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/TargetInstrInfo.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Assembly/Writer.h"
28 #include "llvm/ADT/SmallString.h"
29 #include "llvm/ADT/SmallPtrSet.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/LeakDetector.h"
32 #include "llvm/Support/raw_ostream.h"
36 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
37 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
42 MachineBasicBlock::~MachineBasicBlock() {
43 LeakDetector::removeGarbageObject(this);
46 /// getSymbol - Return the MCSymbol for this basic block.
48 MCSymbol *MachineBasicBlock::getSymbol() const {
49 const MachineFunction *MF = getParent();
50 MCContext &Ctx = MF->getContext();
51 const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix();
52 return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
53 Twine(MF->getFunctionNumber()) + "_" +
58 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
63 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the
64 /// parent pointer of the MBB, the MBB numbering, and any instructions in the
65 /// MBB to be on the right operand list for registers.
67 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
68 /// gets the next available unique MBB number. If it is removed from a
69 /// MachineFunction, it goes back to being #-1.
70 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
71 MachineFunction &MF = *N->getParent();
72 N->Number = MF.addToMBBNumbering(N);
74 // Make sure the instructions have their operands in the reginfo lists.
75 MachineRegisterInfo &RegInfo = MF.getRegInfo();
76 for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I)
77 I->AddRegOperandsToUseLists(RegInfo);
79 LeakDetector::removeGarbageObject(N);
82 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
83 N->getParent()->removeFromMBBNumbering(N->Number);
85 LeakDetector::addGarbageObject(N);
89 /// addNodeToList (MI) - When we add an instruction to a basic block
90 /// list, we update its parent pointer and add its operands from reg use/def
91 /// lists if appropriate.
92 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
93 assert(N->getParent() == 0 && "machine instruction already in a basic block");
96 // Add the instruction's register operands to their corresponding
98 MachineFunction *MF = Parent->getParent();
99 N->AddRegOperandsToUseLists(MF->getRegInfo());
101 LeakDetector::removeGarbageObject(N);
104 /// removeNodeFromList (MI) - When we remove an instruction from a basic block
105 /// list, we update its parent pointer and remove its operands from reg use/def
106 /// lists if appropriate.
107 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
108 assert(N->getParent() != 0 && "machine instruction not in a basic block");
110 // Remove from the use/def lists.
111 N->RemoveRegOperandsFromUseLists();
115 LeakDetector::addGarbageObject(N);
118 /// transferNodesFromList (MI) - When moving a range of instructions from one
119 /// MBB list to another, we need to update the parent pointers and the use/def
121 void ilist_traits<MachineInstr>::
122 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
123 MachineBasicBlock::iterator first,
124 MachineBasicBlock::iterator last) {
125 assert(Parent->getParent() == fromList.Parent->getParent() &&
126 "MachineInstr parent mismatch!");
128 // Splice within the same MBB -> no change.
129 if (Parent == fromList.Parent) return;
131 // If splicing between two blocks within the same function, just update the
133 for (; first != last; ++first)
134 first->setParent(Parent);
137 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
138 assert(!MI->getParent() && "MI is still in a block!");
139 Parent->getParent()->DeleteMachineInstr(MI);
142 MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
143 iterator I = begin();
144 while (I != end() && I->isPHI())
149 MachineBasicBlock::iterator
150 MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
151 while (I != end() && (I->isPHI() || I->isLabel() || I->isDebugValue()))
156 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
158 while (I != begin() && ((--I)->getDesc().isTerminator() || I->isDebugValue()))
160 while (I != end() && !I->getDesc().isTerminator())
165 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {
166 iterator B = begin(), I = end();
169 if (I->isDebugValue())
173 // The block is all debug values.
177 const MachineBasicBlock *MachineBasicBlock::getLandingPadSuccessor() const {
178 // A block with a landing pad successor only has one other successor.
181 for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I)
182 if ((*I)->isLandingPad())
187 void MachineBasicBlock::dump() const {
191 StringRef MachineBasicBlock::getName() const {
192 if (const BasicBlock *LBB = getBasicBlock())
193 return LBB->getName();
198 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
199 const MachineFunction *MF = getParent();
201 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
207 OS << Indexes->getMBBStartIdx(this) << '\t';
209 OS << "BB#" << getNumber() << ": ";
211 const char *Comma = "";
212 if (const BasicBlock *LBB = getBasicBlock()) {
213 OS << Comma << "derived from LLVM BB ";
214 WriteAsOperand(OS, LBB, /*PrintType=*/false);
217 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
218 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
220 OS << Comma << "Align " << Alignment << " (" << (1u << Alignment)
227 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
228 if (!livein_empty()) {
229 if (Indexes) OS << '\t';
231 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
232 OS << ' ' << PrintReg(*I, TRI);
235 // Print the preds of this block according to the CFG.
237 if (Indexes) OS << '\t';
238 OS << " Predecessors according to CFG:";
239 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
240 OS << " BB#" << (*PI)->getNumber();
244 for (const_iterator I = begin(); I != end(); ++I) {
246 if (Indexes->hasIndex(I))
247 OS << Indexes->getInstructionIndex(I);
251 I->print(OS, &getParent()->getTarget());
254 // Print the successors of this block according to the CFG.
256 if (Indexes) OS << '\t';
257 OS << " Successors according to CFG:";
258 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
259 OS << " BB#" << (*SI)->getNumber();
264 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
265 std::vector<unsigned>::iterator I =
266 std::find(LiveIns.begin(), LiveIns.end(), Reg);
267 assert(I != LiveIns.end() && "Not a live in!");
271 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
272 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
273 return I != livein_end();
276 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
277 getParent()->splice(NewAfter, this);
280 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
281 MachineFunction::iterator BBI = NewBefore;
282 getParent()->splice(++BBI, this);
285 void MachineBasicBlock::updateTerminator() {
286 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
287 // A block with no successors has no concerns with fall-through edges.
288 if (this->succ_empty()) return;
290 MachineBasicBlock *TBB = 0, *FBB = 0;
291 SmallVector<MachineOperand, 4> Cond;
292 DebugLoc dl; // FIXME: this is nowhere
293 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
295 assert(!B && "UpdateTerminators requires analyzable predecessors!");
298 // The block has an unconditional branch. If its successor is now
299 // its layout successor, delete the branch.
300 if (isLayoutSuccessor(TBB))
301 TII->RemoveBranch(*this);
303 // The block has an unconditional fallthrough. If its successor is not
304 // its layout successor, insert a branch. First we have to locate the
305 // only non-landing-pad successor, as that is the fallthrough block.
306 for (succ_iterator SI = succ_begin(), SE = succ_end(); SI != SE; ++SI) {
307 if ((*SI)->isLandingPad())
309 assert(!TBB && "Found more than one non-landing-pad successor!");
313 // If there is no non-landing-pad successor, the block has no
314 // fall-through edges to be concerned with.
318 // Finally update the unconditional successor to be reached via a branch
319 // if it would not be reached by fallthrough.
320 if (!isLayoutSuccessor(TBB))
321 TII->InsertBranch(*this, TBB, 0, Cond, dl);
325 // The block has a non-fallthrough conditional branch. If one of its
326 // successors is its layout successor, rewrite it to a fallthrough
327 // conditional branch.
328 if (isLayoutSuccessor(TBB)) {
329 if (TII->ReverseBranchCondition(Cond))
331 TII->RemoveBranch(*this);
332 TII->InsertBranch(*this, FBB, 0, Cond, dl);
333 } else if (isLayoutSuccessor(FBB)) {
334 TII->RemoveBranch(*this);
335 TII->InsertBranch(*this, TBB, 0, Cond, dl);
338 // The block has a fallthrough conditional branch.
339 MachineBasicBlock *MBBA = *succ_begin();
340 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
341 if (MBBA == TBB) std::swap(MBBB, MBBA);
342 if (isLayoutSuccessor(TBB)) {
343 if (TII->ReverseBranchCondition(Cond)) {
344 // We can't reverse the condition, add an unconditional branch.
346 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
349 TII->RemoveBranch(*this);
350 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
351 } else if (!isLayoutSuccessor(MBBA)) {
352 TII->RemoveBranch(*this);
353 TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
359 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
361 // If we see non-zero value for the first time it means we actually use Weight
362 // list, so we fill all Weights with 0's.
363 if (weight != 0 && Weights.empty())
364 Weights.resize(Successors.size());
366 if (weight != 0 || !Weights.empty())
367 Weights.push_back(weight);
369 Successors.push_back(succ);
370 succ->addPredecessor(this);
373 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
374 succ->removePredecessor(this);
375 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
376 assert(I != Successors.end() && "Not a current successor!");
378 // If Weight list is empty it means we don't use it (disabled optimization).
379 if (!Weights.empty()) {
380 weight_iterator WI = getWeightIterator(I);
387 MachineBasicBlock::succ_iterator
388 MachineBasicBlock::removeSuccessor(succ_iterator I) {
389 assert(I != Successors.end() && "Not a current successor!");
391 // If Weight list is empty it means we don't use it (disabled optimization).
392 if (!Weights.empty()) {
393 weight_iterator WI = getWeightIterator(I);
397 (*I)->removePredecessor(this);
398 return Successors.erase(I);
401 void MachineBasicBlock::replaceSuccessor(MachineBasicBlock *Old,
402 MachineBasicBlock *New) {
404 succ_iterator SI = std::find(Successors.begin(), Successors.end(), Old);
406 // If Weight list is empty it means we don't use it (disabled optimization).
407 if (!Weights.empty()) {
408 weight_iterator WI = getWeightIterator(SI);
412 // Update the successor information.
414 addSuccessor(New, weight);
417 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
418 Predecessors.push_back(pred);
421 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
422 pred_iterator I = std::find(Predecessors.begin(), Predecessors.end(), pred);
423 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
424 Predecessors.erase(I);
427 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
431 while (!fromMBB->succ_empty()) {
432 MachineBasicBlock *Succ = *fromMBB->succ_begin();
436 // If Weight list is empty it means we don't use it (disabled optimization).
437 if (!fromMBB->Weights.empty())
438 weight = *fromMBB->Weights.begin();
440 addSuccessor(Succ, weight);
441 fromMBB->removeSuccessor(Succ);
446 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
450 while (!fromMBB->succ_empty()) {
451 MachineBasicBlock *Succ = *fromMBB->succ_begin();
453 fromMBB->removeSuccessor(Succ);
455 // Fix up any PHI nodes in the successor.
456 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
457 MI != ME && MI->isPHI(); ++MI)
458 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
459 MachineOperand &MO = MI->getOperand(i);
460 if (MO.getMBB() == fromMBB)
466 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
467 const_succ_iterator I = std::find(Successors.begin(), Successors.end(), MBB);
468 return I != Successors.end();
471 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
472 MachineFunction::const_iterator I(this);
473 return llvm::next(I) == MachineFunction::const_iterator(MBB);
476 bool MachineBasicBlock::canFallThrough() {
477 MachineFunction::iterator Fallthrough = this;
479 // If FallthroughBlock is off the end of the function, it can't fall through.
480 if (Fallthrough == getParent()->end())
483 // If FallthroughBlock isn't a successor, no fallthrough is possible.
484 if (!isSuccessor(Fallthrough))
487 // Analyze the branches, if any, at the end of the block.
488 MachineBasicBlock *TBB = 0, *FBB = 0;
489 SmallVector<MachineOperand, 4> Cond;
490 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
491 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
492 // If we couldn't analyze the branch, examine the last instruction.
493 // If the block doesn't end in a known control barrier, assume fallthrough
494 // is possible. The isPredicable check is needed because this code can be
495 // called during IfConversion, where an instruction which is normally a
496 // Barrier is predicated and thus no longer an actual control barrier. This
497 // is over-conservative though, because if an instruction isn't actually
498 // predicated we could still treat it like a barrier.
499 return empty() || !back().getDesc().isBarrier() ||
500 back().getDesc().isPredicable();
503 // If there is no branch, control always falls through.
504 if (TBB == 0) return true;
506 // If there is some explicit branch to the fallthrough block, it can obviously
507 // reach, even though the branch should get folded to fall through implicitly.
508 if (MachineFunction::iterator(TBB) == Fallthrough ||
509 MachineFunction::iterator(FBB) == Fallthrough)
512 // If it's an unconditional branch to some block not the fall through, it
513 // doesn't fall through.
514 if (Cond.empty()) return false;
516 // Otherwise, if it is conditional and has no explicit false block, it falls
522 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
523 MachineFunction *MF = getParent();
524 DebugLoc dl; // FIXME: this is nowhere
526 // We may need to update this's terminator, but we can't do that if
527 // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
528 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
529 MachineBasicBlock *TBB = 0, *FBB = 0;
530 SmallVector<MachineOperand, 4> Cond;
531 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
534 // Avoid bugpoint weirdness: A block may end with a conditional branch but
535 // jumps to the same MBB is either case. We have duplicate CFG edges in that
536 // case that we can't handle. Since this never happens in properly optimized
537 // code, just skip those edges.
538 if (TBB && TBB == FBB) {
539 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
540 << getNumber() << '\n');
544 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
545 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
546 DEBUG(dbgs() << "Splitting critical edge:"
547 " BB#" << getNumber()
548 << " -- BB#" << NMBB->getNumber()
549 << " -- BB#" << Succ->getNumber() << '\n');
551 // On some targets like Mips, branches may kill virtual registers. Make sure
552 // that LiveVariables is properly updated after updateTerminator replaces the
554 LiveVariables *LV = P->getAnalysisIfAvailable<LiveVariables>();
556 // Collect a list of virtual registers killed by the terminators.
557 SmallVector<unsigned, 4> KilledRegs;
559 for (iterator I = getFirstTerminator(), E = end(); I != E; ++I) {
560 MachineInstr *MI = I;
561 for (MachineInstr::mop_iterator OI = MI->operands_begin(),
562 OE = MI->operands_end(); OI != OE; ++OI) {
563 if (!OI->isReg() || !OI->isUse() || !OI->isKill() || OI->isUndef())
565 unsigned Reg = OI->getReg();
566 if (TargetRegisterInfo::isVirtualRegister(Reg) &&
567 LV->getVarInfo(Reg).removeKill(MI)) {
568 KilledRegs.push_back(Reg);
569 DEBUG(dbgs() << "Removing terminator kill: " << *MI);
570 OI->setIsKill(false);
575 ReplaceUsesOfBlockWith(Succ, NMBB);
578 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
579 NMBB->addSuccessor(Succ);
580 if (!NMBB->isLayoutSuccessor(Succ)) {
582 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
585 // Fix PHI nodes in Succ so they refer to NMBB instead of this
586 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
587 i != e && i->isPHI(); ++i)
588 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
589 if (i->getOperand(ni+1).getMBB() == this)
590 i->getOperand(ni+1).setMBB(NMBB);
592 // Inherit live-ins from the successor
593 for (MachineBasicBlock::livein_iterator I = Succ->livein_begin(),
594 E = Succ->livein_end(); I != E; ++I)
597 // Update LiveVariables.
599 // Restore kills of virtual registers that were killed by the terminators.
600 while (!KilledRegs.empty()) {
601 unsigned Reg = KilledRegs.pop_back_val();
602 for (iterator I = end(), E = begin(); I != E;) {
603 if (!(--I)->addRegisterKilled(Reg, NULL, /* addIfNotFound= */ false))
605 LV->getVarInfo(Reg).Kills.push_back(I);
606 DEBUG(dbgs() << "Restored terminator kill: " << *I);
610 // Update relevant live-through information.
611 LV->addNewBlock(NMBB, this, Succ);
614 if (MachineDominatorTree *MDT =
615 P->getAnalysisIfAvailable<MachineDominatorTree>()) {
616 // Update dominator information.
617 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
619 bool IsNewIDom = true;
620 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
622 MachineBasicBlock *PredBB = *PI;
625 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
631 // We know "this" dominates the newly created basic block.
632 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
634 // If all the other predecessors of "Succ" are dominated by "Succ" itself
635 // then the new block is the new immediate dominator of "Succ". Otherwise,
636 // the new block doesn't dominate anything.
638 MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
641 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
642 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
643 // If one or the other blocks were not in a loop, the new block is not
644 // either, and thus LI doesn't need to be updated.
645 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
646 if (TIL == DestLoop) {
647 // Both in the same loop, the NMBB joins loop.
648 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
649 } else if (TIL->contains(DestLoop)) {
650 // Edge from an outer loop to an inner loop. Add to the outer loop.
651 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
652 } else if (DestLoop->contains(TIL)) {
653 // Edge from an inner loop to an outer loop. Add to the outer loop.
654 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
656 // Edge from two loops with no containment relation. Because these
657 // are natural loops, we know that the destination block must be the
658 // header of its loop (adding a branch into a loop elsewhere would
659 // create an irreducible loop).
660 assert(DestLoop->getHeader() == Succ &&
661 "Should not create irreducible loops!");
662 if (MachineLoop *P = DestLoop->getParentLoop())
663 P->addBasicBlockToLoop(NMBB, MLI->getBase());
671 /// removeFromParent - This method unlinks 'this' from the containing function,
672 /// and returns it, but does not delete it.
673 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
674 assert(getParent() && "Not embedded in a function!");
675 getParent()->remove(this);
680 /// eraseFromParent - This method unlinks 'this' from the containing function,
682 void MachineBasicBlock::eraseFromParent() {
683 assert(getParent() && "Not embedded in a function!");
684 getParent()->erase(this);
688 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
689 /// 'Old', change the code and CFG so that it branches to 'New' instead.
690 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
691 MachineBasicBlock *New) {
692 assert(Old != New && "Cannot replace self with self!");
694 MachineBasicBlock::iterator I = end();
695 while (I != begin()) {
697 if (!I->getDesc().isTerminator()) break;
699 // Scan the operands of this machine instruction, replacing any uses of Old
701 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
702 if (I->getOperand(i).isMBB() &&
703 I->getOperand(i).getMBB() == Old)
704 I->getOperand(i).setMBB(New);
707 // Update the successor information.
708 replaceSuccessor(Old, New);
711 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
712 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
713 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
716 /// Besides DestA and DestB, retain other edges leading to LandingPads
717 /// (currently there can be only one; we don't check or require that here).
718 /// Note it is possible that DestA and/or DestB are LandingPads.
719 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
720 MachineBasicBlock *DestB,
722 // The values of DestA and DestB frequently come from a call to the
723 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
724 // values from there.
726 // 1. If both DestA and DestB are null, then the block ends with no branches
727 // (it falls through to its successor).
728 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
729 // with only an unconditional branch.
730 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
731 // with a conditional branch that falls through to a successor (DestB).
732 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
733 // conditional branch followed by an unconditional branch. DestA is the
734 // 'true' destination and DestB is the 'false' destination.
736 bool Changed = false;
738 MachineFunction::iterator FallThru =
739 llvm::next(MachineFunction::iterator(this));
741 if (DestA == 0 && DestB == 0) {
742 // Block falls through to successor.
745 } else if (DestA != 0 && DestB == 0) {
747 // Block ends in conditional jump that falls through to successor.
750 assert(DestA && DestB && isCond &&
751 "CFG in a bad state. Cannot correct CFG edges");
754 // Remove superfluous edges. I.e., those which aren't destinations of this
755 // basic block, duplicate edges, or landing pads.
756 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
757 MachineBasicBlock::succ_iterator SI = succ_begin();
758 while (SI != succ_end()) {
759 const MachineBasicBlock *MBB = *SI;
760 if (!SeenMBBs.insert(MBB) ||
761 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
762 // This is a superfluous edge, remove it.
763 SI = removeSuccessor(SI);
773 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
774 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
776 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
778 MachineBasicBlock::iterator E = end();
780 // Skip debug declarations, we don't want a DebugLoc from them.
781 MachineBasicBlock::iterator MBBI2 = MBBI;
782 while (MBBI2 != E && MBBI2->isDebugValue())
785 DL = MBBI2->getDebugLoc();
790 /// getSuccWeight - Return weight of the edge from this block to MBB.
792 uint32_t MachineBasicBlock::getSuccWeight(MachineBasicBlock *succ) {
796 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
797 return *getWeightIterator(I);
800 /// getWeightIterator - Return wight iterator corresonding to the I successor
802 MachineBasicBlock::weight_iterator MachineBasicBlock::
803 getWeightIterator(MachineBasicBlock::succ_iterator I) {
804 assert(Weights.size() == Successors.size() && "Async weight list!");
805 size_t index = std::distance(Successors.begin(), I);
806 assert(index < Weights.size() && "Not a current successor!");
807 return Weights.begin() + index;
810 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
812 OS << "BB#" << MBB->getNumber();