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/TargetInstrDesc.h"
  26 #include "llvm/Target/TargetInstrInfo.h"
  27 #include "llvm/Target/TargetMachine.h"
  28 #include "llvm/Assembly/Writer.h"
  29 #include "llvm/ADT/SmallString.h"
  30 #include "llvm/ADT/SmallPtrSet.h"
  31 #include "llvm/Support/Debug.h"
  32 #include "llvm/Support/LeakDetector.h"
  33 #include "llvm/Support/raw_ostream.h"
  34 #include <algorithm>
  35 using namespace llvm;
  36
  37 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
  38   : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
  39     AddressTaken(false) {
  40   Insts.Parent = this;
  41 }
  42
  43 MachineBasicBlock::~MachineBasicBlock() {
  44   LeakDetector::removeGarbageObject(this);
  45 }
  46
  47 /// getSymbol - Return the MCSymbol for this basic block.
  48 ///
  49 MCSymbol *MachineBasicBlock::getSymbol() const {
  50   const MachineFunction *MF = getParent();
  51   MCContext &Ctx = MF->getContext();
  52   const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix();
  53   return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
  54                                Twine(MF->getFunctionNumber()) + "_" +
  55                                Twine(getNumber()));
  56 }
  57
  58
  59 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
  60   MBB.print(OS);
  61   return OS;
  62 }
  63
  64 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the
  65 /// parent pointer of the MBB, the MBB numbering, and any instructions in the
  66 /// MBB to be on the right operand list for registers.
  67 ///
  68 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
  69 /// gets the next available unique MBB number. If it is removed from a
  70 /// MachineFunction, it goes back to being #-1.
  71 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
  72   MachineFunction &MF = *N->getParent();
  73   N->Number = MF.addToMBBNumbering(N);
  74
  75   // Make sure the instructions have their operands in the reginfo lists.
  76   MachineRegisterInfo &RegInfo = MF.getRegInfo();
  77   for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I)
  78     I->AddRegOperandsToUseLists(RegInfo);
  79
  80   LeakDetector::removeGarbageObject(N);
  81 }
  82
  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.
  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.
 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>::
 123 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
 124                       MachineBasicBlock::iterator first,
 125                       MachineBasicBlock::iterator 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
 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
 143 MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
 144   iterator I = begin();
 145   while (I != end() && I->isPHI())
 146     ++I;
 147   return I;
 148 }
 149
 150 MachineBasicBlock::iterator
 151 MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
 152   while (I != end() && (I->isPHI() || I->isLabel() || I->isDebugValue()))
 153     ++I;
 154   return I;
 155 }
 156
 157 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
 158   iterator I = end();
 159   while (I != begin() && (--I)->getDesc().isTerminator())
 160     ; /*noop */
 161   if (I != end() && !I->getDesc().isTerminator()) ++I;
 162   return I;
 163 }
 164
 165 void MachineBasicBlock::dump() const {
 166   print(dbgs());
 167 }
 168
 169 static inline void OutputReg(raw_ostream &os, unsigned RegNo,
 170                              const TargetRegisterInfo *TRI = 0) {
 171   if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) {
 172     if (TRI)
 173       os << " %" << TRI->get(RegNo).Name;
 174     else
 175       os << " %physreg" << RegNo;
 176   } else
 177     os << " %reg" << RegNo;
 178 }
 179
 180 StringRef MachineBasicBlock::getName() const {
 181   if (const BasicBlock *LBB = getBasicBlock())
 182     return LBB->getName();
 183   else
 184     return "(null)";
 185 }
 186
 187 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
 188   const MachineFunction *MF = getParent();
 189   if (!MF) {
 190     OS << "Can't print out MachineBasicBlock because parent MachineFunction"
 191        << " is null\n";
 192     return;
 193   }
 194
 195   if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
 196
 197   if (Indexes)
 198     OS << Indexes->getMBBStartIdx(this) << '\t';
 199
 200   OS << "BB#" << getNumber() << ": ";
 201
 202   const char *Comma = "";
 203   if (const BasicBlock *LBB = getBasicBlock()) {
 204     OS << Comma << "derived from LLVM BB ";
 205     WriteAsOperand(OS, LBB, /*PrintType=*/false);
 206     Comma = ", ";
 207   }
 208   if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
 209   if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
 210   OS << '\n';
 211
 212   const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
 213   if (!livein_empty()) {
 214     if (Indexes) OS << '\t';
 215     OS << "    Live Ins:";
 216     for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
 217       OutputReg(OS, *I, TRI);
 218     OS << '\n';
 219   }
 220   // Print the preds of this block according to the CFG.
 221   if (!pred_empty()) {
 222     if (Indexes) OS << '\t';
 223     OS << "    Predecessors according to CFG:";
 224     for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
 225       OS << " BB#" << (*PI)->getNumber();
 226     OS << '\n';
 227   }
 228
 229   for (const_iterator I = begin(); I != end(); ++I) {
 230     if (Indexes) {
 231       if (Indexes->hasIndex(I))
 232         OS << Indexes->getInstructionIndex(I);
 233       OS << '\t';
 234     }
 235     OS << '\t';
 236     I->print(OS, &getParent()->getTarget());
 237   }
 238
 239   // Print the successors of this block according to the CFG.
 240   if (!succ_empty()) {
 241     if (Indexes) OS << '\t';
 242     OS << "    Successors according to CFG:";
 243     for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
 244       OS << " BB#" << (*SI)->getNumber();
 245     OS << '\n';
 246   }
 247 }
 248
 249 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
 250   std::vector<unsigned>::iterator I =
 251     std::find(LiveIns.begin(), LiveIns.end(), Reg);
 252   assert(I != LiveIns.end() && "Not a live in!");
 253   LiveIns.erase(I);
 254 }
 255
 256 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
 257   livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
 258   return I != livein_end();
 259 }
 260
 261 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
 262   getParent()->splice(NewAfter, this);
 263 }
 264
 265 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
 266   MachineFunction::iterator BBI = NewBefore;
 267   getParent()->splice(++BBI, this);
 268 }
 269
 270 void MachineBasicBlock::updateTerminator() {
 271   const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
 272   // A block with no successors has no concerns with fall-through edges.
 273   if (this->succ_empty()) return;
 274
 275   MachineBasicBlock *TBB = 0, *FBB = 0;
 276   SmallVector<MachineOperand, 4> Cond;
 277   DebugLoc dl;  // FIXME: this is nowhere
 278   bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
 279   (void) B;
 280   assert(!B && "UpdateTerminators requires analyzable predecessors!");
 281   if (Cond.empty()) {
 282     if (TBB) {
 283       // The block has an unconditional branch. If its successor is now
 284       // its layout successor, delete the branch.
 285       if (isLayoutSuccessor(TBB))
 286         TII->RemoveBranch(*this);
 287     } else {
 288       // The block has an unconditional fallthrough. If its successor is not
 289       // its layout successor, insert a branch.
 290       TBB = *succ_begin();
 291       if (!isLayoutSuccessor(TBB))
 292         TII->InsertBranch(*this, TBB, 0, Cond, dl);
 293     }
 294   } else {
 295     if (FBB) {
 296       // The block has a non-fallthrough conditional branch. If one of its
 297       // successors is its layout successor, rewrite it to a fallthrough
 298       // conditional branch.
 299       if (isLayoutSuccessor(TBB)) {
 300         if (TII->ReverseBranchCondition(Cond))
 301           return;
 302         TII->RemoveBranch(*this);
 303         TII->InsertBranch(*this, FBB, 0, Cond, dl);
 304       } else if (isLayoutSuccessor(FBB)) {
 305         TII->RemoveBranch(*this);
 306         TII->InsertBranch(*this, TBB, 0, Cond, dl);
 307       }
 308     } else {
 309       // The block has a fallthrough conditional branch.
 310       MachineBasicBlock *MBBA = *succ_begin();
 311       MachineBasicBlock *MBBB = *llvm::next(succ_begin());
 312       if (MBBA == TBB) std::swap(MBBB, MBBA);
 313       if (isLayoutSuccessor(TBB)) {
 314         if (TII->ReverseBranchCondition(Cond)) {
 315           // We can't reverse the condition, add an unconditional branch.
 316           Cond.clear();
 317           TII->InsertBranch(*this, MBBA, 0, Cond, dl);
 318           return;
 319         }
 320         TII->RemoveBranch(*this);
 321         TII->InsertBranch(*this, MBBA, 0, Cond, dl);
 322       } else if (!isLayoutSuccessor(MBBA)) {
 323         TII->RemoveBranch(*this);
 324         TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
 325       }
 326     }
 327   }
 328 }
 329
 330 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
 331   Successors.push_back(succ);
 332   succ->addPredecessor(this);
 333 }
 334
 335 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
 336   succ->removePredecessor(this);
 337   succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
 338   assert(I != Successors.end() && "Not a current successor!");
 339   Successors.erase(I);
 340 }
 341
 342 MachineBasicBlock::succ_iterator
 343 MachineBasicBlock::removeSuccessor(succ_iterator I) {
 344   assert(I != Successors.end() && "Not a current successor!");
 345   (*I)->removePredecessor(this);
 346   return Successors.erase(I);
 347 }
 348
 349 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
 350   Predecessors.push_back(pred);
 351 }
 352
 353 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
 354   std::vector<MachineBasicBlock *>::iterator I =
 355     std::find(Predecessors.begin(), Predecessors.end(), pred);
 356   assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
 357   Predecessors.erase(I);
 358 }
 359
 360 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
 361   if (this == fromMBB)
 362     return;
 363
 364   while (!fromMBB->succ_empty()) {
 365     MachineBasicBlock *Succ = *fromMBB->succ_begin();
 366     addSuccessor(Succ);
 367     fromMBB->removeSuccessor(Succ);
 368   }
 369 }
 370
 371 void
 372 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
 373   if (this == fromMBB)
 374     return;
 375
 376   while (!fromMBB->succ_empty()) {
 377     MachineBasicBlock *Succ = *fromMBB->succ_begin();
 378     addSuccessor(Succ);
 379     fromMBB->removeSuccessor(Succ);
 380
 381     // Fix up any PHI nodes in the successor.
 382     for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
 383          MI != ME && MI->isPHI(); ++MI)
 384       for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
 385         MachineOperand &MO = MI->getOperand(i);
 386         if (MO.getMBB() == fromMBB)
 387           MO.setMBB(this);
 388       }
 389   }
 390 }
 391
 392 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
 393   std::vector<MachineBasicBlock *>::const_iterator I =
 394     std::find(Successors.begin(), Successors.end(), MBB);
 395   return I != Successors.end();
 396 }
 397
 398 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
 399   MachineFunction::const_iterator I(this);
 400   return llvm::next(I) == MachineFunction::const_iterator(MBB);
 401 }
 402
 403 bool MachineBasicBlock::canFallThrough() {
 404   MachineFunction::iterator Fallthrough = this;
 405   ++Fallthrough;
 406   // If FallthroughBlock is off the end of the function, it can't fall through.
 407   if (Fallthrough == getParent()->end())
 408     return false;
 409
 410   // If FallthroughBlock isn't a successor, no fallthrough is possible.
 411   if (!isSuccessor(Fallthrough))
 412     return false;
 413
 414   // Analyze the branches, if any, at the end of the block.
 415   MachineBasicBlock *TBB = 0, *FBB = 0;
 416   SmallVector<MachineOperand, 4> Cond;
 417   const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
 418   if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
 419     // If we couldn't analyze the branch, examine the last instruction.
 420     // If the block doesn't end in a known control barrier, assume fallthrough
 421     // is possible. The isPredicable check is needed because this code can be
 422     // called during IfConversion, where an instruction which is normally a
 423     // Barrier is predicated and thus no longer an actual control barrier. This
 424     // is over-conservative though, because if an instruction isn't actually
 425     // predicated we could still treat it like a barrier.
 426     return empty() || !back().getDesc().isBarrier() ||
 427            back().getDesc().isPredicable();
 428   }
 429
 430   // If there is no branch, control always falls through.
 431   if (TBB == 0) return true;
 432
 433   // If there is some explicit branch to the fallthrough block, it can obviously
 434   // reach, even though the branch should get folded to fall through implicitly.
 435   if (MachineFunction::iterator(TBB) == Fallthrough ||
 436       MachineFunction::iterator(FBB) == Fallthrough)
 437     return true;
 438
 439   // If it's an unconditional branch to some block not the fall through, it
 440   // doesn't fall through.
 441   if (Cond.empty()) return false;
 442
 443   // Otherwise, if it is conditional and has no explicit false block, it falls
 444   // through.
 445   return FBB == 0;
 446 }
 447
 448 MachineBasicBlock *
 449 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
 450   MachineFunction *MF = getParent();
 451   DebugLoc dl;  // FIXME: this is nowhere
 452
 453   // We may need to update this's terminator, but we can't do that if
 454   // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
 455   const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
 456   MachineBasicBlock *TBB = 0, *FBB = 0;
 457   SmallVector<MachineOperand, 4> Cond;
 458   if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
 459     return NULL;
 460
 461   // Avoid bugpoint weirdness: A block may end with a conditional branch but
 462   // jumps to the same MBB is either case. We have duplicate CFG edges in that
 463   // case that we can't handle. Since this never happens in properly optimized
 464   // code, just skip those edges.
 465   if (TBB && TBB == FBB) {
 466     DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
 467                  << getNumber() << '\n');
 468     return NULL;
 469   }
 470
 471   MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
 472   MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
 473   DEBUG(dbgs() << "Splitting critical edge:"
 474         " BB#" << getNumber()
 475         << " -- BB#" << NMBB->getNumber()
 476         << " -- BB#" << Succ->getNumber() << '\n');
 477
 478   ReplaceUsesOfBlockWith(Succ, NMBB);
 479   updateTerminator();
 480
 481   // Insert unconditional "jump Succ" instruction in NMBB if necessary.
 482   NMBB->addSuccessor(Succ);
 483   if (!NMBB->isLayoutSuccessor(Succ)) {
 484     Cond.clear();
 485     MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
 486   }
 487
 488   // Fix PHI nodes in Succ so they refer to NMBB instead of this
 489   for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
 490        i != e && i->isPHI(); ++i)
 491     for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
 492       if (i->getOperand(ni+1).getMBB() == this)
 493         i->getOperand(ni+1).setMBB(NMBB);
 494
 495   if (LiveVariables *LV =
 496         P->getAnalysisIfAvailable<LiveVariables>())
 497     LV->addNewBlock(NMBB, this, Succ);
 498
 499   if (MachineDominatorTree *MDT =
 500       P->getAnalysisIfAvailable<MachineDominatorTree>()) {
 501     // Update dominator information.
 502     MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ);
 503
 504     bool IsNewIDom = true;
 505     for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end();
 506          PI != E; ++PI) {
 507       MachineBasicBlock *PredBB = *PI;
 508       if (PredBB == NMBB)
 509         continue;
 510       if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) {
 511         IsNewIDom = false;
 512         break;
 513       }
 514     }
 515
 516     // We know "this" dominates the newly created basic block.
 517     MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this);
 518
 519     // If all the other predecessors of "Succ" are dominated by "Succ" itself
 520     // then the new block is the new immediate dominator of "Succ". Otherwise,
 521     // the new block doesn't dominate anything.
 522     if (IsNewIDom)
 523       MDT->changeImmediateDominator(SucccDTNode, NewDTNode);
 524   }
 525
 526   if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
 527     if (MachineLoop *TIL = MLI->getLoopFor(this)) {
 528       // If one or the other blocks were not in a loop, the new block is not
 529       // either, and thus LI doesn't need to be updated.
 530       if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
 531         if (TIL == DestLoop) {
 532           // Both in the same loop, the NMBB joins loop.
 533           DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
 534         } else if (TIL->contains(DestLoop)) {
 535           // Edge from an outer loop to an inner loop.  Add to the outer loop.
 536           TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
 537         } else if (DestLoop->contains(TIL)) {
 538           // Edge from an inner loop to an outer loop.  Add to the outer loop.
 539           DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
 540         } else {
 541           // Edge from two loops with no containment relation.  Because these
 542           // are natural loops, we know that the destination block must be the
 543           // header of its loop (adding a branch into a loop elsewhere would
 544           // create an irreducible loop).
 545           assert(DestLoop->getHeader() == Succ &&
 546                  "Should not create irreducible loops!");
 547           if (MachineLoop *P = DestLoop->getParentLoop())
 548             P->addBasicBlockToLoop(NMBB, MLI->getBase());
 549         }
 550       }
 551     }
 552
 553   return NMBB;
 554 }
 555
 556 /// removeFromParent - This method unlinks 'this' from the containing function,
 557 /// and returns it, but does not delete it.
 558 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
 559   assert(getParent() && "Not embedded in a function!");
 560   getParent()->remove(this);
 561   return this;
 562 }
 563
 564
 565 /// eraseFromParent - This method unlinks 'this' from the containing function,
 566 /// and deletes it.
 567 void MachineBasicBlock::eraseFromParent() {
 568   assert(getParent() && "Not embedded in a function!");
 569   getParent()->erase(this);
 570 }
 571
 572
 573 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
 574 /// 'Old', change the code and CFG so that it branches to 'New' instead.
 575 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
 576                                                MachineBasicBlock *New) {
 577   assert(Old != New && "Cannot replace self with self!");
 578
 579   MachineBasicBlock::iterator I = end();
 580   while (I != begin()) {
 581     --I;
 582     if (!I->getDesc().isTerminator()) break;
 583
 584     // Scan the operands of this machine instruction, replacing any uses of Old
 585     // with New.
 586     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
 587       if (I->getOperand(i).isMBB() &&
 588           I->getOperand(i).getMBB() == Old)
 589         I->getOperand(i).setMBB(New);
 590   }
 591
 592   // Update the successor information.
 593   removeSuccessor(Old);
 594   addSuccessor(New);
 595 }
 596
 597 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
 598 /// CFG to be inserted.  If we have proven that MBB can only branch to DestA and
 599 /// DestB, remove any other MBB successors from the CFG.  DestA and DestB can be
 600 /// null.
 601 ///
 602 /// Besides DestA and DestB, retain other edges leading to LandingPads
 603 /// (currently there can be only one; we don't check or require that here).
 604 /// Note it is possible that DestA and/or DestB are LandingPads.
 605 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
 606                                              MachineBasicBlock *DestB,
 607                                              bool isCond) {
 608   // The values of DestA and DestB frequently come from a call to the
 609   // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
 610   // values from there.
 611   //
 612   // 1. If both DestA and DestB are null, then the block ends with no branches
 613   //    (it falls through to its successor).
 614   // 2. If DestA is set, DestB is null, and isCond is false, then the block ends
 615   //    with only an unconditional branch.
 616   // 3. If DestA is set, DestB is null, and isCond is true, then the block ends
 617   //    with a conditional branch that falls through to a successor (DestB).
 618   // 4. If DestA and DestB is set and isCond is true, then the block ends with a
 619   //    conditional branch followed by an unconditional branch. DestA is the
 620   //    'true' destination and DestB is the 'false' destination.
 621
 622   bool Changed = false;
 623
 624   MachineFunction::iterator FallThru =
 625     llvm::next(MachineFunction::iterator(this));
 626
 627   if (DestA == 0 && DestB == 0) {
 628     // Block falls through to successor.
 629     DestA = FallThru;
 630     DestB = FallThru;
 631   } else if (DestA != 0 && DestB == 0) {
 632     if (isCond)
 633       // Block ends in conditional jump that falls through to successor.
 634       DestB = FallThru;
 635   } else {
 636     assert(DestA && DestB && isCond &&
 637            "CFG in a bad state. Cannot correct CFG edges");
 638   }
 639
 640   // Remove superfluous edges. I.e., those which aren't destinations of this
 641   // basic block, duplicate edges, or landing pads.
 642   SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
 643   MachineBasicBlock::succ_iterator SI = succ_begin();
 644   while (SI != succ_end()) {
 645     const MachineBasicBlock *MBB = *SI;
 646     if (!SeenMBBs.insert(MBB) ||
 647         (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
 648       // This is a superfluous edge, remove it.
 649       SI = removeSuccessor(SI);
 650       Changed = true;
 651     } else {
 652       ++SI;
 653     }
 654   }
 655
 656   return Changed;
 657 }
 658
 659 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
 660 /// any DBG_VALUE instructions.  Return UnknownLoc if there is none.
 661 DebugLoc
 662 MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
 663   DebugLoc DL;
 664   MachineBasicBlock::iterator E = end();
 665   if (MBBI != E) {
 666     // Skip debug declarations, we don't want a DebugLoc from them.
 667     MachineBasicBlock::iterator MBBI2 = MBBI;
 668     while (MBBI2 != E && MBBI2->isDebugValue())
 669       MBBI2++;
 670     if (MBBI2 != E)
 671       DL = MBBI2->getDebugLoc();
 672   }
 673   return DL;
 674 }
 675
 676 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
 677                           bool t) {
 678   OS << "BB#" << MBB->getNumber();
 679 }
 680