1 //===-- TailDuplication.cpp - Duplicate blocks into predecessors' tails ---===//
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 pass duplicates basic blocks ending in unconditional branches into
11 // the tails of their predecessors.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "tailduplication"
16 #include "llvm/Function.h"
17 #include "llvm/CodeGen/Passes.h"
18 #include "llvm/CodeGen/MachineModuleInfo.h"
19 #include "llvm/CodeGen/MachineFunctionPass.h"
20 #include "llvm/CodeGen/MachineInstrBuilder.h"
21 #include "llvm/CodeGen/MachineRegisterInfo.h"
22 #include "llvm/CodeGen/MachineSSAUpdater.h"
23 #include "llvm/Target/TargetInstrInfo.h"
24 #include "llvm/Support/CommandLine.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Support/raw_ostream.h"
28 #include "llvm/ADT/SmallSet.h"
29 #include "llvm/ADT/SetVector.h"
30 #include "llvm/ADT/Statistic.h"
33 STATISTIC(NumTails , "Number of tails duplicated");
34 STATISTIC(NumTailDups , "Number of tail duplicated blocks");
35 STATISTIC(NumInstrDups , "Additional instructions due to tail duplication");
36 STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
37 STATISTIC(NumAddedPHIs , "Number of phis added");
39 // Heuristic for tail duplication.
40 static cl::opt<unsigned>
41 TailDuplicateSize("tail-dup-size",
42 cl::desc("Maximum instructions to consider tail duplicating"),
43 cl::init(2), cl::Hidden);
46 TailDupVerify("tail-dup-verify",
47 cl::desc("Verify sanity of PHI instructions during taildup"),
48 cl::init(false), cl::Hidden);
50 static cl::opt<unsigned>
51 TailDupLimit("tail-dup-limit", cl::init(~0U), cl::Hidden);
53 typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy;
56 /// TailDuplicatePass - Perform tail duplication.
57 class TailDuplicatePass : public MachineFunctionPass {
59 const TargetInstrInfo *TII;
60 MachineModuleInfo *MMI;
61 MachineRegisterInfo *MRI;
63 // SSAUpdateVRs - A list of virtual registers for which to update SSA form.
64 SmallVector<unsigned, 16> SSAUpdateVRs;
66 // SSAUpdateVals - For each virtual register in SSAUpdateVals keep a list of
67 // source virtual registers.
68 DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;
72 explicit TailDuplicatePass(bool PreRA) :
73 MachineFunctionPass(ID), PreRegAlloc(PreRA) {}
75 virtual bool runOnMachineFunction(MachineFunction &MF);
76 virtual const char *getPassName() const { return "Tail Duplication"; }
79 void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
80 MachineBasicBlock *BB);
81 void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
82 MachineBasicBlock *PredBB,
83 DenseMap<unsigned, unsigned> &LocalVRMap,
84 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies,
85 const DenseSet<unsigned> &UsedByPhi,
87 void DuplicateInstruction(MachineInstr *MI,
88 MachineBasicBlock *TailBB,
89 MachineBasicBlock *PredBB,
91 DenseMap<unsigned, unsigned> &LocalVRMap,
92 const DenseSet<unsigned> &UsedByPhi);
93 void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
94 SmallVector<MachineBasicBlock*, 8> &TDBBs,
95 SmallSetVector<MachineBasicBlock*, 8> &Succs);
96 bool TailDuplicateBlocks(MachineFunction &MF);
97 bool shouldTailDuplicate(const MachineFunction &MF,
98 bool IsSimple, MachineBasicBlock &TailBB);
99 bool isSimpleBB(MachineBasicBlock *TailBB);
100 bool canCompletelyDuplicateBB(MachineBasicBlock &BB);
101 bool duplicateSimpleBB(MachineBasicBlock *TailBB,
102 SmallVector<MachineBasicBlock*, 8> &TDBBs,
103 const DenseSet<unsigned> &RegsUsedByPhi,
104 SmallVector<MachineInstr*, 16> &Copies);
105 bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
106 SmallVector<MachineBasicBlock*, 8> &TDBBs,
107 SmallVector<MachineInstr*, 16> &Copies);
108 void RemoveDeadBlock(MachineBasicBlock *MBB);
111 char TailDuplicatePass::ID = 0;
114 FunctionPass *llvm::createTailDuplicatePass(bool PreRegAlloc) {
115 return new TailDuplicatePass(PreRegAlloc);
118 bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
119 TII = MF.getTarget().getInstrInfo();
120 MRI = &MF.getRegInfo();
121 MMI = getAnalysisIfAvailable<MachineModuleInfo>();
123 bool MadeChange = false;
124 while (TailDuplicateBlocks(MF))
130 static void VerifyPHIs(MachineFunction &MF, bool CheckExtra) {
131 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ++I) {
132 MachineBasicBlock *MBB = I;
133 SmallSetVector<MachineBasicBlock*, 8> Preds(MBB->pred_begin(),
135 MachineBasicBlock::iterator MI = MBB->begin();
136 while (MI != MBB->end()) {
139 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
140 PE = Preds.end(); PI != PE; ++PI) {
141 MachineBasicBlock *PredBB = *PI;
143 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
144 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
145 if (PHIBB == PredBB) {
151 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
152 dbgs() << " missing input from predecessor BB#"
153 << PredBB->getNumber() << '\n';
158 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
159 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
160 if (CheckExtra && !Preds.count(PHIBB)) {
161 dbgs() << "Warning: malformed PHI in BB#" << MBB->getNumber()
163 dbgs() << " extra input from predecessor BB#"
164 << PHIBB->getNumber() << '\n';
167 if (PHIBB->getNumber() < 0) {
168 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
169 dbgs() << " non-existing BB#" << PHIBB->getNumber() << '\n';
178 /// TailDuplicateBlocks - Look for small blocks that are unconditionally
179 /// branched to and do not fall through. Tail-duplicate their instructions
180 /// into their predecessors to eliminate (dynamic) branches.
181 bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
182 bool MadeChange = false;
184 if (PreRegAlloc && TailDupVerify) {
185 DEBUG(dbgs() << "\n*** Before tail-duplicating\n");
186 VerifyPHIs(MF, true);
189 SmallVector<MachineInstr*, 8> NewPHIs;
190 MachineSSAUpdater SSAUpdate(MF, &NewPHIs);
192 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
193 MachineBasicBlock *MBB = I++;
195 if (NumTails == TailDupLimit)
198 // Save the successors list.
199 SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
202 SmallVector<MachineBasicBlock*, 8> TDBBs;
203 SmallVector<MachineInstr*, 16> Copies;
204 if (!TailDuplicate(MBB, MF, TDBBs, Copies))
209 // TailBB's immediate successors are now successors of those predecessors
210 // which duplicated TailBB. Add the predecessors as sources to the PHI
212 bool isDead = MBB->pred_empty() && !MBB->hasAddressTaken();
214 UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
216 // If it is dead, remove it.
218 NumInstrDups -= MBB->size();
219 RemoveDeadBlock(MBB);
224 if (!SSAUpdateVRs.empty()) {
226 for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
227 unsigned VReg = SSAUpdateVRs[i];
228 SSAUpdate.Initialize(VReg);
230 // If the original definition is still around, add it as an available
232 MachineInstr *DefMI = MRI->getVRegDef(VReg);
233 MachineBasicBlock *DefBB = 0;
235 DefBB = DefMI->getParent();
236 SSAUpdate.AddAvailableValue(DefBB, VReg);
239 // Add the new vregs as available values.
240 DenseMap<unsigned, AvailableValsTy>::iterator LI =
241 SSAUpdateVals.find(VReg);
242 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
243 MachineBasicBlock *SrcBB = LI->second[j].first;
244 unsigned SrcReg = LI->second[j].second;
245 SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
248 // Rewrite uses that are outside of the original def's block.
249 MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
250 while (UI != MRI->use_end()) {
251 MachineOperand &UseMO = UI.getOperand();
252 MachineInstr *UseMI = &*UI;
254 if (UseMI->isDebugValue()) {
255 // SSAUpdate can replace the use with an undef. That creates
256 // a debug instruction that is a kill.
257 // FIXME: Should it SSAUpdate job to delete debug instructions
258 // instead of replacing the use with undef?
259 UseMI->eraseFromParent();
262 if (UseMI->getParent() == DefBB && !UseMI->isPHI())
264 SSAUpdate.RewriteUse(UseMO);
268 SSAUpdateVRs.clear();
269 SSAUpdateVals.clear();
272 // Eliminate some of the copies inserted by tail duplication to maintain
274 for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
275 MachineInstr *Copy = Copies[i];
278 unsigned Dst = Copy->getOperand(0).getReg();
279 unsigned Src = Copy->getOperand(1).getReg();
280 MachineRegisterInfo::use_iterator UI = MRI->use_begin(Src);
281 if (++UI == MRI->use_end()) {
282 // Copy is the only use. Do trivial copy propagation here.
283 MRI->replaceRegWith(Dst, Src);
284 Copy->eraseFromParent();
288 if (PreRegAlloc && TailDupVerify)
289 VerifyPHIs(MF, false);
293 NumAddedPHIs += NewPHIs.size();
300 static bool isDefLiveOut(unsigned Reg, MachineBasicBlock *BB,
301 const MachineRegisterInfo *MRI) {
302 for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
303 UE = MRI->use_end(); UI != UE; ++UI) {
304 MachineInstr *UseMI = &*UI;
305 if (UseMI->isDebugValue())
307 if (UseMI->getParent() != BB)
313 static unsigned getPHISrcRegOpIdx(MachineInstr *MI, MachineBasicBlock *SrcBB) {
314 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2)
315 if (MI->getOperand(i+1).getMBB() == SrcBB)
321 // Remember which registers are used by phis in this block. This is
322 // used to determine which registers are liveout while modifying the
323 // block (which is why we need to copy the information).
324 static void getRegsUsedByPHIs(const MachineBasicBlock &BB,
325 DenseSet<unsigned> *UsedByPhi) {
326 for(MachineBasicBlock::const_iterator I = BB.begin(), E = BB.end();
328 const MachineInstr &MI = *I;
331 for (unsigned i = 1, e = MI.getNumOperands(); i != e; i += 2) {
332 unsigned SrcReg = MI.getOperand(i).getReg();
333 UsedByPhi->insert(SrcReg);
338 /// AddSSAUpdateEntry - Add a definition and source virtual registers pair for
340 void TailDuplicatePass::AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
341 MachineBasicBlock *BB) {
342 DenseMap<unsigned, AvailableValsTy>::iterator LI= SSAUpdateVals.find(OrigReg);
343 if (LI != SSAUpdateVals.end())
344 LI->second.push_back(std::make_pair(BB, NewReg));
346 AvailableValsTy Vals;
347 Vals.push_back(std::make_pair(BB, NewReg));
348 SSAUpdateVals.insert(std::make_pair(OrigReg, Vals));
349 SSAUpdateVRs.push_back(OrigReg);
353 /// ProcessPHI - Process PHI node in TailBB by turning it into a copy in PredBB.
354 /// Remember the source register that's contributed by PredBB and update SSA
356 void TailDuplicatePass::ProcessPHI(MachineInstr *MI,
357 MachineBasicBlock *TailBB,
358 MachineBasicBlock *PredBB,
359 DenseMap<unsigned, unsigned> &LocalVRMap,
360 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies,
361 const DenseSet<unsigned> &RegsUsedByPhi,
363 unsigned DefReg = MI->getOperand(0).getReg();
364 unsigned SrcOpIdx = getPHISrcRegOpIdx(MI, PredBB);
365 assert(SrcOpIdx && "Unable to find matching PHI source?");
366 unsigned SrcReg = MI->getOperand(SrcOpIdx).getReg();
367 const TargetRegisterClass *RC = MRI->getRegClass(DefReg);
368 LocalVRMap.insert(std::make_pair(DefReg, SrcReg));
370 // Insert a copy from source to the end of the block. The def register is the
371 // available value liveout of the block.
372 unsigned NewDef = MRI->createVirtualRegister(RC);
373 Copies.push_back(std::make_pair(NewDef, SrcReg));
374 if (isDefLiveOut(DefReg, TailBB, MRI) || RegsUsedByPhi.count(DefReg))
375 AddSSAUpdateEntry(DefReg, NewDef, PredBB);
380 // Remove PredBB from the PHI node.
381 MI->RemoveOperand(SrcOpIdx+1);
382 MI->RemoveOperand(SrcOpIdx);
383 if (MI->getNumOperands() == 1)
384 MI->eraseFromParent();
387 /// DuplicateInstruction - Duplicate a TailBB instruction to PredBB and update
388 /// the source operands due to earlier PHI translation.
389 void TailDuplicatePass::DuplicateInstruction(MachineInstr *MI,
390 MachineBasicBlock *TailBB,
391 MachineBasicBlock *PredBB,
393 DenseMap<unsigned, unsigned> &LocalVRMap,
394 const DenseSet<unsigned> &UsedByPhi) {
395 MachineInstr *NewMI = TII->duplicate(MI, MF);
396 for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
397 MachineOperand &MO = NewMI->getOperand(i);
400 unsigned Reg = MO.getReg();
401 if (!TargetRegisterInfo::isVirtualRegister(Reg))
404 const TargetRegisterClass *RC = MRI->getRegClass(Reg);
405 unsigned NewReg = MRI->createVirtualRegister(RC);
407 LocalVRMap.insert(std::make_pair(Reg, NewReg));
408 if (isDefLiveOut(Reg, TailBB, MRI) || UsedByPhi.count(Reg))
409 AddSSAUpdateEntry(Reg, NewReg, PredBB);
411 DenseMap<unsigned, unsigned>::iterator VI = LocalVRMap.find(Reg);
412 if (VI != LocalVRMap.end())
413 MO.setReg(VI->second);
416 PredBB->insert(PredBB->end(), NewMI);
419 /// UpdateSuccessorsPHIs - After FromBB is tail duplicated into its predecessor
420 /// blocks, the successors have gained new predecessors. Update the PHI
421 /// instructions in them accordingly.
423 TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
424 SmallVector<MachineBasicBlock*, 8> &TDBBs,
425 SmallSetVector<MachineBasicBlock*,8> &Succs) {
426 for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(),
427 SE = Succs.end(); SI != SE; ++SI) {
428 MachineBasicBlock *SuccBB = *SI;
429 for (MachineBasicBlock::iterator II = SuccBB->begin(), EE = SuccBB->end();
434 for (unsigned i = 1, e = II->getNumOperands(); i != e; i += 2) {
435 MachineOperand &MO = II->getOperand(i+1);
436 if (MO.getMBB() == FromBB) {
443 MachineOperand &MO0 = II->getOperand(Idx);
444 unsigned Reg = MO0.getReg();
446 // Folded into the previous BB.
447 // There could be duplicate phi source entries. FIXME: Should sdisel
448 // or earlier pass fixed this?
449 for (unsigned i = II->getNumOperands()-2; i != Idx; i -= 2) {
450 MachineOperand &MO = II->getOperand(i+1);
451 if (MO.getMBB() == FromBB) {
452 II->RemoveOperand(i+1);
453 II->RemoveOperand(i);
459 // If Idx is set, the operands at Idx and Idx+1 must be removed.
460 // We reuse the location to avoid expensive RemoveOperand calls.
462 DenseMap<unsigned,AvailableValsTy>::iterator LI=SSAUpdateVals.find(Reg);
463 if (LI != SSAUpdateVals.end()) {
464 // This register is defined in the tail block.
465 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
466 MachineBasicBlock *SrcBB = LI->second[j].first;
467 // If we didn't duplicate a bb into a particular predecessor, we
468 // might still have added an entry to SSAUpdateVals to correcly
469 // recompute SSA. If that case, avoid adding a dummy extra argument
471 if (!SrcBB->isSuccessor(SuccBB))
474 unsigned SrcReg = LI->second[j].second;
476 II->getOperand(Idx).setReg(SrcReg);
477 II->getOperand(Idx+1).setMBB(SrcBB);
480 II->addOperand(MachineOperand::CreateReg(SrcReg, false));
481 II->addOperand(MachineOperand::CreateMBB(SrcBB));
485 // Live in tail block, must also be live in predecessors.
486 for (unsigned j = 0, ee = TDBBs.size(); j != ee; ++j) {
487 MachineBasicBlock *SrcBB = TDBBs[j];
489 II->getOperand(Idx).setReg(Reg);
490 II->getOperand(Idx+1).setMBB(SrcBB);
493 II->addOperand(MachineOperand::CreateReg(Reg, false));
494 II->addOperand(MachineOperand::CreateMBB(SrcBB));
499 II->RemoveOperand(Idx+1);
500 II->RemoveOperand(Idx);
506 /// shouldTailDuplicate - Determine if it is profitable to duplicate this block.
508 TailDuplicatePass::shouldTailDuplicate(const MachineFunction &MF,
510 MachineBasicBlock &TailBB) {
511 // Only duplicate blocks that end with unconditional branches.
512 if (TailBB.canFallThrough())
515 // Don't try to tail-duplicate single-block loops.
516 if (TailBB.isSuccessor(&TailBB))
519 // Set the limit on the cost to duplicate. When optimizing for size,
520 // duplicate only one, because one branch instruction can be eliminated to
521 // compensate for the duplication.
522 unsigned MaxDuplicateCount;
523 if (TailDuplicateSize.getNumOccurrences() == 0 &&
524 MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
525 MaxDuplicateCount = 1;
527 MaxDuplicateCount = TailDuplicateSize;
529 // If the target has hardware branch prediction that can handle indirect
530 // branches, duplicating them can often make them predictable when there
531 // are common paths through the code. The limit needs to be high enough
532 // to allow undoing the effects of tail merging and other optimizations
533 // that rearrange the predecessors of the indirect branch.
535 bool hasIndirectBR = false;
536 if (PreRegAlloc && !TailBB.empty()) {
537 const MCInstrDesc &MCID = TailBB.back().getDesc();
538 if (MCID.isIndirectBranch()) {
539 MaxDuplicateCount = 20;
540 hasIndirectBR = true;
544 // Check the instructions in the block to determine whether tail-duplication
545 // is invalid or unlikely to be profitable.
546 unsigned InstrCount = 0;
547 for (MachineBasicBlock::const_iterator I = TailBB.begin(); I != TailBB.end();
549 // Non-duplicable things shouldn't be tail-duplicated.
550 if (I->getDesc().isNotDuplicable())
553 // Do not duplicate 'return' instructions if this is a pre-regalloc run.
554 // A return may expand into a lot more instructions (e.g. reload of callee
555 // saved registers) after PEI.
556 if (PreRegAlloc && I->getDesc().isReturn())
559 // Avoid duplicating calls before register allocation. Calls presents a
560 // barrier to register allocation so duplicating them may end up increasing
562 if (PreRegAlloc && I->getDesc().isCall())
565 if (!I->isPHI() && !I->isDebugValue())
568 if (InstrCount > MaxDuplicateCount)
581 return canCompletelyDuplicateBB(TailBB);
584 /// isSimpleBB - True if this BB has only one unconditional jump.
586 TailDuplicatePass::isSimpleBB(MachineBasicBlock *TailBB) {
587 if (TailBB->succ_size() != 1)
589 if (TailBB->pred_empty())
591 MachineBasicBlock::iterator I = TailBB->begin();
592 MachineBasicBlock::iterator E = TailBB->end();
593 while (I != E && I->isDebugValue())
597 return I->getDesc().isUnconditionalBranch();
601 bothUsedInPHI(const MachineBasicBlock &A,
602 SmallPtrSet<MachineBasicBlock*, 8> SuccsB) {
603 for (MachineBasicBlock::const_succ_iterator SI = A.succ_begin(),
604 SE = A.succ_end(); SI != SE; ++SI) {
605 MachineBasicBlock *BB = *SI;
606 if (SuccsB.count(BB) && !BB->empty() && BB->begin()->isPHI())
614 TailDuplicatePass::canCompletelyDuplicateBB(MachineBasicBlock &BB) {
615 SmallPtrSet<MachineBasicBlock*, 8> Succs(BB.succ_begin(), BB.succ_end());
617 for (MachineBasicBlock::pred_iterator PI = BB.pred_begin(),
618 PE = BB.pred_end(); PI != PE; ++PI) {
619 MachineBasicBlock *PredBB = *PI;
621 if (PredBB->succ_size() > 1)
624 MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
625 SmallVector<MachineOperand, 4> PredCond;
626 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
629 if (!PredCond.empty())
636 TailDuplicatePass::duplicateSimpleBB(MachineBasicBlock *TailBB,
637 SmallVector<MachineBasicBlock*, 8> &TDBBs,
638 const DenseSet<unsigned> &UsedByPhi,
639 SmallVector<MachineInstr*, 16> &Copies) {
640 SmallPtrSet<MachineBasicBlock*, 8> Succs(TailBB->succ_begin(),
642 SmallVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
644 bool Changed = false;
645 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
646 PE = Preds.end(); PI != PE; ++PI) {
647 MachineBasicBlock *PredBB = *PI;
649 if (PredBB->getLandingPadSuccessor())
652 if (bothUsedInPHI(*PredBB, Succs))
655 MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
656 SmallVector<MachineOperand, 4> PredCond;
657 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
661 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
662 << "From simple Succ: " << *TailBB);
664 MachineBasicBlock *NewTarget = *TailBB->succ_begin();
665 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(PredBB));
667 // Make PredFBB explicit.
668 if (PredCond.empty())
671 // Make fall through explicit.
678 if (PredFBB == TailBB)
680 if (PredTBB == TailBB)
683 // Make the branch unconditional if possible
684 if (PredTBB == PredFBB) {
689 // Avoid adding fall through branches.
690 if (PredFBB == NextBB)
692 if (PredTBB == NextBB && PredFBB == NULL)
695 TII->RemoveBranch(*PredBB);
698 TII->InsertBranch(*PredBB, PredTBB, PredFBB, PredCond, DebugLoc());
700 PredBB->removeSuccessor(TailBB);
701 unsigned NumSuccessors = PredBB->succ_size();
702 assert(NumSuccessors <= 1);
703 if (NumSuccessors == 0 || *PredBB->succ_begin() != NewTarget)
704 PredBB->addSuccessor(NewTarget);
706 TDBBs.push_back(PredBB);
711 /// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
712 /// of its predecessors.
714 TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
715 SmallVector<MachineBasicBlock*, 8> &TDBBs,
716 SmallVector<MachineInstr*, 16> &Copies) {
717 bool IsSimple = isSimpleBB(TailBB);
719 if (!shouldTailDuplicate(MF, IsSimple, *TailBB))
722 DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');
724 DenseSet<unsigned> UsedByPhi;
725 getRegsUsedByPHIs(*TailBB, &UsedByPhi);
728 return duplicateSimpleBB(TailBB, TDBBs, UsedByPhi, Copies);
730 // Iterate through all the unique predecessors and tail-duplicate this
731 // block into them, if possible. Copying the list ahead of time also
732 // avoids trouble with the predecessor list reallocating.
733 bool Changed = false;
734 SmallSetVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
736 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
737 PE = Preds.end(); PI != PE; ++PI) {
738 MachineBasicBlock *PredBB = *PI;
740 assert(TailBB != PredBB &&
741 "Single-block loop should have been rejected earlier!");
742 // EH edges are ignored by AnalyzeBranch.
743 if (PredBB->succ_size() > 1)
746 MachineBasicBlock *PredTBB, *PredFBB;
747 SmallVector<MachineOperand, 4> PredCond;
748 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
750 if (!PredCond.empty())
752 // Don't duplicate into a fall-through predecessor (at least for now).
753 if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
756 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
757 << "From Succ: " << *TailBB);
759 TDBBs.push_back(PredBB);
761 // Remove PredBB's unconditional branch.
762 TII->RemoveBranch(*PredBB);
764 // Clone the contents of TailBB into PredBB.
765 DenseMap<unsigned, unsigned> LocalVRMap;
766 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
767 MachineBasicBlock::iterator I = TailBB->begin();
768 while (I != TailBB->end()) {
769 MachineInstr *MI = &*I;
772 // Replace the uses of the def of the PHI with the register coming
774 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, true);
776 // Replace def of virtual registers with new registers, and update
777 // uses with PHI source register or the new registers.
778 DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap, UsedByPhi);
781 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
782 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
783 Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
784 TII->get(TargetOpcode::COPY),
785 CopyInfos[i].first).addReg(CopyInfos[i].second));
789 TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
791 NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
794 PredBB->removeSuccessor(PredBB->succ_begin());
795 assert(PredBB->succ_empty() &&
796 "TailDuplicate called on block with multiple successors!");
797 for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
798 E = TailBB->succ_end(); I != E; ++I)
799 PredBB->addSuccessor(*I);
805 // If TailBB was duplicated into all its predecessors except for the prior
806 // block, which falls through unconditionally, move the contents of this
807 // block into the prior block.
808 MachineBasicBlock *PrevBB = prior(MachineFunction::iterator(TailBB));
809 MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
810 SmallVector<MachineOperand, 4> PriorCond;
811 // This has to check PrevBB->succ_size() because EH edges are ignored by
813 if (PrevBB->succ_size() == 1 &&
814 !TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true) &&
815 PriorCond.empty() && !PriorTBB && TailBB->pred_size() == 1 &&
816 !TailBB->hasAddressTaken()) {
817 DEBUG(dbgs() << "\nMerging into block: " << *PrevBB
818 << "From MBB: " << *TailBB);
820 DenseMap<unsigned, unsigned> LocalVRMap;
821 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
822 MachineBasicBlock::iterator I = TailBB->begin();
823 // Process PHI instructions first.
824 while (I != TailBB->end() && I->isPHI()) {
825 // Replace the uses of the def of the PHI with the register coming
827 MachineInstr *MI = &*I++;
828 ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos, UsedByPhi, true);
830 MI->eraseFromParent();
833 // Now copy the non-PHI instructions.
834 while (I != TailBB->end()) {
835 // Replace def of virtual registers with new registers, and update
836 // uses with PHI source register or the new registers.
837 MachineInstr *MI = &*I++;
838 DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap, UsedByPhi);
839 MI->eraseFromParent();
841 MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
842 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
843 Copies.push_back(BuildMI(*PrevBB, Loc, DebugLoc(),
844 TII->get(TargetOpcode::COPY),
846 .addReg(CopyInfos[i].second));
849 // No PHIs to worry about, just splice the instructions over.
850 PrevBB->splice(PrevBB->end(), TailBB, TailBB->begin(), TailBB->end());
852 PrevBB->removeSuccessor(PrevBB->succ_begin());
853 assert(PrevBB->succ_empty());
854 PrevBB->transferSuccessors(TailBB);
855 TDBBs.push_back(PrevBB);
859 // If this is after register allocation, there are no phis to fix.
863 // If we made no changes so far, we are safe.
868 // Handle the nasty case in that we duplicated a block that is part of a loop
869 // into some but not all of its predecessors. For example:
873 // if we duplicate 2 into 1 but not into 3, we end up with
874 // 12 -> 3 <-> 2 -> rest |
877 // If there was a "var = phi(1, 3)" in 2, it has to be ultimately replaced
878 // with a phi in 3 (which now dominates 2).
879 // What we do here is introduce a copy in 3 of the register defined by the
880 // phi, just like when we are duplicating 2 into 3, but we don't copy any
881 // real instructions or remove the 3 -> 2 edge from the phi in 2.
882 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
883 PE = Preds.end(); PI != PE; ++PI) {
884 MachineBasicBlock *PredBB = *PI;
885 if (std::find(TDBBs.begin(), TDBBs.end(), PredBB) != TDBBs.end())
889 if (PredBB->succ_size() != 1)
892 DenseMap<unsigned, unsigned> LocalVRMap;
893 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
894 MachineBasicBlock::iterator I = TailBB->begin();
895 // Process PHI instructions first.
896 while (I != TailBB->end() && I->isPHI()) {
897 // Replace the uses of the def of the PHI with the register coming
899 MachineInstr *MI = &*I++;
900 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, false);
902 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
903 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
904 Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
905 TII->get(TargetOpcode::COPY),
906 CopyInfos[i].first).addReg(CopyInfos[i].second));
913 /// RemoveDeadBlock - Remove the specified dead machine basic block from the
914 /// function, updating the CFG.
915 void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
916 assert(MBB->pred_empty() && "MBB must be dead!");
917 DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
919 // Remove all successors.
920 while (!MBB->succ_empty())
921 MBB->removeSuccessor(MBB->succ_end()-1);
924 MBB->eraseFromParent();