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 "LiveIntervalUnion.h"
17 #include "RegAllocBase.h"
18 #include "RenderMachineFunction.h"
20 #include "VirtRegMap.h"
21 #include "VirtRegRewriter.h"
22 #include "llvm/ADT/OwningPtr.h"
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Function.h"
25 #include "llvm/PassAnalysisSupport.h"
26 #include "llvm/CodeGen/CalcSpillWeights.h"
27 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
28 #include "llvm/CodeGen/LiveStackAnalysis.h"
29 #include "llvm/CodeGen/MachineFunctionPass.h"
30 #include "llvm/CodeGen/MachineInstr.h"
31 #include "llvm/CodeGen/MachineLoopInfo.h"
32 #include "llvm/CodeGen/MachineRegisterInfo.h"
33 #include "llvm/CodeGen/Passes.h"
34 #include "llvm/CodeGen/RegAllocRegistry.h"
35 #include "llvm/CodeGen/RegisterCoalescer.h"
36 #include "llvm/Target/TargetMachine.h"
37 #include "llvm/Target/TargetOptions.h"
38 #include "llvm/Target/TargetRegisterInfo.h"
40 #include "llvm/ADT/SparseBitVector.h"
42 #include "llvm/Support/Debug.h"
43 #include "llvm/Support/ErrorHandling.h"
44 #include "llvm/Support/raw_ostream.h"
52 static RegisterRegAlloc basicRegAlloc("basic", "basic register allocator",
53 createBasicRegisterAllocator);
55 // Temporary verification option until we can put verification inside
58 VerifyRegAlloc("verify-regalloc",
59 cl::desc("Verify live intervals before renaming"));
63 class PhysicalRegisterDescription : public AbstractRegisterDescription {
64 const TargetRegisterInfo *TRI;
66 PhysicalRegisterDescription(const TargetRegisterInfo *T): TRI(T) {}
67 virtual const char *getName(unsigned Reg) const { return TRI->getName(Reg); }
70 /// RABasic provides a minimal implementation of the basic register allocation
71 /// algorithm. It prioritizes live virtual registers by spill weight and spills
72 /// whenever a register is unavailable. This is not practical in production but
73 /// provides a useful baseline both for measuring other allocators and comparing
74 /// the speed of the basic algorithm against other styles of allocators.
75 class RABasic : public MachineFunctionPass, public RegAllocBase
79 const TargetMachine *TM;
80 MachineRegisterInfo *MRI;
82 BitVector ReservedRegs;
86 RenderMachineFunction *RMF;
89 std::auto_ptr<Spiller> SpillerInstance;
94 /// Return the pass name.
95 virtual const char* getPassName() const {
96 return "Basic Register Allocator";
99 /// RABasic analysis usage.
100 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
102 virtual void releaseMemory();
104 virtual Spiller &spiller() { return *SpillerInstance; }
106 virtual unsigned selectOrSplit(LiveInterval &VirtReg,
107 SmallVectorImpl<LiveInterval*> &SplitVRegs);
109 /// Perform register allocation.
110 virtual bool runOnMachineFunction(MachineFunction &mf);
115 char RABasic::ID = 0;
117 } // end anonymous namespace
119 RABasic::RABasic(): MachineFunctionPass(ID) {
120 initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
121 initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
122 initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
123 initializeRegisterCoalescerAnalysisGroup(*PassRegistry::getPassRegistry());
124 initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
125 initializeLiveStacksPass(*PassRegistry::getPassRegistry());
126 initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
127 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
128 initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
129 initializeRenderMachineFunctionPass(*PassRegistry::getPassRegistry());
132 void RABasic::getAnalysisUsage(AnalysisUsage &AU) const {
133 AU.setPreservesCFG();
134 AU.addRequired<AliasAnalysis>();
135 AU.addPreserved<AliasAnalysis>();
136 AU.addRequired<LiveIntervals>();
137 AU.addPreserved<SlotIndexes>();
139 AU.addRequiredID(StrongPHIEliminationID);
140 AU.addRequiredTransitive<RegisterCoalescer>();
141 AU.addRequired<CalculateSpillWeights>();
142 AU.addRequired<LiveStacks>();
143 AU.addPreserved<LiveStacks>();
144 AU.addRequiredID(MachineDominatorsID);
145 AU.addPreservedID(MachineDominatorsID);
146 AU.addRequired<MachineLoopInfo>();
147 AU.addPreserved<MachineLoopInfo>();
148 AU.addRequired<VirtRegMap>();
149 AU.addPreserved<VirtRegMap>();
150 DEBUG(AU.addRequired<RenderMachineFunction>());
151 MachineFunctionPass::getAnalysisUsage(AU);
154 void RABasic::releaseMemory() {
155 SpillerInstance.reset(0);
156 RegAllocBase::releaseMemory();
160 // Verify each LiveIntervalUnion.
161 void RegAllocBase::verify() {
162 LiveVirtRegBitSet VisitedVRegs;
163 OwningArrayPtr<LiveVirtRegBitSet>
164 unionVRegs(new LiveVirtRegBitSet[PhysReg2LiveUnion.numRegs()]);
166 // Verify disjoint unions.
167 for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
168 DEBUG(PhysicalRegisterDescription PRD(TRI);
169 PhysReg2LiveUnion[PhysReg].dump(&PRD));
170 LiveVirtRegBitSet &VRegs = unionVRegs[PhysReg];
171 PhysReg2LiveUnion[PhysReg].verify(VRegs);
172 // Union + intersection test could be done efficiently in one pass, but
173 // don't add a method to SparseBitVector unless we really need it.
174 assert(!VisitedVRegs.intersects(VRegs) && "vreg in multiple unions");
175 VisitedVRegs |= VRegs;
178 // Verify vreg coverage.
179 for (LiveIntervals::iterator liItr = LIS->begin(), liEnd = LIS->end();
180 liItr != liEnd; ++liItr) {
181 unsigned reg = liItr->first;
182 if (TargetRegisterInfo::isPhysicalRegister(reg)) continue;
183 if (!VRM->hasPhys(reg)) continue; // spilled?
184 unsigned PhysReg = VRM->getPhys(reg);
185 if (!unionVRegs[PhysReg].test(reg)) {
186 dbgs() << "LiveVirtReg " << reg << " not in union " <<
187 TRI->getName(PhysReg) << "\n";
188 llvm_unreachable("unallocated live vreg");
191 // FIXME: I'm not sure how to verify spilled intervals.
195 //===----------------------------------------------------------------------===//
196 // RegAllocBase Implementation
197 //===----------------------------------------------------------------------===//
199 // Instantiate a LiveIntervalUnion for each physical register.
200 void RegAllocBase::LiveUnionArray::init(LiveIntervalUnion::Allocator &allocator,
204 static_cast<LiveIntervalUnion*>(malloc(sizeof(LiveIntervalUnion)*NRegs));
205 for (unsigned r = 0; r != NRegs; ++r)
206 new(Array + r) LiveIntervalUnion(r, allocator);
209 void RegAllocBase::init(const TargetRegisterInfo &tri, VirtRegMap &vrm,
210 LiveIntervals &lis) {
214 PhysReg2LiveUnion.init(UnionAllocator, TRI->getNumRegs());
215 // Cache an interferece query for each physical reg
216 Queries.reset(new LiveIntervalUnion::Query[PhysReg2LiveUnion.numRegs()]);
219 void RegAllocBase::LiveUnionArray::clear() {
222 for (unsigned r = 0; r != NumRegs; ++r)
223 Array[r].~LiveIntervalUnion();
229 void RegAllocBase::releaseMemory() {
230 PhysReg2LiveUnion.clear();
234 /// This class defines a queue of live virtual registers prioritized by spill
235 /// weight. The heaviest vreg is popped first.
237 /// Currently, this is trivial wrapper that gives us an opaque type in the
238 /// header, but we may later give it a virtual interface for register allocators
239 /// to override the priority queue comparator.
240 class LiveVirtRegQueue {
241 typedef std::priority_queue
242 <LiveInterval*, std::vector<LiveInterval*>, LessSpillWeightPriority>
247 // Is the queue empty?
248 bool empty() { return PQ.empty(); }
250 // Get the highest priority lvr (top + pop)
251 LiveInterval *get() {
252 LiveInterval *VirtReg = PQ.top();
256 // Add this lvr to the queue
257 void push(LiveInterval *VirtReg) {
261 } // end namespace llvm
263 // Visit all the live virtual registers. If they are already assigned to a
264 // physical register, unify them with the corresponding LiveIntervalUnion,
265 // otherwise push them on the priority queue for later assignment.
266 void RegAllocBase::seedLiveVirtRegs(LiveVirtRegQueue &VirtRegQ) {
267 for (LiveIntervals::iterator I = LIS->begin(), E = LIS->end(); I != E; ++I) {
268 unsigned RegNum = I->first;
269 LiveInterval &VirtReg = *I->second;
270 if (TargetRegisterInfo::isPhysicalRegister(RegNum)) {
271 PhysReg2LiveUnion[RegNum].unify(VirtReg);
274 VirtRegQ.push(&VirtReg);
279 // Top-level driver to manage the queue of unassigned VirtRegs and call the
280 // selectOrSplit implementation.
281 void RegAllocBase::allocatePhysRegs() {
283 // Push each vreg onto a queue or "precolor" by adding it to a physreg union.
284 LiveVirtRegQueue VirtRegQ;
285 seedLiveVirtRegs(VirtRegQ);
287 // Continue assigning vregs one at a time to available physical registers.
288 while (!VirtRegQ.empty()) {
289 // Pop the highest priority vreg.
290 LiveInterval *VirtReg = VirtRegQ.get();
292 // selectOrSplit requests the allocator to return an available physical
293 // register if possible and populate a list of new live intervals that
294 // result from splitting.
295 typedef SmallVector<LiveInterval*, 4> VirtRegVec;
296 VirtRegVec SplitVRegs;
297 unsigned AvailablePhysReg = selectOrSplit(*VirtReg, SplitVRegs);
299 if (AvailablePhysReg) {
300 DEBUG(dbgs() << "allocating: " << TRI->getName(AvailablePhysReg) <<
301 " " << *VirtReg << '\n');
302 assert(!VRM->hasPhys(VirtReg->reg) && "duplicate vreg in union");
303 VRM->assignVirt2Phys(VirtReg->reg, AvailablePhysReg);
304 PhysReg2LiveUnion[AvailablePhysReg].unify(*VirtReg);
306 for (VirtRegVec::iterator I = SplitVRegs.begin(), E = SplitVRegs.end();
308 LiveInterval* SplitVirtReg = *I;
309 if (SplitVirtReg->empty()) continue;
310 DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
311 assert(TargetRegisterInfo::isVirtualRegister(SplitVirtReg->reg) &&
312 "expect split value in virtual register");
313 VirtRegQ.push(SplitVirtReg);
318 // Check if this live virtual register interferes with a physical register. If
319 // not, then check for interference on each register that aliases with the
320 // physical register. Return the interfering register.
321 unsigned RegAllocBase::checkPhysRegInterference(LiveInterval &VirtReg,
323 if (query(VirtReg, PhysReg).checkInterference())
325 for (const unsigned *AliasI = TRI->getAliasSet(PhysReg); *AliasI; ++AliasI) {
326 if (query(VirtReg, *AliasI).checkInterference())
332 // Helper for spillInteferences() that spills all interfering vregs currently
333 // assigned to this physical register.
334 void RegAllocBase::spillReg(LiveInterval& VirtReg, unsigned PhysReg,
335 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
336 LiveIntervalUnion::Query &Q = query(VirtReg, PhysReg);
337 assert(Q.seenAllInterferences() && "need collectInterferences()");
338 const SmallVectorImpl<LiveInterval*> &PendingSpills = Q.interferingVRegs();
340 for (SmallVectorImpl<LiveInterval*>::const_iterator I = PendingSpills.begin(),
341 E = PendingSpills.end(); I != E; ++I) {
342 LiveInterval &SpilledVReg = **I;
343 DEBUG(dbgs() << "extracting from " <<
344 TRI->getName(PhysReg) << " " << SpilledVReg << '\n');
346 // Deallocate the interfering vreg by removing it from the union.
347 // A LiveInterval instance may not be in a union during modification!
348 PhysReg2LiveUnion[PhysReg].extract(SpilledVReg);
350 // Clear the vreg assignment.
351 VRM->clearVirt(SpilledVReg.reg);
353 // Spill the extracted interval.
354 spiller().spill(&SpilledVReg, SplitVRegs, PendingSpills);
356 // After extracting segments, the query's results are invalid. But keep the
357 // contents valid until we're done accessing pendingSpills.
361 // Spill or split all live virtual registers currently unified under PhysReg
362 // that interfere with VirtReg. The newly spilled or split live intervals are
363 // returned by appending them to SplitVRegs.
365 RegAllocBase::spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
366 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
367 // Record each interference and determine if all are spillable before mutating
368 // either the union or live intervals.
370 // Collect interferences assigned to the requested physical register.
371 LiveIntervalUnion::Query &QPreg = query(VirtReg, PhysReg);
372 unsigned NumInterferences = QPreg.collectInterferingVRegs();
373 if (QPreg.seenUnspillableVReg()) {
376 // Collect interferences assigned to any alias of the physical register.
377 for (const unsigned *asI = TRI->getAliasSet(PhysReg); *asI; ++asI) {
378 LiveIntervalUnion::Query &QAlias = query(VirtReg, *asI);
379 NumInterferences += QAlias.collectInterferingVRegs();
380 if (QAlias.seenUnspillableVReg()) {
384 DEBUG(dbgs() << "spilling " << TRI->getName(PhysReg) <<
385 " interferences with " << VirtReg << "\n");
386 assert(NumInterferences > 0 && "expect interference");
388 // Spill each interfering vreg allocated to PhysReg or an alias.
389 spillReg(VirtReg, PhysReg, SplitVRegs);
390 for (const unsigned *AliasI = TRI->getAliasSet(PhysReg); *AliasI; ++AliasI)
391 spillReg(VirtReg, *AliasI, SplitVRegs);
395 // Add newly allocated physical registers to the MBB live in sets.
396 void RegAllocBase::addMBBLiveIns(MachineFunction *MF) {
397 typedef SmallVector<MachineBasicBlock*, 8> MBBVec;
399 MachineBasicBlock &entryMBB = *MF->begin();
401 for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
402 LiveIntervalUnion &LiveUnion = PhysReg2LiveUnion[PhysReg];
403 if (LiveUnion.empty())
405 for (LiveIntervalUnion::SegmentIter SI = LiveUnion.begin(); SI.valid();
408 // Find the set of basic blocks which this range is live into...
410 if (!LIS->findLiveInMBBs(SI.start(), SI.stop(), liveInMBBs)) continue;
412 // And add the physreg for this interval to their live-in sets.
413 for (MBBVec::iterator I = liveInMBBs.begin(), E = liveInMBBs.end();
415 MachineBasicBlock *MBB = *I;
416 if (MBB == &entryMBB) continue;
417 if (MBB->isLiveIn(PhysReg)) continue;
418 MBB->addLiveIn(PhysReg);
425 //===----------------------------------------------------------------------===//
426 // RABasic Implementation
427 //===----------------------------------------------------------------------===//
429 // Driver for the register assignment and splitting heuristics.
430 // Manages iteration over the LiveIntervalUnions.
432 // This is a minimal implementation of register assignment and splitting that
433 // spills whenever we run out of registers.
435 // selectOrSplit can only be called once per live virtual register. We then do a
436 // single interference test for each register the correct class until we find an
437 // available register. So, the number of interference tests in the worst case is
438 // |vregs| * |machineregs|. And since the number of interference tests is
439 // minimal, there is no value in caching them outside the scope of
441 unsigned RABasic::selectOrSplit(LiveInterval &VirtReg,
442 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
443 // Populate a list of physical register spill candidates.
444 SmallVector<unsigned, 8> PhysRegSpillCands;
446 // Check for an available register in this class.
447 const TargetRegisterClass *TRC = MRI->getRegClass(VirtReg.reg);
448 DEBUG(dbgs() << "RegClass: " << TRC->getName() << ' ');
450 for (TargetRegisterClass::iterator I = TRC->allocation_order_begin(*MF),
451 E = TRC->allocation_order_end(*MF);
454 unsigned PhysReg = *I;
455 if (ReservedRegs.test(PhysReg)) continue;
457 // Check interference and as a side effect, intialize queries for this
458 // VirtReg and its aliases.
459 unsigned interfReg = checkPhysRegInterference(VirtReg, PhysReg);
460 if (interfReg == 0) {
461 // Found an available register.
464 LiveInterval *interferingVirtReg =
465 Queries[interfReg].firstInterference().liveUnionPos().value();
467 // The current VirtReg must either spillable, or one of its interferences
468 // must have less spill weight.
469 if (interferingVirtReg->weight < VirtReg.weight ) {
470 PhysRegSpillCands.push_back(PhysReg);
473 // Try to spill another interfering reg with less spill weight.
475 // FIXME: RAGreedy will sort this list by spill weight.
476 for (SmallVectorImpl<unsigned>::iterator PhysRegI = PhysRegSpillCands.begin(),
477 PhysRegE = PhysRegSpillCands.end(); PhysRegI != PhysRegE; ++PhysRegI) {
479 if (!spillInterferences(VirtReg, *PhysRegI, SplitVRegs)) continue;
481 assert(checkPhysRegInterference(VirtReg, *PhysRegI) == 0 &&
482 "Interference after spill.");
483 // Tell the caller to allocate to this newly freed physical register.
486 // No other spill candidates were found, so spill the current VirtReg.
487 DEBUG(dbgs() << "spilling: " << VirtReg << '\n');
488 SmallVector<LiveInterval*, 1> pendingSpills;
490 spiller().spill(&VirtReg, SplitVRegs, pendingSpills);
492 // The live virtual register requesting allocation was spilled, so tell
493 // the caller not to allocate anything during this round.
497 bool RABasic::runOnMachineFunction(MachineFunction &mf) {
498 DEBUG(dbgs() << "********** BASIC REGISTER ALLOCATION **********\n"
499 << "********** Function: "
500 << ((Value*)mf.getFunction())->getName() << '\n');
503 TM = &mf.getTarget();
504 MRI = &mf.getRegInfo();
506 DEBUG(RMF = &getAnalysis<RenderMachineFunction>());
508 const TargetRegisterInfo *TRI = TM->getRegisterInfo();
509 RegAllocBase::init(*TRI, getAnalysis<VirtRegMap>(),
510 getAnalysis<LiveIntervals>());
512 ReservedRegs = TRI->getReservedRegs(*MF);
514 SpillerInstance.reset(createSpiller(*this, *MF, *VRM));
520 // Diagnostic output before rewriting
521 DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *VRM << "\n");
523 // optional HTML output
524 DEBUG(RMF->renderMachineFunction("After basic register allocation.", VRM));
526 // FIXME: Verification currently must run before VirtRegRewriter. We should
527 // make the rewriter a separate pass and override verifyAnalysis instead. When
528 // that happens, verification naturally falls under VerifyMachineCode.
530 if (VerifyRegAlloc) {
531 // Verify accuracy of LiveIntervals. The standard machine code verifier
532 // ensures that each LiveIntervals covers all uses of the virtual reg.
534 // FIXME: MachineVerifier is badly broken when using the standard
535 // spiller. Always use -spiller=inline with -verify-regalloc. Even with the
536 // inline spiller, some tests fail to verify because the coalescer does not
537 // always generate verifiable code.
540 // Verify that LiveIntervals are partitioned into unions and disjoint within
547 std::auto_ptr<VirtRegRewriter> rewriter(createVirtRegRewriter());
548 rewriter->runOnMachineFunction(*MF, *VRM, LIS);
550 // The pass output is in VirtRegMap. Release all the transient data.
556 FunctionPass* llvm::createBasicRegisterAllocator()
558 return new RABasic();