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/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/Target/TargetRegisterInfo.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/Target/TargetInstrDesc.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::getFirstTerminator() {
144 while (I != begin() && (--I)->getDesc().isTerminator())
146 if (I != end() && !I->getDesc().isTerminator()) ++I;
150 void MachineBasicBlock::dump() const {
154 static inline void OutputReg(raw_ostream &os, unsigned RegNo,
155 const TargetRegisterInfo *TRI = 0) {
156 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) {
158 os << " %" << TRI->get(RegNo).Name;
160 os << " %physreg" << RegNo;
162 os << " %reg" << RegNo;
165 StringRef MachineBasicBlock::getName() const {
166 if (const BasicBlock *LBB = getBasicBlock())
167 return LBB->getName();
172 void MachineBasicBlock::print(raw_ostream &OS) const {
173 const MachineFunction *MF = getParent();
175 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
180 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
182 OS << "BB#" << getNumber() << ": ";
184 const char *Comma = "";
185 if (const BasicBlock *LBB = getBasicBlock()) {
186 OS << Comma << "derived from LLVM BB ";
187 WriteAsOperand(OS, LBB, /*PrintType=*/false);
190 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
191 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
194 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
195 if (!livein_empty()) {
197 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
198 OutputReg(OS, *I, TRI);
201 // Print the preds of this block according to the CFG.
203 OS << " Predecessors according to CFG:";
204 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
205 OS << " BB#" << (*PI)->getNumber();
209 for (const_iterator I = begin(); I != end(); ++I) {
211 I->print(OS, &getParent()->getTarget());
214 // Print the successors of this block according to the CFG.
216 OS << " Successors according to CFG:";
217 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
218 OS << " BB#" << (*SI)->getNumber();
223 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
224 std::vector<unsigned>::iterator I =
225 std::find(LiveIns.begin(), LiveIns.end(), Reg);
226 assert(I != LiveIns.end() && "Not a live in!");
230 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
231 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
232 return I != livein_end();
235 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
236 getParent()->splice(NewAfter, this);
239 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
240 MachineFunction::iterator BBI = NewBefore;
241 getParent()->splice(++BBI, this);
244 void MachineBasicBlock::updateTerminator() {
245 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
246 // A block with no successors has no concerns with fall-through edges.
247 if (this->succ_empty()) return;
249 MachineBasicBlock *TBB = 0, *FBB = 0;
250 SmallVector<MachineOperand, 4> Cond;
251 DebugLoc dl; // FIXME: this is nowhere
252 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
254 assert(!B && "UpdateTerminators requires analyzable predecessors!");
257 // The block has an unconditional branch. If its successor is now
258 // its layout successor, delete the branch.
259 if (isLayoutSuccessor(TBB))
260 TII->RemoveBranch(*this);
262 // The block has an unconditional fallthrough. If its successor is not
263 // its layout successor, insert a branch.
265 if (!isLayoutSuccessor(TBB))
266 TII->InsertBranch(*this, TBB, 0, Cond, dl);
270 // The block has a non-fallthrough conditional branch. If one of its
271 // successors is its layout successor, rewrite it to a fallthrough
272 // conditional branch.
273 if (isLayoutSuccessor(TBB)) {
274 if (TII->ReverseBranchCondition(Cond))
276 TII->RemoveBranch(*this);
277 TII->InsertBranch(*this, FBB, 0, Cond, dl);
278 } else if (isLayoutSuccessor(FBB)) {
279 TII->RemoveBranch(*this);
280 TII->InsertBranch(*this, TBB, 0, Cond, dl);
283 // The block has a fallthrough conditional branch.
284 MachineBasicBlock *MBBA = *succ_begin();
285 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
286 if (MBBA == TBB) std::swap(MBBB, MBBA);
287 if (isLayoutSuccessor(TBB)) {
288 if (TII->ReverseBranchCondition(Cond)) {
289 // We can't reverse the condition, add an unconditional branch.
291 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
294 TII->RemoveBranch(*this);
295 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
296 } else if (!isLayoutSuccessor(MBBA)) {
297 TII->RemoveBranch(*this);
298 TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
304 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
305 Successors.push_back(succ);
306 succ->addPredecessor(this);
309 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
310 succ->removePredecessor(this);
311 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
312 assert(I != Successors.end() && "Not a current successor!");
316 MachineBasicBlock::succ_iterator
317 MachineBasicBlock::removeSuccessor(succ_iterator I) {
318 assert(I != Successors.end() && "Not a current successor!");
319 (*I)->removePredecessor(this);
320 return Successors.erase(I);
323 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
324 Predecessors.push_back(pred);
327 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
328 std::vector<MachineBasicBlock *>::iterator I =
329 std::find(Predecessors.begin(), Predecessors.end(), pred);
330 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
331 Predecessors.erase(I);
334 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
338 for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(),
339 E = fromMBB->succ_end(); I != E; ++I)
342 while (!fromMBB->succ_empty())
343 fromMBB->removeSuccessor(fromMBB->succ_begin());
346 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
347 std::vector<MachineBasicBlock *>::const_iterator I =
348 std::find(Successors.begin(), Successors.end(), MBB);
349 return I != Successors.end();
352 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
353 MachineFunction::const_iterator I(this);
354 return llvm::next(I) == MachineFunction::const_iterator(MBB);
357 bool MachineBasicBlock::canFallThrough() {
358 MachineFunction::iterator Fallthrough = this;
360 // If FallthroughBlock is off the end of the function, it can't fall through.
361 if (Fallthrough == getParent()->end())
364 // If FallthroughBlock isn't a successor, no fallthrough is possible.
365 if (!isSuccessor(Fallthrough))
368 // Analyze the branches, if any, at the end of the block.
369 MachineBasicBlock *TBB = 0, *FBB = 0;
370 SmallVector<MachineOperand, 4> Cond;
371 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
372 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
373 // If we couldn't analyze the branch, examine the last instruction.
374 // If the block doesn't end in a known control barrier, assume fallthrough
375 // is possible. The isPredicable check is needed because this code can be
376 // called during IfConversion, where an instruction which is normally a
377 // Barrier is predicated and thus no longer an actual control barrier. This
378 // is over-conservative though, because if an instruction isn't actually
379 // predicated we could still treat it like a barrier.
380 return empty() || !back().getDesc().isBarrier() ||
381 back().getDesc().isPredicable();
384 // If there is no branch, control always falls through.
385 if (TBB == 0) return true;
387 // If there is some explicit branch to the fallthrough block, it can obviously
388 // reach, even though the branch should get folded to fall through implicitly.
389 if (MachineFunction::iterator(TBB) == Fallthrough ||
390 MachineFunction::iterator(FBB) == Fallthrough)
393 // If it's an unconditional branch to some block not the fall through, it
394 // doesn't fall through.
395 if (Cond.empty()) return false;
397 // Otherwise, if it is conditional and has no explicit false block, it falls
403 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
404 MachineFunction *MF = getParent();
405 DebugLoc dl; // FIXME: this is nowhere
407 // We may need to update this's terminator, but we can't do that if AnalyzeBranch
408 // fails. If this uses a jump table, we won't touch it.
409 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
410 MachineBasicBlock *TBB = 0, *FBB = 0;
411 SmallVector<MachineOperand, 4> Cond;
412 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
415 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
416 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
417 DEBUG(dbgs() << "PHIElimination splitting critical edge:"
418 " BB#" << getNumber()
419 << " -- BB#" << NMBB->getNumber()
420 << " -- BB#" << Succ->getNumber() << '\n');
422 ReplaceUsesOfBlockWith(Succ, NMBB);
425 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
426 NMBB->addSuccessor(Succ);
427 if (!NMBB->isLayoutSuccessor(Succ)) {
429 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
432 // Fix PHI nodes in Succ so they refer to NMBB instead of this
433 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
434 i != e && i->isPHI(); ++i)
435 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
436 if (i->getOperand(ni+1).getMBB() == this)
437 i->getOperand(ni+1).setMBB(NMBB);
439 if (LiveVariables *LV =
440 P->getAnalysisIfAvailable<LiveVariables>())
441 LV->addNewBlock(NMBB, this, Succ);
443 if (MachineDominatorTree *MDT =
444 P->getAnalysisIfAvailable<MachineDominatorTree>())
445 MDT->addNewBlock(NMBB, this);
447 if (MachineLoopInfo *MLI =
448 P->getAnalysisIfAvailable<MachineLoopInfo>())
449 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
450 // If one or the other blocks were not in a loop, the new block is not
451 // either, and thus LI doesn't need to be updated.
452 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
453 if (TIL == DestLoop) {
454 // Both in the same loop, the NMBB joins loop.
455 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
456 } else if (TIL->contains(DestLoop)) {
457 // Edge from an outer loop to an inner loop. Add to the outer loop.
458 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
459 } else if (DestLoop->contains(TIL)) {
460 // Edge from an inner loop to an outer loop. Add to the outer loop.
461 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
463 // Edge from two loops with no containment relation. Because these
464 // are natural loops, we know that the destination block must be the
465 // header of its loop (adding a branch into a loop elsewhere would
466 // create an irreducible loop).
467 assert(DestLoop->getHeader() == Succ &&
468 "Should not create irreducible loops!");
469 if (MachineLoop *P = DestLoop->getParentLoop())
470 P->addBasicBlockToLoop(NMBB, MLI->getBase());
478 /// removeFromParent - This method unlinks 'this' from the containing function,
479 /// and returns it, but does not delete it.
480 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
481 assert(getParent() && "Not embedded in a function!");
482 getParent()->remove(this);
487 /// eraseFromParent - This method unlinks 'this' from the containing function,
489 void MachineBasicBlock::eraseFromParent() {
490 assert(getParent() && "Not embedded in a function!");
491 getParent()->erase(this);
495 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
496 /// 'Old', change the code and CFG so that it branches to 'New' instead.
497 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
498 MachineBasicBlock *New) {
499 assert(Old != New && "Cannot replace self with self!");
501 MachineBasicBlock::iterator I = end();
502 while (I != begin()) {
504 if (!I->getDesc().isTerminator()) break;
506 // Scan the operands of this machine instruction, replacing any uses of Old
508 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
509 if (I->getOperand(i).isMBB() &&
510 I->getOperand(i).getMBB() == Old)
511 I->getOperand(i).setMBB(New);
514 // Update the successor information.
515 removeSuccessor(Old);
519 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
520 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
521 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
524 /// Besides DestA and DestB, retain other edges leading to LandingPads
525 /// (currently there can be only one; we don't check or require that here).
526 /// Note it is possible that DestA and/or DestB are LandingPads.
527 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
528 MachineBasicBlock *DestB,
530 // The values of DestA and DestB frequently come from a call to the
531 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
532 // values from there.
534 // 1. If both DestA and DestB are null, then the block ends with no branches
535 // (it falls through to its successor).
536 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
537 // with only an unconditional branch.
538 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
539 // with a conditional branch that falls through to a successor (DestB).
540 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
541 // conditional branch followed by an unconditional branch. DestA is the
542 // 'true' destination and DestB is the 'false' destination.
544 bool Changed = false;
546 MachineFunction::iterator FallThru =
547 llvm::next(MachineFunction::iterator(this));
549 if (DestA == 0 && DestB == 0) {
550 // Block falls through to successor.
553 } else if (DestA != 0 && DestB == 0) {
555 // Block ends in conditional jump that falls through to successor.
558 assert(DestA && DestB && isCond &&
559 "CFG in a bad state. Cannot correct CFG edges");
562 // Remove superfluous edges. I.e., those which aren't destinations of this
563 // basic block, duplicate edges, or landing pads.
564 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
565 MachineBasicBlock::succ_iterator SI = succ_begin();
566 while (SI != succ_end()) {
567 const MachineBasicBlock *MBB = *SI;
568 if (!SeenMBBs.insert(MBB) ||
569 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
570 // This is a superfluous edge, remove it.
571 SI = removeSuccessor(SI);
581 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
582 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
584 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
586 MachineBasicBlock::iterator E = end();
588 // Skip debug declarations, we don't want a DebugLoc from them.
589 MachineBasicBlock::iterator MBBI2 = MBBI;
590 while (MBBI2 != E && MBBI2->isDebugValue())
593 DL = MBBI2->getDebugLoc();
598 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
600 OS << "BB#" << MBB->getNumber();