid].rename = true; + } + + if (fromRename->renameUnblock[tid]) { + assert(stalls[tid].rename); + stalls[tid].rename = false; + } + + if (fromIEW->iewBlock[tid]) { + stalls[tid].iew = true; + } + + if (fromIEW->iewUnblock[tid]) { + assert(stalls[tid].iew); + stalls[tid].iew = false; + } + + if (fromCommit->commitBlock[tid]) { + stalls[tid].commit = true; + } + + if (fromCommit->commitUnblock[tid]) { + assert(stalls[tid].commit); + stalls[tid].commit = false; + } +} + +template <class Impl> +bool +DefaultDecode<Impl>::checkSignalsAndUpdate(unsigned tid) +{ + // Check if there's a squash signal, squash if there is. + // Check stall signals, block if necessary. + // If status was blocked + // Check if stall conditions have passed + // if so then go to unblocking + // If status was Squashing + // check if squashing is not high. Switch to running this cycle. + + // Update the per thread stall statuses. + readStallSignals(tid); + + // Check squash signals from commit. + if (fromCommit->commitInfo[tid].squash) { + + DPRINTF(Decode, "[tid:%u]: Squashing instructions due to squash " + "from commit.\n", tid); + + squash(tid); + + return true; + } + + // Check ROB squash signals from commit. + if (fromCommit->commitInfo[tid].robSquashing) { + DPRINTF(Decode, "[tid:%]: ROB is still squashing.\n",tid); + + // Continue to squash. + decodeStatus[tid] = Squashing; + + return true; + } + + if (checkStall(tid)) { + return block(tid); + } + + if (decodeStatus[tid] == Blocked) { + DPRINTF(Decode, "[tid:%u]: Done blocking, switching to unblocking.\n", + tid); + + decodeStatus[tid] = Unblocking; + + unblock(tid); + + return true; + } + + if (decodeStatus[tid] == Squashing) { + // Switch status to running if decode isn't being told to block or + // squash this cycle. + DPRINTF(Decode, "[tid:%u]: Done squashing, switching to running.\n", + tid); + + decodeStatus[tid] = Running; + + return false; + } + + // If we've reached this point, we have not gotten any signals that + // cause decode to change its status. Decode remains the same as before. + return false; +} + +template<class Impl> +void +DefaultDecode<Impl>::tick() +{ + wroteToTimeBuffer = false; + + bool status_change = false; + + 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; + inst->setNextPC(inst->branchTarget()); + + if (inst->mispredicted()) { + ++decodeBranchMispred; + + // Might want to set some sort of boolean and just do + // a check at the end + squash(inst, inst->threadNumber); + + 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; + } +} |