lib/CodeGen/MachineBasicBlock.cpp

   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
  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
  42 MachineBasicBlock::~MachineBasicBlock() {
  43   LeakDetector::removeGarbageObject(this);
  44 }
  45
  46 /// getSymbol - Return the MCSymbol for this basic block.
  47 ///
  48 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
  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.
  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
  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.
  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.
 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>::
 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
 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
 142 MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
 143   iterator I = begin();
 144   while (I != end() && I->isPHI())
 145     ++I;
 146   return I;
 147 }
 148
 149 MachineBasicBlock::iterator
 150 MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
 151   while (I != end() && (I->isPHI() || I->isLabel() || I->isDebugValue()))
 152     ++I;
 153   return I;
 154 }
 155
 156 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
 157   iterator I = end();
 158   while (I != begin() && ((--I)->getDesc().isTerminator() || I->isDebugValue()))
 159     ; /*noop */
 160   while (I != end() && !I->getDesc().isTerminator())
 161     ++I;
 162   return I;
 163 }
 164
 165 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {
 166   iterator B = begin(), I = end();
 167   while (I != B) {
 168     --I;
 169     if (I->isDebugValue())
 170       continue;
 171     return I;
 172   }
 173   // The block is all debug values.
 174   return end();
 175 }
 176
 177 const MachineBasicBlock *MachineBasicBlock::getLandingPadSuccessor() const {
 178   // A block with a landing pad successor only has one other successor.
 179   if (succ_size() > 2)
 180     return 0;
 181   for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I)
 182     if ((*I)->isLandingPad())
 183       return *I;
 184   return 0;
 185 }
 186
 187 void MachineBasicBlock::dump() const {
 188   print(dbgs());
 189 }
 190
 191 StringRef MachineBasicBlock::getName() const {
 192   if (const BasicBlock *LBB = getBasicBlock())
 193     return LBB->getName();
 194   else
 195     return "(null)";
 196 }
 197
 198 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
 199   const MachineFunction *MF = getParent();
 200   if (!MF) {
 201     OS << "Can't print out MachineBasicBlock because parent MachineFunction"
 202        << " is null\n";
 203     return;
 204   }
 205
 206   if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
 207
 208   if (Indexes)
 209     OS << Indexes->getMBBStartIdx(this) << '\t';
 210
 211   OS << "BB#" << getNumber() << ": ";
 212
 213   const char *Comma = "";
 214   if (const BasicBlock *LBB = getBasicBlock()) {
 215     OS << Comma << "derived from LLVM BB ";
 216     WriteAsOperand(OS, LBB, /*PrintType=*/false);
 217     Comma = ", ";
 218   }
 219   if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
 220   if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
 221   OS << '\n';
 222
 223   const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
 224   if (!livein_empty()) {
 225     if (Indexes) OS << '\t';
 226     OS << "    Live Ins:";
 227     for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
 228       OS << ' ' << PrintReg(*I, TRI);
 229     OS << '\n';
 230   }
 231   // Print the preds of this block according to the CFG.
 232   if (!pred_empty()) {
 233     if (Indexes) OS << '\t';
 234     OS << "    Predecessors according to CFG:";
 235     for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
 236       OS << " BB#" << (*PI)->getNumber();
 237     OS << '\n';
 238   }
 239
 240   for (const_iterator I = begin(); I != end(); ++I) {
 241     if (Indexes) {
 242       if (Indexes->hasIndex(I))
 243         OS << Indexes->getInstructionIndex(I);
 244       OS << '\t';
 245     }
 246     OS << '\t';
 247     I->print(OS, &getParent()->getTarget());
 248   }
 249
 250   // Print the successors of this block according to the CFG.
 251   if (!succ_empty()) {
 252     if (Indexes) OS << '\t';
 253     OS << "    Successors according to CFG:";
 254     for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
 255       OS << " BB#" << (*SI)->getNumber();
 256     OS << '\n';
 257   }
 258 }
 259
 260 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
 261   std::vector<unsigned>::iterator I =
 262     std::find(LiveIns.begin(), LiveIns.end(), Reg);
 263   assert(I != LiveIns.end() && "Not a live in!");
 264   LiveIns.erase(I);
 265 }
 266
 267 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
 268   livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
 269   return I != livein_end();
 270 }
 271
 272 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
 273   getParent()->splice(NewAfter, this);
 274 }
 275
 276 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
 277   MachineFunction::iterator BBI = NewBefore;
 278   getParent()->splice(++BBI, this);
 279 }
 280
 281 void MachineBasicBlock::updateTerminator() {
 282   const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
 283   // A block with no successors has no concerns with fall-through edges.
 284   if (this->succ_empty()) return;
 285
 286   MachineBasicBlock *TBB = 0, *FBB = 0;
 287   SmallVector<MachineOperand, 4> Cond;
 288   DebugLoc dl;  // FIXME: this is nowhere
 289   bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
 290   (void) B;
 291   assert(!B && "UpdateTerminators requires analyzable predecessors!");
 292   if (Cond.empty()) {
 293     if (TBB) {
 294       // The block has an unconditional branch. If its successor is now
 295       // its layout successor, delete the branch.
 296       if (isLayoutSuccessor(TBB))
 297         TII->RemoveBranch(*this);
 298     } else {
 299       // The block has an unconditional fallthrough. If its successor is not
 300       // its layout successor, insert a branch.
 301       TBB = *succ_begin();
 302       if (!isLayoutSuccessor(TBB))
 303         TII->InsertBranch(*this, TBB, 0, Cond, dl);
 304     }
 305   } else {
 306     if (FBB) {
 307       // The block has a non-fallthrough conditional branch. If one of its
 308       // successors is its layout successor, rewrite it to a fallthrough
 309       // conditional branch.
 310       if (isLayoutSuccessor(TBB)) {
 311         if (TII->ReverseBranchCondition(Cond))
 312           return;
 313         TII->RemoveBranch(*this);
 314         TII->InsertBranch(*this, FBB, 0, Cond, dl);
 315       } else if (isLayoutSuccessor(FBB)) {
 316         TII->RemoveBranch(*this);
 317         TII->InsertBranch(*this, TBB, 0, Cond, dl);
 318       }
 319     } else {
 320       // The block has a fallthrough conditional branch.
 321       MachineBasicBlock *MBBA = *succ_begin();
 322       MachineBasicBlock *MBBB = *llvm::next(succ_begin());
 323       if (MBBA == TBB) std::swap(MBBB, MBBA);
 324       if (isLayoutSuccessor(TBB)) {
 325         if (TII->ReverseBranchCondition(Cond)) {
 326           // We can't reverse the condition, add an unconditional branch.
 327           Cond.clear();
 328           TII->InsertBranch(*this, MBBA, 0, Cond, dl);
 329           return;
 330         }
 331         TII->RemoveBranch(*this);
 332         TII->InsertBranch(*this, MBBA, 0, Cond, dl);
 333       } else if (!isLayoutSuccessor(MBBA)) {
 334         TII->RemoveBranch(*this);
 335         TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
 336       }
 337     }
 338   }
 339 }
 340
 341 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
 342
 343   // If we see non-zero value for the first time it means we actually use Weight
 344   // list, so we fill all Weights with 0's.
 345   if (weight != 0 && Weights.empty())
 346     Weights.resize(Successors.size());
 347
 348   if (weight != 0 || !Weights.empty())
 349     Weights.push_back(weight);
 350
 351    Successors.push_back(succ);
 352    succ->addPredecessor(this);
 353  }
 354
 355 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
 356   succ->removePredecessor(this);
 357   succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
 358   assert(I != Successors.end() && "Not a current successor!");
 359
 360   // If Weight list is empty it means we don't use it (disabled optimization).
 361   if (!Weights.empty()) {
 362     weight_iterator WI = getWeightIterator(I);
 363     Weights.erase(WI);
 364   }
 365
 366   Successors.erase(I);
 367 }
 368
 369 MachineBasicBlock::succ_iterator
 370 MachineBasicBlock::removeSuccessor(succ_iterator I) {
 371   assert(I != Successors.end() && "Not a current successor!");
 372
 373   // If Weight list is empty it means we don't use it (disabled optimization).
 374   if (!Weights.empty()) {
 375     weight_iterator WI = getWeightIterator(I);
 376     Weights.erase(WI);
 377   }
 378
 379   (*I)->removePredecessor(this);
 380   return Successors.erase(I);
 381 }
 382
 383 void MachineBasicBlock::replaceSuccessor(MachineBasicBlock *Old,
 384                                          MachineBasicBlock *New) {
 385   uint32_t weight = 0;
 386   succ_iterator SI = std::find(Successors.begin(), Successors.end(), Old);
 387
 388   // If Weight list is empty it means we don't use it (disabled optimization).
 389   if (!Weights.empty()) {
 390     weight_iterator WI = getWeightIterator(SI);
 391     weight = *WI;
 392   }
 393
 394   // Update the successor information.
 395   removeSuccessor(SI);
 396   addSuccessor(New, weight);
 397 }
 398
 399 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
 400   Predecessors.push_back(pred);
 401 }
 402
 403 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
 404   pred_iterator I = std::find(Predecessors.begin(), Predecessors.end(), pred);
 405   assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
 406   Predecessors.erase(I);
 407 }
 408
 409 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
 410   if (this == fromMBB)
 411     return;
 412
 413   while (!fromMBB->succ_empty()) {
 414     MachineBasicBlock *Succ = *fromMBB->succ_begin();
 415     uint32_t weight = 0;
 416
 417
 418     // If Weight list is empty it means we don't use it (disabled optimization).
 419     if (!fromMBB->Weights.empty())
 420       weight = *fromMBB->Weights.begin();
 421
 422     addSuccessor(Succ, weight);
 423     fromMBB->removeSuccessor(Succ);
 424   }
 425 }
 426
 427 void
 428 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
 429   if (this == fromMBB)
 430     return;
 431
 432   while (!fromMBB->succ_empty()) {
 433     MachineBasicBlock *Succ = *fromMBB->succ_begin();
 434     addSuccessor(Succ);
 435     fromMBB->removeSuccessor(Succ);
 436
 437     // Fix up any PHI nodes in the successor.
 438     for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
 439          MI != ME && MI->isPHI(); ++MI)
 440       for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
 441         MachineOperand &MO = MI->getOperand(i);
 442         if (MO.getMBB() == fromMBB)
 443           MO.setMBB(this);
 444       }
 445   }
 446 }
 447
 448 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
 449   const_succ_iterator I = std::find(Successors.begin(), Successors.end(), MBB);
 450   return I != Successors.end();
 451 }
 452
 453 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
 454   MachineFunction::const_iterator I(this);
 455   return llvm::next(I) == MachineFunction::const_iterator(MBB);
 456 }
 457
 458 bool MachineBasicBlock::canFallThrough() {
 459   MachineFunction::iterator Fallthrough = this;
 460   ++Fallthrough;
 461   // If FallthroughBlock is off the end of the function, it can't fall through.
 462   if (Fallthrough == getParent()->end())
 463     return false;
 464
 465   // If FallthroughBlock isn't a successor, no fallthrough is possible.
 466   if (!isSuccessor(Fallthrough))
 467     return false;
 468
 469   // Analyze the branches, if any, at the end of the block.
 470   MachineBasicBlock *TBB = 0, *FBB = 0;
 471   SmallVector<MachineOperand, 4> Cond;
 472   const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
 473   if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
 474     // If we couldn't analyze the branch, examine the last instruction.
 475     // If the block doesn't end in a known control barrier, assume fallthrough
 476     // is possible. The isPredicable check is needed because this code can be
 477     // called during IfConversion, where an instruction which is normally a
 478     // Barrier is predicated and thus no longer an actual control barrier. This
 479     // is over-conservative though, because if an instruction isn't actually
 480     // predicated we could still treat it like a barrier.
 481     return empty() || !back().getDesc().isBarrier() ||
 482            back().getDesc().isPredicable();
 483   }
 484
 485   // If there is no branch, control always falls through.
 486   if (TBB == 0) return true;
 487
 488   // If there is some explicit branch to the fallthrough block, it can obviously
 489   // reach, even though the branch should get folded to fall through implicitly.
 490   if (MachineFunction::iterator(TBB) == Fallthrough ||
 491       MachineFunction::iterator(FBB) == Fallthrough)
 492     return true;
 493
 494   // If it's an unconditional branch to some block not the fall through, it
 495   // doesn't fall through.
 496   if (Cond.empty()) return false;
 497
 498   // Otherwise, if it is conditional and has no explicit false block, it falls
 499   // through.
 500   return FBB == 0;
 501 }
 502
 503 MachineBasicBlock *
 504 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
 505   MachineFunction *MF = getParent();
 506   DebugLoc dl;  // FIXME: this is nowhere
 507
 508   // We may need to update this's terminator, but we can't do that if
 509   // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
 510   const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
 511   MachineBasicBlock *TBB = 0, *FBB = 0;
 512   SmallVector<MachineOperand, 4> Cond;
 513   if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
 514     return NULL;
 515
 516   // Avoid bugpoint weirdness: A block may end with a conditional branch but
 517   // jumps to the same MBB is either case. We have duplicate CFG edges in that
 518   // case that we can't handle. Since this never happens in properly optimized
 519   // code, just skip those edges.
 520   if (TBB && TBB == FBB) {
 521     DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
 522                  << getNumber() << '\n');
 523     return NULL;
 524   }
 525
 526   MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
 527   MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
 528   DEBUG(dbgs() << "Splitting critical edge:"
 529         " BB#" << getNumber()
 530         << " -- BB#" << NMBB->getNumber()
 531         << " -- BB#" << Succ->getNumber() << '\n');
 532
 533   // On some targets like Mips, branches may kill virtual registers. Make sure
 534   // that LiveVariables is properly updated after updateTerminator replaces the
 535   // terminators.
 536   LiveVariables *LV = P->getAnalysisIfAvailable<LiveVariables>();
 537
 538   // Collect a list of virtual registers killed by the terminators.
 539   SmallVector<unsigned, 4> KilledRegs;
 540   if (LV)
 541     for (iterator I = getFirstTerminator(), E = end(); I != E; ++I) {
 542       MachineInstr *MI = I;
 543       for (MachineInstr::mop_iterator OI = MI->operands_begin(),
 544            OE = MI->operands_end(); OI != OE; ++OI) {
 545         if (!OI->isReg() || !OI->isUse() || !OI->isKill() || OI->isUndef())
 546           continue;
 547         unsigned Reg = OI->getReg();
 548         if (TargetRegisterInfo::isVirtualRegister(Reg) &&
 549             LV->getVarInfo(Reg).removeKill(MI)) {
 550           KilledRegs.push_back(Reg);
 551           DEBUG(dbgs() << "Removing terminator kill: " << *MI);
 552           OI->setIsKill(false);
 553         }
 554       }
 555     }
 556
 557   ReplaceUsesOfBlockWith(Succ, NMBB);
 558   updateTerminator();
 559
 560   // Insert unconditional "jump Succ" instruction in NMBB if necessary.
 561   NMBB->addSuccessor(Succ);
 562   if (!NMBB->isLayoutSuccessor(Succ)) {
 563     Cond.clear();
 564     MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
 565   }
 566
 567   // Fix PHI nodes in Succ so they refer to NMBB instead of this
 568   for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
 569        i != e && i->isPHI(); ++i)
 570     for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
 571       if (i->getOperand(ni+1).getMBB() == this)
 572         i->getOperand(ni+1).setMBB(NMBB);
 573
 574   // Update LiveVariables.
 575   if (LV) {
 576     // Restore kills of virtual registers that were killed by the terminators.
 577     while (!KilledRegs.empty()) {
 578       unsigned Reg = KilledRegs.pop_back_val();
 579       for (iterator I = end(), E = begin(); I != E;) {
 580         if (!(--I)->addRegisterKilled(Reg, NULL, /* addIfNotFound= */ false))
 581           continue;
 582         LV->getVarInfo(Reg).Kills.push_back(I);
 583         DEBUG(dbgs() << "Restored terminator kill: " << *I);
 584         break;
 585       }
 586     }
 587     // Update relevant live-through information.
 588     LV->addNewBlock(NMBB, this, Succ);
 589   }
 590
 591   if (MachineDominatorTree *MDT =
 592       P->getAnalysisIfAvailable<MachineDominatorTree>()) {
 593     // Update dominator information.
 594     MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
 595
 596     bool IsNewIDom = true;
 597     for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
 598          PI != E; ++PI) {
 599       MachineBasicBlock *PredBB = *PI;
 600       if (PredBB == NMBB)
 601         continue;
 602       if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
 603         IsNewIDom = false;
 604         break;
 605       }
 606     }
 607
 608     // We know "this" dominates the newly created basic block.
 609     MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
 610
 611     // If all the other predecessors of "Succ" are dominated by "Succ" itself
 612     // then the new block is the new immediate dominator of "Succ". Otherwise,
 613     // the new block doesn't dominate anything.
 614     if (IsNewIDom)
 615       MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
 616   }
 617
 618   if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
 619     if (MachineLoop *TIL = MLI->getLoopFor(this)) {
 620       // If one or the other blocks were not in a loop, the new block is not
 621       // either, and thus LI doesn't need to be updated.
 622       if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
 623         if (TIL == DestLoop) {
 624           // Both in the same loop, the NMBB joins loop.
 625           DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
 626         } else if (TIL->contains(DestLoop)) {
 627           // Edge from an outer loop to an inner loop.  Add to the outer loop.
 628           TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
 629         } else if (DestLoop->contains(TIL)) {
 630           // Edge from an inner loop to an outer loop.  Add to the outer loop.
 631           DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
 632         } else {
 633           // Edge from two loops with no containment relation.  Because these
 634           // are natural loops, we know that the destination block must be the
 635           // header of its loop (adding a branch into a loop elsewhere would
 636           // create an irreducible loop).
 637           assert(DestLoop->getHeader() == Succ &&
 638                  "Should not create irreducible loops!");
 639           if (MachineLoop *P = DestLoop->getParentLoop())
 640             P->addBasicBlockToLoop(NMBB, MLI->getBase());
 641         }
 642       }
 643     }
 644
 645   return NMBB;
 646 }
 647
 648 /// removeFromParent - This method unlinks 'this' from the containing function,
 649 /// and returns it, but does not delete it.
 650 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
 651   assert(getParent() && "Not embedded in a function!");
 652   getParent()->remove(this);
 653   return this;
 654 }
 655
 656
 657 /// eraseFromParent - This method unlinks 'this' from the containing function,
 658 /// and deletes it.
 659 void MachineBasicBlock::eraseFromParent() {
 660   assert(getParent() && "Not embedded in a function!");
 661   getParent()->erase(this);
 662 }
 663
 664
 665 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
 666 /// 'Old', change the code and CFG so that it branches to 'New' instead.
 667 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
 668                                                MachineBasicBlock *New) {
 669   assert(Old != New && "Cannot replace self with self!");
 670
 671   MachineBasicBlock::iterator I = end();
 672   while (I != begin()) {
 673     --I;
 674     if (!I->getDesc().isTerminator()) break;
 675
 676     // Scan the operands of this machine instruction, replacing any uses of Old
 677     // with New.
 678     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
 679       if (I->getOperand(i).isMBB() &&
 680           I->getOperand(i).getMBB() == Old)
 681         I->getOperand(i).setMBB(New);
 682   }
 683
 684   // Update the successor information.
 685   replaceSuccessor(Old, New);
 686 }
 687
 688 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
 689 /// CFG to be inserted.  If we have proven that MBB can only branch to DestA and
 690 /// DestB, remove any other MBB successors from the CFG.  DestA and DestB can be
 691 /// null.
 692 ///
 693 /// Besides DestA and DestB, retain other edges leading to LandingPads
 694 /// (currently there can be only one; we don't check or require that here).
 695 /// Note it is possible that DestA and/or DestB are LandingPads.
 696 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
 697                                              MachineBasicBlock *DestB,
 698                                              bool isCond) {
 699   // The values of DestA and DestB frequently come from a call to the
 700   // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
 701   // values from there.
 702   //
 703   // 1. If both DestA and DestB are null, then the block ends with no branches
 704   //    (it falls through to its successor).
 705   // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
 706   //    with only an unconditional branch.
 707   // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
 708   //    with a conditional branch that falls through to a successor (DestB).
 709   // 4. If DestA and DestB is set and isCond is true, then the block ends with a
 710   //    conditional branch followed by an unconditional branch. DestA is the
 711   //    'true' destination and DestB is the 'false' destination.
 712
 713   bool Changed = false;
 714
 715   MachineFunction::iterator FallThru =
 716     llvm::next(MachineFunction::iterator(this));
 717
 718   if (DestA == 0 && DestB == 0) {
 719     // Block falls through to successor.
 720     DestA = FallThru;
 721     DestB = FallThru;
 722   } else if (DestA != 0 && DestB == 0) {
 723     if (isCond)
 724       // Block ends in conditional jump that falls through to successor.
 725       DestB = FallThru;
 726   } else {
 727     assert(DestA && DestB && isCond &&
 728            "CFG in a bad state. Cannot correct CFG edges");
 729   }
 730
 731   // Remove superfluous edges. I.e., those which aren't destinations of this
 732   // basic block, duplicate edges, or landing pads.
 733   SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
 734   MachineBasicBlock::succ_iterator SI = succ_begin();
 735   while (SI != succ_end()) {
 736     const MachineBasicBlock *MBB = *SI;
 737     if (!SeenMBBs.insert(MBB) ||
 738         (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
 739       // This is a superfluous edge, remove it.
 740       SI = removeSuccessor(SI);
 741       Changed = true;
 742     } else {
 743       ++SI;
 744     }
 745   }
 746
 747   return Changed;
 748 }
 749
 750 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
 751 /// any DBG_VALUE instructions.  Return UnknownLoc if there is none.
 752 DebugLoc
 753 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
 754   DebugLoc DL;
 755   MachineBasicBlock::iterator E = end();
 756   if (MBBI != E) {
 757     // Skip debug declarations, we don't want a DebugLoc from them.
 758     MachineBasicBlock::iterator MBBI2 = MBBI;
 759     while (MBBI2 != E && MBBI2->isDebugValue())
 760       MBBI2++;
 761     if (MBBI2 != E)
 762       DL = MBBI2->getDebugLoc();
 763   }
 764   return DL;
 765 }
 766
 767 /// getSuccWeight - Return weight of the edge from this block to MBB.
 768 ///
 769 uint32_t MachineBasicBlock::getSuccWeight(MachineBasicBlock *succ) {
 770   if (Weights.empty())
 771     return 0;
 772
 773   succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
 774   return *getWeightIterator(I);
 775 }
 776
 777 /// getWeightIterator - Return wight iterator corresonding to the I successor
 778 /// iterator
 779 MachineBasicBlock::weight_iterator MachineBasicBlock::
 780 getWeightIterator(MachineBasicBlock::succ_iterator I) {
 781   assert(Weights.size() == Successors.size() && "Async weight list!");
 782   size_t index = std::distance(Successors.begin(), I);
 783   assert(index < Weights.size() && "Not a current successor!");
 784   return Weights.begin() + index;
 785 }
 786
 787 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
 788                           bool t) {
 789   OS << "BB#" << MBB->getNumber();
 790 }
 791