MachineBasicBlock.cpp revision 04223909b74fd0634ba26d434fa7fdf2f3c7444f
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() || I->isDebugValue())) 160 ; /*noop */ 161 while (I != end() && !I->getDesc().isTerminator()) 162 ++I; 163 return I; 164} 165 166MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() { 167 iterator B = begin(), I = end(); 168 while (I != B) { 169 --I; 170 if (I->isDebugValue()) 171 continue; 172 return I; 173 } 174 // The block is all debug values. 175 return end(); 176} 177 178void MachineBasicBlock::dump() const { 179 print(dbgs()); 180} 181 182StringRef MachineBasicBlock::getName() const { 183 if (const BasicBlock *LBB = getBasicBlock()) 184 return LBB->getName(); 185 else 186 return "(null)"; 187} 188 189void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const { 190 const MachineFunction *MF = getParent(); 191 if (!MF) { 192 OS << "Can't print out MachineBasicBlock because parent MachineFunction" 193 << " is null\n"; 194 return; 195 } 196 197 if (Alignment) { OS << "Alignment " << Alignment << "\n"; } 198 199 if (Indexes) 200 OS << Indexes->getMBBStartIdx(this) << '\t'; 201 202 OS << "BB#" << getNumber() << ": "; 203 204 const char *Comma = ""; 205 if (const BasicBlock *LBB = getBasicBlock()) { 206 OS << Comma << "derived from LLVM BB "; 207 WriteAsOperand(OS, LBB, /*PrintType=*/false); 208 Comma = ", "; 209 } 210 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; } 211 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; } 212 OS << '\n'; 213 214 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo(); 215 if (!livein_empty()) { 216 if (Indexes) OS << '\t'; 217 OS << " Live Ins:"; 218 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I) 219 OS << ' ' << PrintReg(*I, TRI); 220 OS << '\n'; 221 } 222 // Print the preds of this block according to the CFG. 223 if (!pred_empty()) { 224 if (Indexes) OS << '\t'; 225 OS << " Predecessors according to CFG:"; 226 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI) 227 OS << " BB#" << (*PI)->getNumber(); 228 OS << '\n'; 229 } 230 231 for (const_iterator I = begin(); I != end(); ++I) { 232 if (Indexes) { 233 if (Indexes->hasIndex(I)) 234 OS << Indexes->getInstructionIndex(I); 235 OS << '\t'; 236 } 237 OS << '\t'; 238 I->print(OS, &getParent()->getTarget()); 239 } 240 241 // Print the successors of this block according to the CFG. 242 if (!succ_empty()) { 243 if (Indexes) OS << '\t'; 244 OS << " Successors according to CFG:"; 245 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI) 246 OS << " BB#" << (*SI)->getNumber(); 247 OS << '\n'; 248 } 249} 250 251void MachineBasicBlock::removeLiveIn(unsigned Reg) { 252 std::vector<unsigned>::iterator I = 253 std::find(LiveIns.begin(), LiveIns.end(), Reg); 254 assert(I != LiveIns.end() && "Not a live in!"); 255 LiveIns.erase(I); 256} 257 258bool MachineBasicBlock::isLiveIn(unsigned Reg) const { 259 livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 260 return I != livein_end(); 261} 262 263void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) { 264 getParent()->splice(NewAfter, this); 265} 266 267void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) { 268 MachineFunction::iterator BBI = NewBefore; 269 getParent()->splice(++BBI, this); 270} 271 272void MachineBasicBlock::updateTerminator() { 273 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 274 // A block with no successors has no concerns with fall-through edges. 275 if (this->succ_empty()) return; 276 277 MachineBasicBlock *TBB = 0, *FBB = 0; 278 SmallVector<MachineOperand, 4> Cond; 279 DebugLoc dl; // FIXME: this is nowhere 280 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond); 281 (void) B; 282 assert(!B && "UpdateTerminators requires analyzable predecessors!"); 283 if (Cond.empty()) { 284 if (TBB) { 285 // The block has an unconditional branch. If its successor is now 286 // its layout successor, delete the branch. 287 if (isLayoutSuccessor(TBB)) 288 TII->RemoveBranch(*this); 289 } else { 290 // The block has an unconditional fallthrough. If its successor is not 291 // its layout successor, insert a branch. 292 TBB = *succ_begin(); 293 if (!isLayoutSuccessor(TBB)) 294 TII->InsertBranch(*this, TBB, 0, Cond, dl); 295 } 296 } else { 297 if (FBB) { 298 // The block has a non-fallthrough conditional branch. If one of its 299 // successors is its layout successor, rewrite it to a fallthrough 300 // conditional branch. 301 if (isLayoutSuccessor(TBB)) { 302 if (TII->ReverseBranchCondition(Cond)) 303 return; 304 TII->RemoveBranch(*this); 305 TII->InsertBranch(*this, FBB, 0, Cond, dl); 306 } else if (isLayoutSuccessor(FBB)) { 307 TII->RemoveBranch(*this); 308 TII->InsertBranch(*this, TBB, 0, Cond, dl); 309 } 310 } else { 311 // The block has a fallthrough conditional branch. 312 MachineBasicBlock *MBBA = *succ_begin(); 313 MachineBasicBlock *MBBB = *llvm::next(succ_begin()); 314 if (MBBA == TBB) std::swap(MBBB, MBBA); 315 if (isLayoutSuccessor(TBB)) { 316 if (TII->ReverseBranchCondition(Cond)) { 317 // We can't reverse the condition, add an unconditional branch. 318 Cond.clear(); 319 TII->InsertBranch(*this, MBBA, 0, Cond, dl); 320 return; 321 } 322 TII->RemoveBranch(*this); 323 TII->InsertBranch(*this, MBBA, 0, Cond, dl); 324 } else if (!isLayoutSuccessor(MBBA)) { 325 TII->RemoveBranch(*this); 326 TII->InsertBranch(*this, TBB, MBBA, Cond, dl); 327 } 328 } 329 } 330} 331 332void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) { 333 Successors.push_back(succ); 334 succ->addPredecessor(this); 335} 336 337void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) { 338 succ->removePredecessor(this); 339 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ); 340 assert(I != Successors.end() && "Not a current successor!"); 341 Successors.erase(I); 342} 343 344MachineBasicBlock::succ_iterator 345MachineBasicBlock::removeSuccessor(succ_iterator I) { 346 assert(I != Successors.end() && "Not a current successor!"); 347 (*I)->removePredecessor(this); 348 return Successors.erase(I); 349} 350 351void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) { 352 Predecessors.push_back(pred); 353} 354 355void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) { 356 std::vector<MachineBasicBlock *>::iterator I = 357 std::find(Predecessors.begin(), Predecessors.end(), pred); 358 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!"); 359 Predecessors.erase(I); 360} 361 362void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) { 363 if (this == fromMBB) 364 return; 365 366 while (!fromMBB->succ_empty()) { 367 MachineBasicBlock *Succ = *fromMBB->succ_begin(); 368 addSuccessor(Succ); 369 fromMBB->removeSuccessor(Succ); 370 } 371} 372 373void 374MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) { 375 if (this == fromMBB) 376 return; 377 378 while (!fromMBB->succ_empty()) { 379 MachineBasicBlock *Succ = *fromMBB->succ_begin(); 380 addSuccessor(Succ); 381 fromMBB->removeSuccessor(Succ); 382 383 // Fix up any PHI nodes in the successor. 384 for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end(); 385 MI != ME && MI->isPHI(); ++MI) 386 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) { 387 MachineOperand &MO = MI->getOperand(i); 388 if (MO.getMBB() == fromMBB) 389 MO.setMBB(this); 390 } 391 } 392} 393 394bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const { 395 std::vector<MachineBasicBlock *>::const_iterator I = 396 std::find(Successors.begin(), Successors.end(), MBB); 397 return I != Successors.end(); 398} 399 400bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const { 401 MachineFunction::const_iterator I(this); 402 return llvm::next(I) == MachineFunction::const_iterator(MBB); 403} 404 405bool MachineBasicBlock::canFallThrough() { 406 MachineFunction::iterator Fallthrough = this; 407 ++Fallthrough; 408 // If FallthroughBlock is off the end of the function, it can't fall through. 409 if (Fallthrough == getParent()->end()) 410 return false; 411 412 // If FallthroughBlock isn't a successor, no fallthrough is possible. 413 if (!isSuccessor(Fallthrough)) 414 return false; 415 416 // Analyze the branches, if any, at the end of the block. 417 MachineBasicBlock *TBB = 0, *FBB = 0; 418 SmallVector<MachineOperand, 4> Cond; 419 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 420 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) { 421 // If we couldn't analyze the branch, examine the last instruction. 422 // If the block doesn't end in a known control barrier, assume fallthrough 423 // is possible. The isPredicable check is needed because this code can be 424 // called during IfConversion, where an instruction which is normally a 425 // Barrier is predicated and thus no longer an actual control barrier. This 426 // is over-conservative though, because if an instruction isn't actually 427 // predicated we could still treat it like a barrier. 428 return empty() || !back().getDesc().isBarrier() || 429 back().getDesc().isPredicable(); 430 } 431 432 // If there is no branch, control always falls through. 433 if (TBB == 0) return true; 434 435 // If there is some explicit branch to the fallthrough block, it can obviously 436 // reach, even though the branch should get folded to fall through implicitly. 437 if (MachineFunction::iterator(TBB) == Fallthrough || 438 MachineFunction::iterator(FBB) == Fallthrough) 439 return true; 440 441 // If it's an unconditional branch to some block not the fall through, it 442 // doesn't fall through. 443 if (Cond.empty()) return false; 444 445 // Otherwise, if it is conditional and has no explicit false block, it falls 446 // through. 447 return FBB == 0; 448} 449 450MachineBasicBlock * 451MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) { 452 MachineFunction *MF = getParent(); 453 DebugLoc dl; // FIXME: this is nowhere 454 455 // We may need to update this's terminator, but we can't do that if 456 // AnalyzeBranch fails. If this uses a jump table, we won't touch it. 457 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo(); 458 MachineBasicBlock *TBB = 0, *FBB = 0; 459 SmallVector<MachineOperand, 4> Cond; 460 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) 461 return NULL; 462 463 // Avoid bugpoint weirdness: A block may end with a conditional branch but 464 // jumps to the same MBB is either case. We have duplicate CFG edges in that 465 // case that we can't handle. Since this never happens in properly optimized 466 // code, just skip those edges. 467 if (TBB && TBB == FBB) { 468 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#" 469 << getNumber() << '\n'); 470 return NULL; 471 } 472 473 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(); 474 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB); 475 DEBUG(dbgs() << "Splitting critical edge:" 476 " BB#" << getNumber() 477 << " -- BB#" << NMBB->getNumber() 478 << " -- BB#" << Succ->getNumber() << '\n'); 479 480 ReplaceUsesOfBlockWith(Succ, NMBB); 481 updateTerminator(); 482 483 // Insert unconditional "jump Succ" instruction in NMBB if necessary. 484 NMBB->addSuccessor(Succ); 485 if (!NMBB->isLayoutSuccessor(Succ)) { 486 Cond.clear(); 487 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl); 488 } 489 490 // Fix PHI nodes in Succ so they refer to NMBB instead of this 491 for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end(); 492 i != e && i->isPHI(); ++i) 493 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2) 494 if (i->getOperand(ni+1).getMBB() == this) 495 i->getOperand(ni+1).setMBB(NMBB); 496 497 if (LiveVariables *LV = 498 P->getAnalysisIfAvailable<LiveVariables>()) 499 LV->addNewBlock(NMBB, this, Succ); 500 501 if (MachineDominatorTree *MDT = 502 P->getAnalysisIfAvailable<MachineDominatorTree>()) { 503 // Update dominator information. 504 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ); 505 506 bool IsNewIDom = true; 507 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end(); 508 PI != E; ++PI) { 509 MachineBasicBlock *PredBB = *PI; 510 if (PredBB == NMBB) 511 continue; 512 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) { 513 IsNewIDom = false; 514 break; 515 } 516 } 517 518 // We know "this" dominates the newly created basic block. 519 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this); 520 521 // If all the other predecessors of "Succ" are dominated by "Succ" itself 522 // then the new block is the new immediate dominator of "Succ". Otherwise, 523 // the new block doesn't dominate anything. 524 if (IsNewIDom) 525 MDT->changeImmediateDominator(SucccDTNode, NewDTNode); 526 } 527 528 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>()) 529 if (MachineLoop *TIL = MLI->getLoopFor(this)) { 530 // If one or the other blocks were not in a loop, the new block is not 531 // either, and thus LI doesn't need to be updated. 532 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) { 533 if (TIL == DestLoop) { 534 // Both in the same loop, the NMBB joins loop. 535 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase()); 536 } else if (TIL->contains(DestLoop)) { 537 // Edge from an outer loop to an inner loop. Add to the outer loop. 538 TIL->addBasicBlockToLoop(NMBB, MLI->getBase()); 539 } else if (DestLoop->contains(TIL)) { 540 // Edge from an inner loop to an outer loop. Add to the outer loop. 541 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase()); 542 } else { 543 // Edge from two loops with no containment relation. Because these 544 // are natural loops, we know that the destination block must be the 545 // header of its loop (adding a branch into a loop elsewhere would 546 // create an irreducible loop). 547 assert(DestLoop->getHeader() == Succ && 548 "Should not create irreducible loops!"); 549 if (MachineLoop *P = DestLoop->getParentLoop()) 550 P->addBasicBlockToLoop(NMBB, MLI->getBase()); 551 } 552 } 553 } 554 555 return NMBB; 556} 557 558/// removeFromParent - This method unlinks 'this' from the containing function, 559/// and returns it, but does not delete it. 560MachineBasicBlock *MachineBasicBlock::removeFromParent() { 561 assert(getParent() && "Not embedded in a function!"); 562 getParent()->remove(this); 563 return this; 564} 565 566 567/// eraseFromParent - This method unlinks 'this' from the containing function, 568/// and deletes it. 569void MachineBasicBlock::eraseFromParent() { 570 assert(getParent() && "Not embedded in a function!"); 571 getParent()->erase(this); 572} 573 574 575/// ReplaceUsesOfBlockWith - Given a machine basic block that branched to 576/// 'Old', change the code and CFG so that it branches to 'New' instead. 577void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old, 578 MachineBasicBlock *New) { 579 assert(Old != New && "Cannot replace self with self!"); 580 581 MachineBasicBlock::iterator I = end(); 582 while (I != begin()) { 583 --I; 584 if (!I->getDesc().isTerminator()) break; 585 586 // Scan the operands of this machine instruction, replacing any uses of Old 587 // with New. 588 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 589 if (I->getOperand(i).isMBB() && 590 I->getOperand(i).getMBB() == Old) 591 I->getOperand(i).setMBB(New); 592 } 593 594 // Update the successor information. 595 removeSuccessor(Old); 596 addSuccessor(New); 597} 598 599/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the 600/// CFG to be inserted. If we have proven that MBB can only branch to DestA and 601/// DestB, remove any other MBB successors from the CFG. DestA and DestB can be 602/// null. 603/// 604/// Besides DestA and DestB, retain other edges leading to LandingPads 605/// (currently there can be only one; we don't check or require that here). 606/// Note it is possible that DestA and/or DestB are LandingPads. 607bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA, 608 MachineBasicBlock *DestB, 609 bool isCond) { 610 // The values of DestA and DestB frequently come from a call to the 611 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial 612 // values from there. 613 // 614 // 1. If both DestA and DestB are null, then the block ends with no branches 615 // (it falls through to its successor). 616 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends 617 // with only an unconditional branch. 618 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends 619 // with a conditional branch that falls through to a successor (DestB). 620 // 4. If DestA and DestB is set and isCond is true, then the block ends with a 621 // conditional branch followed by an unconditional branch. DestA is the 622 // 'true' destination and DestB is the 'false' destination. 623 624 bool Changed = false; 625 626 MachineFunction::iterator FallThru = 627 llvm::next(MachineFunction::iterator(this)); 628 629 if (DestA == 0 && DestB == 0) { 630 // Block falls through to successor. 631 DestA = FallThru; 632 DestB = FallThru; 633 } else if (DestA != 0 && DestB == 0) { 634 if (isCond) 635 // Block ends in conditional jump that falls through to successor. 636 DestB = FallThru; 637 } else { 638 assert(DestA && DestB && isCond && 639 "CFG in a bad state. Cannot correct CFG edges"); 640 } 641 642 // Remove superfluous edges. I.e., those which aren't destinations of this 643 // basic block, duplicate edges, or landing pads. 644 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs; 645 MachineBasicBlock::succ_iterator SI = succ_begin(); 646 while (SI != succ_end()) { 647 const MachineBasicBlock *MBB = *SI; 648 if (!SeenMBBs.insert(MBB) || 649 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) { 650 // This is a superfluous edge, remove it. 651 SI = removeSuccessor(SI); 652 Changed = true; 653 } else { 654 ++SI; 655 } 656 } 657 658 return Changed; 659} 660 661/// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping 662/// any DBG_VALUE instructions. Return UnknownLoc if there is none. 663DebugLoc 664MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) { 665 DebugLoc DL; 666 MachineBasicBlock::iterator E = end(); 667 if (MBBI != E) { 668 // Skip debug declarations, we don't want a DebugLoc from them. 669 MachineBasicBlock::iterator MBBI2 = MBBI; 670 while (MBBI2 != E && MBBI2->isDebugValue()) 671 MBBI2++; 672 if (MBBI2 != E) 673 DL = MBBI2->getDebugLoc(); 674 } 675 return DL; 676} 677 678void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB, 679 bool t) { 680 OS << "BB#" << MBB->getNumber(); 681} 682 683