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 {
45 const MachineFunction *MF = getParent();
46 const char *Prefix = MF->getTarget().getMCAsmInfo()->getPrivateGlobalPrefix();
47 return Ctx.GetOrCreateTemporarySymbol(Twine(Prefix) + "BB" +
48 Twine(MF->getFunctionNumber()) + "_" +
53 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
58 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the
59 /// parent pointer of the MBB, the MBB numbering, and any instructions in the
60 /// MBB to be on the right operand list for registers.
62 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
63 /// gets the next available unique MBB number. If it is removed from a
64 /// MachineFunction, it goes back to being #-1.
65 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
66 MachineFunction &MF = *N->getParent();
67 N->Number = MF.addToMBBNumbering(N);
69 // Make sure the instructions have their operands in the reginfo lists.
70 MachineRegisterInfo &RegInfo = MF.getRegInfo();
71 for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I)
72 I->AddRegOperandsToUseLists(RegInfo);
74 LeakDetector::removeGarbageObject(N);
77 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
78 N->getParent()->removeFromMBBNumbering(N->Number);
80 LeakDetector::addGarbageObject(N);
84 /// addNodeToList (MI) - When we add an instruction to a basic block
85 /// list, we update its parent pointer and add its operands from reg use/def
86 /// lists if appropriate.
87 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
88 assert(N->getParent() == 0 && "machine instruction already in a basic block");
91 // Add the instruction's register operands to their corresponding
93 MachineFunction *MF = Parent->getParent();
94 N->AddRegOperandsToUseLists(MF->getRegInfo());
96 LeakDetector::removeGarbageObject(N);
99 /// removeNodeFromList (MI) - When we remove an instruction from a basic block
100 /// list, we update its parent pointer and remove its operands from reg use/def
101 /// lists if appropriate.
102 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
103 assert(N->getParent() != 0 && "machine instruction not in a basic block");
105 // Remove from the use/def lists.
106 N->RemoveRegOperandsFromUseLists();
110 LeakDetector::addGarbageObject(N);
113 /// transferNodesFromList (MI) - When moving a range of instructions from one
114 /// MBB list to another, we need to update the parent pointers and the use/def
116 void ilist_traits<MachineInstr>::
117 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
118 MachineBasicBlock::iterator first,
119 MachineBasicBlock::iterator last) {
120 assert(Parent->getParent() == fromList.Parent->getParent() &&
121 "MachineInstr parent mismatch!");
123 // Splice within the same MBB -> no change.
124 if (Parent == fromList.Parent) return;
126 // If splicing between two blocks within the same function, just update the
128 for (; first != last; ++first)
129 first->setParent(Parent);
132 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
133 assert(!MI->getParent() && "MI is still in a block!");
134 Parent->getParent()->DeleteMachineInstr(MI);
137 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
139 while (I != begin() && (--I)->getDesc().isTerminator())
141 if (I != end() && !I->getDesc().isTerminator()) ++I;
145 void MachineBasicBlock::dump() const {
149 static inline void OutputReg(raw_ostream &os, unsigned RegNo,
150 const TargetRegisterInfo *TRI = 0) {
151 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) {
153 os << " %" << TRI->get(RegNo).Name;
155 os << " %physreg" << RegNo;
157 os << " %reg" << RegNo;
160 StringRef MachineBasicBlock::getName() const {
161 if (const BasicBlock *LBB = getBasicBlock())
162 return LBB->getName();
167 void MachineBasicBlock::print(raw_ostream &OS) const {
168 const MachineFunction *MF = getParent();
170 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
175 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
177 OS << "BB#" << getNumber() << ": ";
179 const char *Comma = "";
180 if (const BasicBlock *LBB = getBasicBlock()) {
181 OS << Comma << "derived from LLVM BB ";
182 WriteAsOperand(OS, LBB, /*PrintType=*/false);
185 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
186 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
189 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
190 if (!livein_empty()) {
192 for (const_livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
193 OutputReg(OS, *I, TRI);
196 // Print the preds of this block according to the CFG.
198 OS << " Predecessors according to CFG:";
199 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
200 OS << " BB#" << (*PI)->getNumber();
204 for (const_iterator I = begin(); I != end(); ++I) {
206 I->print(OS, &getParent()->getTarget());
209 // Print the successors of this block according to the CFG.
211 OS << " Successors according to CFG:";
212 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
213 OS << " BB#" << (*SI)->getNumber();
218 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
219 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
220 assert(I != livein_end() && "Not a live in!");
224 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
225 const_livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
226 return I != livein_end();
229 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
230 getParent()->splice(NewAfter, this);
233 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
234 MachineFunction::iterator BBI = NewBefore;
235 getParent()->splice(++BBI, this);
238 void MachineBasicBlock::updateTerminator() {
239 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
240 // A block with no successors has no concerns with fall-through edges.
241 if (this->succ_empty()) return;
243 MachineBasicBlock *TBB = 0, *FBB = 0;
244 SmallVector<MachineOperand, 4> Cond;
245 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
247 assert(!B && "UpdateTerminators requires analyzable predecessors!");
250 // The block has an unconditional branch. If its successor is now
251 // its layout successor, delete the branch.
252 if (isLayoutSuccessor(TBB))
253 TII->RemoveBranch(*this);
255 // The block has an unconditional fallthrough. If its successor is not
256 // its layout successor, insert a branch.
258 if (!isLayoutSuccessor(TBB))
259 TII->InsertBranch(*this, TBB, 0, Cond);
263 // The block has a non-fallthrough conditional branch. If one of its
264 // successors is its layout successor, rewrite it to a fallthrough
265 // conditional branch.
266 if (isLayoutSuccessor(TBB)) {
267 if (TII->ReverseBranchCondition(Cond))
269 TII->RemoveBranch(*this);
270 TII->InsertBranch(*this, FBB, 0, Cond);
271 } else if (isLayoutSuccessor(FBB)) {
272 TII->RemoveBranch(*this);
273 TII->InsertBranch(*this, TBB, 0, Cond);
276 // The block has a fallthrough conditional branch.
277 MachineBasicBlock *MBBA = *succ_begin();
278 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
279 if (MBBA == TBB) std::swap(MBBB, MBBA);
280 if (isLayoutSuccessor(TBB)) {
281 if (TII->ReverseBranchCondition(Cond)) {
282 // We can't reverse the condition, add an unconditional branch.
284 TII->InsertBranch(*this, MBBA, 0, Cond);
287 TII->RemoveBranch(*this);
288 TII->InsertBranch(*this, MBBA, 0, Cond);
289 } else if (!isLayoutSuccessor(MBBA)) {
290 TII->RemoveBranch(*this);
291 TII->InsertBranch(*this, TBB, MBBA, Cond);
297 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
298 Successors.push_back(succ);
299 succ->addPredecessor(this);
302 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
303 succ->removePredecessor(this);
304 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
305 assert(I != Successors.end() && "Not a current successor!");
309 MachineBasicBlock::succ_iterator
310 MachineBasicBlock::removeSuccessor(succ_iterator I) {
311 assert(I != Successors.end() && "Not a current successor!");
312 (*I)->removePredecessor(this);
313 return Successors.erase(I);
316 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
317 Predecessors.push_back(pred);
320 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
321 std::vector<MachineBasicBlock *>::iterator I =
322 std::find(Predecessors.begin(), Predecessors.end(), pred);
323 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
324 Predecessors.erase(I);
327 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
331 for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(),
332 E = fromMBB->succ_end(); I != E; ++I)
335 while (!fromMBB->succ_empty())
336 fromMBB->removeSuccessor(fromMBB->succ_begin());
339 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
340 std::vector<MachineBasicBlock *>::const_iterator I =
341 std::find(Successors.begin(), Successors.end(), MBB);
342 return I != Successors.end();
345 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
346 MachineFunction::const_iterator I(this);
347 return llvm::next(I) == MachineFunction::const_iterator(MBB);
350 bool MachineBasicBlock::canFallThrough() {
351 MachineFunction::iterator Fallthrough = this;
353 // If FallthroughBlock is off the end of the function, it can't fall through.
354 if (Fallthrough == getParent()->end())
357 // If FallthroughBlock isn't a successor, no fallthrough is possible.
358 if (!isSuccessor(Fallthrough))
361 // Analyze the branches, if any, at the end of the block.
362 MachineBasicBlock *TBB = 0, *FBB = 0;
363 SmallVector<MachineOperand, 4> Cond;
364 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
365 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
366 // If we couldn't analyze the branch, examine the last instruction.
367 // If the block doesn't end in a known control barrier, assume fallthrough
368 // is possible. The isPredicable check is needed because this code can be
369 // called during IfConversion, where an instruction which is normally a
370 // Barrier is predicated and thus no longer an actual control barrier. This
371 // is over-conservative though, because if an instruction isn't actually
372 // predicated we could still treat it like a barrier.
373 return empty() || !back().getDesc().isBarrier() ||
374 back().getDesc().isPredicable();
377 // If there is no branch, control always falls through.
378 if (TBB == 0) return true;
380 // If there is some explicit branch to the fallthrough block, it can obviously
381 // reach, even though the branch should get folded to fall through implicitly.
382 if (MachineFunction::iterator(TBB) == Fallthrough ||
383 MachineFunction::iterator(FBB) == Fallthrough)
386 // If it's an unconditional branch to some block not the fall through, it
387 // doesn't fall through.
388 if (Cond.empty()) return false;
390 // Otherwise, if it is conditional and has no explicit false block, it falls
395 /// removeFromParent - This method unlinks 'this' from the containing function,
396 /// and returns it, but does not delete it.
397 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
398 assert(getParent() && "Not embedded in a function!");
399 getParent()->remove(this);
404 /// eraseFromParent - This method unlinks 'this' from the containing function,
406 void MachineBasicBlock::eraseFromParent() {
407 assert(getParent() && "Not embedded in a function!");
408 getParent()->erase(this);
412 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
413 /// 'Old', change the code and CFG so that it branches to 'New' instead.
414 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
415 MachineBasicBlock *New) {
416 assert(Old != New && "Cannot replace self with self!");
418 MachineBasicBlock::iterator I = end();
419 while (I != begin()) {
421 if (!I->getDesc().isTerminator()) break;
423 // Scan the operands of this machine instruction, replacing any uses of Old
425 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
426 if (I->getOperand(i).isMBB() &&
427 I->getOperand(i).getMBB() == Old)
428 I->getOperand(i).setMBB(New);
431 // Update the successor information.
432 removeSuccessor(Old);
436 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
437 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
438 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
441 /// Besides DestA and DestB, retain other edges leading to LandingPads
442 /// (currently there can be only one; we don't check or require that here).
443 /// Note it is possible that DestA and/or DestB are LandingPads.
444 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
445 MachineBasicBlock *DestB,
447 // The values of DestA and DestB frequently come from a call to the
448 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
449 // values from there.
451 // 1. If both DestA and DestB are null, then the block ends with no branches
452 // (it falls through to its successor).
453 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
454 // with only an unconditional branch.
455 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
456 // with a conditional branch that falls through to a successor (DestB).
457 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
458 // conditional branch followed by an unconditional branch. DestA is the
459 // 'true' destination and DestB is the 'false' destination.
461 bool MadeChange = false;
462 bool AddedFallThrough = false;
464 MachineFunction::iterator FallThru =
465 llvm::next(MachineFunction::iterator(this));
468 // If this block ends with a conditional branch that falls through to its
469 // successor, set DestB as the successor.
470 if (DestB == 0 && FallThru != getParent()->end()) {
472 AddedFallThrough = true;
475 // If this is an unconditional branch with no explicit dest, it must just be
476 // a fallthrough into DestA.
477 if (DestA == 0 && FallThru != getParent()->end()) {
479 AddedFallThrough = true;
483 MachineBasicBlock::succ_iterator SI = succ_begin();
484 MachineBasicBlock *OrigDestA = DestA, *OrigDestB = DestB;
485 while (SI != succ_end()) {
486 const MachineBasicBlock *MBB = *SI;
490 } else if (MBB == DestB) {
493 } else if (MBB->isLandingPad() &&
494 MBB != OrigDestA && MBB != OrigDestB) {
497 // Otherwise, this is a superfluous edge, remove it.
498 SI = removeSuccessor(SI);
503 if (!AddedFallThrough)
504 assert(DestA == 0 && DestB == 0 && "MachineCFG is missing edges!");
506 assert(DestA == 0 && "MachineCFG is missing edges!");
511 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
512 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
514 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
516 MachineBasicBlock::iterator E = end();
518 // Skip debug declarations, we don't want a DebugLoc from them.
519 MachineBasicBlock::iterator MBBI2 = MBBI;
520 while (MBBI2 != E && MBBI2->isDebugValue())
523 DL = MBBI2->getDebugLoc();
528 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
530 OS << "BB#" << MBB->getNumber();