/// CanCauseHighRegPressure - Visit BBs from header to current BB,
/// check if hoisting an instruction of the given cost matrix can cause high
/// register pressure.
- bool CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost);
+ bool CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost, bool Cheap);
/// UpdateBackTraceRegPressure - Traverse the back trace from header to
/// the current block and update their register pressures to reflect the
DEBUG(dbgs() << "******** Pre-regalloc Machine LICM: ");
else
DEBUG(dbgs() << "******** Post-regalloc Machine LICM: ");
- DEBUG(dbgs() << MF.getFunction()->getName() << " ********\n");
+ DEBUG(dbgs() << MF.getName() << " ********\n");
if (PreRegAlloc) {
// Estimate register pressure during pre-regalloc pass.
}
if (MO.isImplicit()) {
- for (const uint16_t *AS = TRI->getOverlaps(Reg); *AS; ++AS)
- PhysRegClobbers.set(*AS);
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ PhysRegClobbers.set(*AI);
if (!MO.isDead())
// Non-dead implicit def? This cannot be hoisted.
RuledOut = true;
// If we have already seen another instruction that defines the same
// register, then this is not safe. Two defs is indicated by setting a
// PhysRegClobbers bit.
- for (const uint16_t *AS = TRI->getOverlaps(Reg); *AS; ++AS) {
+ for (MCRegAliasIterator AS(Reg, TRI, true); AS.isValid(); ++AS) {
if (PhysRegDefs.test(*AS))
PhysRegClobbers.set(*AS);
if (PhysRegClobbers.test(*AS))
for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
E = BB->livein_end(); I != E; ++I) {
unsigned Reg = *I;
- for (const uint16_t *AS = TRI->getOverlaps(Reg); *AS; ++AS)
- PhysRegDefs.set(*AS);
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ PhysRegDefs.set(*AI);
}
SpeculationState = SpeculateUnknown;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
- for (const uint16_t *AS = TRI->getOverlaps(Reg); *AS; ++AS)
- TermRegs.set(*AS);
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ TermRegs.set(*AI);
}
}
/// CanCauseHighRegPressure - Visit BBs from header to current BB, check
/// if hoisting an instruction of the given cost matrix can cause high
/// register pressure.
-bool MachineLICM::CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost) {
+bool MachineLICM::CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost,
+ bool CheapInstr) {
for (DenseMap<unsigned, int>::iterator CI = Cost.begin(), CE = Cost.end();
CI != CE; ++CI) {
if (CI->second <= 0)
unsigned RCId = CI->first;
unsigned Limit = RegLimit[RCId];
int Cost = CI->second;
+
+ // Don't hoist cheap instructions if they would increase register pressure,
+ // even if we're under the limit.
+ if (CheapInstr)
+ return true;
+
for (unsigned i = BackTrace.size(); i != 0; --i) {
SmallVector<unsigned, 8> &RP = BackTrace[i-1];
if (RP[RCId] + Cost >= Limit)
if (MI.isImplicitDef())
return true;
- // If the instruction is cheap, only hoist if it is re-materilizable. LICM
- // will increase register pressure. It's probably not worth it if the
- // instruction is cheap.
- // Also hoist loads from constant memory, e.g. load from stubs, GOT. Hoisting
- // these tend to help performance in low register pressure situation. The
- // trade off is it may cause spill in high pressure situation. It will end up
- // adding a store in the loop preheader. But the reload is no more expensive.
- // The side benefit is these loads are frequently CSE'ed.
- if (IsCheapInstruction(MI)) {
- if (!TII->isTriviallyReMaterializable(&MI, AA))
- return false;
- } else {
- // Estimate register pressure to determine whether to LICM the instruction.
- // In low register pressure situation, we can be more aggressive about
- // hoisting. Also, favors hoisting long latency instructions even in
- // moderately high pressure situation.
- // FIXME: If there are long latency loop-invariant instructions inside the
- // loop at this point, why didn't the optimizer's LICM hoist them?
- DenseMap<unsigned, int> Cost;
- for (unsigned i = 0, e = MI.getDesc().getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = MI.getOperand(i);
- if (!MO.isReg() || MO.isImplicit())
- continue;
- unsigned Reg = MO.getReg();
- if (!TargetRegisterInfo::isVirtualRegister(Reg))
- continue;
+ // Besides removing computation from the loop, hoisting an instruction has
+ // these effects:
+ //
+ // - The value defined by the instruction becomes live across the entire
+ // loop. This increases register pressure in the loop.
+ //
+ // - If the value is used by a PHI in the loop, a copy will be required for
+ // lowering the PHI after extending the live range.
+ //
+ // - When hoisting the last use of a value in the loop, that value no longer
+ // needs to be live in the loop. This lowers register pressure in the loop.
+
+ bool CheapInstr = IsCheapInstruction(MI);
+ bool CreatesCopy = HasLoopPHIUse(&MI);
+
+ // Don't hoist a cheap instruction if it would create a copy in the loop.
+ if (CheapInstr && CreatesCopy) {
+ DEBUG(dbgs() << "Won't hoist cheap instr with loop PHI use: " << MI);
+ return false;
+ }
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(&MI, Reg, i, RCId, RCCost);
- if (MO.isDef()) {
- if (HasHighOperandLatency(MI, i, Reg)) {
- ++NumHighLatency;
- return true;
- }
+ // Rematerializable instructions should always be hoisted since the register
+ // allocator can just pull them down again when needed.
+ if (TII->isTriviallyReMaterializable(&MI, AA))
+ return true;
- DenseMap<unsigned, int>::iterator CI = Cost.find(RCId);
- if (CI != Cost.end())
- CI->second += RCCost;
- else
- Cost.insert(std::make_pair(RCId, RCCost));
- } else if (isOperandKill(MO, MRI)) {
- // Is a virtual register use is a kill, hoisting it out of the loop
- // may actually reduce register pressure or be register pressure
- // neutral.
- DenseMap<unsigned, int>::iterator CI = Cost.find(RCId);
- if (CI != Cost.end())
- CI->second -= RCCost;
- else
- Cost.insert(std::make_pair(RCId, -RCCost));
+ // Estimate register pressure to determine whether to LICM the instruction.
+ // In low register pressure situation, we can be more aggressive about
+ // hoisting. Also, favors hoisting long latency instructions even in
+ // moderately high pressure situation.
+ // Cheap instructions will only be hoisted if they don't increase register
+ // pressure at all.
+ // FIXME: If there are long latency loop-invariant instructions inside the
+ // loop at this point, why didn't the optimizer's LICM hoist them?
+ DenseMap<unsigned, int> Cost;
+ for (unsigned i = 0, e = MI.getDesc().getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI.getOperand(i);
+ if (!MO.isReg() || MO.isImplicit())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!TargetRegisterInfo::isVirtualRegister(Reg))
+ continue;
+
+ unsigned RCId, RCCost;
+ getRegisterClassIDAndCost(&MI, Reg, i, RCId, RCCost);
+ if (MO.isDef()) {
+ if (HasHighOperandLatency(MI, i, Reg)) {
+ DEBUG(dbgs() << "Hoist High Latency: " << MI);
+ ++NumHighLatency;
+ return true;
}
+ Cost[RCId] += RCCost;
+ } else if (isOperandKill(MO, MRI)) {
+ // Is a virtual register use is a kill, hoisting it out of the loop
+ // may actually reduce register pressure or be register pressure
+ // neutral.
+ Cost[RCId] -= RCCost;
}
+ }
- // Visit BBs from header to current BB, if hoisting this doesn't cause
- // high register pressure, then it's safe to proceed.
- if (!CanCauseHighRegPressure(Cost)) {
- ++NumLowRP;
- return true;
- }
+ // Visit BBs from header to current BB, if hoisting this doesn't cause
+ // high register pressure, then it's safe to proceed.
+ if (!CanCauseHighRegPressure(Cost, CheapInstr)) {
+ DEBUG(dbgs() << "Hoist non-reg-pressure: " << MI);
+ ++NumLowRP;
+ return true;
+ }
- // Do not "speculate" in high register pressure situation. If an
- // instruction is not guaranteed to be executed in the loop, it's best to be
- // conservative.
- if (AvoidSpeculation &&
- (!IsGuaranteedToExecute(MI.getParent()) && !MayCSE(&MI)))
- return false;
+ // Don't risk increasing register pressure if it would create copies.
+ if (CreatesCopy) {
+ DEBUG(dbgs() << "Won't hoist instr with loop PHI use: " << MI);
+ return false;
+ }
- // High register pressure situation, only hoist if the instruction is going
- // to be remat'ed.
- if (!TII->isTriviallyReMaterializable(&MI, AA) &&
- !MI.isInvariantLoad(AA))
- return false;
+ // Do not "speculate" in high register pressure situation. If an
+ // instruction is not guaranteed to be executed in the loop, it's best to be
+ // conservative.
+ if (AvoidSpeculation &&
+ (!IsGuaranteedToExecute(MI.getParent()) && !MayCSE(&MI))) {
+ DEBUG(dbgs() << "Won't speculate: " << MI);
+ return false;
}
- // If result(s) of this instruction is used by PHIs inside the loop, then
- // don't hoist it because it will introduce an extra copy.
- if (HasLoopPHIUse(&MI))
+ // High register pressure situation, only hoist if the instruction is going
+ // to be remat'ed.
+ if (!TII->isTriviallyReMaterializable(&MI, AA) &&
+ !MI.isInvariantLoad(AA)) {
+ DEBUG(dbgs() << "Can't remat / high reg-pressure: " << MI);
return false;
+ }
return true;
}
if (NewOpc == 0) return 0;
const MCInstrDesc &MID = TII->get(NewOpc);
if (MID.getNumDefs() != 1) return 0;
- const TargetRegisterClass *RC = TII->getRegClass(MID, LoadRegIndex, TRI);
+ MachineFunction &MF = *MI->getParent()->getParent();
+ const TargetRegisterClass *RC = TII->getRegClass(MID, LoadRegIndex, TRI, MF);
// Ok, we're unfolding. Create a temporary register and do the unfold.
unsigned Reg = MRI->createVirtualRegister(RC);
- MachineFunction &MF = *MI->getParent()->getParent();
SmallVector<MachineInstr *, 2> NewMIs;
bool Success =
TII->unfoldMemoryOperand(MF, MI, Reg,
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