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llvm-project/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp

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//===---- ScheduleDAGInstrs.cpp - MachineInstr Rescheduling ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements the ScheduleDAGInstrs class, which implements re-scheduling
// of MachineInstrs.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sched-instrs"
#include "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/ScheduleDAGILP.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/Format.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()), LIS(lis),
IsPostRA(IsPostRAFlag), CanHandleTerminators(false), FirstDbgValue(0) {
assert((IsPostRA || LIS) && "PreRA scheduling requires LiveIntervals");
DbgValues.clear();
assert(!(IsPostRA && MRI.getNumVirtRegs()) &&
"Virtual registers must be removed prior to PostRA scheduling");
const TargetSubtargetInfo &ST = TM.getSubtarget<TargetSubtargetInfo>();
SchedModel.init(*ST.getSchedModel(), &ST, TII);
}
/// 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
// identifiable 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;
}
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();
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(PhysRegSUOper(&ExitSU, -1));
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(PhysRegSUOper(&ExitSU, -1));
}
}
}
/// 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, unsigned OperIdx) {
const MachineOperand &MO = SU->getInstr()->getOperand(OperIdx);
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>();
for (MCRegAliasIterator Alias(MO.getReg(), TRI, true);
Alias.isValid(); ++Alias) {
if (!Uses.contains(*Alias))
continue;
std::vector<PhysRegSUOper> &UseList = Uses[*Alias];
for (unsigned i = 0, e = UseList.size(); i != e; ++i) {
SUnit *UseSU = UseList[i].SU;
if (UseSU == SU)
continue;
SDep dep(SU, SDep::Data, 1, *Alias);
// Adjust the dependence latency using operand def/use information,
// then allow the target to perform its own adjustments.
int UseOp = UseList[i].OpIdx;
MachineInstr *RegUse = UseOp < 0 ? 0 : UseSU->getInstr();
dep.setLatency(
SchedModel.computeOperandLatency(SU->getInstr(), OperIdx,
RegUse, UseOp, /*FindMin=*/false));
dep.setMinLatency(
SchedModel.computeOperandLatency(SU->getInstr(), OperIdx,
RegUse, UseOp, /*FindMin=*/true));
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<PhysRegSUOper> &DefList = Defs[*Alias];
for (unsigned i = 0, e = DefList.size(); i != e; ++i) {
SUnit *DefSU = DefList[i].SU;
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 =
SchedModel.computeOutputLatency(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(PhysRegSUOper(SU, OperIdx));
}
else {
addPhysRegDataDeps(SU, OperIdx);
// Either insert a new Reg2SUnits entry with an empty SUnits list, or
// retrieve the existing SUnits list for this register's defs.
std::vector<PhysRegSUOper> &DefList = Defs[MO.getReg()];
// 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().SU->isCall)
DefList.pop_back();
}
// Defs are pushed in the order they are visited and never reordered.
DefList.push_back(PhysRegSUOper(SU, OperIdx));
}
}
/// 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 =
SchedModel.computeOutputLatency(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.
SDep dep(DefSU, SDep::Data, 1, Reg);
// Adjust the dependence latency using operand def/use information, then
// allow the target to perform its own adjustments.
int DefOp = Def->findRegisterDefOperandIdx(Reg);
dep.setLatency(
SchedModel.computeOperandLatency(Def, DefOp, MI, OperIdx, false));
dep.setMinLatency(
SchedModel.computeOperandLatency(Def, DefOp, MI, OperIdx, true));
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->hasOrderedMemoryRef() &&
(!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.
SU->Latency = SchedModel.computeInstrLatency(SU->getInstr());
}
}
/// 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::dumpNode(const SUnit *SU) const {
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
SU->getInstr()->dump();
#endif
}
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();
}
namespace {
/// \brief Manage the stack used by a reverse depth-first search over the DAG.
class SchedDAGReverseDFS {
std::vector<std::pair<const SUnit*, SUnit::const_pred_iterator> > DFSStack;
public:
bool isComplete() const { return DFSStack.empty(); }
void follow(const SUnit *SU) {
DFSStack.push_back(std::make_pair(SU, SU->Preds.begin()));
}
void advance() { ++DFSStack.back().second; }
void backtrack() { DFSStack.pop_back(); }
const SUnit *getCurr() const { return DFSStack.back().first; }
SUnit::const_pred_iterator getPred() const { return DFSStack.back().second; }
SUnit::const_pred_iterator getPredEnd() const {
return getCurr()->Preds.end();
}
};
} // anonymous
void ScheduleDAGILP::resize(unsigned NumSUnits) {
ILPValues.resize(NumSUnits);
}
ILPValue ScheduleDAGILP::getILP(const SUnit *SU) {
return ILPValues[SU->NodeNum];
}
// A leaf node has an ILP of 1/1.
static ILPValue initILP(const SUnit *SU) {
unsigned Cnt = SU->getInstr()->isTransient() ? 0 : 1;
return ILPValue(Cnt, 1 + SU->getDepth());
}
/// Compute an ILP metric for all nodes in the subDAG reachable via depth-first
/// search from this root.
void ScheduleDAGILP::computeILP(const SUnit *Root) {
if (!IsBottomUp)
llvm_unreachable("Top-down ILP metric is unimplemnted");
SchedDAGReverseDFS DFS;
// Mark a node visited by validating it.
ILPValues[Root->NodeNum] = initILP(Root);
DFS.follow(Root);
for (;;) {
// Traverse the leftmost path as far as possible.
while (DFS.getPred() != DFS.getPredEnd()) {
const SUnit *PredSU = DFS.getPred()->getSUnit();
DFS.advance();
// If the pred is already valid, skip it.
if (ILPValues[PredSU->NodeNum].isValid())
continue;
ILPValues[PredSU->NodeNum] = initILP(PredSU);
DFS.follow(PredSU);
}
// Visit the top of the stack in postorder and backtrack.
unsigned PredCount = ILPValues[DFS.getCurr()->NodeNum].InstrCount;
DFS.backtrack();
if (DFS.isComplete())
break;
// Add the recently finished predecessor's bottom-up descendent count.
ILPValues[DFS.getCurr()->NodeNum].InstrCount += PredCount;
}
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void ILPValue::print(raw_ostream &OS) const {
if (!isValid())
OS << "BADILP";
OS << InstrCount << " / " << Cycles << " = "
<< format("%g", ((double)InstrCount / Cycles));
}
void ILPValue::dump() const {
dbgs() << *this << '\n';
}
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, const ILPValue &Val) {
Val.print(OS);
return OS;
}
} // namespace llvm
#endif // !NDEBUG || LLVM_ENABLE_DUMP
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