1 //===---------- SplitKit.cpp - Toolkit for splitting live ranges ----------===//
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 contains the SplitAnalysis class as well as mutator functions for
11 // live range splitting.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "splitter"
17 #include "VirtRegMap.h"
18 #include "llvm/CodeGen/CalcSpillWeights.h"
19 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/MachineInstrBuilder.h"
22 #include "llvm/CodeGen/MachineLoopInfo.h"
23 #include "llvm/CodeGen/MachineRegisterInfo.h"
24 #include "llvm/Support/CommandLine.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/Target/TargetInstrInfo.h"
28 #include "llvm/Target/TargetMachine.h"
33 AllowSplit("spiller-splits-edges",
34 cl::desc("Allow critical edge splitting during spilling"));
36 //===----------------------------------------------------------------------===//
38 //===----------------------------------------------------------------------===//
40 SplitAnalysis::SplitAnalysis(const MachineFunction &mf,
41 const LiveIntervals &lis,
42 const MachineLoopInfo &mli)
46 tii_(*mf.getTarget().getInstrInfo()),
49 void SplitAnalysis::clear() {
56 bool SplitAnalysis::canAnalyzeBranch(const MachineBasicBlock *MBB) {
57 MachineBasicBlock *T, *F;
58 SmallVector<MachineOperand, 4> Cond;
59 return !tii_.AnalyzeBranch(const_cast<MachineBasicBlock&>(*MBB), T, F, Cond);
62 /// analyzeUses - Count instructions, basic blocks, and loops using curli.
63 void SplitAnalysis::analyzeUses() {
64 const MachineRegisterInfo &MRI = mf_.getRegInfo();
65 for (MachineRegisterInfo::reg_iterator I = MRI.reg_begin(curli_->reg);
66 MachineInstr *MI = I.skipInstruction();) {
67 if (MI->isDebugValue() || !usingInstrs_.insert(MI))
69 MachineBasicBlock *MBB = MI->getParent();
70 if (usingBlocks_[MBB]++)
72 if (MachineLoop *Loop = loops_.getLoopFor(MBB))
73 usingLoops_.insert(Loop);
75 DEBUG(dbgs() << "Counted "
76 << usingInstrs_.size() << " instrs, "
77 << usingBlocks_.size() << " blocks, "
78 << usingLoops_.size() << " loops in "
82 // Get three sets of basic blocks surrounding a loop: Blocks inside the loop,
83 // predecessor blocks, and exit blocks.
84 void SplitAnalysis::getLoopBlocks(const MachineLoop *Loop, LoopBlocks &Blocks) {
87 // Blocks in the loop.
88 Blocks.Loop.insert(Loop->block_begin(), Loop->block_end());
90 // Predecessor blocks.
91 const MachineBasicBlock *Header = Loop->getHeader();
92 for (MachineBasicBlock::const_pred_iterator I = Header->pred_begin(),
93 E = Header->pred_end(); I != E; ++I)
94 if (!Blocks.Loop.count(*I))
95 Blocks.Preds.insert(*I);
98 for (MachineLoop::block_iterator I = Loop->block_begin(),
99 E = Loop->block_end(); I != E; ++I) {
100 const MachineBasicBlock *MBB = *I;
101 for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
102 SE = MBB->succ_end(); SI != SE; ++SI)
103 if (!Blocks.Loop.count(*SI))
104 Blocks.Exits.insert(*SI);
108 /// analyzeLoopPeripheralUse - Return an enum describing how curli_ is used in
109 /// and around the Loop.
110 SplitAnalysis::LoopPeripheralUse SplitAnalysis::
111 analyzeLoopPeripheralUse(const SplitAnalysis::LoopBlocks &Blocks) {
112 LoopPeripheralUse use = ContainedInLoop;
113 for (BlockCountMap::iterator I = usingBlocks_.begin(), E = usingBlocks_.end();
115 const MachineBasicBlock *MBB = I->first;
116 // Is this a peripheral block?
117 if (use < MultiPeripheral &&
118 (Blocks.Preds.count(MBB) || Blocks.Exits.count(MBB))) {
119 if (I->second > 1) use = MultiPeripheral;
120 else use = SinglePeripheral;
123 // Is it a loop block?
124 if (Blocks.Loop.count(MBB))
126 // It must be an unrelated block.
132 /// getCriticalExits - It may be necessary to partially break critical edges
133 /// leaving the loop if an exit block has phi uses of curli. Collect the exit
134 /// blocks that need special treatment into CriticalExits.
135 void SplitAnalysis::getCriticalExits(const SplitAnalysis::LoopBlocks &Blocks,
136 BlockPtrSet &CriticalExits) {
137 CriticalExits.clear();
139 // A critical exit block contains a phi def of curli, and has a predecessor
140 // that is not in the loop nor a loop predecessor.
141 // For such an exit block, the edges carrying the new variable must be moved
142 // to a new pre-exit block.
143 for (BlockPtrSet::iterator I = Blocks.Exits.begin(), E = Blocks.Exits.end();
145 const MachineBasicBlock *Succ = *I;
146 SlotIndex SuccIdx = lis_.getMBBStartIdx(Succ);
147 VNInfo *SuccVNI = curli_->getVNInfoAt(SuccIdx);
148 // This exit may not have curli live in at all. No need to split.
151 // If this is not a PHI def, it is either using a value from before the
152 // loop, or a value defined inside the loop. Both are safe.
153 if (!SuccVNI->isPHIDef() || SuccVNI->def.getBaseIndex() != SuccIdx)
155 // This exit block does have a PHI. Does it also have a predecessor that is
156 // not a loop block or loop predecessor?
157 for (MachineBasicBlock::const_pred_iterator PI = Succ->pred_begin(),
158 PE = Succ->pred_end(); PI != PE; ++PI) {
159 const MachineBasicBlock *Pred = *PI;
160 if (Blocks.Loop.count(Pred) || Blocks.Preds.count(Pred))
162 // This is a critical exit block, and we need to split the exit edge.
163 CriticalExits.insert(Succ);
169 /// canSplitCriticalExits - Return true if it is possible to insert new exit
170 /// blocks before the blocks in CriticalExits.
172 SplitAnalysis::canSplitCriticalExits(const SplitAnalysis::LoopBlocks &Blocks,
173 BlockPtrSet &CriticalExits) {
174 // If we don't allow critical edge splitting, require no critical exits.
176 return CriticalExits.empty();
178 for (BlockPtrSet::iterator I = CriticalExits.begin(), E = CriticalExits.end();
180 const MachineBasicBlock *Succ = *I;
181 // We want to insert a new pre-exit MBB before Succ, and change all the
182 // in-loop blocks to branch to the pre-exit instead of Succ.
183 // Check that all the in-loop predecessors can be changed.
184 for (MachineBasicBlock::const_pred_iterator PI = Succ->pred_begin(),
185 PE = Succ->pred_end(); PI != PE; ++PI) {
186 const MachineBasicBlock *Pred = *PI;
187 // The external predecessors won't be altered.
188 if (!Blocks.Loop.count(Pred) && !Blocks.Preds.count(Pred))
190 if (!canAnalyzeBranch(Pred))
194 // If Succ's layout predecessor falls through, that too must be analyzable.
195 // We need to insert the pre-exit block in the gap.
196 MachineFunction::const_iterator MFI = Succ;
197 if (MFI == mf_.begin())
199 if (!canAnalyzeBranch(--MFI))
202 // No problems found.
206 void SplitAnalysis::analyze(const LiveInterval *li) {
212 const MachineLoop *SplitAnalysis::getBestSplitLoop() {
213 assert(curli_ && "Call analyze() before getBestSplitLoop");
214 if (usingLoops_.empty())
217 LoopPtrSet Loops, SecondLoops;
219 BlockPtrSet CriticalExits;
221 // Find first-class and second class candidate loops.
222 // We prefer to split around loops where curli is used outside the periphery.
223 for (LoopPtrSet::const_iterator I = usingLoops_.begin(),
224 E = usingLoops_.end(); I != E; ++I) {
225 getLoopBlocks(*I, Blocks);
227 // FIXME: We need an SSA updater to properly handle multiple exit blocks.
228 if (Blocks.Exits.size() > 1) {
229 DEBUG(dbgs() << "MultipleExits: " << **I);
234 switch(analyzeLoopPeripheralUse(Blocks)) {
238 case MultiPeripheral:
241 case ContainedInLoop:
242 DEBUG(dbgs() << "ContainedInLoop: " << **I);
244 case SinglePeripheral:
245 DEBUG(dbgs() << "SinglePeripheral: " << **I);
248 // Will it be possible to split around this loop?
249 getCriticalExits(Blocks, CriticalExits);
250 DEBUG(dbgs() << CriticalExits.size() << " critical exits: " << **I);
251 if (!canSplitCriticalExits(Blocks, CriticalExits))
253 // This is a possible split.
258 DEBUG(dbgs() << "Got " << Loops.size() << " + " << SecondLoops.size()
259 << " candidate loops\n");
261 // If there are no first class loops available, look at second class loops.
268 // Pick the earliest loop.
269 // FIXME: Are there other heuristics to consider?
270 const MachineLoop *Best = 0;
272 for (LoopPtrSet::const_iterator I = Loops.begin(), E = Loops.end(); I != E;
274 SlotIndex Idx = lis_.getMBBStartIdx((*I)->getHeader());
275 if (!Best || Idx < BestIdx)
276 Best = *I, BestIdx = Idx;
278 DEBUG(dbgs() << "Best: " << *Best);
283 //===----------------------------------------------------------------------===//
285 //===----------------------------------------------------------------------===//
287 /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
288 SplitEditor::SplitEditor(SplitAnalysis &sa, LiveIntervals &lis, VirtRegMap &vrm,
289 std::vector<LiveInterval*> &intervals)
290 : sa_(sa), lis_(lis), vrm_(vrm),
291 mri_(vrm.getMachineFunction().getRegInfo()),
292 tii_(*vrm.getMachineFunction().getTarget().getInstrInfo()),
293 curli_(sa_.getCurLI()),
294 dupli_(0), openli_(0),
295 intervals_(intervals),
296 firstInterval(intervals_.size())
298 assert(curli_ && "SplitEditor created from empty SplitAnalysis");
300 // Make sure curli_ is assigned a stack slot, so all our intervals get the
301 // same slot as curli_.
302 if (vrm_.getStackSlot(curli_->reg) == VirtRegMap::NO_STACK_SLOT)
303 vrm_.assignVirt2StackSlot(curli_->reg);
307 LiveInterval *SplitEditor::createInterval() {
308 unsigned curli = sa_.getCurLI()->reg;
309 unsigned Reg = mri_.createVirtualRegister(mri_.getRegClass(curli));
310 LiveInterval &Intv = lis_.getOrCreateInterval(Reg);
312 vrm_.assignVirt2StackSlot(Reg, vrm_.getStackSlot(curli));
316 LiveInterval *SplitEditor::getDupLI() {
318 // Create an interval for dupli that is a copy of curli.
319 dupli_ = createInterval();
320 dupli_->Copy(*curli_, &mri_, lis_.getVNInfoAllocator());
321 DEBUG(dbgs() << "SplitEditor DupLI: " << *dupli_ << '\n');
326 VNInfo *SplitEditor::mapValue(const VNInfo *curliVNI) {
327 VNInfo *&VNI = valueMap_[curliVNI];
329 VNI = openli_->createValueCopy(curliVNI, lis_.getVNInfoAllocator());
333 /// Insert a COPY instruction curli -> li. Allocate a new value from li
334 /// defined by the COPY. Note that rewrite() will deal with the curli
335 /// register, so this function can be used to copy from any interval - openli,
337 VNInfo *SplitEditor::insertCopy(LiveInterval &LI,
338 MachineBasicBlock &MBB,
339 MachineBasicBlock::iterator I) {
340 MachineInstr *MI = BuildMI(MBB, I, DebugLoc(), tii_.get(TargetOpcode::COPY),
341 LI.reg).addReg(curli_->reg);
342 SlotIndex DefIdx = lis_.InsertMachineInstrInMaps(MI).getDefIndex();
343 return LI.getNextValue(DefIdx, MI, true, lis_.getVNInfoAllocator());
346 /// Create a new virtual register and live interval.
347 void SplitEditor::openIntv() {
348 assert(!openli_ && "Previous LI not closed before openIntv");
349 openli_ = createInterval();
350 intervals_.push_back(openli_);
351 liveThrough_ = false;
354 /// enterIntvAtEnd - Enter openli at the end of MBB.
355 /// PhiMBB is a successor inside openli where a PHI value is created.
356 /// Currently, all entries must share the same PhiMBB.
357 void SplitEditor::enterIntvAtEnd(MachineBasicBlock &A, MachineBasicBlock &B) {
358 assert(openli_ && "openIntv not called before enterIntvAtEnd");
360 SlotIndex EndA = lis_.getMBBEndIdx(&A);
361 VNInfo *CurVNIA = curli_->getVNInfoAt(EndA.getPrevIndex());
363 DEBUG(dbgs() << " ignoring enterIntvAtEnd, curli not live out of BB#"
364 << A.getNumber() << ".\n");
368 // Add a phi kill value and live range out of A.
369 VNInfo *VNIA = insertCopy(*openli_, A, A.getFirstTerminator());
370 openli_->addRange(LiveRange(VNIA->def, EndA, VNIA));
372 // FIXME: If this is the only entry edge, we don't need the extra PHI value.
373 // FIXME: If there are multiple entry blocks (so not a loop), we need proper
376 // Now look at the start of B.
377 SlotIndex StartB = lis_.getMBBStartIdx(&B);
378 SlotIndex EndB = lis_.getMBBEndIdx(&B);
379 const LiveRange *CurB = curli_->getLiveRangeContaining(StartB);
381 DEBUG(dbgs() << " enterIntvAtEnd: curli not live in to BB#"
382 << B.getNumber() << ".\n");
386 VNInfo *VNIB = openli_->getVNInfoAt(StartB);
388 // Create a phi value.
389 VNIB = openli_->getNextValue(SlotIndex(StartB, true), 0, false,
390 lis_.getVNInfoAllocator());
391 VNIB->setIsPHIDef(true);
392 // Add a minimal range for the new value.
393 openli_->addRange(LiveRange(VNIB->def, std::min(EndB, CurB->end), VNIB));
395 VNInfo *&mapVNI = valueMap_[CurB->valno];
397 // Multiple copies - must create PHI value.
400 // This is the first copy of dupLR. Mark the mapping.
406 DEBUG(dbgs() << " enterIntvAtEnd: " << *openli_ << '\n');
409 /// useIntv - indicate that all instructions in MBB should use openli.
410 void SplitEditor::useIntv(const MachineBasicBlock &MBB) {
411 useIntv(lis_.getMBBStartIdx(&MBB), lis_.getMBBEndIdx(&MBB));
414 void SplitEditor::useIntv(SlotIndex Start, SlotIndex End) {
415 assert(openli_ && "openIntv not called before useIntv");
417 // Map the curli values from the interval into openli_
418 LiveInterval::const_iterator B = curli_->begin(), E = curli_->end();
419 LiveInterval::const_iterator I = std::lower_bound(B, E, Start);
423 // I begins before Start, but overlaps. openli may already have a value.
424 if (I->end > Start && !openli_->liveAt(Start))
425 openli_->addRange(LiveRange(Start, std::min(End, I->end),
426 mapValue(I->valno)));
430 // The remaining ranges begin after Start.
431 for (;I != E && I->start < End; ++I)
432 openli_->addRange(LiveRange(I->start, std::min(End, I->end),
433 mapValue(I->valno)));
434 DEBUG(dbgs() << " added range [" << Start << ';' << End << "): " << *openli_
438 /// leaveIntvAtTop - Leave the interval at the top of MBB.
439 /// Currently, only one value can leave the interval.
440 void SplitEditor::leaveIntvAtTop(MachineBasicBlock &MBB) {
441 assert(openli_ && "openIntv not called before leaveIntvAtTop");
443 SlotIndex Start = lis_.getMBBStartIdx(&MBB);
444 const LiveRange *CurLR = curli_->getLiveRangeContaining(Start);
446 // Is curli even live-in to MBB?
448 DEBUG(dbgs() << " leaveIntvAtTop at " << Start << ": not live\n");
452 // Is curli defined by PHI at the beginning of MBB?
453 bool isPHIDef = CurLR->valno->isPHIDef() &&
454 CurLR->valno->def.getBaseIndex() == Start;
456 // If MBB is using a value of curli that was defined outside the openli range,
457 // we don't want to copy it back here.
458 if (!isPHIDef && !openli_->liveAt(CurLR->valno->def)) {
459 DEBUG(dbgs() << " leaveIntvAtTop at " << Start
460 << ": using external value\n");
465 // We are going to insert a back copy, so we must have a dupli_.
466 LiveRange *DupLR = getDupLI()->getLiveRangeContaining(Start);
467 assert(DupLR && "dupli not live into black, but curli is?");
469 // Insert the COPY instruction.
470 MachineInstr *MI = BuildMI(MBB, MBB.begin(), DebugLoc(),
471 tii_.get(TargetOpcode::COPY), dupli_->reg)
472 .addReg(openli_->reg);
473 SlotIndex Idx = lis_.InsertMachineInstrInMaps(MI).getDefIndex();
475 // Adjust dupli and openli values.
477 // dupli was already a PHI on entry to MBB. Simply insert an openli PHI,
478 // and shift the dupli def down to the COPY.
479 VNInfo *VNI = openli_->getNextValue(SlotIndex(Start, true), 0, false,
480 lis_.getVNInfoAllocator());
481 VNI->setIsPHIDef(true);
482 openli_->addRange(LiveRange(VNI->def, Idx, VNI));
484 dupli_->removeRange(Start, Idx);
485 DupLR->valno->def = Idx;
486 DupLR->valno->setIsPHIDef(false);
488 // The dupli value was defined somewhere inside the openli range.
489 DEBUG(dbgs() << " leaveIntvAtTop source value defined at "
490 << DupLR->valno->def << "\n");
491 // FIXME: We may not need a PHI here if all predecessors have the same
493 VNInfo *VNI = openli_->getNextValue(SlotIndex(Start, true), 0, false,
494 lis_.getVNInfoAllocator());
495 VNI->setIsPHIDef(true);
496 openli_->addRange(LiveRange(VNI->def, Idx, VNI));
498 // FIXME: What if DupLR->valno is used by multiple exits? SSA Update.
500 // closeIntv is going to remove the superfluous live ranges.
501 DupLR->valno->def = Idx;
502 DupLR->valno->setIsPHIDef(false);
505 DEBUG(dbgs() << " leaveIntvAtTop at " << Idx << ": " << *openli_ << '\n');
508 /// closeIntv - Indicate that we are done editing the currently open
509 /// LiveInterval, and ranges can be trimmed.
510 void SplitEditor::closeIntv() {
511 assert(openli_ && "openIntv not called before closeIntv");
513 DEBUG(dbgs() << " closeIntv cleaning up\n");
514 DEBUG(dbgs() << " open " << *openli_ << '\n');
517 DEBUG(dbgs() << " value live through region, leaving dupli as is.\n");
519 // live out with copies inserted, or killed by region. Either way we need to
520 // remove the overlapping region from dupli.
522 for (LiveInterval::iterator I = openli_->begin(), E = openli_->end();
524 dupli_->removeRange(I->start, I->end);
526 // FIXME: A block branching to the entry block may also branch elsewhere
527 // curli is live. We need both openli and curli to be live in that case.
528 DEBUG(dbgs() << " dup2 " << *dupli_ << '\n');
533 /// rewrite - after all the new live ranges have been created, rewrite
534 /// instructions using curli to use the new intervals.
535 void SplitEditor::rewrite() {
536 assert(!openli_ && "Previous LI not closed before rewrite");
537 const LiveInterval *curli = sa_.getCurLI();
538 for (MachineRegisterInfo::reg_iterator RI = mri_.reg_begin(curli->reg),
539 RE = mri_.reg_end(); RI != RE;) {
540 MachineOperand &MO = RI.getOperand();
541 MachineInstr *MI = MO.getParent();
543 if (MI->isDebugValue()) {
544 DEBUG(dbgs() << "Zapping " << *MI);
545 // FIXME: We can do much better with debug values.
549 SlotIndex Idx = lis_.getInstructionIndex(MI);
550 Idx = MO.isUse() ? Idx.getUseIndex() : Idx.getDefIndex();
551 LiveInterval *LI = dupli_;
552 for (unsigned i = firstInterval, e = intervals_.size(); i != e; ++i) {
553 LiveInterval *testli = intervals_[i];
554 if (testli->liveAt(Idx)) {
561 DEBUG(dbgs() << "rewrite " << Idx << '\t' << *MI);
564 // dupli_ goes in last, after rewriting.
566 dupli_->RenumberValues();
567 intervals_.push_back(dupli_);
570 // Calculate spill weight and allocation hints for new intervals.
571 VirtRegAuxInfo vrai(vrm_.getMachineFunction(), lis_, sa_.loops_);
572 for (unsigned i = firstInterval, e = intervals_.size(); i != e; ++i) {
573 LiveInterval &li = *intervals_[i];
574 vrai.CalculateRegClass(li.reg);
575 vrai.CalculateWeightAndHint(li);
580 //===----------------------------------------------------------------------===//
582 //===----------------------------------------------------------------------===//
584 bool SplitEditor::splitAroundLoop(const MachineLoop *Loop) {
585 SplitAnalysis::LoopBlocks Blocks;
586 sa_.getLoopBlocks(Loop, Blocks);
588 // Break critical edges as needed.
589 SplitAnalysis::BlockPtrSet CriticalExits;
590 sa_.getCriticalExits(Blocks, CriticalExits);
591 assert(CriticalExits.empty() && "Cannot break critical exits yet");
593 // Create new live interval for the loop.
596 // Insert copies in the predecessors.
597 for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Preds.begin(),
598 E = Blocks.Preds.end(); I != E; ++I) {
599 MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);
600 enterIntvAtEnd(MBB, *Loop->getHeader());
603 // Switch all loop blocks.
604 for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Loop.begin(),
605 E = Blocks.Loop.end(); I != E; ++I)
608 // Insert back copies in the exit blocks.
609 for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Exits.begin(),
610 E = Blocks.Exits.end(); I != E; ++I) {
611 MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);