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/ADT/SmallPtrSet.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/LeakDetector.h"
29 #include "llvm/Support/raw_ostream.h"
33 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
34 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
39 MachineBasicBlock::~MachineBasicBlock() {
40 LeakDetector::removeGarbageObject(this);
43 /// getSymbol - Return the MCSymbol for this basic block.
45 MCSymbol *MachineBasicBlock::getSymbol() const {
46 const MachineFunction *MF = getParent();
47 MCContext &Ctx = MF->getContext();
48 const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix();
49 return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
50 Twine(MF->getFunctionNumber()) + "_" +
55 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
60 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the
61 /// parent pointer of the MBB, the MBB numbering, and any instructions in the
62 /// MBB to be on the right operand list for registers.
64 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
65 /// gets the next available unique MBB number. If it is removed from a
66 /// MachineFunction, it goes back to being #-1.
67 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
68 MachineFunction &MF = *N->getParent();
69 N->Number = MF.addToMBBNumbering(N);
71 // Make sure the instructions have their operands in the reginfo lists.
72 MachineRegisterInfo &RegInfo = MF.getRegInfo();
73 for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I)
74 I->AddRegOperandsToUseLists(RegInfo);
76 LeakDetector::removeGarbageObject(N);
79 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
80 N->getParent()->removeFromMBBNumbering(N->Number);
82 LeakDetector::addGarbageObject(N);
86 /// addNodeToList (MI) - When we add an instruction to a basic block
87 /// list, we update its parent pointer and add its operands from reg use/def
88 /// lists if appropriate.
89 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
90 assert(N->getParent() == 0 && "machine instruction already in a basic block");
93 // Add the instruction's register operands to their corresponding
95 MachineFunction *MF = Parent->getParent();
96 N->AddRegOperandsToUseLists(MF->getRegInfo());
98 LeakDetector::removeGarbageObject(N);
101 /// removeNodeFromList (MI) - When we remove an instruction from a basic block
102 /// list, we update its parent pointer and remove its operands from reg use/def
103 /// lists if appropriate.
104 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
105 assert(N->getParent() != 0 && "machine instruction not in a basic block");
107 // Remove from the use/def lists.
108 N->RemoveRegOperandsFromUseLists();
112 LeakDetector::addGarbageObject(N);
115 /// transferNodesFromList (MI) - When moving a range of instructions from one
116 /// MBB list to another, we need to update the parent pointers and the use/def
118 void ilist_traits<MachineInstr>::
119 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
120 MachineBasicBlock::iterator first,
121 MachineBasicBlock::iterator last) {
122 assert(Parent->getParent() == fromList.Parent->getParent() &&
123 "MachineInstr parent mismatch!");
125 // Splice within the same MBB -> no change.
126 if (Parent == fromList.Parent) return;
128 // If splicing between two blocks within the same function, just update the
130 for (; first != last; ++first)
131 first->setParent(Parent);
134 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
135 assert(!MI->getParent() && "MI is still in a block!");
136 Parent->getParent()->DeleteMachineInstr(MI);
139 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
141 while (I != begin() && (--I)->getDesc().isTerminator())
143 if (I != end() && !I->getDesc().isTerminator()) ++I;
147 void MachineBasicBlock::dump() const {
151 static inline void OutputReg(raw_ostream &os, unsigned RegNo,
152 const TargetRegisterInfo *TRI = 0) {
153 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) {
155 os << " %" << TRI->get(RegNo).Name;
157 os << " %physreg" << RegNo;
159 os << " %reg" << RegNo;
162 StringRef MachineBasicBlock::getName() const {
163 if (const BasicBlock *LBB = getBasicBlock())
164 return LBB->getName();
169 void MachineBasicBlock::print(raw_ostream &OS) const {
170 const MachineFunction *MF = getParent();
172 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
177 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
179 OS << "BB#" << getNumber() << ": ";
181 const char *Comma = "";
182 if (const BasicBlock *LBB = getBasicBlock()) {
183 OS << Comma << "derived from LLVM BB ";
184 WriteAsOperand(OS, LBB, /*PrintType=*/false);
187 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
188 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
191 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
192 if (!livein_empty()) {
194 for (const_livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
195 OutputReg(OS, *I, TRI);
198 // Print the preds of this block according to the CFG.
200 OS << " Predecessors according to CFG:";
201 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
202 OS << " BB#" << (*PI)->getNumber();
206 for (const_iterator I = begin(); I != end(); ++I) {
208 I->print(OS, &getParent()->getTarget());
211 // Print the successors of this block according to the CFG.
213 OS << " Successors according to CFG:";
214 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
215 OS << " BB#" << (*SI)->getNumber();
220 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
221 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
222 assert(I != livein_end() && "Not a live in!");
226 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
227 const_livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
228 return I != livein_end();
231 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
232 getParent()->splice(NewAfter, this);
235 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
236 MachineFunction::iterator BBI = NewBefore;
237 getParent()->splice(++BBI, this);
240 void MachineBasicBlock::updateTerminator() {
241 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
242 // A block with no successors has no concerns with fall-through edges.
243 if (this->succ_empty()) return;
245 MachineBasicBlock *TBB = 0, *FBB = 0;
246 SmallVector<MachineOperand, 4> Cond;
247 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
249 assert(!B && "UpdateTerminators requires analyzable predecessors!");
252 // The block has an unconditional branch. If its successor is now
253 // its layout successor, delete the branch.
254 if (isLayoutSuccessor(TBB))
255 TII->RemoveBranch(*this);
257 // The block has an unconditional fallthrough. If its successor is not
258 // its layout successor, insert a branch.
260 if (!isLayoutSuccessor(TBB))
261 TII->InsertBranch(*this, TBB, 0, Cond);
265 // The block has a non-fallthrough conditional branch. If one of its
266 // successors is its layout successor, rewrite it to a fallthrough
267 // conditional branch.
268 if (isLayoutSuccessor(TBB)) {
269 if (TII->ReverseBranchCondition(Cond))
271 TII->RemoveBranch(*this);
272 TII->InsertBranch(*this, FBB, 0, Cond);
273 } else if (isLayoutSuccessor(FBB)) {
274 TII->RemoveBranch(*this);
275 TII->InsertBranch(*this, TBB, 0, Cond);
278 // The block has a fallthrough conditional branch.
279 MachineBasicBlock *MBBA = *succ_begin();
280 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
281 if (MBBA == TBB) std::swap(MBBB, MBBA);
282 if (isLayoutSuccessor(TBB)) {
283 if (TII->ReverseBranchCondition(Cond)) {
284 // We can't reverse the condition, add an unconditional branch.
286 TII->InsertBranch(*this, MBBA, 0, Cond);
289 TII->RemoveBranch(*this);
290 TII->InsertBranch(*this, MBBA, 0, Cond);
291 } else if (!isLayoutSuccessor(MBBA)) {
292 TII->RemoveBranch(*this);
293 TII->InsertBranch(*this, TBB, MBBA, Cond);
299 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
300 Successors.push_back(succ);
301 succ->addPredecessor(this);
304 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
305 succ->removePredecessor(this);
306 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
307 assert(I != Successors.end() && "Not a current successor!");
311 MachineBasicBlock::succ_iterator
312 MachineBasicBlock::removeSuccessor(succ_iterator I) {
313 assert(I != Successors.end() && "Not a current successor!");
314 (*I)->removePredecessor(this);
315 return Successors.erase(I);
318 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
319 Predecessors.push_back(pred);
322 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
323 std::vector<MachineBasicBlock *>::iterator I =
324 std::find(Predecessors.begin(), Predecessors.end(), pred);
325 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
326 Predecessors.erase(I);
329 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
333 for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(),
334 E = fromMBB->succ_end(); I != E; ++I)
337 while (!fromMBB->succ_empty())
338 fromMBB->removeSuccessor(fromMBB->succ_begin());
341 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
342 std::vector<MachineBasicBlock *>::const_iterator I =
343 std::find(Successors.begin(), Successors.end(), MBB);
344 return I != Successors.end();
347 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
348 MachineFunction::const_iterator I(this);
349 return llvm::next(I) == MachineFunction::const_iterator(MBB);
352 bool MachineBasicBlock::canFallThrough() {
353 MachineFunction::iterator Fallthrough = this;
355 // If FallthroughBlock is off the end of the function, it can't fall through.
356 if (Fallthrough == getParent()->end())
359 // If FallthroughBlock isn't a successor, no fallthrough is possible.
360 if (!isSuccessor(Fallthrough))
363 // Analyze the branches, if any, at the end of the block.
364 MachineBasicBlock *TBB = 0, *FBB = 0;
365 SmallVector<MachineOperand, 4> Cond;
366 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
367 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
368 // If we couldn't analyze the branch, examine the last instruction.
369 // If the block doesn't end in a known control barrier, assume fallthrough
370 // is possible. The isPredicable check is needed because this code can be
371 // called during IfConversion, where an instruction which is normally a
372 // Barrier is predicated and thus no longer an actual control barrier. This
373 // is over-conservative though, because if an instruction isn't actually
374 // predicated we could still treat it like a barrier.
375 return empty() || !back().getDesc().isBarrier() ||
376 back().getDesc().isPredicable();
379 // If there is no branch, control always falls through.
380 if (TBB == 0) return true;
382 // If there is some explicit branch to the fallthrough block, it can obviously
383 // reach, even though the branch should get folded to fall through implicitly.
384 if (MachineFunction::iterator(TBB) == Fallthrough ||
385 MachineFunction::iterator(FBB) == Fallthrough)
388 // If it's an unconditional branch to some block not the fall through, it
389 // doesn't fall through.
390 if (Cond.empty()) return false;
392 // Otherwise, if it is conditional and has no explicit false block, it falls
397 /// removeFromParent - This method unlinks 'this' from the containing function,
398 /// and returns it, but does not delete it.
399 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
400 assert(getParent() && "Not embedded in a function!");
401 getParent()->remove(this);
406 /// eraseFromParent - This method unlinks 'this' from the containing function,
408 void MachineBasicBlock::eraseFromParent() {
409 assert(getParent() && "Not embedded in a function!");
410 getParent()->erase(this);
414 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
415 /// 'Old', change the code and CFG so that it branches to 'New' instead.
416 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
417 MachineBasicBlock *New) {
418 assert(Old != New && "Cannot replace self with self!");
420 MachineBasicBlock::iterator I = end();
421 while (I != begin()) {
423 if (!I->getDesc().isTerminator()) break;
425 // Scan the operands of this machine instruction, replacing any uses of Old
427 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
428 if (I->getOperand(i).isMBB() &&
429 I->getOperand(i).getMBB() == Old)
430 I->getOperand(i).setMBB(New);
433 // Update the successor information.
434 removeSuccessor(Old);
438 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
439 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
440 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
443 /// Besides DestA and DestB, retain other edges leading to LandingPads
444 /// (currently there can be only one; we don't check or require that here).
445 /// Note it is possible that DestA and/or DestB are LandingPads.
446 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
447 MachineBasicBlock *DestB,
449 // The values of DestA and DestB frequently come from a call to the
450 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
451 // values from there.
453 // 1. If both DestA and DestB are null, then the block ends with no branches
454 // (it falls through to its successor).
455 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
456 // with only an unconditional branch.
457 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
458 // with a conditional branch that falls through to a successor (DestB).
459 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
460 // conditional branch followed by an unconditional branch. DestA is the
461 // 'true' destination and DestB is the 'false' destination.
463 bool Changed = false;
465 MachineFunction::iterator FallThru =
466 llvm::next(MachineFunction::iterator(this));
468 if (DestA == 0 && DestB == 0) {
469 // Block falls through to successor.
472 } else if (DestA != 0 && DestB == 0) {
474 // Block ends in conditional jump that falls through to successor.
477 assert(DestA && DestB && isCond &&
478 "CFG in a bad state. Cannot correct CFG edges");
481 // Remove superfluous edges. I.e., those which aren't destinations of this
482 // basic block, duplicate edges, or landing pads.
483 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
484 MachineBasicBlock::succ_iterator SI = succ_begin();
485 while (SI != succ_end()) {
486 const MachineBasicBlock *MBB = *SI;
487 if (!SeenMBBs.insert(MBB) ||
488 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
489 // This is a superfluous edge, remove it.
490 SI = removeSuccessor(SI);
500 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
501 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
503 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
505 MachineBasicBlock::iterator E = end();
507 // Skip debug declarations, we don't want a DebugLoc from them.
508 MachineBasicBlock::iterator MBBI2 = MBBI;
509 while (MBBI2 != E && MBBI2->isDebugValue())
512 DL = MBBI2->getDebugLoc();
517 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
519 OS << "BB#" << MBB->getNumber();