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llvm-mirror/lib/CodeGen/ScheduleDAGInstrs.cpp
Dan Gohman 5bfc2416fe Factor out LiveIntervalAnalysis' code to determine whether an instruction 
is trivially rematerializable and integrate it into
TargetInstrInfo::isTriviallyReMaterializable. This way, all places that
need to know whether an instruction is rematerializable will get the
same answer.

This enables the useful parts of the aggressive-remat option by
default -- using AliasAnalysis to determine whether a memory location
is invariant, and removes the questionable parts -- rematting operations
with virtual register inputs that may not be live everywhere.

llvm-svn: 83687
2009-10-09 23:27:56 +00:00

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//===---- ScheduleDAGInstrs.cpp - MachineInstr Rescheduling ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements the ScheduleDAGInstrs class, which implements re-scheduling
// of MachineInstrs.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sched-instrs"
#include "ScheduleDAGInstrs.h"
#include "llvm/Operator.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtarget.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallSet.h"
using namespace llvm;
ScheduleDAGInstrs::ScheduleDAGInstrs(MachineFunction &mf,
const MachineLoopInfo &mli,
const MachineDominatorTree &mdt)
: ScheduleDAG(mf), MLI(mli), MDT(mdt), LoopRegs(MLI, MDT) {}
/// Run - perform scheduling.
///
void ScheduleDAGInstrs::Run(MachineBasicBlock *bb,
MachineBasicBlock::iterator begin,
MachineBasicBlock::iterator end,
unsigned endcount) {
BB = bb;
Begin = begin;
InsertPosIndex = endcount;
ScheduleDAG::Run(bb, end);
}
/// getUnderlyingObjectFromInt - This is the function that does the work of
/// looking through basic ptrtoint+arithmetic+inttoptr sequences.
static const Value *getUnderlyingObjectFromInt(const Value *V) {
do {
if (const Operator *U = dyn_cast<Operator>(V)) {
// If we find a ptrtoint, we can transfer control back to the
// regular getUnderlyingObjectFromInt.
if (U->getOpcode() == Instruction::PtrToInt)
return U->getOperand(0);
// If we find an add of a constant or a multiplied value, it's
// likely that the other operand will lead us to the base
// object. We don't have to worry about the case where the
// object address is somehow being computed by the multiply,
// because our callers only care when the result is an
// identifibale object.
if (U->getOpcode() != Instruction::Add ||
(!isa<ConstantInt>(U->getOperand(1)) &&
Operator::getOpcode(U->getOperand(1)) != Instruction::Mul))
return V;
V = U->getOperand(0);
} else {
return V;
}
assert(isa<IntegerType>(V->getType()) && "Unexpected operand type!");
} while (1);
}
/// getUnderlyingObject - This is a wrapper around Value::getUnderlyingObject
/// and adds support for basic ptrtoint+arithmetic+inttoptr sequences.
static const Value *getUnderlyingObject(const Value *V) {
// First just call Value::getUnderlyingObject to let it do what it does.
do {
V = V->getUnderlyingObject();
// If it found an inttoptr, use special code to continue climing.
if (Operator::getOpcode(V) != Instruction::IntToPtr)
break;
const Value *O = getUnderlyingObjectFromInt(cast<User>(V)->getOperand(0));
// If that succeeded in finding a pointer, continue the search.
if (!isa<PointerType>(O->getType()))
break;
V = O;
} while (1);
return V;
}
/// getUnderlyingObjectForInstr - If this machine instr has memory reference
/// information and it can be tracked to a normal reference to a known
/// object, return the Value for that object. Otherwise return null.
static const Value *getUnderlyingObjectForInstr(const MachineInstr *MI) {
if (!MI->hasOneMemOperand() ||
!(*MI->memoperands_begin())->getValue() ||
(*MI->memoperands_begin())->isVolatile())
return 0;
const Value *V = (*MI->memoperands_begin())->getValue();
if (!V)
return 0;
V = getUnderlyingObject(V);
if (!isa<PseudoSourceValue>(V) && !isIdentifiedObject(V))
return 0;
return V;
}
void ScheduleDAGInstrs::StartBlock(MachineBasicBlock *BB) {
if (MachineLoop *ML = MLI.getLoopFor(BB))
if (BB == ML->getLoopLatch()) {
MachineBasicBlock *Header = ML->getHeader();
for (MachineBasicBlock::livein_iterator I = Header->livein_begin(),
E = Header->livein_end(); I != E; ++I)
LoopLiveInRegs.insert(*I);
LoopRegs.VisitLoop(ML);
}
}
void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
// We'll be allocating one SUnit for each instruction, plus one for
// the region exit node.
SUnits.reserve(BB->size());
// We build scheduling units by walking a block's instruction list from bottom
// to top.
// Remember where a generic side-effecting instruction is as we procede. If
// ChainMMO is null, this is assumed to have arbitrary side-effects. If
// ChainMMO is non-null, then Chain makes only a single memory reference.
SUnit *Chain = 0;
MachineMemOperand *ChainMMO = 0;
// Memory references to specific known memory locations are tracked so that
// they can be given more precise dependencies.
std::map<const Value *, SUnit *> MemDefs;
std::map<const Value *, std::vector<SUnit *> > MemUses;
// Check to see if the scheduler cares about latencies.
bool UnitLatencies = ForceUnitLatencies();
// Ask the target if address-backscheduling is desirable, and if so how much.
const TargetSubtarget &ST = TM.getSubtarget<TargetSubtarget>();
unsigned SpecialAddressLatency = ST.getSpecialAddressLatency();
// Walk the list of instructions, from bottom moving up.
for (MachineBasicBlock::iterator MII = InsertPos, MIE = Begin;
MII != MIE; --MII) {
MachineInstr *MI = prior(MII);
const TargetInstrDesc &TID = MI->getDesc();
assert(!TID.isTerminator() && !MI->isLabel() &&
"Cannot schedule terminators or labels!");
// Create the SUnit for this MI.
SUnit *SU = NewSUnit(MI);
// Assign the Latency field of SU using target-provided information.
if (UnitLatencies)
SU->Latency = 1;
else
ComputeLatency(SU);
// Add register-based dependencies (data, anti, and output).
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];
std::vector<SUnit *> &DefList = Defs[Reg];
// Optionally add output and anti dependencies. For anti
// dependencies we use a latency of 0 because for a multi-issue
// target we want to allow the defining instruction to issue
// in the same cycle as the using instruction.
// TODO: Using a latency of 1 here for output dependencies assumes
// there's no cost for reusing registers.
SDep::Kind Kind = MO.isUse() ? SDep::Anti : SDep::Output;
unsigned AOLatency = (Kind == SDep::Anti) ? 0 : 1;
for (unsigned i = 0, e = DefList.size(); i != e; ++i) {
SUnit *DefSU = DefList[i];
if (DefSU != SU &&
(Kind != SDep::Output || !MO.isDead() ||
!DefSU->getInstr()->registerDefIsDead(Reg)))
DefSU->addPred(SDep(SU, Kind, AOLatency, /*Reg=*/Reg));
}
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
std::vector<SUnit *> &DefList = Defs[*Alias];
for (unsigned i = 0, e = DefList.size(); i != e; ++i) {
SUnit *DefSU = DefList[i];
if (DefSU != SU &&
(Kind != SDep::Output || !MO.isDead() ||
!DefSU->getInstr()->registerDefIsDead(Reg)))
DefSU->addPred(SDep(SU, Kind, AOLatency, /*Reg=*/ *Alias));
}
}
if (MO.isDef()) {
// Add any data dependencies.
unsigned DataLatency = SU->Latency;
for (unsigned i = 0, e = UseList.size(); i != e; ++i) {
SUnit *UseSU = UseList[i];
if (UseSU != SU) {
unsigned LDataLatency = DataLatency;
// Optionally add in a special extra latency for nodes that
// feed addresses.
// TODO: Do this for register aliases too.
// TODO: Perhaps we should get rid of
// SpecialAddressLatency and just move this into
// adjustSchedDependency for the targets that care about
// it.
if (SpecialAddressLatency != 0 && !UnitLatencies) {
MachineInstr *UseMI = UseSU->getInstr();
const TargetInstrDesc &UseTID = UseMI->getDesc();
int RegUseIndex = UseMI->findRegisterUseOperandIdx(Reg);
assert(RegUseIndex >= 0 && "UseMI doesn's use register!");
if ((UseTID.mayLoad() || UseTID.mayStore()) &&
(unsigned)RegUseIndex < UseTID.getNumOperands() &&
UseTID.OpInfo[RegUseIndex].isLookupPtrRegClass())
LDataLatency += SpecialAddressLatency;
}
// Adjust the dependence latency using operand def/use
// information (if any), and then allow the target to
// perform its own adjustments.
const SDep& dep = SDep(SU, SDep::Data, LDataLatency, Reg);
if (!UnitLatencies) {
ComputeOperandLatency(SU, UseSU, (SDep &)dep);
ST.adjustSchedDependency(SU, UseSU, (SDep &)dep);
}
UseSU->addPred(dep);
}
}
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) {
SUnit *UseSU = UseList[i];
if (UseSU != SU) {
const SDep& dep = SDep(SU, SDep::Data, DataLatency, *Alias);
if (!UnitLatencies) {
ComputeOperandLatency(SU, UseSU, (SDep &)dep);
ST.adjustSchedDependency(SU, UseSU, (SDep &)dep);
}
UseSU->addPred(dep);
}
}
}
// If a def is going to wrap back around to the top of the loop,
// backschedule it.
if (!UnitLatencies && DefList.empty()) {
LoopDependencies::LoopDeps::iterator I = LoopRegs.Deps.find(Reg);
if (I != LoopRegs.Deps.end()) {
const MachineOperand *UseMO = I->second.first;
unsigned Count = I->second.second;
const MachineInstr *UseMI = UseMO->getParent();
unsigned UseMOIdx = UseMO - &UseMI->getOperand(0);
const TargetInstrDesc &UseTID = UseMI->getDesc();
// TODO: If we knew the total depth of the region here, we could
// handle the case where the whole loop is inside the region but
// is large enough that the isScheduleHigh trick isn't needed.
if (UseMOIdx < UseTID.getNumOperands()) {
// Currently, we only support scheduling regions consisting of
// single basic blocks. Check to see if the instruction is in
// the same region by checking to see if it has the same parent.
if (UseMI->getParent() != MI->getParent()) {
unsigned Latency = SU->Latency;
if (UseTID.OpInfo[UseMOIdx].isLookupPtrRegClass())
Latency += SpecialAddressLatency;
// This is a wild guess as to the portion of the latency which
// will be overlapped by work done outside the current
// scheduling region.
Latency -= std::min(Latency, Count);
// Add the artifical edge.
ExitSU.addPred(SDep(SU, SDep::Order, Latency,
/*Reg=*/0, /*isNormalMemory=*/false,
/*isMustAlias=*/false,
/*isArtificial=*/true));
} else if (SpecialAddressLatency > 0 &&
UseTID.OpInfo[UseMOIdx].isLookupPtrRegClass()) {
// The entire loop body is within the current scheduling region
// and the latency of this operation is assumed to be greater
// than the latency of the loop.
// TODO: Recursively mark data-edge predecessors as
// isScheduleHigh too.
SU->isScheduleHigh = true;
}
}
LoopRegs.Deps.erase(I);
}
}
UseList.clear();
if (!MO.isDead())
DefList.clear();
DefList.push_back(SU);
} else {
UseList.push_back(SU);
}
}
// Add chain dependencies.
// Note that isStoreToStackSlot and isLoadFromStackSLot are not usable
// after stack slots are lowered to actual addresses.
// TODO: Use an AliasAnalysis and do real alias-analysis queries, and
// produce more precise dependence information.
if (TID.isCall() || TID.hasUnmodeledSideEffects()) {
new_chain:
// This is the conservative case. Add dependencies on all memory
// references.
if (Chain)
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
Chain = SU;
for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
PendingLoads[k]->addPred(SDep(SU, SDep::Order, SU->Latency));
PendingLoads.clear();
for (std::map<const Value *, SUnit *>::iterator I = MemDefs.begin(),
E = MemDefs.end(); I != E; ++I) {
I->second->addPred(SDep(SU, SDep::Order, SU->Latency));
I->second = SU;
}
for (std::map<const Value *, std::vector<SUnit *> >::iterator I =
MemUses.begin(), E = MemUses.end(); I != E; ++I) {
for (unsigned i = 0, e = I->second.size(); i != e; ++i)
I->second[i]->addPred(SDep(SU, SDep::Order, SU->Latency));
I->second.clear();
}
// See if it is known to just have a single memory reference.
MachineInstr *ChainMI = Chain->getInstr();
const TargetInstrDesc &ChainTID = ChainMI->getDesc();
if (!ChainTID.isCall() &&
!ChainTID.hasUnmodeledSideEffects() &&
ChainMI->hasOneMemOperand() &&
!(*ChainMI->memoperands_begin())->isVolatile() &&
(*ChainMI->memoperands_begin())->getValue())
// We know that the Chain accesses one specific memory location.
ChainMMO = *ChainMI->memoperands_begin();
else
// Unknown memory accesses. Assume the worst.
ChainMMO = 0;
} else if (TID.mayStore()) {
if (const Value *V = getUnderlyingObjectForInstr(MI)) {
// A store to a specific PseudoSourceValue. Add precise dependencies.
// Handle the def in MemDefs, if there is one.
std::map<const Value *, SUnit *>::iterator I = MemDefs.find(V);
if (I != MemDefs.end()) {
I->second->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
/*isNormalMemory=*/true));
I->second = SU;
} else {
MemDefs[V] = SU;
}
// Handle the uses in MemUses, if there are any.
std::map<const Value *, std::vector<SUnit *> >::iterator J =
MemUses.find(V);
if (J != MemUses.end()) {
for (unsigned i = 0, e = J->second.size(); i != e; ++i)
J->second[i]->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
/*isNormalMemory=*/true));
J->second.clear();
}
// Add dependencies from all the PendingLoads, since without
// memoperands we must assume they alias anything.
for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
PendingLoads[k]->addPred(SDep(SU, SDep::Order, SU->Latency));
// Add a general dependence too, if needed.
if (Chain)
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
} else
// Treat all other stores conservatively.
goto new_chain;
} else if (TID.mayLoad()) {
if (MI->isInvariantLoad(AA)) {
// Invariant load, no chain dependencies needed!
} else if (const Value *V = getUnderlyingObjectForInstr(MI)) {
// A load from a specific PseudoSourceValue. Add precise dependencies.
std::map<const Value *, SUnit *>::iterator I = MemDefs.find(V);
if (I != MemDefs.end())
I->second->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
/*isNormalMemory=*/true));
MemUses[V].push_back(SU);
// Add a general dependence too, if needed.
if (Chain && (!ChainMMO ||
(ChainMMO->isStore() || ChainMMO->isVolatile())))
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
} else if (MI->hasVolatileMemoryRef()) {
// Treat volatile loads conservatively. Note that this includes
// cases where memoperand information is unavailable.
goto new_chain;
} else {
// A normal load. Depend on the general chain, as well as on
// all stores. In the absense of MachineMemOperand information,
// we can't even assume that the load doesn't alias well-behaved
// memory locations.
if (Chain)
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
for (std::map<const Value *, SUnit *>::iterator I = MemDefs.begin(),
E = MemDefs.end(); I != E; ++I)
I->second->addPred(SDep(SU, SDep::Order, SU->Latency));
PendingLoads.push_back(SU);
}
}
}
for (int i = 0, e = TRI->getNumRegs(); i != e; ++i) {
Defs[i].clear();
Uses[i].clear();
}
PendingLoads.clear();
}
void ScheduleDAGInstrs::FinishBlock() {
// Nothing to do.
}
void ScheduleDAGInstrs::ComputeLatency(SUnit *SU) {
const InstrItineraryData &InstrItins = TM.getInstrItineraryData();
// Compute the latency for the node.
SU->Latency =
InstrItins.getStageLatency(SU->getInstr()->getDesc().getSchedClass());
// Simplistic target-independent heuristic: assume that loads take
// extra time.
if (InstrItins.isEmpty())
if (SU->getInstr()->getDesc().mayLoad())
SU->Latency += 2;
}
void ScheduleDAGInstrs::ComputeOperandLatency(SUnit *Def, SUnit *Use,
SDep& dep) const {
const InstrItineraryData &InstrItins = TM.getInstrItineraryData();
if (InstrItins.isEmpty())
return;
// For a data dependency with a known register...
if ((dep.getKind() != SDep::Data) || (dep.getReg() == 0))
return;
const unsigned Reg = dep.getReg();
// ... find the definition of the register in the defining
// instruction
MachineInstr *DefMI = Def->getInstr();
int DefIdx = DefMI->findRegisterDefOperandIdx(Reg);
if (DefIdx != -1) {
int DefCycle = InstrItins.getOperandCycle(DefMI->getDesc().getSchedClass(), DefIdx);
if (DefCycle >= 0) {
MachineInstr *UseMI = Use->getInstr();
const unsigned UseClass = UseMI->getDesc().getSchedClass();
// For all uses of the register, calculate the maxmimum latency
int Latency = -1;
for (unsigned i = 0, e = UseMI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = UseMI->getOperand(i);
if (!MO.isReg() || !MO.isUse())
continue;
unsigned MOReg = MO.getReg();
if (MOReg != Reg)
continue;
int UseCycle = InstrItins.getOperandCycle(UseClass, i);
if (UseCycle >= 0)
Latency = std::max(Latency, DefCycle - UseCycle + 1);
}
// If we found a latency, then replace the existing dependence latency.
if (Latency >= 0)
dep.setLatency(Latency);
}
}
}
void ScheduleDAGInstrs::dumpNode(const SUnit *SU) const {
SU->getInstr()->dump();
}
std::string ScheduleDAGInstrs::getGraphNodeLabel(const SUnit *SU) const {
std::string s;
raw_string_ostream oss(s);
if (SU == &EntrySU)
oss << "<entry>";
else if (SU == &ExitSU)
oss << "<exit>";
else
SU->getInstr()->print(oss);
return oss.str();
}
// EmitSchedule - Emit the machine code in scheduled order.
MachineBasicBlock *ScheduleDAGInstrs::
EmitSchedule(DenseMap<MachineBasicBlock*, MachineBasicBlock*> *EM) {
// For MachineInstr-based scheduling, we're rescheduling the instructions in
// the block, so start by removing them from the block.
while (Begin != InsertPos) {
MachineBasicBlock::iterator I = Begin;
++Begin;
BB->remove(I);
}
// Then re-insert them according to the given schedule.
for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
SUnit *SU = Sequence[i];
if (!SU) {
// Null SUnit* is a noop.
EmitNoop();
continue;
}
BB->insert(InsertPos, SU->getInstr());
}
// Update the Begin iterator, as the first instruction in the block
// may have been scheduled later.
if (!Sequence.empty())
Begin = Sequence[0]->getInstr();
return BB;
}
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