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llvm-project/llvm/lib/CodeGen/SelectionDAG/ResourcePriorityQueue.cpp

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//===- ResourcePriorityQueue.cpp - A DFA-oriented priority queue -*- C++ -*-==//
//
// 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 ResourcePriorityQueue class, which is a
// SchedulingPriorityQueue that prioritizes instructions using DFA state to
// reduce the length of the critical path through the basic block
// on VLIW platforms.
// The scheduler is basically a top-down adaptable list scheduler with DFA
// resource tracking added to the cost function.
// DFA is queried as a state machine to model "packets/bundles" during
// schedule. Currently packets/bundles are discarded at the end of
// scheduling, affecting only order of instructions.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "scheduler"
#include "llvm/CodeGen/ResourcePriorityQueue.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/SelectionDAGNodes.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetLowering.h"
using namespace llvm;
static cl::opt<bool> DisableDFASched("disable-dfa-sched", cl::Hidden,
cl::ZeroOrMore, cl::init(false),
cl::desc("Disable use of DFA during scheduling"));
static cl::opt<signed> RegPressureThreshold(
"dfa-sched-reg-pressure-threshold", cl::Hidden, cl::ZeroOrMore, cl::init(5),
cl::desc("Track reg pressure and switch priority to in-depth"));
ResourcePriorityQueue::ResourcePriorityQueue(SelectionDAGISel *IS) :
Picker(this),
InstrItins(IS->getTargetLowering().getTargetMachine().getInstrItineraryData())
{
TII = IS->getTargetLowering().getTargetMachine().getInstrInfo();
TRI = IS->getTargetLowering().getTargetMachine().getRegisterInfo();
TLI = &IS->getTargetLowering();
const TargetMachine &tm = (*IS->MF).getTarget();
ResourcesModel = tm.getInstrInfo()->CreateTargetScheduleState(&tm,NULL);
// This hard requirment could be relaxed, but for now
// do not let it procede.
assert (ResourcesModel && "Unimplemented CreateTargetScheduleState.");
unsigned NumRC = TRI->getNumRegClasses();
RegLimit.resize(NumRC);
RegPressure.resize(NumRC);
std::fill(RegLimit.begin(), RegLimit.end(), 0);
std::fill(RegPressure.begin(), RegPressure.end(), 0);
for (TargetRegisterInfo::regclass_iterator I = TRI->regclass_begin(),
E = TRI->regclass_end(); I != E; ++I)
RegLimit[(*I)->getID()] = TRI->getRegPressureLimit(*I, *IS->MF);
ParallelLiveRanges = 0;
HorizontalVerticalBalance = 0;
}
unsigned
ResourcePriorityQueue::numberRCValPredInSU(SUnit *SU, unsigned RCId) {
unsigned NumberDeps = 0;
for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
if (I->isCtrl())
continue;
SUnit *PredSU = I->getSUnit();
const SDNode *ScegN = PredSU->getNode();
if (!ScegN)
continue;
// If value is passed to CopyToReg, it is probably
// live outside BB.
switch (ScegN->getOpcode()) {
default: break;
case ISD::TokenFactor: break;
case ISD::CopyFromReg: NumberDeps++; break;
case ISD::CopyToReg: break;
case ISD::INLINEASM: break;
}
if (!ScegN->isMachineOpcode())
continue;
for (unsigned i = 0, e = ScegN->getNumValues(); i != e; ++i) {
EVT VT = ScegN->getValueType(i);
if (TLI->isTypeLegal(VT)
&& (TLI->getRegClassFor(VT)->getID() == RCId)) {
NumberDeps++;
break;
}
}
}
return NumberDeps;
}
unsigned ResourcePriorityQueue::numberRCValSuccInSU(SUnit *SU,
unsigned RCId) {
unsigned NumberDeps = 0;
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
if (I->isCtrl())
continue;
SUnit *SuccSU = I->getSUnit();
const SDNode *ScegN = SuccSU->getNode();
if (!ScegN)
continue;
// If value is passed to CopyToReg, it is probably
// live outside BB.
switch (ScegN->getOpcode()) {
default: break;
case ISD::TokenFactor: break;
case ISD::CopyFromReg: break;
case ISD::CopyToReg: NumberDeps++; break;
case ISD::INLINEASM: break;
}
if (!ScegN->isMachineOpcode())
continue;
for (unsigned i = 0, e = ScegN->getNumOperands(); i != e; ++i) {
const SDValue &Op = ScegN->getOperand(i);
EVT VT = Op.getNode()->getValueType(Op.getResNo());
if (TLI->isTypeLegal(VT)
&& (TLI->getRegClassFor(VT)->getID() == RCId)) {
NumberDeps++;
break;
}
}
}
return NumberDeps;
}
static unsigned numberCtrlDepsInSU(SUnit *SU) {
unsigned NumberDeps = 0;
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I)
if (I->isCtrl())
NumberDeps++;
return NumberDeps;
}
static unsigned numberCtrlPredInSU(SUnit *SU) {
unsigned NumberDeps = 0;
for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I)
if (I->isCtrl())
NumberDeps++;
return NumberDeps;
}
///
/// Initialize nodes.
///
void ResourcePriorityQueue::initNodes(std::vector<SUnit> &sunits) {
SUnits = &sunits;
NumNodesSolelyBlocking.resize(SUnits->size(), 0);
for (unsigned i = 0, e = SUnits->size(); i != e; ++i) {
SUnit *SU = &(*SUnits)[i];
initNumRegDefsLeft(SU);
SU->NodeQueueId = 0;
}
}
/// This heuristic is used if DFA scheduling is not desired
/// for some VLIW platform.
bool resource_sort::operator()(const SUnit *LHS, const SUnit *RHS) const {
// The isScheduleHigh flag allows nodes with wraparound dependencies that
// cannot easily be modeled as edges with latencies to be scheduled as
// soon as possible in a top-down schedule.
if (LHS->isScheduleHigh && !RHS->isScheduleHigh)
return false;
if (!LHS->isScheduleHigh && RHS->isScheduleHigh)
return true;
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;
}
/// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor
/// of SU, return it, otherwise return null.
SUnit *ResourcePriorityQueue::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->getSUnit();
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 ResourcePriorityQueue::push(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->getSUnit()) == SU)
++NumNodesBlocking;
NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking;
Queue.push_back(SU);
}
/// Check if scheduling of this SU is possible
/// in the current packet.
bool ResourcePriorityQueue::isResourceAvailable(SUnit *SU) {
if (!SU || !SU->getNode())
return false;
// If this is a compound instruction,
// it is likely to be a call. Do not delay it.
if (SU->getNode()->getGluedNode())
return true;
// First see if the pipeline could receive this instruction
// in the current cycle.
if (SU->getNode()->isMachineOpcode())
switch (SU->getNode()->getMachineOpcode()) {
default:
if (!ResourcesModel->canReserveResources(&TII->get(
SU->getNode()->getMachineOpcode())))
return false;
case TargetOpcode::EXTRACT_SUBREG:
case TargetOpcode::INSERT_SUBREG:
case TargetOpcode::SUBREG_TO_REG:
case TargetOpcode::REG_SEQUENCE:
case TargetOpcode::IMPLICIT_DEF:
break;
}
// Now see if there are no other dependencies
// to instructions alredy in the packet.
for (unsigned i = 0, e = Packet.size(); i != e; ++i)
for (SUnit::const_succ_iterator I = Packet[i]->Succs.begin(),
E = Packet[i]->Succs.end(); I != E; ++I) {
// Since we do not add pseudos to packets, might as well
// ignor order deps.
if (I->isCtrl())
continue;
if (I->getSUnit() == SU)
return false;
}
return true;
}
/// Keep track of available resources.
void ResourcePriorityQueue::reserveResources(SUnit *SU) {
// If this SU does not fit in the packet
// start a new one.
if (!isResourceAvailable(SU) || SU->getNode()->getGluedNode()) {
ResourcesModel->clearResources();
Packet.clear();
}
if (SU->getNode() && SU->getNode()->isMachineOpcode()) {
switch (SU->getNode()->getMachineOpcode()) {
default:
ResourcesModel->reserveResources(&TII->get(
SU->getNode()->getMachineOpcode()));
break;
case TargetOpcode::EXTRACT_SUBREG:
case TargetOpcode::INSERT_SUBREG:
case TargetOpcode::SUBREG_TO_REG:
case TargetOpcode::REG_SEQUENCE:
case TargetOpcode::IMPLICIT_DEF:
break;
}
Packet.push_back(SU);
}
// Forcefully end packet for PseudoOps.
else {
ResourcesModel->clearResources();
Packet.clear();
}
// If packet is now full, reset the state so in the next cycle
// we start fresh.
if (Packet.size() >= InstrItins->IssueWidth) {
ResourcesModel->clearResources();
Packet.clear();
}
}
signed ResourcePriorityQueue::rawRegPressureDelta(SUnit *SU, unsigned RCId) {
signed RegBalance = 0;
if (!SU || !SU->getNode() || !SU->getNode()->isMachineOpcode())
return RegBalance;
// Gen estimate.
for (unsigned i = 0, e = SU->getNode()->getNumValues(); i != e; ++i) {
EVT VT = SU->getNode()->getValueType(i);
if (TLI->isTypeLegal(VT)
&& TLI->getRegClassFor(VT)
&& TLI->getRegClassFor(VT)->getID() == RCId)
RegBalance += numberRCValSuccInSU(SU, RCId);
}
// Kill estimate.
for (unsigned i = 0, e = SU->getNode()->getNumOperands(); i != e; ++i) {
const SDValue &Op = SU->getNode()->getOperand(i);
EVT VT = Op.getNode()->getValueType(Op.getResNo());
if (isa<ConstantSDNode>(Op.getNode()))
continue;
if (TLI->isTypeLegal(VT) && TLI->getRegClassFor(VT)
&& TLI->getRegClassFor(VT)->getID() == RCId)
RegBalance -= numberRCValPredInSU(SU, RCId);
}
return RegBalance;
}
/// Estimates change in reg pressure from this SU.
/// It is acheived by trivial tracking of defined
/// and used vregs in dependent instructions.
/// The RawPressure flag makes this function to ignore
/// existing reg file sizes, and report raw def/use
/// balance.
signed ResourcePriorityQueue::regPressureDelta(SUnit *SU, bool RawPressure) {
signed RegBalance = 0;
if (!SU || !SU->getNode() || !SU->getNode()->isMachineOpcode())
return RegBalance;
if (RawPressure) {
for (TargetRegisterInfo::regclass_iterator I = TRI->regclass_begin(),
E = TRI->regclass_end(); I != E; ++I) {
const TargetRegisterClass *RC = *I;
RegBalance += rawRegPressureDelta(SU, RC->getID());
}
}
else {
for (TargetRegisterInfo::regclass_iterator I = TRI->regclass_begin(),
E = TRI->regclass_end(); I != E; ++I) {
const TargetRegisterClass *RC = *I;
if ((RegPressure[RC->getID()] +
rawRegPressureDelta(SU, RC->getID()) > 0) &&
(RegPressure[RC->getID()] +
rawRegPressureDelta(SU, RC->getID()) >= RegLimit[RC->getID()]))
RegBalance += rawRegPressureDelta(SU, RC->getID());
}
}
return RegBalance;
}
// Constants used to denote relative importance of
// heuristic components for cost computation.
static const unsigned PriorityOne = 200;
static const unsigned PriorityTwo = 100;
static const unsigned PriorityThree = 50;
static const unsigned PriorityFour = 15;
static const unsigned PriorityFive = 5;
static const unsigned ScaleOne = 20;
static const unsigned ScaleTwo = 10;
static const unsigned ScaleThree = 5;
static const unsigned FactorOne = 2;
/// Returns single number reflecting benefit of scheduling SU
/// in the current cycle.
signed ResourcePriorityQueue::SUSchedulingCost(SUnit *SU) {
// Initial trivial priority.
signed ResCount = 1;
// Do not waste time on a node that is already scheduled.
if (SU->isScheduled)
return ResCount;
// Forced priority is high.
if (SU->isScheduleHigh)
ResCount += PriorityOne;
// Adaptable scheduling
// A small, but very parallel
// region, where reg pressure is an issue.
if (HorizontalVerticalBalance > RegPressureThreshold) {
// Critical path first
ResCount += (SU->getHeight() * ScaleTwo);
// If resources are available for it, multiply the
// chance of scheduling.
if (isResourceAvailable(SU))
ResCount <<= FactorOne;
// Consider change to reg pressure from scheduling
// this SU.
ResCount -= (regPressureDelta(SU,true) * ScaleOne);
}
// Default heuristic, greeady and
// critical path driven.
else {
// Critical path first.
ResCount += (SU->getHeight() * ScaleTwo);
// Now see how many instructions is blocked by this SU.
ResCount += (NumNodesSolelyBlocking[SU->NodeNum] * ScaleTwo);
// If resources are available for it, multiply the
// chance of scheduling.
if (isResourceAvailable(SU))
ResCount <<= FactorOne;
ResCount -= (regPressureDelta(SU) * ScaleTwo);
}
// These are platform specific things.
// Will need to go into the back end
// and accessed from here via a hook.
for (SDNode *N = SU->getNode(); N; N = N->getGluedNode()) {
if (N->isMachineOpcode()) {
const MCInstrDesc &TID = TII->get(N->getMachineOpcode());
if (TID.isCall())
ResCount += (PriorityThree + (ScaleThree*N->getNumValues()));
}
else
switch (N->getOpcode()) {
default: break;
case ISD::TokenFactor:
case ISD::CopyFromReg:
case ISD::CopyToReg:
ResCount += PriorityFive;
break;
case ISD::INLINEASM:
ResCount += PriorityFour;
break;
}
}
return ResCount;
}
/// Main resource tracking point.
void ResourcePriorityQueue::scheduledNode(SUnit *SU) {
// Use NULL entry as an event marker to reset
// the DFA state.
if (!SU) {
ResourcesModel->clearResources();
Packet.clear();
return;
}
const SDNode *ScegN = SU->getNode();
// Update reg pressure tracking.
// First update current node.
if (ScegN->isMachineOpcode()) {
// Estimate generated regs.
for (unsigned i = 0, e = ScegN->getNumValues(); i != e; ++i) {
EVT VT = ScegN->getValueType(i);
if (TLI->isTypeLegal(VT)) {
const TargetRegisterClass *RC = TLI->getRegClassFor(VT);
if (RC)
RegPressure[RC->getID()] += numberRCValSuccInSU(SU, RC->getID());
}
}
// Estimate killed regs.
for (unsigned i = 0, e = ScegN->getNumOperands(); i != e; ++i) {
const SDValue &Op = ScegN->getOperand(i);
EVT VT = Op.getNode()->getValueType(Op.getResNo());
if (TLI->isTypeLegal(VT)) {
const TargetRegisterClass *RC = TLI->getRegClassFor(VT);
if (RC) {
if (RegPressure[RC->getID()] >
(numberRCValPredInSU(SU, RC->getID())))
RegPressure[RC->getID()] -= numberRCValPredInSU(SU, RC->getID());
else RegPressure[RC->getID()] = 0;
}
}
}
for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
if (I->isCtrl() || (I->getSUnit()->NumRegDefsLeft == 0))
continue;
--I->getSUnit()->NumRegDefsLeft;
}
}
// Reserve resources for this SU.
reserveResources(SU);
// Adjust number of parallel live ranges.
// Heuristic is simple - node with no data successors reduces
// number of live ranges. All others, increase it.
unsigned NumberNonControlDeps = 0;
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
adjustPriorityOfUnscheduledPreds(I->getSUnit());
if (!I->isCtrl())
NumberNonControlDeps++;
}
if (!NumberNonControlDeps) {
if (ParallelLiveRanges >= SU->NumPreds)
ParallelLiveRanges -= SU->NumPreds;
else
ParallelLiveRanges = 0;
}
else
ParallelLiveRanges += SU->NumRegDefsLeft;
// Track parallel live chains.
HorizontalVerticalBalance += (SU->Succs.size() - numberCtrlDepsInSU(SU));
HorizontalVerticalBalance -= (SU->Preds.size() - numberCtrlPredInSU(SU));
}
void ResourcePriorityQueue::initNumRegDefsLeft(SUnit *SU) {
unsigned NodeNumDefs = 0;
for (SDNode *N = SU->getNode(); N; N = N->getGluedNode())
if (N->isMachineOpcode()) {
const MCInstrDesc &TID = TII->get(N->getMachineOpcode());
// No register need be allocated for this.
if (N->getMachineOpcode() == TargetOpcode::IMPLICIT_DEF) {
NodeNumDefs = 0;
break;
}
NodeNumDefs = std::min(N->getNumValues(), TID.getNumDefs());
}
else
switch(N->getOpcode()) {
default: break;
case ISD::CopyFromReg:
NodeNumDefs++;
break;
case ISD::INLINEASM:
NodeNumDefs++;
break;
}
SU->NumRegDefsLeft = NodeNumDefs;
}
/// 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 ResourcePriorityQueue::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);
}
/// Main access point - returns next instructions
/// to be placed in scheduling sequence.
SUnit *ResourcePriorityQueue::pop() {
if (empty())
return 0;
std::vector<SUnit *>::iterator Best = Queue.begin();
if (!DisableDFASched) {
signed BestCost = SUSchedulingCost(*Best);
for (std::vector<SUnit *>::iterator I = Queue.begin(),
E = Queue.end(); I != E; ++I) {
if (*I == *Best)
continue;
if (SUSchedulingCost(*I) > BestCost) {
BestCost = SUSchedulingCost(*I);
Best = I;
}
}
}
// Use default TD scheduling mechanism.
else {
for (std::vector<SUnit *>::iterator I = llvm::next(Queue.begin()),
E = Queue.end(); I != E; ++I)
if (Picker(*Best, *I))
Best = I;
}
SUnit *V = *Best;
if (Best != prior(Queue.end()))
std::swap(*Best, Queue.back());
Queue.pop_back();
return V;
}
void ResourcePriorityQueue::remove(SUnit *SU) {
assert(!Queue.empty() && "Queue is empty!");
std::vector<SUnit *>::iterator I = std::find(Queue.begin(), Queue.end(), SU);
if (I != prior(Queue.end()))
std::swap(*I, Queue.back());
Queue.pop_back();
}
#ifdef NDEBUG
void ResourcePriorityQueue::dump(ScheduleDAG *DAG) const {}
#else
void ResourcePriorityQueue::dump(ScheduleDAG *DAG) const {
ResourcePriorityQueue q = *this;
while (!q.empty()) {
SUnit *su = q.pop();
dbgs() << "Height " << su->getHeight() << ": ";
su->dump(DAG);
}
}
#endif
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