[llvm-commits] [llvm] r52554 - /llvm/trunk/lib/CodeGen/RegAllocLinearScan.cpp
Evan Cheng
evan.cheng at apple.com
Fri Jun 20 14:45:17 PDT 2008
Author: evancheng
Date: Fri Jun 20 16:45:16 2008
New Revision: 52554
URL: http://llvm.org/viewvc/llvm-project?rev=52554&view=rev
Log:
Enhanced heuristic to determine the *best* register to spill. Instead of picking the register with the lowest spill weight. Consider (up to) 2 additional registers with spill weights that are close to the lowest spill weight. The one with fewest defs and uses that conflicts with the current interval (weighted by loop depth) is the spill candidate.
This is not always a win, but there are much more wins than loses and wins tend to be more noticeable.
Modified:
llvm/trunk/lib/CodeGen/RegAllocLinearScan.cpp
Modified: llvm/trunk/lib/CodeGen/RegAllocLinearScan.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocLinearScan.cpp?rev=52554&r1=52553&r2=52554&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegAllocLinearScan.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegAllocLinearScan.cpp Fri Jun 20 16:45:16 2008
@@ -43,6 +43,11 @@
STATISTIC(NumBacktracks, "Number of times we had to backtrack");
STATISTIC(NumCoalesce, "Number of copies coalesced");
+static cl::opt<bool>
+NewHeuristic("new-spilling-heuristic",
+ cl::desc("Use new spilling heuristic"),
+ cl::init(false), cl::Hidden);
+
static RegisterRegAlloc
linearscanRegAlloc("linearscan", " linear scan register allocator",
createLinearScanRegisterAllocator);
@@ -62,6 +67,7 @@
std::map<unsigned, const TargetRegisterClass*> OneClassForEachPhysReg;
MachineFunction* mf_;
+ MachineRegisterInfo* mri_;
const TargetMachine* tm_;
const TargetRegisterInfo* tri_;
const TargetInstrInfo* tii_;
@@ -136,6 +142,15 @@
/// is available, or spill.
void assignRegOrStackSlotAtInterval(LiveInterval* cur);
+ /// findIntervalsToSpill - Determine the intervals to spill for the
+ /// specified interval. It's passed the physical registers whose spill
+ /// weight is the lowest among all the registers whose live intervals
+ /// conflict with the interval.
+ void findIntervalsToSpill(LiveInterval *cur,
+ std::vector<std::pair<unsigned,float> > &Candidates,
+ unsigned NumCands,
+ SmallVector<LiveInterval*, 8> &SpillIntervals);
+
/// attemptTrivialCoalescing - If a simple interval is defined by a copy,
/// try allocate the definition the same register as the source register
/// if the register is not defined during live time of the interval. This
@@ -259,6 +274,7 @@
bool RALinScan::runOnMachineFunction(MachineFunction &fn) {
mf_ = &fn;
+ mri_ = &fn.getRegInfo();
tm_ = &fn.getTarget();
tri_ = tm_->getRegisterInfo();
tii_ = tm_->getInstrInfo();
@@ -534,6 +550,107 @@
SI.MergeRangesInAsValue(RI, VNI);
}
+/// getConflictWeight - Return the number of conflicts between cur
+/// live interval and defs and uses of Reg weighted by loop depthes.
+static float getConflictWeight(LiveInterval *cur, unsigned Reg,
+ LiveIntervals *li_,
+ MachineRegisterInfo *mri_,
+ const MachineLoopInfo *loopInfo) {
+ float Conflicts = 0;
+ for (MachineRegisterInfo::reg_iterator I = mri_->reg_begin(Reg),
+ E = mri_->reg_end(); I != E; ++I) {
+ MachineInstr *MI = &*I;
+ if (cur->liveAt(li_->getInstructionIndex(MI))) {
+ unsigned loopDepth = loopInfo->getLoopDepth(MI->getParent());
+ Conflicts += powf(10.0f, (float)loopDepth);
+ }
+ }
+ return Conflicts;
+}
+
+/// findIntervalsToSpill - Determine the intervals to spill for the
+/// specified interval. It's passed the physical registers whose spill
+/// weight is the lowest among all the registers whose live intervals
+/// conflict with the interval.
+void RALinScan::findIntervalsToSpill(LiveInterval *cur,
+ std::vector<std::pair<unsigned,float> > &Candidates,
+ unsigned NumCands,
+ SmallVector<LiveInterval*, 8> &SpillIntervals) {
+ // We have figured out the *best* register to spill. But there are other
+ // registers that are pretty good as well (spill weight within 3%). Spill
+ // the one that has fewest defs and uses that conflict with cur.
+ float Conflicts[3] = { 0.0f, 0.0f, 0.0f };
+ SmallVector<LiveInterval*, 8> SLIs[3];
+
+ DOUT << "\tConsidering " << NumCands << " candidates: ";
+ DEBUG(for (unsigned i = 0; i != NumCands; ++i)
+ DOUT << tri_->getName(Candidates[i].first) << " ";
+ DOUT << "\n";);
+
+ // Calculate the number of conflicts of each candidate.
+ for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ++i) {
+ unsigned Reg = i->first->reg;
+ unsigned PhysReg = vrm_->getPhys(Reg);
+ if (!cur->overlapsFrom(*i->first, i->second))
+ continue;
+ for (unsigned j = 0; j < NumCands; ++j) {
+ unsigned Candidate = Candidates[j].first;
+ if (tri_->regsOverlap(PhysReg, Candidate)) {
+ if (NumCands > 1)
+ Conflicts[j] += getConflictWeight(cur, Reg, li_, mri_, loopInfo);
+ SLIs[j].push_back(i->first);
+ }
+ }
+ }
+
+ for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end(); ++i){
+ unsigned Reg = i->first->reg;
+ unsigned PhysReg = vrm_->getPhys(Reg);
+ if (!cur->overlapsFrom(*i->first, i->second-1))
+ continue;
+ for (unsigned j = 0; j < NumCands; ++j) {
+ unsigned Candidate = Candidates[j].first;
+ if (tri_->regsOverlap(PhysReg, Candidate)) {
+ if (NumCands > 1)
+ Conflicts[j] += getConflictWeight(cur, Reg, li_, mri_, loopInfo);
+ SLIs[j].push_back(i->first);
+ }
+ }
+ }
+
+ // Which is the best candidate?
+ unsigned BestCandidate = 0;
+ float MinConflicts = Conflicts[0];
+ for (unsigned i = 1; i != NumCands; ++i) {
+ if (Conflicts[i] < MinConflicts) {
+ BestCandidate = i;
+ MinConflicts = Conflicts[i];
+ }
+ }
+
+ std::copy(SLIs[BestCandidate].begin(), SLIs[BestCandidate].end(),
+ std::back_inserter(SpillIntervals));
+}
+
+namespace {
+ struct WeightCompare {
+ typedef std::pair<unsigned, float> RegWeightPair;
+ bool operator()(const RegWeightPair &LHS, const RegWeightPair &RHS) const {
+ return LHS.second < RHS.second;
+ }
+ };
+}
+
+static bool weightsAreClose(float w1, float w2) {
+ if (!NewHeuristic)
+ return false;
+
+ float diff = w1 - w2;
+ if (diff <= 0.02f) // Within 0.02f
+ return true;
+ return (diff / w2) <= 0.05f; // Within 5%.
+}
+
/// assignRegOrStackSlotAtInterval - assign a register if one is available, or
/// spill.
void RALinScan::assignRegOrStackSlotAtInterval(LiveInterval* cur)
@@ -682,7 +799,7 @@
DOUT << "no free registers\n";
// Compile the spill weights into an array that is better for scanning.
- std::vector<float> SpillWeights(tri_->getNumRegs(), 0.0);
+ std::vector<float> SpillWeights(tri_->getNumRegs(), 0.0f);
for (std::vector<std::pair<unsigned, float> >::iterator
I = SpillWeightsToAdd.begin(), E = SpillWeightsToAdd.end(); I != E; ++I)
updateSpillWeights(SpillWeights, I->first, I->second, tri_);
@@ -701,44 +818,56 @@
// Find a register to spill.
float minWeight = HUGE_VALF;
- unsigned minReg = cur->preference; // Try the preferred register first.
-
+ unsigned minReg = 0; /*cur->preference*/; // Try the preferred register first.
+
+ bool Found = false;
+ std::vector<std::pair<unsigned,float> > RegsWeights;
if (!minReg || SpillWeights[minReg] == HUGE_VALF)
for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
e = RC->allocation_order_end(*mf_); i != e; ++i) {
unsigned reg = *i;
- if (minWeight > SpillWeights[reg]) {
- minWeight = SpillWeights[reg];
- minReg = reg;
- }
+ float regWeight = SpillWeights[reg];
+ if (minWeight > regWeight)
+ Found = true;
+ RegsWeights.push_back(std::make_pair(reg, regWeight));
}
// If we didn't find a register that is spillable, try aliases?
- if (!minReg) {
+ if (!Found) {
for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
e = RC->allocation_order_end(*mf_); i != e; ++i) {
unsigned reg = *i;
// No need to worry about if the alias register size < regsize of RC.
// We are going to spill all registers that alias it anyway.
- for (const unsigned* as = tri_->getAliasSet(reg); *as; ++as) {
- if (minWeight > SpillWeights[*as]) {
- minWeight = SpillWeights[*as];
- minReg = *as;
- }
- }
+ for (const unsigned* as = tri_->getAliasSet(reg); *as; ++as)
+ RegsWeights.push_back(std::make_pair(*as, SpillWeights[*as]));
}
+ }
+ // Sort all potential spill candidates by weight.
+ std::sort(RegsWeights.begin(), RegsWeights.end(), WeightCompare());
+ minReg = RegsWeights[0].first;
+ minWeight = RegsWeights[0].second;
+ if (minWeight == HUGE_VALF) {
// All registers must have inf weight. Just grab one!
- if (!minReg) {
- minReg = BestPhysReg ? BestPhysReg : *RC->allocation_order_begin(*mf_);
- if (cur->weight == HUGE_VALF || cur->getSize() == 1)
- // Spill a physical register around defs and uses.
- li_->spillPhysRegAroundRegDefsUses(*cur, minReg, *vrm_);
- }
+ minReg = BestPhysReg ? BestPhysReg : *RC->allocation_order_begin(*mf_);
+ if (cur->weight == HUGE_VALF || cur->getSize() == 1)
+ // Spill a physical register around defs and uses.
+ li_->spillPhysRegAroundRegDefsUses(*cur, minReg, *vrm_);
+ }
+
+ // Find up to 3 registers to consider as spill candidates.
+ unsigned LastCandidate = RegsWeights.size() >= 3 ? 3 : 1;
+ while (LastCandidate > 1) {
+ if (weightsAreClose(RegsWeights[LastCandidate-1].second, minWeight))
+ break;
+ --LastCandidate;
}
-
- DOUT << "\t\tregister with min weight: "
- << tri_->getName(minReg) << " (" << minWeight << ")\n";
+
+ DOUT << "\t\tregister(s) with min weight(s): ";
+ DEBUG(for (unsigned i = 0; i != LastCandidate; ++i)
+ DOUT << tri_->getName(RegsWeights[i].first)
+ << " (" << RegsWeights[i].second << ")\n");
// if the current has the minimum weight, we need to spill it and
// add any added intervals back to unhandled, and restart
@@ -767,60 +896,41 @@
// should go back right in the front of the list
unhandled_.push(cur);
- // otherwise we spill all intervals aliasing the register with
- // minimum weight, rollback to the interval with the earliest
- // start point and let the linear scan algorithm run again
- std::vector<LiveInterval*> added;
assert(TargetRegisterInfo::isPhysicalRegister(minReg) &&
"did not choose a register to spill?");
- BitVector toSpill(tri_->getNumRegs());
- // We are going to spill minReg and all its aliases.
- toSpill[minReg] = true;
- for (const unsigned* as = tri_->getAliasSet(minReg); *as; ++as)
- toSpill[*as] = true;
+ // We spill all intervals aliasing the register with
+ // minimum weight, rollback to the interval with the earliest
+ // start point and let the linear scan algorithm run again
+ SmallVector<LiveInterval*, 8> spillIs;
+
+ // Determine which intervals have to be spilled.
+ findIntervalsToSpill(cur, RegsWeights, LastCandidate, spillIs);
+
+ // Set of spilled vregs (used later to rollback properly)
+ SmallSet<unsigned, 8> spilled;
- // the earliest start of a spilled interval indicates up to where
+ // The earliest start of a Spilled interval indicates up to where
// in handled we need to roll back
unsigned earliestStart = cur->beginNumber();
- // set of spilled vregs (used later to rollback properly)
- SmallSet<unsigned, 32> spilled;
-
- // spill live intervals of virtual regs mapped to the physical register we
+ // Spill live intervals of virtual regs mapped to the physical register we
// want to clear (and its aliases). We only spill those that overlap with the
// current interval as the rest do not affect its allocation. we also keep
// track of the earliest start of all spilled live intervals since this will
// mark our rollback point.
- for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ++i) {
- unsigned reg = i->first->reg;
- if (//TargetRegisterInfo::isVirtualRegister(reg) &&
- toSpill[vrm_->getPhys(reg)] &&
- cur->overlapsFrom(*i->first, i->second)) {
- DOUT << "\t\t\tspilling(a): " << *i->first << '\n';
- earliestStart = std::min(earliestStart, i->first->beginNumber());
- float SSWeight;
- std::vector<LiveInterval*> newIs =
- li_->addIntervalsForSpills(*i->first, loopInfo, *vrm_, SSWeight);
- addStackInterval(i->first, ls_, li_, SSWeight, *vrm_);
- std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
- spilled.insert(reg);
- }
- }
- for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end(); ++i){
- unsigned reg = i->first->reg;
- if (//TargetRegisterInfo::isVirtualRegister(reg) &&
- toSpill[vrm_->getPhys(reg)] &&
- cur->overlapsFrom(*i->first, i->second-1)) {
- DOUT << "\t\t\tspilling(i): " << *i->first << '\n';
- earliestStart = std::min(earliestStart, i->first->beginNumber());
- float SSWeight;
- std::vector<LiveInterval*> newIs =
- li_->addIntervalsForSpills(*i->first, loopInfo, *vrm_, SSWeight);
- addStackInterval(i->first, ls_, li_, SSWeight, *vrm_);
- std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
- spilled.insert(reg);
- }
+ std::vector<LiveInterval*> added;
+ while (!spillIs.empty()) {
+ LiveInterval *sli = spillIs.back();
+ spillIs.pop_back();
+ DOUT << "\t\t\tspilling(a): " << *sli << '\n';
+ earliestStart = std::min(earliestStart, sli->beginNumber());
+ float SSWeight;
+ std::vector<LiveInterval*> newIs =
+ li_->addIntervalsForSpills(*sli, loopInfo, *vrm_, SSWeight);
+ addStackInterval(sli, ls_, li_, SSWeight, *vrm_);
+ std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
+ spilled.insert(sli->reg);
}
DOUT << "\t\trolling back to: " << earliestStart << '\n';
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