[llvm] r234325 - Cleanup register pressure calculation in MachineLICM.
Daniel Jasper
djasper at google.com
Tue Apr 7 09:42:35 PDT 2015
Author: djasper
Date: Tue Apr 7 11:42:35 2015
New Revision: 234325
URL: http://llvm.org/viewvc/llvm-project?rev=234325&view=rev
Log:
Cleanup register pressure calculation in MachineLICM.
There were four almost identical implementations of calculating/updating
the register pressure for a certain MachineInstr. Cleanup to have a
single implementation (well, controlled with two bool flags until this
is cleaned up more).
No functional changes intended.
Tested by verify that there are no binary changes in the entire llvm
test-suite. A new test was added separately in r234309 as it revealed a
pre-existing error in the register pressure calculation.
Modified:
llvm/trunk/lib/CodeGen/MachineLICM.cpp
Modified: llvm/trunk/lib/CodeGen/MachineLICM.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineLICM.cpp?rev=234325&r1=234324&r2=234325&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineLICM.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineLICM.cpp Tue Apr 7 11:42:35 2015
@@ -263,9 +263,20 @@ namespace {
/// this does not count live through (livein but not used) registers.
void InitRegPressure(MachineBasicBlock *BB);
+ /// calcRegisterCost - Calculate the additional register pressure that the
+ /// registers used in MI cause.
+ ///
+ /// If 'ConsiderSeen' is true, updates 'RegSeen' and uses the information to
+ /// figure out which usages are live-ins.
+ /// FIXME: Figure out a way to consider 'RegSeen' from all code paths.
+ DenseMap<unsigned, int> calcRegisterCost(const MachineInstr *MI,
+ bool ConsiderSeen,
+ bool ConsiderUnseenAsDef);
+
/// UpdateRegPressure - Update estimate of register pressure after the
/// specified instruction.
- void UpdateRegPressure(const MachineInstr *MI);
+ void UpdateRegPressure(const MachineInstr *MI,
+ bool ConsiderUnseenAsDef = false);
/// ExtractHoistableLoad - Unfold a load from the given machineinstr if
/// the load itself could be hoisted. Return the unfolded and hoistable
@@ -867,41 +878,30 @@ void MachineLICM::InitRegPressure(Machin
InitRegPressure(*BB->pred_begin());
}
- for (MachineBasicBlock::iterator MII = BB->begin(), E = BB->end();
- MII != E; ++MII) {
- MachineInstr *MI = &*MII;
- 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;
-
- bool isNew = RegSeen.insert(Reg).second;
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(MI, Reg, i, RCId, RCCost);
- if (MO.isDef())
- RegPressure[RCId] += RCCost;
- else {
- bool isKill = isOperandKill(MO, MRI);
- if (isNew && !isKill)
- // Haven't seen this, it must be a livein.
- RegPressure[RCId] += RCCost;
- else if (!isNew && isKill)
- RegPressure[RCId] -= RCCost;
- }
- }
- }
+ for (const MachineInstr &MI : *BB)
+ UpdateRegPressure(&MI, /*ConsiderUnseenAsDef=*/true);
}
/// UpdateRegPressure - Update estimate of register pressure after the
/// specified instruction.
-void MachineLICM::UpdateRegPressure(const MachineInstr *MI) {
- if (MI->isImplicitDef())
- return;
+void MachineLICM::UpdateRegPressure(const MachineInstr *MI,
+ bool ConsiderUnseenAsDef) {
+ auto Cost = calcRegisterCost(MI, /*ConsiderSeen=*/true, ConsiderUnseenAsDef);
+ for (const auto &ClassAndCost : Cost) {
+ unsigned Class = ClassAndCost.first;
+ if (static_cast<int>(RegPressure[Class]) < -ClassAndCost.second)
+ RegPressure[Class] = 0;
+ else
+ RegPressure[Class] += ClassAndCost.second;
+ }
+}
- SmallVector<unsigned, 4> Defs;
+DenseMap<unsigned, int>
+MachineLICM::calcRegisterCost(const MachineInstr *MI, bool ConsiderSeen,
+ bool ConsiderUnseenAsDef) {
+ DenseMap<unsigned, int> Cost;
+ if (MI->isImplicitDef())
+ return Cost;
for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || MO.isImplicit())
@@ -910,27 +910,25 @@ void MachineLICM::UpdateRegPressure(cons
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
- bool isNew = RegSeen.insert(Reg).second;
+ // FIXME: It seems bad to use RegSeen only for some of these calculations.
+ bool isNew = ConsiderSeen ? RegSeen.insert(Reg).second : false;
+ unsigned RCId, RCCost;
+ getRegisterClassIDAndCost(MI, Reg, i, RCId, RCCost);
+ int PriorCost = 0;
+ if (Cost.find(RCId) != Cost.end())
+ PriorCost = Cost[RCId];
if (MO.isDef())
- Defs.push_back(Reg);
- else if (!isNew && isOperandKill(MO, MRI)) {
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(MI, Reg, i, RCId, RCCost);
- if (RCCost > RegPressure[RCId])
- RegPressure[RCId] = 0;
- else
- RegPressure[RCId] -= RCCost;
+ Cost[RCId] = PriorCost + RCCost;
+ else {
+ bool isKill = isOperandKill(MO, MRI);
+ if (isNew && !isKill && ConsiderUnseenAsDef)
+ // Haven't seen this, it must be a livein.
+ Cost[RCId] = PriorCost + RCCost;
+ else if (!isNew && isKill)
+ Cost[RCId] = PriorCost - RCCost;
}
}
-
- unsigned Idx = 0;
- while (!Defs.empty()) {
- unsigned Reg = Defs.pop_back_val();
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(MI, Reg, Idx, RCId, RCCost);
- RegPressure[RCId] += RCCost;
- ++Idx;
- }
+ return Cost;
}
/// isLoadFromGOTOrConstantPool - Return true if this machine instruction
@@ -1148,46 +1146,15 @@ bool MachineLICM::CanCauseHighRegPressur
/// current block and update their register pressures to reflect the effect
/// of hoisting MI from the current block to the preheader.
void MachineLICM::UpdateBackTraceRegPressure(const MachineInstr *MI) {
- if (MI->isImplicitDef())
- return;
-
// First compute the 'cost' of the instruction, i.e. its contribution
// to register pressure.
- 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()) {
- 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)) {
- DenseMap<unsigned, int>::iterator CI = Cost.find(RCId);
- if (CI != Cost.end())
- CI->second -= RCCost;
- else
- Cost.insert(std::make_pair(RCId, -RCCost));
- }
- }
+ auto Cost = calcRegisterCost(MI, /*ConsiderSeen=*/false,
+ /*ConsiderUnseenAsDef=*/false);
// Update register pressure of blocks from loop header to current block.
- for (unsigned i = 0, e = BackTrace.size(); i != e; ++i) {
- SmallVectorImpl<unsigned> &RP = BackTrace[i];
- for (DenseMap<unsigned, int>::iterator CI = Cost.begin(), CE = Cost.end();
- CI != CE; ++CI) {
- unsigned RCId = CI->first;
- RP[RCId] += CI->second;
- }
- }
+ for (auto &RP : BackTrace)
+ for (const auto &ClassAndCost : Cost)
+ RP[ClassAndCost.first] += ClassAndCost.second;
}
/// IsProfitableToHoist - Return true if it is potentially profitable to hoist
@@ -1222,15 +1189,8 @@ bool MachineLICM::IsProfitableToHoist(Ma
if (TII->isTriviallyReMaterializable(&MI, AA))
return true;
- // 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())
@@ -1238,24 +1198,22 @@ bool MachineLICM::IsProfitableToHoist(Ma
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;
+ if (MO.isDef() && HasHighOperandLatency(MI, i, Reg)) {
+ DEBUG(dbgs() << "Hoist High Latency: " << MI);
+ ++NumHighLatency;
+ return true;
}
}
+ // 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.
+ auto Cost = calcRegisterCost(&MI, /*ConsiderSeen=*/false,
+ /*ConsiderUnseenAsDef=*/false);
+
// 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)) {
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