1 //===-- llvm/CodeGen/MachineBasicBlock.cpp ----------------------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Collect the sequence of machine instructions for a basic block.
11 //
12 //===----------------------------------------------------------------------===//
13
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"
33 #include <algorithm>
34 using namespace llvm;
35
MachineBasicBlock(MachineFunction & mf,const BasicBlock * bb)36 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
37 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
38 AddressTaken(false) {
39 Insts.Parent = this;
40 }
41
~MachineBasicBlock()42 MachineBasicBlock::~MachineBasicBlock() {
43 LeakDetector::removeGarbageObject(this);
44 }
45
46 /// getSymbol - Return the MCSymbol for this basic block.
47 ///
getSymbol() const48 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()) + "_" +
54 Twine(getNumber()));
55 }
56
57
operator <<(raw_ostream & OS,const MachineBasicBlock & MBB)58 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
59 MBB.print(OS);
60 return OS;
61 }
62
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.
66 ///
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.
addNodeToList(MachineBasicBlock * N)70 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
71 MachineFunction &MF = *N->getParent();
72 N->Number = MF.addToMBBNumbering(N);
73
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);
78
79 LeakDetector::removeGarbageObject(N);
80 }
81
removeNodeFromList(MachineBasicBlock * N)82 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
83 N->getParent()->removeFromMBBNumbering(N->Number);
84 N->Number = -1;
85 LeakDetector::addGarbageObject(N);
86 }
87
88
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.
addNodeToList(MachineInstr * N)92 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
93 assert(N->getParent() == 0 && "machine instruction already in a basic block");
94 N->setParent(Parent);
95
96 // Add the instruction's register operands to their corresponding
97 // use/def lists.
98 MachineFunction *MF = Parent->getParent();
99 N->AddRegOperandsToUseLists(MF->getRegInfo());
100
101 LeakDetector::removeGarbageObject(N);
102 }
103
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.
removeNodeFromList(MachineInstr * N)107 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
108 assert(N->getParent() != 0 && "machine instruction not in a basic block");
109
110 // Remove from the use/def lists.
111 N->RemoveRegOperandsFromUseLists();
112
113 N->setParent(0);
114
115 LeakDetector::addGarbageObject(N);
116 }
117
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
120 /// lists.
121 void ilist_traits<MachineInstr>::
transferNodesFromList(ilist_traits<MachineInstr> & fromList,MachineBasicBlock::iterator first,MachineBasicBlock::iterator last)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!");
127
128 // Splice within the same MBB -> no change.
129 if (Parent == fromList.Parent) return;
130
131 // If splicing between two blocks within the same function, just update the
132 // parent pointers.
133 for (; first != last; ++first)
134 first->setParent(Parent);
135 }
136
deleteNode(MachineInstr * MI)137 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
138 assert(!MI->getParent() && "MI is still in a block!");
139 Parent->getParent()->DeleteMachineInstr(MI);
140 }
141
getFirstNonPHI()142 MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
143 iterator I = begin();
144 while (I != end() && I->isPHI())
145 ++I;
146 return I;
147 }
148
getFirstTerminator()149 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
150 iterator I = end();
151 while (I != begin() && (--I)->getDesc().isTerminator())
152 ; /*noop */
153 if (I != end() && !I->getDesc().isTerminator()) ++I;
154 return I;
155 }
156
dump() const157 void MachineBasicBlock::dump() const {
158 print(dbgs());
159 }
160
OutputReg(raw_ostream & os,unsigned RegNo,const TargetRegisterInfo * TRI=0)161 static inline void OutputReg(raw_ostream &os, unsigned RegNo,
162 const TargetRegisterInfo *TRI = 0) {
163 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) {
164 if (TRI)
165 os << " %" << TRI->get(RegNo).Name;
166 else
167 os << " %physreg" << RegNo;
168 } else
169 os << " %reg" << RegNo;
170 }
171
getName() const172 StringRef MachineBasicBlock::getName() const {
173 if (const BasicBlock *LBB = getBasicBlock())
174 return LBB->getName();
175 else
176 return "(null)";
177 }
178
print(raw_ostream & OS) const179 void MachineBasicBlock::print(raw_ostream &OS) const {
180 const MachineFunction *MF = getParent();
181 if (!MF) {
182 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
183 << " is null\n";
184 return;
185 }
186
187 if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
188
189 OS << "BB#" << getNumber() << ": ";
190
191 const char *Comma = "";
192 if (const BasicBlock *LBB = getBasicBlock()) {
193 OS << Comma << "derived from LLVM BB ";
194 WriteAsOperand(OS, LBB, /*PrintType=*/false);
195 Comma = ", ";
196 }
197 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
198 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
199 OS << '\n';
200
201 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
202 if (!livein_empty()) {
203 OS << " Live Ins:";
204 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
205 OutputReg(OS, *I, TRI);
206 OS << '\n';
207 }
208 // Print the preds of this block according to the CFG.
209 if (!pred_empty()) {
210 OS << " Predecessors according to CFG:";
211 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
212 OS << " BB#" << (*PI)->getNumber();
213 OS << '\n';
214 }
215
216 for (const_iterator I = begin(); I != end(); ++I) {
217 OS << '\t';
218 I->print(OS, &getParent()->getTarget());
219 }
220
221 // Print the successors of this block according to the CFG.
222 if (!succ_empty()) {
223 OS << " Successors according to CFG:";
224 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
225 OS << " BB#" << (*SI)->getNumber();
226 OS << '\n';
227 }
228 }
229
removeLiveIn(unsigned Reg)230 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
231 std::vector<unsigned>::iterator I =
232 std::find(LiveIns.begin(), LiveIns.end(), Reg);
233 assert(I != LiveIns.end() && "Not a live in!");
234 LiveIns.erase(I);
235 }
236
isLiveIn(unsigned Reg) const237 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
238 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
239 return I != livein_end();
240 }
241
moveBefore(MachineBasicBlock * NewAfter)242 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
243 getParent()->splice(NewAfter, this);
244 }
245
moveAfter(MachineBasicBlock * NewBefore)246 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
247 MachineFunction::iterator BBI = NewBefore;
248 getParent()->splice(++BBI, this);
249 }
250
updateTerminator()251 void MachineBasicBlock::updateTerminator() {
252 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
253 // A block with no successors has no concerns with fall-through edges.
254 if (this->succ_empty()) return;
255
256 MachineBasicBlock *TBB = 0, *FBB = 0;
257 SmallVector<MachineOperand, 4> Cond;
258 DebugLoc dl; // FIXME: this is nowhere
259 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
260 (void) B;
261 assert(!B && "UpdateTerminators requires analyzable predecessors!");
262 if (Cond.empty()) {
263 if (TBB) {
264 // The block has an unconditional branch. If its successor is now
265 // its layout successor, delete the branch.
266 if (isLayoutSuccessor(TBB))
267 TII->RemoveBranch(*this);
268 } else {
269 // The block has an unconditional fallthrough. If its successor is not
270 // its layout successor, insert a branch.
271 TBB = *succ_begin();
272 if (!isLayoutSuccessor(TBB))
273 TII->InsertBranch(*this, TBB, 0, Cond, dl);
274 }
275 } else {
276 if (FBB) {
277 // The block has a non-fallthrough conditional branch. If one of its
278 // successors is its layout successor, rewrite it to a fallthrough
279 // conditional branch.
280 if (isLayoutSuccessor(TBB)) {
281 if (TII->ReverseBranchCondition(Cond))
282 return;
283 TII->RemoveBranch(*this);
284 TII->InsertBranch(*this, FBB, 0, Cond, dl);
285 } else if (isLayoutSuccessor(FBB)) {
286 TII->RemoveBranch(*this);
287 TII->InsertBranch(*this, TBB, 0, Cond, dl);
288 }
289 } else {
290 // The block has a fallthrough conditional branch.
291 MachineBasicBlock *MBBA = *succ_begin();
292 MachineBasicBlock *MBBB = *llvm::next(succ_begin());
293 if (MBBA == TBB) std::swap(MBBB, MBBA);
294 if (isLayoutSuccessor(TBB)) {
295 if (TII->ReverseBranchCondition(Cond)) {
296 // We can't reverse the condition, add an unconditional branch.
297 Cond.clear();
298 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
299 return;
300 }
301 TII->RemoveBranch(*this);
302 TII->InsertBranch(*this, MBBA, 0, Cond, dl);
303 } else if (!isLayoutSuccessor(MBBA)) {
304 TII->RemoveBranch(*this);
305 TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
306 }
307 }
308 }
309 }
310
addSuccessor(MachineBasicBlock * succ)311 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
312 Successors.push_back(succ);
313 succ->addPredecessor(this);
314 }
315
removeSuccessor(MachineBasicBlock * succ)316 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
317 succ->removePredecessor(this);
318 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
319 assert(I != Successors.end() && "Not a current successor!");
320 Successors.erase(I);
321 }
322
323 MachineBasicBlock::succ_iterator
removeSuccessor(succ_iterator I)324 MachineBasicBlock::removeSuccessor(succ_iterator I) {
325 assert(I != Successors.end() && "Not a current successor!");
326 (*I)->removePredecessor(this);
327 return Successors.erase(I);
328 }
329
addPredecessor(MachineBasicBlock * pred)330 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
331 Predecessors.push_back(pred);
332 }
333
removePredecessor(MachineBasicBlock * pred)334 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
335 std::vector<MachineBasicBlock *>::iterator I =
336 std::find(Predecessors.begin(), Predecessors.end(), pred);
337 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
338 Predecessors.erase(I);
339 }
340
transferSuccessors(MachineBasicBlock * fromMBB)341 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
342 if (this == fromMBB)
343 return;
344
345 while (!fromMBB->succ_empty()) {
346 MachineBasicBlock *Succ = *fromMBB->succ_begin();
347 addSuccessor(Succ);
348 fromMBB->removeSuccessor(Succ);
349 }
350 }
351
352 void
transferSuccessorsAndUpdatePHIs(MachineBasicBlock * fromMBB)353 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
354 if (this == fromMBB)
355 return;
356
357 while (!fromMBB->succ_empty()) {
358 MachineBasicBlock *Succ = *fromMBB->succ_begin();
359 addSuccessor(Succ);
360 fromMBB->removeSuccessor(Succ);
361
362 // Fix up any PHI nodes in the successor.
363 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
364 MI != ME && MI->isPHI(); ++MI)
365 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
366 MachineOperand &MO = MI->getOperand(i);
367 if (MO.getMBB() == fromMBB)
368 MO.setMBB(this);
369 }
370 }
371 }
372
isSuccessor(const MachineBasicBlock * MBB) const373 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
374 std::vector<MachineBasicBlock *>::const_iterator I =
375 std::find(Successors.begin(), Successors.end(), MBB);
376 return I != Successors.end();
377 }
378
isLayoutSuccessor(const MachineBasicBlock * MBB) const379 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
380 MachineFunction::const_iterator I(this);
381 return llvm::next(I) == MachineFunction::const_iterator(MBB);
382 }
383
canFallThrough()384 bool MachineBasicBlock::canFallThrough() {
385 MachineFunction::iterator Fallthrough = this;
386 ++Fallthrough;
387 // If FallthroughBlock is off the end of the function, it can't fall through.
388 if (Fallthrough == getParent()->end())
389 return false;
390
391 // If FallthroughBlock isn't a successor, no fallthrough is possible.
392 if (!isSuccessor(Fallthrough))
393 return false;
394
395 // Analyze the branches, if any, at the end of the block.
396 MachineBasicBlock *TBB = 0, *FBB = 0;
397 SmallVector<MachineOperand, 4> Cond;
398 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
399 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
400 // If we couldn't analyze the branch, examine the last instruction.
401 // If the block doesn't end in a known control barrier, assume fallthrough
402 // is possible. The isPredicable check is needed because this code can be
403 // called during IfConversion, where an instruction which is normally a
404 // Barrier is predicated and thus no longer an actual control barrier. This
405 // is over-conservative though, because if an instruction isn't actually
406 // predicated we could still treat it like a barrier.
407 return empty() || !back().getDesc().isBarrier() ||
408 back().getDesc().isPredicable();
409 }
410
411 // If there is no branch, control always falls through.
412 if (TBB == 0) return true;
413
414 // If there is some explicit branch to the fallthrough block, it can obviously
415 // reach, even though the branch should get folded to fall through implicitly.
416 if (MachineFunction::iterator(TBB) == Fallthrough ||
417 MachineFunction::iterator(FBB) == Fallthrough)
418 return true;
419
420 // If it's an unconditional branch to some block not the fall through, it
421 // doesn't fall through.
422 if (Cond.empty()) return false;
423
424 // Otherwise, if it is conditional and has no explicit false block, it falls
425 // through.
426 return FBB == 0;
427 }
428
429 MachineBasicBlock *
SplitCriticalEdge(MachineBasicBlock * Succ,Pass * P)430 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
431 MachineFunction *MF = getParent();
432 DebugLoc dl; // FIXME: this is nowhere
433
434 // We may need to update this's terminator, but we can't do that if AnalyzeBranch
435 // fails. If this uses a jump table, we won't touch it.
436 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
437 MachineBasicBlock *TBB = 0, *FBB = 0;
438 SmallVector<MachineOperand, 4> Cond;
439 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
440 return NULL;
441
442 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
443 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
444 DEBUG(dbgs() << "Splitting critical edge:"
445 " BB#" << getNumber()
446 << " -- BB#" << NMBB->getNumber()
447 << " -- BB#" << Succ->getNumber() << '\n');
448
449 ReplaceUsesOfBlockWith(Succ, NMBB);
450 updateTerminator();
451
452 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
453 NMBB->addSuccessor(Succ);
454 if (!NMBB->isLayoutSuccessor(Succ)) {
455 Cond.clear();
456 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
457 }
458
459 // Fix PHI nodes in Succ so they refer to NMBB instead of this
460 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
461 i != e && i->isPHI(); ++i)
462 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
463 if (i->getOperand(ni+1).getMBB() == this)
464 i->getOperand(ni+1).setMBB(NMBB);
465
466 if (LiveVariables *LV =
467 P->getAnalysisIfAvailable<LiveVariables>())
468 LV->addNewBlock(NMBB, this, Succ);
469
470 if (MachineDominatorTree *MDT =
471 P->getAnalysisIfAvailable<MachineDominatorTree>()) {
472 // Update dominator information.
473 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
474
475 bool IsNewIDom = true;
476 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
477 PI != E; ++PI) {
478 MachineBasicBlock *PredBB = *PI;
479 if (PredBB == NMBB)
480 continue;
481 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
482 IsNewIDom = false;
483 break;
484 }
485 }
486
487 // We know "this" dominates the newly created basic block.
488 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
489
490 // If all the other predecessors of "Succ" are dominated by "Succ" itself
491 // then the new block is the new immediate dominator of "Succ". Otherwise,
492 // the new block doesn't dominate anything.
493 if (IsNewIDom)
494 MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
495 }
496
497 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
498 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
499 // If one or the other blocks were not in a loop, the new block is not
500 // either, and thus LI doesn't need to be updated.
501 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
502 if (TIL == DestLoop) {
503 // Both in the same loop, the NMBB joins loop.
504 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
505 } else if (TIL->contains(DestLoop)) {
506 // Edge from an outer loop to an inner loop. Add to the outer loop.
507 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
508 } else if (DestLoop->contains(TIL)) {
509 // Edge from an inner loop to an outer loop. Add to the outer loop.
510 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
511 } else {
512 // Edge from two loops with no containment relation. Because these
513 // are natural loops, we know that the destination block must be the
514 // header of its loop (adding a branch into a loop elsewhere would
515 // create an irreducible loop).
516 assert(DestLoop->getHeader() == Succ &&
517 "Should not create irreducible loops!");
518 if (MachineLoop *P = DestLoop->getParentLoop())
519 P->addBasicBlockToLoop(NMBB, MLI->getBase());
520 }
521 }
522 }
523
524 return NMBB;
525 }
526
527 /// removeFromParent - This method unlinks 'this' from the containing function,
528 /// and returns it, but does not delete it.
removeFromParent()529 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
530 assert(getParent() && "Not embedded in a function!");
531 getParent()->remove(this);
532 return this;
533 }
534
535
536 /// eraseFromParent - This method unlinks 'this' from the containing function,
537 /// and deletes it.
eraseFromParent()538 void MachineBasicBlock::eraseFromParent() {
539 assert(getParent() && "Not embedded in a function!");
540 getParent()->erase(this);
541 }
542
543
544 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
545 /// 'Old', change the code and CFG so that it branches to 'New' instead.
ReplaceUsesOfBlockWith(MachineBasicBlock * Old,MachineBasicBlock * New)546 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
547 MachineBasicBlock *New) {
548 assert(Old != New && "Cannot replace self with self!");
549
550 MachineBasicBlock::iterator I = end();
551 while (I != begin()) {
552 --I;
553 if (!I->getDesc().isTerminator()) break;
554
555 // Scan the operands of this machine instruction, replacing any uses of Old
556 // with New.
557 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
558 if (I->getOperand(i).isMBB() &&
559 I->getOperand(i).getMBB() == Old)
560 I->getOperand(i).setMBB(New);
561 }
562
563 // Update the successor information.
564 removeSuccessor(Old);
565 addSuccessor(New);
566 }
567
568 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
569 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
570 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
571 /// null.
572 ///
573 /// Besides DestA and DestB, retain other edges leading to LandingPads
574 /// (currently there can be only one; we don't check or require that here).
575 /// Note it is possible that DestA and/or DestB are LandingPads.
CorrectExtraCFGEdges(MachineBasicBlock * DestA,MachineBasicBlock * DestB,bool isCond)576 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
577 MachineBasicBlock *DestB,
578 bool isCond) {
579 // The values of DestA and DestB frequently come from a call to the
580 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
581 // values from there.
582 //
583 // 1. If both DestA and DestB are null, then the block ends with no branches
584 // (it falls through to its successor).
585 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
586 // with only an unconditional branch.
587 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
588 // with a conditional branch that falls through to a successor (DestB).
589 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
590 // conditional branch followed by an unconditional branch. DestA is the
591 // 'true' destination and DestB is the 'false' destination.
592
593 bool Changed = false;
594
595 MachineFunction::iterator FallThru =
596 llvm::next(MachineFunction::iterator(this));
597
598 if (DestA == 0 && DestB == 0) {
599 // Block falls through to successor.
600 DestA = FallThru;
601 DestB = FallThru;
602 } else if (DestA != 0 && DestB == 0) {
603 if (isCond)
604 // Block ends in conditional jump that falls through to successor.
605 DestB = FallThru;
606 } else {
607 assert(DestA && DestB && isCond &&
608 "CFG in a bad state. Cannot correct CFG edges");
609 }
610
611 // Remove superfluous edges. I.e., those which aren't destinations of this
612 // basic block, duplicate edges, or landing pads.
613 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
614 MachineBasicBlock::succ_iterator SI = succ_begin();
615 while (SI != succ_end()) {
616 const MachineBasicBlock *MBB = *SI;
617 if (!SeenMBBs.insert(MBB) ||
618 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
619 // This is a superfluous edge, remove it.
620 SI = removeSuccessor(SI);
621 Changed = true;
622 } else {
623 ++SI;
624 }
625 }
626
627 return Changed;
628 }
629
630 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
631 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
632 DebugLoc
findDebugLoc(MachineBasicBlock::iterator & MBBI)633 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
634 DebugLoc DL;
635 MachineBasicBlock::iterator E = end();
636 if (MBBI != E) {
637 // Skip debug declarations, we don't want a DebugLoc from them.
638 MachineBasicBlock::iterator MBBI2 = MBBI;
639 while (MBBI2 != E && MBBI2->isDebugValue())
640 MBBI2++;
641 if (MBBI2 != E)
642 DL = MBBI2->getDebugLoc();
643 }
644 return DL;
645 }
646
WriteAsOperand(raw_ostream & OS,const MachineBasicBlock * MBB,bool t)647 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
648 bool t) {
649 OS << "BB#" << MBB->getNumber();
650 }
651
652