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)) {
207 // TailBB's immediate successors are now successors of those predecessors
208 // which duplicated TailBB. Add the predecessors as sources to the PHI
210 bool isDead = MBB->pred_empty() && !MBB->hasAddressTaken();
212 UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
214 // If it is dead, remove it.
216 NumInstrDups -= MBB->size();
217 RemoveDeadBlock(MBB);
222 if (!SSAUpdateVRs.empty()) {
223 for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
224 unsigned VReg = SSAUpdateVRs[i];
225 SSAUpdate.Initialize(VReg);
227 // If the original definition is still around, add it as an available
229 MachineInstr *DefMI = MRI->getVRegDef(VReg);
230 MachineBasicBlock *DefBB = 0;
232 DefBB = DefMI->getParent();
233 SSAUpdate.AddAvailableValue(DefBB, VReg);
236 // Add the new vregs as available values.
237 DenseMap<unsigned, AvailableValsTy>::iterator LI =
238 SSAUpdateVals.find(VReg);
239 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
240 MachineBasicBlock *SrcBB = LI->second[j].first;
241 unsigned SrcReg = LI->second[j].second;
242 SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
245 // Rewrite uses that are outside of the original def's block.
246 MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
247 while (UI != MRI->use_end()) {
248 MachineOperand &UseMO = UI.getOperand();
249 MachineInstr *UseMI = &*UI;
251 if (UseMI->isDebugValue()) {
252 // SSAUpdate can replace the use with an undef. That creates
253 // a debug instruction that is a kill.
254 // FIXME: Should it SSAUpdate job to delete debug instructions
255 // instead of replacing the use with undef?
256 UseMI->eraseFromParent();
259 if (UseMI->getParent() == DefBB && !UseMI->isPHI())
261 SSAUpdate.RewriteUse(UseMO);
265 SSAUpdateVRs.clear();
266 SSAUpdateVals.clear();
269 // Eliminate some of the copies inserted by tail duplication to maintain
271 for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
272 MachineInstr *Copy = Copies[i];
275 unsigned Dst = Copy->getOperand(0).getReg();
276 unsigned Src = Copy->getOperand(1).getReg();
277 MachineRegisterInfo::use_iterator UI = MRI->use_begin(Src);
278 if (++UI == MRI->use_end()) {
279 // Copy is the only use. Do trivial copy propagation here.
280 MRI->replaceRegWith(Dst, Src);
281 Copy->eraseFromParent();
285 if (PreRegAlloc && TailDupVerify)
286 VerifyPHIs(MF, false);
290 NumAddedPHIs += NewPHIs.size();
295 static bool isDefLiveOut(unsigned Reg, MachineBasicBlock *BB,
296 const MachineRegisterInfo *MRI) {
297 for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
298 UE = MRI->use_end(); UI != UE; ++UI) {
299 MachineInstr *UseMI = &*UI;
300 if (UseMI->isDebugValue())
302 if (UseMI->getParent() != BB)
308 static unsigned getPHISrcRegOpIdx(MachineInstr *MI, MachineBasicBlock *SrcBB) {
309 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2)
310 if (MI->getOperand(i+1).getMBB() == SrcBB)
316 // Remember which registers are used by phis in this block. This is
317 // used to determine which registers are liveout while modifying the
318 // block (which is why we need to copy the information).
319 static void getRegsUsedByPHIs(const MachineBasicBlock &BB,
320 DenseSet<unsigned> *UsedByPhi) {
321 for(MachineBasicBlock::const_iterator I = BB.begin(), E = BB.end();
323 const MachineInstr &MI = *I;
326 for (unsigned i = 1, e = MI.getNumOperands(); i != e; i += 2) {
327 unsigned SrcReg = MI.getOperand(i).getReg();
328 UsedByPhi->insert(SrcReg);
333 /// AddSSAUpdateEntry - Add a definition and source virtual registers pair for
335 void TailDuplicatePass::AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
336 MachineBasicBlock *BB) {
337 DenseMap<unsigned, AvailableValsTy>::iterator LI= SSAUpdateVals.find(OrigReg);
338 if (LI != SSAUpdateVals.end())
339 LI->second.push_back(std::make_pair(BB, NewReg));
341 AvailableValsTy Vals;
342 Vals.push_back(std::make_pair(BB, NewReg));
343 SSAUpdateVals.insert(std::make_pair(OrigReg, Vals));
344 SSAUpdateVRs.push_back(OrigReg);
348 /// ProcessPHI - Process PHI node in TailBB by turning it into a copy in PredBB.
349 /// Remember the source register that's contributed by PredBB and update SSA
351 void TailDuplicatePass::ProcessPHI(MachineInstr *MI,
352 MachineBasicBlock *TailBB,
353 MachineBasicBlock *PredBB,
354 DenseMap<unsigned, unsigned> &LocalVRMap,
355 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies,
356 const DenseSet<unsigned> &RegsUsedByPhi,
358 unsigned DefReg = MI->getOperand(0).getReg();
359 unsigned SrcOpIdx = getPHISrcRegOpIdx(MI, PredBB);
360 assert(SrcOpIdx && "Unable to find matching PHI source?");
361 unsigned SrcReg = MI->getOperand(SrcOpIdx).getReg();
362 const TargetRegisterClass *RC = MRI->getRegClass(DefReg);
363 LocalVRMap.insert(std::make_pair(DefReg, SrcReg));
365 // Insert a copy from source to the end of the block. The def register is the
366 // available value liveout of the block.
367 unsigned NewDef = MRI->createVirtualRegister(RC);
368 Copies.push_back(std::make_pair(NewDef, SrcReg));
369 if (isDefLiveOut(DefReg, TailBB, MRI) || RegsUsedByPhi.count(DefReg))
370 AddSSAUpdateEntry(DefReg, NewDef, PredBB);
375 // Remove PredBB from the PHI node.
376 MI->RemoveOperand(SrcOpIdx+1);
377 MI->RemoveOperand(SrcOpIdx);
378 if (MI->getNumOperands() == 1)
379 MI->eraseFromParent();
382 /// DuplicateInstruction - Duplicate a TailBB instruction to PredBB and update
383 /// the source operands due to earlier PHI translation.
384 void TailDuplicatePass::DuplicateInstruction(MachineInstr *MI,
385 MachineBasicBlock *TailBB,
386 MachineBasicBlock *PredBB,
388 DenseMap<unsigned, unsigned> &LocalVRMap,
389 const DenseSet<unsigned> &UsedByPhi) {
390 MachineInstr *NewMI = TII->duplicate(MI, MF);
391 for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
392 MachineOperand &MO = NewMI->getOperand(i);
395 unsigned Reg = MO.getReg();
396 if (!TargetRegisterInfo::isVirtualRegister(Reg))
399 const TargetRegisterClass *RC = MRI->getRegClass(Reg);
400 unsigned NewReg = MRI->createVirtualRegister(RC);
402 LocalVRMap.insert(std::make_pair(Reg, NewReg));
403 if (isDefLiveOut(Reg, TailBB, MRI) || UsedByPhi.count(Reg))
404 AddSSAUpdateEntry(Reg, NewReg, PredBB);
406 DenseMap<unsigned, unsigned>::iterator VI = LocalVRMap.find(Reg);
407 if (VI != LocalVRMap.end())
408 MO.setReg(VI->second);
411 PredBB->insert(PredBB->end(), NewMI);
414 /// UpdateSuccessorsPHIs - After FromBB is tail duplicated into its predecessor
415 /// blocks, the successors have gained new predecessors. Update the PHI
416 /// instructions in them accordingly.
418 TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
419 SmallVector<MachineBasicBlock*, 8> &TDBBs,
420 SmallSetVector<MachineBasicBlock*,8> &Succs) {
421 for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(),
422 SE = Succs.end(); SI != SE; ++SI) {
423 MachineBasicBlock *SuccBB = *SI;
424 for (MachineBasicBlock::iterator II = SuccBB->begin(), EE = SuccBB->end();
429 for (unsigned i = 1, e = II->getNumOperands(); i != e; i += 2) {
430 MachineOperand &MO = II->getOperand(i+1);
431 if (MO.getMBB() == FromBB) {
438 MachineOperand &MO0 = II->getOperand(Idx);
439 unsigned Reg = MO0.getReg();
441 // Folded into the previous BB.
442 // There could be duplicate phi source entries. FIXME: Should sdisel
443 // or earlier pass fixed this?
444 for (unsigned i = II->getNumOperands()-2; i != Idx; i -= 2) {
445 MachineOperand &MO = II->getOperand(i+1);
446 if (MO.getMBB() == FromBB) {
447 II->RemoveOperand(i+1);
448 II->RemoveOperand(i);
454 // If Idx is set, the operands at Idx and Idx+1 must be removed.
455 // We reuse the location to avoid expensive RemoveOperand calls.
457 DenseMap<unsigned,AvailableValsTy>::iterator LI=SSAUpdateVals.find(Reg);
458 if (LI != SSAUpdateVals.end()) {
459 // This register is defined in the tail block.
460 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
461 MachineBasicBlock *SrcBB = LI->second[j].first;
462 // If we didn't duplicate a bb into a particular predecessor, we
463 // might still have added an entry to SSAUpdateVals to correcly
464 // recompute SSA. If that case, avoid adding a dummy extra argument
466 if (!SrcBB->isSuccessor(SuccBB))
469 unsigned SrcReg = LI->second[j].second;
471 II->getOperand(Idx).setReg(SrcReg);
472 II->getOperand(Idx+1).setMBB(SrcBB);
475 II->addOperand(MachineOperand::CreateReg(SrcReg, false));
476 II->addOperand(MachineOperand::CreateMBB(SrcBB));
480 // Live in tail block, must also be live in predecessors.
481 for (unsigned j = 0, ee = TDBBs.size(); j != ee; ++j) {
482 MachineBasicBlock *SrcBB = TDBBs[j];
484 II->getOperand(Idx).setReg(Reg);
485 II->getOperand(Idx+1).setMBB(SrcBB);
488 II->addOperand(MachineOperand::CreateReg(Reg, false));
489 II->addOperand(MachineOperand::CreateMBB(SrcBB));
494 II->RemoveOperand(Idx+1);
495 II->RemoveOperand(Idx);
501 /// shouldTailDuplicate - Determine if it is profitable to duplicate this block.
503 TailDuplicatePass::shouldTailDuplicate(const MachineFunction &MF,
505 MachineBasicBlock &TailBB) {
506 // Only duplicate blocks that end with unconditional branches.
507 if (TailBB.canFallThrough())
510 // Don't try to tail-duplicate single-block loops.
511 if (TailBB.isSuccessor(&TailBB))
514 // Set the limit on the cost to duplicate. When optimizing for size,
515 // duplicate only one, because one branch instruction can be eliminated to
516 // compensate for the duplication.
517 unsigned MaxDuplicateCount;
518 if (TailDuplicateSize.getNumOccurrences() == 0 &&
519 MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
520 MaxDuplicateCount = 1;
522 MaxDuplicateCount = TailDuplicateSize;
524 // If the target has hardware branch prediction that can handle indirect
525 // branches, duplicating them can often make them predictable when there
526 // are common paths through the code. The limit needs to be high enough
527 // to allow undoing the effects of tail merging and other optimizations
528 // that rearrange the predecessors of the indirect branch.
530 bool hasIndirectBR = false;
531 if (PreRegAlloc && !TailBB.empty()) {
532 const MCInstrDesc &MCID = TailBB.back().getDesc();
533 if (MCID.isIndirectBranch()) {
534 MaxDuplicateCount = 20;
535 hasIndirectBR = true;
539 // Check the instructions in the block to determine whether tail-duplication
540 // is invalid or unlikely to be profitable.
541 unsigned InstrCount = 0;
542 for (MachineBasicBlock::const_iterator I = TailBB.begin(); I != TailBB.end();
544 // Non-duplicable things shouldn't be tail-duplicated.
545 if (I->getDesc().isNotDuplicable())
548 // Do not duplicate 'return' instructions if this is a pre-regalloc run.
549 // A return may expand into a lot more instructions (e.g. reload of callee
550 // saved registers) after PEI.
551 if (PreRegAlloc && I->getDesc().isReturn())
554 // Avoid duplicating calls before register allocation. Calls presents a
555 // barrier to register allocation so duplicating them may end up increasing
557 if (PreRegAlloc && I->getDesc().isCall())
560 if (!I->isPHI() && !I->isDebugValue())
563 if (InstrCount > MaxDuplicateCount)
576 return canCompletelyDuplicateBB(TailBB);
579 /// isSimpleBB - True if this BB has only one unconditional jump.
581 TailDuplicatePass::isSimpleBB(MachineBasicBlock *TailBB) {
582 if (TailBB->succ_size() != 1)
584 if (TailBB->pred_empty())
586 MachineBasicBlock::iterator I = TailBB->begin();
587 MachineBasicBlock::iterator E = TailBB->end();
588 while (I != E && I->isDebugValue())
592 return I->getDesc().isUnconditionalBranch();
596 bothUsedInPHI(const MachineBasicBlock &A,
597 SmallPtrSet<MachineBasicBlock*, 8> SuccsB) {
598 for (MachineBasicBlock::const_succ_iterator SI = A.succ_begin(),
599 SE = A.succ_end(); SI != SE; ++SI) {
600 MachineBasicBlock *BB = *SI;
601 if (SuccsB.count(BB) && !BB->empty() && BB->begin()->isPHI())
609 TailDuplicatePass::canCompletelyDuplicateBB(MachineBasicBlock &BB) {
610 SmallPtrSet<MachineBasicBlock*, 8> Succs(BB.succ_begin(), BB.succ_end());
612 for (MachineBasicBlock::pred_iterator PI = BB.pred_begin(),
613 PE = BB.pred_end(); PI != PE; ++PI) {
614 MachineBasicBlock *PredBB = *PI;
616 if (PredBB->succ_size() > 1)
619 MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
620 SmallVector<MachineOperand, 4> PredCond;
621 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
624 if (!PredCond.empty())
631 TailDuplicatePass::duplicateSimpleBB(MachineBasicBlock *TailBB,
632 SmallVector<MachineBasicBlock*, 8> &TDBBs,
633 const DenseSet<unsigned> &UsedByPhi,
634 SmallVector<MachineInstr*, 16> &Copies) {
635 SmallPtrSet<MachineBasicBlock*, 8> Succs(TailBB->succ_begin(),
637 SmallVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
639 bool Changed = false;
640 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
641 PE = Preds.end(); PI != PE; ++PI) {
642 MachineBasicBlock *PredBB = *PI;
644 if (PredBB->getLandingPadSuccessor())
647 if (bothUsedInPHI(*PredBB, Succs))
650 MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
651 SmallVector<MachineOperand, 4> PredCond;
652 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
656 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
657 << "From simple Succ: " << *TailBB);
659 MachineBasicBlock *NewTarget = *TailBB->succ_begin();
660 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(PredBB));
662 // Make PredFBB explicit.
663 if (PredCond.empty())
666 // Make fall through explicit.
673 if (PredFBB == TailBB)
675 if (PredTBB == TailBB)
678 // Make the branch unconditional if possible
679 if (PredTBB == PredFBB) {
684 // Avoid adding fall through branches.
685 if (PredFBB == NextBB)
687 if (PredTBB == NextBB && PredFBB == NULL)
690 TII->RemoveBranch(*PredBB);
693 TII->InsertBranch(*PredBB, PredTBB, PredFBB, PredCond, DebugLoc());
695 PredBB->removeSuccessor(TailBB);
696 unsigned NumSuccessors = PredBB->succ_size();
697 assert(NumSuccessors <= 1);
698 if (NumSuccessors == 0 || *PredBB->succ_begin() != NewTarget)
699 PredBB->addSuccessor(NewTarget);
701 TDBBs.push_back(PredBB);
706 /// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
707 /// of its predecessors.
709 TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
710 SmallVector<MachineBasicBlock*, 8> &TDBBs,
711 SmallVector<MachineInstr*, 16> &Copies) {
712 bool IsSimple = isSimpleBB(TailBB);
714 if (!shouldTailDuplicate(MF, IsSimple, *TailBB))
717 DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');
719 DenseSet<unsigned> UsedByPhi;
720 getRegsUsedByPHIs(*TailBB, &UsedByPhi);
723 return duplicateSimpleBB(TailBB, TDBBs, UsedByPhi, Copies);
725 // Iterate through all the unique predecessors and tail-duplicate this
726 // block into them, if possible. Copying the list ahead of time also
727 // avoids trouble with the predecessor list reallocating.
728 bool Changed = false;
729 SmallSetVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
731 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
732 PE = Preds.end(); PI != PE; ++PI) {
733 MachineBasicBlock *PredBB = *PI;
735 assert(TailBB != PredBB &&
736 "Single-block loop should have been rejected earlier!");
737 // EH edges are ignored by AnalyzeBranch.
738 if (PredBB->succ_size() > 1)
741 MachineBasicBlock *PredTBB, *PredFBB;
742 SmallVector<MachineOperand, 4> PredCond;
743 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
745 if (!PredCond.empty())
747 // Don't duplicate into a fall-through predecessor (at least for now).
748 if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
751 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
752 << "From Succ: " << *TailBB);
754 TDBBs.push_back(PredBB);
756 // Remove PredBB's unconditional branch.
757 TII->RemoveBranch(*PredBB);
759 // Clone the contents of TailBB into PredBB.
760 DenseMap<unsigned, unsigned> LocalVRMap;
761 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
762 MachineBasicBlock::iterator I = TailBB->begin();
763 while (I != TailBB->end()) {
764 MachineInstr *MI = &*I;
767 // Replace the uses of the def of the PHI with the register coming
769 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, true);
771 // Replace def of virtual registers with new registers, and update
772 // uses with PHI source register or the new registers.
773 DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap, UsedByPhi);
776 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
777 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
778 Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
779 TII->get(TargetOpcode::COPY),
780 CopyInfos[i].first).addReg(CopyInfos[i].second));
784 TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
786 NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
789 PredBB->removeSuccessor(PredBB->succ_begin());
790 assert(PredBB->succ_empty() &&
791 "TailDuplicate called on block with multiple successors!");
792 for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
793 E = TailBB->succ_end(); I != E; ++I)
794 PredBB->addSuccessor(*I);
800 // If TailBB was duplicated into all its predecessors except for the prior
801 // block, which falls through unconditionally, move the contents of this
802 // block into the prior block.
803 MachineBasicBlock *PrevBB = prior(MachineFunction::iterator(TailBB));
804 MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
805 SmallVector<MachineOperand, 4> PriorCond;
806 // This has to check PrevBB->succ_size() because EH edges are ignored by
808 if (PrevBB->succ_size() == 1 &&
809 !TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true) &&
810 PriorCond.empty() && !PriorTBB && TailBB->pred_size() == 1 &&
811 !TailBB->hasAddressTaken()) {
812 DEBUG(dbgs() << "\nMerging into block: " << *PrevBB
813 << "From MBB: " << *TailBB);
815 DenseMap<unsigned, unsigned> LocalVRMap;
816 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
817 MachineBasicBlock::iterator I = TailBB->begin();
818 // Process PHI instructions first.
819 while (I != TailBB->end() && I->isPHI()) {
820 // Replace the uses of the def of the PHI with the register coming
822 MachineInstr *MI = &*I++;
823 ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos, UsedByPhi, true);
825 MI->eraseFromParent();
828 // Now copy the non-PHI instructions.
829 while (I != TailBB->end()) {
830 // Replace def of virtual registers with new registers, and update
831 // uses with PHI source register or the new registers.
832 MachineInstr *MI = &*I++;
833 DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap, UsedByPhi);
834 MI->eraseFromParent();
836 MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
837 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
838 Copies.push_back(BuildMI(*PrevBB, Loc, DebugLoc(),
839 TII->get(TargetOpcode::COPY),
841 .addReg(CopyInfos[i].second));
844 // No PHIs to worry about, just splice the instructions over.
845 PrevBB->splice(PrevBB->end(), TailBB, TailBB->begin(), TailBB->end());
847 PrevBB->removeSuccessor(PrevBB->succ_begin());
848 assert(PrevBB->succ_empty());
849 PrevBB->transferSuccessors(TailBB);
850 TDBBs.push_back(PrevBB);
854 // If this is after register allocation, there are no phis to fix.
858 // If we made no changes so far, we are safe.
863 // Handle the nasty case in that we duplicated a block that is part of a loop
864 // into some but not all of its predecessors. For example:
868 // if we duplicate 2 into 1 but not into 3, we end up with
869 // 12 -> 3 <-> 2 -> rest |
872 // If there was a "var = phi(1, 3)" in 2, it has to be ultimately replaced
873 // with a phi in 3 (which now dominates 2).
874 // What we do here is introduce a copy in 3 of the register defined by the
875 // phi, just like when we are duplicating 2 into 3, but we don't copy any
876 // real instructions or remove the 3 -> 2 edge from the phi in 2.
877 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
878 PE = Preds.end(); PI != PE; ++PI) {
879 MachineBasicBlock *PredBB = *PI;
880 if (std::find(TDBBs.begin(), TDBBs.end(), PredBB) != TDBBs.end())
884 if (PredBB->succ_size() != 1)
887 DenseMap<unsigned, unsigned> LocalVRMap;
888 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
889 MachineBasicBlock::iterator I = TailBB->begin();
890 // Process PHI instructions first.
891 while (I != TailBB->end() && I->isPHI()) {
892 // Replace the uses of the def of the PHI with the register coming
894 MachineInstr *MI = &*I++;
895 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, false);
897 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
898 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
899 Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
900 TII->get(TargetOpcode::COPY),
901 CopyInfos[i].first).addReg(CopyInfos[i].second));
908 /// RemoveDeadBlock - Remove the specified dead machine basic block from the
909 /// function, updating the CFG.
910 void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
911 assert(MBB->pred_empty() && "MBB must be dead!");
912 DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
914 // Remove all successors.
915 while (!MBB->succ_empty())
916 MBB->removeSuccessor(MBB->succ_end()-1);
919 MBB->eraseFromParent();