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-rw-r--r--lib/CodeGen/RegAllocGreedy.cpp131
1 files changed, 74 insertions, 57 deletions
diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index 912d899..4402694 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -76,6 +76,7 @@ class RAGreedy : public MachineFunctionPass,
// state
std::auto_ptr<Spiller> SpillerInstance;
std::priority_queue<std::pair<unsigned, unsigned> > Queue;
+ unsigned NextCascade;
// Live ranges pass through a number of stages as we try to allocate them.
// Some of the stages may also create new live ranges:
@@ -101,31 +102,37 @@ class RAGreedy : public MachineFunctionPass,
static const char *const StageName[];
- IndexedMap<unsigned char, VirtReg2IndexFunctor> LRStage;
+ // RegInfo - Keep additional information about each live range.
+ struct RegInfo {
+ LiveRangeStage Stage;
+
+ // Cascade - Eviction loop prevention. See canEvictInterference().
+ unsigned Cascade;
+
+ RegInfo() : Stage(RS_New), Cascade(0) {}
+ };
+
+ IndexedMap<RegInfo, VirtReg2IndexFunctor> ExtraRegInfo;
LiveRangeStage getStage(const LiveInterval &VirtReg) const {
- return LiveRangeStage(LRStage[VirtReg.reg]);
+ return ExtraRegInfo[VirtReg.reg].Stage;
+ }
+
+ void setStage(const LiveInterval &VirtReg, LiveRangeStage Stage) {
+ ExtraRegInfo.resize(MRI->getNumVirtRegs());
+ ExtraRegInfo[VirtReg.reg].Stage = Stage;
}
template<typename Iterator>
void setStage(Iterator Begin, Iterator End, LiveRangeStage NewStage) {
- LRStage.resize(MRI->getNumVirtRegs());
+ ExtraRegInfo.resize(MRI->getNumVirtRegs());
for (;Begin != End; ++Begin) {
unsigned Reg = (*Begin)->reg;
- if (LRStage[Reg] == RS_New)
- LRStage[Reg] = NewStage;
+ if (ExtraRegInfo[Reg].Stage == RS_New)
+ ExtraRegInfo[Reg].Stage = NewStage;
}
}
- // Eviction. Sometimes an assigned live range can be evicted without
- // conditions, but other times it must be split after being evicted to avoid
- // infinite loops.
- enum CanEvict {
- CE_Never, ///< Can never evict.
- CE_Always, ///< Can always evict.
- CE_WithSplit ///< Can evict only if range is also split or spilled.
- };
-
// splitting state.
std::auto_ptr<SplitAnalysis> SA;
std::auto_ptr<SplitEditor> SE;
@@ -190,7 +197,7 @@ private:
void splitAroundRegion(LiveInterval&, GlobalSplitCandidate&,
SmallVectorImpl<LiveInterval*>&);
void calcGapWeights(unsigned, SmallVectorImpl<float>&);
- CanEvict canEvict(LiveInterval &A, LiveInterval &B);
+ bool canEvict(LiveInterval &A, LiveInterval &B);
bool canEvictInterference(LiveInterval&, unsigned, float&);
unsigned tryAssign(LiveInterval&, AllocationOrder&,
@@ -228,7 +235,7 @@ FunctionPass* llvm::createGreedyRegisterAllocator() {
return new RAGreedy();
}
-RAGreedy::RAGreedy(): MachineFunctionPass(ID), LRStage(RS_New) {
+RAGreedy::RAGreedy(): MachineFunctionPass(ID) {
initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
@@ -308,13 +315,13 @@ void RAGreedy::LRE_DidCloneVirtReg(unsigned New, unsigned Old) {
// LRE may clone a virtual register because dead code elimination causes it to
// be split into connected components. Ensure that the new register gets the
// same stage as the parent.
- LRStage.grow(New);
- LRStage[New] = LRStage[Old];
+ ExtraRegInfo.grow(New);
+ ExtraRegInfo[New] = ExtraRegInfo[Old];
}
void RAGreedy::releaseMemory() {
SpillerInstance.reset(0);
- LRStage.clear();
+ ExtraRegInfo.clear();
GlobalCand.clear();
RegAllocBase::releaseMemory();
}
@@ -328,11 +335,11 @@ void RAGreedy::enqueue(LiveInterval *LI) {
"Can only enqueue virtual registers");
unsigned Prio;
- LRStage.grow(Reg);
- if (LRStage[Reg] == RS_New)
- LRStage[Reg] = RS_First;
+ ExtraRegInfo.grow(Reg);
+ if (ExtraRegInfo[Reg].Stage == RS_New)
+ ExtraRegInfo[Reg].Stage = RS_First;
- if (LRStage[Reg] == RS_Second)
+ if (ExtraRegInfo[Reg].Stage == RS_Second)
// Unsplit ranges that couldn't be allocated immediately are deferred until
// everything else has been allocated. Long ranges are allocated last so
// they are split against realistic interference.
@@ -398,13 +405,10 @@ unsigned RAGreedy::tryAssign(LiveInterval &VirtReg,
/// by enqueue() decides which registers ultimately end up being split and
/// spilled.
///
-/// This function must define a non-circular relation when it returns CE_Always,
-/// otherwise infinite eviction loops are possible. When evicting a <= RS_Second
-/// range, it is possible to return CE_WithSplit which forces the evicted
-/// register to be split or spilled before it can evict anything again. That
-/// guarantees progress.
-RAGreedy::CanEvict RAGreedy::canEvict(LiveInterval &A, LiveInterval &B) {
- return A.weight > B.weight ? CE_Always : CE_Never;
+/// Cascade numbers are used to prevent infinite loops if this function is a
+/// cyclic relation.
+bool RAGreedy::canEvict(LiveInterval &A, LiveInterval &B) {
+ return A.weight > B.weight;
}
/// canEvict - Return true if all interferences between VirtReg and PhysReg can
@@ -413,6 +417,17 @@ RAGreedy::CanEvict RAGreedy::canEvict(LiveInterval &A, LiveInterval &B) {
/// On return, set MaxWeight to the maximal spill weight of an interference.
bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg,
float &MaxWeight) {
+ // 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
+ // infinite eviction loops.
+ //
+ // This works out so a register without a cascade number is allowed to evict
+ // anything, and it can be evicted by anything.
+ unsigned Cascade = ExtraRegInfo[VirtReg.reg].Cascade;
+ if (!Cascade)
+ Cascade = NextCascade;
+
float Weight = 0;
for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
@@ -425,18 +440,12 @@ bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg,
LiveInterval *Intf = Q.interferingVRegs()[i - 1];
if (TargetRegisterInfo::isPhysicalRegister(Intf->reg))
return false;
+ if (Cascade <= ExtraRegInfo[Intf->reg].Cascade)
+ return false;
if (Intf->weight >= MaxWeight)
return false;
- switch (canEvict(VirtReg, *Intf)) {
- case CE_Always:
- break;
- case CE_Never:
+ if (!canEvict(VirtReg, *Intf))
return false;
- case CE_WithSplit:
- if (getStage(*Intf) > RS_Second)
- return false;
- break;
- }
Weight = std::max(Weight, Intf->weight);
}
}
@@ -487,20 +496,27 @@ unsigned RAGreedy::tryEvict(LiveInterval &VirtReg,
if (!BestPhys)
return 0;
- DEBUG(dbgs() << "evicting " << PrintReg(BestPhys, TRI) << " interference\n");
+ // 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);
- // Prevent looping by forcing the evicted ranges to be split before they
- // can evict anything else.
- if (getStage(*Intf) < RS_Second &&
- canEvict(VirtReg, *Intf) == CE_WithSplit)
- LRStage[Intf->reg] = RS_Second;
}
}
return BestPhys;
@@ -1097,7 +1113,7 @@ void RAGreedy::splitAroundRegion(LiveInterval &VirtReg,
SE->finish(&IntvMap);
DebugVars->splitRegister(VirtReg.reg, LREdit.regs());
- LRStage.resize(MRI->getNumVirtRegs());
+ ExtraRegInfo.resize(MRI->getNumVirtRegs());
unsigned OrigBlocks = SA->getNumLiveBlocks();
// Sort out the new intervals created by splitting. We get four kinds:
@@ -1106,27 +1122,27 @@ void RAGreedy::splitAroundRegion(LiveInterval &VirtReg,
// - Block-local splits are candidates for local splitting.
// - DCE leftovers should go back on the queue.
for (unsigned i = 0, e = LREdit.size(); i != e; ++i) {
- unsigned Reg = LREdit.get(i)->reg;
+ LiveInterval &Reg = *LREdit.get(i);
// Ignore old intervals from DCE.
- if (LRStage[Reg] != RS_New)
+ if (getStage(Reg) != RS_New)
continue;
// Remainder interval. Don't try splitting again, spill if it doesn't
// allocate.
if (IntvMap[i] == 0) {
- LRStage[Reg] = RS_Global;
+ setStage(Reg, RS_Global);
continue;
}
// Main interval. Allow repeated splitting as long as the number of live
// blocks is strictly decreasing.
if (IntvMap[i] == MainIntv) {
- if (SA->countLiveBlocks(LREdit.get(i)) >= OrigBlocks) {
+ if (SA->countLiveBlocks(&Reg) >= OrigBlocks) {
DEBUG(dbgs() << "Main interval covers the same " << OrigBlocks
<< " blocks as original.\n");
// Don't allow repeated splitting as a safe guard against looping.
- LRStage[Reg] = RS_Global;
+ setStage(Reg, RS_Global);
}
continue;
}
@@ -1432,10 +1448,9 @@ unsigned RAGreedy::tryLocalSplit(LiveInterval &VirtReg, AllocationOrder &Order,
if (NewGaps >= NumGaps) {
DEBUG(dbgs() << "Tagging non-progress ranges: ");
assert(!ProgressRequired && "Didn't make progress when it was required.");
- LRStage.resize(MRI->getNumVirtRegs());
for (unsigned i = 0, e = IntvMap.size(); i != e; ++i)
if (IntvMap[i] == 1) {
- LRStage[LREdit.get(i)->reg] = RS_Local;
+ setStage(*LREdit.get(i), RS_Local);
DEBUG(dbgs() << PrintReg(LREdit.get(i)->reg));
}
DEBUG(dbgs() << '\n');
@@ -1514,7 +1529,8 @@ unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
return PhysReg;
LiveRangeStage Stage = getStage(VirtReg);
- DEBUG(dbgs() << StageName[Stage] << '\n');
+ DEBUG(dbgs() << StageName[Stage]
+ << " Cascade " << ExtraRegInfo[VirtReg.reg].Cascade << '\n');
// Try to evict a less worthy live range, but only for ranges from the primary
// queue. The RS_Second ranges already failed to do this, and they should not
@@ -1529,7 +1545,7 @@ unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
// Wait until the second time, when all smaller ranges have been allocated.
// This gives a better picture of the interference to split around.
if (Stage == RS_First) {
- LRStage[VirtReg.reg] = RS_Second;
+ setStage(VirtReg, RS_Second);
DEBUG(dbgs() << "wait for second round\n");
NewVRegs.push_back(&VirtReg);
return 0;
@@ -1580,8 +1596,9 @@ bool RAGreedy::runOnMachineFunction(MachineFunction &mf) {
SA.reset(new SplitAnalysis(*VRM, *LIS, *Loops));
SE.reset(new SplitEditor(*SA, *LIS, *VRM, *DomTree));
- LRStage.clear();
- LRStage.resize(MRI->getNumVirtRegs());
+ ExtraRegInfo.clear();
+ ExtraRegInfo.resize(MRI->getNumVirtRegs());
+ NextCascade = 1;
IntfCache.init(MF, &PhysReg2LiveUnion[0], Indexes, TRI);
allocatePhysRegs();
generated by cgit v1.1 at 2024-09-12 11:17:31 +0000