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/MachineFunction.h"
17 #include "llvm/MC/MCAsmInfo.h"
18 #include "llvm/MC/MCContext.h"
19 #include "llvm/Target/TargetRegisterInfo.h"
20 #include "llvm/Target/TargetData.h"
21 #include "llvm/Target/TargetInstrDesc.h"
22 #include "llvm/Target/TargetInstrInfo.h"
23 #include "llvm/Target/TargetMachine.h"
24 #include "llvm/Assembly/Writer.h"
25 #include "llvm/ADT/SmallString.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/LeakDetector.h"
28 #include "llvm/Support/raw_ostream.h"
32 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
33 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
38 MachineBasicBlock::~MachineBasicBlock() {
39 LeakDetector::removeGarbageObject(this);
42 /// getSymbol - Return the MCSymbol for this basic block.
44 MCSymbol *MachineBasicBlock::getSymbol(MCContext &Ctx) const {
46 const MachineFunction *MF = getParent();
47 raw_svector_ostream(Name)
48 << MF->getTarget().getMCAsmInfo()->getPrivateGlobalPrefix() << "BB"
49 << MF->getFunctionNumber() << '_' << getNumber();
50 return Ctx.GetOrCreateSymbol(Name.str());
54 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
59 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the
60 /// parent pointer of the MBB, the MBB numbering, and any instructions in the
61 /// MBB to be on the right operand list for registers.
63 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
64 /// gets the next available unique MBB number. If it is removed from a
65 /// MachineFunction, it goes back to being #-1.
66 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
67 MachineFunction &MF = *N->getParent();
68 N->Number = MF.addToMBBNumbering(N);
70 // Make sure the instructions have their operands in the reginfo lists.
71 MachineRegisterInfo &RegInfo = MF.getRegInfo();
72 for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I)
73 I->AddRegOperandsToUseLists(RegInfo);
75 LeakDetector::removeGarbageObject(N);
78 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
79 N->getParent()->removeFromMBBNumbering(N->Number);
81 LeakDetector::addGarbageObject(N);
85 /// addNodeToList (MI) - When we add an instruction to a basic block
86 /// list, we update its parent pointer and add its operands from reg use/def
87 /// lists if appropriate.
88 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
89 assert(N->getParent() == 0 && "machine instruction already in a basic block");
92 // Add the instruction's register operands to their corresponding
94 MachineFunction *MF = Parent->getParent();
95 N->AddRegOperandsToUseLists(MF->getRegInfo());
97 LeakDetector::removeGarbageObject(N);
100 /// removeNodeFromList (MI) - When we remove an instruction from a basic block
101 /// list, we update its parent pointer and remove its operands from reg use/def
102 /// lists if appropriate.
103 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
104 assert(N->getParent() != 0 && "machine instruction not in a basic block");
106 // Remove from the use/def lists.
107 N->RemoveRegOperandsFromUseLists();
111 LeakDetector::addGarbageObject(N);
114 /// transferNodesFromList (MI) - When moving a range of instructions from one
115 /// MBB list to another, we need to update the parent pointers and the use/def
117 void ilist_traits<MachineInstr>::
118 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
119 MachineBasicBlock::iterator first,
120 MachineBasicBlock::iterator last) {
121 assert(Parent->getParent() == fromList.Parent->getParent() &&
122 "MachineInstr parent mismatch!");
124 // Splice within the same MBB -> no change.
125 if (Parent == fromList.Parent) return;
127 // If splicing between two blocks within the same function, just update the
129 for (; first != last; ++first)
130 first->setParent(Parent);
133 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
134 assert(!MI->getParent() && "MI is still in a block!");
135 Parent->getParent()->DeleteMachineInstr(MI);
138 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
140 while (I != begin() && (--I)->getDesc().isTerminator())
142 if (I != end() && !I->getDesc().isTerminator()) ++I;
146 /// isOnlyReachableViaFallthough - Return true if this basic block has
147 /// exactly one predecessor and the control transfer mechanism between
148 /// the predecessor and this block is a fall-through.
149 bool MachineBasicBlock::isOnlyReachableByFallthrough() const {
150 // If this is a landing pad, it isn't a fall through. If it has no preds,
151 // then nothing falls through to it.
152 if (isLandingPad() || pred_empty())
155 // If there isn't exactly one predecessor, it can't be a fall through.
156 const_pred_iterator PI = pred_begin(), PI2 = PI;
158 if (PI2 != pred_end())
161 // The predecessor has to be immediately before this block.
162 const MachineBasicBlock *Pred = *PI;
164 if (!Pred->isLayoutSuccessor(this))
167 // If the block is completely empty, then it definitely does fall through.
171 // Otherwise, check the last instruction.
172 const MachineInstr &LastInst = Pred->back();
173 return !LastInst.getDesc().isBarrier();
176 void MachineBasicBlock::dump() const {
180 static inline void OutputReg(raw_ostream &os, unsigned RegNo,
181 const TargetRegisterInfo *TRI = 0) {
182 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) {
184 os << " %" << TRI->get(RegNo).Name;
186 os << " %physreg" << RegNo;
188 os << " %reg" << RegNo;
191 StringRef MachineBasicBlock::getName() const {
192 if (const BasicBlock *LBB = getBasicBlock())
193 return LBB->getName();
198 void MachineBasicBlock::print(raw_ostream &OS) const {
199 const MachineFunction *MF = getParent();
201 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
206 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
208 OS << "BB#" << getNumber() << ": ";
210 const char *Comma = "";
211 if (const BasicBlock *LBB = getBasicBlock()) {
212 OS << Comma << "derived from LLVM BB ";
213 WriteAsOperand(OS, LBB, /*PrintType=*/false);
216 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
217 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
220 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
221 if (!livein_empty()) {
223 for (const_livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
224 OutputReg(OS, *I, TRI);
227 // Print the preds of this block according to the CFG.
229 OS << " Predecessors according to CFG:";
230 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
231 OS << " BB#" << (*PI)->getNumber();
235 for (const_iterator I = begin(); I != end(); ++I) {
237 I->print(OS, &getParent()->getTarget());
240 // Print the successors of this block according to the CFG.
242 OS << " Successors according to CFG:";
243 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
244 OS << " BB#" << (*SI)->getNumber();
249 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
250 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
251 assert(I != livein_end() && "Not a live in!");
255 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
256 const_livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
257 return I != livein_end();
260 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
261 getParent()->splice(NewAfter, this);
264 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
265 MachineFunction::iterator BBI = NewBefore;
266 getParent()->splice(++BBI, this);
269 void MachineBasicBlock::updateTerminator() {
270 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
271 // A block with no successors has no concerns with fall-through edges.
272 if (this->succ_empty()) return;
274 MachineBasicBlock *TBB = 0, *FBB = 0;
275 SmallVector<MachineOperand, 4> Cond;
276 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
278 assert(!B && "UpdateTerminators requires analyzable predecessors!");
281 // The block has an unconditional branch. If its successor is now
282 // its layout successor, delete the branch.
283 if (isLayoutSuccessor(TBB))
284 TII->RemoveBranch(*this);
286 // The block has an unconditional fallthrough. If its successor is not
287 // its layout successor, insert a branch.
289 if (!isLayoutSuccessor(TBB))
290 TII->InsertBranch(*this, TBB, 0, Cond);
294 // The block has a non-fallthrough conditional branch. If one of its
295 // successors is its layout successor, rewrite it to a fallthrough
296 // conditional branch.
297 if (isLayoutSuccessor(TBB)) {
298 if (TII->ReverseBranchCondition(Cond))
300 TII->RemoveBranch(*this);
301 TII->InsertBranch(*this, FBB, 0, Cond);
302 } else if (isLayoutSuccessor(FBB)) {
303 TII->RemoveBranch(*this);
304 TII->InsertBranch(*this, TBB, 0, Cond);
307 // The block has a fallthrough conditional branch.
308 MachineBasicBlock *MBBA = *succ_begin();
309 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
310 if (MBBA == TBB) std::swap(MBBB, MBBA);
311 if (isLayoutSuccessor(TBB)) {
312 if (TII->ReverseBranchCondition(Cond)) {
313 // We can't reverse the condition, add an unconditional branch.
315 TII->InsertBranch(*this, MBBA, 0, Cond);
318 TII->RemoveBranch(*this);
319 TII->InsertBranch(*this, MBBA, 0, Cond);
320 } else if (!isLayoutSuccessor(MBBA)) {
321 TII->RemoveBranch(*this);
322 TII->InsertBranch(*this, TBB, MBBA, Cond);
328 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
329 Successors.push_back(succ);
330 succ->addPredecessor(this);
333 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
334 succ->removePredecessor(this);
335 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
336 assert(I != Successors.end() && "Not a current successor!");
340 MachineBasicBlock::succ_iterator
341 MachineBasicBlock::removeSuccessor(succ_iterator I) {
342 assert(I != Successors.end() && "Not a current successor!");
343 (*I)->removePredecessor(this);
344 return Successors.erase(I);
347 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
348 Predecessors.push_back(pred);
351 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
352 std::vector<MachineBasicBlock *>::iterator I =
353 std::find(Predecessors.begin(), Predecessors.end(), pred);
354 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
355 Predecessors.erase(I);
358 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
362 for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(),
363 E = fromMBB->succ_end(); I != E; ++I)
366 while (!fromMBB->succ_empty())
367 fromMBB->removeSuccessor(fromMBB->succ_begin());
370 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
371 std::vector<MachineBasicBlock *>::const_iterator I =
372 std::find(Successors.begin(), Successors.end(), MBB);
373 return I != Successors.end();
376 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
377 MachineFunction::const_iterator I(this);
378 return llvm::next(I) == MachineFunction::const_iterator(MBB);
381 bool MachineBasicBlock::canFallThrough() {
382 MachineFunction::iterator Fallthrough = this;
384 // If FallthroughBlock is off the end of the function, it can't fall through.
385 if (Fallthrough == getParent()->end())
388 // If FallthroughBlock isn't a successor, no fallthrough is possible.
389 if (!isSuccessor(Fallthrough))
392 // Analyze the branches, if any, at the end of the block.
393 MachineBasicBlock *TBB = 0, *FBB = 0;
394 SmallVector<MachineOperand, 4> Cond;
395 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
396 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
397 // If we couldn't analyze the branch, examine the last instruction.
398 // If the block doesn't end in a known control barrier, assume fallthrough
399 // is possible. The isPredicable check is needed because this code can be
400 // called during IfConversion, where an instruction which is normally a
401 // Barrier is predicated and thus no longer an actual control barrier. This
402 // is over-conservative though, because if an instruction isn't actually
403 // predicated we could still treat it like a barrier.
404 return empty() || !back().getDesc().isBarrier() ||
405 back().getDesc().isPredicable();
408 // If there is no branch, control always falls through.
409 if (TBB == 0) return true;
411 // If there is some explicit branch to the fallthrough block, it can obviously
412 // reach, even though the branch should get folded to fall through implicitly.
413 if (MachineFunction::iterator(TBB) == Fallthrough ||
414 MachineFunction::iterator(FBB) == Fallthrough)
417 // If it's an unconditional branch to some block not the fall through, it
418 // doesn't fall through.
419 if (Cond.empty()) return false;
421 // Otherwise, if it is conditional and has no explicit false block, it falls
426 /// removeFromParent - This method unlinks 'this' from the containing function,
427 /// and returns it, but does not delete it.
428 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
429 assert(getParent() && "Not embedded in a function!");
430 getParent()->remove(this);
435 /// eraseFromParent - This method unlinks 'this' from the containing function,
437 void MachineBasicBlock::eraseFromParent() {
438 assert(getParent() && "Not embedded in a function!");
439 getParent()->erase(this);
443 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
444 /// 'Old', change the code and CFG so that it branches to 'New' instead.
445 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
446 MachineBasicBlock *New) {
447 assert(Old != New && "Cannot replace self with self!");
449 MachineBasicBlock::iterator I = end();
450 while (I != begin()) {
452 if (!I->getDesc().isTerminator()) break;
454 // Scan the operands of this machine instruction, replacing any uses of Old
456 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
457 if (I->getOperand(i).isMBB() &&
458 I->getOperand(i).getMBB() == Old)
459 I->getOperand(i).setMBB(New);
462 // Update the successor information.
463 removeSuccessor(Old);
467 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
468 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
469 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
472 /// Besides DestA and DestB, retain other edges leading to LandingPads
473 /// (currently there can be only one; we don't check or require that here).
474 /// Note it is possible that DestA and/or DestB are LandingPads.
475 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
476 MachineBasicBlock *DestB,
478 // The values of DestA and DestB frequently come from a call to the
479 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
480 // values from there.
482 // 1. If both DestA and DestB are null, then the block ends with no branches
483 // (it falls through to its successor).
484 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
485 // with only an unconditional branch.
486 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
487 // with a conditional branch that falls through to a successor (DestB).
488 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
489 // conditional branch followed by an unconditional branch. DestA is the
490 // 'true' destination and DestB is the 'false' destination.
492 bool MadeChange = false;
493 bool AddedFallThrough = false;
495 MachineFunction::iterator FallThru =
496 llvm::next(MachineFunction::iterator(this));
499 // If this block ends with a conditional branch that falls through to its
500 // successor, set DestB as the successor.
501 if (DestB == 0 && FallThru != getParent()->end()) {
503 AddedFallThrough = true;
506 // If this is an unconditional branch with no explicit dest, it must just be
507 // a fallthrough into DestA.
508 if (DestA == 0 && FallThru != getParent()->end()) {
510 AddedFallThrough = true;
514 MachineBasicBlock::succ_iterator SI = succ_begin();
515 MachineBasicBlock *OrigDestA = DestA, *OrigDestB = DestB;
516 while (SI != succ_end()) {
517 const MachineBasicBlock *MBB = *SI;
521 } else if (MBB == DestB) {
524 } else if (MBB->isLandingPad() &&
525 MBB != OrigDestA && MBB != OrigDestB) {
528 // Otherwise, this is a superfluous edge, remove it.
529 SI = removeSuccessor(SI);
534 if (!AddedFallThrough)
535 assert(DestA == 0 && DestB == 0 && "MachineCFG is missing edges!");
537 assert(DestA == 0 && "MachineCFG is missing edges!");
542 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
543 /// any DEBUG_VALUE instructions. Return UnknownLoc if there is none.
545 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
547 MachineBasicBlock::iterator E = end();
549 // Skip debug declarations, we don't want a DebugLoc from them.
550 MachineBasicBlock::iterator MBBI2 = MBBI;
552 MBBI2->getOpcode()==TargetInstrInfo::DEBUG_VALUE)
555 DL = MBBI2->getDebugLoc();
560 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
562 OS << "BB#" << MBB->getNumber();