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llvm-6502/lib/CodeGen/ScheduleDAGInstrs.cpp
Dan Gohman 91203cf87b When checking whether a def of an aliased register is dead, ask the 
machineinstr whether the aliased register is dead, rather than the original
register is dead. This allows it to get the correct answer when examining
an instruction like this:
  CALLpcrel32 <ga:foo>, %AL<imp-def>, %EAX<imp-def,dead>
where EAX is dead but a subregister of it is still live. This fixes PR5294.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85135 91177308-0d34-0410-b5e6-96231b3b80d8
2009-10-26 18:26:18 +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) {
MFI = mf.getFrameInfo();
}
/// 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,
const MachineFrameInfo *MFI) {
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 (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V)) {
// For now, ignore PseudoSourceValues which may alias LLVM IR values
// because the code that uses this function has no way to cope with
// such aliases.
if (PSV->isAliased(MFI))
return 0;
return V;
}
if (isIdentifiedObject(V))
return V;
return 0;
}
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(*Alias)))
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, MFI)) {
// 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, MFI)) {
// 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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