llvm-6502/lib/CodeGen/SelectionDAG/LatencyPriorityQueue.cpp
2008-11-17 16:37:30 +00:00

166 lines
6.0 KiB
C++

//===---- LatencyPriorityQueue.cpp - A latency-oriented priority queue ----===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LatencyPriorityQueue class, which is a
// SchedulingPriorityQueue that schedules using latency information to
// reduce the length of the critical path through the basic block.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "scheduler"
#include "LatencyPriorityQueue.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
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;
std::vector<const SUnit*> WorkList;
WorkList.push_back(&SU);
while (!WorkList.empty()) {
const SUnit *Cur = WorkList.back();
bool AllDone = true;
int MaxSuccLatency = 0;
for (SUnit::const_succ_iterator I = Cur->Succs.begin(),E = Cur->Succs.end();
I != E; ++I) {
int SuccLatency = Latencies[I->Dep->NodeNum];
if (SuccLatency == -1) {
AllDone = false;
WorkList.push_back(I->Dep);
} else {
MaxSuccLatency = std::max(MaxSuccLatency, SuccLatency);
}
}
if (AllDone) {
Latencies[Cur->NodeNum] = MaxSuccLatency + Cur->Latency;
WorkList.pop_back();
}
}
return Latency;
}
/// CalculatePriorities - Calculate priorities of all scheduling units.
void LatencyPriorityQueue::CalculatePriorities() {
Latencies.assign(SUnits->size(), -1);
NumNodesSolelyBlocking.assign(SUnits->size(), 0);
// For each node, calculate the maximal path from the node to the exit.
std::vector<std::pair<const SUnit*, unsigned> > WorkList;
for (unsigned i = 0, e = SUnits->size(); i != e; ++i) {
const SUnit *SU = &(*SUnits)[i];
if (SU->Succs.empty())
WorkList.push_back(std::make_pair(SU, 0U));
}
while (!WorkList.empty()) {
const SUnit *SU = WorkList.back().first;
unsigned SuccLat = WorkList.back().second;
WorkList.pop_back();
int &Latency = Latencies[SU->NodeNum];
if (Latency == -1 || (SU->Latency + SuccLat) > (unsigned)Latency) {
Latency = SU->Latency + SuccLat;
for (SUnit::const_pred_iterator I = SU->Preds.begin(),E = SU->Preds.end();
I != E; ++I)
WorkList.push_back(std::make_pair(I->Dep, Latency));
}
}
}
/// 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->Dep;
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->Dep) == 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->Dep);
}
/// 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->isAvailable) 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.
remove(OnlyAvailablePred);
// Reinsert the node into the priority queue, which recomputes its
// NumNodesSolelyBlocking value.
push(OnlyAvailablePred);
}