MachineBasicBlock.cpp revision a851fd8cd8e5c256651b3afeb8ebd539c28dfda7
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> 35using namespace llvm; 36 37MachineBasicBlock::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 43MachineBasicBlock::~MachineBasicBlock() { 44 LeakDetector::removeGarbageObject(this); 45} 46 47/// getSymbol - Return the MCSymbol for this basic block. 48/// 49MCSymbol *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 59raw_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. 71void 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 83void 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. 93void 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. 108void 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. 122void ilist_traits<MachineInstr>:: 123transferNodesFromList(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 138void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) { 139 assert(!MI->getParent() && "MI is still in a block!"); 140 Parent->getParent()->DeleteMachineInstr(MI); 141} 142 143MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() { 144 iterator I = begin(); 145 while (I != end() && I->isPHI()) 146 ++I; 147 return I; 148} 149 150MachineBasicBlock::iterator 151MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) { 152 while (I != end() && (I->isPHI() || I->isLabel() || I->isDebugValue())) 153 ++I; 154 return I; 155} 156 157MachineBasicBlock::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 165void MachineBasicBlock::dump() const { 166 print(dbgs()); 167} 168 169StringRef MachineBasicBlock::getName() const { 170 if (const BasicBlock *LBB = getBasicBlock()) 171 return LBB->getName(); 172 else 173 return "(null)"; 174} 175 176void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const { 177 const MachineFunction *MF = getParent(); 178 if (!MF) { 179 OS << "Can't print out MachineBasicBlock because parent MachineFunction" 180 << " is null\n"; 181 return; 182 } 183 184 if (Alignment) { OS << "Alignment " << Alignment << "\n"; } 185 186 if (Indexes) 187 OS << Indexes->getMBBStartIdx(this) << '\t'; 188 189 OS << "BB#" << getNumber() << ": "; 190 191 const char *Comma = ""; 192 if (const BasicBlock *LBB = getBasicBlock()) { 193 OS << Comma << "derived from LLVM BB "; 194 WriteAsOperand(OS, LBB, /*PrintType=*/false); 195 Comma = ", "; 196 } 197 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; } 198 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; } 199 OS << '\n'; 200 201 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo(); 202 if (!livein_empty()) { 203 if (Indexes) OS << '\t'; 204 OS << " Live Ins:"; 205 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I) 206 OS << ' ' << PrintReg(*I, TRI); 207 OS << '\n'; 208 } 209 // Print the preds of this block according to the CFG. 210 if (!pred_empty()) { 211 if (Indexes) OS << '\t'; 212 OS << " Predecessors according to CFG:"; 213 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI) 214 OS << " BB#" << (*PI)->getNumber(); 215 OS << '\n'; 216 } 217 218 for (const_iterator I = begin(); I != end(); ++I) { 219 if (Indexes) { 220 if (Indexes->hasIndex(I)) 221 OS << Indexes->getInstructionIndex(I); 222 OS << '\t'; 223 } 224 OS << '\t'; 225 I->print(OS, &getParent()->getTarget()); 226 } 227 228 // Print the successors of this block according to the CFG. 229 if (!succ_empty()) { 230 if (Indexes) OS << '\t'; 231 OS << " Successors according to CFG:"; 232 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI) 233 OS << " BB#" << (*SI)->getNumber(); 234 OS << '\n'; 235 } 236} 237 238void MachineBasicBlock::removeLiveIn(unsigned Reg) { 239 std::vector<unsigned>::iterator I = 240 std::find(LiveIns.begin(), LiveIns.end(), Reg); 241 assert(I != LiveIns.end() && "Not a live in!"); 242 LiveIns.erase(I); 243} 244 245bool MachineBasicBlock::isLiveIn(unsigned Reg) const { 246 livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 247 return I != livein_end(); 248} 249 250void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) { 251 getParent()->splice(NewAfter, this); 252} 253 254void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) { 255 MachineFunction::iterator BBI = NewBefore; 256 getParent()->splice(++BBI, this); 257} 258 259void MachineBasicBlock::updateTerminator() { 260 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 261 // A block with no successors has no concerns with fall-through edges. 262 if (this->succ_empty()) return; 263 264 MachineBasicBlock *TBB = 0, *FBB = 0; 265 SmallVector<MachineOperand, 4> Cond; 266 DebugLoc dl; // FIXME: this is nowhere 267 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond); 268 (void) B; 269 assert(!B && "UpdateTerminators requires analyzable predecessors!"); 270 if (Cond.empty()) { 271 if (TBB) { 272 // The block has an unconditional branch. If its successor is now 273 // its layout successor, delete the branch. 274 if (isLayoutSuccessor(TBB)) 275 TII->RemoveBranch(*this); 276 } else { 277 // The block has an unconditional fallthrough. If its successor is not 278 // its layout successor, insert a branch. 279 TBB = *succ_begin(); 280 if (!isLayoutSuccessor(TBB)) 281 TII->InsertBranch(*this, TBB, 0, Cond, dl); 282 } 283 } else { 284 if (FBB) { 285 // The block has a non-fallthrough conditional branch. If one of its 286 // successors is its layout successor, rewrite it to a fallthrough 287 // conditional branch. 288 if (isLayoutSuccessor(TBB)) { 289 if (TII->ReverseBranchCondition(Cond)) 290 return; 291 TII->RemoveBranch(*this); 292 TII->InsertBranch(*this, FBB, 0, Cond, dl); 293 } else if (isLayoutSuccessor(FBB)) { 294 TII->RemoveBranch(*this); 295 TII->InsertBranch(*this, TBB, 0, Cond, dl); 296 } 297 } else { 298 // The block has a fallthrough conditional branch. 299 MachineBasicBlock *MBBA = *succ_begin(); 300 MachineBasicBlock *MBBB = *llvm::next(succ_begin()); 301 if (MBBA == TBB) std::swap(MBBB, MBBA); 302 if (isLayoutSuccessor(TBB)) { 303 if (TII->ReverseBranchCondition(Cond)) { 304 // We can't reverse the condition, add an unconditional branch. 305 Cond.clear(); 306 TII->InsertBranch(*this, MBBA, 0, Cond, dl); 307 return; 308 } 309 TII->RemoveBranch(*this); 310 TII->InsertBranch(*this, MBBA, 0, Cond, dl); 311 } else if (!isLayoutSuccessor(MBBA)) { 312 TII->RemoveBranch(*this); 313 TII->InsertBranch(*this, TBB, MBBA, Cond, dl); 314 } 315 } 316 } 317} 318 319void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) { 320 Successors.push_back(succ); 321 succ->addPredecessor(this); 322} 323 324void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) { 325 succ->removePredecessor(this); 326 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ); 327 assert(I != Successors.end() && "Not a current successor!"); 328 Successors.erase(I); 329} 330 331MachineBasicBlock::succ_iterator 332MachineBasicBlock::removeSuccessor(succ_iterator I) { 333 assert(I != Successors.end() && "Not a current successor!"); 334 (*I)->removePredecessor(this); 335 return Successors.erase(I); 336} 337 338void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) { 339 Predecessors.push_back(pred); 340} 341 342void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) { 343 std::vector<MachineBasicBlock *>::iterator I = 344 std::find(Predecessors.begin(), Predecessors.end(), pred); 345 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!"); 346 Predecessors.erase(I); 347} 348 349void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) { 350 if (this == fromMBB) 351 return; 352 353 while (!fromMBB->succ_empty()) { 354 MachineBasicBlock *Succ = *fromMBB->succ_begin(); 355 addSuccessor(Succ); 356 fromMBB->removeSuccessor(Succ); 357 } 358} 359 360void 361MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) { 362 if (this == fromMBB) 363 return; 364 365 while (!fromMBB->succ_empty()) { 366 MachineBasicBlock *Succ = *fromMBB->succ_begin(); 367 addSuccessor(Succ); 368 fromMBB->removeSuccessor(Succ); 369 370 // Fix up any PHI nodes in the successor. 371 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end(); 372 MI != ME && MI->isPHI(); ++MI) 373 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) { 374 MachineOperand &MO = MI->getOperand(i); 375 if (MO.getMBB() == fromMBB) 376 MO.setMBB(this); 377 } 378 } 379} 380 381bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const { 382 std::vector<MachineBasicBlock *>::const_iterator I = 383 std::find(Successors.begin(), Successors.end(), MBB); 384 return I != Successors.end(); 385} 386 387bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const { 388 MachineFunction::const_iterator I(this); 389 return llvm::next(I) == MachineFunction::const_iterator(MBB); 390} 391 392bool MachineBasicBlock::canFallThrough() { 393 MachineFunction::iterator Fallthrough = this; 394 ++Fallthrough; 395 // If FallthroughBlock is off the end of the function, it can't fall through. 396 if (Fallthrough == getParent()->end()) 397 return false; 398 399 // If FallthroughBlock isn't a successor, no fallthrough is possible. 400 if (!isSuccessor(Fallthrough)) 401 return false; 402 403 // Analyze the branches, if any, at the end of the block. 404 MachineBasicBlock *TBB = 0, *FBB = 0; 405 SmallVector<MachineOperand, 4> Cond; 406 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 407 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) { 408 // If we couldn't analyze the branch, examine the last instruction. 409 // If the block doesn't end in a known control barrier, assume fallthrough 410 // is possible. The isPredicable check is needed because this code can be 411 // called during IfConversion, where an instruction which is normally a 412 // Barrier is predicated and thus no longer an actual control barrier. This 413 // is over-conservative though, because if an instruction isn't actually 414 // predicated we could still treat it like a barrier. 415 return empty() || !back().getDesc().isBarrier() || 416 back().getDesc().isPredicable(); 417 } 418 419 // If there is no branch, control always falls through. 420 if (TBB == 0) return true; 421 422 // If there is some explicit branch to the fallthrough block, it can obviously 423 // reach, even though the branch should get folded to fall through implicitly. 424 if (MachineFunction::iterator(TBB) == Fallthrough || 425 MachineFunction::iterator(FBB) == Fallthrough) 426 return true; 427 428 // If it's an unconditional branch to some block not the fall through, it 429 // doesn't fall through. 430 if (Cond.empty()) return false; 431 432 // Otherwise, if it is conditional and has no explicit false block, it falls 433 // through. 434 return FBB == 0; 435} 436 437MachineBasicBlock * 438MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) { 439 MachineFunction *MF = getParent(); 440 DebugLoc dl; // FIXME: this is nowhere 441 442 // We may need to update this's terminator, but we can't do that if 443 // AnalyzeBranch fails. If this uses a jump table, we won't touch it. 444 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo(); 445 MachineBasicBlock *TBB = 0, *FBB = 0; 446 SmallVector<MachineOperand, 4> Cond; 447 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) 448 return NULL; 449 450 // Avoid bugpoint weirdness: A block may end with a conditional branch but 451 // jumps to the same MBB is either case. We have duplicate CFG edges in that 452 // case that we can't handle. Since this never happens in properly optimized 453 // code, just skip those edges. 454 if (TBB && TBB == FBB) { 455 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#" 456 << getNumber() << '\n'); 457 return NULL; 458 } 459 460 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(); 461 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB); 462 DEBUG(dbgs() << "Splitting critical edge:" 463 " BB#" << getNumber() 464 << " -- BB#" << NMBB->getNumber() 465 << " -- BB#" << Succ->getNumber() << '\n'); 466 467 ReplaceUsesOfBlockWith(Succ, NMBB); 468 updateTerminator(); 469 470 // Insert unconditional "jump Succ" instruction in NMBB if necessary. 471 NMBB->addSuccessor(Succ); 472 if (!NMBB->isLayoutSuccessor(Succ)) { 473 Cond.clear(); 474 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl); 475 } 476 477 // Fix PHI nodes in Succ so they refer to NMBB instead of this 478 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end(); 479 i != e && i->isPHI(); ++i) 480 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2) 481 if (i->getOperand(ni+1).getMBB() == this) 482 i->getOperand(ni+1).setMBB(NMBB); 483 484 if (LiveVariables *LV = 485 P->getAnalysisIfAvailable<LiveVariables>()) 486 LV->addNewBlock(NMBB, this, Succ); 487 488 if (MachineDominatorTree *MDT = 489 P->getAnalysisIfAvailable<MachineDominatorTree>()) { 490 // Update dominator information. 491 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ); 492 493 bool IsNewIDom = true; 494 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end(); 495 PI != E; ++PI) { 496 MachineBasicBlock *PredBB = *PI; 497 if (PredBB == NMBB) 498 continue; 499 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) { 500 IsNewIDom = false; 501 break; 502 } 503 } 504 505 // We know "this" dominates the newly created basic block. 506 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this); 507 508 // If all the other predecessors of "Succ" are dominated by "Succ" itself 509 // then the new block is the new immediate dominator of "Succ". Otherwise, 510 // the new block doesn't dominate anything. 511 if (IsNewIDom) 512 MDT->changeImmediateDominator(SucccDTNode, NewDTNode); 513 } 514 515 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>()) 516 if (MachineLoop *TIL = MLI->getLoopFor(this)) { 517 // If one or the other blocks were not in a loop, the new block is not 518 // either, and thus LI doesn't need to be updated. 519 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) { 520 if (TIL == DestLoop) { 521 // Both in the same loop, the NMBB joins loop. 522 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase()); 523 } else if (TIL->contains(DestLoop)) { 524 // Edge from an outer loop to an inner loop. Add to the outer loop. 525 TIL->addBasicBlockToLoop(NMBB, MLI->getBase()); 526 } else if (DestLoop->contains(TIL)) { 527 // Edge from an inner loop to an outer loop. Add to the outer loop. 528 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase()); 529 } else { 530 // Edge from two loops with no containment relation. Because these 531 // are natural loops, we know that the destination block must be the 532 // header of its loop (adding a branch into a loop elsewhere would 533 // create an irreducible loop). 534 assert(DestLoop->getHeader() == Succ && 535 "Should not create irreducible loops!"); 536 if (MachineLoop *P = DestLoop->getParentLoop()) 537 P->addBasicBlockToLoop(NMBB, MLI->getBase()); 538 } 539 } 540 } 541 542 return NMBB; 543} 544 545/// removeFromParent - This method unlinks 'this' from the containing function, 546/// and returns it, but does not delete it. 547MachineBasicBlock *MachineBasicBlock::removeFromParent() { 548 assert(getParent() && "Not embedded in a function!"); 549 getParent()->remove(this); 550 return this; 551} 552 553 554/// eraseFromParent - This method unlinks 'this' from the containing function, 555/// and deletes it. 556void MachineBasicBlock::eraseFromParent() { 557 assert(getParent() && "Not embedded in a function!"); 558 getParent()->erase(this); 559} 560 561 562/// ReplaceUsesOfBlockWith - Given a machine basic block that branched to 563/// 'Old', change the code and CFG so that it branches to 'New' instead. 564void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old, 565 MachineBasicBlock *New) { 566 assert(Old != New && "Cannot replace self with self!"); 567 568 MachineBasicBlock::iterator I = end(); 569 while (I != begin()) { 570 --I; 571 if (!I->getDesc().isTerminator()) break; 572 573 // Scan the operands of this machine instruction, replacing any uses of Old 574 // with New. 575 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 576 if (I->getOperand(i).isMBB() && 577 I->getOperand(i).getMBB() == Old) 578 I->getOperand(i).setMBB(New); 579 } 580 581 // Update the successor information. 582 removeSuccessor(Old); 583 addSuccessor(New); 584} 585 586/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the 587/// CFG to be inserted. If we have proven that MBB can only branch to DestA and 588/// DestB, remove any other MBB successors from the CFG. DestA and DestB can be 589/// null. 590/// 591/// Besides DestA and DestB, retain other edges leading to LandingPads 592/// (currently there can be only one; we don't check or require that here). 593/// Note it is possible that DestA and/or DestB are LandingPads. 594bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA, 595 MachineBasicBlock *DestB, 596 bool isCond) { 597 // The values of DestA and DestB frequently come from a call to the 598 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial 599 // values from there. 600 // 601 // 1. If both DestA and DestB are null, then the block ends with no branches 602 // (it falls through to its successor). 603 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends 604 // with only an unconditional branch. 605 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends 606 // with a conditional branch that falls through to a successor (DestB). 607 // 4. If DestA and DestB is set and isCond is true, then the block ends with a 608 // conditional branch followed by an unconditional branch. DestA is the 609 // 'true' destination and DestB is the 'false' destination. 610 611 bool Changed = false; 612 613 MachineFunction::iterator FallThru = 614 llvm::next(MachineFunction::iterator(this)); 615 616 if (DestA == 0 && DestB == 0) { 617 // Block falls through to successor. 618 DestA = FallThru; 619 DestB = FallThru; 620 } else if (DestA != 0 && DestB == 0) { 621 if (isCond) 622 // Block ends in conditional jump that falls through to successor. 623 DestB = FallThru; 624 } else { 625 assert(DestA && DestB && isCond && 626 "CFG in a bad state. Cannot correct CFG edges"); 627 } 628 629 // Remove superfluous edges. I.e., those which aren't destinations of this 630 // basic block, duplicate edges, or landing pads. 631 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs; 632 MachineBasicBlock::succ_iterator SI = succ_begin(); 633 while (SI != succ_end()) { 634 const MachineBasicBlock *MBB = *SI; 635 if (!SeenMBBs.insert(MBB) || 636 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) { 637 // This is a superfluous edge, remove it. 638 SI = removeSuccessor(SI); 639 Changed = true; 640 } else { 641 ++SI; 642 } 643 } 644 645 return Changed; 646} 647 648/// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping 649/// any DBG_VALUE instructions. Return UnknownLoc if there is none. 650DebugLoc 651MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) { 652 DebugLoc DL; 653 MachineBasicBlock::iterator E = end(); 654 if (MBBI != E) { 655 // Skip debug declarations, we don't want a DebugLoc from them. 656 MachineBasicBlock::iterator MBBI2 = MBBI; 657 while (MBBI2 != E && MBBI2->isDebugValue()) 658 MBBI2++; 659 if (MBBI2 != E) 660 DL = MBBI2->getDebugLoc(); 661 } 662 return DL; 663} 664 665void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB, 666 bool t) { 667 OS << "BB#" << MBB->getNumber(); 668} 669 670