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/LiveIntervalAnalysis.h"
19 #include "llvm/CodeGen/MachineFunctionPass.h"
20 #include "llvm/CodeGen/MachineInstrBuilder.h"
21 #include "llvm/CodeGen/MachineLoopInfo.h"
22 #include "llvm/CodeGen/MachineRegisterInfo.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/raw_ostream.h"
26 #include "llvm/Target/TargetInstrInfo.h"
27 #include "llvm/Target/TargetMachine.h"
32 AllowSplit("spiller-splits-edges",
33 cl::desc("Allow critical edge splitting during spilling"));
35 //===----------------------------------------------------------------------===//
37 //===----------------------------------------------------------------------===//
39 SplitAnalysis::SplitAnalysis(const MachineFunction &mf,
40 const LiveIntervals &lis,
41 const MachineLoopInfo &mli)
45 tii_(*mf.getTarget().getInstrInfo()),
48 void SplitAnalysis::clear() {
55 bool SplitAnalysis::canAnalyzeBranch(const MachineBasicBlock *MBB) {
56 MachineBasicBlock *T, *F;
57 SmallVector<MachineOperand, 4> Cond;
58 return !tii_.AnalyzeBranch(const_cast<MachineBasicBlock&>(*MBB), T, F, Cond);
61 /// analyzeUses - Count instructions, basic blocks, and loops using curli.
62 void SplitAnalysis::analyzeUses() {
63 const MachineRegisterInfo &MRI = mf_.getRegInfo();
64 for (MachineRegisterInfo::reg_iterator I = MRI.reg_begin(curli_->reg);
65 MachineInstr *MI = I.skipInstruction();) {
66 if (MI->isDebugValue() || !usingInstrs_.insert(MI))
68 MachineBasicBlock *MBB = MI->getParent();
69 if (usingBlocks_[MBB]++)
71 if (MachineLoop *Loop = loops_.getLoopFor(MBB))
72 usingLoops_.insert(Loop);
74 DEBUG(dbgs() << "Counted "
75 << usingInstrs_.size() << " instrs, "
76 << usingBlocks_.size() << " blocks, "
77 << usingLoops_.size() << " loops in "
81 // Get three sets of basic blocks surrounding a loop: Blocks inside the loop,
82 // predecessor blocks, and exit blocks.
83 void SplitAnalysis::getLoopBlocks(const MachineLoop *Loop, LoopBlocks &Blocks) {
86 // Blocks in the loop.
87 Blocks.Loop.insert(Loop->block_begin(), Loop->block_end());
89 // Predecessor blocks.
90 const MachineBasicBlock *Header = Loop->getHeader();
91 for (MachineBasicBlock::const_pred_iterator I = Header->pred_begin(),
92 E = Header->pred_end(); I != E; ++I)
93 if (!Blocks.Loop.count(*I))
94 Blocks.Preds.insert(*I);
97 for (MachineLoop::block_iterator I = Loop->block_begin(),
98 E = Loop->block_end(); I != E; ++I) {
99 const MachineBasicBlock *MBB = *I;
100 for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
101 SE = MBB->succ_end(); SI != SE; ++SI)
102 if (!Blocks.Loop.count(*SI))
103 Blocks.Exits.insert(*SI);
107 /// analyzeLoopPeripheralUse - Return an enum describing how curli_ is used in
108 /// and around the Loop.
109 SplitAnalysis::LoopPeripheralUse SplitAnalysis::
110 analyzeLoopPeripheralUse(const SplitAnalysis::LoopBlocks &Blocks) {
111 LoopPeripheralUse use = ContainedInLoop;
112 for (BlockCountMap::iterator I = usingBlocks_.begin(), E = usingBlocks_.end();
114 const MachineBasicBlock *MBB = I->first;
115 // Is this a peripheral block?
116 if (use < MultiPeripheral &&
117 (Blocks.Preds.count(MBB) || Blocks.Exits.count(MBB))) {
118 if (I->second > 1) use = MultiPeripheral;
119 else use = SinglePeripheral;
122 // Is it a loop block?
123 if (Blocks.Loop.count(MBB))
125 // It must be an unrelated block.
131 /// getCriticalExits - It may be necessary to partially break critical edges
132 /// leaving the loop if an exit block has phi uses of curli. Collect the exit
133 /// blocks that need special treatment into CriticalExits.
134 void SplitAnalysis::getCriticalExits(const SplitAnalysis::LoopBlocks &Blocks,
135 BlockPtrSet &CriticalExits) {
136 CriticalExits.clear();
138 // A critical exit block contains a phi def of curli, and has a predecessor
139 // that is not in the loop nor a loop predecessor.
140 // For such an exit block, the edges carrying the new variable must be moved
141 // to a new pre-exit block.
142 for (BlockPtrSet::iterator I = Blocks.Exits.begin(), E = Blocks.Exits.end();
144 const MachineBasicBlock *Succ = *I;
145 SlotIndex SuccIdx = lis_.getMBBStartIdx(Succ);
146 VNInfo *SuccVNI = curli_->getVNInfoAt(SuccIdx);
147 // This exit may not have curli live in at all. No need to split.
150 // If this is not a PHI def, it is either using a value from before the
151 // loop, or a value defined inside the loop. Both are safe.
152 if (!SuccVNI->isPHIDef() || SuccVNI->def.getBaseIndex() != SuccIdx)
154 // This exit block does have a PHI. Does it also have a predecessor that is
155 // not a loop block or loop predecessor?
156 for (MachineBasicBlock::const_pred_iterator PI = Succ->pred_begin(),
157 PE = Succ->pred_end(); PI != PE; ++PI) {
158 const MachineBasicBlock *Pred = *PI;
159 if (Blocks.Loop.count(Pred) || Blocks.Preds.count(Pred))
161 // This is a critical exit block, and we need to split the exit edge.
162 CriticalExits.insert(Succ);
168 /// canSplitCriticalExits - Return true if it is possible to insert new exit
169 /// blocks before the blocks in CriticalExits.
171 SplitAnalysis::canSplitCriticalExits(const SplitAnalysis::LoopBlocks &Blocks,
172 BlockPtrSet &CriticalExits) {
173 // If we don't allow critical edge splitting, require no critical exits.
175 return CriticalExits.empty();
177 for (BlockPtrSet::iterator I = CriticalExits.begin(), E = CriticalExits.end();
179 const MachineBasicBlock *Succ = *I;
180 // We want to insert a new pre-exit MBB before Succ, and change all the
181 // in-loop blocks to branch to the pre-exit instead of Succ.
182 // Check that all the in-loop predecessors can be changed.
183 for (MachineBasicBlock::const_pred_iterator PI = Succ->pred_begin(),
184 PE = Succ->pred_end(); PI != PE; ++PI) {
185 const MachineBasicBlock *Pred = *PI;
186 // The external predecessors won't be altered.
187 if (!Blocks.Loop.count(Pred) && !Blocks.Preds.count(Pred))
189 if (!canAnalyzeBranch(Pred))
193 // If Succ's layout predecessor falls through, that too must be analyzable.
194 // We need to insert the pre-exit block in the gap.
195 MachineFunction::const_iterator MFI = Succ;
196 if (MFI == mf_.begin())
198 if (!canAnalyzeBranch(--MFI))
201 // No problems found.
205 void SplitAnalysis::analyze(const LiveInterval *li) {
211 const MachineLoop *SplitAnalysis::getBestSplitLoop() {
212 assert(curli_ && "Call analyze() before getBestSplitLoop");
213 if (usingLoops_.empty())
216 LoopPtrSet Loops, SecondLoops;
218 BlockPtrSet CriticalExits;
220 // Find first-class and second class candidate loops.
221 // We prefer to split around loops where curli is used outside the periphery.
222 for (LoopPtrSet::const_iterator I = usingLoops_.begin(),
223 E = usingLoops_.end(); I != E; ++I) {
224 getLoopBlocks(*I, Blocks);
226 // FIXME: We need an SSA updater to properly handle multiple exit blocks.
227 if (Blocks.Exits.size() > 1) {
228 DEBUG(dbgs() << "MultipleExits: " << **I);
233 switch(analyzeLoopPeripheralUse(Blocks)) {
237 case MultiPeripheral:
240 case ContainedInLoop:
241 DEBUG(dbgs() << "ContainedInLoop: " << **I);
243 case SinglePeripheral:
244 DEBUG(dbgs() << "SinglePeripheral: " << **I);
247 // Will it be possible to split around this loop?
248 getCriticalExits(Blocks, CriticalExits);
249 DEBUG(dbgs() << CriticalExits.size() << " critical exits: " << **I);
250 if (!canSplitCriticalExits(Blocks, CriticalExits))
252 // This is a possible split.
257 DEBUG(dbgs() << "Got " << Loops.size() << " + " << SecondLoops.size()
258 << " candidate loops\n");
260 // If there are no first class loops available, look at second class loops.
267 // Pick the earliest loop.
268 // FIXME: Are there other heuristics to consider?
269 const MachineLoop *Best = 0;
271 for (LoopPtrSet::const_iterator I = Loops.begin(), E = Loops.end(); I != E;
273 SlotIndex Idx = lis_.getMBBStartIdx((*I)->getHeader());
274 if (!Best || Idx < BestIdx)
275 Best = *I, BestIdx = Idx;
277 DEBUG(dbgs() << "Best: " << *Best);
282 //===----------------------------------------------------------------------===//
284 //===----------------------------------------------------------------------===//
286 /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
287 SplitEditor::SplitEditor(SplitAnalysis &sa, LiveIntervals &lis, VirtRegMap &vrm,
288 std::vector<LiveInterval*> &intervals)
289 : sa_(sa), lis_(lis), vrm_(vrm),
290 mri_(vrm.getMachineFunction().getRegInfo()),
291 tii_(*vrm.getMachineFunction().getTarget().getInstrInfo()),
292 curli_(sa_.getCurLI()),
293 dupli_(0), openli_(0),
294 intervals_(intervals),
295 firstInterval(intervals_.size())
297 assert(curli_ && "SplitEditor created from empty SplitAnalysis");
299 // Make sure curli_ is assigned a stack slot, so all our intervals get the
300 // same slot as curli_.
301 if (vrm_.getStackSlot(curli_->reg) == VirtRegMap::NO_STACK_SLOT)
302 vrm_.assignVirt2StackSlot(curli_->reg);
306 LiveInterval *SplitEditor::createInterval() {
307 unsigned curli = sa_.getCurLI()->reg;
308 unsigned Reg = mri_.createVirtualRegister(mri_.getRegClass(curli));
309 LiveInterval &Intv = lis_.getOrCreateInterval(Reg);
311 vrm_.assignVirt2StackSlot(Reg, vrm_.getStackSlot(curli));
315 LiveInterval *SplitEditor::getDupLI() {
317 // Create an interval for dupli that is a copy of curli.
318 dupli_ = createInterval();
319 dupli_->Copy(*curli_, &mri_, lis_.getVNInfoAllocator());
320 DEBUG(dbgs() << "SplitEditor DupLI: " << *dupli_ << '\n');
325 VNInfo *SplitEditor::mapValue(const VNInfo *curliVNI) {
326 VNInfo *&VNI = valueMap_[curliVNI];
328 VNI = openli_->createValueCopy(curliVNI, lis_.getVNInfoAllocator());
332 /// Insert a COPY instruction curli -> li. Allocate a new value from li
333 /// defined by the COPY. Note that rewrite() will deal with the curli
334 /// register, so this function can be used to copy from any interval - openli,
336 VNInfo *SplitEditor::insertCopy(LiveInterval &LI,
337 MachineBasicBlock &MBB,
338 MachineBasicBlock::iterator I) {
339 MachineInstr *MI = BuildMI(MBB, I, DebugLoc(), tii_.get(TargetOpcode::COPY),
340 LI.reg).addReg(curli_->reg);
341 SlotIndex DefIdx = lis_.InsertMachineInstrInMaps(MI).getDefIndex();
342 return LI.getNextValue(DefIdx, MI, true, lis_.getVNInfoAllocator());
345 /// Create a new virtual register and live interval.
346 void SplitEditor::openIntv() {
347 assert(!openli_ && "Previous LI not closed before openIntv");
348 openli_ = createInterval();
349 intervals_.push_back(openli_);
350 liveThrough_ = false;
353 /// enterIntvAtEnd - Enter openli at the end of MBB.
354 /// PhiMBB is a successor inside openli where a PHI value is created.
355 /// Currently, all entries must share the same PhiMBB.
356 void SplitEditor::enterIntvAtEnd(MachineBasicBlock &A, MachineBasicBlock &B) {
357 assert(openli_ && "openIntv not called before enterIntvAtEnd");
359 SlotIndex EndA = lis_.getMBBEndIdx(&A);
360 VNInfo *CurVNIA = curli_->getVNInfoAt(EndA.getPrevIndex());
362 DEBUG(dbgs() << " ignoring enterIntvAtEnd, curli not live out of BB#"
363 << A.getNumber() << ".\n");
367 // Add a phi kill value and live range out of A.
368 VNInfo *VNIA = insertCopy(*openli_, A, A.getFirstTerminator());
369 openli_->addRange(LiveRange(VNIA->def, EndA, VNIA));
371 // FIXME: If this is the only entry edge, we don't need the extra PHI value.
372 // FIXME: If there are multiple entry blocks (so not a loop), we need proper
375 // Now look at the start of B.
376 SlotIndex StartB = lis_.getMBBStartIdx(&B);
377 SlotIndex EndB = lis_.getMBBEndIdx(&B);
378 const LiveRange *CurB = curli_->getLiveRangeContaining(StartB);
380 DEBUG(dbgs() << " enterIntvAtEnd: curli not live in to BB#"
381 << B.getNumber() << ".\n");
385 VNInfo *VNIB = openli_->getVNInfoAt(StartB);
387 // Create a phi value.
388 VNIB = openli_->getNextValue(SlotIndex(StartB, true), 0, false,
389 lis_.getVNInfoAllocator());
390 VNIB->setIsPHIDef(true);
391 // Add a minimal range for the new value.
392 openli_->addRange(LiveRange(VNIB->def, std::min(EndB, CurB->end), VNIB));
394 VNInfo *&mapVNI = valueMap_[CurB->valno];
396 // Multiple copies - must create PHI value.
399 // This is the first copy of dupLR. Mark the mapping.
405 DEBUG(dbgs() << " enterIntvAtEnd: " << *openli_ << '\n');
408 /// useIntv - indicate that all instructions in MBB should use openli.
409 void SplitEditor::useIntv(const MachineBasicBlock &MBB) {
410 useIntv(lis_.getMBBStartIdx(&MBB), lis_.getMBBEndIdx(&MBB));
413 void SplitEditor::useIntv(SlotIndex Start, SlotIndex End) {
414 assert(openli_ && "openIntv not called before useIntv");
416 // Map the curli values from the interval into openli_
417 LiveInterval::const_iterator B = curli_->begin(), E = curli_->end();
418 LiveInterval::const_iterator I = std::lower_bound(B, E, Start);
422 // I begins before Start, but overlaps. openli may already have a value.
423 if (I->end > Start && !openli_->liveAt(Start))
424 openli_->addRange(LiveRange(Start, std::min(End, I->end),
425 mapValue(I->valno)));
429 // The remaining ranges begin after Start.
430 for (;I != E && I->start < End; ++I)
431 openli_->addRange(LiveRange(I->start, std::min(End, I->end),
432 mapValue(I->valno)));
433 DEBUG(dbgs() << " added range [" << Start << ';' << End << "): " << *openli_
437 /// leaveIntvAtTop - Leave the interval at the top of MBB.
438 /// Currently, only one value can leave the interval.
439 void SplitEditor::leaveIntvAtTop(MachineBasicBlock &MBB) {
440 assert(openli_ && "openIntv not called before leaveIntvAtTop");
442 SlotIndex Start = lis_.getMBBStartIdx(&MBB);
443 const LiveRange *CurLR = curli_->getLiveRangeContaining(Start);
445 // Is curli even live-in to MBB?
447 DEBUG(dbgs() << " leaveIntvAtTop at " << Start << ": not live\n");
451 // Is curli defined by PHI at the beginning of MBB?
452 bool isPHIDef = CurLR->valno->isPHIDef() &&
453 CurLR->valno->def.getBaseIndex() == Start;
455 // If MBB is using a value of curli that was defined outside the openli range,
456 // we don't want to copy it back here.
457 if (!isPHIDef && !openli_->liveAt(CurLR->valno->def)) {
458 DEBUG(dbgs() << " leaveIntvAtTop at " << Start
459 << ": using external value\n");
464 // We are going to insert a back copy, so we must have a dupli_.
465 LiveRange *DupLR = getDupLI()->getLiveRangeContaining(Start);
466 assert(DupLR && "dupli not live into black, but curli is?");
468 // Insert the COPY instruction.
469 MachineInstr *MI = BuildMI(MBB, MBB.begin(), DebugLoc(),
470 tii_.get(TargetOpcode::COPY), dupli_->reg)
471 .addReg(openli_->reg);
472 SlotIndex Idx = lis_.InsertMachineInstrInMaps(MI).getDefIndex();
474 // Adjust dupli and openli values.
476 // dupli was already a PHI on entry to MBB. Simply insert an openli PHI,
477 // and shift the dupli def down to the COPY.
478 VNInfo *VNI = openli_->getNextValue(SlotIndex(Start, true), 0, false,
479 lis_.getVNInfoAllocator());
480 VNI->setIsPHIDef(true);
481 openli_->addRange(LiveRange(VNI->def, Idx, VNI));
483 dupli_->removeRange(Start, Idx);
484 DupLR->valno->def = Idx;
485 DupLR->valno->setIsPHIDef(false);
487 // The dupli value was defined somewhere inside the openli range.
488 DEBUG(dbgs() << " leaveIntvAtTop source value defined at "
489 << DupLR->valno->def << "\n");
490 // FIXME: We may not need a PHI here if all predecessors have the same
492 VNInfo *VNI = openli_->getNextValue(SlotIndex(Start, true), 0, false,
493 lis_.getVNInfoAllocator());
494 VNI->setIsPHIDef(true);
495 openli_->addRange(LiveRange(VNI->def, Idx, VNI));
497 // FIXME: What if DupLR->valno is used by multiple exits? SSA Update.
499 // closeIntv is going to remove the superfluous live ranges.
500 DupLR->valno->def = Idx;
501 DupLR->valno->setIsPHIDef(false);
504 DEBUG(dbgs() << " leaveIntvAtTop at " << Idx << ": " << *openli_ << '\n');
507 /// closeIntv - Indicate that we are done editing the currently open
508 /// LiveInterval, and ranges can be trimmed.
509 void SplitEditor::closeIntv() {
510 assert(openli_ && "openIntv not called before closeIntv");
512 DEBUG(dbgs() << " closeIntv cleaning up\n");
513 DEBUG(dbgs() << " open " << *openli_ << '\n');
516 DEBUG(dbgs() << " value live through region, leaving dupli as is.\n");
518 // live out with copies inserted, or killed by region. Either way we need to
519 // remove the overlapping region from dupli.
521 for (LiveInterval::iterator I = openli_->begin(), E = openli_->end();
523 dupli_->removeRange(I->start, I->end);
525 // FIXME: A block branching to the entry block may also branch elsewhere
526 // curli is live. We need both openli and curli to be live in that case.
527 DEBUG(dbgs() << " dup2 " << *dupli_ << '\n');
532 /// rewrite - after all the new live ranges have been created, rewrite
533 /// instructions using curli to use the new intervals.
534 void SplitEditor::rewrite() {
535 assert(!openli_ && "Previous LI not closed before rewrite");
536 const LiveInterval *curli = sa_.getCurLI();
537 for (MachineRegisterInfo::reg_iterator RI = mri_.reg_begin(curli->reg),
538 RE = mri_.reg_end(); RI != RE;) {
539 MachineOperand &MO = RI.getOperand();
540 MachineInstr *MI = MO.getParent();
542 if (MI->isDebugValue()) {
543 DEBUG(dbgs() << "Zapping " << *MI);
544 // FIXME: We can do much better with debug values.
548 SlotIndex Idx = lis_.getInstructionIndex(MI);
549 Idx = MO.isUse() ? Idx.getUseIndex() : Idx.getDefIndex();
550 LiveInterval *LI = dupli_;
551 for (unsigned i = firstInterval, e = intervals_.size(); i != e; ++i) {
552 LiveInterval *testli = intervals_[i];
553 if (testli->liveAt(Idx)) {
560 DEBUG(dbgs() << "rewrite " << Idx << '\t' << *MI);
563 // dupli_ goes in last, after rewriting.
565 dupli_->RenumberValues();
566 intervals_.push_back(dupli_);
569 // FIXME: *Calculate spill weights, allocation hints, and register classes for
574 //===----------------------------------------------------------------------===//
576 //===----------------------------------------------------------------------===//
578 bool SplitEditor::splitAroundLoop(const MachineLoop *Loop) {
579 SplitAnalysis::LoopBlocks Blocks;
580 sa_.getLoopBlocks(Loop, Blocks);
582 // Break critical edges as needed.
583 SplitAnalysis::BlockPtrSet CriticalExits;
584 sa_.getCriticalExits(Blocks, CriticalExits);
585 assert(CriticalExits.empty() && "Cannot break critical exits yet");
587 // Create new live interval for the loop.
590 // Insert copies in the predecessors.
591 for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Preds.begin(),
592 E = Blocks.Preds.end(); I != E; ++I) {
593 MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);
594 enterIntvAtEnd(MBB, *Loop->getHeader());
597 // Switch all loop blocks.
598 for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Loop.begin(),
599 E = Blocks.Loop.end(); I != E; ++I)
602 // Insert back copies in the exit blocks.
603 for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Exits.begin(),
604 E = Blocks.Exits.end(); I != E; ++I) {
605 MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);