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//===---- ScheduleDAGList.cpp - Implement a list scheduler for isel DAG ---===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Evan Cheng and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements a top-down list scheduler, using standard algorithms.
// The basic approach uses a priority queue of available nodes to schedule.
// One at a time, nodes are taken from the priority queue (thus in priority
// order), checked for legality to schedule, and emitted if legal.
//
// Nodes may not be legal to schedule either due to structural hazards (e.g.
// pipeline or resource constraints) or because an input to the instruction has
// not completed execution.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "pre-RA-sched"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/SchedulerRegistry.h"
#include "llvm/CodeGen/SelectionDAGISel.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Compiler.h"
#include "llvm/ADT/Statistic.h"
#include <climits>
#include <queue>
using namespace llvm;
STATISTIC(NumNoops , "Number of noops inserted");
STATISTIC(NumStalls, "Number of pipeline stalls");
static RegisterScheduler
tdListDAGScheduler("list-td", " Top-down list scheduler",
createTDListDAGScheduler);
namespace {
//===----------------------------------------------------------------------===//
/// ScheduleDAGList - The actual list scheduler implementation. This supports
/// top-down scheduling.
///
class VISIBILITY_HIDDEN ScheduleDAGList : public ScheduleDAG {
private:
/// AvailableQueue - The priority queue to use for the available SUnits.
///
SchedulingPriorityQueue *AvailableQueue;
/// PendingQueue - This contains all of the instructions whose operands have
/// been issued, but their results are not ready yet (due to the latency of
/// the operation). Once the operands becomes available, the instruction is
/// added to the AvailableQueue. This keeps track of each SUnit and the
/// number of cycles left to execute before the operation is available.
std::vector<std::pair<unsigned, SUnit*> > PendingQueue;
/// HazardRec - The hazard recognizer to use.
HazardRecognizer *HazardRec;
public:
ScheduleDAGList(SelectionDAG &dag, MachineBasicBlock *bb,
const TargetMachine &tm,
SchedulingPriorityQueue *availqueue,
HazardRecognizer *HR)
: ScheduleDAG(dag, bb, tm),
AvailableQueue(availqueue), HazardRec(HR) {
}
~ScheduleDAGList() {
delete HazardRec;
delete AvailableQueue;
}
void Schedule();
private:
void ReleaseSucc(SUnit *SuccSU, bool isChain);
void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
void ListScheduleTopDown();
};
} // end anonymous namespace
HazardRecognizer::~HazardRecognizer() {}
/// Schedule - Schedule the DAG using list scheduling.
void ScheduleDAGList::Schedule() {
DOUT << "********** List Scheduling **********\n";
// Build scheduling units.
BuildSchedUnits();
AvailableQueue->initNodes(SUnitMap, SUnits);
ListScheduleTopDown();
AvailableQueue->releaseState();
DOUT << "*** Final schedule ***\n";
DEBUG(dumpSchedule());
DOUT << "\n";
// Emit in scheduled order
EmitSchedule();
}
//===----------------------------------------------------------------------===//
// Top-Down Scheduling
//===----------------------------------------------------------------------===//
/// ReleaseSucc - Decrement the NumPredsLeft count of a successor. Add it to
/// the PendingQueue if the count reaches zero.
void ScheduleDAGList::ReleaseSucc(SUnit *SuccSU, bool isChain) {
if (!isChain)
SuccSU->NumPredsLeft--;
else
SuccSU->NumChainPredsLeft--;
assert(SuccSU->NumPredsLeft >= 0 && SuccSU->NumChainPredsLeft >= 0 &&
"List scheduling internal error");
if ((SuccSU->NumPredsLeft + SuccSU->NumChainPredsLeft) == 0) {
// Compute how many cycles it will be before this actually becomes
// available. This is the max of the start time of all predecessors plus
// their latencies.
unsigned AvailableCycle = 0;
for (SUnit::pred_iterator I = SuccSU->Preds.begin(),
E = SuccSU->Preds.end(); I != E; ++I) {
// If this is a token edge, we don't need to wait for the latency of the
// preceeding instruction (e.g. a long-latency load) unless there is also
// some other data dependence.
SUnit &Pred = *I->first;
unsigned PredDoneCycle = Pred.Cycle;
if (!I->second)
PredDoneCycle += Pred.Latency;
else if (Pred.Latency)
PredDoneCycle += 1;
AvailableCycle = std::max(AvailableCycle, PredDoneCycle);
}
PendingQueue.push_back(std::make_pair(AvailableCycle, SuccSU));
}
}
/// ScheduleNodeTopDown - Add the node to the schedule. Decrement the pending
/// count of its successors. If a successor pending count is zero, add it to
/// the Available queue.
void ScheduleDAGList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
DOUT << "*** Scheduling [" << CurCycle << "]: ";
DEBUG(SU->dump(&DAG));
Sequence.push_back(SU);
SU->Cycle = CurCycle;
// Bottom up: release successors.
for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I)
ReleaseSucc(I->first, I->second);
}
/// ListScheduleTopDown - The main loop of list scheduling for top-down
/// schedulers.
void ScheduleDAGList::ListScheduleTopDown() {
unsigned CurCycle = 0;
SUnit *Entry = SUnitMap[DAG.getEntryNode().Val];
// All leaves to Available queue.
for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
// It is available if it has no predecessors.
if (SUnits[i].Preds.size() == 0 && &SUnits[i] != Entry) {
AvailableQueue->push(&SUnits[i]);
SUnits[i].isAvailable = SUnits[i].isPending = true;
}
}
// Emit the entry node first.
ScheduleNodeTopDown(Entry, CurCycle);
HazardRec->EmitInstruction(Entry->Node);
// While Available queue is not empty, grab the node with the highest
// priority. If it is not ready put it back. Schedule the node.
std::vector<SUnit*> NotReady;
while (!AvailableQueue->empty() || !PendingQueue.empty()) {
// Check to see if any of the pending instructions are ready to issue. If
// so, add them to the available queue.
for (unsigned i = 0, e = PendingQueue.size(); i != e; ++i) {
if (PendingQueue[i].first == CurCycle) {
AvailableQueue->push(PendingQueue[i].second);
PendingQueue[i].second->isAvailable = true;
PendingQueue[i] = PendingQueue.back();
PendingQueue.pop_back();
--i; --e;
} else {
assert(PendingQueue[i].first > CurCycle && "Negative latency?");
}
}
// If there are no instructions available, don't try to issue anything, and
// don't advance the hazard recognizer.
if (AvailableQueue->empty()) {
++CurCycle;
continue;
}
SUnit *FoundSUnit = 0;
SDNode *FoundNode = 0;
bool HasNoopHazards = false;
while (!AvailableQueue->empty()) {
SUnit *CurSUnit = AvailableQueue->pop();
// Get the node represented by this SUnit.
FoundNode = CurSUnit->Node;
// If this is a pseudo op, like copyfromreg, look to see if there is a
// real target node flagged to it. If so, use the target node.
for (unsigned i = 0, e = CurSUnit->FlaggedNodes.size();
FoundNode->getOpcode() < ISD::BUILTIN_OP_END && i != e; ++i)
FoundNode = CurSUnit->FlaggedNodes[i];
HazardRecognizer::HazardType HT = HazardRec->getHazardType(FoundNode);
if (HT == HazardRecognizer::NoHazard) {
FoundSUnit = CurSUnit;
break;
}
// Remember if this is a noop hazard.
HasNoopHazards |= HT == HazardRecognizer::NoopHazard;
NotReady.push_back(CurSUnit);
}
// Add the nodes that aren't ready back onto the available list.
if (!NotReady.empty()) {
AvailableQueue->push_all(NotReady);
NotReady.clear();
}
// If we found a node to schedule, do it now.
if (FoundSUnit) {
ScheduleNodeTopDown(FoundSUnit, CurCycle);
HazardRec->EmitInstruction(FoundNode);
FoundSUnit->isScheduled = true;
AvailableQueue->ScheduledNode(FoundSUnit);
// If this is a pseudo-op node, we don't want to increment the current
// cycle.
if (FoundSUnit->Latency) // Don't increment CurCycle for pseudo-ops!
++CurCycle;
} else if (!HasNoopHazards) {
// Otherwise, we have a pipeline stall, but no other problem, just advance
// the current cycle and try again.
DOUT << "*** Advancing cycle, no work to do\n";
HazardRec->AdvanceCycle();
++NumStalls;
++CurCycle;
} else {
// Otherwise, we have no instructions to issue and we have instructions
// that will fault if we don't do this right. This is the case for
// processors without pipeline interlocks and other cases.
DOUT << "*** Emitting noop\n";
HazardRec->EmitNoop();
Sequence.push_back(0); // NULL SUnit* -> noop
++NumNoops;
++CurCycle;
}
}
#ifndef NDEBUG
// Verify that all SUnits were scheduled.
bool AnyNotSched = false;
for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
if (SUnits[i].NumPredsLeft != 0 || SUnits[i].NumChainPredsLeft != 0) {
if (!AnyNotSched)
cerr << "*** List scheduling failed! ***\n";
SUnits[i].dump(&DAG);
cerr << "has not been scheduled!\n";
AnyNotSched = true;
}
}
assert(!AnyNotSched);
#endif
}
//===----------------------------------------------------------------------===//
// LatencyPriorityQueue Implementation
//===----------------------------------------------------------------------===//
//
// This is a SchedulingPriorityQueue that schedules using latency information to
// reduce the length of the critical path through the basic block.
//
namespace {
class LatencyPriorityQueue;
/// Sorting functions for the Available queue.
struct latency_sort : public std::binary_function<SUnit*, SUnit*, bool> {
LatencyPriorityQueue *PQ;
latency_sort(LatencyPriorityQueue *pq) : PQ(pq) {}
latency_sort(const latency_sort &RHS) : PQ(RHS.PQ) {}
bool operator()(const SUnit* left, const SUnit* right) const;
};
} // end anonymous namespace
namespace {
class LatencyPriorityQueue : public SchedulingPriorityQueue {
// SUnits - The SUnits for the current graph.
std::vector<SUnit> *SUnits;
// Latencies - The latency (max of latency from this node to the bb exit)
// for each node.
std::vector<int> Latencies;
/// NumNodesSolelyBlocking - This vector contains, for every node in the
/// Queue, the number of nodes that the node is the sole unscheduled
/// predecessor for. This is used as a tie-breaker heuristic for better
/// mobility.
std::vector<unsigned> NumNodesSolelyBlocking;
std::priority_queue<SUnit*, std::vector<SUnit*>, latency_sort> Queue;
public:
LatencyPriorityQueue() : Queue(latency_sort(this)) {
}
void initNodes(DenseMap<SDNode*, SUnit*> &sumap,
std::vector<SUnit> &sunits) {
SUnits = &sunits;
// Calculate node priorities.
CalculatePriorities();
}
void releaseState() {
SUnits = 0;
Latencies.clear();
}
unsigned getLatency(unsigned NodeNum) const {
assert(NodeNum < Latencies.size());
return Latencies[NodeNum];
}
unsigned getNumSolelyBlockNodes(unsigned NodeNum) const {
assert(NodeNum < NumNodesSolelyBlocking.size());
return NumNodesSolelyBlocking[NodeNum];
}
bool empty() const { return Queue.empty(); }
virtual void push(SUnit *U) {
push_impl(U);
}
void push_impl(SUnit *U);
void push_all(const std::vector<SUnit *> &Nodes) {
for (unsigned i = 0, e = Nodes.size(); i != e; ++i)
push_impl(Nodes[i]);
}
SUnit *pop() {
if (empty()) return NULL;
SUnit *V = Queue.top();
Queue.pop();
return V;
}
// ScheduledNode - As nodes are scheduled, we look to see if there are any
// successor nodes that have a single unscheduled predecessor. If so, that
// single predecessor has a higher priority, since scheduling it will make
// the node available.
void ScheduledNode(SUnit *Node);
private:
void CalculatePriorities();
int CalcLatency(const SUnit &SU);
void AdjustPriorityOfUnscheduledPreds(SUnit *SU);
SUnit *getSingleUnscheduledPred(SUnit *SU);
/// RemoveFromPriorityQueue - This is a really inefficient way to remove a
/// node from a priority queue. We should roll our own heap to make this
/// better or something.
void RemoveFromPriorityQueue(SUnit *SU) {
std::vector<SUnit*> Temp;
assert(!Queue.empty() && "Not in queue!");
while (Queue.top() != SU) {
Temp.push_back(Queue.top());
Queue.pop();
assert(!Queue.empty() && "Not in queue!");
}
// Remove the node from the PQ.
Queue.pop();
// Add all the other nodes back.
for (unsigned i = 0, e = Temp.size(); i != e; ++i)
Queue.push(Temp[i]);
}
};
}
bool latency_sort::operator()(const SUnit *LHS, const SUnit *RHS) const {
unsigned LHSNum = LHS->NodeNum;
unsigned RHSNum = RHS->NodeNum;
// The most important heuristic is scheduling the critical path.
unsigned LHSLatency = PQ->getLatency(LHSNum);
unsigned RHSLatency = PQ->getLatency(RHSNum);
if (LHSLatency < RHSLatency) return true;
if (LHSLatency > RHSLatency) return false;
// After that, if two nodes have identical latencies, look to see if one will
// unblock more other nodes than the other.
unsigned LHSBlocked = PQ->getNumSolelyBlockNodes(LHSNum);
unsigned RHSBlocked = PQ->getNumSolelyBlockNodes(RHSNum);
if (LHSBlocked < RHSBlocked) return true;
if (LHSBlocked > RHSBlocked) return false;
// Finally, just to provide a stable ordering, use the node number as a
// deciding factor.
return LHSNum < RHSNum;
}
/// CalcNodePriority - Calculate the maximal path from the node to the exit.
///
int LatencyPriorityQueue::CalcLatency(const SUnit &SU) {
int &Latency = Latencies[SU.NodeNum];
if (Latency != -1)
return Latency;
int MaxSuccLatency = 0;
for (SUnit::const_succ_iterator I = SU.Succs.begin(), E = SU.Succs.end();
I != E; ++I)
MaxSuccLatency = std::max(MaxSuccLatency, CalcLatency(*I->first));
return Latency = MaxSuccLatency + SU.Latency;
}
/// CalculatePriorities - Calculate priorities of all scheduling units.
void LatencyPriorityQueue::CalculatePriorities() {
Latencies.assign(SUnits->size(), -1);
NumNodesSolelyBlocking.assign(SUnits->size(), 0);
for (unsigned i = 0, e = SUnits->size(); i != e; ++i)
CalcLatency((*SUnits)[i]);
}
/// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor
/// of SU, return it, otherwise return null.
SUnit *LatencyPriorityQueue::getSingleUnscheduledPred(SUnit *SU) {
SUnit *OnlyAvailablePred = 0;
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
SUnit &Pred = *I->first;
if (!Pred.isScheduled) {
// We found an available, but not scheduled, predecessor. If it's the
// only one we have found, keep track of it... otherwise give up.
if (OnlyAvailablePred && OnlyAvailablePred != &Pred)
return 0;
OnlyAvailablePred = &Pred;
}
}
return OnlyAvailablePred;
}
void LatencyPriorityQueue::push_impl(SUnit *SU) {
// Look at all of the successors of this node. Count the number of nodes that
// this node is the sole unscheduled node for.
unsigned NumNodesBlocking = 0;
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I)
if (getSingleUnscheduledPred(I->first) == SU)
++NumNodesBlocking;
NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking;
Queue.push(SU);
}
// ScheduledNode - As nodes are scheduled, we look to see if there are any
// successor nodes that have a single unscheduled predecessor. If so, that
// single predecessor has a higher priority, since scheduling it will make
// the node available.
void LatencyPriorityQueue::ScheduledNode(SUnit *SU) {
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I)
AdjustPriorityOfUnscheduledPreds(I->first);
}
/// AdjustPriorityOfUnscheduledPreds - One of the predecessors of SU was just
/// scheduled. If SU is not itself available, then there is at least one
/// predecessor node that has not been scheduled yet. If SU has exactly ONE
/// unscheduled predecessor, we want to increase its priority: it getting
/// scheduled will make this node available, so it is better than some other
/// node of the same priority that will not make a node available.
void LatencyPriorityQueue::AdjustPriorityOfUnscheduledPreds(SUnit *SU) {
if (SU->isPending) return; // All preds scheduled.
SUnit *OnlyAvailablePred = getSingleUnscheduledPred(SU);
if (OnlyAvailablePred == 0 || !OnlyAvailablePred->isAvailable) return;
// Okay, we found a single predecessor that is available, but not scheduled.
// Since it is available, it must be in the priority queue. First remove it.
RemoveFromPriorityQueue(OnlyAvailablePred);
// Reinsert the node into the priority queue, which recomputes its
// NumNodesSolelyBlocking value.
push(OnlyAvailablePred);
}
//===----------------------------------------------------------------------===//
// Public Constructor Functions
//===----------------------------------------------------------------------===//
/// createTDListDAGScheduler - This creates a top-down list scheduler with a
/// new hazard recognizer. This scheduler takes ownership of the hazard
/// recognizer and deletes it when done.
ScheduleDAG* llvm::createTDListDAGScheduler(SelectionDAGISel *IS,
SelectionDAG *DAG,
MachineBasicBlock *BB) {
return new ScheduleDAGList(*DAG, BB, DAG->getTarget(),
new LatencyPriorityQueue(),
IS->CreateTargetHazardRecognizer());
}