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llvm-mirror/lib/CodeGen/ScheduleDAGInstrs.cpp
Dan Gohman 3d0633627d Instead of adding dependence edges between terminator instructions 
and every other instruction in their blocks to keep the terminator
instructions at the end, teach the post-RA scheduler how to operate
on ranges of instructions, and exclude terminators from the range
of instructions that get scheduled.

Also, exclude mid-block labels, such as EH_LABEL instructions, and
schedule code before them separately from code after them. This
fixes problems with the post-RA scheduler moving code past
EH_LABELs.

llvm-svn: 62366
2009-01-16 22:10:20 +00:00

457 lines
18 KiB
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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/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/ScheduleDAGInstrs.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtarget.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallSet.h"
#include <map>
using namespace llvm;
namespace {
class VISIBILITY_HIDDEN LoopDependencies {
const MachineLoopInfo &MLI;
const MachineDominatorTree &MDT;
public:
typedef std::map<unsigned, std::pair<const MachineOperand *, unsigned> >
LoopDeps;
LoopDeps Deps;
LoopDependencies(const MachineLoopInfo &mli,
const MachineDominatorTree &mdt) :
MLI(mli), MDT(mdt) {}
void VisitLoop(const MachineLoop *Loop) {
Deps.clear();
MachineBasicBlock *Header = Loop->getHeader();
SmallSet<unsigned, 8> LoopLiveIns;
for (MachineBasicBlock::livein_iterator LI = Header->livein_begin(),
LE = Header->livein_end(); LI != LE; ++LI)
LoopLiveIns.insert(*LI);
const MachineDomTreeNode *Node = MDT.getNode(Header);
const MachineBasicBlock *MBB = Node->getBlock();
assert(Loop->contains(MBB) &&
"Loop does not contain header!");
VisitRegion(Node, MBB, Loop, LoopLiveIns);
}
private:
void VisitRegion(const MachineDomTreeNode *Node,
const MachineBasicBlock *MBB,
const MachineLoop *Loop,
const SmallSet<unsigned, 8> &LoopLiveIns) {
unsigned Count = 0;
for (MachineBasicBlock::const_iterator I = MBB->begin(), E = MBB->end();
I != E; ++I, ++Count) {
const MachineInstr *MI = I;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isUse())
continue;
unsigned MOReg = MO.getReg();
if (LoopLiveIns.count(MOReg))
Deps.insert(std::make_pair(MOReg, std::make_pair(&MO, Count)));
}
}
const std::vector<MachineDomTreeNode*> &Children = Node->getChildren();
for (std::vector<MachineDomTreeNode*>::const_iterator I =
Children.begin(), E = Children.end(); I != E; ++I) {
const MachineDomTreeNode *ChildNode = *I;
MachineBasicBlock *ChildBlock = ChildNode->getBlock();
if (Loop->contains(ChildBlock))
VisitRegion(ChildNode, ChildBlock, Loop, LoopLiveIns);
}
}
};
}
ScheduleDAGInstrs::ScheduleDAGInstrs(MachineFunction &mf,
const MachineLoopInfo &mli,
const MachineDominatorTree &mdt)
: ScheduleDAG(mf), MLI(mli), MDT(mdt) {}
void ScheduleDAGInstrs::BuildSchedGraph() {
SUnits.reserve(BB->size());
// We build scheduling units by walking a block's instruction list from bottom
// to top.
// Remember where a generic side-effecting instruction is as we procede. If
// ChainMMO is null, this is assumed to have arbitrary side-effects. If
// ChainMMO is non-null, then Chain makes only a single memory reference.
SUnit *Chain = 0;
MachineMemOperand *ChainMMO = 0;
// Memory references to specific known memory locations are tracked so that
// they can be given more precise dependencies.
std::map<const Value *, SUnit *> MemDefs;
std::map<const Value *, std::vector<SUnit *> > MemUses;
// If we have an SUnit which is representing a terminator instruction, we
// can use it as a place-holder successor for inter-block dependencies.
SUnit *Terminator = 0;
// Terminators can perform control transfers, we we need to make sure that
// all the work of the block is done before the terminator. Labels can
// mark points of interest for various types of meta-data (eg. EH data),
// and we need to make sure nothing is scheduled around them.
SUnit *SchedulingBarrier = 0;
LoopDependencies LoopRegs(MLI, MDT);
// Track which regs are live into a loop, to help guide back-edge-aware
// scheduling.
SmallSet<unsigned, 8> LoopLiveInRegs;
if (MachineLoop *ML = MLI.getLoopFor(BB))
if (BB == ML->getLoopLatch()) {
MachineBasicBlock *Header = ML->getHeader();
for (MachineBasicBlock::livein_iterator I = Header->livein_begin(),
E = Header->livein_end(); I != E; ++I)
LoopLiveInRegs.insert(*I);
LoopRegs.VisitLoop(ML);
}
// Check to see if the scheduler cares about latencies.
bool UnitLatencies = ForceUnitLatencies();
// Ask the target if address-backscheduling is desirable, and if so how much.
unsigned SpecialAddressLatency =
TM.getSubtarget<TargetSubtarget>().getSpecialAddressLatency();
for (MachineBasicBlock::iterator MII = End, MIE = Begin;
MII != MIE; --MII) {
MachineInstr *MI = prior(MII);
const TargetInstrDesc &TID = MI->getDesc();
SUnit *SU = NewSUnit(MI);
// Assign the Latency field of SU using target-provided information.
if (UnitLatencies)
SU->Latency = 1;
else
ComputeLatency(SU);
// Add register-based dependencies (data, anti, and output).
for (unsigned j = 0, n = MI->getNumOperands(); j != n; ++j) {
const MachineOperand &MO = MI->getOperand(j);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (Reg == 0) continue;
assert(TRI->isPhysicalRegister(Reg) && "Virtual register encountered!");
std::vector<SUnit *> &UseList = Uses[Reg];
std::vector<SUnit *> &DefList = Defs[Reg];
// Optionally add output and anti dependencies.
// TODO: Using a latency of 1 here assumes there's no cost for
// reusing registers.
SDep::Kind Kind = MO.isUse() ? SDep::Anti : SDep::Output;
for (unsigned i = 0, e = DefList.size(); i != e; ++i) {
SUnit *DefSU = DefList[i];
if (DefSU != SU &&
(Kind != SDep::Output || !MO.isDead() ||
!DefSU->getInstr()->registerDefIsDead(Reg)))
DefSU->addPred(SDep(SU, Kind, /*Latency=*/1, /*Reg=*/Reg));
}
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
std::vector<SUnit *> &DefList = Defs[*Alias];
for (unsigned i = 0, e = DefList.size(); i != e; ++i) {
SUnit *DefSU = DefList[i];
if (DefSU != SU &&
(Kind != SDep::Output || !MO.isDead() ||
!DefSU->getInstr()->registerDefIsDead(Reg)))
DefSU->addPred(SDep(SU, Kind, /*Latency=*/1, /*Reg=*/ *Alias));
}
}
if (MO.isDef()) {
// Add any data dependencies.
unsigned DataLatency = SU->Latency;
for (unsigned i = 0, e = UseList.size(); i != e; ++i) {
SUnit *UseSU = UseList[i];
if (UseSU != SU) {
unsigned LDataLatency = DataLatency;
// Optionally add in a special extra latency for nodes that
// feed addresses.
// TODO: Do this for register aliases too.
if (SpecialAddressLatency != 0 && !UnitLatencies) {
MachineInstr *UseMI = UseSU->getInstr();
const TargetInstrDesc &UseTID = UseMI->getDesc();
int RegUseIndex = UseMI->findRegisterUseOperandIdx(Reg);
assert(RegUseIndex >= 0 && "UseMI doesn's use register!");
if ((UseTID.mayLoad() || UseTID.mayStore()) &&
(unsigned)RegUseIndex < UseTID.getNumOperands() &&
UseTID.OpInfo[RegUseIndex].isLookupPtrRegClass())
LDataLatency += SpecialAddressLatency;
}
UseSU->addPred(SDep(SU, SDep::Data, LDataLatency, Reg));
}
}
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
std::vector<SUnit *> &UseList = Uses[*Alias];
for (unsigned i = 0, e = UseList.size(); i != e; ++i) {
SUnit *UseSU = UseList[i];
if (UseSU != SU)
UseSU->addPred(SDep(SU, SDep::Data, DataLatency, *Alias));
}
}
// If a def is going to wrap back around to the top of the loop,
// backschedule it.
// TODO: Blocks in loops without terminators can benefit too.
if (!UnitLatencies && Terminator && DefList.empty()) {
LoopDependencies::LoopDeps::iterator I = LoopRegs.Deps.find(Reg);
if (I != LoopRegs.Deps.end()) {
const MachineOperand *UseMO = I->second.first;
unsigned Count = I->second.second;
const MachineInstr *UseMI = UseMO->getParent();
unsigned UseMOIdx = UseMO - &UseMI->getOperand(0);
const TargetInstrDesc &UseTID = UseMI->getDesc();
// TODO: If we knew the total depth of the region here, we could
// handle the case where the whole loop is inside the region but
// is large enough that the isScheduleHigh trick isn't needed.
if (UseMOIdx < UseTID.getNumOperands()) {
// Currently, we only support scheduling regions consisting of
// single basic blocks. Check to see if the instruction is in
// the same region by checking to see if it has the same parent.
if (UseMI->getParent() != MI->getParent()) {
unsigned Latency = SU->Latency;
if (UseTID.OpInfo[UseMOIdx].isLookupPtrRegClass())
Latency += SpecialAddressLatency;
// This is a wild guess as to the portion of the latency which
// will be overlapped by work done outside the current
// scheduling region.
Latency -= std::min(Latency, Count);
// Add the artifical edge.
Terminator->addPred(SDep(SU, SDep::Order, Latency,
/*Reg=*/0, /*isNormalMemory=*/false,
/*isMustAlias=*/false,
/*isArtificial=*/true));
} else if (SpecialAddressLatency > 0 &&
UseTID.OpInfo[UseMOIdx].isLookupPtrRegClass()) {
// The entire loop body is within the current scheduling region
// and the latency of this operation is assumed to be greater
// than the latency of the loop.
// TODO: Recursively mark data-edge predecessors as
// isScheduleHigh too.
SU->isScheduleHigh = true;
}
}
LoopRegs.Deps.erase(I);
}
}
UseList.clear();
if (!MO.isDead())
DefList.clear();
DefList.push_back(SU);
} else {
UseList.push_back(SU);
}
}
// Add chain dependencies.
// Note that isStoreToStackSlot and isLoadFromStackSLot are not usable
// after stack slots are lowered to actual addresses.
// TODO: Use an AliasAnalysis and do real alias-analysis queries, and
// produce more precise dependence information.
if (TID.isCall() || TID.isTerminator() || TID.hasUnmodeledSideEffects()) {
new_chain:
// This is the conservative case. Add dependencies on all memory
// references.
if (Chain)
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
Chain = SU;
for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
PendingLoads[k]->addPred(SDep(SU, SDep::Order, SU->Latency));
PendingLoads.clear();
for (std::map<const Value *, SUnit *>::iterator I = MemDefs.begin(),
E = MemDefs.end(); I != E; ++I) {
I->second->addPred(SDep(SU, SDep::Order, SU->Latency));
I->second = SU;
}
for (std::map<const Value *, std::vector<SUnit *> >::iterator I =
MemUses.begin(), E = MemUses.end(); I != E; ++I) {
for (unsigned i = 0, e = I->second.size(); i != e; ++i)
I->second[i]->addPred(SDep(SU, SDep::Order, SU->Latency));
I->second.clear();
}
// See if it is known to just have a single memory reference.
MachineInstr *ChainMI = Chain->getInstr();
const TargetInstrDesc &ChainTID = ChainMI->getDesc();
if (!ChainTID.isCall() && !ChainTID.isTerminator() &&
!ChainTID.hasUnmodeledSideEffects() &&
ChainMI->hasOneMemOperand() &&
!ChainMI->memoperands_begin()->isVolatile() &&
ChainMI->memoperands_begin()->getValue())
// We know that the Chain accesses one specific memory location.
ChainMMO = &*ChainMI->memoperands_begin();
else
// Unknown memory accesses. Assume the worst.
ChainMMO = 0;
} else if (TID.mayStore()) {
if (MI->hasOneMemOperand() &&
MI->memoperands_begin()->getValue() &&
!MI->memoperands_begin()->isVolatile() &&
isa<PseudoSourceValue>(MI->memoperands_begin()->getValue())) {
// A store to a specific PseudoSourceValue. Add precise dependencies.
const Value *V = MI->memoperands_begin()->getValue();
// Handle the def in MemDefs, if there is one.
std::map<const Value *, SUnit *>::iterator I = MemDefs.find(V);
if (I != MemDefs.end()) {
I->second->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
/*isNormalMemory=*/true));
I->second = SU;
} else {
MemDefs[V] = SU;
}
// Handle the uses in MemUses, if there are any.
std::map<const Value *, std::vector<SUnit *> >::iterator J =
MemUses.find(V);
if (J != MemUses.end()) {
for (unsigned i = 0, e = J->second.size(); i != e; ++i)
J->second[i]->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
/*isNormalMemory=*/true));
J->second.clear();
}
// Add a general dependence too, if needed.
if (Chain)
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
} else
// Treat all other stores conservatively.
goto new_chain;
} else if (TID.mayLoad()) {
if (TII->isInvariantLoad(MI)) {
// Invariant load, no chain dependencies needed!
} else if (MI->hasOneMemOperand() &&
MI->memoperands_begin()->getValue() &&
!MI->memoperands_begin()->isVolatile() &&
isa<PseudoSourceValue>(MI->memoperands_begin()->getValue())) {
// A load from a specific PseudoSourceValue. Add precise dependencies.
const Value *V = MI->memoperands_begin()->getValue();
std::map<const Value *, SUnit *>::iterator I = MemDefs.find(V);
if (I != MemDefs.end())
I->second->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
/*isNormalMemory=*/true));
MemUses[V].push_back(SU);
// Add a general dependence too, if needed.
if (Chain && (!ChainMMO ||
(ChainMMO->isStore() || ChainMMO->isVolatile())))
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
} else if (MI->hasVolatileMemoryRef()) {
// Treat volatile loads conservatively. Note that this includes
// cases where memoperand information is unavailable.
goto new_chain;
} else {
// A normal load. Just depend on the general chain.
if (Chain)
Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
PendingLoads.push_back(SU);
}
}
// Add chain edges from terminators and labels to ensure that no
// instructions are scheduled past them.
if (SchedulingBarrier && SU->Succs.empty())
SchedulingBarrier->addPred(SDep(SU, SDep::Order, SU->Latency));
// If we encounter a mid-block label, we need to go back and add
// dependencies on SUnits we've already processed to prevent the
// label from moving downward.
if (MI->isLabel())
for (SUnit *I = SU; I != &SUnits[0]; --I) {
SUnit *SuccSU = SU-1;
SuccSU->addPred(SDep(SU, SDep::Order, SU->Latency));
MachineInstr *SuccMI = SuccSU->getInstr();
if (SuccMI->getDesc().isTerminator() || SuccMI->isLabel())
break;
}
// If this instruction obstructs all scheduling, remember it.
if (TID.isTerminator() || MI->isLabel())
SchedulingBarrier = SU;
// If this instruction is a terminator, remember it.
if (TID.isTerminator())
Terminator = SU;
}
for (int i = 0, e = TRI->getNumRegs(); i != e; ++i) {
Defs[i].clear();
Uses[i].clear();
}
PendingLoads.clear();
}
void ScheduleDAGInstrs::ComputeLatency(SUnit *SU) {
const InstrItineraryData &InstrItins = TM.getInstrItineraryData();
// Compute the latency for the node. We use the sum of the latencies for
// all nodes flagged together into this SUnit.
SU->Latency =
InstrItins.getLatency(SU->getInstr()->getDesc().getSchedClass());
// Simplistic target-independent heuristic: assume that loads take
// extra time.
if (InstrItins.isEmpty())
if (SU->getInstr()->getDesc().mayLoad())
SU->Latency += 2;
}
void ScheduleDAGInstrs::dumpNode(const SUnit *SU) const {
SU->getInstr()->dump();
}
std::string ScheduleDAGInstrs::getGraphNodeLabel(const SUnit *SU) const {
std::string s;
raw_string_ostream oss(s);
SU->getInstr()->print(oss);
return oss.str();
}
// EmitSchedule - Emit the machine code in scheduled order.
MachineBasicBlock *ScheduleDAGInstrs::EmitSchedule() {
// For MachineInstr-based scheduling, we're rescheduling the instructions in
// the block, so start by removing them from the block.
while (Begin != End) {
MachineBasicBlock::iterator I = Begin;
++Begin;
BB->remove(I);
}
// Then re-insert them according to the given schedule.
for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
SUnit *SU = Sequence[i];
if (!SU) {
// Null SUnit* is a noop.
EmitNoop();
continue;
}
BB->insert(End, SU->getInstr());
}
return BB;
}
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