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"
50 static RegisterRegAlloc basicRegAlloc("basic", "basic register allocator",
51 createBasicRegisterAllocator);
53 // Temporary verification option until we can put verification inside
56 VerifyRegAlloc("verify-regalloc",
57 cl::desc("Verify live intervals before renaming"));
61 class PhysicalRegisterDescription : public AbstractRegisterDescription {
62 const TargetRegisterInfo *TRI;
64 PhysicalRegisterDescription(const TargetRegisterInfo *T): TRI(T) {}
65 virtual const char *getName(unsigned Reg) const { return TRI->getName(Reg); }
68 /// RABasic provides a minimal implementation of the basic register allocation
69 /// algorithm. It prioritizes live virtual registers by spill weight and spills
70 /// whenever a register is unavailable. This is not practical in production but
71 /// provides a useful baseline both for measuring other allocators and comparing
72 /// the speed of the basic algorithm against other styles of allocators.
73 class RABasic : public MachineFunctionPass, public RegAllocBase
77 BitVector ReservedRegs;
81 RenderMachineFunction *RMF;
84 std::auto_ptr<Spiller> SpillerInstance;
89 /// Return the pass name.
90 virtual const char* getPassName() const {
91 return "Basic Register Allocator";
94 /// RABasic analysis usage.
95 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
97 virtual void releaseMemory();
99 virtual Spiller &spiller() { return *SpillerInstance; }
101 virtual float getPriority(LiveInterval *LI) { return LI->weight; }
103 virtual unsigned selectOrSplit(LiveInterval &VirtReg,
104 SmallVectorImpl<LiveInterval*> &SplitVRegs);
106 /// Perform register allocation.
107 virtual bool runOnMachineFunction(MachineFunction &mf);
112 char RABasic::ID = 0;
114 } // end anonymous namespace
116 RABasic::RABasic(): MachineFunctionPass(ID) {
117 initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
118 initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
119 initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
120 initializeRegisterCoalescerAnalysisGroup(*PassRegistry::getPassRegistry());
121 initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
122 initializeLiveStacksPass(*PassRegistry::getPassRegistry());
123 initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
124 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
125 initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
126 initializeRenderMachineFunctionPass(*PassRegistry::getPassRegistry());
129 void RABasic::getAnalysisUsage(AnalysisUsage &AU) const {
130 AU.setPreservesCFG();
131 AU.addRequired<AliasAnalysis>();
132 AU.addPreserved<AliasAnalysis>();
133 AU.addRequired<LiveIntervals>();
134 AU.addPreserved<SlotIndexes>();
136 AU.addRequiredID(StrongPHIEliminationID);
137 AU.addRequiredTransitive<RegisterCoalescer>();
138 AU.addRequired<CalculateSpillWeights>();
139 AU.addRequired<LiveStacks>();
140 AU.addPreserved<LiveStacks>();
141 AU.addRequiredID(MachineDominatorsID);
142 AU.addPreservedID(MachineDominatorsID);
143 AU.addRequired<MachineLoopInfo>();
144 AU.addPreserved<MachineLoopInfo>();
145 AU.addRequired<VirtRegMap>();
146 AU.addPreserved<VirtRegMap>();
147 DEBUG(AU.addRequired<RenderMachineFunction>());
148 MachineFunctionPass::getAnalysisUsage(AU);
151 void RABasic::releaseMemory() {
152 SpillerInstance.reset(0);
153 RegAllocBase::releaseMemory();
157 // Verify each LiveIntervalUnion.
158 void RegAllocBase::verify() {
159 LiveVirtRegBitSet VisitedVRegs;
160 OwningArrayPtr<LiveVirtRegBitSet>
161 unionVRegs(new LiveVirtRegBitSet[PhysReg2LiveUnion.numRegs()]);
163 // Verify disjoint unions.
164 for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
165 DEBUG(PhysicalRegisterDescription PRD(TRI);
166 PhysReg2LiveUnion[PhysReg].dump(&PRD));
167 LiveVirtRegBitSet &VRegs = unionVRegs[PhysReg];
168 PhysReg2LiveUnion[PhysReg].verify(VRegs);
169 // Union + intersection test could be done efficiently in one pass, but
170 // don't add a method to SparseBitVector unless we really need it.
171 assert(!VisitedVRegs.intersects(VRegs) && "vreg in multiple unions");
172 VisitedVRegs |= VRegs;
175 // Verify vreg coverage.
176 for (LiveIntervals::iterator liItr = LIS->begin(), liEnd = LIS->end();
177 liItr != liEnd; ++liItr) {
178 unsigned reg = liItr->first;
179 if (TargetRegisterInfo::isPhysicalRegister(reg)) continue;
180 if (!VRM->hasPhys(reg)) continue; // spilled?
181 unsigned PhysReg = VRM->getPhys(reg);
182 if (!unionVRegs[PhysReg].test(reg)) {
183 dbgs() << "LiveVirtReg " << reg << " not in union " <<
184 TRI->getName(PhysReg) << "\n";
185 llvm_unreachable("unallocated live vreg");
188 // FIXME: I'm not sure how to verify spilled intervals.
192 //===----------------------------------------------------------------------===//
193 // RegAllocBase Implementation
194 //===----------------------------------------------------------------------===//
196 // Instantiate a LiveIntervalUnion for each physical register.
197 void RegAllocBase::LiveUnionArray::init(LiveIntervalUnion::Allocator &allocator,
201 static_cast<LiveIntervalUnion*>(malloc(sizeof(LiveIntervalUnion)*NRegs));
202 for (unsigned r = 0; r != NRegs; ++r)
203 new(Array + r) LiveIntervalUnion(r, allocator);
206 void RegAllocBase::init(VirtRegMap &vrm, LiveIntervals &lis) {
207 TRI = &vrm.getTargetRegInfo();
208 MRI = &vrm.getRegInfo();
211 PhysReg2LiveUnion.init(UnionAllocator, TRI->getNumRegs());
212 // Cache an interferece query for each physical reg
213 Queries.reset(new LiveIntervalUnion::Query[PhysReg2LiveUnion.numRegs()]);
216 void RegAllocBase::LiveUnionArray::clear() {
219 for (unsigned r = 0; r != NumRegs; ++r)
220 Array[r].~LiveIntervalUnion();
226 void RegAllocBase::releaseMemory() {
227 PhysReg2LiveUnion.clear();
230 // Visit all the live virtual registers. If they are already assigned to a
231 // physical register, unify them with the corresponding LiveIntervalUnion,
232 // otherwise push them on the priority queue for later assignment.
234 seedLiveVirtRegs(std::priority_queue<std::pair<float, unsigned> > &VirtRegQ) {
235 for (LiveIntervals::iterator I = LIS->begin(), E = LIS->end(); I != E; ++I) {
236 unsigned RegNum = I->first;
237 LiveInterval &VirtReg = *I->second;
238 if (TargetRegisterInfo::isPhysicalRegister(RegNum))
239 PhysReg2LiveUnion[RegNum].unify(VirtReg);
241 VirtRegQ.push(std::make_pair(getPriority(&VirtReg), RegNum));
245 // Top-level driver to manage the queue of unassigned VirtRegs and call the
246 // selectOrSplit implementation.
247 void RegAllocBase::allocatePhysRegs() {
249 // Push each vreg onto a queue or "precolor" by adding it to a physreg union.
250 std::priority_queue<std::pair<float, unsigned> > VirtRegQ;
251 seedLiveVirtRegs(VirtRegQ);
253 // Continue assigning vregs one at a time to available physical registers.
254 while (!VirtRegQ.empty()) {
255 // Pop the highest priority vreg.
256 LiveInterval &VirtReg = LIS->getInterval(VirtRegQ.top().second);
259 // selectOrSplit requests the allocator to return an available physical
260 // register if possible and populate a list of new live intervals that
261 // result from splitting.
262 DEBUG(dbgs() << "\nselectOrSplit " << MRI->getRegClass(VirtReg.reg)->getName()
263 << ':' << VirtReg << '\n');
264 typedef SmallVector<LiveInterval*, 4> VirtRegVec;
265 VirtRegVec SplitVRegs;
266 unsigned AvailablePhysReg = selectOrSplit(VirtReg, SplitVRegs);
268 if (AvailablePhysReg) {
269 DEBUG(dbgs() << "allocating: " << TRI->getName(AvailablePhysReg)
270 << " for " << VirtReg << '\n');
271 assert(!VRM->hasPhys(VirtReg.reg) && "duplicate vreg in union");
272 VRM->assignVirt2Phys(VirtReg.reg, AvailablePhysReg);
273 PhysReg2LiveUnion[AvailablePhysReg].unify(VirtReg);
275 for (VirtRegVec::iterator I = SplitVRegs.begin(), E = SplitVRegs.end();
277 LiveInterval* SplitVirtReg = *I;
278 if (SplitVirtReg->empty()) continue;
279 DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
280 assert(TargetRegisterInfo::isVirtualRegister(SplitVirtReg->reg) &&
281 "expect split value in virtual register");
282 VirtRegQ.push(std::make_pair(getPriority(SplitVirtReg),
288 // Check if this live virtual register interferes with a physical register. If
289 // not, then check for interference on each register that aliases with the
290 // physical register. Return the interfering register.
291 unsigned RegAllocBase::checkPhysRegInterference(LiveInterval &VirtReg,
293 if (query(VirtReg, PhysReg).checkInterference())
295 for (const unsigned *AliasI = TRI->getAliasSet(PhysReg); *AliasI; ++AliasI) {
296 if (query(VirtReg, *AliasI).checkInterference())
302 // Helper for spillInteferences() that spills all interfering vregs currently
303 // assigned to this physical register.
304 void RegAllocBase::spillReg(LiveInterval& VirtReg, unsigned PhysReg,
305 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
306 LiveIntervalUnion::Query &Q = query(VirtReg, PhysReg);
307 assert(Q.seenAllInterferences() && "need collectInterferences()");
308 const SmallVectorImpl<LiveInterval*> &PendingSpills = Q.interferingVRegs();
310 for (SmallVectorImpl<LiveInterval*>::const_iterator I = PendingSpills.begin(),
311 E = PendingSpills.end(); I != E; ++I) {
312 LiveInterval &SpilledVReg = **I;
313 DEBUG(dbgs() << "extracting from " <<
314 TRI->getName(PhysReg) << " " << SpilledVReg << '\n');
316 // Deallocate the interfering vreg by removing it from the union.
317 // A LiveInterval instance may not be in a union during modification!
318 PhysReg2LiveUnion[PhysReg].extract(SpilledVReg);
320 // Clear the vreg assignment.
321 VRM->clearVirt(SpilledVReg.reg);
323 // Spill the extracted interval.
324 spiller().spill(&SpilledVReg, SplitVRegs, PendingSpills);
326 // After extracting segments, the query's results are invalid. But keep the
327 // contents valid until we're done accessing pendingSpills.
331 // Spill or split all live virtual registers currently unified under PhysReg
332 // that interfere with VirtReg. The newly spilled or split live intervals are
333 // returned by appending them to SplitVRegs.
335 RegAllocBase::spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
336 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
337 // Record each interference and determine if all are spillable before mutating
338 // either the union or live intervals.
340 // Collect interferences assigned to the requested physical register.
341 LiveIntervalUnion::Query &QPreg = query(VirtReg, PhysReg);
342 unsigned NumInterferences = QPreg.collectInterferingVRegs();
343 if (QPreg.seenUnspillableVReg()) {
346 // Collect interferences assigned to any alias of the physical register.
347 for (const unsigned *asI = TRI->getAliasSet(PhysReg); *asI; ++asI) {
348 LiveIntervalUnion::Query &QAlias = query(VirtReg, *asI);
349 NumInterferences += QAlias.collectInterferingVRegs();
350 if (QAlias.seenUnspillableVReg()) {
354 DEBUG(dbgs() << "spilling " << TRI->getName(PhysReg) <<
355 " interferences with " << VirtReg << "\n");
356 assert(NumInterferences > 0 && "expect interference");
358 // Spill each interfering vreg allocated to PhysReg or an alias.
359 spillReg(VirtReg, PhysReg, SplitVRegs);
360 for (const unsigned *AliasI = TRI->getAliasSet(PhysReg); *AliasI; ++AliasI)
361 spillReg(VirtReg, *AliasI, SplitVRegs);
365 // Add newly allocated physical registers to the MBB live in sets.
366 void RegAllocBase::addMBBLiveIns(MachineFunction *MF) {
367 typedef SmallVector<MachineBasicBlock*, 8> MBBVec;
369 MachineBasicBlock &entryMBB = *MF->begin();
371 for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
372 LiveIntervalUnion &LiveUnion = PhysReg2LiveUnion[PhysReg];
373 if (LiveUnion.empty())
375 for (LiveIntervalUnion::SegmentIter SI = LiveUnion.begin(); SI.valid();
378 // Find the set of basic blocks which this range is live into...
380 if (!LIS->findLiveInMBBs(SI.start(), SI.stop(), liveInMBBs)) continue;
382 // And add the physreg for this interval to their live-in sets.
383 for (MBBVec::iterator I = liveInMBBs.begin(), E = liveInMBBs.end();
385 MachineBasicBlock *MBB = *I;
386 if (MBB == &entryMBB) continue;
387 if (MBB->isLiveIn(PhysReg)) continue;
388 MBB->addLiveIn(PhysReg);
395 //===----------------------------------------------------------------------===//
396 // RABasic Implementation
397 //===----------------------------------------------------------------------===//
399 // Driver for the register assignment and splitting heuristics.
400 // Manages iteration over the LiveIntervalUnions.
402 // This is a minimal implementation of register assignment and splitting that
403 // spills whenever we run out of registers.
405 // selectOrSplit can only be called once per live virtual register. We then do a
406 // single interference test for each register the correct class until we find an
407 // available register. So, the number of interference tests in the worst case is
408 // |vregs| * |machineregs|. And since the number of interference tests is
409 // minimal, there is no value in caching them outside the scope of
411 unsigned RABasic::selectOrSplit(LiveInterval &VirtReg,
412 SmallVectorImpl<LiveInterval*> &SplitVRegs) {
413 // Populate a list of physical register spill candidates.
414 SmallVector<unsigned, 8> PhysRegSpillCands;
416 // Check for an available register in this class.
417 const TargetRegisterClass *TRC = MRI->getRegClass(VirtReg.reg);
419 for (TargetRegisterClass::iterator I = TRC->allocation_order_begin(*MF),
420 E = TRC->allocation_order_end(*MF);
423 unsigned PhysReg = *I;
424 if (ReservedRegs.test(PhysReg)) continue;
426 // Check interference and as a side effect, intialize queries for this
427 // VirtReg and its aliases.
428 unsigned interfReg = checkPhysRegInterference(VirtReg, PhysReg);
429 if (interfReg == 0) {
430 // Found an available register.
433 LiveInterval *interferingVirtReg =
434 Queries[interfReg].firstInterference().liveUnionPos().value();
436 // The current VirtReg must either be spillable, or one of its interferences
437 // must have less spill weight.
438 if (interferingVirtReg->weight < VirtReg.weight ) {
439 PhysRegSpillCands.push_back(PhysReg);
442 // Try to spill another interfering reg with less spill weight.
443 for (SmallVectorImpl<unsigned>::iterator PhysRegI = PhysRegSpillCands.begin(),
444 PhysRegE = PhysRegSpillCands.end(); PhysRegI != PhysRegE; ++PhysRegI) {
446 if (!spillInterferences(VirtReg, *PhysRegI, SplitVRegs)) continue;
448 assert(checkPhysRegInterference(VirtReg, *PhysRegI) == 0 &&
449 "Interference after spill.");
450 // Tell the caller to allocate to this newly freed physical register.
453 // No other spill candidates were found, so spill the current VirtReg.
454 DEBUG(dbgs() << "spilling: " << VirtReg << '\n');
455 SmallVector<LiveInterval*, 1> pendingSpills;
457 spiller().spill(&VirtReg, SplitVRegs, pendingSpills);
459 // The live virtual register requesting allocation was spilled, so tell
460 // the caller not to allocate anything during this round.
464 bool RABasic::runOnMachineFunction(MachineFunction &mf) {
465 DEBUG(dbgs() << "********** BASIC REGISTER ALLOCATION **********\n"
466 << "********** Function: "
467 << ((Value*)mf.getFunction())->getName() << '\n');
470 DEBUG(RMF = &getAnalysis<RenderMachineFunction>());
472 RegAllocBase::init(getAnalysis<VirtRegMap>(), getAnalysis<LiveIntervals>());
474 ReservedRegs = TRI->getReservedRegs(*MF);
476 SpillerInstance.reset(createSpiller(*this, *MF, *VRM));
482 // Diagnostic output before rewriting
483 DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *VRM << "\n");
485 // optional HTML output
486 DEBUG(RMF->renderMachineFunction("After basic register allocation.", VRM));
488 // FIXME: Verification currently must run before VirtRegRewriter. We should
489 // make the rewriter a separate pass and override verifyAnalysis instead. When
490 // that happens, verification naturally falls under VerifyMachineCode.
492 if (VerifyRegAlloc) {
493 // Verify accuracy of LiveIntervals. The standard machine code verifier
494 // ensures that each LiveIntervals covers all uses of the virtual reg.
496 // FIXME: MachineVerifier is badly broken when using the standard
497 // spiller. Always use -spiller=inline with -verify-regalloc. Even with the
498 // inline spiller, some tests fail to verify because the coalescer does not
499 // always generate verifiable code.
502 // Verify that LiveIntervals are partitioned into unions and disjoint within
509 std::auto_ptr<VirtRegRewriter> rewriter(createVirtRegRewriter());
510 rewriter->runOnMachineFunction(*MF, *VRM, LIS);
512 // The pass output is in VirtRegMap. Release all the transient data.
518 FunctionPass* llvm::createBasicRegisterAllocator()
520 return new RABasic();