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 void MachineBasicBlock::dump() const {
182 StringRef MachineBasicBlock::getName() const {
183 if (const BasicBlock *LBB = getBasicBlock())
184 return LBB->getName();
189 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
190 const MachineFunction *MF = getParent();
192 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
197 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
200 OS << Indexes->getMBBStartIdx(this) << '\t';
202 OS << "BB#" << getNumber() << ": ";
204 const char *Comma = "";
205 if (const BasicBlock *LBB = getBasicBlock()) {
206 OS << Comma << "derived from LLVM BB ";
207 WriteAsOperand(OS, LBB, /*PrintType=*/false);
210 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
211 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
214 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
215 if (!livein_empty()) {
216 if (Indexes) OS << '\t';
218 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
219 OS << ' ' << PrintReg(*I, TRI);
222 // Print the preds of this block according to the CFG.
224 if (Indexes) OS << '\t';
225 OS << " Predecessors according to CFG:";
226 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
227 OS << " BB#" << (*PI)->getNumber();
231 for (const_iterator I = begin(); I != end(); ++I) {
233 if (Indexes->hasIndex(I))
234 OS << Indexes->getInstructionIndex(I);
238 I->print(OS, &getParent()->getTarget());
241 // Print the successors of this block according to the CFG.
243 if (Indexes) OS << '\t';
244 OS << " Successors according to CFG:";
245 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
246 OS << " BB#" << (*SI)->getNumber();
251 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
252 std::vector<unsigned>::iterator I =
253 std::find(LiveIns.begin(), LiveIns.end(), Reg);
254 assert(I != LiveIns.end() && "Not a live in!");
258 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
259 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
260 return I != livein_end();
263 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
264 getParent()->splice(NewAfter, this);
267 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
268 MachineFunction::iterator BBI = NewBefore;
269 getParent()->splice(++BBI, this);
272 void MachineBasicBlock::updateTerminator() {
273 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
274 // A block with no successors has no concerns with fall-through edges.
275 if (this->succ_empty()) return;
277 MachineBasicBlock *TBB = 0, *FBB = 0;
278 SmallVector<MachineOperand, 4> Cond;
279 DebugLoc dl; // FIXME: this is nowhere
280 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
282 assert(!B && "UpdateTerminators requires analyzable predecessors!");
285 // The block has an unconditional branch. If its successor is now
286 // its layout successor, delete the branch.
287 if (isLayoutSuccessor(TBB))
288 TII->RemoveBranch(*this);
290 // The block has an unconditional fallthrough. If its successor is not
291 // its layout successor, insert a branch.
293 if (!isLayoutSuccessor(TBB))
294 TII->InsertBranch(*this, TBB, 0, Cond, dl);
298 // The block has a non-fallthrough conditional branch. If one of its
299 // successors is its layout successor, rewrite it to a fallthrough
300 // conditional branch.
301 if (isLayoutSuccessor(TBB)) {
302 if (TII->ReverseBranchCondition(Cond))
304 TII->RemoveBranch(*this);
305 TII->InsertBranch(*this, FBB, 0, Cond, dl);
306 } else if (isLayoutSuccessor(FBB)) {
307 TII->RemoveBranch(*this);
308 TII->InsertBranch(*this, TBB, 0, Cond, dl);
311 // The block has a fallthrough conditional branch.
312 MachineBasicBlock *MBBA = *succ_begin();
313 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
314 if (MBBA == TBB) std::swap(MBBB, MBBA);
315 if (isLayoutSuccessor(TBB)) {
316 if (TII->ReverseBranchCondition(Cond)) {
317 // We can't reverse the condition, add an unconditional branch.
319 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
322 TII->RemoveBranch(*this);
323 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
324 } else if (!isLayoutSuccessor(MBBA)) {
325 TII->RemoveBranch(*this);
326 TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
332 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
333 Successors.push_back(succ);
334 succ->addPredecessor(this);
337 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
338 succ->removePredecessor(this);
339 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
340 assert(I != Successors.end() && "Not a current successor!");
344 MachineBasicBlock::succ_iterator
345 MachineBasicBlock::removeSuccessor(succ_iterator I) {
346 assert(I != Successors.end() && "Not a current successor!");
347 (*I)->removePredecessor(this);
348 return Successors.erase(I);
351 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
352 Predecessors.push_back(pred);
355 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
356 std::vector<MachineBasicBlock *>::iterator I =
357 std::find(Predecessors.begin(), Predecessors.end(), pred);
358 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
359 Predecessors.erase(I);
362 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
366 while (!fromMBB->succ_empty()) {
367 MachineBasicBlock *Succ = *fromMBB->succ_begin();
369 fromMBB->removeSuccessor(Succ);
374 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
378 while (!fromMBB->succ_empty()) {
379 MachineBasicBlock *Succ = *fromMBB->succ_begin();
381 fromMBB->removeSuccessor(Succ);
383 // Fix up any PHI nodes in the successor.
384 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
385 MI != ME && MI->isPHI(); ++MI)
386 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
387 MachineOperand &MO = MI->getOperand(i);
388 if (MO.getMBB() == fromMBB)
394 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
395 std::vector<MachineBasicBlock *>::const_iterator I =
396 std::find(Successors.begin(), Successors.end(), MBB);
397 return I != Successors.end();
400 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
401 MachineFunction::const_iterator I(this);
402 return llvm::next(I) == MachineFunction::const_iterator(MBB);
405 bool MachineBasicBlock::canFallThrough() {
406 MachineFunction::iterator Fallthrough = this;
408 // If FallthroughBlock is off the end of the function, it can't fall through.
409 if (Fallthrough == getParent()->end())
412 // If FallthroughBlock isn't a successor, no fallthrough is possible.
413 if (!isSuccessor(Fallthrough))
416 // Analyze the branches, if any, at the end of the block.
417 MachineBasicBlock *TBB = 0, *FBB = 0;
418 SmallVector<MachineOperand, 4> Cond;
419 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
420 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
421 // If we couldn't analyze the branch, examine the last instruction.
422 // If the block doesn't end in a known control barrier, assume fallthrough
423 // is possible. The isPredicable check is needed because this code can be
424 // called during IfConversion, where an instruction which is normally a
425 // Barrier is predicated and thus no longer an actual control barrier. This
426 // is over-conservative though, because if an instruction isn't actually
427 // predicated we could still treat it like a barrier.
428 return empty() || !back().getDesc().isBarrier() ||
429 back().getDesc().isPredicable();
432 // If there is no branch, control always falls through.
433 if (TBB == 0) return true;
435 // If there is some explicit branch to the fallthrough block, it can obviously
436 // reach, even though the branch should get folded to fall through implicitly.
437 if (MachineFunction::iterator(TBB) == Fallthrough ||
438 MachineFunction::iterator(FBB) == Fallthrough)
441 // If it's an unconditional branch to some block not the fall through, it
442 // doesn't fall through.
443 if (Cond.empty()) return false;
445 // Otherwise, if it is conditional and has no explicit false block, it falls
451 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
452 MachineFunction *MF = getParent();
453 DebugLoc dl; // FIXME: this is nowhere
455 // We may need to update this's terminator, but we can't do that if
456 // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
457 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
458 MachineBasicBlock *TBB = 0, *FBB = 0;
459 SmallVector<MachineOperand, 4> Cond;
460 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
463 // Avoid bugpoint weirdness: A block may end with a conditional branch but
464 // jumps to the same MBB is either case. We have duplicate CFG edges in that
465 // case that we can't handle. Since this never happens in properly optimized
466 // code, just skip those edges.
467 if (TBB && TBB == FBB) {
468 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
469 << getNumber() << '\n');
473 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
474 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
475 DEBUG(dbgs() << "Splitting critical edge:"
476 " BB#" << getNumber()
477 << " -- BB#" << NMBB->getNumber()
478 << " -- BB#" << Succ->getNumber() << '\n');
480 ReplaceUsesOfBlockWith(Succ, NMBB);
483 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
484 NMBB->addSuccessor(Succ);
485 if (!NMBB->isLayoutSuccessor(Succ)) {
487 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
490 // Fix PHI nodes in Succ so they refer to NMBB instead of this
491 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
492 i != e && i->isPHI(); ++i)
493 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
494 if (i->getOperand(ni+1).getMBB() == this)
495 i->getOperand(ni+1).setMBB(NMBB);
497 if (LiveVariables *LV =
498 P->getAnalysisIfAvailable<LiveVariables>())
499 LV->addNewBlock(NMBB, this, Succ);
501 if (MachineDominatorTree *MDT =
502 P->getAnalysisIfAvailable<MachineDominatorTree>()) {
503 // Update dominator information.
504 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
506 bool IsNewIDom = true;
507 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
509 MachineBasicBlock *PredBB = *PI;
512 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
518 // We know "this" dominates the newly created basic block.
519 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
521 // If all the other predecessors of "Succ" are dominated by "Succ" itself
522 // then the new block is the new immediate dominator of "Succ". Otherwise,
523 // the new block doesn't dominate anything.
525 MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
528 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
529 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
530 // If one or the other blocks were not in a loop, the new block is not
531 // either, and thus LI doesn't need to be updated.
532 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
533 if (TIL == DestLoop) {
534 // Both in the same loop, the NMBB joins loop.
535 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
536 } else if (TIL->contains(DestLoop)) {
537 // Edge from an outer loop to an inner loop. Add to the outer loop.
538 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
539 } else if (DestLoop->contains(TIL)) {
540 // Edge from an inner loop to an outer loop. Add to the outer loop.
541 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
543 // Edge from two loops with no containment relation. Because these
544 // are natural loops, we know that the destination block must be the
545 // header of its loop (adding a branch into a loop elsewhere would
546 // create an irreducible loop).
547 assert(DestLoop->getHeader() == Succ &&
548 "Should not create irreducible loops!");
549 if (MachineLoop *P = DestLoop->getParentLoop())
550 P->addBasicBlockToLoop(NMBB, MLI->getBase());
558 /// removeFromParent - This method unlinks 'this' from the containing function,
559 /// and returns it, but does not delete it.
560 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
561 assert(getParent() && "Not embedded in a function!");
562 getParent()->remove(this);
567 /// eraseFromParent - This method unlinks 'this' from the containing function,
569 void MachineBasicBlock::eraseFromParent() {
570 assert(getParent() && "Not embedded in a function!");
571 getParent()->erase(this);
575 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
576 /// 'Old', change the code and CFG so that it branches to 'New' instead.
577 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
578 MachineBasicBlock *New) {
579 assert(Old != New && "Cannot replace self with self!");
581 MachineBasicBlock::iterator I = end();
582 while (I != begin()) {
584 if (!I->getDesc().isTerminator()) break;
586 // Scan the operands of this machine instruction, replacing any uses of Old
588 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
589 if (I->getOperand(i).isMBB() &&
590 I->getOperand(i).getMBB() == Old)
591 I->getOperand(i).setMBB(New);
594 // Update the successor information.
595 removeSuccessor(Old);
599 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
600 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
601 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
604 /// Besides DestA and DestB, retain other edges leading to LandingPads
605 /// (currently there can be only one; we don't check or require that here).
606 /// Note it is possible that DestA and/or DestB are LandingPads.
607 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
608 MachineBasicBlock *DestB,
610 // The values of DestA and DestB frequently come from a call to the
611 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
612 // values from there.
614 // 1. If both DestA and DestB are null, then the block ends with no branches
615 // (it falls through to its successor).
616 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
617 // with only an unconditional branch.
618 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
619 // with a conditional branch that falls through to a successor (DestB).
620 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
621 // conditional branch followed by an unconditional branch. DestA is the
622 // 'true' destination and DestB is the 'false' destination.
624 bool Changed = false;
626 MachineFunction::iterator FallThru =
627 llvm::next(MachineFunction::iterator(this));
629 if (DestA == 0 && DestB == 0) {
630 // Block falls through to successor.
633 } else if (DestA != 0 && DestB == 0) {
635 // Block ends in conditional jump that falls through to successor.
638 assert(DestA && DestB && isCond &&
639 "CFG in a bad state. Cannot correct CFG edges");
642 // Remove superfluous edges. I.e., those which aren't destinations of this
643 // basic block, duplicate edges, or landing pads.
644 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
645 MachineBasicBlock::succ_iterator SI = succ_begin();
646 while (SI != succ_end()) {
647 const MachineBasicBlock *MBB = *SI;
648 if (!SeenMBBs.insert(MBB) ||
649 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
650 // This is a superfluous edge, remove it.
651 SI = removeSuccessor(SI);
661 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
662 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
664 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
666 MachineBasicBlock::iterator E = end();
668 // Skip debug declarations, we don't want a DebugLoc from them.
669 MachineBasicBlock::iterator MBBI2 = MBBI;
670 while (MBBI2 != E && MBBI2->isDebugValue())
673 DL = MBBI2->getDebugLoc();
678 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
680 OS << "BB#" << MBB->getNumber();