1 //===-- llvm/CodeGen/MachineBasicBlock.cpp ----------------------*- C++ -*-===//
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 // Collect the sequence of machine instructions for a basic block.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/CodeGen/MachineBasicBlock.h"
15 #include "llvm/BasicBlock.h"
16 #include "llvm/CodeGen/LiveVariables.h"
17 #include "llvm/CodeGen/MachineDominators.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineLoopInfo.h"
20 #include "llvm/CodeGen/SlotIndexes.h"
21 #include "llvm/MC/MCAsmInfo.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/Target/TargetRegisterInfo.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Target/TargetInstrDesc.h"
26 #include "llvm/Target/TargetInstrInfo.h"
27 #include "llvm/Target/TargetMachine.h"
28 #include "llvm/Assembly/Writer.h"
29 #include "llvm/ADT/SmallString.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/LeakDetector.h"
33 #include "llvm/Support/raw_ostream.h"
37 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
38 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
43 MachineBasicBlock::~MachineBasicBlock() {
44 LeakDetector::removeGarbageObject(this);
47 /// getSymbol - Return the MCSymbol for this basic block.
49 MCSymbol *MachineBasicBlock::getSymbol() const {
50 const MachineFunction *MF = getParent();
51 MCContext &Ctx = MF->getContext();
52 const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix();
53 return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
54 Twine(MF->getFunctionNumber()) + "_" +
59 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
64 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the
65 /// parent pointer of the MBB, the MBB numbering, and any instructions in the
66 /// MBB to be on the right operand list for registers.
68 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
69 /// gets the next available unique MBB number. If it is removed from a
70 /// MachineFunction, it goes back to being #-1.
71 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
72 MachineFunction &MF = *N->getParent();
73 N->Number = MF.addToMBBNumbering(N);
75 // Make sure the instructions have their operands in the reginfo lists.
76 MachineRegisterInfo &RegInfo = MF.getRegInfo();
77 for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I)
78 I->AddRegOperandsToUseLists(RegInfo);
80 LeakDetector::removeGarbageObject(N);
83 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
84 N->getParent()->removeFromMBBNumbering(N->Number);
86 LeakDetector::addGarbageObject(N);
90 /// addNodeToList (MI) - When we add an instruction to a basic block
91 /// list, we update its parent pointer and add its operands from reg use/def
92 /// lists if appropriate.
93 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
94 assert(N->getParent() == 0 && "machine instruction already in a basic block");
97 // Add the instruction's register operands to their corresponding
99 MachineFunction *MF = Parent->getParent();
100 N->AddRegOperandsToUseLists(MF->getRegInfo());
102 LeakDetector::removeGarbageObject(N);
105 /// removeNodeFromList (MI) - When we remove an instruction from a basic block
106 /// list, we update its parent pointer and remove its operands from reg use/def
107 /// lists if appropriate.
108 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
109 assert(N->getParent() != 0 && "machine instruction not in a basic block");
111 // Remove from the use/def lists.
112 N->RemoveRegOperandsFromUseLists();
116 LeakDetector::addGarbageObject(N);
119 /// transferNodesFromList (MI) - When moving a range of instructions from one
120 /// MBB list to another, we need to update the parent pointers and the use/def
122 void ilist_traits<MachineInstr>::
123 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
124 MachineBasicBlock::iterator first,
125 MachineBasicBlock::iterator last) {
126 assert(Parent->getParent() == fromList.Parent->getParent() &&
127 "MachineInstr parent mismatch!");
129 // Splice within the same MBB -> no change.
130 if (Parent == fromList.Parent) return;
132 // If splicing between two blocks within the same function, just update the
134 for (; first != last; ++first)
135 first->setParent(Parent);
138 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
139 assert(!MI->getParent() && "MI is still in a block!");
140 Parent->getParent()->DeleteMachineInstr(MI);
143 MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
144 iterator I = begin();
145 while (I != end() && I->isPHI())
150 MachineBasicBlock::iterator
151 MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
152 while (I != end() && (I->isPHI() || I->isLabel() || I->isDebugValue()))
157 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
159 while (I != begin() && ((--I)->getDesc().isTerminator() || I->isDebugValue()))
161 while (I != end() && !I->getDesc().isTerminator())
166 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {
167 iterator B = begin(), I = end();
170 if (I->isDebugValue())
174 // The block is all debug values.
178 const MachineBasicBlock *MachineBasicBlock::getLandingPadSuccessor() const {
179 // A block with a landing pad successor only has one other successor.
182 for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I)
183 if ((*I)->isLandingPad())
188 void MachineBasicBlock::dump() const {
192 StringRef MachineBasicBlock::getName() const {
193 if (const BasicBlock *LBB = getBasicBlock())
194 return LBB->getName();
199 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
200 const MachineFunction *MF = getParent();
202 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
207 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
210 OS << Indexes->getMBBStartIdx(this) << '\t';
212 OS << "BB#" << getNumber() << ": ";
214 const char *Comma = "";
215 if (const BasicBlock *LBB = getBasicBlock()) {
216 OS << Comma << "derived from LLVM BB ";
217 WriteAsOperand(OS, LBB, /*PrintType=*/false);
220 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
221 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
224 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
225 if (!livein_empty()) {
226 if (Indexes) OS << '\t';
228 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
229 OS << ' ' << PrintReg(*I, TRI);
232 // Print the preds of this block according to the CFG.
234 if (Indexes) OS << '\t';
235 OS << " Predecessors according to CFG:";
236 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
237 OS << " BB#" << (*PI)->getNumber();
241 for (const_iterator I = begin(); I != end(); ++I) {
243 if (Indexes->hasIndex(I))
244 OS << Indexes->getInstructionIndex(I);
248 I->print(OS, &getParent()->getTarget());
251 // Print the successors of this block according to the CFG.
253 if (Indexes) OS << '\t';
254 OS << " Successors according to CFG:";
255 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
256 OS << " BB#" << (*SI)->getNumber();
261 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
262 std::vector<unsigned>::iterator I =
263 std::find(LiveIns.begin(), LiveIns.end(), Reg);
264 assert(I != LiveIns.end() && "Not a live in!");
268 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
269 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
270 return I != livein_end();
273 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
274 getParent()->splice(NewAfter, this);
277 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
278 MachineFunction::iterator BBI = NewBefore;
279 getParent()->splice(++BBI, this);
282 void MachineBasicBlock::updateTerminator() {
283 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
284 // A block with no successors has no concerns with fall-through edges.
285 if (this->succ_empty()) return;
287 MachineBasicBlock *TBB = 0, *FBB = 0;
288 SmallVector<MachineOperand, 4> Cond;
289 DebugLoc dl; // FIXME: this is nowhere
290 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
292 assert(!B && "UpdateTerminators requires analyzable predecessors!");
295 // The block has an unconditional branch. If its successor is now
296 // its layout successor, delete the branch.
297 if (isLayoutSuccessor(TBB))
298 TII->RemoveBranch(*this);
300 // The block has an unconditional fallthrough. If its successor is not
301 // its layout successor, insert a branch.
303 if (!isLayoutSuccessor(TBB))
304 TII->InsertBranch(*this, TBB, 0, Cond, dl);
308 // The block has a non-fallthrough conditional branch. If one of its
309 // successors is its layout successor, rewrite it to a fallthrough
310 // conditional branch.
311 if (isLayoutSuccessor(TBB)) {
312 if (TII->ReverseBranchCondition(Cond))
314 TII->RemoveBranch(*this);
315 TII->InsertBranch(*this, FBB, 0, Cond, dl);
316 } else if (isLayoutSuccessor(FBB)) {
317 TII->RemoveBranch(*this);
318 TII->InsertBranch(*this, TBB, 0, Cond, dl);
321 // The block has a fallthrough conditional branch.
322 MachineBasicBlock *MBBA = *succ_begin();
323 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
324 if (MBBA == TBB) std::swap(MBBB, MBBA);
325 if (isLayoutSuccessor(TBB)) {
326 if (TII->ReverseBranchCondition(Cond)) {
327 // We can't reverse the condition, add an unconditional branch.
329 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
332 TII->RemoveBranch(*this);
333 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
334 } else if (!isLayoutSuccessor(MBBA)) {
335 TII->RemoveBranch(*this);
336 TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
342 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
344 // If we see non-zero value for the first time it means we actually use Weight
345 // list, so we fill all Weights with 0's.
346 if (weight != 0 && Weights.empty())
347 Weights.resize(Successors.size());
349 if (weight != 0 || !Weights.empty())
350 Weights.push_back(weight);
352 Successors.push_back(succ);
353 succ->addPredecessor(this);
356 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
357 succ->removePredecessor(this);
358 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
359 assert(I != Successors.end() && "Not a current successor!");
361 // If Weight list is empty it means we don't use it (disabled optimization).
362 if (!Weights.empty()) {
363 weight_iterator WI = getWeightIterator(I);
370 MachineBasicBlock::succ_iterator
371 MachineBasicBlock::removeSuccessor(succ_iterator I) {
372 assert(I != Successors.end() && "Not a current successor!");
374 // If Weight list is empty it means we don't use it (disabled optimization).
375 if (!Weights.empty()) {
376 weight_iterator WI = getWeightIterator(I);
380 (*I)->removePredecessor(this);
381 return Successors.erase(I);
384 void MachineBasicBlock::replaceSuccessor(MachineBasicBlock *Old,
385 MachineBasicBlock *New) {
387 succ_iterator SI = std::find(Successors.begin(), Successors.end(), Old);
389 // If Weight list is empty it means we don't use it (disabled optimization).
390 if (!Weights.empty()) {
391 weight_iterator WI = getWeightIterator(SI);
395 // Update the successor information.
397 addSuccessor(New, weight);
400 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
401 Predecessors.push_back(pred);
404 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
405 pred_iterator I = std::find(Predecessors.begin(), Predecessors.end(), pred);
406 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
407 Predecessors.erase(I);
410 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
414 while (!fromMBB->succ_empty()) {
415 MachineBasicBlock *Succ = *fromMBB->succ_begin();
419 // If Weight list is empty it means we don't use it (disabled optimization).
420 if (!fromMBB->Weights.empty())
421 weight = *fromMBB->Weights.begin();
423 addSuccessor(Succ, weight);
424 fromMBB->removeSuccessor(Succ);
429 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
433 while (!fromMBB->succ_empty()) {
434 MachineBasicBlock *Succ = *fromMBB->succ_begin();
436 fromMBB->removeSuccessor(Succ);
438 // Fix up any PHI nodes in the successor.
439 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
440 MI != ME && MI->isPHI(); ++MI)
441 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
442 MachineOperand &MO = MI->getOperand(i);
443 if (MO.getMBB() == fromMBB)
449 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
450 const_succ_iterator I = std::find(Successors.begin(), Successors.end(), MBB);
451 return I != Successors.end();
454 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
455 MachineFunction::const_iterator I(this);
456 return llvm::next(I) == MachineFunction::const_iterator(MBB);
459 bool MachineBasicBlock::canFallThrough() {
460 MachineFunction::iterator Fallthrough = this;
462 // If FallthroughBlock is off the end of the function, it can't fall through.
463 if (Fallthrough == getParent()->end())
466 // If FallthroughBlock isn't a successor, no fallthrough is possible.
467 if (!isSuccessor(Fallthrough))
470 // Analyze the branches, if any, at the end of the block.
471 MachineBasicBlock *TBB = 0, *FBB = 0;
472 SmallVector<MachineOperand, 4> Cond;
473 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
474 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
475 // If we couldn't analyze the branch, examine the last instruction.
476 // If the block doesn't end in a known control barrier, assume fallthrough
477 // is possible. The isPredicable check is needed because this code can be
478 // called during IfConversion, where an instruction which is normally a
479 // Barrier is predicated and thus no longer an actual control barrier. This
480 // is over-conservative though, because if an instruction isn't actually
481 // predicated we could still treat it like a barrier.
482 return empty() || !back().getDesc().isBarrier() ||
483 back().getDesc().isPredicable();
486 // If there is no branch, control always falls through.
487 if (TBB == 0) return true;
489 // If there is some explicit branch to the fallthrough block, it can obviously
490 // reach, even though the branch should get folded to fall through implicitly.
491 if (MachineFunction::iterator(TBB) == Fallthrough ||
492 MachineFunction::iterator(FBB) == Fallthrough)
495 // If it's an unconditional branch to some block not the fall through, it
496 // doesn't fall through.
497 if (Cond.empty()) return false;
499 // Otherwise, if it is conditional and has no explicit false block, it falls
505 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
506 MachineFunction *MF = getParent();
507 DebugLoc dl; // FIXME: this is nowhere
509 // We may need to update this's terminator, but we can't do that if
510 // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
511 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
512 MachineBasicBlock *TBB = 0, *FBB = 0;
513 SmallVector<MachineOperand, 4> Cond;
514 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
517 // Avoid bugpoint weirdness: A block may end with a conditional branch but
518 // jumps to the same MBB is either case. We have duplicate CFG edges in that
519 // case that we can't handle. Since this never happens in properly optimized
520 // code, just skip those edges.
521 if (TBB && TBB == FBB) {
522 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
523 << getNumber() << '\n');
527 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
528 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
529 DEBUG(dbgs() << "Splitting critical edge:"
530 " BB#" << getNumber()
531 << " -- BB#" << NMBB->getNumber()
532 << " -- BB#" << Succ->getNumber() << '\n');
534 // On some targets like Mips, branches may kill virtual registers. Make sure
535 // that LiveVariables is properly updated after updateTerminator replaces the
537 LiveVariables *LV = P->getAnalysisIfAvailable<LiveVariables>();
539 // Collect a list of virtual registers killed by the terminators.
540 SmallVector<unsigned, 4> KilledRegs;
542 for (iterator I = getFirstTerminator(), E = end(); I != E; ++I) {
543 MachineInstr *MI = I;
544 for (MachineInstr::mop_iterator OI = MI->operands_begin(),
545 OE = MI->operands_end(); OI != OE; ++OI) {
546 if (!OI->isReg() || !OI->isUse() || !OI->isKill() || OI->isUndef())
548 unsigned Reg = OI->getReg();
549 if (TargetRegisterInfo::isVirtualRegister(Reg) &&
550 LV->getVarInfo(Reg).removeKill(MI)) {
551 KilledRegs.push_back(Reg);
552 DEBUG(dbgs() << "Removing terminator kill: " << *MI);
553 OI->setIsKill(false);
558 ReplaceUsesOfBlockWith(Succ, NMBB);
561 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
562 NMBB->addSuccessor(Succ);
563 if (!NMBB->isLayoutSuccessor(Succ)) {
565 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
568 // Fix PHI nodes in Succ so they refer to NMBB instead of this
569 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
570 i != e && i->isPHI(); ++i)
571 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
572 if (i->getOperand(ni+1).getMBB() == this)
573 i->getOperand(ni+1).setMBB(NMBB);
575 // Update LiveVariables.
577 // Restore kills of virtual registers that were killed by the terminators.
578 while (!KilledRegs.empty()) {
579 unsigned Reg = KilledRegs.pop_back_val();
580 for (iterator I = end(), E = begin(); I != E;) {
581 if (!(--I)->addRegisterKilled(Reg, NULL, /* addIfNotFound= */ false))
583 LV->getVarInfo(Reg).Kills.push_back(I);
584 DEBUG(dbgs() << "Restored terminator kill: " << *I);
588 // Update relevant live-through information.
589 LV->addNewBlock(NMBB, this, Succ);
592 if (MachineDominatorTree *MDT =
593 P->getAnalysisIfAvailable<MachineDominatorTree>()) {
594 // Update dominator information.
595 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
597 bool IsNewIDom = true;
598 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
600 MachineBasicBlock *PredBB = *PI;
603 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
609 // We know "this" dominates the newly created basic block.
610 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
612 // If all the other predecessors of "Succ" are dominated by "Succ" itself
613 // then the new block is the new immediate dominator of "Succ". Otherwise,
614 // the new block doesn't dominate anything.
616 MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
619 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
620 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
621 // If one or the other blocks were not in a loop, the new block is not
622 // either, and thus LI doesn't need to be updated.
623 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
624 if (TIL == DestLoop) {
625 // Both in the same loop, the NMBB joins loop.
626 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
627 } else if (TIL->contains(DestLoop)) {
628 // Edge from an outer loop to an inner loop. Add to the outer loop.
629 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
630 } else if (DestLoop->contains(TIL)) {
631 // Edge from an inner loop to an outer loop. Add to the outer loop.
632 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
634 // Edge from two loops with no containment relation. Because these
635 // are natural loops, we know that the destination block must be the
636 // header of its loop (adding a branch into a loop elsewhere would
637 // create an irreducible loop).
638 assert(DestLoop->getHeader() == Succ &&
639 "Should not create irreducible loops!");
640 if (MachineLoop *P = DestLoop->getParentLoop())
641 P->addBasicBlockToLoop(NMBB, MLI->getBase());
649 /// removeFromParent - This method unlinks 'this' from the containing function,
650 /// and returns it, but does not delete it.
651 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
652 assert(getParent() && "Not embedded in a function!");
653 getParent()->remove(this);
658 /// eraseFromParent - This method unlinks 'this' from the containing function,
660 void MachineBasicBlock::eraseFromParent() {
661 assert(getParent() && "Not embedded in a function!");
662 getParent()->erase(this);
666 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
667 /// 'Old', change the code and CFG so that it branches to 'New' instead.
668 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
669 MachineBasicBlock *New) {
670 assert(Old != New && "Cannot replace self with self!");
672 MachineBasicBlock::iterator I = end();
673 while (I != begin()) {
675 if (!I->getDesc().isTerminator()) break;
677 // Scan the operands of this machine instruction, replacing any uses of Old
679 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
680 if (I->getOperand(i).isMBB() &&
681 I->getOperand(i).getMBB() == Old)
682 I->getOperand(i).setMBB(New);
685 // Update the successor information.
686 replaceSuccessor(Old, New);
689 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
690 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
691 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
694 /// Besides DestA and DestB, retain other edges leading to LandingPads
695 /// (currently there can be only one; we don't check or require that here).
696 /// Note it is possible that DestA and/or DestB are LandingPads.
697 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
698 MachineBasicBlock *DestB,
700 // The values of DestA and DestB frequently come from a call to the
701 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
702 // values from there.
704 // 1. If both DestA and DestB are null, then the block ends with no branches
705 // (it falls through to its successor).
706 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
707 // with only an unconditional branch.
708 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
709 // with a conditional branch that falls through to a successor (DestB).
710 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
711 // conditional branch followed by an unconditional branch. DestA is the
712 // 'true' destination and DestB is the 'false' destination.
714 bool Changed = false;
716 MachineFunction::iterator FallThru =
717 llvm::next(MachineFunction::iterator(this));
719 if (DestA == 0 && DestB == 0) {
720 // Block falls through to successor.
723 } else if (DestA != 0 && DestB == 0) {
725 // Block ends in conditional jump that falls through to successor.
728 assert(DestA && DestB && isCond &&
729 "CFG in a bad state. Cannot correct CFG edges");
732 // Remove superfluous edges. I.e., those which aren't destinations of this
733 // basic block, duplicate edges, or landing pads.
734 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
735 MachineBasicBlock::succ_iterator SI = succ_begin();
736 while (SI != succ_end()) {
737 const MachineBasicBlock *MBB = *SI;
738 if (!SeenMBBs.insert(MBB) ||
739 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
740 // This is a superfluous edge, remove it.
741 SI = removeSuccessor(SI);
751 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
752 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
754 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
756 MachineBasicBlock::iterator E = end();
758 // Skip debug declarations, we don't want a DebugLoc from them.
759 MachineBasicBlock::iterator MBBI2 = MBBI;
760 while (MBBI2 != E && MBBI2->isDebugValue())
763 DL = MBBI2->getDebugLoc();
768 /// getSuccWeight - Return weight of the edge from this block to MBB.
770 uint32_t MachineBasicBlock::getSuccWeight(MachineBasicBlock *succ) {
774 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
775 return *getWeightIterator(I);
778 /// getWeightIterator - Return wight iterator corresonding to the I successor
780 MachineBasicBlock::weight_iterator MachineBasicBlock::
781 getWeightIterator(MachineBasicBlock::succ_iterator I) {
782 assert(Weights.size() == Successors.size() && "Async weight list!");
783 size_t index = std::distance(Successors.begin(), I);
784 assert(index < Weights.size() && "Not a current successor!");
785 return Weights.begin() + index;
788 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
790 OS << "BB#" << MBB->getNumber();