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llvm-mirror/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
Dan Gohman 521cee6a9c Add support for building a ScheduleDAG from MachineInstrs. This is currently 
fairly conservative; it doesn't do alias-analysis queries and it doesn't
attempt to break anti-dependencies.

llvm-svn: 59324
2008-11-14 21:47:58 +00:00

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//===---- 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"
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();
}
/// CheckForPhysRegDependency - Check if the dependency between def and use of
/// a specified operand is a physical register dependency. If so, returns the
/// register and the cost of copying the register.
static void CheckForPhysRegDependency(SDNode *Def, SDNode *User, unsigned Op,
const TargetRegisterInfo *TRI,
const TargetInstrInfo *TII,
unsigned &PhysReg, int &Cost) {
if (Op != 2 || User->getOpcode() != ISD::CopyToReg)
return;
unsigned Reg = cast<RegisterSDNode>(User->getOperand(1))->getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg))
return;
unsigned ResNo = User->getOperand(2).getResNo();
if (Def->isMachineOpcode()) {
const TargetInstrDesc &II = TII->get(Def->getMachineOpcode());
if (ResNo >= II.getNumDefs() &&
II.ImplicitDefs[ResNo - II.getNumDefs()] == Reg) {
PhysReg = Reg;
const TargetRegisterClass *RC =
TRI->getPhysicalRegisterRegClass(Reg, Def->getValueType(ResNo));
Cost = RC->getCopyCost();
}
}
}
SUnit *ScheduleDAG::Clone(SUnit *Old) {
SUnit *SU = NewSUnit(Old->getNode());
SU->OrigNode = Old->OrigNode;
SU->Latency = Old->Latency;
SU->isTwoAddress = Old->isTwoAddress;
SU->isCommutable = Old->isCommutable;
SU->hasPhysRegDefs = Old->hasPhysRegDefs;
return SU;
}
/// BuildSchedUnits - Build SUnits from the selection dag that we are input.
/// This SUnit graph is similar to the SelectionDAG, but represents flagged
/// together nodes with a single SUnit.
void ScheduleDAG::BuildSchedUnits() {
// For post-regalloc scheduling, build the SUnits from the MachineInstrs
// in the MachineBasicBlock.
if (!DAG) {
BuildSchedUnitsFromMBB();
return;
}
// Reserve entries in the vector for each of the SUnits we are creating. This
// ensure that reallocation of the vector won't happen, so SUnit*'s won't get
// invalidated.
SUnits.reserve(DAG->allnodes_size());
// During scheduling, the NodeId field of SDNode is used to map SDNodes
// to their associated SUnits by holding SUnits table indices. A value
// of -1 means the SDNode does not yet have an associated SUnit.
for (SelectionDAG::allnodes_iterator NI = DAG->allnodes_begin(),
E = DAG->allnodes_end(); NI != E; ++NI)
NI->setNodeId(-1);
for (SelectionDAG::allnodes_iterator NI = DAG->allnodes_begin(),
E = DAG->allnodes_end(); NI != E; ++NI) {
if (isPassiveNode(NI)) // Leaf node, e.g. a TargetImmediate.
continue;
// If this node has already been processed, stop now.
if (NI->getNodeId() != -1) continue;
SUnit *NodeSUnit = NewSUnit(NI);
// See if anything is flagged to this node, if so, add them to flagged
// nodes. Nodes can have at most one flag input and one flag output. Flags
// are required the be the last operand and result of a node.
// Scan up to find flagged preds.
SDNode *N = NI;
if (N->getNumOperands() &&
N->getOperand(N->getNumOperands()-1).getValueType() == MVT::Flag) {
do {
N = N->getOperand(N->getNumOperands()-1).getNode();
assert(N->getNodeId() == -1 && "Node already inserted!");
N->setNodeId(NodeSUnit->NodeNum);
} while (N->getNumOperands() &&
N->getOperand(N->getNumOperands()-1).getValueType()== MVT::Flag);
}
// Scan down to find any flagged succs.
N = NI;
while (N->getValueType(N->getNumValues()-1) == MVT::Flag) {
SDValue FlagVal(N, N->getNumValues()-1);
// There are either zero or one users of the Flag result.
bool HasFlagUse = false;
for (SDNode::use_iterator UI = N->use_begin(), E = N->use_end();
UI != E; ++UI)
if (FlagVal.isOperandOf(*UI)) {
HasFlagUse = true;
assert(N->getNodeId() == -1 && "Node already inserted!");
N->setNodeId(NodeSUnit->NodeNum);
N = *UI;
break;
}
if (!HasFlagUse) break;
}
// If there are flag operands involved, N is now the bottom-most node
// of the sequence of nodes that are flagged together.
// Update the SUnit.
NodeSUnit->setNode(N);
assert(N->getNodeId() == -1 && "Node already inserted!");
N->setNodeId(NodeSUnit->NodeNum);
ComputeLatency(NodeSUnit);
}
// Pass 2: add the preds, succs, etc.
for (unsigned su = 0, e = SUnits.size(); su != e; ++su) {
SUnit *SU = &SUnits[su];
SDNode *MainNode = SU->getNode();
if (MainNode->isMachineOpcode()) {
unsigned Opc = MainNode->getMachineOpcode();
const TargetInstrDesc &TID = TII->get(Opc);
for (unsigned i = 0; i != TID.getNumOperands(); ++i) {
if (TID.getOperandConstraint(i, TOI::TIED_TO) != -1) {
SU->isTwoAddress = true;
break;
}
}
if (TID.isCommutable())
SU->isCommutable = true;
}
// Find all predecessors and successors of the group.
for (SDNode *N = SU->getNode(); N; N = N->getFlaggedNode()) {
if (N->isMachineOpcode() &&
TII->get(N->getMachineOpcode()).getImplicitDefs() &&
CountResults(N) > TII->get(N->getMachineOpcode()).getNumDefs())
SU->hasPhysRegDefs = true;
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
SDNode *OpN = N->getOperand(i).getNode();
if (isPassiveNode(OpN)) continue; // Not scheduled.
SUnit *OpSU = &SUnits[OpN->getNodeId()];
assert(OpSU && "Node has no SUnit!");
if (OpSU == SU) continue; // In the same group.
MVT OpVT = N->getOperand(i).getValueType();
assert(OpVT != MVT::Flag && "Flagged nodes should be in same sunit!");
bool isChain = OpVT == MVT::Other;
unsigned PhysReg = 0;
int Cost = 1;
// Determine if this is a physical register dependency.
CheckForPhysRegDependency(OpN, N, i, TRI, TII, PhysReg, Cost);
SU->addPred(OpSU, isChain, false, PhysReg, Cost);
}
}
}
}
void ScheduleDAG::BuildSchedUnitsFromMBB() {
SUnits.clear();
SUnits.reserve(BB->size());
std::vector<SUnit *> PendingLoads;
SUnit *Terminator = 0;
SUnit *Chain = 0;
SUnit *Defs[TargetRegisterInfo::FirstVirtualRegister] = {};
std::vector<SUnit *> Uses[TargetRegisterInfo::FirstVirtualRegister] = {};
int Cost = 1; // FIXME
for (MachineBasicBlock::iterator MII = BB->end(), MIE = BB->begin();
MII != MIE; --MII) {
MachineInstr *MI = prior(MII);
SUnit *SU = NewSUnit(MI);
for (unsigned j = 0, n = MI->getNumOperands(); j != n; ++j) {
const MachineOperand &MO = MI->getOperand(j);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (Reg == 0) continue;
assert(TRI->isPhysicalRegister(Reg) && "Virtual register encountered!");
std::vector<SUnit *> &UseList = Uses[Reg];
SUnit *&Def = Defs[Reg];
// Optionally add output and anti dependences
if (Def && Def != SU)
Def->addPred(SU, /*isCtrl=*/true, /*isSpecial=*/false,
/*PhyReg=*/Reg, Cost);
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
SUnit *&Def = Defs[*Alias];
if (Def && Def != SU)
Def->addPred(SU, /*isCtrl=*/true, /*isSpecial=*/false,
/*PhyReg=*/*Alias, Cost);
}
if (MO.isDef()) {
// Add any data dependencies.
for (unsigned i = 0, e = UseList.size(); i != e; ++i)
if (UseList[i] != SU)
UseList[i]->addPred(SU, /*isCtrl=*/false, /*isSpecial=*/false,
/*PhysReg=*/Reg, Cost);
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
std::vector<SUnit *> &UseList = Uses[*Alias];
for (unsigned i = 0, e = UseList.size(); i != e; ++i)
if (UseList[i] != SU)
UseList[i]->addPred(SU, /*isCtrl=*/false, /*isSpecial=*/false,
/*PhysReg=*/*Alias, Cost);
}
UseList.clear();
Def = SU;
} else {
UseList.push_back(SU);
}
}
bool False = false;
bool True = true;
if (!MI->isSafeToMove(TII, False)) {
if (Chain)
Chain->addPred(SU, /*isCtrl=*/false, /*isSpecial=*/false);
for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
PendingLoads[k]->addPred(SU, /*isCtrl=*/false, /*isSpecial=*/false);
PendingLoads.clear();
Chain = SU;
} else if (!MI->isSafeToMove(TII, True)) {
if (Chain)
Chain->addPred(SU, /*isCtrl=*/false, /*isSpecial=*/false);
PendingLoads.push_back(SU);
}
if (Terminator && SU->Succs.empty())
Terminator->addPred(SU, /*isCtrl=*/false, /*isSpecial=*/false);
if (MI->getDesc().isTerminator())
Terminator = SU;
}
}
void ScheduleDAG::ComputeLatency(SUnit *SU) {
const InstrItineraryData &InstrItins = TM.getInstrItineraryData();
// Compute the latency for the node. We use the sum of the latencies for
// all nodes flagged together into this SUnit.
if (InstrItins.isEmpty()) {
// No latency information.
SU->Latency = 1;
return;
}
SU->Latency = 0;
for (SDNode *N = SU->getNode(); N; N = N->getFlaggedNode()) {
if (N->isMachineOpcode()) {
unsigned SchedClass = TII->get(N->getMachineOpcode()).getSchedClass();
const InstrStage *S = InstrItins.begin(SchedClass);
const InstrStage *E = InstrItins.end(SchedClass);
for (; S != E; ++S)
SU->Latency += S->Cycles;
}
}
}
/// 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->Dep->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->Dep;
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->Dep->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->Dep;
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);
}
}
}
/// CountResults - The results of target nodes have register or immediate
/// operands first, then an optional chain, and optional flag operands (which do
/// not go into the resulting MachineInstr).
unsigned ScheduleDAG::CountResults(SDNode *Node) {
unsigned N = Node->getNumValues();
while (N && Node->getValueType(N - 1) == MVT::Flag)
--N;
if (N && Node->getValueType(N - 1) == MVT::Other)
--N; // Skip over chain result.
return N;
}
/// CountOperands - The inputs to target nodes have any actual inputs first,
/// followed by special operands that describe memory references, then an
/// optional chain operand, then an optional flag operand. Compute the number
/// of actual operands that will go into the resulting MachineInstr.
unsigned ScheduleDAG::CountOperands(SDNode *Node) {
unsigned N = ComputeMemOperandsEnd(Node);
while (N && isa<MemOperandSDNode>(Node->getOperand(N - 1).getNode()))
--N; // Ignore MEMOPERAND nodes
return N;
}
/// ComputeMemOperandsEnd - Find the index one past the last MemOperandSDNode
/// operand
unsigned ScheduleDAG::ComputeMemOperandsEnd(SDNode *Node) {
unsigned N = Node->getNumOperands();
while (N && Node->getOperand(N - 1).getValueType() == MVT::Flag)
--N;
if (N && Node->getOperand(N - 1).getValueType() == MVT::Other)
--N; // Ignore chain if it exists.
return N;
}
/// 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(DAG);
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 SelectionDAG *G) const {
cerr << "SU(" << NodeNum << "): ";
if (getNode())
getNode()->dump(G);
else
cerr << "CROSS RC COPY ";
cerr << "\n";
SmallVector<SDNode *, 4> FlaggedNodes;
for (SDNode *N = getNode()->getFlaggedNode(); N; N = N->getFlaggedNode())
FlaggedNodes.push_back(N);
while (!FlaggedNodes.empty()) {
cerr << " ";
FlaggedNodes.back()->dump(G);
cerr << "\n";
FlaggedNodes.pop_back();
}
}
void SUnit::dumpAll(const SelectionDAG *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) {
if (I->isCtrl)
cerr << " ch #";
else
cerr << " val #";
cerr << I->Dep << " - SU(" << I->Dep->NodeNum << ")";
if (I->isSpecial)
cerr << " *";
cerr << "\n";
}
}
if (Succs.size() != 0) {
cerr << " Successors:\n";
for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
I != E; ++I) {
if (I->isCtrl)
cerr << " ch #";
else
cerr << " val #";
cerr << I->Dep << " - SU(" << I->Dep->NodeNum << ")";
if (I->isSpecial)
cerr << " *";
cerr << "\n";
}
}
cerr << "\n";
}
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