llvm-6502/lib/CodeGen/ScheduleDAG.cpp
Dan Gohman 54e4c36a73 Rewrite the SDep class, and simplify some of the related code.
The Cost field is removed. It was only being used in a very limited way,
to indicate when the scheduler should attempt to protect a live register,
and it isn't really needed to do that. If we ever want the scheduler to
start inserting copies in non-prohibitive situations, we'll have to
rethink some things anyway.

A Latency field is added. Instead of giving each node a single
fixed latency, each edge can have its own latency. This will eventually
be used to model various micro-architecture properties more accurately.

The PointerIntPair class and an internal union are now used, which
reduce the overall size.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60806 91177308-0d34-0410-b5e6-96231b3b80d8
2008-12-09 22:54:47 +00:00

478 lines
15 KiB
C++

//===---- ScheduleDAG.cpp - Implement the ScheduleDAG class ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements the ScheduleDAG class, which is a base class used by
// scheduling implementation classes.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "pre-RA-sched"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include <climits>
using namespace llvm;
ScheduleDAG::ScheduleDAG(SelectionDAG *dag, MachineBasicBlock *bb,
const TargetMachine &tm)
: DAG(dag), BB(bb), TM(tm), MRI(BB->getParent()->getRegInfo()) {
TII = TM.getInstrInfo();
MF = BB->getParent();
TRI = TM.getRegisterInfo();
TLI = TM.getTargetLowering();
ConstPool = MF->getConstantPool();
}
ScheduleDAG::~ScheduleDAG() {}
/// CalculateDepths - compute depths using algorithms for the longest
/// paths in the DAG
void ScheduleDAG::CalculateDepths() {
unsigned DAGSize = SUnits.size();
std::vector<SUnit*> WorkList;
WorkList.reserve(DAGSize);
// Initialize the data structures
for (unsigned i = 0, e = DAGSize; i != e; ++i) {
SUnit *SU = &SUnits[i];
unsigned Degree = SU->Preds.size();
// Temporarily use the Depth field as scratch space for the degree count.
SU->Depth = Degree;
// Is it a node without dependencies?
if (Degree == 0) {
assert(SU->Preds.empty() && "SUnit should have no predecessors");
// Collect leaf nodes
WorkList.push_back(SU);
}
}
// Process nodes in the topological order
while (!WorkList.empty()) {
SUnit *SU = WorkList.back();
WorkList.pop_back();
unsigned SUDepth = 0;
// Use dynamic programming:
// When current node is being processed, all of its dependencies
// are already processed.
// So, just iterate over all predecessors and take the longest path
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
unsigned PredDepth = I->getSUnit()->Depth;
if (PredDepth+1 > SUDepth) {
SUDepth = PredDepth + 1;
}
}
SU->Depth = SUDepth;
// Update degrees of all nodes depending on current SUnit
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
SUnit *SU = I->getSUnit();
if (!--SU->Depth)
// If all dependencies of the node are processed already,
// then the longest path for the node can be computed now
WorkList.push_back(SU);
}
}
}
/// CalculateHeights - compute heights using algorithms for the longest
/// paths in the DAG
void ScheduleDAG::CalculateHeights() {
unsigned DAGSize = SUnits.size();
std::vector<SUnit*> WorkList;
WorkList.reserve(DAGSize);
// Initialize the data structures
for (unsigned i = 0, e = DAGSize; i != e; ++i) {
SUnit *SU = &SUnits[i];
unsigned Degree = SU->Succs.size();
// Temporarily use the Height field as scratch space for the degree count.
SU->Height = Degree;
// Is it a node without dependencies?
if (Degree == 0) {
assert(SU->Succs.empty() && "Something wrong");
assert(WorkList.empty() && "Should be empty");
// Collect leaf nodes
WorkList.push_back(SU);
}
}
// Process nodes in the topological order
while (!WorkList.empty()) {
SUnit *SU = WorkList.back();
WorkList.pop_back();
unsigned SUHeight = 0;
// Use dynamic programming:
// When current node is being processed, all of its dependencies
// are already processed.
// So, just iterate over all successors and take the longest path
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
unsigned SuccHeight = I->getSUnit()->Height;
if (SuccHeight+1 > SUHeight) {
SUHeight = SuccHeight + 1;
}
}
SU->Height = SUHeight;
// Update degrees of all nodes depending on current SUnit
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
SUnit *SU = I->getSUnit();
if (!--SU->Height)
// If all dependencies of the node are processed already,
// then the longest path for the node can be computed now
WorkList.push_back(SU);
}
}
}
/// dump - dump the schedule.
void ScheduleDAG::dumpSchedule() const {
for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
if (SUnit *SU = Sequence[i])
SU->dump(this);
else
cerr << "**** NOOP ****\n";
}
}
/// Run - perform scheduling.
///
void ScheduleDAG::Run() {
Schedule();
DOUT << "*** Final schedule ***\n";
DEBUG(dumpSchedule());
DOUT << "\n";
}
/// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
/// a group of nodes flagged together.
void SUnit::dump(const ScheduleDAG *G) const {
cerr << "SU(" << NodeNum << "): ";
G->dumpNode(this);
}
void SUnit::dumpAll(const ScheduleDAG *G) const {
dump(G);
cerr << " # preds left : " << NumPredsLeft << "\n";
cerr << " # succs left : " << NumSuccsLeft << "\n";
cerr << " Latency : " << Latency << "\n";
cerr << " Depth : " << Depth << "\n";
cerr << " Height : " << Height << "\n";
if (Preds.size() != 0) {
cerr << " Predecessors:\n";
for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
I != E; ++I) {
cerr << " ";
switch (I->getKind()) {
case SDep::Data: cerr << "val "; break;
case SDep::Anti: cerr << "anti"; break;
case SDep::Output: cerr << "out "; break;
case SDep::Order: cerr << "ch "; break;
}
cerr << "#";
cerr << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
if (I->isArtificial())
cerr << " *";
cerr << "\n";
}
}
if (Succs.size() != 0) {
cerr << " Successors:\n";
for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
I != E; ++I) {
cerr << " ";
switch (I->getKind()) {
case SDep::Data: cerr << "val "; break;
case SDep::Anti: cerr << "anti"; break;
case SDep::Output: cerr << "out "; break;
case SDep::Order: cerr << "ch "; break;
}
cerr << "#";
cerr << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
if (I->isArtificial())
cerr << " *";
cerr << "\n";
}
}
cerr << "\n";
}
#ifndef NDEBUG
/// VerifySchedule - Verify that all SUnits were scheduled and that
/// their state is consistent.
///
void ScheduleDAG::VerifySchedule(bool isBottomUp) {
bool AnyNotSched = false;
unsigned DeadNodes = 0;
unsigned Noops = 0;
for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
if (!SUnits[i].isScheduled) {
if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
++DeadNodes;
continue;
}
if (!AnyNotSched)
cerr << "*** Scheduling failed! ***\n";
SUnits[i].dump(this);
cerr << "has not been scheduled!\n";
AnyNotSched = true;
}
if (SUnits[i].isScheduled && SUnits[i].Cycle > (unsigned)INT_MAX) {
if (!AnyNotSched)
cerr << "*** Scheduling failed! ***\n";
SUnits[i].dump(this);
cerr << "has an unexpected Cycle value!\n";
AnyNotSched = true;
}
if (isBottomUp) {
if (SUnits[i].NumSuccsLeft != 0) {
if (!AnyNotSched)
cerr << "*** Scheduling failed! ***\n";
SUnits[i].dump(this);
cerr << "has successors left!\n";
AnyNotSched = true;
}
} else {
if (SUnits[i].NumPredsLeft != 0) {
if (!AnyNotSched)
cerr << "*** Scheduling failed! ***\n";
SUnits[i].dump(this);
cerr << "has predecessors left!\n";
AnyNotSched = true;
}
}
}
for (unsigned i = 0, e = Sequence.size(); i != e; ++i)
if (!Sequence[i])
++Noops;
assert(!AnyNotSched);
assert(Sequence.size() + DeadNodes - Noops == SUnits.size() &&
"The number of nodes scheduled doesn't match the expected number!");
}
#endif
/// InitDAGTopologicalSorting - create the initial topological
/// ordering from the DAG to be scheduled.
///
/// 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.
void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
unsigned DAGSize = SUnits.size();
std::vector<SUnit*> WorkList;
WorkList.reserve(DAGSize);
Index2Node.resize(DAGSize);
Node2Index.resize(DAGSize);
// Initialize the data structures.
for (unsigned i = 0, e = DAGSize; i != e; ++i) {
SUnit *SU = &SUnits[i];
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();
Allocate(SU->NodeNum, --Id);
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
SUnit *SU = I->getSUnit();
if (!--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);
#ifndef NDEBUG
// Check correctness of the ordering
for (unsigned i = 0, e = DAGSize; i != e; ++i) {
SUnit *SU = &SUnits[i];
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
"Wrong topological sorting");
}
}
#endif
}
/// AddPred - Updates the topological ordering to accomodate an edge
/// to be added from SUnit X to SUnit Y.
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);
}
}
/// RemovePred - Updates the topological ordering to accomodate an
/// an edge to be removed from the specified node N from the predecessors
/// of the current node M.
void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
// InitDAGTopologicalSorting();
}
/// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
/// all nodes affected by the edge insertion. These nodes will later get new
/// topological indexes by means of the Shift method.
void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
bool& HasLoop) {
std::vector<const SUnit*> WorkList;
WorkList.reserve(SUnits.size());
WorkList.push_back(SU);
while (!WorkList.empty()) {
SU = WorkList.back();
WorkList.pop_back();
Visited.set(SU->NodeNum);
for (int I = SU->Succs.size()-1; I >= 0; --I) {
int s = SU->Succs[I].getSUnit()->NodeNum;
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(SU->Succs[I].getSUnit());
}
}
}
}
/// Shift - Renumber the nodes so that the topological ordering is
/// preserved.
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 j = 0; j < L.size(); ++j) {
Allocate(L[j], i - shift);
i = i + 1;
}
}
/// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
/// create a cycle.
bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
if (IsReachable(TargetSU, SU))
return true;
for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I)
if (I->isAssignedRegDep() &&
IsReachable(TargetSU, I->getSUnit()))
return true;
return false;
}
/// IsReachable - Checks if SU is reachable from TargetSU.
bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
const SUnit *TargetSU) {
// 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;
}
/// Allocate - assign the topological index to the node n.
void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
Node2Index[n] = index;
Index2Node[index] = n;
}
ScheduleDAGTopologicalSort::ScheduleDAGTopologicalSort(
std::vector<SUnit> &sunits)
: SUnits(sunits) {}