1 //===-- llvm/CodeGen/MachineBasicBlock.cpp ----------------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // Collect the sequence of machine instructions for a basic block. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/CodeGen/MachineBasicBlock.h" 15 #include "llvm/BasicBlock.h" 16 #include "llvm/CodeGen/LiveVariables.h" 17 #include "llvm/CodeGen/MachineDominators.h" 18 #include "llvm/CodeGen/MachineFunction.h" 19 #include "llvm/CodeGen/MachineLoopInfo.h" 20 #include "llvm/CodeGen/SlotIndexes.h" 21 #include "llvm/MC/MCAsmInfo.h" 22 #include "llvm/MC/MCContext.h" 23 #include "llvm/Target/TargetRegisterInfo.h" 24 #include "llvm/Target/TargetData.h" 25 #include "llvm/Target/TargetInstrInfo.h" 26 #include "llvm/Target/TargetMachine.h" 27 #include "llvm/Assembly/Writer.h" 28 #include "llvm/ADT/SmallString.h" 29 #include "llvm/ADT/SmallPtrSet.h" 30 #include "llvm/Support/Debug.h" 31 #include "llvm/Support/LeakDetector.h" 32 #include "llvm/Support/raw_ostream.h" 33 #include <algorithm> 34 using namespace llvm; 35 36 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb) 37 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false), 38 AddressTaken(false) { 39 Insts.Parent = this; 40 } 41 42 MachineBasicBlock::~MachineBasicBlock() { 43 LeakDetector::removeGarbageObject(this); 44 } 45 46 /// getSymbol - Return the MCSymbol for this basic block. 47 /// 48 MCSymbol *MachineBasicBlock::getSymbol() const { 49 const MachineFunction *MF = getParent(); 50 MCContext &Ctx = MF->getContext(); 51 const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix(); 52 return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" + 53 Twine(MF->getFunctionNumber()) + "_" + 54 Twine(getNumber())); 55 } 56 57 58 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) { 59 MBB.print(OS); 60 return OS; 61 } 62 63 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the 64 /// parent pointer of the MBB, the MBB numbering, and any instructions in the 65 /// MBB to be on the right operand list for registers. 66 /// 67 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it 68 /// gets the next available unique MBB number. If it is removed from a 69 /// MachineFunction, it goes back to being #-1. 70 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) { 71 MachineFunction &MF = *N->getParent(); 72 N->Number = MF.addToMBBNumbering(N); 73 74 // Make sure the instructions have their operands in the reginfo lists. 75 MachineRegisterInfo &RegInfo = MF.getRegInfo(); 76 for (MachineBasicBlock::instr_iterator 77 I = N->instr_begin(), E = N->instr_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 ilist_iterator<MachineInstr> first, 125 ilist_iterator<MachineInstr> 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 instr_iterator I = instr_begin(), E = instr_end(); 145 while (I != E && I->isPHI()) 146 ++I; 147 assert(!I->isInsideBundle() && "First non-phi MI cannot be inside a bundle!"); 148 return I; 149 } 150 151 MachineBasicBlock::iterator 152 MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) { 153 iterator E = end(); 154 while (I != E && (I->isPHI() || I->isLabel() || I->isDebugValue())) 155 ++I; 156 // FIXME: This needs to change if we wish to bundle labels / dbg_values 157 // inside the bundle. 158 assert(!I->isInsideBundle() && 159 "First non-phi / non-label instruction is inside a bundle!"); 160 return I; 161 } 162 163 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() { 164 iterator B = begin(), E = end(), I = E; 165 while (I != B && ((--I)->isTerminator() || I->isDebugValue())) 166 ; /*noop */ 167 while (I != E && !I->isTerminator()) 168 ++I; 169 return I; 170 } 171 172 MachineBasicBlock::const_iterator 173 MachineBasicBlock::getFirstTerminator() const { 174 const_iterator B = begin(), E = end(), I = E; 175 while (I != B && ((--I)->isTerminator() || I->isDebugValue())) 176 ; /*noop */ 177 while (I != E && !I->isTerminator()) 178 ++I; 179 return I; 180 } 181 182 MachineBasicBlock::instr_iterator MachineBasicBlock::getFirstInstrTerminator() { 183 instr_iterator B = instr_begin(), E = instr_end(), I = E; 184 while (I != B && ((--I)->isTerminator() || I->isDebugValue())) 185 ; /*noop */ 186 while (I != E && !I->isTerminator()) 187 ++I; 188 return I; 189 } 190 191 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() { 192 // Skip over end-of-block dbg_value instructions. 193 instr_iterator B = instr_begin(), I = instr_end(); 194 while (I != B) { 195 --I; 196 // Return instruction that starts a bundle. 197 if (I->isDebugValue() || I->isInsideBundle()) 198 continue; 199 return I; 200 } 201 // The block is all debug values. 202 return end(); 203 } 204 205 MachineBasicBlock::const_iterator 206 MachineBasicBlock::getLastNonDebugInstr() const { 207 // Skip over end-of-block dbg_value instructions. 208 const_instr_iterator B = instr_begin(), I = instr_end(); 209 while (I != B) { 210 --I; 211 // Return instruction that starts a bundle. 212 if (I->isDebugValue() || I->isInsideBundle()) 213 continue; 214 return I; 215 } 216 // The block is all debug values. 217 return end(); 218 } 219 220 const MachineBasicBlock *MachineBasicBlock::getLandingPadSuccessor() const { 221 // A block with a landing pad successor only has one other successor. 222 if (succ_size() > 2) 223 return 0; 224 for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I) 225 if ((*I)->isLandingPad()) 226 return *I; 227 return 0; 228 } 229 230 void MachineBasicBlock::dump() const { 231 print(dbgs()); 232 } 233 234 StringRef MachineBasicBlock::getName() const { 235 if (const BasicBlock *LBB = getBasicBlock()) 236 return LBB->getName(); 237 else 238 return "(null)"; 239 } 240 241 /// Return a hopefully unique identifier for this block. 242 std::string MachineBasicBlock::getFullName() const { 243 std::string Name; 244 if (getParent()) 245 Name = (getParent()->getFunction()->getName() + ":").str(); 246 if (getBasicBlock()) 247 Name += getBasicBlock()->getName(); 248 else 249 Name += (Twine("BB") + Twine(getNumber())).str(); 250 return Name; 251 } 252 253 void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const { 254 const MachineFunction *MF = getParent(); 255 if (!MF) { 256 OS << "Can't print out MachineBasicBlock because parent MachineFunction" 257 << " is null\n"; 258 return; 259 } 260 261 if (Indexes) 262 OS << Indexes->getMBBStartIdx(this) << '\t'; 263 264 OS << "BB#" << getNumber() << ": "; 265 266 const char *Comma = ""; 267 if (const BasicBlock *LBB = getBasicBlock()) { 268 OS << Comma << "derived from LLVM BB "; 269 WriteAsOperand(OS, LBB, /*PrintType=*/false); 270 Comma = ", "; 271 } 272 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; } 273 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; } 274 if (Alignment) { 275 OS << Comma << "Align " << Alignment << " (" << (1u << Alignment) 276 << " bytes)"; 277 Comma = ", "; 278 } 279 280 OS << '\n'; 281 282 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo(); 283 if (!livein_empty()) { 284 if (Indexes) OS << '\t'; 285 OS << " Live Ins:"; 286 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I) 287 OS << ' ' << PrintReg(*I, TRI); 288 OS << '\n'; 289 } 290 // Print the preds of this block according to the CFG. 291 if (!pred_empty()) { 292 if (Indexes) OS << '\t'; 293 OS << " Predecessors according to CFG:"; 294 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI) 295 OS << " BB#" << (*PI)->getNumber(); 296 OS << '\n'; 297 } 298 299 for (const_instr_iterator I = instr_begin(); I != instr_end(); ++I) { 300 if (Indexes) { 301 if (Indexes->hasIndex(I)) 302 OS << Indexes->getInstructionIndex(I); 303 OS << '\t'; 304 } 305 OS << '\t'; 306 if (I->isInsideBundle()) 307 OS << " * "; 308 I->print(OS, &getParent()->getTarget()); 309 } 310 311 // Print the successors of this block according to the CFG. 312 if (!succ_empty()) { 313 if (Indexes) OS << '\t'; 314 OS << " Successors according to CFG:"; 315 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI) 316 OS << " BB#" << (*SI)->getNumber(); 317 OS << '\n'; 318 } 319 } 320 321 void MachineBasicBlock::removeLiveIn(unsigned Reg) { 322 std::vector<unsigned>::iterator I = 323 std::find(LiveIns.begin(), LiveIns.end(), Reg); 324 if (I != LiveIns.end()) 325 LiveIns.erase(I); 326 } 327 328 bool MachineBasicBlock::isLiveIn(unsigned Reg) const { 329 livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 330 return I != livein_end(); 331 } 332 333 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) { 334 getParent()->splice(NewAfter, this); 335 } 336 337 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) { 338 MachineFunction::iterator BBI = NewBefore; 339 getParent()->splice(++BBI, this); 340 } 341 342 void MachineBasicBlock::updateTerminator() { 343 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 344 // A block with no successors has no concerns with fall-through edges. 345 if (this->succ_empty()) return; 346 347 MachineBasicBlock *TBB = 0, *FBB = 0; 348 SmallVector<MachineOperand, 4> Cond; 349 DebugLoc dl; // FIXME: this is nowhere 350 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond); 351 (void) B; 352 assert(!B && "UpdateTerminators requires analyzable predecessors!"); 353 if (Cond.empty()) { 354 if (TBB) { 355 // The block has an unconditional branch. If its successor is now 356 // its layout successor, delete the branch. 357 if (isLayoutSuccessor(TBB)) 358 TII->RemoveBranch(*this); 359 } else { 360 // The block has an unconditional fallthrough. If its successor is not 361 // its layout successor, insert a branch. First we have to locate the 362 // only non-landing-pad successor, as that is the fallthrough block. 363 for (succ_iterator SI = succ_begin(), SE = succ_end(); SI != SE; ++SI) { 364 if ((*SI)->isLandingPad()) 365 continue; 366 assert(!TBB && "Found more than one non-landing-pad successor!"); 367 TBB = *SI; 368 } 369 370 // If there is no non-landing-pad successor, the block has no 371 // fall-through edges to be concerned with. 372 if (!TBB) 373 return; 374 375 // Finally update the unconditional successor to be reached via a branch 376 // if it would not be reached by fallthrough. 377 if (!isLayoutSuccessor(TBB)) 378 TII->InsertBranch(*this, TBB, 0, Cond, dl); 379 } 380 } else { 381 if (FBB) { 382 // The block has a non-fallthrough conditional branch. If one of its 383 // successors is its layout successor, rewrite it to a fallthrough 384 // conditional branch. 385 if (isLayoutSuccessor(TBB)) { 386 if (TII->ReverseBranchCondition(Cond)) 387 return; 388 TII->RemoveBranch(*this); 389 TII->InsertBranch(*this, FBB, 0, Cond, dl); 390 } else if (isLayoutSuccessor(FBB)) { 391 TII->RemoveBranch(*this); 392 TII->InsertBranch(*this, TBB, 0, Cond, dl); 393 } 394 } else { 395 // Walk through the successors and find the successor which is not 396 // a landing pad and is not the conditional branch destination (in TBB) 397 // as the fallthrough successor. 398 MachineBasicBlock *FallthroughBB = 0; 399 for (succ_iterator SI = succ_begin(), SE = succ_end(); SI != SE; ++SI) { 400 if ((*SI)->isLandingPad() || *SI == TBB) 401 continue; 402 assert(!FallthroughBB && "Found more than one fallthrough successor."); 403 FallthroughBB = *SI; 404 } 405 if (!FallthroughBB && canFallThrough()) { 406 // We fallthrough to the same basic block as the conditional jump 407 // targets. Remove the conditional jump, leaving unconditional 408 // fallthrough. 409 // FIXME: This does not seem like a reasonable pattern to support, but it 410 // has been seen in the wild coming out of degenerate ARM test cases. 411 TII->RemoveBranch(*this); 412 413 // Finally update the unconditional successor to be reached via a branch 414 // if it would not be reached by fallthrough. 415 if (!isLayoutSuccessor(TBB)) 416 TII->InsertBranch(*this, TBB, 0, Cond, dl); 417 return; 418 } 419 420 // The block has a fallthrough conditional branch. 421 if (isLayoutSuccessor(TBB)) { 422 if (TII->ReverseBranchCondition(Cond)) { 423 // We can't reverse the condition, add an unconditional branch. 424 Cond.clear(); 425 TII->InsertBranch(*this, FallthroughBB, 0, Cond, dl); 426 return; 427 } 428 TII->RemoveBranch(*this); 429 TII->InsertBranch(*this, FallthroughBB, 0, Cond, dl); 430 } else if (!isLayoutSuccessor(FallthroughBB)) { 431 TII->RemoveBranch(*this); 432 TII->InsertBranch(*this, TBB, FallthroughBB, Cond, dl); 433 } 434 } 435 } 436 } 437 438 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) { 439 440 // If we see non-zero value for the first time it means we actually use Weight 441 // list, so we fill all Weights with 0's. 442 if (weight != 0 && Weights.empty()) 443 Weights.resize(Successors.size()); 444 445 if (weight != 0 || !Weights.empty()) 446 Weights.push_back(weight); 447 448 Successors.push_back(succ); 449 succ->addPredecessor(this); 450 } 451 452 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) { 453 succ->removePredecessor(this); 454 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ); 455 assert(I != Successors.end() && "Not a current successor!"); 456 457 // If Weight list is empty it means we don't use it (disabled optimization). 458 if (!Weights.empty()) { 459 weight_iterator WI = getWeightIterator(I); 460 Weights.erase(WI); 461 } 462 463 Successors.erase(I); 464 } 465 466 MachineBasicBlock::succ_iterator 467 MachineBasicBlock::removeSuccessor(succ_iterator I) { 468 assert(I != Successors.end() && "Not a current successor!"); 469 470 // If Weight list is empty it means we don't use it (disabled optimization). 471 if (!Weights.empty()) { 472 weight_iterator WI = getWeightIterator(I); 473 Weights.erase(WI); 474 } 475 476 (*I)->removePredecessor(this); 477 return Successors.erase(I); 478 } 479 480 void MachineBasicBlock::replaceSuccessor(MachineBasicBlock *Old, 481 MachineBasicBlock *New) { 482 uint32_t weight = 0; 483 succ_iterator SI = std::find(Successors.begin(), Successors.end(), Old); 484 485 // If Weight list is empty it means we don't use it (disabled optimization). 486 if (!Weights.empty()) { 487 weight_iterator WI = getWeightIterator(SI); 488 weight = *WI; 489 } 490 491 // Update the successor information. 492 removeSuccessor(SI); 493 addSuccessor(New, weight); 494 } 495 496 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) { 497 Predecessors.push_back(pred); 498 } 499 500 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) { 501 pred_iterator I = std::find(Predecessors.begin(), Predecessors.end(), pred); 502 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!"); 503 Predecessors.erase(I); 504 } 505 506 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) { 507 if (this == fromMBB) 508 return; 509 510 while (!fromMBB->succ_empty()) { 511 MachineBasicBlock *Succ = *fromMBB->succ_begin(); 512 uint32_t weight = 0; 513 514 515 // If Weight list is empty it means we don't use it (disabled optimization). 516 if (!fromMBB->Weights.empty()) 517 weight = *fromMBB->Weights.begin(); 518 519 addSuccessor(Succ, weight); 520 fromMBB->removeSuccessor(Succ); 521 } 522 } 523 524 void 525 MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) { 526 if (this == fromMBB) 527 return; 528 529 while (!fromMBB->succ_empty()) { 530 MachineBasicBlock *Succ = *fromMBB->succ_begin(); 531 addSuccessor(Succ); 532 fromMBB->removeSuccessor(Succ); 533 534 // Fix up any PHI nodes in the successor. 535 for (MachineBasicBlock::instr_iterator MI = Succ->instr_begin(), 536 ME = Succ->instr_end(); MI != ME && MI->isPHI(); ++MI) 537 for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) { 538 MachineOperand &MO = MI->getOperand(i); 539 if (MO.getMBB() == fromMBB) 540 MO.setMBB(this); 541 } 542 } 543 } 544 545 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const { 546 const_succ_iterator I = std::find(Successors.begin(), Successors.end(), MBB); 547 return I != Successors.end(); 548 } 549 550 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const { 551 MachineFunction::const_iterator I(this); 552 return llvm::next(I) == MachineFunction::const_iterator(MBB); 553 } 554 555 bool MachineBasicBlock::canFallThrough() { 556 MachineFunction::iterator Fallthrough = this; 557 ++Fallthrough; 558 // If FallthroughBlock is off the end of the function, it can't fall through. 559 if (Fallthrough == getParent()->end()) 560 return false; 561 562 // If FallthroughBlock isn't a successor, no fallthrough is possible. 563 if (!isSuccessor(Fallthrough)) 564 return false; 565 566 // Analyze the branches, if any, at the end of the block. 567 MachineBasicBlock *TBB = 0, *FBB = 0; 568 SmallVector<MachineOperand, 4> Cond; 569 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 570 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) { 571 // If we couldn't analyze the branch, examine the last instruction. 572 // If the block doesn't end in a known control barrier, assume fallthrough 573 // is possible. The isPredicated check is needed because this code can be 574 // called during IfConversion, where an instruction which is normally a 575 // Barrier is predicated and thus no longer an actual control barrier. 576 return empty() || !back().isBarrier() || TII->isPredicated(&back()); 577 } 578 579 // If there is no branch, control always falls through. 580 if (TBB == 0) return true; 581 582 // If there is some explicit branch to the fallthrough block, it can obviously 583 // reach, even though the branch should get folded to fall through implicitly. 584 if (MachineFunction::iterator(TBB) == Fallthrough || 585 MachineFunction::iterator(FBB) == Fallthrough) 586 return true; 587 588 // If it's an unconditional branch to some block not the fall through, it 589 // doesn't fall through. 590 if (Cond.empty()) return false; 591 592 // Otherwise, if it is conditional and has no explicit false block, it falls 593 // through. 594 return FBB == 0; 595 } 596 597 MachineBasicBlock * 598 MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) { 599 MachineFunction *MF = getParent(); 600 DebugLoc dl; // FIXME: this is nowhere 601 602 // We may need to update this's terminator, but we can't do that if 603 // AnalyzeBranch fails. If this uses a jump table, we won't touch it. 604 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo(); 605 MachineBasicBlock *TBB = 0, *FBB = 0; 606 SmallVector<MachineOperand, 4> Cond; 607 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) 608 return NULL; 609 610 // Avoid bugpoint weirdness: A block may end with a conditional branch but 611 // jumps to the same MBB is either case. We have duplicate CFG edges in that 612 // case that we can't handle. Since this never happens in properly optimized 613 // code, just skip those edges. 614 if (TBB && TBB == FBB) { 615 DEBUG(dbgs() << "Won't split critical edge after degenerate BB#" 616 << getNumber() << '\n'); 617 return NULL; 618 } 619 620 MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(); 621 MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB); 622 DEBUG(dbgs() << "Splitting critical edge:" 623 " BB#" << getNumber() 624 << " -- BB#" << NMBB->getNumber() 625 << " -- BB#" << Succ->getNumber() << '\n'); 626 627 // On some targets like Mips, branches may kill virtual registers. Make sure 628 // that LiveVariables is properly updated after updateTerminator replaces the 629 // terminators. 630 LiveVariables *LV = P->getAnalysisIfAvailable<LiveVariables>(); 631 632 // Collect a list of virtual registers killed by the terminators. 633 SmallVector<unsigned, 4> KilledRegs; 634 if (LV) 635 for (instr_iterator I = getFirstInstrTerminator(), E = instr_end(); 636 I != E; ++I) { 637 MachineInstr *MI = I; 638 for (MachineInstr::mop_iterator OI = MI->operands_begin(), 639 OE = MI->operands_end(); OI != OE; ++OI) { 640 if (!OI->isReg() || OI->getReg() == 0 || 641 !OI->isUse() || !OI->isKill() || OI->isUndef()) 642 continue; 643 unsigned Reg = OI->getReg(); 644 if (TargetRegisterInfo::isPhysicalRegister(Reg) || 645 LV->getVarInfo(Reg).removeKill(MI)) { 646 KilledRegs.push_back(Reg); 647 DEBUG(dbgs() << "Removing terminator kill: " << *MI); 648 OI->setIsKill(false); 649 } 650 } 651 } 652 653 ReplaceUsesOfBlockWith(Succ, NMBB); 654 updateTerminator(); 655 656 // Insert unconditional "jump Succ" instruction in NMBB if necessary. 657 NMBB->addSuccessor(Succ); 658 if (!NMBB->isLayoutSuccessor(Succ)) { 659 Cond.clear(); 660 MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl); 661 } 662 663 // Fix PHI nodes in Succ so they refer to NMBB instead of this 664 for (MachineBasicBlock::instr_iterator 665 i = Succ->instr_begin(),e = Succ->instr_end(); 666 i != e && i->isPHI(); ++i) 667 for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2) 668 if (i->getOperand(ni+1).getMBB() == this) 669 i->getOperand(ni+1).setMBB(NMBB); 670 671 // Inherit live-ins from the successor 672 for (MachineBasicBlock::livein_iterator I = Succ->livein_begin(), 673 E = Succ->livein_end(); I != E; ++I) 674 NMBB->addLiveIn(*I); 675 676 // Update LiveVariables. 677 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo(); 678 if (LV) { 679 // Restore kills of virtual registers that were killed by the terminators. 680 while (!KilledRegs.empty()) { 681 unsigned Reg = KilledRegs.pop_back_val(); 682 for (instr_iterator I = instr_end(), E = instr_begin(); I != E;) { 683 if (!(--I)->addRegisterKilled(Reg, TRI, /* addIfNotFound= */ false)) 684 continue; 685 if (TargetRegisterInfo::isVirtualRegister(Reg)) 686 LV->getVarInfo(Reg).Kills.push_back(I); 687 DEBUG(dbgs() << "Restored terminator kill: " << *I); 688 break; 689 } 690 } 691 // Update relevant live-through information. 692 LV->addNewBlock(NMBB, this, Succ); 693 } 694 695 if (MachineDominatorTree *MDT = 696 P->getAnalysisIfAvailable<MachineDominatorTree>()) { 697 // Update dominator information. 698 MachineDomTreeNode *SucccDTNode = MDT->getNode(Succ); 699 700 bool IsNewIDom = true; 701 for (const_pred_iterator PI = Succ->pred_begin(), E = Succ->pred_end(); 702 PI != E; ++PI) { 703 MachineBasicBlock *PredBB = *PI; 704 if (PredBB == NMBB) 705 continue; 706 if (!MDT->dominates(SucccDTNode, MDT->getNode(PredBB))) { 707 IsNewIDom = false; 708 break; 709 } 710 } 711 712 // We know "this" dominates the newly created basic block. 713 MachineDomTreeNode *NewDTNode = MDT->addNewBlock(NMBB, this); 714 715 // If all the other predecessors of "Succ" are dominated by "Succ" itself 716 // then the new block is the new immediate dominator of "Succ". Otherwise, 717 // the new block doesn't dominate anything. 718 if (IsNewIDom) 719 MDT->changeImmediateDominator(SucccDTNode, NewDTNode); 720 } 721 722 if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>()) 723 if (MachineLoop *TIL = MLI->getLoopFor(this)) { 724 // If one or the other blocks were not in a loop, the new block is not 725 // either, and thus LI doesn't need to be updated. 726 if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) { 727 if (TIL == DestLoop) { 728 // Both in the same loop, the NMBB joins loop. 729 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase()); 730 } else if (TIL->contains(DestLoop)) { 731 // Edge from an outer loop to an inner loop. Add to the outer loop. 732 TIL->addBasicBlockToLoop(NMBB, MLI->getBase()); 733 } else if (DestLoop->contains(TIL)) { 734 // Edge from an inner loop to an outer loop. Add to the outer loop. 735 DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase()); 736 } else { 737 // Edge from two loops with no containment relation. Because these 738 // are natural loops, we know that the destination block must be the 739 // header of its loop (adding a branch into a loop elsewhere would 740 // create an irreducible loop). 741 assert(DestLoop->getHeader() == Succ && 742 "Should not create irreducible loops!"); 743 if (MachineLoop *P = DestLoop->getParentLoop()) 744 P->addBasicBlockToLoop(NMBB, MLI->getBase()); 745 } 746 } 747 } 748 749 return NMBB; 750 } 751 752 MachineBasicBlock::iterator 753 MachineBasicBlock::erase(MachineBasicBlock::iterator I) { 754 if (I->isBundle()) { 755 MachineBasicBlock::iterator E = llvm::next(I); 756 return Insts.erase(I.getInstrIterator(), E.getInstrIterator()); 757 } 758 759 return Insts.erase(I.getInstrIterator()); 760 } 761 762 MachineInstr *MachineBasicBlock::remove(MachineInstr *I) { 763 if (I->isBundle()) { 764 instr_iterator MII = llvm::next(I); 765 iterator E = end(); 766 while (MII != E && MII->isInsideBundle()) { 767 MachineInstr *MI = &*MII++; 768 Insts.remove(MI); 769 } 770 } 771 772 return Insts.remove(I); 773 } 774 775 void MachineBasicBlock::splice(MachineBasicBlock::iterator where, 776 MachineBasicBlock *Other, 777 MachineBasicBlock::iterator From) { 778 if (From->isBundle()) { 779 MachineBasicBlock::iterator To = llvm::next(From); 780 Insts.splice(where.getInstrIterator(), Other->Insts, 781 From.getInstrIterator(), To.getInstrIterator()); 782 return; 783 } 784 785 Insts.splice(where.getInstrIterator(), Other->Insts, From.getInstrIterator()); 786 } 787 788 /// removeFromParent - This method unlinks 'this' from the containing function, 789 /// and returns it, but does not delete it. 790 MachineBasicBlock *MachineBasicBlock::removeFromParent() { 791 assert(getParent() && "Not embedded in a function!"); 792 getParent()->remove(this); 793 return this; 794 } 795 796 797 /// eraseFromParent - This method unlinks 'this' from the containing function, 798 /// and deletes it. 799 void MachineBasicBlock::eraseFromParent() { 800 assert(getParent() && "Not embedded in a function!"); 801 getParent()->erase(this); 802 } 803 804 805 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to 806 /// 'Old', change the code and CFG so that it branches to 'New' instead. 807 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old, 808 MachineBasicBlock *New) { 809 assert(Old != New && "Cannot replace self with self!"); 810 811 MachineBasicBlock::instr_iterator I = instr_end(); 812 while (I != instr_begin()) { 813 --I; 814 if (!I->isTerminator()) break; 815 816 // Scan the operands of this machine instruction, replacing any uses of Old 817 // with New. 818 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 819 if (I->getOperand(i).isMBB() && 820 I->getOperand(i).getMBB() == Old) 821 I->getOperand(i).setMBB(New); 822 } 823 824 // Update the successor information. 825 replaceSuccessor(Old, New); 826 } 827 828 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the 829 /// CFG to be inserted. If we have proven that MBB can only branch to DestA and 830 /// DestB, remove any other MBB successors from the CFG. DestA and DestB can be 831 /// null. 832 /// 833 /// Besides DestA and DestB, retain other edges leading to LandingPads 834 /// (currently there can be only one; we don't check or require that here). 835 /// Note it is possible that DestA and/or DestB are LandingPads. 836 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA, 837 MachineBasicBlock *DestB, 838 bool isCond) { 839 // The values of DestA and DestB frequently come from a call to the 840 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial 841 // values from there. 842 // 843 // 1. If both DestA and DestB are null, then the block ends with no branches 844 // (it falls through to its successor). 845 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends 846 // with only an unconditional branch. 847 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends 848 // with a conditional branch that falls through to a successor (DestB). 849 // 4. If DestA and DestB is set and isCond is true, then the block ends with a 850 // conditional branch followed by an unconditional branch. DestA is the 851 // 'true' destination and DestB is the 'false' destination. 852 853 bool Changed = false; 854 855 MachineFunction::iterator FallThru = 856 llvm::next(MachineFunction::iterator(this)); 857 858 if (DestA == 0 && DestB == 0) { 859 // Block falls through to successor. 860 DestA = FallThru; 861 DestB = FallThru; 862 } else if (DestA != 0 && DestB == 0) { 863 if (isCond) 864 // Block ends in conditional jump that falls through to successor. 865 DestB = FallThru; 866 } else { 867 assert(DestA && DestB && isCond && 868 "CFG in a bad state. Cannot correct CFG edges"); 869 } 870 871 // Remove superfluous edges. I.e., those which aren't destinations of this 872 // basic block, duplicate edges, or landing pads. 873 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs; 874 MachineBasicBlock::succ_iterator SI = succ_begin(); 875 while (SI != succ_end()) { 876 const MachineBasicBlock *MBB = *SI; 877 if (!SeenMBBs.insert(MBB) || 878 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) { 879 // This is a superfluous edge, remove it. 880 SI = removeSuccessor(SI); 881 Changed = true; 882 } else { 883 ++SI; 884 } 885 } 886 887 return Changed; 888 } 889 890 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping 891 /// any DBG_VALUE instructions. Return UnknownLoc if there is none. 892 DebugLoc 893 MachineBasicBlock::findDebugLoc(instr_iterator MBBI) { 894 DebugLoc DL; 895 instr_iterator E = instr_end(); 896 if (MBBI == E) 897 return DL; 898 899 // Skip debug declarations, we don't want a DebugLoc from them. 900 while (MBBI != E && MBBI->isDebugValue()) 901 MBBI++; 902 if (MBBI != E) 903 DL = MBBI->getDebugLoc(); 904 return DL; 905 } 906 907 /// getSuccWeight - Return weight of the edge from this block to MBB. 908 /// 909 uint32_t MachineBasicBlock::getSuccWeight(const MachineBasicBlock *succ) const { 910 if (Weights.empty()) 911 return 0; 912 913 const_succ_iterator I = std::find(Successors.begin(), Successors.end(), succ); 914 return *getWeightIterator(I); 915 } 916 917 /// getWeightIterator - Return wight iterator corresonding to the I successor 918 /// iterator 919 MachineBasicBlock::weight_iterator MachineBasicBlock:: 920 getWeightIterator(MachineBasicBlock::succ_iterator I) { 921 assert(Weights.size() == Successors.size() && "Async weight list!"); 922 size_t index = std::distance(Successors.begin(), I); 923 assert(index < Weights.size() && "Not a current successor!"); 924 return Weights.begin() + index; 925 } 926 927 /// getWeightIterator - Return wight iterator corresonding to the I successor 928 /// iterator 929 MachineBasicBlock::const_weight_iterator MachineBasicBlock:: 930 getWeightIterator(MachineBasicBlock::const_succ_iterator I) const { 931 assert(Weights.size() == Successors.size() && "Async weight list!"); 932 const size_t index = std::distance(Successors.begin(), I); 933 assert(index < Weights.size() && "Not a current successor!"); 934 return Weights.begin() + index; 935 } 936 937 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB, 938 bool t) { 939 OS << "BB#" << MBB->getNumber(); 940 } 941 942