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Diffstat (limited to 'contrib/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp')
| -rw-r--r-- | contrib/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp | 1031 |
1 files changed, 1031 insertions, 0 deletions
diff --git a/contrib/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp b/contrib/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp new file mode 100644 index 0000000..9c1dba3 --- /dev/null +++ b/contrib/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp @@ -0,0 +1,1031 @@ +//===---- 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 "llvm/Operator.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/CodeGen/LiveIntervalAnalysis.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineMemOperand.h" +#include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/CodeGen/PseudoSourceValue.h" +#include "llvm/CodeGen/RegisterPressure.h" +#include "llvm/CodeGen/ScheduleDAGInstrs.h" +#include "llvm/MC/MCInstrItineraries.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Target/TargetInstrInfo.h" +#include "llvm/Target/TargetRegisterInfo.h" +#include "llvm/Target/TargetSubtargetInfo.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallPtrSet.h" +using namespace llvm; + +static cl::opt<bool> EnableAASchedMI("enable-aa-sched-mi", cl::Hidden, + cl::ZeroOrMore, cl::init(false), + cl::desc("Enable use of AA during MI GAD construction")); + +ScheduleDAGInstrs::ScheduleDAGInstrs(MachineFunction &mf, + const MachineLoopInfo &mli, + const MachineDominatorTree &mdt, + bool IsPostRAFlag, + LiveIntervals *lis) + : ScheduleDAG(mf), MLI(mli), MDT(mdt), MFI(mf.getFrameInfo()), + InstrItins(mf.getTarget().getInstrItineraryData()), LIS(lis), + IsPostRA(IsPostRAFlag), UnitLatencies(false), CanHandleTerminators(false), + LoopRegs(MDT), FirstDbgValue(0) { + assert((IsPostRA || LIS) && "PreRA scheduling requires LiveIntervals"); + DbgValues.clear(); + assert(!(IsPostRA && MRI.getNumVirtRegs()) && + "Virtual registers must be removed prior to PostRA scheduling"); +} + +/// 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(V->getType()->isIntegerTy() && "Unexpected operand type!"); + } while (1); +} + +/// getUnderlyingObject - This is a wrapper around 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 = GetUnderlyingObject(V); + // 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 (!O->getType()->isPointerTy()) + 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, + bool &MayAlias) { + MayAlias = true; + 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; + + MayAlias = PSV->mayAlias(MFI); + return V; + } + + if (isIdentifiedObject(V)) + return V; + + return 0; +} + +void ScheduleDAGInstrs::startBlock(MachineBasicBlock *bb) { + BB = bb; + LoopRegs.Deps.clear(); + if (MachineLoop *ML = MLI.getLoopFor(BB)) + if (BB == ML->getLoopLatch()) + LoopRegs.VisitLoop(ML); +} + +void ScheduleDAGInstrs::finishBlock() { + // Subclasses should no longer refer to the old block. + BB = 0; +} + +/// Initialize the map with the number of registers. +void Reg2SUnitsMap::setRegLimit(unsigned Limit) { + PhysRegSet.setUniverse(Limit); + SUnits.resize(Limit); +} + +/// Clear the map without deallocating storage. +void Reg2SUnitsMap::clear() { + for (const_iterator I = reg_begin(), E = reg_end(); I != E; ++I) { + SUnits[*I].clear(); + } + PhysRegSet.clear(); +} + +/// Initialize the DAG and common scheduler state for the current scheduling +/// region. This does not actually create the DAG, only clears it. The +/// scheduling driver may call BuildSchedGraph multiple times per scheduling +/// region. +void ScheduleDAGInstrs::enterRegion(MachineBasicBlock *bb, + MachineBasicBlock::iterator begin, + MachineBasicBlock::iterator end, + unsigned endcount) { + assert(bb == BB && "startBlock should set BB"); + RegionBegin = begin; + RegionEnd = end; + EndIndex = endcount; + MISUnitMap.clear(); + + // Check to see if the scheduler cares about latencies. + UnitLatencies = forceUnitLatencies(); + + ScheduleDAG::clearDAG(); +} + +/// Close the current scheduling region. Don't clear any state in case the +/// driver wants to refer to the previous scheduling region. +void ScheduleDAGInstrs::exitRegion() { + // Nothing to do. +} + +/// addSchedBarrierDeps - Add dependencies from instructions in the current +/// list of instructions being scheduled to scheduling barrier by adding +/// the exit SU to the register defs and use list. This is because we want to +/// make sure instructions which define registers that are either used by +/// the terminator or are live-out are properly scheduled. This is +/// especially important when the definition latency of the return value(s) +/// are too high to be hidden by the branch or when the liveout registers +/// used by instructions in the fallthrough block. +void ScheduleDAGInstrs::addSchedBarrierDeps() { + MachineInstr *ExitMI = RegionEnd != BB->end() ? &*RegionEnd : 0; + ExitSU.setInstr(ExitMI); + bool AllDepKnown = ExitMI && + (ExitMI->isCall() || ExitMI->isBarrier()); + if (ExitMI && AllDepKnown) { + // If it's a call or a barrier, add dependencies on the defs and uses of + // instruction. + for (unsigned i = 0, e = ExitMI->getNumOperands(); i != e; ++i) { + const MachineOperand &MO = ExitMI->getOperand(i); + if (!MO.isReg() || MO.isDef()) continue; + unsigned Reg = MO.getReg(); + if (Reg == 0) continue; + + if (TRI->isPhysicalRegister(Reg)) + Uses[Reg].push_back(&ExitSU); + else { + assert(!IsPostRA && "Virtual register encountered after regalloc."); + addVRegUseDeps(&ExitSU, i); + } + } + } else { + // For others, e.g. fallthrough, conditional branch, assume the exit + // uses all the registers that are livein to the successor blocks. + assert(Uses.empty() && "Uses in set before adding deps?"); + for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), + SE = BB->succ_end(); SI != SE; ++SI) + for (MachineBasicBlock::livein_iterator I = (*SI)->livein_begin(), + E = (*SI)->livein_end(); I != E; ++I) { + unsigned Reg = *I; + if (!Uses.contains(Reg)) + Uses[Reg].push_back(&ExitSU); + } + } +} + +/// MO is an operand of SU's instruction that defines a physical register. Add +/// data dependencies from SU to any uses of the physical register. +void ScheduleDAGInstrs::addPhysRegDataDeps(SUnit *SU, + const MachineOperand &MO) { + assert(MO.isDef() && "expect physreg def"); + + // Ask the target if address-backscheduling is desirable, and if so how much. + const TargetSubtargetInfo &ST = TM.getSubtarget<TargetSubtargetInfo>(); + unsigned SpecialAddressLatency = ST.getSpecialAddressLatency(); + unsigned DataLatency = SU->Latency; + + for (MCRegAliasIterator Alias(MO.getReg(), TRI, true); + Alias.isValid(); ++Alias) { + if (!Uses.contains(*Alias)) + continue; + std::vector<SUnit*> &UseList = Uses[*Alias]; + for (unsigned i = 0, e = UseList.size(); i != e; ++i) { + SUnit *UseSU = UseList[i]; + if (UseSU == SU) + continue; + unsigned LDataLatency = DataLatency; + // Optionally add in a special extra latency for nodes that + // feed addresses. + // 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 && + UseSU != &ExitSU) { + MachineInstr *UseMI = UseSU->getInstr(); + const MCInstrDesc &UseMCID = UseMI->getDesc(); + int RegUseIndex = UseMI->findRegisterUseOperandIdx(*Alias); + assert(RegUseIndex >= 0 && "UseMI doesn't use register!"); + if (RegUseIndex >= 0 && + (UseMI->mayLoad() || UseMI->mayStore()) && + (unsigned)RegUseIndex < UseMCID.getNumOperands() && + UseMCID.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. + SDep dep(SU, SDep::Data, LDataLatency, *Alias); + if (!UnitLatencies) { + unsigned Latency = computeOperandLatency(SU, UseSU, dep); + dep.setLatency(Latency); + + ST.adjustSchedDependency(SU, UseSU, dep); + } + UseSU->addPred(dep); + } + } +} + +/// addPhysRegDeps - Add register dependencies (data, anti, and output) from +/// this SUnit to following instructions in the same scheduling region that +/// depend the physical register referenced at OperIdx. +void ScheduleDAGInstrs::addPhysRegDeps(SUnit *SU, unsigned OperIdx) { + const MachineInstr *MI = SU->getInstr(); + const MachineOperand &MO = MI->getOperand(OperIdx); + + // 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; + for (MCRegAliasIterator Alias(MO.getReg(), TRI, true); + Alias.isValid(); ++Alias) { + if (!Defs.contains(*Alias)) + continue; + std::vector<SUnit *> &DefList = Defs[*Alias]; + for (unsigned i = 0, e = DefList.size(); i != e; ++i) { + SUnit *DefSU = DefList[i]; + if (DefSU == &ExitSU) + continue; + if (DefSU != SU && + (Kind != SDep::Output || !MO.isDead() || + !DefSU->getInstr()->registerDefIsDead(*Alias))) { + if (Kind == SDep::Anti) + DefSU->addPred(SDep(SU, Kind, 0, /*Reg=*/*Alias)); + else { + unsigned AOLat = TII->getOutputLatency(InstrItins, MI, OperIdx, + DefSU->getInstr()); + DefSU->addPred(SDep(SU, Kind, AOLat, /*Reg=*/*Alias)); + } + } + } + } + + if (!MO.isDef()) { + // Either insert a new Reg2SUnits entry with an empty SUnits list, or + // retrieve the existing SUnits list for this register's uses. + // Push this SUnit on the use list. + Uses[MO.getReg()].push_back(SU); + } + else { + addPhysRegDataDeps(SU, MO); + + // Either insert a new Reg2SUnits entry with an empty SUnits list, or + // retrieve the existing SUnits list for this register's defs. + std::vector<SUnit *> &DefList = Defs[MO.getReg()]; + + // 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(MO.getReg()); + 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 MCInstrDesc &UseMCID = UseMI->getDesc(); + const TargetSubtargetInfo &ST = + TM.getSubtarget<TargetSubtargetInfo>(); + unsigned SpecialAddressLatency = ST.getSpecialAddressLatency(); + // 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 < UseMCID.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 (UseMCID.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 artificial edge. + ExitSU.addPred(SDep(SU, SDep::Order, Latency, + /*Reg=*/0, /*isNormalMemory=*/false, + /*isMustAlias=*/false, + /*isArtificial=*/true)); + } else if (SpecialAddressLatency > 0 && + UseMCID.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); + } + } + + // clear this register's use list + if (Uses.contains(MO.getReg())) + Uses[MO.getReg()].clear(); + + if (!MO.isDead()) + DefList.clear(); + + // Calls will not be reordered because of chain dependencies (see + // below). Since call operands are dead, calls may continue to be added + // to the DefList making dependence checking quadratic in the size of + // the block. Instead, we leave only one call at the back of the + // DefList. + if (SU->isCall) { + while (!DefList.empty() && DefList.back()->isCall) + DefList.pop_back(); + } + // Defs are pushed in the order they are visited and never reordered. + DefList.push_back(SU); + } +} + +/// addVRegDefDeps - Add register output and data dependencies from this SUnit +/// to instructions that occur later in the same scheduling region if they read +/// from or write to the virtual register defined at OperIdx. +/// +/// TODO: Hoist loop induction variable increments. This has to be +/// reevaluated. Generally, IV scheduling should be done before coalescing. +void ScheduleDAGInstrs::addVRegDefDeps(SUnit *SU, unsigned OperIdx) { + const MachineInstr *MI = SU->getInstr(); + unsigned Reg = MI->getOperand(OperIdx).getReg(); + + // Singly defined vregs do not have output/anti dependencies. + // The current operand is a def, so we have at least one. + // Check here if there are any others... + if (MRI.hasOneDef(Reg)) + return; + + // Add output dependence to the next nearest def of this vreg. + // + // Unless this definition is dead, the output dependence should be + // transitively redundant with antidependencies from this definition's + // uses. We're conservative for now until we have a way to guarantee the uses + // are not eliminated sometime during scheduling. The output dependence edge + // is also useful if output latency exceeds def-use latency. + VReg2SUnitMap::iterator DefI = VRegDefs.find(Reg); + if (DefI == VRegDefs.end()) + VRegDefs.insert(VReg2SUnit(Reg, SU)); + else { + SUnit *DefSU = DefI->SU; + if (DefSU != SU && DefSU != &ExitSU) { + unsigned OutLatency = TII->getOutputLatency(InstrItins, MI, OperIdx, + DefSU->getInstr()); + DefSU->addPred(SDep(SU, SDep::Output, OutLatency, Reg)); + } + DefI->SU = SU; + } +} + +/// addVRegUseDeps - Add a register data dependency if the instruction that +/// defines the virtual register used at OperIdx is mapped to an SUnit. Add a +/// register antidependency from this SUnit to instructions that occur later in +/// the same scheduling region if they write the virtual register. +/// +/// TODO: Handle ExitSU "uses" properly. +void ScheduleDAGInstrs::addVRegUseDeps(SUnit *SU, unsigned OperIdx) { + MachineInstr *MI = SU->getInstr(); + unsigned Reg = MI->getOperand(OperIdx).getReg(); + + // Lookup this operand's reaching definition. + assert(LIS && "vreg dependencies requires LiveIntervals"); + LiveRangeQuery LRQ(LIS->getInterval(Reg), LIS->getInstructionIndex(MI)); + VNInfo *VNI = LRQ.valueIn(); + + // VNI will be valid because MachineOperand::readsReg() is checked by caller. + assert(VNI && "No value to read by operand"); + MachineInstr *Def = LIS->getInstructionFromIndex(VNI->def); + // Phis and other noninstructions (after coalescing) have a NULL Def. + if (Def) { + SUnit *DefSU = getSUnit(Def); + if (DefSU) { + // The reaching Def lives within this scheduling region. + // Create a data dependence. + // + // TODO: Handle "special" address latencies cleanly. + SDep dep(DefSU, SDep::Data, DefSU->Latency, Reg); + if (!UnitLatencies) { + // Adjust the dependence latency using operand def/use information, then + // allow the target to perform its own adjustments. + unsigned Latency = computeOperandLatency(DefSU, SU, const_cast<SDep &>(dep)); + dep.setLatency(Latency); + + const TargetSubtargetInfo &ST = TM.getSubtarget<TargetSubtargetInfo>(); + ST.adjustSchedDependency(DefSU, SU, const_cast<SDep &>(dep)); + } + SU->addPred(dep); + } + } + + // Add antidependence to the following def of the vreg it uses. + VReg2SUnitMap::iterator DefI = VRegDefs.find(Reg); + if (DefI != VRegDefs.end() && DefI->SU != SU) + DefI->SU->addPred(SDep(SU, SDep::Anti, 0, Reg)); +} + +/// Return true if MI is an instruction we are unable to reason about +/// (like a call or something with unmodeled side effects). +static inline bool isGlobalMemoryObject(AliasAnalysis *AA, MachineInstr *MI) { + if (MI->isCall() || MI->hasUnmodeledSideEffects() || + (MI->hasVolatileMemoryRef() && + (!MI->mayLoad() || !MI->isInvariantLoad(AA)))) + return true; + return false; +} + +// This MI might have either incomplete info, or known to be unsafe +// to deal with (i.e. volatile object). +static inline bool isUnsafeMemoryObject(MachineInstr *MI, + const MachineFrameInfo *MFI) { + if (!MI || MI->memoperands_empty()) + return true; + // We purposefully do no check for hasOneMemOperand() here + // in hope to trigger an assert downstream in order to + // finish implementation. + if ((*MI->memoperands_begin())->isVolatile() || + MI->hasUnmodeledSideEffects()) + return true; + + const Value *V = (*MI->memoperands_begin())->getValue(); + if (!V) + return true; + + V = getUnderlyingObject(V); + if (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V)) { + // Similarly to getUnderlyingObjectForInstr: + // 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 true; + } + // Does this pointer refer to a distinct and identifiable object? + if (!isIdentifiedObject(V)) + return true; + + return false; +} + +/// This returns true if the two MIs need a chain edge betwee them. +/// If these are not even memory operations, we still may need +/// chain deps between them. The question really is - could +/// these two MIs be reordered during scheduling from memory dependency +/// point of view. +static bool MIsNeedChainEdge(AliasAnalysis *AA, const MachineFrameInfo *MFI, + MachineInstr *MIa, + MachineInstr *MIb) { + // Cover a trivial case - no edge is need to itself. + if (MIa == MIb) + return false; + + if (isUnsafeMemoryObject(MIa, MFI) || isUnsafeMemoryObject(MIb, MFI)) + return true; + + // If we are dealing with two "normal" loads, we do not need an edge + // between them - they could be reordered. + if (!MIa->mayStore() && !MIb->mayStore()) + return false; + + // To this point analysis is generic. From here on we do need AA. + if (!AA) + return true; + + MachineMemOperand *MMOa = *MIa->memoperands_begin(); + MachineMemOperand *MMOb = *MIb->memoperands_begin(); + + // FIXME: Need to handle multiple memory operands to support all targets. + if (!MIa->hasOneMemOperand() || !MIb->hasOneMemOperand()) + llvm_unreachable("Multiple memory operands."); + + // The following interface to AA is fashioned after DAGCombiner::isAlias + // and operates with MachineMemOperand offset with some important + // assumptions: + // - LLVM fundamentally assumes flat address spaces. + // - MachineOperand offset can *only* result from legalization and + // cannot affect queries other than the trivial case of overlap + // checking. + // - These offsets never wrap and never step outside + // of allocated objects. + // - There should never be any negative offsets here. + // + // FIXME: Modify API to hide this math from "user" + // FIXME: Even before we go to AA we can reason locally about some + // memory objects. It can save compile time, and possibly catch some + // corner cases not currently covered. + + assert ((MMOa->getOffset() >= 0) && "Negative MachineMemOperand offset"); + assert ((MMOb->getOffset() >= 0) && "Negative MachineMemOperand offset"); + + int64_t MinOffset = std::min(MMOa->getOffset(), MMOb->getOffset()); + int64_t Overlapa = MMOa->getSize() + MMOa->getOffset() - MinOffset; + int64_t Overlapb = MMOb->getSize() + MMOb->getOffset() - MinOffset; + + AliasAnalysis::AliasResult AAResult = AA->alias( + AliasAnalysis::Location(MMOa->getValue(), Overlapa, + MMOa->getTBAAInfo()), + AliasAnalysis::Location(MMOb->getValue(), Overlapb, + MMOb->getTBAAInfo())); + + return (AAResult != AliasAnalysis::NoAlias); +} + +/// This recursive function iterates over chain deps of SUb looking for +/// "latest" node that needs a chain edge to SUa. +static unsigned +iterateChainSucc(AliasAnalysis *AA, const MachineFrameInfo *MFI, + SUnit *SUa, SUnit *SUb, SUnit *ExitSU, unsigned *Depth, + SmallPtrSet<const SUnit*, 16> &Visited) { + if (!SUa || !SUb || SUb == ExitSU) + return *Depth; + + // Remember visited nodes. + if (!Visited.insert(SUb)) + return *Depth; + // If there is _some_ dependency already in place, do not + // descend any further. + // TODO: Need to make sure that if that dependency got eliminated or ignored + // for any reason in the future, we would not violate DAG topology. + // Currently it does not happen, but makes an implicit assumption about + // future implementation. + // + // Independently, if we encounter node that is some sort of global + // object (like a call) we already have full set of dependencies to it + // and we can stop descending. + if (SUa->isSucc(SUb) || + isGlobalMemoryObject(AA, SUb->getInstr())) + return *Depth; + + // If we do need an edge, or we have exceeded depth budget, + // add that edge to the predecessors chain of SUb, + // and stop descending. + if (*Depth > 200 || + MIsNeedChainEdge(AA, MFI, SUa->getInstr(), SUb->getInstr())) { + SUb->addPred(SDep(SUa, SDep::Order, /*Latency=*/0, /*Reg=*/0, + /*isNormalMemory=*/true)); + return *Depth; + } + // Track current depth. + (*Depth)++; + // Iterate over chain dependencies only. + for (SUnit::const_succ_iterator I = SUb->Succs.begin(), E = SUb->Succs.end(); + I != E; ++I) + if (I->isCtrl()) + iterateChainSucc (AA, MFI, SUa, I->getSUnit(), ExitSU, Depth, Visited); + return *Depth; +} + +/// This function assumes that "downward" from SU there exist +/// tail/leaf of already constructed DAG. It iterates downward and +/// checks whether SU can be aliasing any node dominated +/// by it. +static void adjustChainDeps(AliasAnalysis *AA, const MachineFrameInfo *MFI, + SUnit *SU, SUnit *ExitSU, std::set<SUnit *> &CheckList, + unsigned LatencyToLoad) { + if (!SU) + return; + + SmallPtrSet<const SUnit*, 16> Visited; + unsigned Depth = 0; + + for (std::set<SUnit *>::iterator I = CheckList.begin(), IE = CheckList.end(); + I != IE; ++I) { + if (SU == *I) + continue; + if (MIsNeedChainEdge(AA, MFI, SU->getInstr(), (*I)->getInstr())) { + unsigned Latency = ((*I)->getInstr()->mayLoad()) ? LatencyToLoad : 0; + (*I)->addPred(SDep(SU, SDep::Order, Latency, /*Reg=*/0, + /*isNormalMemory=*/true)); + } + // Now go through all the chain successors and iterate from them. + // Keep track of visited nodes. + for (SUnit::const_succ_iterator J = (*I)->Succs.begin(), + JE = (*I)->Succs.end(); J != JE; ++J) + if (J->isCtrl()) + iterateChainSucc (AA, MFI, SU, J->getSUnit(), + ExitSU, &Depth, Visited); + } +} + +/// Check whether two objects need a chain edge, if so, add it +/// otherwise remember the rejected SU. +static inline +void addChainDependency (AliasAnalysis *AA, const MachineFrameInfo *MFI, + SUnit *SUa, SUnit *SUb, + std::set<SUnit *> &RejectList, + unsigned TrueMemOrderLatency = 0, + bool isNormalMemory = false) { + // If this is a false dependency, + // do not add the edge, but rememeber the rejected node. + if (!EnableAASchedMI || + MIsNeedChainEdge(AA, MFI, SUa->getInstr(), SUb->getInstr())) + SUb->addPred(SDep(SUa, SDep::Order, TrueMemOrderLatency, /*Reg=*/0, + isNormalMemory)); + else { + // Duplicate entries should be ignored. + RejectList.insert(SUb); + DEBUG(dbgs() << "\tReject chain dep between SU(" + << SUa->NodeNum << ") and SU(" + << SUb->NodeNum << ")\n"); + } +} + +/// Create an SUnit for each real instruction, numbered in top-down toplological +/// order. The instruction order A < B, implies that no edge exists from B to A. +/// +/// Map each real instruction to its SUnit. +/// +/// After initSUnits, the SUnits vector cannot be resized and the scheduler may +/// hang onto SUnit pointers. We may relax this in the future by using SUnit IDs +/// instead of pointers. +/// +/// MachineScheduler relies on initSUnits numbering the nodes by their order in +/// the original instruction list. +void ScheduleDAGInstrs::initSUnits() { + // We'll be allocating one SUnit for each real instruction in the region, + // which is contained within a basic block. + SUnits.reserve(BB->size()); + + for (MachineBasicBlock::iterator I = RegionBegin; I != RegionEnd; ++I) { + MachineInstr *MI = I; + if (MI->isDebugValue()) + continue; + + SUnit *SU = newSUnit(MI); + MISUnitMap[MI] = SU; + + SU->isCall = MI->isCall(); + SU->isCommutable = MI->isCommutable(); + + // Assign the Latency field of SU using target-provided information. + if (UnitLatencies) + SU->Latency = 1; + else + computeLatency(SU); + } +} + +/// If RegPressure is non null, compute register pressure as a side effect. The +/// DAG builder is an efficient place to do it because it already visits +/// operands. +void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA, + RegPressureTracker *RPTracker) { + // Create an SUnit for each real instruction. + initSUnits(); + + // 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. + SUnit *BarrierChain = 0, *AliasChain = 0; + + // Memory references to specific known memory locations are tracked + // so that they can be given more precise dependencies. We track + // separately the known memory locations that may alias and those + // that are known not to alias + std::map<const Value *, SUnit *> AliasMemDefs, NonAliasMemDefs; + std::map<const Value *, std::vector<SUnit *> > AliasMemUses, NonAliasMemUses; + std::set<SUnit*> RejectMemNodes; + + // Remove any stale debug info; sometimes BuildSchedGraph is called again + // without emitting the info from the previous call. + DbgValues.clear(); + FirstDbgValue = NULL; + + assert(Defs.empty() && Uses.empty() && + "Only BuildGraph should update Defs/Uses"); + Defs.setRegLimit(TRI->getNumRegs()); + Uses.setRegLimit(TRI->getNumRegs()); + + assert(VRegDefs.empty() && "Only BuildSchedGraph may access VRegDefs"); + // FIXME: Allow SparseSet to reserve space for the creation of virtual + // registers during scheduling. Don't artificially inflate the Universe + // because we want to assert that vregs are not created during DAG building. + VRegDefs.setUniverse(MRI.getNumVirtRegs()); + + // Model data dependencies between instructions being scheduled and the + // ExitSU. + addSchedBarrierDeps(); + + // Walk the list of instructions, from bottom moving up. + MachineInstr *PrevMI = NULL; + for (MachineBasicBlock::iterator MII = RegionEnd, MIE = RegionBegin; + MII != MIE; --MII) { + MachineInstr *MI = prior(MII); + if (MI && PrevMI) { + DbgValues.push_back(std::make_pair(PrevMI, MI)); + PrevMI = NULL; + } + + if (MI->isDebugValue()) { + PrevMI = MI; + continue; + } + if (RPTracker) { + RPTracker->recede(); + assert(RPTracker->getPos() == prior(MII) && "RPTracker can't find MI"); + } + + assert((!MI->isTerminator() || CanHandleTerminators) && !MI->isLabel() && + "Cannot schedule terminators or labels!"); + + SUnit *SU = MISUnitMap[MI]; + assert(SU && "No SUnit mapped to this MI"); + + // 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; + + if (TRI->isPhysicalRegister(Reg)) + addPhysRegDeps(SU, j); + else { + assert(!IsPostRA && "Virtual register encountered!"); + if (MO.isDef()) + addVRegDefDeps(SU, j); + else if (MO.readsReg()) // ignore undef operands + addVRegUseDeps(SU, j); + } + } + + // Add chain dependencies. + // Chain dependencies used to enforce memory order should have + // latency of 0 (except for true dependency of Store followed by + // aliased Load... we estimate that with a single cycle of latency + // assuming the hardware will bypass) + // 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. + unsigned TrueMemOrderLatency = MI->mayStore() ? 1 : 0; + if (isGlobalMemoryObject(AA, MI)) { + // Be conservative with these and add dependencies on all memory + // references, even those that are known to not alias. + for (std::map<const Value *, SUnit *>::iterator I = + NonAliasMemDefs.begin(), E = NonAliasMemDefs.end(); I != E; ++I) { + I->second->addPred(SDep(SU, SDep::Order, /*Latency=*/0)); + } + for (std::map<const Value *, std::vector<SUnit *> >::iterator I = + NonAliasMemUses.begin(), E = NonAliasMemUses.end(); I != E; ++I) { + for (unsigned i = 0, e = I->second.size(); i != e; ++i) + I->second[i]->addPred(SDep(SU, SDep::Order, TrueMemOrderLatency)); + } + // Add SU to the barrier chain. + if (BarrierChain) + BarrierChain->addPred(SDep(SU, SDep::Order, /*Latency=*/0)); + BarrierChain = SU; + // This is a barrier event that acts as a pivotal node in the DAG, + // so it is safe to clear list of exposed nodes. + adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes, + TrueMemOrderLatency); + RejectMemNodes.clear(); + NonAliasMemDefs.clear(); + NonAliasMemUses.clear(); + + // fall-through + new_alias_chain: + // Chain all possibly aliasing memory references though SU. + if (AliasChain) { + unsigned ChainLatency = 0; + if (AliasChain->getInstr()->mayLoad()) + ChainLatency = TrueMemOrderLatency; + addChainDependency(AA, MFI, SU, AliasChain, RejectMemNodes, + ChainLatency); + } + AliasChain = SU; + for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k) + addChainDependency(AA, MFI, SU, PendingLoads[k], RejectMemNodes, + TrueMemOrderLatency); + for (std::map<const Value *, SUnit *>::iterator I = AliasMemDefs.begin(), + E = AliasMemDefs.end(); I != E; ++I) + addChainDependency(AA, MFI, SU, I->second, RejectMemNodes); + for (std::map<const Value *, std::vector<SUnit *> >::iterator I = + AliasMemUses.begin(), E = AliasMemUses.end(); I != E; ++I) { + for (unsigned i = 0, e = I->second.size(); i != e; ++i) + addChainDependency(AA, MFI, SU, I->second[i], RejectMemNodes, + TrueMemOrderLatency); + } + adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes, + TrueMemOrderLatency); + PendingLoads.clear(); + AliasMemDefs.clear(); + AliasMemUses.clear(); + } else if (MI->mayStore()) { + bool MayAlias = true; + if (const Value *V = getUnderlyingObjectForInstr(MI, MFI, MayAlias)) { + // A store to a specific PseudoSourceValue. Add precise dependencies. + // Record the def in MemDefs, first adding a dep if there is + // an existing def. + std::map<const Value *, SUnit *>::iterator I = + ((MayAlias) ? AliasMemDefs.find(V) : NonAliasMemDefs.find(V)); + std::map<const Value *, SUnit *>::iterator IE = + ((MayAlias) ? AliasMemDefs.end() : NonAliasMemDefs.end()); + if (I != IE) { + addChainDependency(AA, MFI, SU, I->second, RejectMemNodes, + 0, true); + I->second = SU; + } else { + if (MayAlias) + AliasMemDefs[V] = SU; + else + NonAliasMemDefs[V] = SU; + } + // Handle the uses in MemUses, if there are any. + std::map<const Value *, std::vector<SUnit *> >::iterator J = + ((MayAlias) ? AliasMemUses.find(V) : NonAliasMemUses.find(V)); + std::map<const Value *, std::vector<SUnit *> >::iterator JE = + ((MayAlias) ? AliasMemUses.end() : NonAliasMemUses.end()); + if (J != JE) { + for (unsigned i = 0, e = J->second.size(); i != e; ++i) + addChainDependency(AA, MFI, SU, J->second[i], RejectMemNodes, + TrueMemOrderLatency, true); + J->second.clear(); + } + if (MayAlias) { + // Add dependencies from all the PendingLoads, i.e. loads + // with no underlying object. + for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k) + addChainDependency(AA, MFI, SU, PendingLoads[k], RejectMemNodes, + TrueMemOrderLatency); + // Add dependence on alias chain, if needed. + if (AliasChain) + addChainDependency(AA, MFI, SU, AliasChain, RejectMemNodes); + // But we also should check dependent instructions for the + // SU in question. + adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes, + TrueMemOrderLatency); + } + // Add dependence on barrier chain, if needed. + // There is no point to check aliasing on barrier event. Even if + // SU and barrier _could_ be reordered, they should not. In addition, + // we have lost all RejectMemNodes below barrier. + if (BarrierChain) + BarrierChain->addPred(SDep(SU, SDep::Order, /*Latency=*/0)); + } else { + // Treat all other stores conservatively. + goto new_alias_chain; + } + + if (!ExitSU.isPred(SU)) + // Push store's up a bit to avoid them getting in between cmp + // and branches. + ExitSU.addPred(SDep(SU, SDep::Order, 0, + /*Reg=*/0, /*isNormalMemory=*/false, + /*isMustAlias=*/false, + /*isArtificial=*/true)); + } else if (MI->mayLoad()) { + bool MayAlias = true; + if (MI->isInvariantLoad(AA)) { + // Invariant load, no chain dependencies needed! + } else { + if (const Value *V = + getUnderlyingObjectForInstr(MI, MFI, MayAlias)) { + // A load from a specific PseudoSourceValue. Add precise dependencies. + std::map<const Value *, SUnit *>::iterator I = + ((MayAlias) ? AliasMemDefs.find(V) : NonAliasMemDefs.find(V)); + std::map<const Value *, SUnit *>::iterator IE = + ((MayAlias) ? AliasMemDefs.end() : NonAliasMemDefs.end()); + if (I != IE) + addChainDependency(AA, MFI, SU, I->second, RejectMemNodes, 0, true); + if (MayAlias) + AliasMemUses[V].push_back(SU); + else + NonAliasMemUses[V].push_back(SU); + } else { + // A load with no underlying object. Depend on all + // potentially aliasing stores. + for (std::map<const Value *, SUnit *>::iterator I = + AliasMemDefs.begin(), E = AliasMemDefs.end(); I != E; ++I) + addChainDependency(AA, MFI, SU, I->second, RejectMemNodes); + + PendingLoads.push_back(SU); + MayAlias = true; + } + if (MayAlias) + adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes, /*Latency=*/0); + // Add dependencies on alias and barrier chains, if needed. + if (MayAlias && AliasChain) + addChainDependency(AA, MFI, SU, AliasChain, RejectMemNodes); + if (BarrierChain) + BarrierChain->addPred(SDep(SU, SDep::Order, /*Latency=*/0)); + } + } + } + if (PrevMI) + FirstDbgValue = PrevMI; + + Defs.clear(); + Uses.clear(); + VRegDefs.clear(); + PendingLoads.clear(); +} + +void ScheduleDAGInstrs::computeLatency(SUnit *SU) { + // Compute the latency for the node. We only provide a default for missing + // itineraries. Empty itineraries still have latency properties. + if (!InstrItins) { + SU->Latency = 1; + + // Simplistic target-independent heuristic: assume that loads take + // extra time. + if (SU->getInstr()->mayLoad()) + SU->Latency += 2; + } else { + SU->Latency = TII->getInstrLatency(InstrItins, SU->getInstr()); + } +} + +unsigned ScheduleDAGInstrs::computeOperandLatency(SUnit *Def, SUnit *Use, + const SDep& dep, + bool FindMin) const { + // For a data dependency with a known register... + if ((dep.getKind() != SDep::Data) || (dep.getReg() == 0)) + return 1; + + return TII->computeOperandLatency(InstrItins, TRI, Def->getInstr(), + Use->getInstr(), dep.getReg(), FindMin); +} + +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(); +} + +/// Return the basic block label. It is not necessarilly unique because a block +/// contains multiple scheduling regions. But it is fine for visualization. +std::string ScheduleDAGInstrs::getDAGName() const { + return "dag." + BB->getFullName(); +} |
