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) {
343 Successors.push_back(succ);
344 succ->addPredecessor(this);
347 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
348 succ->removePredecessor(this);
349 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
350 assert(I != Successors.end() && "Not a current successor!");
354 MachineBasicBlock::succ_iterator
355 MachineBasicBlock::removeSuccessor(succ_iterator I) {
356 assert(I != Successors.end() && "Not a current successor!");
357 (*I)->removePredecessor(this);
358 return Successors.erase(I);
361 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
362 Predecessors.push_back(pred);
365 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
366 std::vector<MachineBasicBlock *>::iterator I =
367 std::find(Predecessors.begin(), Predecessors.end(), pred);
368 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
369 Predecessors.erase(I);
372 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
376 while (!fromMBB->succ_empty()) {
377 MachineBasicBlock *Succ = *fromMBB->succ_begin();
379 fromMBB->removeSuccessor(Succ);
384 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
388 while (!fromMBB->succ_empty()) {
389 MachineBasicBlock *Succ = *fromMBB->succ_begin();
391 fromMBB->removeSuccessor(Succ);
393 // Fix up any PHI nodes in the successor.
394 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
395 MI != ME && MI->isPHI(); ++MI)
396 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
397 MachineOperand &MO = MI->getOperand(i);
398 if (MO.getMBB() == fromMBB)
404 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
405 std::vector<MachineBasicBlock *>::const_iterator I =
406 std::find(Successors.begin(), Successors.end(), MBB);
407 return I != Successors.end();
410 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
411 MachineFunction::const_iterator I(this);
412 return llvm::next(I) == MachineFunction::const_iterator(MBB);
415 bool MachineBasicBlock::canFallThrough() {
416 MachineFunction::iterator Fallthrough = this;
418 // If FallthroughBlock is off the end of the function, it can't fall through.
419 if (Fallthrough == getParent()->end())
422 // If FallthroughBlock isn't a successor, no fallthrough is possible.
423 if (!isSuccessor(Fallthrough))
426 // Analyze the branches, if any, at the end of the block.
427 MachineBasicBlock *TBB = 0, *FBB = 0;
428 SmallVector<MachineOperand, 4> Cond;
429 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
430 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
431 // If we couldn't analyze the branch, examine the last instruction.
432 // If the block doesn't end in a known control barrier, assume fallthrough
433 // is possible. The isPredicable check is needed because this code can be
434 // called during IfConversion, where an instruction which is normally a
435 // Barrier is predicated and thus no longer an actual control barrier. This
436 // is over-conservative though, because if an instruction isn't actually
437 // predicated we could still treat it like a barrier.
438 return empty() || !back().getDesc().isBarrier() ||
439 back().getDesc().isPredicable();
442 // If there is no branch, control always falls through.
443 if (TBB == 0) return true;
445 // If there is some explicit branch to the fallthrough block, it can obviously
446 // reach, even though the branch should get folded to fall through implicitly.
447 if (MachineFunction::iterator(TBB) == Fallthrough ||
448 MachineFunction::iterator(FBB) == Fallthrough)
451 // If it's an unconditional branch to some block not the fall through, it
452 // doesn't fall through.
453 if (Cond.empty()) return false;
455 // Otherwise, if it is conditional and has no explicit false block, it falls
461 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
462 MachineFunction *MF = getParent();
463 DebugLoc dl; // FIXME: this is nowhere
465 // We may need to update this's terminator, but we can't do that if
466 // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
467 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
468 MachineBasicBlock *TBB = 0, *FBB = 0;
469 SmallVector<MachineOperand, 4> Cond;
470 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
473 // Avoid bugpoint weirdness: A block may end with a conditional branch but
474 // jumps to the same MBB is either case. We have duplicate CFG edges in that
475 // case that we can't handle. Since this never happens in properly optimized
476 // code, just skip those edges.
477 if (TBB && TBB == FBB) {
478 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
479 << getNumber() << '\n');
483 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
484 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
485 DEBUG(dbgs() << "Splitting critical edge:"
486 " BB#" << getNumber()
487 << " -- BB#" << NMBB->getNumber()
488 << " -- BB#" << Succ->getNumber() << '\n');
490 ReplaceUsesOfBlockWith(Succ, NMBB);
493 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
494 NMBB->addSuccessor(Succ);
495 if (!NMBB->isLayoutSuccessor(Succ)) {
497 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
500 // Fix PHI nodes in Succ so they refer to NMBB instead of this
501 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
502 i != e && i->isPHI(); ++i)
503 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
504 if (i->getOperand(ni+1).getMBB() == this)
505 i->getOperand(ni+1).setMBB(NMBB);
507 if (LiveVariables *LV =
508 P->getAnalysisIfAvailable<LiveVariables>())
509 LV->addNewBlock(NMBB, this, Succ);
511 if (MachineDominatorTree *MDT =
512 P->getAnalysisIfAvailable<MachineDominatorTree>()) {
513 // Update dominator information.
514 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
516 bool IsNewIDom = true;
517 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
519 MachineBasicBlock *PredBB = *PI;
522 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
528 // We know "this" dominates the newly created basic block.
529 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
531 // If all the other predecessors of "Succ" are dominated by "Succ" itself
532 // then the new block is the new immediate dominator of "Succ". Otherwise,
533 // the new block doesn't dominate anything.
535 MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
538 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
539 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
540 // If one or the other blocks were not in a loop, the new block is not
541 // either, and thus LI doesn't need to be updated.
542 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
543 if (TIL == DestLoop) {
544 // Both in the same loop, the NMBB joins loop.
545 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
546 } else if (TIL->contains(DestLoop)) {
547 // Edge from an outer loop to an inner loop. Add to the outer loop.
548 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
549 } else if (DestLoop->contains(TIL)) {
550 // Edge from an inner loop to an outer loop. Add to the outer loop.
551 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
553 // Edge from two loops with no containment relation. Because these
554 // are natural loops, we know that the destination block must be the
555 // header of its loop (adding a branch into a loop elsewhere would
556 // create an irreducible loop).
557 assert(DestLoop->getHeader() == Succ &&
558 "Should not create irreducible loops!");
559 if (MachineLoop *P = DestLoop->getParentLoop())
560 P->addBasicBlockToLoop(NMBB, MLI->getBase());
568 /// removeFromParent - This method unlinks 'this' from the containing function,
569 /// and returns it, but does not delete it.
570 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
571 assert(getParent() && "Not embedded in a function!");
572 getParent()->remove(this);
577 /// eraseFromParent - This method unlinks 'this' from the containing function,
579 void MachineBasicBlock::eraseFromParent() {
580 assert(getParent() && "Not embedded in a function!");
581 getParent()->erase(this);
585 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
586 /// 'Old', change the code and CFG so that it branches to 'New' instead.
587 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
588 MachineBasicBlock *New) {
589 assert(Old != New && "Cannot replace self with self!");
591 MachineBasicBlock::iterator I = end();
592 while (I != begin()) {
594 if (!I->getDesc().isTerminator()) break;
596 // Scan the operands of this machine instruction, replacing any uses of Old
598 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
599 if (I->getOperand(i).isMBB() &&
600 I->getOperand(i).getMBB() == Old)
601 I->getOperand(i).setMBB(New);
604 // Update the successor information.
605 removeSuccessor(Old);
609 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
610 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
611 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
614 /// Besides DestA and DestB, retain other edges leading to LandingPads
615 /// (currently there can be only one; we don't check or require that here).
616 /// Note it is possible that DestA and/or DestB are LandingPads.
617 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
618 MachineBasicBlock *DestB,
620 // The values of DestA and DestB frequently come from a call to the
621 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
622 // values from there.
624 // 1. If both DestA and DestB are null, then the block ends with no branches
625 // (it falls through to its successor).
626 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
627 // with only an unconditional branch.
628 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
629 // with a conditional branch that falls through to a successor (DestB).
630 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
631 // conditional branch followed by an unconditional branch. DestA is the
632 // 'true' destination and DestB is the 'false' destination.
634 bool Changed = false;
636 MachineFunction::iterator FallThru =
637 llvm::next(MachineFunction::iterator(this));
639 if (DestA == 0 && DestB == 0) {
640 // Block falls through to successor.
643 } else if (DestA != 0 && DestB == 0) {
645 // Block ends in conditional jump that falls through to successor.
648 assert(DestA && DestB && isCond &&
649 "CFG in a bad state. Cannot correct CFG edges");
652 // Remove superfluous edges. I.e., those which aren't destinations of this
653 // basic block, duplicate edges, or landing pads.
654 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
655 MachineBasicBlock::succ_iterator SI = succ_begin();
656 while (SI != succ_end()) {
657 const MachineBasicBlock *MBB = *SI;
658 if (!SeenMBBs.insert(MBB) ||
659 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
660 // This is a superfluous edge, remove it.
661 SI = removeSuccessor(SI);
671 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
672 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
674 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
676 MachineBasicBlock::iterator E = end();
678 // Skip debug declarations, we don't want a DebugLoc from them.
679 MachineBasicBlock::iterator MBBI2 = MBBI;
680 while (MBBI2 != E && MBBI2->isDebugValue())
683 DL = MBBI2->getDebugLoc();
688 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
690 OS << "BB#" << MBB->getNumber();