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");
38 // Heuristic for tail duplication.
39 static cl::opt<unsigned>
40 TailDuplicateSize("tail-dup-size",
41 cl::desc("Maximum instructions to consider tail duplicating"),
42 cl::init(2), cl::Hidden);
45 TailDupVerify("tail-dup-verify",
46 cl::desc("Verify sanity of PHI instructions during taildup"),
47 cl::init(false), cl::Hidden);
49 static cl::opt<unsigned>
50 TailDupLimit("tail-dup-limit", cl::init(~0U), cl::Hidden);
52 typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy;
55 /// TailDuplicatePass - Perform tail duplication.
56 class TailDuplicatePass : public MachineFunctionPass {
58 const TargetInstrInfo *TII;
59 MachineModuleInfo *MMI;
60 MachineRegisterInfo *MRI;
62 // SSAUpdateVRs - A list of virtual registers for which to update SSA form.
63 SmallVector<unsigned, 16> SSAUpdateVRs;
65 // SSAUpdateVals - For each virtual register in SSAUpdateVals keep a list of
66 // source virtual registers.
67 DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;
71 explicit TailDuplicatePass(bool PreRA) :
72 MachineFunctionPass(&ID), PreRegAlloc(PreRA) {}
74 virtual bool runOnMachineFunction(MachineFunction &MF);
75 virtual const char *getPassName() const { return "Tail Duplication"; }
78 void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
79 MachineBasicBlock *BB);
80 void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
81 MachineBasicBlock *PredBB,
82 DenseMap<unsigned, unsigned> &LocalVRMap,
83 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies);
84 void DuplicateInstruction(MachineInstr *MI,
85 MachineBasicBlock *TailBB,
86 MachineBasicBlock *PredBB,
88 DenseMap<unsigned, unsigned> &LocalVRMap);
89 void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
90 SmallVector<MachineBasicBlock*, 8> &TDBBs,
91 SmallSetVector<MachineBasicBlock*, 8> &Succs);
92 bool TailDuplicateBlocks(MachineFunction &MF);
93 bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
94 SmallVector<MachineBasicBlock*, 8> &TDBBs,
95 SmallVector<MachineInstr*, 16> &Copies);
96 void RemoveDeadBlock(MachineBasicBlock *MBB);
99 char TailDuplicatePass::ID = 0;
102 FunctionPass *llvm::createTailDuplicatePass(bool PreRegAlloc) {
103 return new TailDuplicatePass(PreRegAlloc);
106 bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
107 TII = MF.getTarget().getInstrInfo();
108 MRI = &MF.getRegInfo();
109 MMI = getAnalysisIfAvailable<MachineModuleInfo>();
111 bool MadeChange = false;
112 while (TailDuplicateBlocks(MF))
118 static void VerifyPHIs(MachineFunction &MF, bool CheckExtra) {
119 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ++I) {
120 MachineBasicBlock *MBB = I;
121 SmallSetVector<MachineBasicBlock*, 8> Preds(MBB->pred_begin(),
123 MachineBasicBlock::iterator MI = MBB->begin();
124 while (MI != MBB->end()) {
127 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
128 PE = Preds.end(); PI != PE; ++PI) {
129 MachineBasicBlock *PredBB = *PI;
131 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
132 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
133 if (PHIBB == PredBB) {
139 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
140 dbgs() << " missing input from predecessor BB#"
141 << PredBB->getNumber() << '\n';
146 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
147 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
148 if (CheckExtra && !Preds.count(PHIBB)) {
149 // This is not a hard error.
150 dbgs() << "Warning: malformed PHI in BB#" << MBB->getNumber()
152 dbgs() << " extra input from predecessor BB#"
153 << PHIBB->getNumber() << '\n';
155 if (PHIBB->getNumber() < 0) {
156 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
157 dbgs() << " non-existing BB#" << PHIBB->getNumber() << '\n';
166 /// TailDuplicateBlocks - Look for small blocks that are unconditionally
167 /// branched to and do not fall through. Tail-duplicate their instructions
168 /// into their predecessors to eliminate (dynamic) branches.
169 bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
170 bool MadeChange = false;
172 if (PreRegAlloc && TailDupVerify) {
173 DEBUG(dbgs() << "\n*** Before tail-duplicating\n");
174 VerifyPHIs(MF, true);
177 SmallVector<MachineInstr*, 8> NewPHIs;
178 MachineSSAUpdater SSAUpdate(MF, &NewPHIs);
180 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
181 MachineBasicBlock *MBB = I++;
183 if (NumTails == TailDupLimit)
186 // Only duplicate blocks that end with unconditional branches.
187 if (MBB->canFallThrough())
190 // Save the successors list.
191 SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
194 SmallVector<MachineBasicBlock*, 8> TDBBs;
195 SmallVector<MachineInstr*, 16> Copies;
196 if (TailDuplicate(MBB, MF, TDBBs, Copies)) {
199 // TailBB's immediate successors are now successors of those predecessors
200 // which duplicated TailBB. Add the predecessors as sources to the PHI
202 bool isDead = MBB->pred_empty();
204 UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
206 // If it is dead, remove it.
208 NumInstrDups -= MBB->size();
209 RemoveDeadBlock(MBB);
214 if (!SSAUpdateVRs.empty()) {
215 for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
216 unsigned VReg = SSAUpdateVRs[i];
217 SSAUpdate.Initialize(VReg);
219 // If the original definition is still around, add it as an available
221 MachineInstr *DefMI = MRI->getVRegDef(VReg);
222 MachineBasicBlock *DefBB = 0;
224 DefBB = DefMI->getParent();
225 SSAUpdate.AddAvailableValue(DefBB, VReg);
228 // Add the new vregs as available values.
229 DenseMap<unsigned, AvailableValsTy>::iterator LI =
230 SSAUpdateVals.find(VReg);
231 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
232 MachineBasicBlock *SrcBB = LI->second[j].first;
233 unsigned SrcReg = LI->second[j].second;
234 SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
237 // Rewrite uses that are outside of the original def's block.
238 MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
239 while (UI != MRI->use_end()) {
240 MachineOperand &UseMO = UI.getOperand();
241 MachineInstr *UseMI = &*UI;
243 if (UseMI->getParent() == DefBB)
245 SSAUpdate.RewriteUse(UseMO);
249 SSAUpdateVRs.clear();
250 SSAUpdateVals.clear();
253 // Eliminate some of the copies inserted by tail duplication to maintain
255 for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
256 MachineInstr *Copy = Copies[i];
257 unsigned Src, Dst, SrcSR, DstSR;
258 if (TII->isMoveInstr(*Copy, Src, Dst, SrcSR, DstSR)) {
259 MachineRegisterInfo::use_iterator UI = MRI->use_begin(Src);
260 if (++UI == MRI->use_end()) {
261 // Copy is the only use. Do trivial copy propagation here.
262 MRI->replaceRegWith(Dst, Src);
263 Copy->eraseFromParent();
268 if (PreRegAlloc && TailDupVerify)
269 VerifyPHIs(MF, false);
277 static bool isDefLiveOut(unsigned Reg, MachineBasicBlock *BB,
278 const MachineRegisterInfo *MRI) {
279 for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
280 UE = MRI->use_end(); UI != UE; ++UI) {
281 MachineInstr *UseMI = &*UI;
282 if (UseMI->getParent() != BB)
288 static unsigned getPHISrcRegOpIdx(MachineInstr *MI, MachineBasicBlock *SrcBB) {
289 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2)
290 if (MI->getOperand(i+1).getMBB() == SrcBB)
295 /// AddSSAUpdateEntry - Add a definition and source virtual registers pair for
297 void TailDuplicatePass::AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
298 MachineBasicBlock *BB) {
299 DenseMap<unsigned, AvailableValsTy>::iterator LI= SSAUpdateVals.find(OrigReg);
300 if (LI != SSAUpdateVals.end())
301 LI->second.push_back(std::make_pair(BB, NewReg));
303 AvailableValsTy Vals;
304 Vals.push_back(std::make_pair(BB, NewReg));
305 SSAUpdateVals.insert(std::make_pair(OrigReg, Vals));
306 SSAUpdateVRs.push_back(OrigReg);
310 /// ProcessPHI - Process PHI node in TailBB by turning it into a copy in PredBB.
311 /// Remember the source register that's contributed by PredBB and update SSA
313 void TailDuplicatePass::ProcessPHI(MachineInstr *MI,
314 MachineBasicBlock *TailBB,
315 MachineBasicBlock *PredBB,
316 DenseMap<unsigned, unsigned> &LocalVRMap,
317 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies) {
318 unsigned DefReg = MI->getOperand(0).getReg();
319 unsigned SrcOpIdx = getPHISrcRegOpIdx(MI, PredBB);
320 assert(SrcOpIdx && "Unable to find matching PHI source?");
321 unsigned SrcReg = MI->getOperand(SrcOpIdx).getReg();
322 const TargetRegisterClass *RC = MRI->getRegClass(DefReg);
323 LocalVRMap.insert(std::make_pair(DefReg, SrcReg));
325 // Insert a copy from source to the end of the block. The def register is the
326 // available value liveout of the block.
327 unsigned NewDef = MRI->createVirtualRegister(RC);
328 Copies.push_back(std::make_pair(NewDef, SrcReg));
329 if (isDefLiveOut(DefReg, TailBB, MRI))
330 AddSSAUpdateEntry(DefReg, NewDef, PredBB);
332 // Remove PredBB from the PHI node.
333 MI->RemoveOperand(SrcOpIdx+1);
334 MI->RemoveOperand(SrcOpIdx);
335 if (MI->getNumOperands() == 1)
336 MI->eraseFromParent();
339 /// DuplicateInstruction - Duplicate a TailBB instruction to PredBB and update
340 /// the source operands due to earlier PHI translation.
341 void TailDuplicatePass::DuplicateInstruction(MachineInstr *MI,
342 MachineBasicBlock *TailBB,
343 MachineBasicBlock *PredBB,
345 DenseMap<unsigned, unsigned> &LocalVRMap) {
346 MachineInstr *NewMI = TII->duplicate(MI, MF);
347 for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
348 MachineOperand &MO = NewMI->getOperand(i);
351 unsigned Reg = MO.getReg();
352 if (!Reg || TargetRegisterInfo::isPhysicalRegister(Reg))
355 const TargetRegisterClass *RC = MRI->getRegClass(Reg);
356 unsigned NewReg = MRI->createVirtualRegister(RC);
358 LocalVRMap.insert(std::make_pair(Reg, NewReg));
359 if (isDefLiveOut(Reg, TailBB, MRI))
360 AddSSAUpdateEntry(Reg, NewReg, PredBB);
362 DenseMap<unsigned, unsigned>::iterator VI = LocalVRMap.find(Reg);
363 if (VI != LocalVRMap.end())
364 MO.setReg(VI->second);
367 PredBB->insert(PredBB->end(), NewMI);
370 /// UpdateSuccessorsPHIs - After FromBB is tail duplicated into its predecessor
371 /// blocks, the successors have gained new predecessors. Update the PHI
372 /// instructions in them accordingly.
374 TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
375 SmallVector<MachineBasicBlock*, 8> &TDBBs,
376 SmallSetVector<MachineBasicBlock*,8> &Succs) {
377 for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(),
378 SE = Succs.end(); SI != SE; ++SI) {
379 MachineBasicBlock *SuccBB = *SI;
380 for (MachineBasicBlock::iterator II = SuccBB->begin(), EE = SuccBB->end();
385 for (unsigned i = 1, e = II->getNumOperands(); i != e; i += 2) {
386 MachineOperand &MO = II->getOperand(i+1);
387 if (MO.getMBB() == FromBB) {
394 MachineOperand &MO0 = II->getOperand(Idx);
395 unsigned Reg = MO0.getReg();
397 // Folded into the previous BB.
398 // There could be duplicate phi source entries. FIXME: Should sdisel
399 // or earlier pass fixed this?
400 for (unsigned i = II->getNumOperands()-2; i != Idx; i -= 2) {
401 MachineOperand &MO = II->getOperand(i+1);
402 if (MO.getMBB() == FromBB) {
403 II->RemoveOperand(i+1);
404 II->RemoveOperand(i);
410 // If Idx is set, the operands at Idx and Idx+1 must be removed.
411 // We reuse the location to avoid expensive RemoveOperand calls.
413 DenseMap<unsigned,AvailableValsTy>::iterator LI=SSAUpdateVals.find(Reg);
414 if (LI != SSAUpdateVals.end()) {
415 // This register is defined in the tail block.
416 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
417 MachineBasicBlock *SrcBB = LI->second[j].first;
418 unsigned SrcReg = LI->second[j].second;
420 II->getOperand(Idx).setReg(SrcReg);
421 II->getOperand(Idx+1).setMBB(SrcBB);
424 II->addOperand(MachineOperand::CreateReg(SrcReg, false));
425 II->addOperand(MachineOperand::CreateMBB(SrcBB));
429 // Live in tail block, must also be live in predecessors.
430 for (unsigned j = 0, ee = TDBBs.size(); j != ee; ++j) {
431 MachineBasicBlock *SrcBB = TDBBs[j];
433 II->getOperand(Idx).setReg(Reg);
434 II->getOperand(Idx+1).setMBB(SrcBB);
437 II->addOperand(MachineOperand::CreateReg(Reg, false));
438 II->addOperand(MachineOperand::CreateMBB(SrcBB));
443 II->RemoveOperand(Idx+1);
444 II->RemoveOperand(Idx);
450 /// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
451 /// of its predecessors.
453 TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
454 SmallVector<MachineBasicBlock*, 8> &TDBBs,
455 SmallVector<MachineInstr*, 16> &Copies) {
456 // Set the limit on the number of instructions to duplicate, with a default
457 // of one less than the tail-merge threshold. When optimizing for size,
458 // duplicate only one, because one branch instruction can be eliminated to
459 // compensate for the duplication.
460 unsigned MaxDuplicateCount;
461 if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
462 MaxDuplicateCount = 1;
464 MaxDuplicateCount = TailDuplicateSize;
467 // Pre-regalloc tail duplication hurts compile time and doesn't help
468 // much except for indirect branches.
469 if (TailBB->empty() || !TailBB->back().getDesc().isIndirectBranch())
471 // If the target has hardware branch prediction that can handle indirect
472 // branches, duplicating them can often make them predictable when there
473 // are common paths through the code. The limit needs to be high enough
474 // to allow undoing the effects of tail merging and other optimizations
475 // that rearrange the predecessors of the indirect branch.
476 MaxDuplicateCount = 20;
479 // Don't try to tail-duplicate single-block loops.
480 if (TailBB->isSuccessor(TailBB))
483 // Check the instructions in the block to determine whether tail-duplication
484 // is invalid or unlikely to be profitable.
485 unsigned InstrCount = 0;
486 bool HasCall = false;
487 for (MachineBasicBlock::iterator I = TailBB->begin();
488 I != TailBB->end(); ++I) {
489 // Non-duplicable things shouldn't be tail-duplicated.
490 if (I->getDesc().isNotDuplicable()) return false;
491 // Do not duplicate 'return' instructions if this is a pre-regalloc run.
492 // A return may expand into a lot more instructions (e.g. reload of callee
493 // saved registers) after PEI.
494 if (PreRegAlloc && I->getDesc().isReturn()) return false;
495 // Don't duplicate more than the threshold.
496 if (InstrCount == MaxDuplicateCount) return false;
497 // Remember if we saw a call.
498 if (I->getDesc().isCall()) HasCall = true;
499 if (!I->isPHI() && !I->isDebugValue())
502 // Heuristically, don't tail-duplicate calls if it would expand code size,
503 // as it's less likely to be worth the extra cost.
504 if (InstrCount > 1 && HasCall)
507 DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');
509 // Iterate through all the unique predecessors and tail-duplicate this
510 // block into them, if possible. Copying the list ahead of time also
511 // avoids trouble with the predecessor list reallocating.
512 bool Changed = false;
513 SmallSetVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
515 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
516 PE = Preds.end(); PI != PE; ++PI) {
517 MachineBasicBlock *PredBB = *PI;
519 assert(TailBB != PredBB &&
520 "Single-block loop should have been rejected earlier!");
521 if (PredBB->succ_size() > 1) continue;
523 MachineBasicBlock *PredTBB, *PredFBB;
524 SmallVector<MachineOperand, 4> PredCond;
525 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
527 if (!PredCond.empty())
529 // EH edges are ignored by AnalyzeBranch.
530 if (PredBB->succ_size() != 1)
532 // Don't duplicate into a fall-through predecessor (at least for now).
533 if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
536 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
537 << "From Succ: " << *TailBB);
539 TDBBs.push_back(PredBB);
541 // Remove PredBB's unconditional branch.
542 TII->RemoveBranch(*PredBB);
544 // Clone the contents of TailBB into PredBB.
545 DenseMap<unsigned, unsigned> LocalVRMap;
546 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
547 MachineBasicBlock::iterator I = TailBB->begin();
548 while (I != TailBB->end()) {
549 MachineInstr *MI = &*I;
552 // Replace the uses of the def of the PHI with the register coming
554 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos);
556 // Replace def of virtual registers with new registers, and update
557 // uses with PHI source register or the new registers.
558 DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap);
561 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
562 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
563 Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
564 TII->get(TargetOpcode::COPY),
565 CopyInfos[i].first).addReg(CopyInfos[i].second));
567 NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
570 PredBB->removeSuccessor(PredBB->succ_begin());
571 assert(PredBB->succ_empty() &&
572 "TailDuplicate called on block with multiple successors!");
573 for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
574 E = TailBB->succ_end(); I != E; ++I)
575 PredBB->addSuccessor(*I);
581 // If TailBB was duplicated into all its predecessors except for the prior
582 // block, which falls through unconditionally, move the contents of this
583 // block into the prior block.
584 MachineBasicBlock *PrevBB = prior(MachineFunction::iterator(TailBB));
585 MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
586 SmallVector<MachineOperand, 4> PriorCond;
587 bool PriorUnAnalyzable =
588 TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true);
589 // This has to check PrevBB->succ_size() because EH edges are ignored by
591 if (!PriorUnAnalyzable && PriorCond.empty() && !PriorTBB &&
592 TailBB->pred_size() == 1 && PrevBB->succ_size() == 1 &&
593 !TailBB->hasAddressTaken()) {
594 DEBUG(dbgs() << "\nMerging into block: " << *PrevBB
595 << "From MBB: " << *TailBB);
597 DenseMap<unsigned, unsigned> LocalVRMap;
598 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
599 MachineBasicBlock::iterator I = TailBB->begin();
600 // Process PHI instructions first.
601 while (I != TailBB->end() && I->isPHI()) {
602 // Replace the uses of the def of the PHI with the register coming
604 MachineInstr *MI = &*I++;
605 ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos);
607 MI->eraseFromParent();
610 // Now copy the non-PHI instructions.
611 while (I != TailBB->end()) {
612 // Replace def of virtual registers with new registers, and update
613 // uses with PHI source register or the new registers.
614 MachineInstr *MI = &*I++;
615 DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap);
616 MI->eraseFromParent();
618 MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
619 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
620 Copies.push_back(BuildMI(*PrevBB, Loc, DebugLoc(),
621 TII->get(TargetOpcode::COPY),
623 .addReg(CopyInfos[i].second));
626 // No PHIs to worry about, just splice the instructions over.
627 PrevBB->splice(PrevBB->end(), TailBB, TailBB->begin(), TailBB->end());
629 PrevBB->removeSuccessor(PrevBB->succ_begin());
630 assert(PrevBB->succ_empty());
631 PrevBB->transferSuccessors(TailBB);
632 TDBBs.push_back(PrevBB);
639 /// RemoveDeadBlock - Remove the specified dead machine basic block from the
640 /// function, updating the CFG.
641 void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
642 assert(MBB->pred_empty() && "MBB must be dead!");
643 DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
645 // Remove all successors.
646 while (!MBB->succ_empty())
647 MBB->removeSuccessor(MBB->succ_end()-1);
650 MBB->eraseFromParent();