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/MachineRegisterInfo.h"
21 #include "llvm/CodeGen/MachineSSAUpdater.h"
22 #include "llvm/Target/TargetInstrInfo.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/ErrorHandling.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/ADT/SmallSet.h"
28 #include "llvm/ADT/SetVector.h"
29 #include "llvm/ADT/Statistic.h"
32 STATISTIC(NumTails , "Number of tails duplicated");
33 STATISTIC(NumTailDups , "Number of tail duplicated blocks");
34 STATISTIC(NumInstrDups , "Additional instructions due to tail duplication");
35 STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
37 // Heuristic for tail duplication.
38 static cl::opt<unsigned>
39 TailDuplicateSize("tail-dup-size",
40 cl::desc("Maximum instructions to consider tail duplicating"),
41 cl::init(2), cl::Hidden);
44 TailDupVerify("tail-dup-verify",
45 cl::desc("Verify sanity of PHI instructions during taildup"),
46 cl::init(false), cl::Hidden);
48 static cl::opt<unsigned>
49 TailDupLimit("tail-dup-limit", cl::init(~0U), cl::Hidden);
51 typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy;
54 /// TailDuplicatePass - Perform tail duplication.
55 class TailDuplicatePass : public MachineFunctionPass {
57 const TargetInstrInfo *TII;
58 MachineModuleInfo *MMI;
59 MachineRegisterInfo *MRI;
61 // SSAUpdateVRs - A list of virtual registers for which to update SSA form.
62 SmallVector<unsigned, 16> SSAUpdateVRs;
64 // SSAUpdateVals - For each virtual register in SSAUpdateVals keep a list of
65 // source virtual registers.
66 DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;
70 explicit TailDuplicatePass(bool PreRA) :
71 MachineFunctionPass(&ID), PreRegAlloc(PreRA) {}
73 virtual bool runOnMachineFunction(MachineFunction &MF);
74 virtual const char *getPassName() const { return "Tail Duplication"; }
77 void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
78 MachineBasicBlock *BB);
79 void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
80 MachineBasicBlock *PredBB,
81 DenseMap<unsigned, unsigned> &LocalVRMap,
82 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies);
83 void DuplicateInstruction(MachineInstr *MI,
84 MachineBasicBlock *TailBB,
85 MachineBasicBlock *PredBB,
87 DenseMap<unsigned, unsigned> &LocalVRMap);
88 void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
89 SmallVector<MachineBasicBlock*, 8> &TDBBs,
90 SmallSetVector<MachineBasicBlock*, 8> &Succs);
91 bool TailDuplicateBlocks(MachineFunction &MF);
92 bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
93 SmallVector<MachineBasicBlock*, 8> &TDBBs,
94 SmallVector<MachineInstr*, 16> &Copies);
95 void RemoveDeadBlock(MachineBasicBlock *MBB);
98 char TailDuplicatePass::ID = 0;
101 FunctionPass *llvm::createTailDuplicatePass(bool PreRegAlloc) {
102 return new TailDuplicatePass(PreRegAlloc);
105 bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
106 TII = MF.getTarget().getInstrInfo();
107 MRI = &MF.getRegInfo();
108 MMI = getAnalysisIfAvailable<MachineModuleInfo>();
110 bool MadeChange = false;
111 while (TailDuplicateBlocks(MF))
117 static void VerifyPHIs(MachineFunction &MF, bool CheckExtra) {
118 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ++I) {
119 MachineBasicBlock *MBB = I;
120 SmallSetVector<MachineBasicBlock*, 8> Preds(MBB->pred_begin(),
122 MachineBasicBlock::iterator MI = MBB->begin();
123 while (MI != MBB->end()) {
124 if (MI->getOpcode() != TargetInstrInfo::PHI)
126 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
127 PE = Preds.end(); PI != PE; ++PI) {
128 MachineBasicBlock *PredBB = *PI;
130 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
131 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
132 if (PHIBB == PredBB) {
138 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
139 dbgs() << " missing input from predecessor BB#"
140 << PredBB->getNumber() << '\n';
145 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
146 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
147 if (CheckExtra && !Preds.count(PHIBB)) {
148 // This is not a hard error.
149 dbgs() << "Warning: malformed PHI in BB#" << MBB->getNumber()
151 dbgs() << " extra input from predecessor BB#"
152 << PHIBB->getNumber() << '\n';
154 if (PHIBB->getNumber() < 0) {
155 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
156 dbgs() << " non-existing BB#" << PHIBB->getNumber() << '\n';
165 /// TailDuplicateBlocks - Look for small blocks that are unconditionally
166 /// branched to and do not fall through. Tail-duplicate their instructions
167 /// into their predecessors to eliminate (dynamic) branches.
168 bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
169 bool MadeChange = false;
171 if (PreRegAlloc && TailDupVerify) {
172 DEBUG(dbgs() << "\n*** Before tail-duplicating\n");
173 VerifyPHIs(MF, true);
176 SmallVector<MachineInstr*, 8> NewPHIs;
177 MachineSSAUpdater SSAUpdate(MF, &NewPHIs);
179 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
180 MachineBasicBlock *MBB = I++;
182 if (NumTails == TailDupLimit)
185 // Only duplicate blocks that end with unconditional branches.
186 if (MBB->canFallThrough())
189 // Save the successors list.
190 SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
193 SmallVector<MachineBasicBlock*, 8> TDBBs;
194 SmallVector<MachineInstr*, 16> Copies;
195 if (TailDuplicate(MBB, MF, TDBBs, Copies)) {
198 // TailBB's immediate successors are now successors of those predecessors
199 // which duplicated TailBB. Add the predecessors as sources to the PHI
201 bool isDead = MBB->pred_empty();
203 UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
205 // If it is dead, remove it.
207 NumInstrDups -= MBB->size();
208 RemoveDeadBlock(MBB);
213 if (!SSAUpdateVRs.empty()) {
214 for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
215 unsigned VReg = SSAUpdateVRs[i];
216 SSAUpdate.Initialize(VReg);
218 // If the original definition is still around, add it as an available
220 MachineInstr *DefMI = MRI->getVRegDef(VReg);
221 MachineBasicBlock *DefBB = 0;
223 DefBB = DefMI->getParent();
224 SSAUpdate.AddAvailableValue(DefBB, VReg);
227 // Add the new vregs as available values.
228 DenseMap<unsigned, AvailableValsTy>::iterator LI =
229 SSAUpdateVals.find(VReg);
230 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
231 MachineBasicBlock *SrcBB = LI->second[j].first;
232 unsigned SrcReg = LI->second[j].second;
233 SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
236 // Rewrite uses that are outside of the original def's block.
237 MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
238 while (UI != MRI->use_end()) {
239 MachineOperand &UseMO = UI.getOperand();
240 MachineInstr *UseMI = &*UI;
242 if (UseMI->getParent() == DefBB)
244 SSAUpdate.RewriteUse(UseMO);
248 SSAUpdateVRs.clear();
249 SSAUpdateVals.clear();
252 // Eliminate some of the copies inserted by tail duplication to maintain
254 for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
255 MachineInstr *Copy = Copies[i];
256 unsigned Src, Dst, SrcSR, DstSR;
257 if (TII->isMoveInstr(*Copy, Src, Dst, SrcSR, DstSR)) {
258 MachineRegisterInfo::use_iterator UI = MRI->use_begin(Src);
259 if (++UI == MRI->use_end()) {
260 // Copy is the only use. Do trivial copy propagation here.
261 MRI->replaceRegWith(Dst, Src);
262 Copy->eraseFromParent();
267 if (PreRegAlloc && TailDupVerify)
268 VerifyPHIs(MF, false);
276 static bool isDefLiveOut(unsigned Reg, MachineBasicBlock *BB,
277 const MachineRegisterInfo *MRI) {
278 for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
279 UE = MRI->use_end(); UI != UE; ++UI) {
280 MachineInstr *UseMI = &*UI;
281 if (UseMI->getParent() != BB)
287 static unsigned getPHISrcRegOpIdx(MachineInstr *MI, MachineBasicBlock *SrcBB) {
288 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2)
289 if (MI->getOperand(i+1).getMBB() == SrcBB)
294 /// AddSSAUpdateEntry - Add a definition and source virtual registers pair for
296 void TailDuplicatePass::AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
297 MachineBasicBlock *BB) {
298 DenseMap<unsigned, AvailableValsTy>::iterator LI= SSAUpdateVals.find(OrigReg);
299 if (LI != SSAUpdateVals.end())
300 LI->second.push_back(std::make_pair(BB, NewReg));
302 AvailableValsTy Vals;
303 Vals.push_back(std::make_pair(BB, NewReg));
304 SSAUpdateVals.insert(std::make_pair(OrigReg, Vals));
305 SSAUpdateVRs.push_back(OrigReg);
309 /// ProcessPHI - Process PHI node in TailBB by turning it into a copy in PredBB.
310 /// Remember the source register that's contributed by PredBB and update SSA
312 void TailDuplicatePass::ProcessPHI(MachineInstr *MI,
313 MachineBasicBlock *TailBB,
314 MachineBasicBlock *PredBB,
315 DenseMap<unsigned, unsigned> &LocalVRMap,
316 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies) {
317 unsigned DefReg = MI->getOperand(0).getReg();
318 unsigned SrcOpIdx = getPHISrcRegOpIdx(MI, PredBB);
319 assert(SrcOpIdx && "Unable to find matching PHI source?");
320 unsigned SrcReg = MI->getOperand(SrcOpIdx).getReg();
321 const TargetRegisterClass *RC = MRI->getRegClass(DefReg);
322 LocalVRMap.insert(std::make_pair(DefReg, SrcReg));
324 // Insert a copy from source to the end of the block. The def register is the
325 // available value liveout of the block.
326 unsigned NewDef = MRI->createVirtualRegister(RC);
327 Copies.push_back(std::make_pair(NewDef, SrcReg));
328 if (isDefLiveOut(DefReg, TailBB, MRI))
329 AddSSAUpdateEntry(DefReg, NewDef, PredBB);
331 // Remove PredBB from the PHI node.
332 MI->RemoveOperand(SrcOpIdx+1);
333 MI->RemoveOperand(SrcOpIdx);
334 if (MI->getNumOperands() == 1)
335 MI->eraseFromParent();
338 /// DuplicateInstruction - Duplicate a TailBB instruction to PredBB and update
339 /// the source operands due to earlier PHI translation.
340 void TailDuplicatePass::DuplicateInstruction(MachineInstr *MI,
341 MachineBasicBlock *TailBB,
342 MachineBasicBlock *PredBB,
344 DenseMap<unsigned, unsigned> &LocalVRMap) {
345 MachineInstr *NewMI = TII->duplicate(MI, MF);
346 for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
347 MachineOperand &MO = NewMI->getOperand(i);
350 unsigned Reg = MO.getReg();
351 if (!Reg || TargetRegisterInfo::isPhysicalRegister(Reg))
354 const TargetRegisterClass *RC = MRI->getRegClass(Reg);
355 unsigned NewReg = MRI->createVirtualRegister(RC);
357 LocalVRMap.insert(std::make_pair(Reg, NewReg));
358 if (isDefLiveOut(Reg, TailBB, MRI))
359 AddSSAUpdateEntry(Reg, NewReg, PredBB);
361 DenseMap<unsigned, unsigned>::iterator VI = LocalVRMap.find(Reg);
362 if (VI != LocalVRMap.end())
363 MO.setReg(VI->second);
366 PredBB->insert(PredBB->end(), NewMI);
369 /// UpdateSuccessorsPHIs - After FromBB is tail duplicated into its predecessor
370 /// blocks, the successors have gained new predecessors. Update the PHI
371 /// instructions in them accordingly.
373 TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
374 SmallVector<MachineBasicBlock*, 8> &TDBBs,
375 SmallSetVector<MachineBasicBlock*,8> &Succs) {
376 for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(),
377 SE = Succs.end(); SI != SE; ++SI) {
378 MachineBasicBlock *SuccBB = *SI;
379 for (MachineBasicBlock::iterator II = SuccBB->begin(), EE = SuccBB->end();
381 if (II->getOpcode() != TargetInstrInfo::PHI)
384 for (unsigned i = 1, e = II->getNumOperands(); i != e; i += 2) {
385 MachineOperand &MO = II->getOperand(i+1);
386 if (MO.getMBB() == FromBB) {
393 MachineOperand &MO0 = II->getOperand(Idx);
394 unsigned Reg = MO0.getReg();
396 // Folded into the previous BB.
397 // There could be duplicate phi source entries. FIXME: Should sdisel
398 // or earlier pass fixed this?
399 for (unsigned i = II->getNumOperands()-2; i != Idx; i -= 2) {
400 MachineOperand &MO = II->getOperand(i+1);
401 if (MO.getMBB() == FromBB) {
402 II->RemoveOperand(i+1);
403 II->RemoveOperand(i);
406 II->RemoveOperand(Idx+1);
407 II->RemoveOperand(Idx);
409 DenseMap<unsigned,AvailableValsTy>::iterator LI=SSAUpdateVals.find(Reg);
410 if (LI != SSAUpdateVals.end()) {
411 // This register is defined in the tail block.
412 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
413 MachineBasicBlock *SrcBB = LI->second[j].first;
414 unsigned SrcReg = LI->second[j].second;
415 II->addOperand(MachineOperand::CreateReg(SrcReg, false));
416 II->addOperand(MachineOperand::CreateMBB(SrcBB));
419 // Live in tail block, must also be live in predecessors.
420 for (unsigned j = 0, ee = TDBBs.size(); j != ee; ++j) {
421 MachineBasicBlock *SrcBB = TDBBs[j];
422 II->addOperand(MachineOperand::CreateReg(Reg, false));
423 II->addOperand(MachineOperand::CreateMBB(SrcBB));
430 /// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
431 /// of its predecessors.
433 TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
434 SmallVector<MachineBasicBlock*, 8> &TDBBs,
435 SmallVector<MachineInstr*, 16> &Copies) {
436 // Set the limit on the number of instructions to duplicate, with a default
437 // of one less than the tail-merge threshold. When optimizing for size,
438 // duplicate only one, because one branch instruction can be eliminated to
439 // compensate for the duplication.
440 unsigned MaxDuplicateCount;
441 if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
442 MaxDuplicateCount = 1;
444 MaxDuplicateCount = TailDuplicateSize;
447 // Pre-regalloc tail duplication hurts compile time and doesn't help
448 // much except for indirect branches.
449 if (TailBB->empty() || !TailBB->back().getDesc().isIndirectBranch())
451 // If the target has hardware branch prediction that can handle indirect
452 // branches, duplicating them can often make them predictable when there
453 // are common paths through the code. The limit needs to be high enough
454 // to allow undoing the effects of tail merging and other optimizations
455 // that rearrange the predecessors of the indirect branch.
456 MaxDuplicateCount = 20;
459 // Don't try to tail-duplicate single-block loops.
460 if (TailBB->isSuccessor(TailBB))
463 // Check the instructions in the block to determine whether tail-duplication
464 // is invalid or unlikely to be profitable.
465 unsigned InstrCount = 0;
466 bool HasCall = false;
467 for (MachineBasicBlock::iterator I = TailBB->begin();
468 I != TailBB->end(); ++I) {
469 // Non-duplicable things shouldn't be tail-duplicated.
470 if (I->getDesc().isNotDuplicable()) return false;
471 // Do not duplicate 'return' instructions if this is a pre-regalloc run.
472 // A return may expand into a lot more instructions (e.g. reload of callee
473 // saved registers) after PEI.
474 if (PreRegAlloc && I->getDesc().isReturn()) return false;
475 // Don't duplicate more than the threshold.
476 if (InstrCount == MaxDuplicateCount) return false;
477 // Remember if we saw a call.
478 if (I->getDesc().isCall()) HasCall = true;
479 if (I->getOpcode() != TargetInstrInfo::PHI)
482 // Heuristically, don't tail-duplicate calls if it would expand code size,
483 // as it's less likely to be worth the extra cost.
484 if (InstrCount > 1 && HasCall)
487 DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');
489 // Iterate through all the unique predecessors and tail-duplicate this
490 // block into them, if possible. Copying the list ahead of time also
491 // avoids trouble with the predecessor list reallocating.
492 bool Changed = false;
493 SmallSetVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
495 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
496 PE = Preds.end(); PI != PE; ++PI) {
497 MachineBasicBlock *PredBB = *PI;
499 assert(TailBB != PredBB &&
500 "Single-block loop should have been rejected earlier!");
501 if (PredBB->succ_size() > 1) continue;
503 MachineBasicBlock *PredTBB, *PredFBB;
504 SmallVector<MachineOperand, 4> PredCond;
505 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
507 if (!PredCond.empty())
509 // EH edges are ignored by AnalyzeBranch.
510 if (PredBB->succ_size() != 1)
512 // Don't duplicate into a fall-through predecessor (at least for now).
513 if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
516 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
517 << "From Succ: " << *TailBB);
519 TDBBs.push_back(PredBB);
521 // Remove PredBB's unconditional branch.
522 TII->RemoveBranch(*PredBB);
524 // Clone the contents of TailBB into PredBB.
525 DenseMap<unsigned, unsigned> LocalVRMap;
526 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
527 MachineBasicBlock::iterator I = TailBB->begin();
528 while (I != TailBB->end()) {
529 MachineInstr *MI = &*I;
531 if (MI->getOpcode() == TargetInstrInfo::PHI) {
532 // Replace the uses of the def of the PHI with the register coming
534 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos);
536 // Replace def of virtual registers with new registers, and update
537 // uses with PHI source register or the new registers.
538 DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap);
541 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
542 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
543 const TargetRegisterClass *RC = MRI->getRegClass(CopyInfos[i].first);
544 TII->copyRegToReg(*PredBB, Loc, CopyInfos[i].first,
545 CopyInfos[i].second, RC,RC);
546 MachineInstr *CopyMI = prior(Loc);
547 Copies.push_back(CopyMI);
549 NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
552 PredBB->removeSuccessor(PredBB->succ_begin());
553 assert(PredBB->succ_empty() &&
554 "TailDuplicate called on block with multiple successors!");
555 for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
556 E = TailBB->succ_end(); I != E; ++I)
557 PredBB->addSuccessor(*I);
563 // If TailBB was duplicated into all its predecessors except for the prior
564 // block, which falls through unconditionally, move the contents of this
565 // block into the prior block.
566 MachineBasicBlock *PrevBB = prior(MachineFunction::iterator(TailBB));
567 MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
568 SmallVector<MachineOperand, 4> PriorCond;
569 bool PriorUnAnalyzable =
570 TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true);
571 // This has to check PrevBB->succ_size() because EH edges are ignored by
573 if (!PriorUnAnalyzable && PriorCond.empty() && !PriorTBB &&
574 TailBB->pred_size() == 1 && PrevBB->succ_size() == 1 &&
575 !TailBB->hasAddressTaken()) {
576 DEBUG(dbgs() << "\nMerging into block: " << *PrevBB
577 << "From MBB: " << *TailBB);
579 DenseMap<unsigned, unsigned> LocalVRMap;
580 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
581 MachineBasicBlock::iterator I = TailBB->begin();
582 // Process PHI instructions first.
583 while (I != TailBB->end() && I->getOpcode() == TargetInstrInfo::PHI) {
584 // Replace the uses of the def of the PHI with the register coming
586 MachineInstr *MI = &*I++;
587 ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos);
589 MI->eraseFromParent();
592 // Now copy the non-PHI instructions.
593 while (I != TailBB->end()) {
594 // Replace def of virtual registers with new registers, and update
595 // uses with PHI source register or the new registers.
596 MachineInstr *MI = &*I++;
597 DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap);
598 MI->eraseFromParent();
600 MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
601 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
602 const TargetRegisterClass *RC = MRI->getRegClass(CopyInfos[i].first);
603 TII->copyRegToReg(*PrevBB, Loc, CopyInfos[i].first,
604 CopyInfos[i].second, RC, RC);
605 MachineInstr *CopyMI = prior(Loc);
606 Copies.push_back(CopyMI);
609 // No PHIs to worry about, just splice the instructions over.
610 PrevBB->splice(PrevBB->end(), TailBB, TailBB->begin(), TailBB->end());
612 PrevBB->removeSuccessor(PrevBB->succ_begin());
613 assert(PrevBB->succ_empty());
614 PrevBB->transferSuccessors(TailBB);
615 TDBBs.push_back(PrevBB);
622 /// RemoveDeadBlock - Remove the specified dead machine basic block from the
623 /// function, updating the CFG.
624 void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
625 assert(MBB->pred_empty() && "MBB must be dead!");
626 DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
628 // Remove all successors.
629 while (!MBB->succ_empty())
630 MBB->removeSuccessor(MBB->succ_end()-1);
632 // If there are any labels in the basic block, unregister them from
633 // MachineModuleInfo.
634 if (MMI && !MBB->empty()) {
635 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
638 // The label ID # is always operand #0, an immediate.
639 MMI->InvalidateLabel(I->getOperand(0).getImm());
644 MBB->eraseFromParent();