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llvm-6502/lib/CodeGen/MachineScheduler.cpp
Benjamin Kramer b754687fd7 Silence GCC warning about falling off the end of a non-void function. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167618 91177308-0d34-0410-b5e6-96231b3b80d8
2012-11-09 15:45:22 +00:00

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//===- MachineScheduler.cpp - Machine Instruction Scheduler ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// MachineScheduler schedules machine instructions after phi elimination. It
// preserves LiveIntervals so it can be invoked before register allocation.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "misched"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineScheduler.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/ScheduleDAGILP.h"
#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/PriorityQueue.h"
#include <queue>
using namespace llvm;
namespace llvm {
cl::opt<bool> ForceTopDown("misched-topdown", cl::Hidden,
cl::desc("Force top-down list scheduling"));
cl::opt<bool> ForceBottomUp("misched-bottomup", cl::Hidden,
cl::desc("Force bottom-up list scheduling"));
}
#ifndef NDEBUG
static cl::opt<bool> ViewMISchedDAGs("view-misched-dags", cl::Hidden,
cl::desc("Pop up a window to show MISched dags after they are processed"));
static cl::opt<unsigned> MISchedCutoff("misched-cutoff", cl::Hidden,
cl::desc("Stop scheduling after N instructions"), cl::init(~0U));
#else
static bool ViewMISchedDAGs = false;
#endif // NDEBUG
// Threshold to very roughly model an out-of-order processor's instruction
// buffers. If the actual value of this threshold matters much in practice, then
// it can be specified by the machine model. For now, it's an experimental
// tuning knob to determine when and if it matters.
static cl::opt<unsigned> ILPWindow("ilp-window", cl::Hidden,
cl::desc("Allow expected latency to exceed the critical path by N cycles "
"before attempting to balance ILP"),
cl::init(10U));
//===----------------------------------------------------------------------===//
// Machine Instruction Scheduling Pass and Registry
//===----------------------------------------------------------------------===//
MachineSchedContext::MachineSchedContext():
MF(0), MLI(0), MDT(0), PassConfig(0), AA(0), LIS(0) {
RegClassInfo = new RegisterClassInfo();
}
MachineSchedContext::~MachineSchedContext() {
delete RegClassInfo;
}
namespace {
/// MachineScheduler runs after coalescing and before register allocation.
class MachineScheduler : public MachineSchedContext,
public MachineFunctionPass {
public:
MachineScheduler();
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual void releaseMemory() {}
virtual bool runOnMachineFunction(MachineFunction&);
virtual void print(raw_ostream &O, const Module* = 0) const;
static char ID; // Class identification, replacement for typeinfo
};
} // namespace
char MachineScheduler::ID = 0;
char &llvm::MachineSchedulerID = MachineScheduler::ID;
INITIALIZE_PASS_BEGIN(MachineScheduler, "misched",
"Machine Instruction Scheduler", false, false)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(MachineScheduler, "misched",
"Machine Instruction Scheduler", false, false)
MachineScheduler::MachineScheduler()
: MachineFunctionPass(ID) {
initializeMachineSchedulerPass(*PassRegistry::getPassRegistry());
}
void MachineScheduler::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequiredID(MachineDominatorsID);
AU.addRequired<MachineLoopInfo>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<TargetPassConfig>();
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
AU.addRequired<LiveIntervals>();
AU.addPreserved<LiveIntervals>();
MachineFunctionPass::getAnalysisUsage(AU);
}
MachinePassRegistry MachineSchedRegistry::Registry;
/// A dummy default scheduler factory indicates whether the scheduler
/// is overridden on the command line.
static ScheduleDAGInstrs *useDefaultMachineSched(MachineSchedContext *C) {
return 0;
}
/// MachineSchedOpt allows command line selection of the scheduler.
static cl::opt<MachineSchedRegistry::ScheduleDAGCtor, false,
RegisterPassParser<MachineSchedRegistry> >
MachineSchedOpt("misched",
cl::init(&useDefaultMachineSched), cl::Hidden,
cl::desc("Machine instruction scheduler to use"));
static MachineSchedRegistry
DefaultSchedRegistry("default", "Use the target's default scheduler choice.",
useDefaultMachineSched);
/// Forward declare the standard machine scheduler. This will be used as the
/// default scheduler if the target does not set a default.
static ScheduleDAGInstrs *createConvergingSched(MachineSchedContext *C);
/// Decrement this iterator until reaching the top or a non-debug instr.
static MachineBasicBlock::iterator
priorNonDebug(MachineBasicBlock::iterator I, MachineBasicBlock::iterator Beg) {
assert(I != Beg && "reached the top of the region, cannot decrement");
while (--I != Beg) {
if (!I->isDebugValue())
break;
}
return I;
}
/// If this iterator is a debug value, increment until reaching the End or a
/// non-debug instruction.
static MachineBasicBlock::iterator
nextIfDebug(MachineBasicBlock::iterator I, MachineBasicBlock::iterator End) {
for(; I != End; ++I) {
if (!I->isDebugValue())
break;
}
return I;
}
/// Top-level MachineScheduler pass driver.
///
/// Visit blocks in function order. Divide each block into scheduling regions
/// and visit them bottom-up. Visiting regions bottom-up is not required, but is
/// consistent with the DAG builder, which traverses the interior of the
/// scheduling regions bottom-up.
///
/// This design avoids exposing scheduling boundaries to the DAG builder,
/// simplifying the DAG builder's support for "special" target instructions.
/// At the same time the design allows target schedulers to operate across
/// scheduling boundaries, for example to bundle the boudary instructions
/// without reordering them. This creates complexity, because the target
/// scheduler must update the RegionBegin and RegionEnd positions cached by
/// ScheduleDAGInstrs whenever adding or removing instructions. A much simpler
/// design would be to split blocks at scheduling boundaries, but LLVM has a
/// general bias against block splitting purely for implementation simplicity.
bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
DEBUG(dbgs() << "Before MISsched:\n"; mf.print(dbgs()));
// Initialize the context of the pass.
MF = &mf;
MLI = &getAnalysis<MachineLoopInfo>();
MDT = &getAnalysis<MachineDominatorTree>();
PassConfig = &getAnalysis<TargetPassConfig>();
AA = &getAnalysis<AliasAnalysis>();
LIS = &getAnalysis<LiveIntervals>();
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
RegClassInfo->runOnMachineFunction(*MF);
// Select the scheduler, or set the default.
MachineSchedRegistry::ScheduleDAGCtor Ctor = MachineSchedOpt;
if (Ctor == useDefaultMachineSched) {
// Get the default scheduler set by the target.
Ctor = MachineSchedRegistry::getDefault();
if (!Ctor) {
Ctor = createConvergingSched;
MachineSchedRegistry::setDefault(Ctor);
}
}
// Instantiate the selected scheduler.
OwningPtr<ScheduleDAGInstrs> Scheduler(Ctor(this));
// Visit all machine basic blocks.
//
// TODO: Visit blocks in global postorder or postorder within the bottom-up
// loop tree. Then we can optionally compute global RegPressure.
for (MachineFunction::iterator MBB = MF->begin(), MBBEnd = MF->end();
MBB != MBBEnd; ++MBB) {
Scheduler->startBlock(MBB);
// Break the block into scheduling regions [I, RegionEnd), and schedule each
// region as soon as it is discovered. RegionEnd points the scheduling
// boundary at the bottom of the region. The DAG does not include RegionEnd,
// but the region does (i.e. the next RegionEnd is above the previous
// RegionBegin). If the current block has no terminator then RegionEnd ==
// MBB->end() for the bottom region.
//
// The Scheduler may insert instructions during either schedule() or
// exitRegion(), even for empty regions. So the local iterators 'I' and
// 'RegionEnd' are invalid across these calls.
unsigned RemainingInstrs = MBB->size();
for(MachineBasicBlock::iterator RegionEnd = MBB->end();
RegionEnd != MBB->begin(); RegionEnd = Scheduler->begin()) {
// Avoid decrementing RegionEnd for blocks with no terminator.
if (RegionEnd != MBB->end()
|| TII->isSchedulingBoundary(llvm::prior(RegionEnd), MBB, *MF)) {
--RegionEnd;
// Count the boundary instruction.
--RemainingInstrs;
}
// The next region starts above the previous region. Look backward in the
// instruction stream until we find the nearest boundary.
MachineBasicBlock::iterator I = RegionEnd;
for(;I != MBB->begin(); --I, --RemainingInstrs) {
if (TII->isSchedulingBoundary(llvm::prior(I), MBB, *MF))
break;
}
// Notify the scheduler of the region, even if we may skip scheduling
// it. Perhaps it still needs to be bundled.
Scheduler->enterRegion(MBB, I, RegionEnd, RemainingInstrs);
// Skip empty scheduling regions (0 or 1 schedulable instructions).
if (I == RegionEnd || I == llvm::prior(RegionEnd)) {
// Close the current region. Bundle the terminator if needed.
// This invalidates 'RegionEnd' and 'I'.
Scheduler->exitRegion();
continue;
}
DEBUG(dbgs() << "********** MI Scheduling **********\n");
DEBUG(dbgs() << MF->getName()
<< ":BB#" << MBB->getNumber() << "\n From: " << *I << " To: ";
if (RegionEnd != MBB->end()) dbgs() << *RegionEnd;
else dbgs() << "End";
dbgs() << " Remaining: " << RemainingInstrs << "\n");
// Schedule a region: possibly reorder instructions.
// This invalidates 'RegionEnd' and 'I'.
Scheduler->schedule();
// Close the current region.
Scheduler->exitRegion();
// Scheduling has invalidated the current iterator 'I'. Ask the
// scheduler for the top of it's scheduled region.
RegionEnd = Scheduler->begin();
}
assert(RemainingInstrs == 0 && "Instruction count mismatch!");
Scheduler->finishBlock();
}
Scheduler->finalizeSchedule();
DEBUG(LIS->print(dbgs()));
return true;
}
void MachineScheduler::print(raw_ostream &O, const Module* m) const {
// unimplemented
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void ReadyQueue::dump() {
dbgs() << Name << ": ";
for (unsigned i = 0, e = Queue.size(); i < e; ++i)
dbgs() << Queue[i]->NodeNum << " ";
dbgs() << "\n";
}
#endif
//===----------------------------------------------------------------------===//
// ScheduleDAGMI - Base class for MachineInstr scheduling with LiveIntervals
// preservation.
//===----------------------------------------------------------------------===//
/// ReleaseSucc - Decrement the NumPredsLeft count of a successor. When
/// NumPredsLeft reaches zero, release the successor node.
///
/// FIXME: Adjust SuccSU height based on MinLatency.
void ScheduleDAGMI::releaseSucc(SUnit *SU, SDep *SuccEdge) {
SUnit *SuccSU = SuccEdge->getSUnit();
#ifndef NDEBUG
if (SuccSU->NumPredsLeft == 0) {
dbgs() << "*** Scheduling failed! ***\n";
SuccSU->dump(this);
dbgs() << " has been released too many times!\n";
llvm_unreachable(0);
}
#endif
--SuccSU->NumPredsLeft;
if (SuccSU->NumPredsLeft == 0 && SuccSU != &ExitSU)
SchedImpl->releaseTopNode(SuccSU);
}
/// releaseSuccessors - Call releaseSucc on each of SU's successors.
void ScheduleDAGMI::releaseSuccessors(SUnit *SU) {
for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
releaseSucc(SU, &*I);
}
}
/// ReleasePred - Decrement the NumSuccsLeft count of a predecessor. When
/// NumSuccsLeft reaches zero, release the predecessor node.
///
/// FIXME: Adjust PredSU height based on MinLatency.
void ScheduleDAGMI::releasePred(SUnit *SU, SDep *PredEdge) {
SUnit *PredSU = PredEdge->getSUnit();
#ifndef NDEBUG
if (PredSU->NumSuccsLeft == 0) {
dbgs() << "*** Scheduling failed! ***\n";
PredSU->dump(this);
dbgs() << " has been released too many times!\n";
llvm_unreachable(0);
}
#endif
--PredSU->NumSuccsLeft;
if (PredSU->NumSuccsLeft == 0 && PredSU != &EntrySU)
SchedImpl->releaseBottomNode(PredSU);
}
/// releasePredecessors - Call releasePred on each of SU's predecessors.
void ScheduleDAGMI::releasePredecessors(SUnit *SU) {
for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
releasePred(SU, &*I);
}
}
void ScheduleDAGMI::moveInstruction(MachineInstr *MI,
MachineBasicBlock::iterator InsertPos) {
// Advance RegionBegin if the first instruction moves down.
if (&*RegionBegin == MI)
++RegionBegin;
// Update the instruction stream.
BB->splice(InsertPos, BB, MI);
// Update LiveIntervals
LIS->handleMove(MI, /*UpdateFlags=*/true);
// Recede RegionBegin if an instruction moves above the first.
if (RegionBegin == InsertPos)
RegionBegin = MI;
}
bool ScheduleDAGMI::checkSchedLimit() {
#ifndef NDEBUG
if (NumInstrsScheduled == MISchedCutoff && MISchedCutoff != ~0U) {
CurrentTop = CurrentBottom;
return false;
}
++NumInstrsScheduled;
#endif
return true;
}
/// enterRegion - Called back from MachineScheduler::runOnMachineFunction after
/// crossing a scheduling boundary. [begin, end) includes all instructions in
/// the region, including the boundary itself and single-instruction regions
/// that don't get scheduled.
void ScheduleDAGMI::enterRegion(MachineBasicBlock *bb,
MachineBasicBlock::iterator begin,
MachineBasicBlock::iterator end,
unsigned endcount)
{
ScheduleDAGInstrs::enterRegion(bb, begin, end, endcount);
// For convenience remember the end of the liveness region.
LiveRegionEnd =
(RegionEnd == bb->end()) ? RegionEnd : llvm::next(RegionEnd);
}
// Setup the register pressure trackers for the top scheduled top and bottom
// scheduled regions.
void ScheduleDAGMI::initRegPressure() {
TopRPTracker.init(&MF, RegClassInfo, LIS, BB, RegionBegin);
BotRPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd);
// Close the RPTracker to finalize live ins.
RPTracker.closeRegion();
DEBUG(RPTracker.getPressure().dump(TRI));
// Initialize the live ins and live outs.
TopRPTracker.addLiveRegs(RPTracker.getPressure().LiveInRegs);
BotRPTracker.addLiveRegs(RPTracker.getPressure().LiveOutRegs);
// Close one end of the tracker so we can call
// getMaxUpward/DownwardPressureDelta before advancing across any
// instructions. This converts currently live regs into live ins/outs.
TopRPTracker.closeTop();
BotRPTracker.closeBottom();
// Account for liveness generated by the region boundary.
if (LiveRegionEnd != RegionEnd)
BotRPTracker.recede();
assert(BotRPTracker.getPos() == RegionEnd && "Can't find the region bottom");
// Cache the list of excess pressure sets in this region. This will also track
// the max pressure in the scheduled code for these sets.
RegionCriticalPSets.clear();
std::vector<unsigned> RegionPressure = RPTracker.getPressure().MaxSetPressure;
for (unsigned i = 0, e = RegionPressure.size(); i < e; ++i) {
unsigned Limit = TRI->getRegPressureSetLimit(i);
DEBUG(dbgs() << TRI->getRegPressureSetName(i)
<< "Limit " << Limit
<< " Actual " << RegionPressure[i] << "\n");
if (RegionPressure[i] > Limit)
RegionCriticalPSets.push_back(PressureElement(i, 0));
}
DEBUG(dbgs() << "Excess PSets: ";
for (unsigned i = 0, e = RegionCriticalPSets.size(); i != e; ++i)
dbgs() << TRI->getRegPressureSetName(
RegionCriticalPSets[i].PSetID) << " ";
dbgs() << "\n");
}
// FIXME: When the pressure tracker deals in pressure differences then we won't
// iterate over all RegionCriticalPSets[i].
void ScheduleDAGMI::
updateScheduledPressure(std::vector<unsigned> NewMaxPressure) {
for (unsigned i = 0, e = RegionCriticalPSets.size(); i < e; ++i) {
unsigned ID = RegionCriticalPSets[i].PSetID;
int &MaxUnits = RegionCriticalPSets[i].UnitIncrease;
if ((int)NewMaxPressure[ID] > MaxUnits)
MaxUnits = NewMaxPressure[ID];
}
}
/// schedule - Called back from MachineScheduler::runOnMachineFunction
/// after setting up the current scheduling region. [RegionBegin, RegionEnd)
/// only includes instructions that have DAG nodes, not scheduling boundaries.
///
/// This is a skeletal driver, with all the functionality pushed into helpers,
/// so that it can be easilly extended by experimental schedulers. Generally,
/// implementing MachineSchedStrategy should be sufficient to implement a new
/// scheduling algorithm. However, if a scheduler further subclasses
/// ScheduleDAGMI then it will want to override this virtual method in order to
/// update any specialized state.
void ScheduleDAGMI::schedule() {
buildDAGWithRegPressure();
postprocessDAG();
DEBUG(for (unsigned su = 0, e = SUnits.size(); su != e; ++su)
SUnits[su].dumpAll(this));
if (ViewMISchedDAGs) viewGraph();
initQueues();
bool IsTopNode = false;
while (SUnit *SU = SchedImpl->pickNode(IsTopNode)) {
assert(!SU->isScheduled && "Node already scheduled");
if (!checkSchedLimit())
break;
scheduleMI(SU, IsTopNode);
updateQueues(SU, IsTopNode);
}
assert(CurrentTop == CurrentBottom && "Nonempty unscheduled zone.");
placeDebugValues();
DEBUG({
unsigned BBNum = top()->getParent()->getNumber();
dbgs() << "*** Final schedule for BB#" << BBNum << " ***\n";
dumpSchedule();
dbgs() << '\n';
});
}
/// Build the DAG and setup three register pressure trackers.
void ScheduleDAGMI::buildDAGWithRegPressure() {
// Initialize the register pressure tracker used by buildSchedGraph.
RPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd);
// Account for liveness generate by the region boundary.
if (LiveRegionEnd != RegionEnd)
RPTracker.recede();
// Build the DAG, and compute current register pressure.
buildSchedGraph(AA, &RPTracker);
if (ViewMISchedDAGs) viewGraph();
// Initialize top/bottom trackers after computing region pressure.
initRegPressure();
}
/// Apply each ScheduleDAGMutation step in order.
void ScheduleDAGMI::postprocessDAG() {
for (unsigned i = 0, e = Mutations.size(); i < e; ++i) {
Mutations[i]->apply(this);
}
}
// Release all DAG roots for scheduling.
void ScheduleDAGMI::releaseRoots() {
SmallVector<SUnit*, 16> BotRoots;
for (std::vector<SUnit>::iterator
I = SUnits.begin(), E = SUnits.end(); I != E; ++I) {
// A SUnit is ready to top schedule if it has no predecessors.
if (I->Preds.empty())
SchedImpl->releaseTopNode(&(*I));
// A SUnit is ready to bottom schedule if it has no successors.
if (I->Succs.empty())
BotRoots.push_back(&(*I));
}
// Release bottom roots in reverse order so the higher priority nodes appear
// first. This is more natural and slightly more efficient.
for (SmallVectorImpl<SUnit*>::const_reverse_iterator
I = BotRoots.rbegin(), E = BotRoots.rend(); I != E; ++I)
SchedImpl->releaseBottomNode(*I);
}
/// Identify DAG roots and setup scheduler queues.
void ScheduleDAGMI::initQueues() {
// Initialize the strategy before modifying the DAG.
SchedImpl->initialize(this);
// Release edges from the special Entry node or to the special Exit node.
releaseSuccessors(&EntrySU);
releasePredecessors(&ExitSU);
// Release all DAG roots for scheduling.
releaseRoots();
SchedImpl->registerRoots();
CurrentTop = nextIfDebug(RegionBegin, RegionEnd);
CurrentBottom = RegionEnd;
}
/// Move an instruction and update register pressure.
void ScheduleDAGMI::scheduleMI(SUnit *SU, bool IsTopNode) {
// Move the instruction to its new location in the instruction stream.
MachineInstr *MI = SU->getInstr();
if (IsTopNode) {
assert(SU->isTopReady() && "node still has unscheduled dependencies");
if (&*CurrentTop == MI)
CurrentTop = nextIfDebug(++CurrentTop, CurrentBottom);
else {
moveInstruction(MI, CurrentTop);
TopRPTracker.setPos(MI);
}
// Update top scheduled pressure.
TopRPTracker.advance();
assert(TopRPTracker.getPos() == CurrentTop && "out of sync");
updateScheduledPressure(TopRPTracker.getPressure().MaxSetPressure);
}
else {
assert(SU->isBottomReady() && "node still has unscheduled dependencies");
MachineBasicBlock::iterator priorII =
priorNonDebug(CurrentBottom, CurrentTop);
if (&*priorII == MI)
CurrentBottom = priorII;
else {
if (&*CurrentTop == MI) {
CurrentTop = nextIfDebug(++CurrentTop, priorII);
TopRPTracker.setPos(CurrentTop);
}
moveInstruction(MI, CurrentBottom);
CurrentBottom = MI;
}
// Update bottom scheduled pressure.
BotRPTracker.recede();
assert(BotRPTracker.getPos() == CurrentBottom && "out of sync");
updateScheduledPressure(BotRPTracker.getPressure().MaxSetPressure);
}
}
/// Update scheduler queues after scheduling an instruction.
void ScheduleDAGMI::updateQueues(SUnit *SU, bool IsTopNode) {
// Release dependent instructions for scheduling.
if (IsTopNode)
releaseSuccessors(SU);
else
releasePredecessors(SU);
SU->isScheduled = true;
// Notify the scheduling strategy after updating the DAG.
SchedImpl->schedNode(SU, IsTopNode);
}
/// Reinsert any remaining debug_values, just like the PostRA scheduler.
void ScheduleDAGMI::placeDebugValues() {
// If first instruction was a DBG_VALUE then put it back.
if (FirstDbgValue) {
BB->splice(RegionBegin, BB, FirstDbgValue);
RegionBegin = FirstDbgValue;
}
for (std::vector<std::pair<MachineInstr *, MachineInstr *> >::iterator
DI = DbgValues.end(), DE = DbgValues.begin(); DI != DE; --DI) {
std::pair<MachineInstr *, MachineInstr *> P = *prior(DI);
MachineInstr *DbgValue = P.first;
MachineBasicBlock::iterator OrigPrevMI = P.second;
BB->splice(++OrigPrevMI, BB, DbgValue);
if (OrigPrevMI == llvm::prior(RegionEnd))
RegionEnd = DbgValue;
}
DbgValues.clear();
FirstDbgValue = NULL;
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void ScheduleDAGMI::dumpSchedule() const {
for (MachineBasicBlock::iterator MI = begin(), ME = end(); MI != ME; ++MI) {
if (SUnit *SU = getSUnit(&(*MI)))
SU->dump(this);
else
dbgs() << "Missing SUnit\n";
}
}
#endif
//===----------------------------------------------------------------------===//
// ConvergingScheduler - Implementation of the standard MachineSchedStrategy.
//===----------------------------------------------------------------------===//
namespace {
/// ConvergingScheduler shrinks the unscheduled zone using heuristics to balance
/// the schedule.
class ConvergingScheduler : public MachineSchedStrategy {
public:
/// Represent the type of SchedCandidate found within a single queue.
/// pickNodeBidirectional depends on these listed by decreasing priority.
enum CandReason {
NoCand, SingleExcess, SingleCritical, ResourceReduce, ResourceDemand,
BotHeightReduce, BotPathReduce, TopDepthReduce, TopPathReduce,
SingleMax, MultiPressure, NextDefUse, NodeOrder};
#ifndef NDEBUG
static const char *getReasonStr(ConvergingScheduler::CandReason Reason);
#endif
/// Policy for scheduling the next instruction in the candidate's zone.
struct CandPolicy {
bool ReduceLatency;
unsigned ReduceResIdx;
unsigned DemandResIdx;
CandPolicy(): ReduceLatency(false), ReduceResIdx(0), DemandResIdx(0) {}
};
/// Status of an instruction's critical resource consumption.
struct SchedResourceDelta {
// Count critical resources in the scheduled region required by SU.
unsigned CritResources;
// Count critical resources from another region consumed by SU.
unsigned DemandedResources;
SchedResourceDelta(): CritResources(0), DemandedResources(0) {}
bool operator==(const SchedResourceDelta &RHS) const {
return CritResources == RHS.CritResources
&& DemandedResources == RHS.DemandedResources;
}
bool operator!=(const SchedResourceDelta &RHS) const {
return !operator==(RHS);
}
};
/// Store the state used by ConvergingScheduler heuristics, required for the
/// lifetime of one invocation of pickNode().
struct SchedCandidate {
CandPolicy Policy;
// The best SUnit candidate.
SUnit *SU;
// The reason for this candidate.
CandReason Reason;
// Register pressure values for the best candidate.
RegPressureDelta RPDelta;
// Critical resource consumption of the best candidate.
SchedResourceDelta ResDelta;
SchedCandidate(const CandPolicy &policy)
: Policy(policy), SU(NULL), Reason(NoCand) {}
bool isValid() const { return SU; }
// Copy the status of another candidate without changing policy.
void setBest(SchedCandidate &Best) {
assert(Best.Reason != NoCand && "uninitialized Sched candidate");
SU = Best.SU;
Reason = Best.Reason;
RPDelta = Best.RPDelta;
ResDelta = Best.ResDelta;
}
void initResourceDelta(const ScheduleDAGMI *DAG,
const TargetSchedModel *SchedModel);
};
/// Summarize the unscheduled region.
struct SchedRemainder {
// Critical path through the DAG in expected latency.
unsigned CriticalPath;
// Unscheduled resources
SmallVector<unsigned, 16> RemainingCounts;
// Critical resource for the unscheduled zone.
unsigned CritResIdx;
// Number of micro-ops left to schedule.
unsigned RemainingMicroOps;
// Is the unscheduled zone resource limited.
bool IsResourceLimited;
unsigned MaxRemainingCount;
void reset() {
CriticalPath = 0;
RemainingCounts.clear();
CritResIdx = 0;
RemainingMicroOps = 0;
IsResourceLimited = false;
MaxRemainingCount = 0;
}
SchedRemainder() { reset(); }
void init(ScheduleDAGMI *DAG, const TargetSchedModel *SchedModel);
};
/// Each Scheduling boundary is associated with ready queues. It tracks the
/// current cycle in the direction of movement, and maintains the state
/// of "hazards" and other interlocks at the current cycle.
struct SchedBoundary {
ScheduleDAGMI *DAG;
const TargetSchedModel *SchedModel;
SchedRemainder *Rem;
ReadyQueue Available;
ReadyQueue Pending;
bool CheckPending;
// For heuristics, keep a list of the nodes that immediately depend on the
// most recently scheduled node.
SmallPtrSet<const SUnit*, 8> NextSUs;
ScheduleHazardRecognizer *HazardRec;
unsigned CurrCycle;
unsigned IssueCount;
/// MinReadyCycle - Cycle of the soonest available instruction.
unsigned MinReadyCycle;
// The expected latency of the critical path in this scheduled zone.
unsigned ExpectedLatency;
// Resources used in the scheduled zone beyond this boundary.
SmallVector<unsigned, 16> ResourceCounts;
// Cache the critical resources ID in this scheduled zone.
unsigned CritResIdx;
// Is the scheduled region resource limited vs. latency limited.
bool IsResourceLimited;
unsigned ExpectedCount;
// Policy flag: attempt to find ILP until expected latency is covered.
bool ShouldIncreaseILP;
#ifndef NDEBUG
// Remember the greatest min operand latency.
unsigned MaxMinLatency;
#endif
void reset() {
Available.clear();
Pending.clear();
CheckPending = false;
NextSUs.clear();
HazardRec = 0;
CurrCycle = 0;
IssueCount = 0;
MinReadyCycle = UINT_MAX;
ExpectedLatency = 0;
ResourceCounts.resize(1);
assert(!ResourceCounts[0] && "nonzero count for bad resource");
CritResIdx = 0;
IsResourceLimited = false;
ExpectedCount = 0;
ShouldIncreaseILP = false;
#ifndef NDEBUG
MaxMinLatency = 0;
#endif
// Reserve a zero-count for invalid CritResIdx.
ResourceCounts.resize(1);
}
/// Pending queues extend the ready queues with the same ID and the
/// PendingFlag set.
SchedBoundary(unsigned ID, const Twine &Name):
DAG(0), SchedModel(0), Rem(0), Available(ID, Name+".A"),
Pending(ID << ConvergingScheduler::LogMaxQID, Name+".P") {
reset();
}
~SchedBoundary() { delete HazardRec; }
void init(ScheduleDAGMI *dag, const TargetSchedModel *smodel,
SchedRemainder *rem);
bool isTop() const {
return Available.getID() == ConvergingScheduler::TopQID;
}
unsigned getUnscheduledLatency(SUnit *SU) const {
if (isTop())
return SU->getHeight();
return SU->getDepth();
}
unsigned getCriticalCount() const {
return ResourceCounts[CritResIdx];
}
bool checkHazard(SUnit *SU);
void checkILPPolicy();
void releaseNode(SUnit *SU, unsigned ReadyCycle);
void bumpCycle();
void countResource(unsigned PIdx, unsigned Cycles);
void bumpNode(SUnit *SU);
void releasePending();
void removeReady(SUnit *SU);
SUnit *pickOnlyChoice();
};
private:
ScheduleDAGMI *DAG;
const TargetSchedModel *SchedModel;
const TargetRegisterInfo *TRI;
// State of the top and bottom scheduled instruction boundaries.
SchedRemainder Rem;
SchedBoundary Top;
SchedBoundary Bot;
public:
/// SUnit::NodeQueueId: 0 (none), 1 (top), 2 (bot), 3 (both)
enum {
TopQID = 1,
BotQID = 2,
LogMaxQID = 2
};
ConvergingScheduler():
DAG(0), SchedModel(0), TRI(0), Top(TopQID, "TopQ"), Bot(BotQID, "BotQ") {}
virtual void initialize(ScheduleDAGMI *dag);
virtual SUnit *pickNode(bool &IsTopNode);
virtual void schedNode(SUnit *SU, bool IsTopNode);
virtual void releaseTopNode(SUnit *SU);
virtual void releaseBottomNode(SUnit *SU);
virtual void registerRoots();
protected:
void balanceZones(
ConvergingScheduler::SchedBoundary &CriticalZone,
ConvergingScheduler::SchedCandidate &CriticalCand,
ConvergingScheduler::SchedBoundary &OppositeZone,
ConvergingScheduler::SchedCandidate &OppositeCand);
void checkResourceLimits(ConvergingScheduler::SchedCandidate &TopCand,
ConvergingScheduler::SchedCandidate &BotCand);
void tryCandidate(SchedCandidate &Cand,
SchedCandidate &TryCand,
SchedBoundary &Zone,
const RegPressureTracker &RPTracker,
RegPressureTracker &TempTracker);
SUnit *pickNodeBidirectional(bool &IsTopNode);
void pickNodeFromQueue(SchedBoundary &Zone,
const RegPressureTracker &RPTracker,
SchedCandidate &Candidate);
#ifndef NDEBUG
void traceCandidate(const SchedCandidate &Cand, const SchedBoundary &Zone);
#endif
};
} // namespace
void ConvergingScheduler::SchedRemainder::
init(ScheduleDAGMI *DAG, const TargetSchedModel *SchedModel) {
reset();
if (!SchedModel->hasInstrSchedModel())
return;
RemainingCounts.resize(SchedModel->getNumProcResourceKinds());
for (std::vector<SUnit>::iterator
I = DAG->SUnits.begin(), E = DAG->SUnits.end(); I != E; ++I) {
const MCSchedClassDesc *SC = DAG->getSchedClass(&*I);
RemainingMicroOps += SchedModel->getNumMicroOps(I->getInstr(), SC);
for (TargetSchedModel::ProcResIter
PI = SchedModel->getWriteProcResBegin(SC),
PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
unsigned PIdx = PI->ProcResourceIdx;
unsigned Factor = SchedModel->getResourceFactor(PIdx);
RemainingCounts[PIdx] += (Factor * PI->Cycles);
}
}
}
void ConvergingScheduler::SchedBoundary::
init(ScheduleDAGMI *dag, const TargetSchedModel *smodel, SchedRemainder *rem) {
reset();
DAG = dag;
SchedModel = smodel;
Rem = rem;
if (SchedModel->hasInstrSchedModel())
ResourceCounts.resize(SchedModel->getNumProcResourceKinds());
}
void ConvergingScheduler::initialize(ScheduleDAGMI *dag) {
DAG = dag;
SchedModel = DAG->getSchedModel();
TRI = DAG->TRI;
Rem.init(DAG, SchedModel);
Top.init(DAG, SchedModel, &Rem);
Bot.init(DAG, SchedModel, &Rem);
// Initialize resource counts.
// Initialize the HazardRecognizers. If itineraries don't exist, are empty, or
// are disabled, then these HazardRecs will be disabled.
const InstrItineraryData *Itin = SchedModel->getInstrItineraries();
const TargetMachine &TM = DAG->MF.getTarget();
Top.HazardRec = TM.getInstrInfo()->CreateTargetMIHazardRecognizer(Itin, DAG);
Bot.HazardRec = TM.getInstrInfo()->CreateTargetMIHazardRecognizer(Itin, DAG);
assert((!ForceTopDown || !ForceBottomUp) &&
"-misched-topdown incompatible with -misched-bottomup");
}
void ConvergingScheduler::releaseTopNode(SUnit *SU) {
if (SU->isScheduled)
return;
for (SUnit::succ_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
unsigned PredReadyCycle = I->getSUnit()->TopReadyCycle;
unsigned MinLatency = I->getMinLatency();
#ifndef NDEBUG
Top.MaxMinLatency = std::max(MinLatency, Top.MaxMinLatency);
#endif
if (SU->TopReadyCycle < PredReadyCycle + MinLatency)
SU->TopReadyCycle = PredReadyCycle + MinLatency;
}
Top.releaseNode(SU, SU->TopReadyCycle);
}
void ConvergingScheduler::releaseBottomNode(SUnit *SU) {
if (SU->isScheduled)
return;
assert(SU->getInstr() && "Scheduled SUnit must have instr");
for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
unsigned SuccReadyCycle = I->getSUnit()->BotReadyCycle;
unsigned MinLatency = I->getMinLatency();
#ifndef NDEBUG
Bot.MaxMinLatency = std::max(MinLatency, Bot.MaxMinLatency);
#endif
if (SU->BotReadyCycle < SuccReadyCycle + MinLatency)
SU->BotReadyCycle = SuccReadyCycle + MinLatency;
}
Bot.releaseNode(SU, SU->BotReadyCycle);
}
void ConvergingScheduler::registerRoots() {
Rem.CriticalPath = DAG->ExitSU.getDepth();
// Some roots may not feed into ExitSU. Check all of them in case.
for (std::vector<SUnit*>::const_iterator
I = Bot.Available.begin(), E = Bot.Available.end(); I != E; ++I) {
if ((*I)->getDepth() > Rem.CriticalPath)
Rem.CriticalPath = (*I)->getDepth();
}
DEBUG(dbgs() << "Critical Path: " << Rem.CriticalPath << '\n');
}
/// Does this SU have a hazard within the current instruction group.
///
/// The scheduler supports two modes of hazard recognition. The first is the
/// ScheduleHazardRecognizer API. It is a fully general hazard recognizer that
/// supports highly complicated in-order reservation tables
/// (ScoreboardHazardRecognizer) and arbitraty target-specific logic.
///
/// The second is a streamlined mechanism that checks for hazards based on
/// simple counters that the scheduler itself maintains. It explicitly checks
/// for instruction dispatch limitations, including the number of micro-ops that
/// can dispatch per cycle.
///
/// TODO: Also check whether the SU must start a new group.
bool ConvergingScheduler::SchedBoundary::checkHazard(SUnit *SU) {
if (HazardRec->isEnabled())
return HazardRec->getHazardType(SU) != ScheduleHazardRecognizer::NoHazard;
unsigned uops = SchedModel->getNumMicroOps(SU->getInstr());
if ((IssueCount > 0) && (IssueCount + uops > SchedModel->getIssueWidth())) {
DEBUG(dbgs() << " SU(" << SU->NodeNum << ") uops="
<< SchedModel->getNumMicroOps(SU->getInstr()) << '\n');
return true;
}
return false;
}
/// If expected latency is covered, disable ILP policy.
void ConvergingScheduler::SchedBoundary::checkILPPolicy() {
if (ShouldIncreaseILP
&& (IsResourceLimited || ExpectedLatency <= CurrCycle)) {
ShouldIncreaseILP = false;
DEBUG(dbgs() << "Disable ILP: " << Available.getName() << '\n');
}
}
void ConvergingScheduler::SchedBoundary::releaseNode(SUnit *SU,
unsigned ReadyCycle) {
if (ReadyCycle < MinReadyCycle)
MinReadyCycle = ReadyCycle;
// Check for interlocks first. For the purpose of other heuristics, an
// instruction that cannot issue appears as if it's not in the ReadyQueue.
if (ReadyCycle > CurrCycle || checkHazard(SU))
Pending.push(SU);
else
Available.push(SU);
// Record this node as an immediate dependent of the scheduled node.
NextSUs.insert(SU);
// If CriticalPath has been computed, then check if the unscheduled nodes
// exceed the ILP window. Before registerRoots, CriticalPath==0.
if (Rem->CriticalPath && (ExpectedLatency + getUnscheduledLatency(SU)
> Rem->CriticalPath + ILPWindow)) {
ShouldIncreaseILP = true;
DEBUG(dbgs() << "Increase ILP: " << Available.getName() << " "
<< ExpectedLatency << " + " << getUnscheduledLatency(SU) << '\n');
}
}
/// Move the boundary of scheduled code by one cycle.
void ConvergingScheduler::SchedBoundary::bumpCycle() {
unsigned Width = SchedModel->getIssueWidth();
IssueCount = (IssueCount <= Width) ? 0 : IssueCount - Width;
unsigned NextCycle = CurrCycle + 1;
assert(MinReadyCycle < UINT_MAX && "MinReadyCycle uninitialized");
if (MinReadyCycle > NextCycle) {
IssueCount = 0;
NextCycle = MinReadyCycle;
}
if (!HazardRec->isEnabled()) {
// Bypass HazardRec virtual calls.
CurrCycle = NextCycle;
}
else {
// Bypass getHazardType calls in case of long latency.
for (; CurrCycle != NextCycle; ++CurrCycle) {
if (isTop())
HazardRec->AdvanceCycle();
else
HazardRec->RecedeCycle();
}
}
CheckPending = true;
IsResourceLimited = getCriticalCount() > std::max(ExpectedLatency, CurrCycle);
DEBUG(dbgs() << " *** " << Available.getName() << " cycle "
<< CurrCycle << '\n');
}
/// Add the given processor resource to this scheduled zone.
void ConvergingScheduler::SchedBoundary::countResource(unsigned PIdx,
unsigned Cycles) {
unsigned Factor = SchedModel->getResourceFactor(PIdx);
DEBUG(dbgs() << " " << SchedModel->getProcResource(PIdx)->Name
<< " +(" << Cycles << "x" << Factor
<< ") / " << SchedModel->getLatencyFactor() << '\n');
unsigned Count = Factor * Cycles;
ResourceCounts[PIdx] += Count;
assert(Rem->RemainingCounts[PIdx] >= Count && "resource double counted");
Rem->RemainingCounts[PIdx] -= Count;
// Reset MaxRemainingCount for sanity.
Rem->MaxRemainingCount = 0;
// Check if this resource exceeds the current critical resource by a full
// cycle. If so, it becomes the critical resource.
if ((int)(ResourceCounts[PIdx] - ResourceCounts[CritResIdx])
>= (int)SchedModel->getLatencyFactor()) {
CritResIdx = PIdx;
DEBUG(dbgs() << " *** Critical resource "
<< SchedModel->getProcResource(PIdx)->Name << " x"
<< ResourceCounts[PIdx] << '\n');
}
}
/// Move the boundary of scheduled code by one SUnit.
void ConvergingScheduler::SchedBoundary::bumpNode(SUnit *SU) {
// Update the reservation table.
if (HazardRec->isEnabled()) {
if (!isTop() && SU->isCall) {
// Calls are scheduled with their preceding instructions. For bottom-up
// scheduling, clear the pipeline state before emitting.
HazardRec->Reset();
}
HazardRec->EmitInstruction(SU);
}
// Update resource counts and critical resource.
if (SchedModel->hasInstrSchedModel()) {
const MCSchedClassDesc *SC = DAG->getSchedClass(SU);
Rem->RemainingMicroOps -= SchedModel->getNumMicroOps(SU->getInstr(), SC);
for (TargetSchedModel::ProcResIter
PI = SchedModel->getWriteProcResBegin(SC),
PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
countResource(PI->ProcResourceIdx, PI->Cycles);
}
}
if (isTop()) {
if (SU->getDepth() > ExpectedLatency)
ExpectedLatency = SU->getDepth();
}
else {
if (SU->getHeight() > ExpectedLatency)
ExpectedLatency = SU->getHeight();
}
IsResourceLimited = getCriticalCount() > std::max(ExpectedLatency, CurrCycle);
// Check the instruction group dispatch limit.
// TODO: Check if this SU must end a dispatch group.
IssueCount += SchedModel->getNumMicroOps(SU->getInstr());
// checkHazard prevents scheduling multiple instructions per cycle that exceed
// issue width. However, we commonly reach the maximum. In this case
// opportunistically bump the cycle to avoid uselessly checking everything in
// the readyQ. Furthermore, a single instruction may produce more than one
// cycle's worth of micro-ops.
if (IssueCount >= SchedModel->getIssueWidth()) {
DEBUG(dbgs() << " *** Max instrs at cycle " << CurrCycle << '\n');
bumpCycle();
}
}
/// Release pending ready nodes in to the available queue. This makes them
/// visible to heuristics.
void ConvergingScheduler::SchedBoundary::releasePending() {
// If the available queue is empty, it is safe to reset MinReadyCycle.
if (Available.empty())
MinReadyCycle = UINT_MAX;
// Check to see if any of the pending instructions are ready to issue. If
// so, add them to the available queue.
for (unsigned i = 0, e = Pending.size(); i != e; ++i) {
SUnit *SU = *(Pending.begin()+i);
unsigned ReadyCycle = isTop() ? SU->TopReadyCycle : SU->BotReadyCycle;
if (ReadyCycle < MinReadyCycle)
MinReadyCycle = ReadyCycle;
if (ReadyCycle > CurrCycle)
continue;
if (checkHazard(SU))
continue;
Available.push(SU);
Pending.remove(Pending.begin()+i);
--i; --e;
}
DEBUG(if (!Pending.empty()) Pending.dump());
CheckPending = false;
}
/// Remove SU from the ready set for this boundary.
void ConvergingScheduler::SchedBoundary::removeReady(SUnit *SU) {
if (Available.isInQueue(SU))
Available.remove(Available.find(SU));
else {
assert(Pending.isInQueue(SU) && "bad ready count");
Pending.remove(Pending.find(SU));
}
}
/// If this queue only has one ready candidate, return it. As a side effect,
/// defer any nodes that now hit a hazard, and advance the cycle until at least
/// one node is ready. If multiple instructions are ready, return NULL.
SUnit *ConvergingScheduler::SchedBoundary::pickOnlyChoice() {
if (CheckPending)
releasePending();
if (IssueCount > 0) {
// Defer any ready instrs that now have a hazard.
for (ReadyQueue::iterator I = Available.begin(); I != Available.end();) {
if (checkHazard(*I)) {
Pending.push(*I);
I = Available.remove(I);
continue;
}
++I;
}
}
for (unsigned i = 0; Available.empty(); ++i) {
assert(i <= (HazardRec->getMaxLookAhead() + MaxMinLatency) &&
"permanent hazard"); (void)i;
bumpCycle();
releasePending();
}
if (Available.size() == 1)
return *Available.begin();
return NULL;
}
/// Record the candidate policy for opposite zones with different critical
/// resources.
///
/// If the CriticalZone is latency limited, don't force a policy for the
/// candidates here. Instead, When releasing each candidate, releaseNode
/// compares the region's critical path to the candidate's height or depth and
/// the scheduled zone's expected latency then sets ShouldIncreaseILP.
void ConvergingScheduler::balanceZones(
ConvergingScheduler::SchedBoundary &CriticalZone,
ConvergingScheduler::SchedCandidate &CriticalCand,
ConvergingScheduler::SchedBoundary &OppositeZone,
ConvergingScheduler::SchedCandidate &OppositeCand) {
if (!CriticalZone.IsResourceLimited)
return;
SchedRemainder *Rem = CriticalZone.Rem;
// If the critical zone is overconsuming a resource relative to the
// remainder, try to reduce it.
unsigned RemainingCritCount =
Rem->RemainingCounts[CriticalZone.CritResIdx];
if ((int)(Rem->MaxRemainingCount - RemainingCritCount)
> (int)SchedModel->getLatencyFactor()) {
CriticalCand.Policy.ReduceResIdx = CriticalZone.CritResIdx;
DEBUG(dbgs() << "Balance " << CriticalZone.Available.getName() << " reduce "
<< SchedModel->getProcResource(CriticalZone.CritResIdx)->Name
<< '\n');
}
// If the other zone is underconsuming a resource relative to the full zone,
// try to increase it.
unsigned OppositeCount =
OppositeZone.ResourceCounts[CriticalZone.CritResIdx];
if ((int)(OppositeZone.ExpectedCount - OppositeCount)
> (int)SchedModel->getLatencyFactor()) {
OppositeCand.Policy.DemandResIdx = CriticalZone.CritResIdx;
DEBUG(dbgs() << "Balance " << OppositeZone.Available.getName() << " demand "
<< SchedModel->getProcResource(OppositeZone.CritResIdx)->Name
<< '\n');
}
}
/// Determine if the scheduled zones exceed resource limits or critical path and
/// set each candidate's ReduceHeight policy accordingly.
void ConvergingScheduler::checkResourceLimits(
ConvergingScheduler::SchedCandidate &TopCand,
ConvergingScheduler::SchedCandidate &BotCand) {
Bot.checkILPPolicy();
Top.checkILPPolicy();
if (Bot.ShouldIncreaseILP)
BotCand.Policy.ReduceLatency = true;
if (Top.ShouldIncreaseILP)
TopCand.Policy.ReduceLatency = true;
// Handle resource-limited regions.
if (Top.IsResourceLimited && Bot.IsResourceLimited
&& Top.CritResIdx == Bot.CritResIdx) {
// If the scheduled critical resource in both zones is no longer the
// critical remaining resource, attempt to reduce resource height both ways.
if (Top.CritResIdx != Rem.CritResIdx) {
TopCand.Policy.ReduceResIdx = Top.CritResIdx;
BotCand.Policy.ReduceResIdx = Bot.CritResIdx;
DEBUG(dbgs() << "Reduce scheduled "
<< SchedModel->getProcResource(Top.CritResIdx)->Name << '\n');
}
return;
}
// Handle latency-limited regions.
if (!Top.IsResourceLimited && !Bot.IsResourceLimited) {
// If the total scheduled expected latency exceeds the region's critical
// path then reduce latency both ways.
//
// Just because a zone is not resource limited does not mean it is latency
// limited. Unbuffered resource, such as max micro-ops may cause CurrCycle
// to exceed expected latency.
if ((Top.ExpectedLatency + Bot.ExpectedLatency >= Rem.CriticalPath)
&& (Rem.CriticalPath > Top.CurrCycle + Bot.CurrCycle)) {
TopCand.Policy.ReduceLatency = true;
BotCand.Policy.ReduceLatency = true;
DEBUG(dbgs() << "Reduce scheduled latency " << Top.ExpectedLatency
<< " + " << Bot.ExpectedLatency << '\n');
}
return;
}
// The critical resource is different in each zone, so request balancing.
// Compute the cost of each zone.
Rem.MaxRemainingCount = std::max(
Rem.RemainingMicroOps * SchedModel->getMicroOpFactor(),
Rem.RemainingCounts[Rem.CritResIdx]);
Top.ExpectedCount = std::max(Top.ExpectedLatency, Top.CurrCycle);
Top.ExpectedCount = std::max(
Top.getCriticalCount(),
Top.ExpectedCount * SchedModel->getLatencyFactor());
Bot.ExpectedCount = std::max(Bot.ExpectedLatency, Bot.CurrCycle);
Bot.ExpectedCount = std::max(
Bot.getCriticalCount(),
Bot.ExpectedCount * SchedModel->getLatencyFactor());
balanceZones(Top, TopCand, Bot, BotCand);
balanceZones(Bot, BotCand, Top, TopCand);
}
void ConvergingScheduler::SchedCandidate::
initResourceDelta(const ScheduleDAGMI *DAG,
const TargetSchedModel *SchedModel) {
if (!Policy.ReduceResIdx && !Policy.DemandResIdx)
return;
const MCSchedClassDesc *SC = DAG->getSchedClass(SU);
for (TargetSchedModel::ProcResIter
PI = SchedModel->getWriteProcResBegin(SC),
PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
if (PI->ProcResourceIdx == Policy.ReduceResIdx)
ResDelta.CritResources += PI->Cycles;
if (PI->ProcResourceIdx == Policy.DemandResIdx)
ResDelta.DemandedResources += PI->Cycles;
}
}
/// Return true if this heuristic determines order.
static bool tryLess(unsigned TryVal, unsigned CandVal,
ConvergingScheduler::SchedCandidate &TryCand,
ConvergingScheduler::SchedCandidate &Cand,
ConvergingScheduler::CandReason Reason) {
if (TryVal < CandVal) {
TryCand.Reason = Reason;
return true;
}
if (TryVal > CandVal) {
if (Cand.Reason > Reason)
Cand.Reason = Reason;
return true;
}
return false;
}
static bool tryGreater(unsigned TryVal, unsigned CandVal,
ConvergingScheduler::SchedCandidate &TryCand,
ConvergingScheduler::SchedCandidate &Cand,
ConvergingScheduler::CandReason Reason) {
if (TryVal > CandVal) {
TryCand.Reason = Reason;
return true;
}
if (TryVal < CandVal) {
if (Cand.Reason > Reason)
Cand.Reason = Reason;
return true;
}
return false;
}
/// Apply a set of heursitics to a new candidate. Heuristics are currently
/// hierarchical. This may be more efficient than a graduated cost model because
/// we don't need to evaluate all aspects of the model for each node in the
/// queue. But it's really done to make the heuristics easier to debug and
/// statistically analyze.
///
/// \param Cand provides the policy and current best candidate.
/// \param TryCand refers to the next SUnit candidate, otherwise uninitialized.
/// \param Zone describes the scheduled zone that we are extending.
/// \param RPTracker describes reg pressure within the scheduled zone.
/// \param TempTracker is a scratch pressure tracker to reuse in queries.
void ConvergingScheduler::tryCandidate(SchedCandidate &Cand,
SchedCandidate &TryCand,
SchedBoundary &Zone,
const RegPressureTracker &RPTracker,
RegPressureTracker &TempTracker) {
// Always initialize TryCand's RPDelta.
TempTracker.getMaxPressureDelta(TryCand.SU->getInstr(), TryCand.RPDelta,
DAG->getRegionCriticalPSets(),
DAG->getRegPressure().MaxSetPressure);
// Initialize the candidate if needed.
if (!Cand.isValid()) {
TryCand.Reason = NodeOrder;
return;
}
// Avoid exceeding the target's limit.
if (tryLess(TryCand.RPDelta.Excess.UnitIncrease,
Cand.RPDelta.Excess.UnitIncrease, TryCand, Cand, SingleExcess))
return;
if (Cand.Reason == SingleExcess)
Cand.Reason = MultiPressure;
// Avoid increasing the max critical pressure in the scheduled region.
if (tryLess(TryCand.RPDelta.CriticalMax.UnitIncrease,
Cand.RPDelta.CriticalMax.UnitIncrease,
TryCand, Cand, SingleCritical))
return;
if (Cand.Reason == SingleCritical)
Cand.Reason = MultiPressure;
// Avoid critical resource consumption and balance the schedule.
TryCand.initResourceDelta(DAG, SchedModel);
if (tryLess(TryCand.ResDelta.CritResources, Cand.ResDelta.CritResources,
TryCand, Cand, ResourceReduce))
return;
if (tryGreater(TryCand.ResDelta.DemandedResources,
Cand.ResDelta.DemandedResources,
TryCand, Cand, ResourceDemand))
return;
// Avoid serializing long latency dependence chains.
if (Cand.Policy.ReduceLatency) {
if (Zone.isTop()) {
if (Cand.SU->getDepth() * SchedModel->getLatencyFactor()
> Zone.ExpectedCount) {
if (tryLess(TryCand.SU->getDepth(), Cand.SU->getDepth(),
TryCand, Cand, TopDepthReduce))
return;
}
if (tryGreater(TryCand.SU->getHeight(), Cand.SU->getHeight(),
TryCand, Cand, TopPathReduce))
return;
}
else {
if (Cand.SU->getHeight() * SchedModel->getLatencyFactor()
> Zone.ExpectedCount) {
if (tryLess(TryCand.SU->getHeight(), Cand.SU->getHeight(),
TryCand, Cand, BotHeightReduce))
return;
}
if (tryGreater(TryCand.SU->getDepth(), Cand.SU->getDepth(),
TryCand, Cand, BotPathReduce))
return;
}
}
// Avoid increasing the max pressure of the entire region.
if (tryLess(TryCand.RPDelta.CurrentMax.UnitIncrease,
Cand.RPDelta.CurrentMax.UnitIncrease, TryCand, Cand, SingleMax))
return;
if (Cand.Reason == SingleMax)
Cand.Reason = MultiPressure;
// Prefer immediate defs/users of the last scheduled instruction. This is a
// nice pressure avoidance strategy that also conserves the processor's
// register renaming resources and keeps the machine code readable.
if (Zone.NextSUs.count(TryCand.SU) && !Zone.NextSUs.count(Cand.SU)) {
TryCand.Reason = NextDefUse;
return;
}
if (!Zone.NextSUs.count(TryCand.SU) && Zone.NextSUs.count(Cand.SU)) {
if (Cand.Reason > NextDefUse)
Cand.Reason = NextDefUse;
return;
}
// Fall through to original instruction order.
if ((Zone.isTop() && TryCand.SU->NodeNum < Cand.SU->NodeNum)
|| (!Zone.isTop() && TryCand.SU->NodeNum > Cand.SU->NodeNum)) {
TryCand.Reason = NodeOrder;
}
}
/// pickNodeFromQueue helper that returns true if the LHS reg pressure effect is
/// more desirable than RHS from scheduling standpoint.
static bool compareRPDelta(const RegPressureDelta &LHS,
const RegPressureDelta &RHS) {
// Compare each component of pressure in decreasing order of importance
// without checking if any are valid. Invalid PressureElements are assumed to
// have UnitIncrease==0, so are neutral.
// Avoid increasing the max critical pressure in the scheduled region.
if (LHS.Excess.UnitIncrease != RHS.Excess.UnitIncrease) {
DEBUG(dbgs() << "RP excess top - bot: "
<< (LHS.Excess.UnitIncrease - RHS.Excess.UnitIncrease) << '\n');
return LHS.Excess.UnitIncrease < RHS.Excess.UnitIncrease;
}
// Avoid increasing the max critical pressure in the scheduled region.
if (LHS.CriticalMax.UnitIncrease != RHS.CriticalMax.UnitIncrease) {
DEBUG(dbgs() << "RP critical top - bot: "
<< (LHS.CriticalMax.UnitIncrease - RHS.CriticalMax.UnitIncrease)
<< '\n');
return LHS.CriticalMax.UnitIncrease < RHS.CriticalMax.UnitIncrease;
}
// Avoid increasing the max pressure of the entire region.
if (LHS.CurrentMax.UnitIncrease != RHS.CurrentMax.UnitIncrease) {
DEBUG(dbgs() << "RP current top - bot: "
<< (LHS.CurrentMax.UnitIncrease - RHS.CurrentMax.UnitIncrease)
<< '\n');
return LHS.CurrentMax.UnitIncrease < RHS.CurrentMax.UnitIncrease;
}
return false;
}
#ifndef NDEBUG
const char *ConvergingScheduler::getReasonStr(
ConvergingScheduler::CandReason Reason) {
switch (Reason) {
case NoCand: return "NOCAND ";
case SingleExcess: return "REG-EXCESS";
case SingleCritical: return "REG-CRIT ";
case SingleMax: return "REG-MAX ";
case MultiPressure: return "REG-MULTI ";
case ResourceReduce: return "RES-REDUCE";
case ResourceDemand: return "RES-DEMAND";
case TopDepthReduce: return "TOP-DEPTH ";
case TopPathReduce: return "TOP-PATH ";
case BotHeightReduce:return "BOT-HEIGHT";
case BotPathReduce: return "BOT-PATH ";
case NextDefUse: return "DEF-USE ";
case NodeOrder: return "ORDER ";
};
llvm_unreachable("Unknown reason!");
}
void ConvergingScheduler::traceCandidate(const SchedCandidate &Cand,
const SchedBoundary &Zone) {
const char *Label = getReasonStr(Cand.Reason);
PressureElement P;
unsigned ResIdx = 0;
unsigned Latency = 0;
switch (Cand.Reason) {
default:
break;
case SingleExcess:
P = Cand.RPDelta.Excess;
break;
case SingleCritical:
P = Cand.RPDelta.CriticalMax;
break;
case SingleMax:
P = Cand.RPDelta.CurrentMax;
break;
case ResourceReduce:
ResIdx = Cand.Policy.ReduceResIdx;
break;
case ResourceDemand:
ResIdx = Cand.Policy.DemandResIdx;
break;
case TopDepthReduce:
Latency = Cand.SU->getDepth();
break;
case TopPathReduce:
Latency = Cand.SU->getHeight();
break;
case BotHeightReduce:
Latency = Cand.SU->getHeight();
break;
case BotPathReduce:
Latency = Cand.SU->getDepth();
break;
}
dbgs() << Label << " " << Zone.Available.getName() << " ";
if (P.isValid())
dbgs() << TRI->getRegPressureSetName(P.PSetID) << ":" << P.UnitIncrease
<< " ";
else
dbgs() << " ";
if (ResIdx)
dbgs() << SchedModel->getProcResource(ResIdx)->Name << " ";
else
dbgs() << " ";
if (Latency)
dbgs() << Latency << " cycles ";
else
dbgs() << " ";
Cand.SU->dump(DAG);
}
#endif
/// Pick the best candidate from the top queue.
///
/// TODO: getMaxPressureDelta results can be mostly cached for each SUnit during
/// DAG building. To adjust for the current scheduling location we need to
/// maintain the number of vreg uses remaining to be top-scheduled.
void ConvergingScheduler::pickNodeFromQueue(SchedBoundary &Zone,
const RegPressureTracker &RPTracker,
SchedCandidate &Cand) {
ReadyQueue &Q = Zone.Available;
DEBUG(Q.dump());
// getMaxPressureDelta temporarily modifies the tracker.
RegPressureTracker &TempTracker = const_cast<RegPressureTracker&>(RPTracker);
for (ReadyQueue::iterator I = Q.begin(), E = Q.end(); I != E; ++I) {
SchedCandidate TryCand(Cand.Policy);
TryCand.SU = *I;
tryCandidate(Cand, TryCand, Zone, RPTracker, TempTracker);
if (TryCand.Reason != NoCand) {
// Initialize resource delta if needed in case future heuristics query it.
if (TryCand.ResDelta == SchedResourceDelta())
TryCand.initResourceDelta(DAG, SchedModel);
Cand.setBest(TryCand);
DEBUG(traceCandidate(Cand, Zone));
}
TryCand.SU = *I;
}
}
static void tracePick(const ConvergingScheduler::SchedCandidate &Cand,
bool IsTop) {
DEBUG(dbgs() << "Pick " << (IsTop ? "top" : "bot")
<< " SU(" << Cand.SU->NodeNum << ") "
<< ConvergingScheduler::getReasonStr(Cand.Reason) << '\n');
}
/// Pick the best candidate node from either the top or bottom queue.
SUnit *ConvergingScheduler::pickNodeBidirectional(bool &IsTopNode) {
// Schedule as far as possible in the direction of no choice. This is most
// efficient, but also provides the best heuristics for CriticalPSets.
if (SUnit *SU = Bot.pickOnlyChoice()) {
IsTopNode = false;
return SU;
}
if (SUnit *SU = Top.pickOnlyChoice()) {
IsTopNode = true;
return SU;
}
CandPolicy NoPolicy;
SchedCandidate BotCand(NoPolicy);
SchedCandidate TopCand(NoPolicy);
checkResourceLimits(TopCand, BotCand);
// Prefer bottom scheduling when heuristics are silent.
pickNodeFromQueue(Bot, DAG->getBotRPTracker(), BotCand);
assert(BotCand.Reason != NoCand && "failed to find the first candidate");
// If either Q has a single candidate that provides the least increase in
// Excess pressure, we can immediately schedule from that Q.
//
// RegionCriticalPSets summarizes the pressure within the scheduled region and
// affects picking from either Q. If scheduling in one direction must
// increase pressure for one of the excess PSets, then schedule in that
// direction first to provide more freedom in the other direction.
if (BotCand.Reason == SingleExcess || BotCand.Reason == SingleCritical) {
IsTopNode = false;
tracePick(BotCand, IsTopNode);
return BotCand.SU;
}
// Check if the top Q has a better candidate.
pickNodeFromQueue(Top, DAG->getTopRPTracker(), TopCand);
assert(TopCand.Reason != NoCand && "failed to find the first candidate");
// If either Q has a single candidate that minimizes pressure above the
// original region's pressure pick it.
if (TopCand.Reason <= SingleMax || BotCand.Reason <= SingleMax) {
if (TopCand.Reason < BotCand.Reason) {
IsTopNode = true;
tracePick(TopCand, IsTopNode);
return TopCand.SU;
}
IsTopNode = false;
tracePick(BotCand, IsTopNode);
return BotCand.SU;
}
// Check for a salient pressure difference and pick the best from either side.
if (compareRPDelta(TopCand.RPDelta, BotCand.RPDelta)) {
IsTopNode = true;
tracePick(TopCand, IsTopNode);
return TopCand.SU;
}
// Otherwise prefer the bottom candidate, in node order if all else failed.
if (TopCand.Reason < BotCand.Reason) {
IsTopNode = true;
tracePick(TopCand, IsTopNode);
return TopCand.SU;
}
IsTopNode = false;
tracePick(BotCand, IsTopNode);
return BotCand.SU;
}
/// Pick the best node to balance the schedule. Implements MachineSchedStrategy.
SUnit *ConvergingScheduler::pickNode(bool &IsTopNode) {
if (DAG->top() == DAG->bottom()) {
assert(Top.Available.empty() && Top.Pending.empty() &&
Bot.Available.empty() && Bot.Pending.empty() && "ReadyQ garbage");
return NULL;
}
SUnit *SU;
do {
if (ForceTopDown) {
SU = Top.pickOnlyChoice();
if (!SU) {
CandPolicy NoPolicy;
SchedCandidate TopCand(NoPolicy);
pickNodeFromQueue(Top, DAG->getTopRPTracker(), TopCand);
assert(TopCand.Reason != NoCand && "failed to find the first candidate");
SU = TopCand.SU;
}
IsTopNode = true;
}
else if (ForceBottomUp) {
SU = Bot.pickOnlyChoice();
if (!SU) {
CandPolicy NoPolicy;
SchedCandidate BotCand(NoPolicy);
pickNodeFromQueue(Bot, DAG->getBotRPTracker(), BotCand);
assert(BotCand.Reason != NoCand && "failed to find the first candidate");
SU = BotCand.SU;
}
IsTopNode = false;
}
else {
SU = pickNodeBidirectional(IsTopNode);
}
} while (SU->isScheduled);
if (SU->isTopReady())
Top.removeReady(SU);
if (SU->isBottomReady())
Bot.removeReady(SU);
DEBUG(dbgs() << "*** " << (IsTopNode ? "Top" : "Bottom")
<< " Scheduling Instruction in cycle "
<< (IsTopNode ? Top.CurrCycle : Bot.CurrCycle) << '\n';
SU->dump(DAG));
return SU;
}
/// Update the scheduler's state after scheduling a node. This is the same node
/// that was just returned by pickNode(). However, ScheduleDAGMI needs to update
/// it's state based on the current cycle before MachineSchedStrategy does.
void ConvergingScheduler::schedNode(SUnit *SU, bool IsTopNode) {
if (IsTopNode) {
SU->TopReadyCycle = Top.CurrCycle;
Top.bumpNode(SU);
}
else {
SU->BotReadyCycle = Bot.CurrCycle;
Bot.bumpNode(SU);
}
}
/// Create the standard converging machine scheduler. This will be used as the
/// default scheduler if the target does not set a default.
static ScheduleDAGInstrs *createConvergingSched(MachineSchedContext *C) {
assert((!ForceTopDown || !ForceBottomUp) &&
"-misched-topdown incompatible with -misched-bottomup");
return new ScheduleDAGMI(C, new ConvergingScheduler());
}
static MachineSchedRegistry
ConvergingSchedRegistry("converge", "Standard converging scheduler.",
createConvergingSched);
//===----------------------------------------------------------------------===//
// ILP Scheduler. Currently for experimental analysis of heuristics.
//===----------------------------------------------------------------------===//
namespace {
/// \brief Order nodes by the ILP metric.
struct ILPOrder {
ScheduleDAGILP *ILP;
bool MaximizeILP;
ILPOrder(ScheduleDAGILP *ilp, bool MaxILP): ILP(ilp), MaximizeILP(MaxILP) {}
/// \brief Apply a less-than relation on node priority.
bool operator()(const SUnit *A, const SUnit *B) const {
// Return true if A comes after B in the Q.
if (MaximizeILP)
return ILP->getILP(A) < ILP->getILP(B);
else
return ILP->getILP(A) > ILP->getILP(B);
}
};
/// \brief Schedule based on the ILP metric.
class ILPScheduler : public MachineSchedStrategy {
ScheduleDAGILP ILP;
ILPOrder Cmp;
std::vector<SUnit*> ReadyQ;
public:
ILPScheduler(bool MaximizeILP)
: ILP(/*BottomUp=*/true), Cmp(&ILP, MaximizeILP) {}
virtual void initialize(ScheduleDAGMI *DAG) {
ReadyQ.clear();
ILP.resize(DAG->SUnits.size());
}
virtual void registerRoots() {
for (std::vector<SUnit*>::const_iterator
I = ReadyQ.begin(), E = ReadyQ.end(); I != E; ++I) {
ILP.computeILP(*I);
}
}
/// Implement MachineSchedStrategy interface.
/// -----------------------------------------
virtual SUnit *pickNode(bool &IsTopNode) {
if (ReadyQ.empty()) return NULL;
pop_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
SUnit *SU = ReadyQ.back();
ReadyQ.pop_back();
IsTopNode = false;
DEBUG(dbgs() << "*** Scheduling " << *SU->getInstr()
<< " ILP: " << ILP.getILP(SU) << '\n');
return SU;
}
virtual void schedNode(SUnit *, bool) {}
virtual void releaseTopNode(SUnit *) { /*only called for top roots*/ }
virtual void releaseBottomNode(SUnit *SU) {
ReadyQ.push_back(SU);
std::push_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
}
};
} // namespace
static ScheduleDAGInstrs *createILPMaxScheduler(MachineSchedContext *C) {
return new ScheduleDAGMI(C, new ILPScheduler(true));
}
static ScheduleDAGInstrs *createILPMinScheduler(MachineSchedContext *C) {
return new ScheduleDAGMI(C, new ILPScheduler(false));
}
static MachineSchedRegistry ILPMaxRegistry(
"ilpmax", "Schedule bottom-up for max ILP", createILPMaxScheduler);
static MachineSchedRegistry ILPMinRegistry(
"ilpmin", "Schedule bottom-up for min ILP", createILPMinScheduler);
//===----------------------------------------------------------------------===//
// Machine Instruction Shuffler for Correctness Testing
//===----------------------------------------------------------------------===//
#ifndef NDEBUG
namespace {
/// Apply a less-than relation on the node order, which corresponds to the
/// instruction order prior to scheduling. IsReverse implements greater-than.
template<bool IsReverse>
struct SUnitOrder {
bool operator()(SUnit *A, SUnit *B) const {
if (IsReverse)
return A->NodeNum > B->NodeNum;
else
return A->NodeNum < B->NodeNum;
}
};
/// Reorder instructions as much as possible.
class InstructionShuffler : public MachineSchedStrategy {
bool IsAlternating;
bool IsTopDown;
// Using a less-than relation (SUnitOrder<false>) for the TopQ priority
// gives nodes with a higher number higher priority causing the latest
// instructions to be scheduled first.
PriorityQueue<SUnit*, std::vector<SUnit*>, SUnitOrder<false> >
TopQ;
// When scheduling bottom-up, use greater-than as the queue priority.
PriorityQueue<SUnit*, std::vector<SUnit*>, SUnitOrder<true> >
BottomQ;
public:
InstructionShuffler(bool alternate, bool topdown)
: IsAlternating(alternate), IsTopDown(topdown) {}
virtual void initialize(ScheduleDAGMI *) {
TopQ.clear();
BottomQ.clear();
}
/// Implement MachineSchedStrategy interface.
/// -----------------------------------------
virtual SUnit *pickNode(bool &IsTopNode) {
SUnit *SU;
if (IsTopDown) {
do {
if (TopQ.empty()) return NULL;
SU = TopQ.top();
TopQ.pop();
} while (SU->isScheduled);
IsTopNode = true;
}
else {
do {
if (BottomQ.empty()) return NULL;
SU = BottomQ.top();
BottomQ.pop();
} while (SU->isScheduled);
IsTopNode = false;
}
if (IsAlternating)
IsTopDown = !IsTopDown;
return SU;
}
virtual void schedNode(SUnit *SU, bool IsTopNode) {}
virtual void releaseTopNode(SUnit *SU) {
TopQ.push(SU);
}
virtual void releaseBottomNode(SUnit *SU) {
BottomQ.push(SU);
}
};
} // namespace
static ScheduleDAGInstrs *createInstructionShuffler(MachineSchedContext *C) {
bool Alternate = !ForceTopDown && !ForceBottomUp;
bool TopDown = !ForceBottomUp;
assert((TopDown || !ForceTopDown) &&
"-misched-topdown incompatible with -misched-bottomup");
return new ScheduleDAGMI(C, new InstructionShuffler(Alternate, TopDown));
}
static MachineSchedRegistry ShufflerRegistry(
"shuffle", "Shuffle machine instructions alternating directions",
createInstructionShuffler);
#endif // !NDEBUG
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