1 //===-- RegAllocBasic.cpp - basic register allocator ----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the RABasic function pass, which provides a minimal
11 // implementation of the basic register allocator.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "regalloc"
16 #include "LiveDebugVariables.h"
17 #include "LiveIntervalUnion.h"
18 #include "LiveRangeEdit.h"
19 #include "RegAllocBase.h"
20 #include "RenderMachineFunction.h"
22 #include "VirtRegMap.h"
23 #include "llvm/ADT/OwningPtr.h"
24 #include "llvm/ADT/Statistic.h"
25 #include "llvm/Analysis/AliasAnalysis.h"
26 #include "llvm/Function.h"
27 #include "llvm/PassAnalysisSupport.h"
28 #include "llvm/CodeGen/CalcSpillWeights.h"
29 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
30 #include "llvm/CodeGen/LiveStackAnalysis.h"
31 #include "llvm/CodeGen/MachineFunctionPass.h"
32 #include "llvm/CodeGen/MachineInstr.h"
33 #include "llvm/CodeGen/MachineLoopInfo.h"
34 #include "llvm/CodeGen/MachineRegisterInfo.h"
35 #include "llvm/CodeGen/Passes.h"
36 #include "llvm/CodeGen/RegAllocRegistry.h"
37 #include "llvm/CodeGen/RegisterCoalescer.h"
38 #include "llvm/Target/TargetMachine.h"
39 #include "llvm/Target/TargetOptions.h"
40 #include "llvm/Target/TargetRegisterInfo.h"
42 #include "llvm/ADT/SparseBitVector.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/ErrorHandling.h"
46 #include "llvm/Support/raw_ostream.h"
47 #include "llvm/Support/Timer.h"
54 STATISTIC(NumAssigned , "Number of registers assigned");
55 STATISTIC(NumUnassigned , "Number of registers unassigned");
56 STATISTIC(NumNewQueued , "Number of new live ranges queued");
58 static RegisterRegAlloc basicRegAlloc("basic", "basic register allocator",
59 createBasicRegisterAllocator);
61 // Temporary verification option until we can put verification inside
63 static cl::opt<bool, true>
64 VerifyRegAlloc("verify-regalloc", cl::location(RegAllocBase::VerifyEnabled),
65 cl::desc("Verify during register allocation"));
67 const char *RegAllocBase::TimerGroupName = "Register Allocation";
68 bool RegAllocBase::VerifyEnabled = false;
71 struct CompSpillWeight {
72 bool operator()(LiveInterval *A, LiveInterval *B) const {
73 return A->weight < B->weight;
79 /// RABasic provides a minimal implementation of the basic register allocation
80 /// algorithm. It prioritizes live virtual registers by spill weight and spills
81 /// whenever a register is unavailable. This is not practical in production but
82 /// provides a useful baseline both for measuring other allocators and comparing
83 /// the speed of the basic algorithm against other styles of allocators.
84 class RABasic : public MachineFunctionPass, public RegAllocBase
88 BitVector ReservedRegs;
92 RenderMachineFunction *RMF;
95 std::auto_ptr<Spiller> SpillerInstance;
96 std::priority_queue<LiveInterval*, std::vector<LiveInterval*>,
97 CompSpillWeight> Queue;
101 /// Return the pass name.
102 virtual const char* getPassName() const {
103 return "Basic Register Allocator";
106 /// RABasic analysis usage.
107 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
109 virtual void releaseMemory();
111 virtual Spiller &spiller() { return *SpillerInstance; }
113 virtual float getPriority(LiveInterval *LI) { return LI->weight; }
115 virtual void enqueue(LiveInterval *LI) {
119 virtual LiveInterval *dequeue() {
122 LiveInterval *LI = Queue.top();
127 virtual unsigned selectOrSplit(LiveInterval &VirtReg,
128 SmallVectorImpl<LiveInterval*> &SplitVRegs);
130 /// Perform register allocation.
131 virtual bool runOnMachineFunction(MachineFunction &mf);
136 char RABasic::ID = 0;
138 } // end anonymous namespace
140 RABasic::RABasic(): MachineFunctionPass(ID) {
141 initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
142 initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
143 initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
144 initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
145 initializeRegisterCoalescerAnalysisGroup(*PassRegistry::getPassRegistry());
146 initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
147 initializeLiveStacksPass(*PassRegistry::getPassRegistry());
148 initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
149 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
150 initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
151 initializeRenderMachineFunctionPass(*PassRegistry::getPassRegistry());
154 void RABasic::getAnalysisUsage(AnalysisUsage &AU) const {
155 AU.setPreservesCFG();
156 AU.addRequired<AliasAnalysis>();
157 AU.addPreserved<AliasAnalysis>();
158 AU.addRequired<LiveIntervals>();
159 AU.addPreserved<SlotIndexes>();
160 AU.addRequired<LiveDebugVariables>();
161 AU.addPreserved<LiveDebugVariables>();
163 AU.addRequiredID(StrongPHIEliminationID);
164 AU.addRequiredTransitive<RegisterCoalescer>();
165 AU.addRequired<CalculateSpillWeights>();
166 AU.addRequired<LiveStacks>();
167 AU.addPreserved<LiveStacks>();
168 AU.addRequiredID(MachineDominatorsID);
169 AU.addPreservedID(MachineDominatorsID);
170 AU.addRequired<MachineLoopInfo>();
171 AU.addPreserved<MachineLoopInfo>();
172 AU.addRequired<VirtRegMap>();
173 AU.addPreserved<VirtRegMap>();
174 DEBUG(AU.addRequired<RenderMachineFunction>());
175 MachineFunctionPass::getAnalysisUsage(AU);
178 void RABasic::releaseMemory() {
179 SpillerInstance.reset(0);
180 RegAllocBase::releaseMemory();
184 // Verify each LiveIntervalUnion.
185 void RegAllocBase::verify() {
186 LiveVirtRegBitSet VisitedVRegs;
187 OwningArrayPtr<LiveVirtRegBitSet>
188 unionVRegs(new LiveVirtRegBitSet[PhysReg2LiveUnion.numRegs()]);
190 // Verify disjoint unions.
191 for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
192 DEBUG(PhysReg2LiveUnion[PhysReg].print(dbgs(), TRI));
193 LiveVirtRegBitSet &VRegs = unionVRegs[PhysReg];
194 PhysReg2LiveUnion[PhysReg].verify(VRegs);
195 // Union + intersection test could be done efficiently in one pass, but
196 // don't add a method to SparseBitVector unless we really need it.
197 assert(!VisitedVRegs.intersects(VRegs) && "vreg in multiple unions");
198 VisitedVRegs |= VRegs;
201 // Verify vreg coverage.
202 for (LiveIntervals::iterator liItr = LIS->begin(), liEnd = LIS->end();
203 liItr != liEnd; ++liItr) {
204 unsigned reg = liItr->first;
205 if (TargetRegisterInfo::isPhysicalRegister(reg)) continue;
206 if (!VRM->hasPhys(reg)) continue; // spilled?
207 unsigned PhysReg = VRM->getPhys(reg);
208 if (!unionVRegs[PhysReg].test(reg)) {
209 dbgs() << "LiveVirtReg " << reg << " not in union " <<
210 TRI->getName(PhysReg) << "\n";
211 llvm_unreachable("unallocated live vreg");
214 // FIXME: I'm not sure how to verify spilled intervals.
218 //===----------------------------------------------------------------------===//
219 // RegAllocBase Implementation
220 //===----------------------------------------------------------------------===//
222 // Instantiate a LiveIntervalUnion for each physical register.
223 void RegAllocBase::LiveUnionArray::init(LiveIntervalUnion::Allocator &allocator,
227 static_cast<LiveIntervalUnion*>(malloc(sizeof(LiveIntervalUnion)*NRegs));
228 for (unsigned r = 0; r != NRegs; ++r)
229 new(Array + r) LiveIntervalUnion(r, allocator);
232 void RegAllocBase::init(VirtRegMap &vrm, LiveIntervals &lis) {
233 NamedRegionTimer T("Initialize", TimerGroupName, TimePassesIsEnabled);
234 TRI = &vrm.getTargetRegInfo();
235 MRI = &vrm.getRegInfo();
238 PhysReg2LiveUnion.init(UnionAllocator, TRI->getNumRegs());
239 // Cache an interferece query for each physical reg
240 Queries.reset(new LiveIntervalUnion::Query[PhysReg2LiveUnion.numRegs()]);
243 void RegAllocBase::LiveUnionArray::clear() {
246 for (unsigned r = 0; r != NumRegs; ++r)
247 Array[r].~LiveIntervalUnion();
253 void RegAllocBase::releaseMemory() {
254 PhysReg2LiveUnion.clear();
257 // Visit all the live registers. If they are already assigned to a physical
258 // register, unify them with the corresponding LiveIntervalUnion, otherwise push
259 // them on the priority queue for later assignment.
260 void RegAllocBase::seedLiveRegs() {
261 NamedRegionTimer T("Seed Live Regs", TimerGroupName, TimePassesIsEnabled);
262 for (LiveIntervals::iterator I = LIS->begin(), E = LIS->end(); I != E; ++I) {
263 unsigned RegNum = I->first;
264 LiveInterval &VirtReg = *I->second;
265 if (TargetRegisterInfo::isPhysicalRegister(RegNum))
266 PhysReg2LiveUnion[RegNum].unify(VirtReg);
272 void RegAllocBase::assign(LiveInterval &VirtReg, unsigned PhysReg) {
273 DEBUG(dbgs() << "assigning " << PrintReg(VirtReg.reg, TRI)
274 << " to " << PrintReg(PhysReg, TRI) << '\n');
275 assert(!VRM->hasPhys(VirtReg.reg) && "Duplicate VirtReg assignment");
276 VRM->assignVirt2Phys(VirtReg.reg, PhysReg);
277 PhysReg2LiveUnion[PhysReg].unify(VirtReg);
281 void RegAllocBase::unassign(LiveInterval &VirtReg, unsigned PhysReg) {
282 DEBUG(dbgs() << "unassigning " << PrintReg(VirtReg.reg, TRI)
283 << " from " << PrintReg(PhysReg, TRI) << '\n');
284 assert(VRM->getPhys(VirtReg.reg) == PhysReg && "Inconsistent unassign");
285 PhysReg2LiveUnion[PhysReg].extract(VirtReg);
286 VRM->clearVirt(VirtReg.reg);
290 // Top-level driver to manage the queue of unassigned VirtRegs and call the
291 // selectOrSplit implementation.
292 void RegAllocBase::allocatePhysRegs() {
295 // Continue assigning vregs one at a time to available physical registers.
296 while (LiveInterval *VirtReg = dequeue()) {
297 assert(!VRM->hasPhys(VirtReg->reg) && "Register already assigned");
299 // Unused registers can appear when the spiller coalesces snippets.
300 if (MRI->reg_nodbg_empty(VirtReg->reg)) {
301 DEBUG(dbgs() << "Dropping unused " << *VirtReg << '\n');
302 LIS->removeInterval(VirtReg->reg);
306 // Invalidate all interference queries, live ranges could have changed.
309 // selectOrSplit requests the allocator to return an available physical
310 // register if possible and populate a list of new live intervals that
311 // result from splitting.
312 DEBUG(dbgs() << "\nselectOrSplit "
313 << MRI->getRegClass(VirtReg->reg)->getName()
314 << ':' << *VirtReg << '\n');
315 typedef SmallVector<LiveInterval*, 4> VirtRegVec;
316 VirtRegVec SplitVRegs;
317 unsigned AvailablePhysReg = selectOrSplit(*VirtReg, SplitVRegs);
319 if (AvailablePhysReg)
320 assign(*VirtReg, AvailablePhysReg);
322 for (VirtRegVec::iterator I = SplitVRegs.begin(), E = SplitVRegs.end();
324 LiveInterval *SplitVirtReg = *I;
325 assert(!VRM->hasPhys(SplitVirtReg->reg) && "Register already assigned");
326 if (MRI->reg_nodbg_empty(SplitVirtReg->reg)) {
327 DEBUG(dbgs() << "not queueing unused " << *SplitVirtReg << '\n');
328 LIS->removeInterval(SplitVirtReg->reg);
331 DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
332 assert(TargetRegisterInfo::isVirtualRegister(SplitVirtReg->reg) &&
333 "expect split value in virtual register");
334 enqueue(SplitVirtReg);
340 // Check if this live virtual register interferes with a physical register. If
341 // not, then check for interference on each register that aliases with the
342 // physical register. Return the interfering register.
343 unsigned RegAllocBase::checkPhysRegInterference(LiveInterval &VirtReg,
345 for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI)
346 if (query(VirtReg, *AliasI).checkInterference())
351 // Helper for spillInteferences() that spills all interfering vregs currently
352 // assigned to this physical register.
353 void RegAllocBase::spillReg(LiveInterval& VirtReg, unsigned PhysReg,
354 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
355 LiveIntervalUnion::Query &Q = query(VirtReg, PhysReg);
356 assert(Q.seenAllInterferences() && "need collectInterferences()");
357 const SmallVectorImpl<LiveInterval*> &PendingSpills = Q.interferingVRegs();
359 for (SmallVectorImpl<LiveInterval*>::const_iterator I = PendingSpills.begin(),
360 E = PendingSpills.end(); I != E; ++I) {
361 LiveInterval &SpilledVReg = **I;
362 DEBUG(dbgs() << "extracting from " <<
363 TRI->getName(PhysReg) << " " << SpilledVReg << '\n');
365 // Deallocate the interfering vreg by removing it from the union.
366 // A LiveInterval instance may not be in a union during modification!
367 unassign(SpilledVReg, PhysReg);
369 // Spill the extracted interval.
370 LiveRangeEdit LRE(SpilledVReg, SplitVRegs, 0, &PendingSpills);
371 spiller().spill(LRE);
373 // After extracting segments, the query's results are invalid. But keep the
374 // contents valid until we're done accessing pendingSpills.
378 // Spill or split all live virtual registers currently unified under PhysReg
379 // that interfere with VirtReg. The newly spilled or split live intervals are
380 // returned by appending them to SplitVRegs.
382 RegAllocBase::spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
383 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
384 // Record each interference and determine if all are spillable before mutating
385 // either the union or live intervals.
386 unsigned NumInterferences = 0;
387 // Collect interferences assigned to any alias of the physical register.
388 for (const unsigned *asI = TRI->getOverlaps(PhysReg); *asI; ++asI) {
389 LiveIntervalUnion::Query &QAlias = query(VirtReg, *asI);
390 NumInterferences += QAlias.collectInterferingVRegs();
391 if (QAlias.seenUnspillableVReg()) {
395 DEBUG(dbgs() << "spilling " << TRI->getName(PhysReg) <<
396 " interferences with " << VirtReg << "\n");
397 assert(NumInterferences > 0 && "expect interference");
399 // Spill each interfering vreg allocated to PhysReg or an alias.
400 for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI)
401 spillReg(VirtReg, *AliasI, SplitVRegs);
405 // Add newly allocated physical registers to the MBB live in sets.
406 void RegAllocBase::addMBBLiveIns(MachineFunction *MF) {
407 NamedRegionTimer T("MBB Live Ins", TimerGroupName, TimePassesIsEnabled);
408 typedef SmallVector<MachineBasicBlock*, 8> MBBVec;
410 MachineBasicBlock &entryMBB = *MF->begin();
412 for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
413 LiveIntervalUnion &LiveUnion = PhysReg2LiveUnion[PhysReg];
414 if (LiveUnion.empty())
416 for (LiveIntervalUnion::SegmentIter SI = LiveUnion.begin(); SI.valid();
419 // Find the set of basic blocks which this range is live into...
421 if (!LIS->findLiveInMBBs(SI.start(), SI.stop(), liveInMBBs)) continue;
423 // And add the physreg for this interval to their live-in sets.
424 for (MBBVec::iterator I = liveInMBBs.begin(), E = liveInMBBs.end();
426 MachineBasicBlock *MBB = *I;
427 if (MBB == &entryMBB) continue;
428 if (MBB->isLiveIn(PhysReg)) continue;
429 MBB->addLiveIn(PhysReg);
436 //===----------------------------------------------------------------------===//
437 // RABasic Implementation
438 //===----------------------------------------------------------------------===//
440 // Driver for the register assignment and splitting heuristics.
441 // Manages iteration over the LiveIntervalUnions.
443 // This is a minimal implementation of register assignment and splitting that
444 // spills whenever we run out of registers.
446 // selectOrSplit can only be called once per live virtual register. We then do a
447 // single interference test for each register the correct class until we find an
448 // available register. So, the number of interference tests in the worst case is
449 // |vregs| * |machineregs|. And since the number of interference tests is
450 // minimal, there is no value in caching them outside the scope of
452 unsigned RABasic::selectOrSplit(LiveInterval &VirtReg,
453 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
454 // Populate a list of physical register spill candidates.
455 SmallVector<unsigned, 8> PhysRegSpillCands;
457 // Check for an available register in this class.
458 const TargetRegisterClass *TRC = MRI->getRegClass(VirtReg.reg);
460 for (TargetRegisterClass::iterator I = TRC->allocation_order_begin(*MF),
461 E = TRC->allocation_order_end(*MF);
464 unsigned PhysReg = *I;
465 if (ReservedRegs.test(PhysReg)) continue;
467 // Check interference and as a side effect, intialize queries for this
468 // VirtReg and its aliases.
469 unsigned interfReg = checkPhysRegInterference(VirtReg, PhysReg);
470 if (interfReg == 0) {
471 // Found an available register.
474 LiveInterval *interferingVirtReg =
475 Queries[interfReg].firstInterference().liveUnionPos().value();
477 // The current VirtReg must either be spillable, or one of its interferences
478 // must have less spill weight.
479 if (interferingVirtReg->weight < VirtReg.weight ) {
480 PhysRegSpillCands.push_back(PhysReg);
483 // Try to spill another interfering reg with less spill weight.
484 for (SmallVectorImpl<unsigned>::iterator PhysRegI = PhysRegSpillCands.begin(),
485 PhysRegE = PhysRegSpillCands.end(); PhysRegI != PhysRegE; ++PhysRegI) {
487 if (!spillInterferences(VirtReg, *PhysRegI, SplitVRegs)) continue;
489 assert(checkPhysRegInterference(VirtReg, *PhysRegI) == 0 &&
490 "Interference after spill.");
491 // Tell the caller to allocate to this newly freed physical register.
494 // No other spill candidates were found, so spill the current VirtReg.
495 DEBUG(dbgs() << "spilling: " << VirtReg << '\n');
496 LiveRangeEdit LRE(VirtReg, SplitVRegs);
497 spiller().spill(LRE);
499 // The live virtual register requesting allocation was spilled, so tell
500 // the caller not to allocate anything during this round.
504 bool RABasic::runOnMachineFunction(MachineFunction &mf) {
505 DEBUG(dbgs() << "********** BASIC REGISTER ALLOCATION **********\n"
506 << "********** Function: "
507 << ((Value*)mf.getFunction())->getName() << '\n');
510 DEBUG(RMF = &getAnalysis<RenderMachineFunction>());
512 RegAllocBase::init(getAnalysis<VirtRegMap>(), getAnalysis<LiveIntervals>());
514 ReservedRegs = TRI->getReservedRegs(*MF);
516 SpillerInstance.reset(createInlineSpiller(*this, *MF, *VRM));
522 // Diagnostic output before rewriting
523 DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *VRM << "\n");
525 // optional HTML output
526 DEBUG(RMF->renderMachineFunction("After basic register allocation.", VRM));
528 // FIXME: Verification currently must run before VirtRegRewriter. We should
529 // make the rewriter a separate pass and override verifyAnalysis instead. When
530 // that happens, verification naturally falls under VerifyMachineCode.
533 // Verify accuracy of LiveIntervals. The standard machine code verifier
534 // ensures that each LiveIntervals covers all uses of the virtual reg.
536 // FIXME: MachineVerifier is badly broken when using the standard
537 // spiller. Always use -spiller=inline with -verify-regalloc. Even with the
538 // inline spiller, some tests fail to verify because the coalescer does not
539 // always generate verifiable code.
540 MF->verify(this, "In RABasic::verify");
542 // Verify that LiveIntervals are partitioned into unions and disjoint within
549 VRM->rewrite(LIS->getSlotIndexes());
551 // Write out new DBG_VALUE instructions.
552 getAnalysis<LiveDebugVariables>().emitDebugValues(VRM);
554 // The pass output is in VirtRegMap. Release all the transient data.
560 FunctionPass* llvm::createBasicRegisterAllocator()
562 return new RABasic();