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())
161 if (I != end() && !I->getDesc().isTerminator()) ++I;
165 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {
166 iterator B = begin(), I = end();
169 if (I->isDebugValue())
173 // The block is all debug values.
177 void MachineBasicBlock::dump() const {
181 StringRef MachineBasicBlock::getName() const {
182 if (const BasicBlock *LBB = getBasicBlock())
183 return LBB->getName();
188 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
189 const MachineFunction *MF = getParent();
191 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
196 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
199 OS << Indexes->getMBBStartIdx(this) << '\t';
201 OS << "BB#" << getNumber() << ": ";
203 const char *Comma = "";
204 if (const BasicBlock *LBB = getBasicBlock()) {
205 OS << Comma << "derived from LLVM BB ";
206 WriteAsOperand(OS, LBB, /*PrintType=*/false);
209 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
210 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
213 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
214 if (!livein_empty()) {
215 if (Indexes) OS << '\t';
217 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
218 OS << ' ' << PrintReg(*I, TRI);
221 // Print the preds of this block according to the CFG.
223 if (Indexes) OS << '\t';
224 OS << " Predecessors according to CFG:";
225 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
226 OS << " BB#" << (*PI)->getNumber();
230 for (const_iterator I = begin(); I != end(); ++I) {
232 if (Indexes->hasIndex(I))
233 OS << Indexes->getInstructionIndex(I);
237 I->print(OS, &getParent()->getTarget());
240 // Print the successors of this block according to the CFG.
242 if (Indexes) OS << '\t';
243 OS << " Successors according to CFG:";
244 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
245 OS << " BB#" << (*SI)->getNumber();
250 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
251 std::vector<unsigned>::iterator I =
252 std::find(LiveIns.begin(), LiveIns.end(), Reg);
253 assert(I != LiveIns.end() && "Not a live in!");
257 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
258 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
259 return I != livein_end();
262 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
263 getParent()->splice(NewAfter, this);
266 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
267 MachineFunction::iterator BBI = NewBefore;
268 getParent()->splice(++BBI, this);
271 void MachineBasicBlock::updateTerminator() {
272 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
273 // A block with no successors has no concerns with fall-through edges.
274 if (this->succ_empty()) return;
276 MachineBasicBlock *TBB = 0, *FBB = 0;
277 SmallVector<MachineOperand, 4> Cond;
278 DebugLoc dl; // FIXME: this is nowhere
279 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
281 assert(!B && "UpdateTerminators requires analyzable predecessors!");
284 // The block has an unconditional branch. If its successor is now
285 // its layout successor, delete the branch.
286 if (isLayoutSuccessor(TBB))
287 TII->RemoveBranch(*this);
289 // The block has an unconditional fallthrough. If its successor is not
290 // its layout successor, insert a branch.
292 if (!isLayoutSuccessor(TBB))
293 TII->InsertBranch(*this, TBB, 0, Cond, dl);
297 // The block has a non-fallthrough conditional branch. If one of its
298 // successors is its layout successor, rewrite it to a fallthrough
299 // conditional branch.
300 if (isLayoutSuccessor(TBB)) {
301 if (TII->ReverseBranchCondition(Cond))
303 TII->RemoveBranch(*this);
304 TII->InsertBranch(*this, FBB, 0, Cond, dl);
305 } else if (isLayoutSuccessor(FBB)) {
306 TII->RemoveBranch(*this);
307 TII->InsertBranch(*this, TBB, 0, Cond, dl);
310 // The block has a fallthrough conditional branch.
311 MachineBasicBlock *MBBA = *succ_begin();
312 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
313 if (MBBA == TBB) std::swap(MBBB, MBBA);
314 if (isLayoutSuccessor(TBB)) {
315 if (TII->ReverseBranchCondition(Cond)) {
316 // We can't reverse the condition, add an unconditional branch.
318 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
321 TII->RemoveBranch(*this);
322 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
323 } else if (!isLayoutSuccessor(MBBA)) {
324 TII->RemoveBranch(*this);
325 TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
331 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
332 Successors.push_back(succ);
333 succ->addPredecessor(this);
336 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
337 succ->removePredecessor(this);
338 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
339 assert(I != Successors.end() && "Not a current successor!");
343 MachineBasicBlock::succ_iterator
344 MachineBasicBlock::removeSuccessor(succ_iterator I) {
345 assert(I != Successors.end() && "Not a current successor!");
346 (*I)->removePredecessor(this);
347 return Successors.erase(I);
350 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
351 Predecessors.push_back(pred);
354 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
355 std::vector<MachineBasicBlock *>::iterator I =
356 std::find(Predecessors.begin(), Predecessors.end(), pred);
357 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
358 Predecessors.erase(I);
361 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
365 while (!fromMBB->succ_empty()) {
366 MachineBasicBlock *Succ = *fromMBB->succ_begin();
368 fromMBB->removeSuccessor(Succ);
373 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
377 while (!fromMBB->succ_empty()) {
378 MachineBasicBlock *Succ = *fromMBB->succ_begin();
380 fromMBB->removeSuccessor(Succ);
382 // Fix up any PHI nodes in the successor.
383 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
384 MI != ME && MI->isPHI(); ++MI)
385 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
386 MachineOperand &MO = MI->getOperand(i);
387 if (MO.getMBB() == fromMBB)
393 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
394 std::vector<MachineBasicBlock *>::const_iterator I =
395 std::find(Successors.begin(), Successors.end(), MBB);
396 return I != Successors.end();
399 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
400 MachineFunction::const_iterator I(this);
401 return llvm::next(I) == MachineFunction::const_iterator(MBB);
404 bool MachineBasicBlock::canFallThrough() {
405 MachineFunction::iterator Fallthrough = this;
407 // If FallthroughBlock is off the end of the function, it can't fall through.
408 if (Fallthrough == getParent()->end())
411 // If FallthroughBlock isn't a successor, no fallthrough is possible.
412 if (!isSuccessor(Fallthrough))
415 // Analyze the branches, if any, at the end of the block.
416 MachineBasicBlock *TBB = 0, *FBB = 0;
417 SmallVector<MachineOperand, 4> Cond;
418 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
419 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
420 // If we couldn't analyze the branch, examine the last instruction.
421 // If the block doesn't end in a known control barrier, assume fallthrough
422 // is possible. The isPredicable check is needed because this code can be
423 // called during IfConversion, where an instruction which is normally a
424 // Barrier is predicated and thus no longer an actual control barrier. This
425 // is over-conservative though, because if an instruction isn't actually
426 // predicated we could still treat it like a barrier.
427 return empty() || !back().getDesc().isBarrier() ||
428 back().getDesc().isPredicable();
431 // If there is no branch, control always falls through.
432 if (TBB == 0) return true;
434 // If there is some explicit branch to the fallthrough block, it can obviously
435 // reach, even though the branch should get folded to fall through implicitly.
436 if (MachineFunction::iterator(TBB) == Fallthrough ||
437 MachineFunction::iterator(FBB) == Fallthrough)
440 // If it's an unconditional branch to some block not the fall through, it
441 // doesn't fall through.
442 if (Cond.empty()) return false;
444 // Otherwise, if it is conditional and has no explicit false block, it falls
450 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
451 MachineFunction *MF = getParent();
452 DebugLoc dl; // FIXME: this is nowhere
454 // We may need to update this's terminator, but we can't do that if
455 // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
456 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
457 MachineBasicBlock *TBB = 0, *FBB = 0;
458 SmallVector<MachineOperand, 4> Cond;
459 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
462 // Avoid bugpoint weirdness: A block may end with a conditional branch but
463 // jumps to the same MBB is either case. We have duplicate CFG edges in that
464 // case that we can't handle. Since this never happens in properly optimized
465 // code, just skip those edges.
466 if (TBB && TBB == FBB) {
467 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
468 << getNumber() << '\n');
472 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
473 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
474 DEBUG(dbgs() << "Splitting critical edge:"
475 " BB#" << getNumber()
476 << " -- BB#" << NMBB->getNumber()
477 << " -- BB#" << Succ->getNumber() << '\n');
479 ReplaceUsesOfBlockWith(Succ, NMBB);
482 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
483 NMBB->addSuccessor(Succ);
484 if (!NMBB->isLayoutSuccessor(Succ)) {
486 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
489 // Fix PHI nodes in Succ so they refer to NMBB instead of this
490 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
491 i != e && i->isPHI(); ++i)
492 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
493 if (i->getOperand(ni+1).getMBB() == this)
494 i->getOperand(ni+1).setMBB(NMBB);
496 if (LiveVariables *LV =
497 P->getAnalysisIfAvailable<LiveVariables>())
498 LV->addNewBlock(NMBB, this, Succ);
500 if (MachineDominatorTree *MDT =
501 P->getAnalysisIfAvailable<MachineDominatorTree>()) {
502 // Update dominator information.
503 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
505 bool IsNewIDom = true;
506 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
508 MachineBasicBlock *PredBB = *PI;
511 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
517 // We know "this" dominates the newly created basic block.
518 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
520 // If all the other predecessors of "Succ" are dominated by "Succ" itself
521 // then the new block is the new immediate dominator of "Succ". Otherwise,
522 // the new block doesn't dominate anything.
524 MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
527 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
528 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
529 // If one or the other blocks were not in a loop, the new block is not
530 // either, and thus LI doesn't need to be updated.
531 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
532 if (TIL == DestLoop) {
533 // Both in the same loop, the NMBB joins loop.
534 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
535 } else if (TIL->contains(DestLoop)) {
536 // Edge from an outer loop to an inner loop. Add to the outer loop.
537 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
538 } else if (DestLoop->contains(TIL)) {
539 // Edge from an inner loop to an outer loop. Add to the outer loop.
540 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
542 // Edge from two loops with no containment relation. Because these
543 // are natural loops, we know that the destination block must be the
544 // header of its loop (adding a branch into a loop elsewhere would
545 // create an irreducible loop).
546 assert(DestLoop->getHeader() == Succ &&
547 "Should not create irreducible loops!");
548 if (MachineLoop *P = DestLoop->getParentLoop())
549 P->addBasicBlockToLoop(NMBB, MLI->getBase());
557 /// removeFromParent - This method unlinks 'this' from the containing function,
558 /// and returns it, but does not delete it.
559 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
560 assert(getParent() && "Not embedded in a function!");
561 getParent()->remove(this);
566 /// eraseFromParent - This method unlinks 'this' from the containing function,
568 void MachineBasicBlock::eraseFromParent() {
569 assert(getParent() && "Not embedded in a function!");
570 getParent()->erase(this);
574 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
575 /// 'Old', change the code and CFG so that it branches to 'New' instead.
576 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
577 MachineBasicBlock *New) {
578 assert(Old != New && "Cannot replace self with self!");
580 MachineBasicBlock::iterator I = end();
581 while (I != begin()) {
583 if (!I->getDesc().isTerminator()) break;
585 // Scan the operands of this machine instruction, replacing any uses of Old
587 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
588 if (I->getOperand(i).isMBB() &&
589 I->getOperand(i).getMBB() == Old)
590 I->getOperand(i).setMBB(New);
593 // Update the successor information.
594 removeSuccessor(Old);
598 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
599 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
600 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
603 /// Besides DestA and DestB, retain other edges leading to LandingPads
604 /// (currently there can be only one; we don't check or require that here).
605 /// Note it is possible that DestA and/or DestB are LandingPads.
606 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
607 MachineBasicBlock *DestB,
609 // The values of DestA and DestB frequently come from a call to the
610 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
611 // values from there.
613 // 1. If both DestA and DestB are null, then the block ends with no branches
614 // (it falls through to its successor).
615 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
616 // with only an unconditional branch.
617 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
618 // with a conditional branch that falls through to a successor (DestB).
619 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
620 // conditional branch followed by an unconditional branch. DestA is the
621 // 'true' destination and DestB is the 'false' destination.
623 bool Changed = false;
625 MachineFunction::iterator FallThru =
626 llvm::next(MachineFunction::iterator(this));
628 if (DestA == 0 && DestB == 0) {
629 // Block falls through to successor.
632 } else if (DestA != 0 && DestB == 0) {
634 // Block ends in conditional jump that falls through to successor.
637 assert(DestA && DestB && isCond &&
638 "CFG in a bad state. Cannot correct CFG edges");
641 // Remove superfluous edges. I.e., those which aren't destinations of this
642 // basic block, duplicate edges, or landing pads.
643 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
644 MachineBasicBlock::succ_iterator SI = succ_begin();
645 while (SI != succ_end()) {
646 const MachineBasicBlock *MBB = *SI;
647 if (!SeenMBBs.insert(MBB) ||
648 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
649 // This is a superfluous edge, remove it.
650 SI = removeSuccessor(SI);
660 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
661 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
663 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
665 MachineBasicBlock::iterator E = end();
667 // Skip debug declarations, we don't want a DebugLoc from them.
668 MachineBasicBlock::iterator MBBI2 = MBBI;
669 while (MBBI2 != E && MBBI2->isDebugValue())
672 DL = MBBI2->getDebugLoc();
677 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
679 OS << "BB#" << MBB->getNumber();