}
}
+ /// Cost of evicting interference.
+ struct EvictionCost {
+ unsigned BrokenHints; ///< Total number of broken hints.
+ float MaxWeight; ///< Maximum spill weight evicted.
+
+ EvictionCost(unsigned B = 0) : BrokenHints(B), MaxWeight(0) {}
+
+ bool operator<(const EvictionCost &O) const {
+ if (BrokenHints != O.BrokenHints)
+ return BrokenHints < O.BrokenHints;
+ return MaxWeight < O.MaxWeight;
+ }
+ };
+
// splitting state.
std::auto_ptr<SplitAnalysis> SA;
std::auto_ptr<SplitEditor> SE;
void splitAroundRegion(LiveInterval&, GlobalSplitCandidate&,
SmallVectorImpl<LiveInterval*>&);
void calcGapWeights(unsigned, SmallVectorImpl<float>&);
- bool canEvict(LiveInterval &A, LiveInterval &B);
- bool canEvictInterference(LiveInterval&, unsigned, float&);
+ bool shouldEvict(LiveInterval &A, bool, LiveInterval &B, bool);
+ bool canEvictInterference(LiveInterval&, unsigned, bool, EvictionCost&);
+ void evictInterference(LiveInterval&, unsigned,
+ SmallVectorImpl<LiveInterval*>&);
unsigned tryAssign(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
if (!PhysReg || Order.isHint(PhysReg))
return PhysReg;
- // PhysReg is available. Try to evict interference from a cheaper alternative.
+ // PhysReg is available, but there may be a better choice.
+
+ // If we missed a simple hint, try to cheaply evict interference from the
+ // preferred register.
+ if (unsigned Hint = MRI->getSimpleHint(VirtReg.reg))
+ if (Order.isHint(Hint)) {
+ DEBUG(dbgs() << "missed hint " << PrintReg(Hint, TRI) << '\n');
+ EvictionCost MaxCost(1);
+ if (canEvictInterference(VirtReg, Hint, true, MaxCost)) {
+ evictInterference(VirtReg, Hint, NewVRegs);
+ return Hint;
+ }
+ }
+
+ // Try to evict interference from a cheaper alternative.
unsigned Cost = TRI->getCostPerUse(PhysReg);
// Most registers have 0 additional cost.
// Interference eviction
//===----------------------------------------------------------------------===//
-/// canEvict - determine if A can evict the assigned live range B. The eviction
-/// policy defined by this function together with the allocation order defined
-/// by enqueue() decides which registers ultimately end up being split and
-/// spilled.
+/// shouldEvict - determine if A should evict the assigned live range B. The
+/// eviction policy defined by this function together with the allocation order
+/// defined by enqueue() decides which registers ultimately end up being split
+/// and spilled.
///
/// Cascade numbers are used to prevent infinite loops if this function is a
/// cyclic relation.
-bool RAGreedy::canEvict(LiveInterval &A, LiveInterval &B) {
+///
+/// @param A The live range to be assigned.
+/// @param IsHint True when A is about to be assigned to its preferred
+/// register.
+/// @param B The live range to be evicted.
+/// @param BreaksHint True when B is already assigned to its preferred register.
+bool RAGreedy::shouldEvict(LiveInterval &A, bool IsHint,
+ LiveInterval &B, bool BreaksHint) {
+ bool CanSplit = getStage(B) <= RS_Second;
+
+ // Be fairly aggressive about following hints as long as the evictee can be
+ // split.
+ if (CanSplit && IsHint && !BreaksHint)
+ return true;
+
return A.weight > B.weight;
}
-/// canEvict - Return true if all interferences between VirtReg and PhysReg can
-/// be evicted.
-/// Return false if any interference is heavier than MaxWeight.
-/// On return, set MaxWeight to the maximal spill weight of an interference.
+/// canEvictInterference - Return true if all interferences between VirtReg and
+/// PhysReg can be evicted. When OnlyCheap is set, don't do anything
+///
+/// @param VirtReg Live range that is about to be assigned.
+/// @param PhysReg Desired register for assignment.
+/// @prarm IsHint True when PhysReg is VirtReg's preferred register.
+/// @param MaxCost Only look for cheaper candidates and update with new cost
+/// when returning true.
+/// @returns True when interference can be evicted cheaper than MaxCost.
bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg,
- float &MaxWeight) {
+ bool IsHint, EvictionCost &MaxCost) {
// Find VirtReg's cascade number. This will be unassigned if VirtReg was never
// involved in an eviction before. If a cascade number was assigned, deny
// evicting anything with the same or a newer cascade number. This prevents
if (!Cascade)
Cascade = NextCascade;
- float Weight = 0;
+ EvictionCost Cost;
for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
// If there is 10 or more interferences, chances are one is heavier.
- if (Q.collectInterferingVRegs(10, MaxWeight) >= 10)
+ if (Q.collectInterferingVRegs(10) >= 10)
return false;
// Check if any interfering live range is heavier than MaxWeight.
LiveInterval *Intf = Q.interferingVRegs()[i - 1];
if (TargetRegisterInfo::isPhysicalRegister(Intf->reg))
return false;
- if (Cascade <= ExtraRegInfo[Intf->reg].Cascade)
+ // Never evict spill products. They cannot split or spill.
+ if (getStage(*Intf) == RS_Spill)
return false;
- if (Intf->weight >= MaxWeight)
+ // Once a live range becomes small enough, it is urgent that we find a
+ // register for it. This is indicated by an infinite spill weight. These
+ // urgent live ranges get to evict almost anything.
+ bool Urgent = !VirtReg.isSpillable() && Intf->isSpillable();
+ // Only evict older cascades or live ranges without a cascade.
+ unsigned IntfCascade = ExtraRegInfo[Intf->reg].Cascade;
+ if (Cascade <= IntfCascade) {
+ if (!Urgent)
+ return false;
+ // We permit breaking cascades for urgent evictions. It should be the
+ // last resort, though, so make it really expensive.
+ Cost.BrokenHints += 10;
+ }
+ // Would this break a satisfied hint?
+ bool BreaksHint = VRM->hasPreferredPhys(Intf->reg);
+ // Update eviction cost.
+ Cost.BrokenHints += BreaksHint;
+ Cost.MaxWeight = std::max(Cost.MaxWeight, Intf->weight);
+ // Abort if this would be too expensive.
+ if (!(Cost < MaxCost))
return false;
- if (!canEvict(VirtReg, *Intf))
+ // Finally, apply the eviction policy for non-urgent evictions.
+ if (!Urgent && !shouldEvict(VirtReg, IsHint, *Intf, BreaksHint))
return false;
- Weight = std::max(Weight, Intf->weight);
}
}
- MaxWeight = Weight;
+ MaxCost = Cost;
return true;
}
+/// evictInterference - Evict any interferring registers that prevent VirtReg
+/// from being assigned to Physreg. This assumes that canEvictInterference
+/// returned true.
+void RAGreedy::evictInterference(LiveInterval &VirtReg, unsigned PhysReg,
+ SmallVectorImpl<LiveInterval*> &NewVRegs) {
+ // Make sure that VirtReg has a cascade number, and assign that cascade
+ // number to every evicted register. These live ranges than then only be
+ // evicted by a newer cascade, preventing infinite loops.
+ unsigned Cascade = ExtraRegInfo[VirtReg.reg].Cascade;
+ if (!Cascade)
+ Cascade = ExtraRegInfo[VirtReg.reg].Cascade = NextCascade++;
+
+ DEBUG(dbgs() << "evicting " << PrintReg(PhysReg, TRI)
+ << " interference: Cascade " << Cascade << '\n');
+ for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
+ LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
+ assert(Q.seenAllInterferences() && "Didn't check all interfererences.");
+ for (unsigned i = 0, e = Q.interferingVRegs().size(); i != e; ++i) {
+ LiveInterval *Intf = Q.interferingVRegs()[i];
+ unassign(*Intf, VRM->getPhys(Intf->reg));
+ assert((ExtraRegInfo[Intf->reg].Cascade < Cascade ||
+ VirtReg.isSpillable() < Intf->isSpillable()) &&
+ "Cannot decrease cascade number, illegal eviction");
+ ExtraRegInfo[Intf->reg].Cascade = Cascade;
+ ++NumEvicted;
+ NewVRegs.push_back(Intf);
+ }
+ }
+}
+
/// tryEvict - Try to evict all interferences for a physreg.
/// @param VirtReg Currently unassigned virtual register.
/// @param Order Physregs to try.
unsigned CostPerUseLimit) {
NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled);
- // Keep track of the lightest single interference seen so far.
- float BestWeight = HUGE_VALF;
+ // Keep track of the cheapest interference seen so far.
+ EvictionCost BestCost(~0u);
unsigned BestPhys = 0;
+ // When we are just looking for a reduced cost per use, don't break any
+ // hints, and only evict smaller spill weights.
+ if (CostPerUseLimit < ~0u) {
+ BestCost.BrokenHints = 0;
+ BestCost.MaxWeight = VirtReg.weight;
+ }
+
Order.rewind();
while (unsigned PhysReg = Order.next()) {
if (TRI->getCostPerUse(PhysReg) >= CostPerUseLimit)
continue;
- // The first use of a register in a function has cost 1.
- if (CostPerUseLimit == 1 && !MRI->isPhysRegUsed(PhysReg))
- continue;
-
- float Weight = BestWeight;
- if (!canEvictInterference(VirtReg, PhysReg, Weight))
- continue;
-
- // This is an eviction candidate.
- DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " interference = "
- << Weight << '\n');
- if (BestPhys && Weight >= BestWeight)
+ // The first use of a callee-saved register in a function has cost 1.
+ // Don't start using a CSR when the CostPerUseLimit is low.
+ if (CostPerUseLimit == 1)
+ if (unsigned CSR = RegClassInfo.getLastCalleeSavedAlias(PhysReg))
+ if (!MRI->isPhysRegUsed(CSR)) {
+ DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " would clobber CSR "
+ << PrintReg(CSR, TRI) << '\n');
+ continue;
+ }
+
+ if (!canEvictInterference(VirtReg, PhysReg, false, BestCost))
continue;
// Best so far.
BestPhys = PhysReg;
- BestWeight = Weight;
+
// Stop if the hint can be used.
if (Order.isHint(PhysReg))
break;
if (!BestPhys)
return 0;
- // We will evict interference. Make sure that VirtReg has a cascade number,
- // and assign that cascade number to every evicted register. These live
- // ranges than then only be evicted by a newer cascade, preventing infinite
- // loops.
- unsigned Cascade = ExtraRegInfo[VirtReg.reg].Cascade;
- if (!Cascade)
- Cascade = ExtraRegInfo[VirtReg.reg].Cascade = NextCascade++;
-
- DEBUG(dbgs() << "evicting " << PrintReg(BestPhys, TRI)
- << " interference: Cascade " << Cascade << '\n');
- for (const unsigned *AliasI = TRI->getOverlaps(BestPhys); *AliasI; ++AliasI) {
- LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
- assert(Q.seenAllInterferences() && "Didn't check all interfererences.");
- for (unsigned i = 0, e = Q.interferingVRegs().size(); i != e; ++i) {
- LiveInterval *Intf = Q.interferingVRegs()[i];
- unassign(*Intf, VRM->getPhys(Intf->reg));
- assert(ExtraRegInfo[Intf->reg].Cascade < Cascade &&
- "Cannot decrease cascade number, illegal eviction");
- ExtraRegInfo[Intf->reg].Cascade = Cascade;
- ++NumEvicted;
- NewVRegs.push_back(Intf);
- }
- }
+ evictInterference(VirtReg, BestPhys, NewVRegs);
return BestPhys;
}
// If we couldn't allocate a register from spilling, there is probably some
// invalid inline assembly. The base class wil report it.
- if (Stage >= RS_Spill)
+ if (Stage >= RS_Spill || !VirtReg.isSpillable())
return ~0u;
// Try splitting VirtReg or interferences.
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