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/CodeGen/RegisterScavenging.h"
24 #include "llvm/Target/TargetInstrInfo.h"
25 #include "llvm/Target/TargetRegisterInfo.h"
26 #include "llvm/Support/CommandLine.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/ADT/DenseSet.h"
31 #include "llvm/ADT/OwningPtr.h"
32 #include "llvm/ADT/SmallSet.h"
33 #include "llvm/ADT/SetVector.h"
34 #include "llvm/ADT/Statistic.h"
37 STATISTIC(NumTails , "Number of tails duplicated");
38 STATISTIC(NumTailDups , "Number of tail duplicated blocks");
39 STATISTIC(NumInstrDups , "Additional instructions due to tail duplication");
40 STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
41 STATISTIC(NumAddedPHIs , "Number of phis added");
43 // Heuristic for tail duplication.
44 static cl::opt<unsigned>
45 TailDuplicateSize("tail-dup-size",
46 cl::desc("Maximum instructions to consider tail duplicating"),
47 cl::init(2), cl::Hidden);
50 TailDupVerify("tail-dup-verify",
51 cl::desc("Verify sanity of PHI instructions during taildup"),
52 cl::init(false), cl::Hidden);
54 static cl::opt<unsigned>
55 TailDupLimit("tail-dup-limit", cl::init(~0U), cl::Hidden);
57 typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy;
60 /// TailDuplicatePass - Perform tail duplication.
61 class TailDuplicatePass : public MachineFunctionPass {
62 const TargetInstrInfo *TII;
63 const TargetRegisterInfo *TRI;
64 MachineModuleInfo *MMI;
65 MachineRegisterInfo *MRI;
66 OwningPtr<RegScavenger> RS;
69 // SSAUpdateVRs - A list of virtual registers for which to update SSA form.
70 SmallVector<unsigned, 16> SSAUpdateVRs;
72 // SSAUpdateVals - For each virtual register in SSAUpdateVals keep a list of
73 // source virtual registers.
74 DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;
78 explicit TailDuplicatePass() :
79 MachineFunctionPass(ID), PreRegAlloc(false) {}
81 virtual bool runOnMachineFunction(MachineFunction &MF);
84 void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
85 MachineBasicBlock *BB);
86 void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
87 MachineBasicBlock *PredBB,
88 DenseMap<unsigned, unsigned> &LocalVRMap,
89 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies,
90 const DenseSet<unsigned> &UsedByPhi,
92 void DuplicateInstruction(MachineInstr *MI,
93 MachineBasicBlock *TailBB,
94 MachineBasicBlock *PredBB,
96 DenseMap<unsigned, unsigned> &LocalVRMap,
97 const DenseSet<unsigned> &UsedByPhi);
98 void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
99 SmallVector<MachineBasicBlock*, 8> &TDBBs,
100 SmallSetVector<MachineBasicBlock*, 8> &Succs);
101 bool TailDuplicateBlocks(MachineFunction &MF);
102 bool shouldTailDuplicate(const MachineFunction &MF,
103 bool IsSimple, MachineBasicBlock &TailBB);
104 bool isSimpleBB(MachineBasicBlock *TailBB);
105 bool canCompletelyDuplicateBB(MachineBasicBlock &BB);
106 bool duplicateSimpleBB(MachineBasicBlock *TailBB,
107 SmallVector<MachineBasicBlock*, 8> &TDBBs,
108 const DenseSet<unsigned> &RegsUsedByPhi,
109 SmallVector<MachineInstr*, 16> &Copies);
110 bool TailDuplicate(MachineBasicBlock *TailBB,
113 SmallVector<MachineBasicBlock*, 8> &TDBBs,
114 SmallVector<MachineInstr*, 16> &Copies);
115 bool TailDuplicateAndUpdate(MachineBasicBlock *MBB,
117 MachineFunction &MF);
119 void RemoveDeadBlock(MachineBasicBlock *MBB);
122 char TailDuplicatePass::ID = 0;
125 char &llvm::TailDuplicateID = TailDuplicatePass::ID;
127 INITIALIZE_PASS(TailDuplicatePass, "tailduplication", "Tail Duplication",
130 bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
131 TII = MF.getTarget().getInstrInfo();
132 TRI = MF.getTarget().getRegisterInfo();
133 MRI = &MF.getRegInfo();
134 MMI = getAnalysisIfAvailable<MachineModuleInfo>();
135 PreRegAlloc = MRI->isSSA();
137 if (MRI->tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF))
138 RS.reset(new RegScavenger());
140 bool MadeChange = false;
141 while (TailDuplicateBlocks(MF))
147 static void VerifyPHIs(MachineFunction &MF, bool CheckExtra) {
148 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ++I) {
149 MachineBasicBlock *MBB = I;
150 SmallSetVector<MachineBasicBlock*, 8> Preds(MBB->pred_begin(),
152 MachineBasicBlock::iterator MI = MBB->begin();
153 while (MI != MBB->end()) {
156 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
157 PE = Preds.end(); PI != PE; ++PI) {
158 MachineBasicBlock *PredBB = *PI;
160 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
161 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
162 if (PHIBB == PredBB) {
168 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
169 dbgs() << " missing input from predecessor BB#"
170 << PredBB->getNumber() << '\n';
175 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
176 MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
177 if (CheckExtra && !Preds.count(PHIBB)) {
178 dbgs() << "Warning: malformed PHI in BB#" << MBB->getNumber()
180 dbgs() << " extra input from predecessor BB#"
181 << PHIBB->getNumber() << '\n';
184 if (PHIBB->getNumber() < 0) {
185 dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
186 dbgs() << " non-existing BB#" << PHIBB->getNumber() << '\n';
195 /// TailDuplicateAndUpdate - Tail duplicate the block and cleanup.
197 TailDuplicatePass::TailDuplicateAndUpdate(MachineBasicBlock *MBB,
199 MachineFunction &MF) {
200 // Save the successors list.
201 SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
204 SmallVector<MachineBasicBlock*, 8> TDBBs;
205 SmallVector<MachineInstr*, 16> Copies;
206 if (!TailDuplicate(MBB, IsSimple, MF, TDBBs, Copies))
211 SmallVector<MachineInstr*, 8> NewPHIs;
212 MachineSSAUpdater SSAUpdate(MF, &NewPHIs);
214 // TailBB's immediate successors are now successors of those predecessors
215 // which duplicated TailBB. Add the predecessors as sources to the PHI
217 bool isDead = MBB->pred_empty() && !MBB->hasAddressTaken();
219 UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
221 // If it is dead, remove it.
223 NumInstrDups -= MBB->size();
224 RemoveDeadBlock(MBB);
229 if (!SSAUpdateVRs.empty()) {
230 for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
231 unsigned VReg = SSAUpdateVRs[i];
232 SSAUpdate.Initialize(VReg);
234 // If the original definition is still around, add it as an available
236 MachineInstr *DefMI = MRI->getVRegDef(VReg);
237 MachineBasicBlock *DefBB = 0;
239 DefBB = DefMI->getParent();
240 SSAUpdate.AddAvailableValue(DefBB, VReg);
243 // Add the new vregs as available values.
244 DenseMap<unsigned, AvailableValsTy>::iterator LI =
245 SSAUpdateVals.find(VReg);
246 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
247 MachineBasicBlock *SrcBB = LI->second[j].first;
248 unsigned SrcReg = LI->second[j].second;
249 SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
252 // Rewrite uses that are outside of the original def's block.
253 MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
254 while (UI != MRI->use_end()) {
255 MachineOperand &UseMO = UI.getOperand();
256 MachineInstr *UseMI = &*UI;
258 if (UseMI->isDebugValue()) {
259 // SSAUpdate can replace the use with an undef. That creates
260 // a debug instruction that is a kill.
261 // FIXME: Should it SSAUpdate job to delete debug instructions
262 // instead of replacing the use with undef?
263 UseMI->eraseFromParent();
266 if (UseMI->getParent() == DefBB && !UseMI->isPHI())
268 SSAUpdate.RewriteUse(UseMO);
272 SSAUpdateVRs.clear();
273 SSAUpdateVals.clear();
276 // Eliminate some of the copies inserted by tail duplication to maintain
278 for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
279 MachineInstr *Copy = Copies[i];
282 unsigned Dst = Copy->getOperand(0).getReg();
283 unsigned Src = Copy->getOperand(1).getReg();
284 if (MRI->hasOneNonDBGUse(Src) &&
285 MRI->constrainRegClass(Src, MRI->getRegClass(Dst))) {
286 // Copy is the only use. Do trivial copy propagation here.
287 MRI->replaceRegWith(Dst, Src);
288 Copy->eraseFromParent();
293 NumAddedPHIs += NewPHIs.size();
298 /// TailDuplicateBlocks - Look for small blocks that are unconditionally
299 /// branched to and do not fall through. Tail-duplicate their instructions
300 /// into their predecessors to eliminate (dynamic) branches.
301 bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
302 bool MadeChange = false;
304 if (PreRegAlloc && TailDupVerify) {
305 DEBUG(dbgs() << "\n*** Before tail-duplicating\n");
306 VerifyPHIs(MF, true);
309 for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
310 MachineBasicBlock *MBB = I++;
312 if (NumTails == TailDupLimit)
315 bool IsSimple = isSimpleBB(MBB);
317 if (!shouldTailDuplicate(MF, IsSimple, *MBB))
320 MadeChange |= TailDuplicateAndUpdate(MBB, IsSimple, MF);
323 if (PreRegAlloc && TailDupVerify)
324 VerifyPHIs(MF, false);
329 static bool isDefLiveOut(unsigned Reg, MachineBasicBlock *BB,
330 const MachineRegisterInfo *MRI) {
331 for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
332 UE = MRI->use_end(); UI != UE; ++UI) {
333 MachineInstr *UseMI = &*UI;
334 if (UseMI->isDebugValue())
336 if (UseMI->getParent() != BB)
342 static unsigned getPHISrcRegOpIdx(MachineInstr *MI, MachineBasicBlock *SrcBB) {
343 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2)
344 if (MI->getOperand(i+1).getMBB() == SrcBB)
350 // Remember which registers are used by phis in this block. This is
351 // used to determine which registers are liveout while modifying the
352 // block (which is why we need to copy the information).
353 static void getRegsUsedByPHIs(const MachineBasicBlock &BB,
354 DenseSet<unsigned> *UsedByPhi) {
355 for(MachineBasicBlock::const_iterator I = BB.begin(), E = BB.end();
357 const MachineInstr &MI = *I;
360 for (unsigned i = 1, e = MI.getNumOperands(); i != e; i += 2) {
361 unsigned SrcReg = MI.getOperand(i).getReg();
362 UsedByPhi->insert(SrcReg);
367 /// AddSSAUpdateEntry - Add a definition and source virtual registers pair for
369 void TailDuplicatePass::AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
370 MachineBasicBlock *BB) {
371 DenseMap<unsigned, AvailableValsTy>::iterator LI= SSAUpdateVals.find(OrigReg);
372 if (LI != SSAUpdateVals.end())
373 LI->second.push_back(std::make_pair(BB, NewReg));
375 AvailableValsTy Vals;
376 Vals.push_back(std::make_pair(BB, NewReg));
377 SSAUpdateVals.insert(std::make_pair(OrigReg, Vals));
378 SSAUpdateVRs.push_back(OrigReg);
382 /// ProcessPHI - Process PHI node in TailBB by turning it into a copy in PredBB.
383 /// Remember the source register that's contributed by PredBB and update SSA
385 void TailDuplicatePass::ProcessPHI(MachineInstr *MI,
386 MachineBasicBlock *TailBB,
387 MachineBasicBlock *PredBB,
388 DenseMap<unsigned, unsigned> &LocalVRMap,
389 SmallVector<std::pair<unsigned,unsigned>, 4> &Copies,
390 const DenseSet<unsigned> &RegsUsedByPhi,
392 unsigned DefReg = MI->getOperand(0).getReg();
393 unsigned SrcOpIdx = getPHISrcRegOpIdx(MI, PredBB);
394 assert(SrcOpIdx && "Unable to find matching PHI source?");
395 unsigned SrcReg = MI->getOperand(SrcOpIdx).getReg();
396 const TargetRegisterClass *RC = MRI->getRegClass(DefReg);
397 LocalVRMap.insert(std::make_pair(DefReg, SrcReg));
399 // Insert a copy from source to the end of the block. The def register is the
400 // available value liveout of the block.
401 unsigned NewDef = MRI->createVirtualRegister(RC);
402 Copies.push_back(std::make_pair(NewDef, SrcReg));
403 if (isDefLiveOut(DefReg, TailBB, MRI) || RegsUsedByPhi.count(DefReg))
404 AddSSAUpdateEntry(DefReg, NewDef, PredBB);
409 // Remove PredBB from the PHI node.
410 MI->RemoveOperand(SrcOpIdx+1);
411 MI->RemoveOperand(SrcOpIdx);
412 if (MI->getNumOperands() == 1)
413 MI->eraseFromParent();
416 /// DuplicateInstruction - Duplicate a TailBB instruction to PredBB and update
417 /// the source operands due to earlier PHI translation.
418 void TailDuplicatePass::DuplicateInstruction(MachineInstr *MI,
419 MachineBasicBlock *TailBB,
420 MachineBasicBlock *PredBB,
422 DenseMap<unsigned, unsigned> &LocalVRMap,
423 const DenseSet<unsigned> &UsedByPhi) {
424 MachineInstr *NewMI = TII->duplicate(MI, MF);
425 for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
426 MachineOperand &MO = NewMI->getOperand(i);
429 unsigned Reg = MO.getReg();
430 if (!TargetRegisterInfo::isVirtualRegister(Reg))
433 const TargetRegisterClass *RC = MRI->getRegClass(Reg);
434 unsigned NewReg = MRI->createVirtualRegister(RC);
436 LocalVRMap.insert(std::make_pair(Reg, NewReg));
437 if (isDefLiveOut(Reg, TailBB, MRI) || UsedByPhi.count(Reg))
438 AddSSAUpdateEntry(Reg, NewReg, PredBB);
440 DenseMap<unsigned, unsigned>::iterator VI = LocalVRMap.find(Reg);
441 if (VI != LocalVRMap.end()) {
442 MO.setReg(VI->second);
443 MRI->constrainRegClass(VI->second, MRI->getRegClass(Reg));
447 PredBB->insert(PredBB->instr_end(), NewMI);
450 /// UpdateSuccessorsPHIs - After FromBB is tail duplicated into its predecessor
451 /// blocks, the successors have gained new predecessors. Update the PHI
452 /// instructions in them accordingly.
454 TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
455 SmallVector<MachineBasicBlock*, 8> &TDBBs,
456 SmallSetVector<MachineBasicBlock*,8> &Succs) {
457 for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(),
458 SE = Succs.end(); SI != SE; ++SI) {
459 MachineBasicBlock *SuccBB = *SI;
460 for (MachineBasicBlock::iterator II = SuccBB->begin(), EE = SuccBB->end();
465 for (unsigned i = 1, e = II->getNumOperands(); i != e; i += 2) {
466 MachineOperand &MO = II->getOperand(i+1);
467 if (MO.getMBB() == FromBB) {
474 MachineOperand &MO0 = II->getOperand(Idx);
475 unsigned Reg = MO0.getReg();
477 // Folded into the previous BB.
478 // There could be duplicate phi source entries. FIXME: Should sdisel
479 // or earlier pass fixed this?
480 for (unsigned i = II->getNumOperands()-2; i != Idx; i -= 2) {
481 MachineOperand &MO = II->getOperand(i+1);
482 if (MO.getMBB() == FromBB) {
483 II->RemoveOperand(i+1);
484 II->RemoveOperand(i);
490 // If Idx is set, the operands at Idx and Idx+1 must be removed.
491 // We reuse the location to avoid expensive RemoveOperand calls.
493 DenseMap<unsigned,AvailableValsTy>::iterator LI=SSAUpdateVals.find(Reg);
494 if (LI != SSAUpdateVals.end()) {
495 // This register is defined in the tail block.
496 for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
497 MachineBasicBlock *SrcBB = LI->second[j].first;
498 // If we didn't duplicate a bb into a particular predecessor, we
499 // might still have added an entry to SSAUpdateVals to correcly
500 // recompute SSA. If that case, avoid adding a dummy extra argument
502 if (!SrcBB->isSuccessor(SuccBB))
505 unsigned SrcReg = LI->second[j].second;
507 II->getOperand(Idx).setReg(SrcReg);
508 II->getOperand(Idx+1).setMBB(SrcBB);
511 II->addOperand(MachineOperand::CreateReg(SrcReg, false));
512 II->addOperand(MachineOperand::CreateMBB(SrcBB));
516 // Live in tail block, must also be live in predecessors.
517 for (unsigned j = 0, ee = TDBBs.size(); j != ee; ++j) {
518 MachineBasicBlock *SrcBB = TDBBs[j];
520 II->getOperand(Idx).setReg(Reg);
521 II->getOperand(Idx+1).setMBB(SrcBB);
524 II->addOperand(MachineOperand::CreateReg(Reg, false));
525 II->addOperand(MachineOperand::CreateMBB(SrcBB));
530 II->RemoveOperand(Idx+1);
531 II->RemoveOperand(Idx);
537 /// shouldTailDuplicate - Determine if it is profitable to duplicate this block.
539 TailDuplicatePass::shouldTailDuplicate(const MachineFunction &MF,
541 MachineBasicBlock &TailBB) {
542 // Only duplicate blocks that end with unconditional branches.
543 if (TailBB.canFallThrough())
546 // Don't try to tail-duplicate single-block loops.
547 if (TailBB.isSuccessor(&TailBB))
550 // Set the limit on the cost to duplicate. When optimizing for size,
551 // duplicate only one, because one branch instruction can be eliminated to
552 // compensate for the duplication.
553 unsigned MaxDuplicateCount;
554 if (TailDuplicateSize.getNumOccurrences() == 0 &&
555 MF.getFunction()->getFnAttributes().
556 hasAttribute(Attributes::OptimizeForSize))
557 MaxDuplicateCount = 1;
559 MaxDuplicateCount = TailDuplicateSize;
561 // If the target has hardware branch prediction that can handle indirect
562 // branches, duplicating them can often make them predictable when there
563 // are common paths through the code. The limit needs to be high enough
564 // to allow undoing the effects of tail merging and other optimizations
565 // that rearrange the predecessors of the indirect branch.
567 bool HasIndirectbr = false;
569 HasIndirectbr = TailBB.back().isIndirectBranch();
571 if (HasIndirectbr && PreRegAlloc)
572 MaxDuplicateCount = 20;
574 // Check the instructions in the block to determine whether tail-duplication
575 // is invalid or unlikely to be profitable.
576 unsigned InstrCount = 0;
577 for (MachineBasicBlock::iterator I = TailBB.begin(); I != TailBB.end(); ++I) {
578 // Non-duplicable things shouldn't be tail-duplicated.
579 if (I->isNotDuplicable())
582 // Do not duplicate 'return' instructions if this is a pre-regalloc run.
583 // A return may expand into a lot more instructions (e.g. reload of callee
584 // saved registers) after PEI.
585 if (PreRegAlloc && I->isReturn())
588 // Avoid duplicating calls before register allocation. Calls presents a
589 // barrier to register allocation so duplicating them may end up increasing
591 if (PreRegAlloc && I->isCall())
594 if (!I->isPHI() && !I->isDebugValue())
597 if (InstrCount > MaxDuplicateCount)
601 if (HasIndirectbr && PreRegAlloc)
610 return canCompletelyDuplicateBB(TailBB);
613 /// isSimpleBB - True if this BB has only one unconditional jump.
615 TailDuplicatePass::isSimpleBB(MachineBasicBlock *TailBB) {
616 if (TailBB->succ_size() != 1)
618 if (TailBB->pred_empty())
620 MachineBasicBlock::iterator I = TailBB->begin();
621 MachineBasicBlock::iterator E = TailBB->end();
622 while (I != E && I->isDebugValue())
626 return I->isUnconditionalBranch();
630 bothUsedInPHI(const MachineBasicBlock &A,
631 SmallPtrSet<MachineBasicBlock*, 8> SuccsB) {
632 for (MachineBasicBlock::const_succ_iterator SI = A.succ_begin(),
633 SE = A.succ_end(); SI != SE; ++SI) {
634 MachineBasicBlock *BB = *SI;
635 if (SuccsB.count(BB) && !BB->empty() && BB->begin()->isPHI())
643 TailDuplicatePass::canCompletelyDuplicateBB(MachineBasicBlock &BB) {
644 SmallPtrSet<MachineBasicBlock*, 8> Succs(BB.succ_begin(), BB.succ_end());
646 for (MachineBasicBlock::pred_iterator PI = BB.pred_begin(),
647 PE = BB.pred_end(); PI != PE; ++PI) {
648 MachineBasicBlock *PredBB = *PI;
650 if (PredBB->succ_size() > 1)
653 MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
654 SmallVector<MachineOperand, 4> PredCond;
655 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
658 if (!PredCond.empty())
665 TailDuplicatePass::duplicateSimpleBB(MachineBasicBlock *TailBB,
666 SmallVector<MachineBasicBlock*, 8> &TDBBs,
667 const DenseSet<unsigned> &UsedByPhi,
668 SmallVector<MachineInstr*, 16> &Copies) {
669 SmallPtrSet<MachineBasicBlock*, 8> Succs(TailBB->succ_begin(),
671 SmallVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
673 bool Changed = false;
674 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
675 PE = Preds.end(); PI != PE; ++PI) {
676 MachineBasicBlock *PredBB = *PI;
678 if (PredBB->getLandingPadSuccessor())
681 if (bothUsedInPHI(*PredBB, Succs))
684 MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
685 SmallVector<MachineOperand, 4> PredCond;
686 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
690 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
691 << "From simple Succ: " << *TailBB);
693 MachineBasicBlock *NewTarget = *TailBB->succ_begin();
694 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(PredBB));
696 // Make PredFBB explicit.
697 if (PredCond.empty())
700 // Make fall through explicit.
707 if (PredFBB == TailBB)
709 if (PredTBB == TailBB)
712 // Make the branch unconditional if possible
713 if (PredTBB == PredFBB) {
718 // Avoid adding fall through branches.
719 if (PredFBB == NextBB)
721 if (PredTBB == NextBB && PredFBB == NULL)
724 TII->RemoveBranch(*PredBB);
727 TII->InsertBranch(*PredBB, PredTBB, PredFBB, PredCond, DebugLoc());
729 PredBB->removeSuccessor(TailBB);
730 unsigned NumSuccessors = PredBB->succ_size();
731 assert(NumSuccessors <= 1);
732 if (NumSuccessors == 0 || *PredBB->succ_begin() != NewTarget)
733 PredBB->addSuccessor(NewTarget);
735 TDBBs.push_back(PredBB);
740 /// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
741 /// of its predecessors.
743 TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB,
746 SmallVector<MachineBasicBlock*, 8> &TDBBs,
747 SmallVector<MachineInstr*, 16> &Copies) {
748 DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');
750 DenseSet<unsigned> UsedByPhi;
751 getRegsUsedByPHIs(*TailBB, &UsedByPhi);
754 return duplicateSimpleBB(TailBB, TDBBs, UsedByPhi, Copies);
756 // Iterate through all the unique predecessors and tail-duplicate this
757 // block into them, if possible. Copying the list ahead of time also
758 // avoids trouble with the predecessor list reallocating.
759 bool Changed = false;
760 SmallSetVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
762 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
763 PE = Preds.end(); PI != PE; ++PI) {
764 MachineBasicBlock *PredBB = *PI;
766 assert(TailBB != PredBB &&
767 "Single-block loop should have been rejected earlier!");
768 // EH edges are ignored by AnalyzeBranch.
769 if (PredBB->succ_size() > 1)
772 MachineBasicBlock *PredTBB, *PredFBB;
773 SmallVector<MachineOperand, 4> PredCond;
774 if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
776 if (!PredCond.empty())
778 // Don't duplicate into a fall-through predecessor (at least for now).
779 if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
782 DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
783 << "From Succ: " << *TailBB);
785 TDBBs.push_back(PredBB);
787 // Remove PredBB's unconditional branch.
788 TII->RemoveBranch(*PredBB);
790 if (RS && !TailBB->livein_empty()) {
791 // Update PredBB livein.
792 RS->enterBasicBlock(PredBB);
793 if (!PredBB->empty())
794 RS->forward(prior(PredBB->end()));
795 BitVector RegsLiveAtExit(TRI->getNumRegs());
796 RS->getRegsUsed(RegsLiveAtExit, false);
797 for (MachineBasicBlock::livein_iterator I = TailBB->livein_begin(),
798 E = TailBB->livein_end(); I != E; ++I) {
799 if (!RegsLiveAtExit[*I])
800 // If a register is previously livein to the tail but it's not live
801 // at the end of predecessor BB, then it should be added to its
803 PredBB->addLiveIn(*I);
807 // Clone the contents of TailBB into PredBB.
808 DenseMap<unsigned, unsigned> LocalVRMap;
809 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
810 // Use instr_iterator here to properly handle bundles, e.g.
811 // ARM Thumb2 IT block.
812 MachineBasicBlock::instr_iterator I = TailBB->instr_begin();
813 while (I != TailBB->instr_end()) {
814 MachineInstr *MI = &*I;
817 // Replace the uses of the def of the PHI with the register coming
819 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, true);
821 // Replace def of virtual registers with new registers, and update
822 // uses with PHI source register or the new registers.
823 DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap, UsedByPhi);
826 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
827 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
828 Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
829 TII->get(TargetOpcode::COPY),
830 CopyInfos[i].first).addReg(CopyInfos[i].second));
834 TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
836 NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
839 PredBB->removeSuccessor(PredBB->succ_begin());
840 assert(PredBB->succ_empty() &&
841 "TailDuplicate called on block with multiple successors!");
842 for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
843 E = TailBB->succ_end(); I != E; ++I)
844 PredBB->addSuccessor(*I);
850 // If TailBB was duplicated into all its predecessors except for the prior
851 // block, which falls through unconditionally, move the contents of this
852 // block into the prior block.
853 MachineBasicBlock *PrevBB = prior(MachineFunction::iterator(TailBB));
854 MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
855 SmallVector<MachineOperand, 4> PriorCond;
856 // This has to check PrevBB->succ_size() because EH edges are ignored by
858 if (PrevBB->succ_size() == 1 &&
859 !TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true) &&
860 PriorCond.empty() && !PriorTBB && TailBB->pred_size() == 1 &&
861 !TailBB->hasAddressTaken()) {
862 DEBUG(dbgs() << "\nMerging into block: " << *PrevBB
863 << "From MBB: " << *TailBB);
865 DenseMap<unsigned, unsigned> LocalVRMap;
866 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
867 MachineBasicBlock::iterator I = TailBB->begin();
868 // Process PHI instructions first.
869 while (I != TailBB->end() && I->isPHI()) {
870 // Replace the uses of the def of the PHI with the register coming
872 MachineInstr *MI = &*I++;
873 ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos, UsedByPhi, true);
875 MI->eraseFromParent();
878 // Now copy the non-PHI instructions.
879 while (I != TailBB->end()) {
880 // Replace def of virtual registers with new registers, and update
881 // uses with PHI source register or the new registers.
882 MachineInstr *MI = &*I++;
883 assert(!MI->isBundle() && "Not expecting bundles before regalloc!");
884 DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap, UsedByPhi);
885 MI->eraseFromParent();
887 MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
888 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
889 Copies.push_back(BuildMI(*PrevBB, Loc, DebugLoc(),
890 TII->get(TargetOpcode::COPY),
892 .addReg(CopyInfos[i].second));
895 // No PHIs to worry about, just splice the instructions over.
896 PrevBB->splice(PrevBB->end(), TailBB, TailBB->begin(), TailBB->end());
898 PrevBB->removeSuccessor(PrevBB->succ_begin());
899 assert(PrevBB->succ_empty());
900 PrevBB->transferSuccessors(TailBB);
901 TDBBs.push_back(PrevBB);
905 // If this is after register allocation, there are no phis to fix.
909 // If we made no changes so far, we are safe.
914 // Handle the nasty case in that we duplicated a block that is part of a loop
915 // into some but not all of its predecessors. For example:
919 // if we duplicate 2 into 1 but not into 3, we end up with
920 // 12 -> 3 <-> 2 -> rest |
923 // If there was a "var = phi(1, 3)" in 2, it has to be ultimately replaced
924 // with a phi in 3 (which now dominates 2).
925 // What we do here is introduce a copy in 3 of the register defined by the
926 // phi, just like when we are duplicating 2 into 3, but we don't copy any
927 // real instructions or remove the 3 -> 2 edge from the phi in 2.
928 for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
929 PE = Preds.end(); PI != PE; ++PI) {
930 MachineBasicBlock *PredBB = *PI;
931 if (std::find(TDBBs.begin(), TDBBs.end(), PredBB) != TDBBs.end())
935 if (PredBB->succ_size() != 1)
938 DenseMap<unsigned, unsigned> LocalVRMap;
939 SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
940 MachineBasicBlock::iterator I = TailBB->begin();
941 // Process PHI instructions first.
942 while (I != TailBB->end() && I->isPHI()) {
943 // Replace the uses of the def of the PHI with the register coming
945 MachineInstr *MI = &*I++;
946 ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, false);
948 MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
949 for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
950 Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
951 TII->get(TargetOpcode::COPY),
952 CopyInfos[i].first).addReg(CopyInfos[i].second));
959 /// RemoveDeadBlock - Remove the specified dead machine basic block from the
960 /// function, updating the CFG.
961 void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
962 assert(MBB->pred_empty() && "MBB must be dead!");
963 DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
965 // Remove all successors.
966 while (!MBB->succ_empty())
967 MBB->removeSuccessor(MBB->succ_end()-1);
970 MBB->eraseFromParent();