MachineBasicBlock.cpp revision 64f865ceca4cdd39fcac3d958071be118cb9c1d3
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 B = begin(), I = end(); 159 iterator Term = I; 160 while (I != B) { 161 --I; 162 // Ignore any debug values after the first terminator. 163 if (I->isDebugValue()) 164 continue; 165 // Stop once we see a non-debug non-terminator. 166 if (!I->getDesc().isTerminator()) 167 break; 168 // Earliest terminator so far. 169 Term = I; 170 } 171 // Return the first terminator, or end(). 172 // Everything after Term is terminators and debug values. 173 return Term; 174} 175 176void MachineBasicBlock::dump() const { 177 print(dbgs()); 178} 179 180StringRef MachineBasicBlock::getName() const { 181 if (const BasicBlock *LBB = getBasicBlock()) 182 return LBB->getName(); 183 else 184 return "(null)"; 185} 186 187void 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 OS << ' ' << PrintReg(*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 249void 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 256bool MachineBasicBlock::isLiveIn(unsigned Reg) const { 257 livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 258 return I != livein_end(); 259} 260 261void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) { 262 getParent()->splice(NewAfter, this); 263} 264 265void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) { 266 MachineFunction::iterator BBI = NewBefore; 267 getParent()->splice(++BBI, this); 268} 269 270void 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 330void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) { 331 Successors.push_back(succ); 332 succ->addPredecessor(this); 333} 334 335void 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 342MachineBasicBlock::succ_iterator 343MachineBasicBlock::removeSuccessor(succ_iterator I) { 344 assert(I != Successors.end() && "Not a current successor!"); 345 (*I)->removePredecessor(this); 346 return Successors.erase(I); 347} 348 349void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) { 350 Predecessors.push_back(pred); 351} 352 353void 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 360void 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 371void 372MachineBasicBlock::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 392bool 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 398bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const { 399 MachineFunction::const_iterator I(this); 400 return llvm::next(I) == MachineFunction::const_iterator(MBB); 401} 402 403bool 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 448MachineBasicBlock * 449MachineBasicBlock::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. 558MachineBasicBlock *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. 567void 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. 575void 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. 605bool 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. 661DebugLoc 662MachineBasicBlock::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 676void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB, 677 bool t) { 678 OS << "BB#" << MBB->getNumber(); 679} 680 681