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llvm-project/llvm/lib/CodeGen/ScheduleDAG.cpp

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//===- ScheduleDAG.cpp - Implement the ScheduleDAG class ------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// \file Implements the ScheduleDAG class, which is a base class used by
/// scheduling implementation classes.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
#include "llvm/CodeGen/SelectionDAGNodes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <iterator>
#include <limits>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "pre-RA-sched"
STATISTIC(NumNewPredsAdded, "Number of times a single predecessor was added");
STATISTIC(NumTopoInits,
"Number of times the topological order has been recomputed");
#ifndef NDEBUG
static cl::opt<bool> StressSchedOpt(
"stress-sched", cl::Hidden, cl::init(false),
cl::desc("Stress test instruction scheduling"));
#endif
void SchedulingPriorityQueue::anchor() {}
ScheduleDAG::ScheduleDAG(MachineFunction &mf)
: TM(mf.getTarget()), TII(mf.getSubtarget().getInstrInfo()),
TRI(mf.getSubtarget().getRegisterInfo()), MF(mf),
MRI(mf.getRegInfo()) {
#ifndef NDEBUG
StressSched = StressSchedOpt;
#endif
}
ScheduleDAG::~ScheduleDAG() = default;
void ScheduleDAG::clearDAG() {
SUnits.clear();
EntrySU = SUnit();
ExitSU = SUnit();
}
const MCInstrDesc *ScheduleDAG::getNodeDesc(const SDNode *Node) const {
if (!Node || !Node->isMachineOpcode()) return nullptr;
return &TII->get(Node->getMachineOpcode());
}
LLVM_DUMP_METHOD void SDep::dump(const TargetRegisterInfo *TRI) const {
switch (getKind()) {
case Data: dbgs() << "Data"; break;
case Anti: dbgs() << "Anti"; break;
case Output: dbgs() << "Out "; break;
case Order: dbgs() << "Ord "; break;
}
switch (getKind()) {
case Data:
dbgs() << " Latency=" << getLatency();
if (TRI && isAssignedRegDep())
dbgs() << " Reg=" << printReg(getReg(), TRI);
break;
case Anti:
case Output:
dbgs() << " Latency=" << getLatency();
break;
case Order:
dbgs() << " Latency=" << getLatency();
switch(Contents.OrdKind) {
case Barrier: dbgs() << " Barrier"; break;
case MayAliasMem:
case MustAliasMem: dbgs() << " Memory"; break;
case Artificial: dbgs() << " Artificial"; break;
case Weak: dbgs() << " Weak"; break;
case Cluster: dbgs() << " Cluster"; break;
}
break;
}
}
bool SUnit::addPred(const SDep &D, bool Required) {
// If this node already has this dependence, don't add a redundant one.
for (SDep &PredDep : Preds) {
// Zero-latency weak edges may be added purely for heuristic ordering. Don't
// add them if another kind of edge already exists.
if (!Required && PredDep.getSUnit() == D.getSUnit())
return false;
if (PredDep.overlaps(D)) {
// Extend the latency if needed. Equivalent to
// removePred(PredDep) + addPred(D).
if (PredDep.getLatency() < D.getLatency()) {
SUnit *PredSU = PredDep.getSUnit();
// Find the corresponding successor in N.
SDep ForwardD = PredDep;
ForwardD.setSUnit(this);
for (SDep &SuccDep : PredSU->Succs) {
if (SuccDep == ForwardD) {
SuccDep.setLatency(D.getLatency());
break;
}
}
PredDep.setLatency(D.getLatency());
}
return false;
}
}
// Now add a corresponding succ to N.
SDep P = D;
P.setSUnit(this);
SUnit *N = D.getSUnit();
// Update the bookkeeping.
if (D.getKind() == SDep::Data) {
assert(NumPreds < std::numeric_limits<unsigned>::max() &&
"NumPreds will overflow!");
assert(N->NumSuccs < std::numeric_limits<unsigned>::max() &&
"NumSuccs will overflow!");
++NumPreds;
++N->NumSuccs;
}
if (!N->isScheduled) {
if (D.isWeak()) {
++WeakPredsLeft;
}
else {
assert(NumPredsLeft < std::numeric_limits<unsigned>::max() &&
"NumPredsLeft will overflow!");
++NumPredsLeft;
}
}
if (!isScheduled) {
if (D.isWeak()) {
++N->WeakSuccsLeft;
}
else {
assert(N->NumSuccsLeft < std::numeric_limits<unsigned>::max() &&
"NumSuccsLeft will overflow!");
++N->NumSuccsLeft;
}
}
Preds.push_back(D);
N->Succs.push_back(P);
if (P.getLatency() != 0) {
this->setDepthDirty();
N->setHeightDirty();
}
return true;
}
void SUnit::removePred(const SDep &D) {
// Find the matching predecessor.
SmallVectorImpl<SDep>::iterator I = llvm::find(Preds, D);
if (I == Preds.end())
return;
// Find the corresponding successor in N.
SDep P = D;
P.setSUnit(this);
SUnit *N = D.getSUnit();
SmallVectorImpl<SDep>::iterator Succ = llvm::find(N->Succs, P);
assert(Succ != N->Succs.end() && "Mismatching preds / succs lists!");
N->Succs.erase(Succ);
Preds.erase(I);
// Update the bookkeeping.
if (P.getKind() == SDep::Data) {
assert(NumPreds > 0 && "NumPreds will underflow!");
assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
--NumPreds;
--N->NumSuccs;
}
if (!N->isScheduled) {
if (D.isWeak())
--WeakPredsLeft;
else {
assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
--NumPredsLeft;
}
}
if (!isScheduled) {
if (D.isWeak())
--N->WeakSuccsLeft;
else {
assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
--N->NumSuccsLeft;
}
}
if (P.getLatency() != 0) {
this->setDepthDirty();
N->setHeightDirty();
}
}
void SUnit::setDepthDirty() {
if (!isDepthCurrent) return;
SmallVector<SUnit*, 8> WorkList;
WorkList.push_back(this);
do {
SUnit *SU = WorkList.pop_back_val();
SU->isDepthCurrent = false;
for (SDep &SuccDep : SU->Succs) {
SUnit *SuccSU = SuccDep.getSUnit();
if (SuccSU->isDepthCurrent)
WorkList.push_back(SuccSU);
}
} while (!WorkList.empty());
}
void SUnit::setHeightDirty() {
if (!isHeightCurrent) return;
SmallVector<SUnit*, 8> WorkList;
WorkList.push_back(this);
do {
SUnit *SU = WorkList.pop_back_val();
SU->isHeightCurrent = false;
for (SDep &PredDep : SU->Preds) {
SUnit *PredSU = PredDep.getSUnit();
if (PredSU->isHeightCurrent)
WorkList.push_back(PredSU);
}
} while (!WorkList.empty());
}
void SUnit::setDepthToAtLeast(unsigned NewDepth) {
if (NewDepth <= getDepth())
return;
setDepthDirty();
Depth = NewDepth;
isDepthCurrent = true;
}
void SUnit::setHeightToAtLeast(unsigned NewHeight) {
if (NewHeight <= getHeight())
return;
setHeightDirty();
Height = NewHeight;
isHeightCurrent = true;
}
/// Calculates the maximal path from the node to the exit.
void SUnit::ComputeDepth() {
SmallVector<SUnit*, 8> WorkList;
WorkList.push_back(this);
do {
SUnit *Cur = WorkList.back();
bool Done = true;
unsigned MaxPredDepth = 0;
for (const SDep &PredDep : Cur->Preds) {
SUnit *PredSU = PredDep.getSUnit();
if (PredSU->isDepthCurrent)
MaxPredDepth = std::max(MaxPredDepth,
PredSU->Depth + PredDep.getLatency());
else {
Done = false;
WorkList.push_back(PredSU);
}
}
if (Done) {
WorkList.pop_back();
if (MaxPredDepth != Cur->Depth) {
Cur->setDepthDirty();
Cur->Depth = MaxPredDepth;
}
Cur->isDepthCurrent = true;
}
} while (!WorkList.empty());
}
/// Calculates the maximal path from the node to the entry.
void SUnit::ComputeHeight() {
SmallVector<SUnit*, 8> WorkList;
WorkList.push_back(this);
do {
SUnit *Cur = WorkList.back();
bool Done = true;
unsigned MaxSuccHeight = 0;
for (const SDep &SuccDep : Cur->Succs) {
SUnit *SuccSU = SuccDep.getSUnit();
if (SuccSU->isHeightCurrent)
MaxSuccHeight = std::max(MaxSuccHeight,
SuccSU->Height + SuccDep.getLatency());
else {
Done = false;
WorkList.push_back(SuccSU);
}
}
if (Done) {
WorkList.pop_back();
if (MaxSuccHeight != Cur->Height) {
Cur->setHeightDirty();
Cur->Height = MaxSuccHeight;
}
Cur->isHeightCurrent = true;
}
} while (!WorkList.empty());
}
void SUnit::biasCriticalPath() {
if (NumPreds < 2)
return;
SUnit::pred_iterator BestI = Preds.begin();
unsigned MaxDepth = BestI->getSUnit()->getDepth();
for (SUnit::pred_iterator I = std::next(BestI), E = Preds.end(); I != E;
++I) {
if (I->getKind() == SDep::Data && I->getSUnit()->getDepth() > MaxDepth)
BestI = I;
}
if (BestI != Preds.begin())
std::swap(*Preds.begin(), *BestI);
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void SUnit::dumpAttributes() const {
dbgs() << " # preds left : " << NumPredsLeft << "\n";
dbgs() << " # succs left : " << NumSuccsLeft << "\n";
if (WeakPredsLeft)
dbgs() << " # weak preds left : " << WeakPredsLeft << "\n";
if (WeakSuccsLeft)
dbgs() << " # weak succs left : " << WeakSuccsLeft << "\n";
dbgs() << " # rdefs left : " << NumRegDefsLeft << "\n";
dbgs() << " Latency : " << Latency << "\n";
dbgs() << " Depth : " << getDepth() << "\n";
dbgs() << " Height : " << getHeight() << "\n";
}
LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeName(const SUnit &SU) const {
if (&SU == &EntrySU)
dbgs() << "EntrySU";
else if (&SU == &ExitSU)
dbgs() << "ExitSU";
else
dbgs() << "SU(" << SU.NodeNum << ")";
}
LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeAll(const SUnit &SU) const {
dumpNode(SU);
SU.dumpAttributes();
if (SU.Preds.size() > 0) {
dbgs() << " Predecessors:\n";
for (const SDep &Dep : SU.Preds) {
dbgs() << " ";
dumpNodeName(*Dep.getSUnit());
dbgs() << ": ";
Dep.dump(TRI);
dbgs() << '\n';
}
}
if (SU.Succs.size() > 0) {
dbgs() << " Successors:\n";
for (const SDep &Dep : SU.Succs) {
dbgs() << " ";
dumpNodeName(*Dep.getSUnit());
dbgs() << ": ";
Dep.dump(TRI);
dbgs() << '\n';
}
}
}
#endif
#ifndef NDEBUG
unsigned ScheduleDAG::VerifyScheduledDAG(bool isBottomUp) {
bool AnyNotSched = false;
unsigned DeadNodes = 0;
for (const SUnit &SUnit : SUnits) {
if (!SUnit.isScheduled) {
if (SUnit.NumPreds == 0 && SUnit.NumSuccs == 0) {
++DeadNodes;
continue;
}
if (!AnyNotSched)
dbgs() << "*** Scheduling failed! ***\n";
dumpNode(SUnit);
dbgs() << "has not been scheduled!\n";
AnyNotSched = true;
}
if (SUnit.isScheduled &&
(isBottomUp ? SUnit.getHeight() : SUnit.getDepth()) >
unsigned(std::numeric_limits<int>::max())) {
if (!AnyNotSched)
dbgs() << "*** Scheduling failed! ***\n";
dumpNode(SUnit);
dbgs() << "has an unexpected "
<< (isBottomUp ? "Height" : "Depth") << " value!\n";
AnyNotSched = true;
}
if (isBottomUp) {
if (SUnit.NumSuccsLeft != 0) {
if (!AnyNotSched)
dbgs() << "*** Scheduling failed! ***\n";
dumpNode(SUnit);
dbgs() << "has successors left!\n";
AnyNotSched = true;
}
} else {
if (SUnit.NumPredsLeft != 0) {
if (!AnyNotSched)
dbgs() << "*** Scheduling failed! ***\n";
dumpNode(SUnit);
dbgs() << "has predecessors left!\n";
AnyNotSched = true;
}
}
}
assert(!AnyNotSched);
return SUnits.size() - DeadNodes;
}
#endif
void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
// The idea of the algorithm is taken from
// "Online algorithms for managing the topological order of
// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
// This is the MNR algorithm, which was first introduced by
// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
// "Maintaining a topological order under edge insertions".
//
// Short description of the algorithm:
//
// Topological ordering, ord, of a DAG maps each node to a topological
// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
//
// This means that if there is a path from the node X to the node Z,
// then ord(X) < ord(Z).
//
// This property can be used to check for reachability of nodes:
// if Z is reachable from X, then an insertion of the edge Z->X would
// create a cycle.
//
// The algorithm first computes a topological ordering for the DAG by
// initializing the Index2Node and Node2Index arrays and then tries to keep
// the ordering up-to-date after edge insertions by reordering the DAG.
//
// On insertion of the edge X->Y, the algorithm first marks by calling DFS
// the nodes reachable from Y, and then shifts them using Shift to lie
// immediately after X in Index2Node.
// Cancel pending updates, mark as valid.
Dirty = false;
Updates.clear();
unsigned DAGSize = SUnits.size();
std::vector<SUnit*> WorkList;
WorkList.reserve(DAGSize);
Index2Node.resize(DAGSize);
Node2Index.resize(DAGSize);
// Initialize the data structures.
if (ExitSU)
WorkList.push_back(ExitSU);
for (SUnit &SU : SUnits) {
int NodeNum = SU.NodeNum;
unsigned Degree = SU.Succs.size();
// Temporarily use the Node2Index array as scratch space for degree counts.
Node2Index[NodeNum] = Degree;
// Is it a node without dependencies?
if (Degree == 0) {
assert(SU.Succs.empty() && "SUnit should have no successors");
// Collect leaf nodes.
WorkList.push_back(&SU);
}
}
int Id = DAGSize;
while (!WorkList.empty()) {
SUnit *SU = WorkList.back();
WorkList.pop_back();
if (SU->NodeNum < DAGSize)
Allocate(SU->NodeNum, --Id);
for (const SDep &PredDep : SU->Preds) {
SUnit *SU = PredDep.getSUnit();
if (SU->NodeNum < DAGSize && !--Node2Index[SU->NodeNum])
// If all dependencies of the node are processed already,
// then the node can be computed now.
WorkList.push_back(SU);
}
}
Visited.resize(DAGSize);
NumTopoInits++;
#ifndef NDEBUG
// Check correctness of the ordering
for (SUnit &SU : SUnits) {
for (const SDep &PD : SU.Preds) {
assert(Node2Index[SU.NodeNum] > Node2Index[PD.getSUnit()->NodeNum] &&
"Wrong topological sorting");
}
}
#endif
}
void ScheduleDAGTopologicalSort::FixOrder() {
// Recompute from scratch after new nodes have been added.
if (Dirty) {
InitDAGTopologicalSorting();
return;
}
// Otherwise apply updates one-by-one.
for (auto &U : Updates)
AddPred(U.first, U.second);
Updates.clear();
}
void ScheduleDAGTopologicalSort::AddPredQueued(SUnit *Y, SUnit *X) {
// Recomputing the order from scratch is likely more efficient than applying
// updates one-by-one for too many updates. The current cut-off is arbitrarily
// chosen.
Dirty = Dirty || Updates.size() > 10;
if (Dirty)
return;
Updates.emplace_back(Y, X);
}
void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
int UpperBound, LowerBound;
LowerBound = Node2Index[Y->NodeNum];
UpperBound = Node2Index[X->NodeNum];
bool HasLoop = false;
// Is Ord(X) < Ord(Y) ?
if (LowerBound < UpperBound) {
// Update the topological order.
Visited.reset();
DFS(Y, UpperBound, HasLoop);
assert(!HasLoop && "Inserted edge creates a loop!");
// Recompute topological indexes.
Shift(Visited, LowerBound, UpperBound);
}
NumNewPredsAdded++;
}
void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
// InitDAGTopologicalSorting();
}
void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
bool &HasLoop) {
std::vector<const SUnit*> WorkList;
WorkList.reserve(SUnits.size());
WorkList.push_back(SU);
do {
SU = WorkList.back();
WorkList.pop_back();
Visited.set(SU->NodeNum);
for (const SDep &SuccDep
: make_range(SU->Succs.rbegin(), SU->Succs.rend())) {
unsigned s = SuccDep.getSUnit()->NodeNum;
// Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
if (s >= Node2Index.size())
continue;
if (Node2Index[s] == UpperBound) {
HasLoop = true;
return;
}
// Visit successors if not already and in affected region.
if (!Visited.test(s) && Node2Index[s] < UpperBound) {
WorkList.push_back(SuccDep.getSUnit());
}
}
} while (!WorkList.empty());
}
std::vector<int> ScheduleDAGTopologicalSort::GetSubGraph(const SUnit &StartSU,
const SUnit &TargetSU,
bool &Success) {
std::vector<const SUnit*> WorkList;
int LowerBound = Node2Index[StartSU.NodeNum];
int UpperBound = Node2Index[TargetSU.NodeNum];
bool Found = false;
BitVector VisitedBack;
std::vector<int> Nodes;
if (LowerBound > UpperBound) {
Success = false;
return Nodes;
}
WorkList.reserve(SUnits.size());
Visited.reset();
// Starting from StartSU, visit all successors up
// to UpperBound.
WorkList.push_back(&StartSU);
do {
const SUnit *SU = WorkList.back();
WorkList.pop_back();
for (int I = SU->Succs.size()-1; I >= 0; --I) {
const SUnit *Succ = SU->Succs[I].getSUnit();
unsigned s = Succ->NodeNum;
// Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
if (Succ->isBoundaryNode())
continue;
if (Node2Index[s] == UpperBound) {
Found = true;
continue;
}
// Visit successors if not already and in affected region.
if (!Visited.test(s) && Node2Index[s] < UpperBound) {
Visited.set(s);
WorkList.push_back(Succ);
}
}
} while (!WorkList.empty());
if (!Found) {
Success = false;
return Nodes;
}
WorkList.clear();
VisitedBack.resize(SUnits.size());
Found = false;
// Starting from TargetSU, visit all predecessors up
// to LowerBound. SUs that are visited by the two
// passes are added to Nodes.
WorkList.push_back(&TargetSU);
do {
const SUnit *SU = WorkList.back();
WorkList.pop_back();
for (int I = SU->Preds.size()-1; I >= 0; --I) {
const SUnit *Pred = SU->Preds[I].getSUnit();
unsigned s = Pred->NodeNum;
// Edges to non-SUnits are allowed but ignored (e.g. EntrySU).
if (Pred->isBoundaryNode())
continue;
if (Node2Index[s] == LowerBound) {
Found = true;
continue;
}
if (!VisitedBack.test(s) && Visited.test(s)) {
VisitedBack.set(s);
WorkList.push_back(Pred);
Nodes.push_back(s);
}
}
} while (!WorkList.empty());
assert(Found && "Error in SUnit Graph!");
Success = true;
return Nodes;
}
void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
int UpperBound) {
std::vector<int> L;
int shift = 0;
int i;
for (i = LowerBound; i <= UpperBound; ++i) {
// w is node at topological index i.
int w = Index2Node[i];
if (Visited.test(w)) {
// Unmark.
Visited.reset(w);
L.push_back(w);
shift = shift + 1;
} else {
Allocate(w, i - shift);
}
}
for (unsigned LI : L) {
Allocate(LI, i - shift);
i = i + 1;
}
}
bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *TargetSU, SUnit *SU) {
FixOrder();
// Is SU reachable from TargetSU via successor edges?
if (IsReachable(SU, TargetSU))
return true;
for (const SDep &PredDep : TargetSU->Preds)
if (PredDep.isAssignedRegDep() &&
IsReachable(SU, PredDep.getSUnit()))
return true;
return false;
}
bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
const SUnit *TargetSU) {
FixOrder();
// If insertion of the edge SU->TargetSU would create a cycle
// then there is a path from TargetSU to SU.
int UpperBound, LowerBound;
LowerBound = Node2Index[TargetSU->NodeNum];
UpperBound = Node2Index[SU->NodeNum];
bool HasLoop = false;
// Is Ord(TargetSU) < Ord(SU) ?
if (LowerBound < UpperBound) {
Visited.reset();
// There may be a path from TargetSU to SU. Check for it.
DFS(TargetSU, UpperBound, HasLoop);
}
return HasLoop;
}
void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
Node2Index[n] = index;
Index2Node[index] = n;
}
ScheduleDAGTopologicalSort::
ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits, SUnit *exitsu)
: SUnits(sunits), ExitSU(exitsu) {}
ScheduleHazardRecognizer::~ScheduleHazardRecognizer() = default;
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