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/CodeGen/SlotIndexes.h"
21 #include "llvm/MC/MCAsmInfo.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/Target/TargetRegisterInfo.h"
24 #include "llvm/Target/TargetData.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::instr_iterator
77 I = N->instr_begin(), E = N->instr_end(); I != E; ++I)
78 I->AddRegOperandsToUseLists(RegInfo);
79
80 LeakDetector::removeGarbageObject(N);
81 }
82
removeNodeFromList(MachineBasicBlock * N)83 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
84 N->getParent()->removeFromMBBNumbering(N->Number);
85 N->Number = -1;
86 LeakDetector::addGarbageObject(N);
87 }
88
89
90 /// addNodeToList (MI) - When we add an instruction to a basic block
91 /// list, we update its parent pointer and add its operands from reg use/def
92 /// lists if appropriate.
addNodeToList(MachineInstr * N)93 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
94 assert(N->getParent() == 0 && "machine instruction already in a basic block");
95 N->setParent(Parent);
96
97 // Add the instruction's register operands to their corresponding
98 // use/def lists.
99 MachineFunction *MF = Parent->getParent();
100 N->AddRegOperandsToUseLists(MF->getRegInfo());
101
102 LeakDetector::removeGarbageObject(N);
103 }
104
105 /// removeNodeFromList (MI) - When we remove an instruction from a basic block
106 /// list, we update its parent pointer and remove its operands from reg use/def
107 /// lists if appropriate.
removeNodeFromList(MachineInstr * N)108 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
109 assert(N->getParent() != 0 && "machine instruction not in a basic block");
110
111 // Remove from the use/def lists.
112 N->RemoveRegOperandsFromUseLists();
113
114 N->setParent(0);
115
116 LeakDetector::addGarbageObject(N);
117 }
118
119 /// transferNodesFromList (MI) - When moving a range of instructions from one
120 /// MBB list to another, we need to update the parent pointers and the use/def
121 /// lists.
122 void ilist_traits<MachineInstr>::
transferNodesFromList(ilist_traits<MachineInstr> & fromList,ilist_iterator<MachineInstr> first,ilist_iterator<MachineInstr> last)123 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
124 ilist_iterator<MachineInstr> first,
125 ilist_iterator<MachineInstr> last) {
126 assert(Parent->getParent() == fromList.Parent->getParent() &&
127 "MachineInstr parent mismatch!");
128
129 // Splice within the same MBB -> no change.
130 if (Parent == fromList.Parent) return;
131
132 // If splicing between two blocks within the same function, just update the
133 // parent pointers.
134 for (; first != last; ++first)
135 first->setParent(Parent);
136 }
137
deleteNode(MachineInstr * MI)138 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
139 assert(!MI->getParent() && "MI is still in a block!");
140 Parent->getParent()->DeleteMachineInstr(MI);
141 }
142
getFirstNonPHI()143 MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
144 instr_iterator I = instr_begin(), E = instr_end();
145 while (I != E && I->isPHI())
146 ++I;
147 assert(!I->isInsideBundle() && "First non-phi MI cannot be inside a bundle!");
148 return I;
149 }
150
151 MachineBasicBlock::iterator
SkipPHIsAndLabels(MachineBasicBlock::iterator I)152 MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
153 iterator E = end();
154 while (I != E && (I->isPHI() || I->isLabel() || I->isDebugValue()))
155 ++I;
156 // FIXME: This needs to change if we wish to bundle labels / dbg_values
157 // inside the bundle.
158 assert(!I->isInsideBundle() &&
159 "First non-phi / non-label instruction is inside a bundle!");
160 return I;
161 }
162
getFirstTerminator()163 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
164 iterator B = begin(), E = end(), I = E;
165 while (I != B && ((--I)->isTerminator() || I->isDebugValue()))
166 ; /*noop */
167 while (I != E && !I->isTerminator())
168 ++I;
169 return I;
170 }
171
172 MachineBasicBlock::const_iterator
getFirstTerminator() const173 MachineBasicBlock::getFirstTerminator() const {
174 const_iterator B = begin(), E = end(), I = E;
175 while (I != B && ((--I)->isTerminator() || I->isDebugValue()))
176 ; /*noop */
177 while (I != E && !I->isTerminator())
178 ++I;
179 return I;
180 }
181
getFirstInstrTerminator()182 MachineBasicBlock::instr_iterator MachineBasicBlock::getFirstInstrTerminator() {
183 instr_iterator B = instr_begin(), E = instr_end(), I = E;
184 while (I != B && ((--I)->isTerminator() || I->isDebugValue()))
185 ; /*noop */
186 while (I != E && !I->isTerminator())
187 ++I;
188 return I;
189 }
190
getLastNonDebugInstr()191 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {
192 // Skip over end-of-block dbg_value instructions.
193 instr_iterator B = instr_begin(), I = instr_end();
194 while (I != B) {
195 --I;
196 // Return instruction that starts a bundle.
197 if (I->isDebugValue() || I->isInsideBundle())
198 continue;
199 return I;
200 }
201 // The block is all debug values.
202 return end();
203 }
204
205 MachineBasicBlock::const_iterator
getLastNonDebugInstr() const206 MachineBasicBlock::getLastNonDebugInstr() const {
207 // Skip over end-of-block dbg_value instructions.
208 const_instr_iterator B = instr_begin(), I = instr_end();
209 while (I != B) {
210 --I;
211 // Return instruction that starts a bundle.
212 if (I->isDebugValue() || I->isInsideBundle())
213 continue;
214 return I;
215 }
216 // The block is all debug values.
217 return end();
218 }
219
getLandingPadSuccessor() const220 const MachineBasicBlock *MachineBasicBlock::getLandingPadSuccessor() const {
221 // A block with a landing pad successor only has one other successor.
222 if (succ_size() > 2)
223 return 0;
224 for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I)
225 if ((*I)->isLandingPad())
226 return *I;
227 return 0;
228 }
229
dump() const230 void MachineBasicBlock::dump() const {
231 print(dbgs());
232 }
233
getName() const234 StringRef MachineBasicBlock::getName() const {
235 if (const BasicBlock *LBB = getBasicBlock())
236 return LBB->getName();
237 else
238 return "(null)";
239 }
240
241 /// Return a hopefully unique identifier for this block.
getFullName() const242 std::string MachineBasicBlock::getFullName() const {
243 std::string Name;
244 if (getParent())
245 Name = (getParent()->getFunction()->getName() + ":").str();
246 if (getBasicBlock())
247 Name += getBasicBlock()->getName();
248 else
249 Name += (Twine("BB") + Twine(getNumber())).str();
250 return Name;
251 }
252
print(raw_ostream & OS,SlotIndexes * Indexes) const253 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
254 const MachineFunction *MF = getParent();
255 if (!MF) {
256 OS << "Can't print out MachineBasicBlock because parent MachineFunction"
257 << " is null\n";
258 return;
259 }
260
261 if (Indexes)
262 OS << Indexes->getMBBStartIdx(this) << '\t';
263
264 OS << "BB#" << getNumber() << ": ";
265
266 const char *Comma = "";
267 if (const BasicBlock *LBB = getBasicBlock()) {
268 OS << Comma << "derived from LLVM BB ";
269 WriteAsOperand(OS, LBB, /*PrintType=*/false);
270 Comma = ", ";
271 }
272 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
273 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
274 if (Alignment) {
275 OS << Comma << "Align " << Alignment << " (" << (1u << Alignment)
276 << " bytes)";
277 Comma = ", ";
278 }
279
280 OS << '\n';
281
282 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
283 if (!livein_empty()) {
284 if (Indexes) OS << '\t';
285 OS << " Live Ins:";
286 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
287 OS << ' ' << PrintReg(*I, TRI);
288 OS << '\n';
289 }
290 // Print the preds of this block according to the CFG.
291 if (!pred_empty()) {
292 if (Indexes) OS << '\t';
293 OS << " Predecessors according to CFG:";
294 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
295 OS << " BB#" << (*PI)->getNumber();
296 OS << '\n';
297 }
298
299 for (const_instr_iterator I = instr_begin(); I != instr_end(); ++I) {
300 if (Indexes) {
301 if (Indexes->hasIndex(I))
302 OS << Indexes->getInstructionIndex(I);
303 OS << '\t';
304 }
305 OS << '\t';
306 if (I->isInsideBundle())
307 OS << " * ";
308 I->print(OS, &getParent()->getTarget());
309 }
310
311 // Print the successors of this block according to the CFG.
312 if (!succ_empty()) {
313 if (Indexes) OS << '\t';
314 OS << " Successors according to CFG:";
315 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
316 OS << " BB#" << (*SI)->getNumber();
317 OS << '\n';
318 }
319 }
320
removeLiveIn(unsigned Reg)321 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
322 std::vector<unsigned>::iterator I =
323 std::find(LiveIns.begin(), LiveIns.end(), Reg);
324 if (I != LiveIns.end())
325 LiveIns.erase(I);
326 }
327
isLiveIn(unsigned Reg) const328 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
329 livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
330 return I != livein_end();
331 }
332
moveBefore(MachineBasicBlock * NewAfter)333 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
334 getParent()->splice(NewAfter, this);
335 }
336
moveAfter(MachineBasicBlock * NewBefore)337 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
338 MachineFunction::iterator BBI = NewBefore;
339 getParent()->splice(++BBI, this);
340 }
341
updateTerminator()342 void MachineBasicBlock::updateTerminator() {
343 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
344 // A block with no successors has no concerns with fall-through edges.
345 if (this->succ_empty()) return;
346
347 MachineBasicBlock *TBB = 0, *FBB = 0;
348 SmallVector<MachineOperand, 4> Cond;
349 DebugLoc dl; // FIXME: this is nowhere
350 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
351 (void) B;
352 assert(!B && "UpdateTerminators requires analyzable predecessors!");
353 if (Cond.empty()) {
354 if (TBB) {
355 // The block has an unconditional branch. If its successor is now
356 // its layout successor, delete the branch.
357 if (isLayoutSuccessor(TBB))
358 TII->RemoveBranch(*this);
359 } else {
360 // The block has an unconditional fallthrough. If its successor is not
361 // its layout successor, insert a branch. First we have to locate the
362 // only non-landing-pad successor, as that is the fallthrough block.
363 for (succ_iterator SI = succ_begin(), SE = succ_end(); SI != SE; ++SI) {
364 if ((*SI)->isLandingPad())
365 continue;
366 assert(!TBB && "Found more than one non-landing-pad successor!");
367 TBB = *SI;
368 }
369
370 // If there is no non-landing-pad successor, the block has no
371 // fall-through edges to be concerned with.
372 if (!TBB)
373 return;
374
375 // Finally update the unconditional successor to be reached via a branch
376 // if it would not be reached by fallthrough.
377 if (!isLayoutSuccessor(TBB))
378 TII->InsertBranch(*this, TBB, 0, Cond, dl);
379 }
380 } else {
381 if (FBB) {
382 // The block has a non-fallthrough conditional branch. If one of its
383 // successors is its layout successor, rewrite it to a fallthrough
384 // conditional branch.
385 if (isLayoutSuccessor(TBB)) {
386 if (TII->ReverseBranchCondition(Cond))
387 return;
388 TII->RemoveBranch(*this);
389 TII->InsertBranch(*this, FBB, 0, Cond, dl);
390 } else if (isLayoutSuccessor(FBB)) {
391 TII->RemoveBranch(*this);
392 TII->InsertBranch(*this, TBB, 0, Cond, dl);
393 }
394 } else {
395 // Walk through the successors and find the successor which is not
396 // a landing pad and is not the conditional branch destination (in TBB)
397 // as the fallthrough successor.
398 MachineBasicBlock *FallthroughBB = 0;
399 for (succ_iterator SI = succ_begin(), SE = succ_end(); SI != SE; ++SI) {
400 if ((*SI)->isLandingPad() || *SI == TBB)
401 continue;
402 assert(!FallthroughBB && "Found more than one fallthrough successor.");
403 FallthroughBB = *SI;
404 }
405 if (!FallthroughBB && canFallThrough()) {
406 // We fallthrough to the same basic block as the conditional jump
407 // targets. Remove the conditional jump, leaving unconditional
408 // fallthrough.
409 // FIXME: This does not seem like a reasonable pattern to support, but it
410 // has been seen in the wild coming out of degenerate ARM test cases.
411 TII->RemoveBranch(*this);
412
413 // Finally update the unconditional successor to be reached via a branch
414 // if it would not be reached by fallthrough.
415 if (!isLayoutSuccessor(TBB))
416 TII->InsertBranch(*this, TBB, 0, Cond, dl);
417 return;
418 }
419
420 // The block has a fallthrough conditional branch.
421 if (isLayoutSuccessor(TBB)) {
422 if (TII->ReverseBranchCondition(Cond)) {
423 // We can't reverse the condition, add an unconditional branch.
424 Cond.clear();
425 TII->InsertBranch(*this, FallthroughBB, 0, Cond, dl);
426 return;
427 }
428 TII->RemoveBranch(*this);
429 TII->InsertBranch(*this, FallthroughBB, 0, Cond, dl);
430 } else if (!isLayoutSuccessor(FallthroughBB)) {
431 TII->RemoveBranch(*this);
432 TII->InsertBranch(*this, TBB, FallthroughBB, Cond, dl);
433 }
434 }
435 }
436 }
437
addSuccessor(MachineBasicBlock * succ,uint32_t weight)438 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
439
440 // If we see non-zero value for the first time it means we actually use Weight
441 // list, so we fill all Weights with 0's.
442 if (weight != 0 && Weights.empty())
443 Weights.resize(Successors.size());
444
445 if (weight != 0 || !Weights.empty())
446 Weights.push_back(weight);
447
448 Successors.push_back(succ);
449 succ->addPredecessor(this);
450 }
451
removeSuccessor(MachineBasicBlock * succ)452 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
453 succ->removePredecessor(this);
454 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
455 assert(I != Successors.end() && "Not a current successor!");
456
457 // If Weight list is empty it means we don't use it (disabled optimization).
458 if (!Weights.empty()) {
459 weight_iterator WI = getWeightIterator(I);
460 Weights.erase(WI);
461 }
462
463 Successors.erase(I);
464 }
465
466 MachineBasicBlock::succ_iterator
removeSuccessor(succ_iterator I)467 MachineBasicBlock::removeSuccessor(succ_iterator I) {
468 assert(I != Successors.end() && "Not a current successor!");
469
470 // If Weight list is empty it means we don't use it (disabled optimization).
471 if (!Weights.empty()) {
472 weight_iterator WI = getWeightIterator(I);
473 Weights.erase(WI);
474 }
475
476 (*I)->removePredecessor(this);
477 return Successors.erase(I);
478 }
479
replaceSuccessor(MachineBasicBlock * Old,MachineBasicBlock * New)480 void MachineBasicBlock::replaceSuccessor(MachineBasicBlock *Old,
481 MachineBasicBlock *New) {
482 uint32_t weight = 0;
483 succ_iterator SI = std::find(Successors.begin(), Successors.end(), Old);
484
485 // If Weight list is empty it means we don't use it (disabled optimization).
486 if (!Weights.empty()) {
487 weight_iterator WI = getWeightIterator(SI);
488 weight = *WI;
489 }
490
491 // Update the successor information.
492 removeSuccessor(SI);
493 addSuccessor(New, weight);
494 }
495
addPredecessor(MachineBasicBlock * pred)496 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
497 Predecessors.push_back(pred);
498 }
499
removePredecessor(MachineBasicBlock * pred)500 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
501 pred_iterator I = std::find(Predecessors.begin(), Predecessors.end(), pred);
502 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
503 Predecessors.erase(I);
504 }
505
transferSuccessors(MachineBasicBlock * fromMBB)506 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
507 if (this == fromMBB)
508 return;
509
510 while (!fromMBB->succ_empty()) {
511 MachineBasicBlock *Succ = *fromMBB->succ_begin();
512 uint32_t weight = 0;
513
514
515 // If Weight list is empty it means we don't use it (disabled optimization).
516 if (!fromMBB->Weights.empty())
517 weight = *fromMBB->Weights.begin();
518
519 addSuccessor(Succ, weight);
520 fromMBB->removeSuccessor(Succ);
521 }
522 }
523
524 void
transferSuccessorsAndUpdatePHIs(MachineBasicBlock * fromMBB)525 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
526 if (this == fromMBB)
527 return;
528
529 while (!fromMBB->succ_empty()) {
530 MachineBasicBlock *Succ = *fromMBB->succ_begin();
531 addSuccessor(Succ);
532 fromMBB->removeSuccessor(Succ);
533
534 // Fix up any PHI nodes in the successor.
535 for (MachineBasicBlock::instr_iterator MI = Succ->instr_begin(),
536 ME = Succ->instr_end(); MI != ME && MI->isPHI(); ++MI)
537 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
538 MachineOperand &MO = MI->getOperand(i);
539 if (MO.getMBB() == fromMBB)
540 MO.setMBB(this);
541 }
542 }
543 }
544
isSuccessor(const MachineBasicBlock * MBB) const545 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
546 const_succ_iterator I = std::find(Successors.begin(), Successors.end(), MBB);
547 return I != Successors.end();
548 }
549
isLayoutSuccessor(const MachineBasicBlock * MBB) const550 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
551 MachineFunction::const_iterator I(this);
552 return llvm::next(I) == MachineFunction::const_iterator(MBB);
553 }
554
canFallThrough()555 bool MachineBasicBlock::canFallThrough() {
556 MachineFunction::iterator Fallthrough = this;
557 ++Fallthrough;
558 // If FallthroughBlock is off the end of the function, it can't fall through.
559 if (Fallthrough == getParent()->end())
560 return false;
561
562 // If FallthroughBlock isn't a successor, no fallthrough is possible.
563 if (!isSuccessor(Fallthrough))
564 return false;
565
566 // Analyze the branches, if any, at the end of the block.
567 MachineBasicBlock *TBB = 0, *FBB = 0;
568 SmallVector<MachineOperand, 4> Cond;
569 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
570 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
571 // If we couldn't analyze the branch, examine the last instruction.
572 // If the block doesn't end in a known control barrier, assume fallthrough
573 // is possible. The isPredicated check is needed because this code can be
574 // called during IfConversion, where an instruction which is normally a
575 // Barrier is predicated and thus no longer an actual control barrier.
576 return empty() || !back().isBarrier() || TII->isPredicated(&back());
577 }
578
579 // If there is no branch, control always falls through.
580 if (TBB == 0) return true;
581
582 // If there is some explicit branch to the fallthrough block, it can obviously
583 // reach, even though the branch should get folded to fall through implicitly.
584 if (MachineFunction::iterator(TBB) == Fallthrough ||
585 MachineFunction::iterator(FBB) == Fallthrough)
586 return true;
587
588 // If it's an unconditional branch to some block not the fall through, it
589 // doesn't fall through.
590 if (Cond.empty()) return false;
591
592 // Otherwise, if it is conditional and has no explicit false block, it falls
593 // through.
594 return FBB == 0;
595 }
596
597 MachineBasicBlock *
SplitCriticalEdge(MachineBasicBlock * Succ,Pass * P)598 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
599 MachineFunction *MF = getParent();
600 DebugLoc dl; // FIXME: this is nowhere
601
602 // We may need to update this's terminator, but we can't do that if
603 // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
604 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
605 MachineBasicBlock *TBB = 0, *FBB = 0;
606 SmallVector<MachineOperand, 4> Cond;
607 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
608 return NULL;
609
610 // Avoid bugpoint weirdness: A block may end with a conditional branch but
611 // jumps to the same MBB is either case. We have duplicate CFG edges in that
612 // case that we can't handle. Since this never happens in properly optimized
613 // code, just skip those edges.
614 if (TBB && TBB == FBB) {
615 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
616 << getNumber() << '\n');
617 return NULL;
618 }
619
620 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
621 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
622 DEBUG(dbgs() << "Splitting critical edge:"
623 " BB#" << getNumber()
624 << " -- BB#" << NMBB->getNumber()
625 << " -- BB#" << Succ->getNumber() << '\n');
626
627 // On some targets like Mips, branches may kill virtual registers. Make sure
628 // that LiveVariables is properly updated after updateTerminator replaces the
629 // terminators.
630 LiveVariables *LV = P->getAnalysisIfAvailable<LiveVariables>();
631
632 // Collect a list of virtual registers killed by the terminators.
633 SmallVector<unsigned, 4> KilledRegs;
634 if (LV)
635 for (instr_iterator I = getFirstInstrTerminator(), E = instr_end();
636 I != E; ++I) {
637 MachineInstr *MI = I;
638 for (MachineInstr::mop_iterator OI = MI->operands_begin(),
639 OE = MI->operands_end(); OI != OE; ++OI) {
640 if (!OI->isReg() || OI->getReg() == 0 ||
641 !OI->isUse() || !OI->isKill() || OI->isUndef())
642 continue;
643 unsigned Reg = OI->getReg();
644 if (TargetRegisterInfo::isPhysicalRegister(Reg) ||
645 LV->getVarInfo(Reg).removeKill(MI)) {
646 KilledRegs.push_back(Reg);
647 DEBUG(dbgs() << "Removing terminator kill: " << *MI);
648 OI->setIsKill(false);
649 }
650 }
651 }
652
653 ReplaceUsesOfBlockWith(Succ, NMBB);
654 updateTerminator();
655
656 // Insert unconditional "jump Succ" instruction in NMBB if necessary.
657 NMBB->addSuccessor(Succ);
658 if (!NMBB->isLayoutSuccessor(Succ)) {
659 Cond.clear();
660 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
661 }
662
663 // Fix PHI nodes in Succ so they refer to NMBB instead of this
664 for (MachineBasicBlock::instr_iterator
665 i = Succ->instr_begin(),e = Succ->instr_end();
666 i != e && i->isPHI(); ++i)
667 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
668 if (i->getOperand(ni+1).getMBB() == this)
669 i->getOperand(ni+1).setMBB(NMBB);
670
671 // Inherit live-ins from the successor
672 for (MachineBasicBlock::livein_iterator I = Succ->livein_begin(),
673 E = Succ->livein_end(); I != E; ++I)
674 NMBB->addLiveIn(*I);
675
676 // Update LiveVariables.
677 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
678 if (LV) {
679 // Restore kills of virtual registers that were killed by the terminators.
680 while (!KilledRegs.empty()) {
681 unsigned Reg = KilledRegs.pop_back_val();
682 for (instr_iterator I = instr_end(), E = instr_begin(); I != E;) {
683 if (!(--I)->addRegisterKilled(Reg, TRI, /* addIfNotFound= */ false))
684 continue;
685 if (TargetRegisterInfo::isVirtualRegister(Reg))
686 LV->getVarInfo(Reg).Kills.push_back(I);
687 DEBUG(dbgs() << "Restored terminator kill: " << *I);
688 break;
689 }
690 }
691 // Update relevant live-through information.
692 LV->addNewBlock(NMBB, this, Succ);
693 }
694
695 if (MachineDominatorTree *MDT =
696 P->getAnalysisIfAvailable<MachineDominatorTree>()) {
697 // Update dominator information.
698 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
699
700 bool IsNewIDom = true;
701 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
702 PI != E; ++PI) {
703 MachineBasicBlock *PredBB = *PI;
704 if (PredBB == NMBB)
705 continue;
706 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
707 IsNewIDom = false;
708 break;
709 }
710 }
711
712 // We know "this" dominates the newly created basic block.
713 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
714
715 // If all the other predecessors of "Succ" are dominated by "Succ" itself
716 // then the new block is the new immediate dominator of "Succ". Otherwise,
717 // the new block doesn't dominate anything.
718 if (IsNewIDom)
719 MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
720 }
721
722 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
723 if (MachineLoop *TIL = MLI->getLoopFor(this)) {
724 // If one or the other blocks were not in a loop, the new block is not
725 // either, and thus LI doesn't need to be updated.
726 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
727 if (TIL == DestLoop) {
728 // Both in the same loop, the NMBB joins loop.
729 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
730 } else if (TIL->contains(DestLoop)) {
731 // Edge from an outer loop to an inner loop. Add to the outer loop.
732 TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
733 } else if (DestLoop->contains(TIL)) {
734 // Edge from an inner loop to an outer loop. Add to the outer loop.
735 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
736 } else {
737 // Edge from two loops with no containment relation. Because these
738 // are natural loops, we know that the destination block must be the
739 // header of its loop (adding a branch into a loop elsewhere would
740 // create an irreducible loop).
741 assert(DestLoop->getHeader() == Succ &&
742 "Should not create irreducible loops!");
743 if (MachineLoop *P = DestLoop->getParentLoop())
744 P->addBasicBlockToLoop(NMBB, MLI->getBase());
745 }
746 }
747 }
748
749 return NMBB;
750 }
751
752 MachineBasicBlock::iterator
erase(MachineBasicBlock::iterator I)753 MachineBasicBlock::erase(MachineBasicBlock::iterator I) {
754 if (I->isBundle()) {
755 MachineBasicBlock::iterator E = llvm::next(I);
756 return Insts.erase(I.getInstrIterator(), E.getInstrIterator());
757 }
758
759 return Insts.erase(I.getInstrIterator());
760 }
761
remove(MachineInstr * I)762 MachineInstr *MachineBasicBlock::remove(MachineInstr *I) {
763 if (I->isBundle()) {
764 instr_iterator MII = llvm::next(I);
765 iterator E = end();
766 while (MII != E && MII->isInsideBundle()) {
767 MachineInstr *MI = &*MII++;
768 Insts.remove(MI);
769 }
770 }
771
772 return Insts.remove(I);
773 }
774
splice(MachineBasicBlock::iterator where,MachineBasicBlock * Other,MachineBasicBlock::iterator From)775 void MachineBasicBlock::splice(MachineBasicBlock::iterator where,
776 MachineBasicBlock *Other,
777 MachineBasicBlock::iterator From) {
778 if (From->isBundle()) {
779 MachineBasicBlock::iterator To = llvm::next(From);
780 Insts.splice(where.getInstrIterator(), Other->Insts,
781 From.getInstrIterator(), To.getInstrIterator());
782 return;
783 }
784
785 Insts.splice(where.getInstrIterator(), Other->Insts, From.getInstrIterator());
786 }
787
788 /// removeFromParent - This method unlinks 'this' from the containing function,
789 /// and returns it, but does not delete it.
removeFromParent()790 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
791 assert(getParent() && "Not embedded in a function!");
792 getParent()->remove(this);
793 return this;
794 }
795
796
797 /// eraseFromParent - This method unlinks 'this' from the containing function,
798 /// and deletes it.
eraseFromParent()799 void MachineBasicBlock::eraseFromParent() {
800 assert(getParent() && "Not embedded in a function!");
801 getParent()->erase(this);
802 }
803
804
805 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
806 /// 'Old', change the code and CFG so that it branches to 'New' instead.
ReplaceUsesOfBlockWith(MachineBasicBlock * Old,MachineBasicBlock * New)807 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
808 MachineBasicBlock *New) {
809 assert(Old != New && "Cannot replace self with self!");
810
811 MachineBasicBlock::instr_iterator I = instr_end();
812 while (I != instr_begin()) {
813 --I;
814 if (!I->isTerminator()) break;
815
816 // Scan the operands of this machine instruction, replacing any uses of Old
817 // with New.
818 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
819 if (I->getOperand(i).isMBB() &&
820 I->getOperand(i).getMBB() == Old)
821 I->getOperand(i).setMBB(New);
822 }
823
824 // Update the successor information.
825 replaceSuccessor(Old, New);
826 }
827
828 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
829 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and
830 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
831 /// null.
832 ///
833 /// Besides DestA and DestB, retain other edges leading to LandingPads
834 /// (currently there can be only one; we don't check or require that here).
835 /// Note it is possible that DestA and/or DestB are LandingPads.
CorrectExtraCFGEdges(MachineBasicBlock * DestA,MachineBasicBlock * DestB,bool isCond)836 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
837 MachineBasicBlock *DestB,
838 bool isCond) {
839 // The values of DestA and DestB frequently come from a call to the
840 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
841 // values from there.
842 //
843 // 1. If both DestA and DestB are null, then the block ends with no branches
844 // (it falls through to its successor).
845 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
846 // with only an unconditional branch.
847 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
848 // with a conditional branch that falls through to a successor (DestB).
849 // 4. If DestA and DestB is set and isCond is true, then the block ends with a
850 // conditional branch followed by an unconditional branch. DestA is the
851 // 'true' destination and DestB is the 'false' destination.
852
853 bool Changed = false;
854
855 MachineFunction::iterator FallThru =
856 llvm::next(MachineFunction::iterator(this));
857
858 if (DestA == 0 && DestB == 0) {
859 // Block falls through to successor.
860 DestA = FallThru;
861 DestB = FallThru;
862 } else if (DestA != 0 && DestB == 0) {
863 if (isCond)
864 // Block ends in conditional jump that falls through to successor.
865 DestB = FallThru;
866 } else {
867 assert(DestA && DestB && isCond &&
868 "CFG in a bad state. Cannot correct CFG edges");
869 }
870
871 // Remove superfluous edges. I.e., those which aren't destinations of this
872 // basic block, duplicate edges, or landing pads.
873 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
874 MachineBasicBlock::succ_iterator SI = succ_begin();
875 while (SI != succ_end()) {
876 const MachineBasicBlock *MBB = *SI;
877 if (!SeenMBBs.insert(MBB) ||
878 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
879 // This is a superfluous edge, remove it.
880 SI = removeSuccessor(SI);
881 Changed = true;
882 } else {
883 ++SI;
884 }
885 }
886
887 return Changed;
888 }
889
890 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
891 /// any DBG_VALUE instructions. Return UnknownLoc if there is none.
892 DebugLoc
findDebugLoc(instr_iterator MBBI)893 MachineBasicBlock::findDebugLoc(instr_iterator MBBI) {
894 DebugLoc DL;
895 instr_iterator E = instr_end();
896 if (MBBI == E)
897 return DL;
898
899 // Skip debug declarations, we don't want a DebugLoc from them.
900 while (MBBI != E && MBBI->isDebugValue())
901 MBBI++;
902 if (MBBI != E)
903 DL = MBBI->getDebugLoc();
904 return DL;
905 }
906
907 /// getSuccWeight - Return weight of the edge from this block to MBB.
908 ///
getSuccWeight(const MachineBasicBlock * succ) const909 uint32_t MachineBasicBlock::getSuccWeight(const MachineBasicBlock *succ) const {
910 if (Weights.empty())
911 return 0;
912
913 const_succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
914 return *getWeightIterator(I);
915 }
916
917 /// getWeightIterator - Return wight iterator corresonding to the I successor
918 /// iterator
919 MachineBasicBlock::weight_iterator MachineBasicBlock::
getWeightIterator(MachineBasicBlock::succ_iterator I)920 getWeightIterator(MachineBasicBlock::succ_iterator I) {
921 assert(Weights.size() == Successors.size() && "Async weight list!");
922 size_t index = std::distance(Successors.begin(), I);
923 assert(index < Weights.size() && "Not a current successor!");
924 return Weights.begin() + index;
925 }
926
927 /// getWeightIterator - Return wight iterator corresonding to the I successor
928 /// iterator
929 MachineBasicBlock::const_weight_iterator MachineBasicBlock::
getWeightIterator(MachineBasicBlock::const_succ_iterator I) const930 getWeightIterator(MachineBasicBlock::const_succ_iterator I) const {
931 assert(Weights.size() == Successors.size() && "Async weight list!");
932 const size_t index = std::distance(Successors.begin(), I);
933 assert(index < Weights.size() && "Not a current successor!");
934 return Weights.begin() + index;
935 }
936
WriteAsOperand(raw_ostream & OS,const MachineBasicBlock * MBB,bool t)937 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
938 bool t) {
939 OS << "BB#" << MBB->getNumber();
940 }
941
942