MachineBasicBlock.cpp revision 4052b296030e3523b9a4a8d1e4a9af9091a8d7e8
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/MachineFunction.h" 17#include "llvm/MC/MCAsmInfo.h" 18#include "llvm/MC/MCContext.h" 19#include "llvm/Target/TargetRegisterInfo.h" 20#include "llvm/Target/TargetData.h" 21#include "llvm/Target/TargetInstrDesc.h" 22#include "llvm/Target/TargetInstrInfo.h" 23#include "llvm/Target/TargetMachine.h" 24#include "llvm/Assembly/Writer.h" 25#include "llvm/ADT/SmallString.h" 26#include "llvm/Support/Debug.h" 27#include "llvm/Support/LeakDetector.h" 28#include "llvm/Support/raw_ostream.h" 29#include <algorithm> 30using namespace llvm; 31 32MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb) 33 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false), 34 AddressTaken(false) { 35 Insts.Parent = this; 36} 37 38MachineBasicBlock::~MachineBasicBlock() { 39 LeakDetector::removeGarbageObject(this); 40} 41 42/// getSymbol - Return the MCSymbol for this basic block. 43/// 44MCSymbol *MachineBasicBlock::getSymbol(MCContext &Ctx) const { 45 SmallString<60> Name; 46 const MachineFunction *MF = getParent(); 47 raw_svector_ostream(Name) 48 << MF->getTarget().getMCAsmInfo()->getPrivateGlobalPrefix() << "BB" 49 << MF->getFunctionNumber() << '_' << getNumber(); 50 return Ctx.GetOrCreateSymbol(Name.str()); 51} 52 53 54raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) { 55 MBB.print(OS); 56 return OS; 57} 58 59/// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the 60/// parent pointer of the MBB, the MBB numbering, and any instructions in the 61/// MBB to be on the right operand list for registers. 62/// 63/// MBBs start out as #-1. When a MBB is added to a MachineFunction, it 64/// gets the next available unique MBB number. If it is removed from a 65/// MachineFunction, it goes back to being #-1. 66void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) { 67 MachineFunction &MF = *N->getParent(); 68 N->Number = MF.addToMBBNumbering(N); 69 70 // Make sure the instructions have their operands in the reginfo lists. 71 MachineRegisterInfo &RegInfo = MF.getRegInfo(); 72 for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I) 73 I->AddRegOperandsToUseLists(RegInfo); 74 75 LeakDetector::removeGarbageObject(N); 76} 77 78void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) { 79 N->getParent()->removeFromMBBNumbering(N->Number); 80 N->Number = -1; 81 LeakDetector::addGarbageObject(N); 82} 83 84 85/// addNodeToList (MI) - When we add an instruction to a basic block 86/// list, we update its parent pointer and add its operands from reg use/def 87/// lists if appropriate. 88void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) { 89 assert(N->getParent() == 0 && "machine instruction already in a basic block"); 90 N->setParent(Parent); 91 92 // Add the instruction's register operands to their corresponding 93 // use/def lists. 94 MachineFunction *MF = Parent->getParent(); 95 N->AddRegOperandsToUseLists(MF->getRegInfo()); 96 97 LeakDetector::removeGarbageObject(N); 98} 99 100/// removeNodeFromList (MI) - When we remove an instruction from a basic block 101/// list, we update its parent pointer and remove its operands from reg use/def 102/// lists if appropriate. 103void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) { 104 assert(N->getParent() != 0 && "machine instruction not in a basic block"); 105 106 // Remove from the use/def lists. 107 N->RemoveRegOperandsFromUseLists(); 108 109 N->setParent(0); 110 111 LeakDetector::addGarbageObject(N); 112} 113 114/// transferNodesFromList (MI) - When moving a range of instructions from one 115/// MBB list to another, we need to update the parent pointers and the use/def 116/// lists. 117void ilist_traits<MachineInstr>:: 118transferNodesFromList(ilist_traits<MachineInstr> &fromList, 119 MachineBasicBlock::iterator first, 120 MachineBasicBlock::iterator last) { 121 assert(Parent->getParent() == fromList.Parent->getParent() && 122 "MachineInstr parent mismatch!"); 123 124 // Splice within the same MBB -> no change. 125 if (Parent == fromList.Parent) return; 126 127 // If splicing between two blocks within the same function, just update the 128 // parent pointers. 129 for (; first != last; ++first) 130 first->setParent(Parent); 131} 132 133void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) { 134 assert(!MI->getParent() && "MI is still in a block!"); 135 Parent->getParent()->DeleteMachineInstr(MI); 136} 137 138MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() { 139 iterator I = end(); 140 while (I != begin() && (--I)->getDesc().isTerminator()) 141 ; /*noop */ 142 if (I != end() && !I->getDesc().isTerminator()) ++I; 143 return I; 144} 145 146/// isOnlyReachableViaFallthough - Return true if this basic block has 147/// exactly one predecessor and the control transfer mechanism between 148/// the predecessor and this block is a fall-through. 149bool MachineBasicBlock::isOnlyReachableByFallthrough() const { 150 // If this is a landing pad, it isn't a fall through. If it has no preds, 151 // then nothing falls through to it. 152 if (isLandingPad() || pred_empty()) 153 return false; 154 155 // If there isn't exactly one predecessor, it can't be a fall through. 156 const_pred_iterator PI = pred_begin(), PI2 = PI; 157 ++PI2; 158 if (PI2 != pred_end()) 159 return false; 160 161 // The predecessor has to be immediately before this block. 162 const MachineBasicBlock *Pred = *PI; 163 164 if (!Pred->isLayoutSuccessor(this)) 165 return false; 166 167 // If the block is completely empty, then it definitely does fall through. 168 if (Pred->empty()) 169 return true; 170 171 // Otherwise, check the last instruction. 172 const MachineInstr &LastInst = Pred->back(); 173 return !LastInst.getDesc().isBarrier(); 174} 175 176void MachineBasicBlock::dump() const { 177 print(dbgs()); 178} 179 180static inline void OutputReg(raw_ostream &os, unsigned RegNo, 181 const TargetRegisterInfo *TRI = 0) { 182 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) { 183 if (TRI) 184 os << " %" << TRI->get(RegNo).Name; 185 else 186 os << " %physreg" << RegNo; 187 } else 188 os << " %reg" << RegNo; 189} 190 191StringRef MachineBasicBlock::getName() const { 192 if (const BasicBlock *LBB = getBasicBlock()) 193 return LBB->getName(); 194 else 195 return "(null)"; 196} 197 198void MachineBasicBlock::print(raw_ostream &OS) const { 199 const MachineFunction *MF = getParent(); 200 if (!MF) { 201 OS << "Can't print out MachineBasicBlock because parent MachineFunction" 202 << " is null\n"; 203 return; 204 } 205 206 if (Alignment) { OS << "Alignment " << Alignment << "\n"; } 207 208 OS << "BB#" << getNumber() << ": "; 209 210 const char *Comma = ""; 211 if (const BasicBlock *LBB = getBasicBlock()) { 212 OS << Comma << "derived from LLVM BB "; 213 WriteAsOperand(OS, LBB, /*PrintType=*/false); 214 Comma = ", "; 215 } 216 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; } 217 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; } 218 OS << '\n'; 219 220 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo(); 221 if (!livein_empty()) { 222 OS << " Live Ins:"; 223 for (const_livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I) 224 OutputReg(OS, *I, TRI); 225 OS << '\n'; 226 } 227 // Print the preds of this block according to the CFG. 228 if (!pred_empty()) { 229 OS << " Predecessors according to CFG:"; 230 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI) 231 OS << " BB#" << (*PI)->getNumber(); 232 OS << '\n'; 233 } 234 235 for (const_iterator I = begin(); I != end(); ++I) { 236 OS << '\t'; 237 I->print(OS, &getParent()->getTarget()); 238 } 239 240 // Print the successors of this block according to the CFG. 241 if (!succ_empty()) { 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 livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 251 assert(I != livein_end() && "Not a live in!"); 252 LiveIns.erase(I); 253} 254 255bool MachineBasicBlock::isLiveIn(unsigned Reg) const { 256 const_livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 257 return I != livein_end(); 258} 259 260void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) { 261 getParent()->splice(NewAfter, this); 262} 263 264void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) { 265 MachineFunction::iterator BBI = NewBefore; 266 getParent()->splice(++BBI, this); 267} 268 269void MachineBasicBlock::updateTerminator() { 270 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 271 // A block with no successors has no concerns with fall-through edges. 272 if (this->succ_empty()) return; 273 274 MachineBasicBlock *TBB = 0, *FBB = 0; 275 SmallVector<MachineOperand, 4> Cond; 276 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond); 277 (void) B; 278 assert(!B && "UpdateTerminators requires analyzable predecessors!"); 279 if (Cond.empty()) { 280 if (TBB) { 281 // The block has an unconditional branch. If its successor is now 282 // its layout successor, delete the branch. 283 if (isLayoutSuccessor(TBB)) 284 TII->RemoveBranch(*this); 285 } else { 286 // The block has an unconditional fallthrough. If its successor is not 287 // its layout successor, insert a branch. 288 TBB = *succ_begin(); 289 if (!isLayoutSuccessor(TBB)) 290 TII->InsertBranch(*this, TBB, 0, Cond); 291 } 292 } else { 293 if (FBB) { 294 // The block has a non-fallthrough conditional branch. If one of its 295 // successors is its layout successor, rewrite it to a fallthrough 296 // conditional branch. 297 if (isLayoutSuccessor(TBB)) { 298 if (TII->ReverseBranchCondition(Cond)) 299 return; 300 TII->RemoveBranch(*this); 301 TII->InsertBranch(*this, FBB, 0, Cond); 302 } else if (isLayoutSuccessor(FBB)) { 303 TII->RemoveBranch(*this); 304 TII->InsertBranch(*this, TBB, 0, Cond); 305 } 306 } else { 307 // The block has a fallthrough conditional branch. 308 MachineBasicBlock *MBBA = *succ_begin(); 309 MachineBasicBlock *MBBB = *llvm::next(succ_begin()); 310 if (MBBA == TBB) std::swap(MBBB, MBBA); 311 if (isLayoutSuccessor(TBB)) { 312 if (TII->ReverseBranchCondition(Cond)) { 313 // We can't reverse the condition, add an unconditional branch. 314 Cond.clear(); 315 TII->InsertBranch(*this, MBBA, 0, Cond); 316 return; 317 } 318 TII->RemoveBranch(*this); 319 TII->InsertBranch(*this, MBBA, 0, Cond); 320 } else if (!isLayoutSuccessor(MBBA)) { 321 TII->RemoveBranch(*this); 322 TII->InsertBranch(*this, TBB, MBBA, Cond); 323 } 324 } 325 } 326} 327 328void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) { 329 Successors.push_back(succ); 330 succ->addPredecessor(this); 331} 332 333void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) { 334 succ->removePredecessor(this); 335 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ); 336 assert(I != Successors.end() && "Not a current successor!"); 337 Successors.erase(I); 338} 339 340MachineBasicBlock::succ_iterator 341MachineBasicBlock::removeSuccessor(succ_iterator I) { 342 assert(I != Successors.end() && "Not a current successor!"); 343 (*I)->removePredecessor(this); 344 return Successors.erase(I); 345} 346 347void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) { 348 Predecessors.push_back(pred); 349} 350 351void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) { 352 std::vector<MachineBasicBlock *>::iterator I = 353 std::find(Predecessors.begin(), Predecessors.end(), pred); 354 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!"); 355 Predecessors.erase(I); 356} 357 358void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) { 359 if (this == fromMBB) 360 return; 361 362 for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(), 363 E = fromMBB->succ_end(); I != E; ++I) 364 addSuccessor(*I); 365 366 while (!fromMBB->succ_empty()) 367 fromMBB->removeSuccessor(fromMBB->succ_begin()); 368} 369 370bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const { 371 std::vector<MachineBasicBlock *>::const_iterator I = 372 std::find(Successors.begin(), Successors.end(), MBB); 373 return I != Successors.end(); 374} 375 376bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const { 377 MachineFunction::const_iterator I(this); 378 return llvm::next(I) == MachineFunction::const_iterator(MBB); 379} 380 381bool MachineBasicBlock::canFallThrough() { 382 MachineFunction::iterator Fallthrough = this; 383 ++Fallthrough; 384 // If FallthroughBlock is off the end of the function, it can't fall through. 385 if (Fallthrough == getParent()->end()) 386 return false; 387 388 // If FallthroughBlock isn't a successor, no fallthrough is possible. 389 if (!isSuccessor(Fallthrough)) 390 return false; 391 392 // Analyze the branches, if any, at the end of the block. 393 MachineBasicBlock *TBB = 0, *FBB = 0; 394 SmallVector<MachineOperand, 4> Cond; 395 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 396 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) { 397 // If we couldn't analyze the branch, examine the last instruction. 398 // If the block doesn't end in a known control barrier, assume fallthrough 399 // is possible. The isPredicable check is needed because this code can be 400 // called during IfConversion, where an instruction which is normally a 401 // Barrier is predicated and thus no longer an actual control barrier. This 402 // is over-conservative though, because if an instruction isn't actually 403 // predicated we could still treat it like a barrier. 404 return empty() || !back().getDesc().isBarrier() || 405 back().getDesc().isPredicable(); 406 } 407 408 // If there is no branch, control always falls through. 409 if (TBB == 0) return true; 410 411 // If there is some explicit branch to the fallthrough block, it can obviously 412 // reach, even though the branch should get folded to fall through implicitly. 413 if (MachineFunction::iterator(TBB) == Fallthrough || 414 MachineFunction::iterator(FBB) == Fallthrough) 415 return true; 416 417 // If it's an unconditional branch to some block not the fall through, it 418 // doesn't fall through. 419 if (Cond.empty()) return false; 420 421 // Otherwise, if it is conditional and has no explicit false block, it falls 422 // through. 423 return FBB == 0; 424} 425 426/// removeFromParent - This method unlinks 'this' from the containing function, 427/// and returns it, but does not delete it. 428MachineBasicBlock *MachineBasicBlock::removeFromParent() { 429 assert(getParent() && "Not embedded in a function!"); 430 getParent()->remove(this); 431 return this; 432} 433 434 435/// eraseFromParent - This method unlinks 'this' from the containing function, 436/// and deletes it. 437void MachineBasicBlock::eraseFromParent() { 438 assert(getParent() && "Not embedded in a function!"); 439 getParent()->erase(this); 440} 441 442 443/// ReplaceUsesOfBlockWith - Given a machine basic block that branched to 444/// 'Old', change the code and CFG so that it branches to 'New' instead. 445void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old, 446 MachineBasicBlock *New) { 447 assert(Old != New && "Cannot replace self with self!"); 448 449 MachineBasicBlock::iterator I = end(); 450 while (I != begin()) { 451 --I; 452 if (!I->getDesc().isTerminator()) break; 453 454 // Scan the operands of this machine instruction, replacing any uses of Old 455 // with New. 456 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 457 if (I->getOperand(i).isMBB() && 458 I->getOperand(i).getMBB() == Old) 459 I->getOperand(i).setMBB(New); 460 } 461 462 // Update the successor information. 463 removeSuccessor(Old); 464 addSuccessor(New); 465} 466 467/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the 468/// CFG to be inserted. If we have proven that MBB can only branch to DestA and 469/// DestB, remove any other MBB successors from the CFG. DestA and DestB can be 470/// null. 471/// 472/// Besides DestA and DestB, retain other edges leading to LandingPads 473/// (currently there can be only one; we don't check or require that here). 474/// Note it is possible that DestA and/or DestB are LandingPads. 475bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA, 476 MachineBasicBlock *DestB, 477 bool isCond) { 478 // The values of DestA and DestB frequently come from a call to the 479 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial 480 // values from there. 481 // 482 // 1. If both DestA and DestB are null, then the block ends with no branches 483 // (it falls through to its successor). 484 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends 485 // with only an unconditional branch. 486 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends 487 // with a conditional branch that falls through to a successor (DestB). 488 // 4. If DestA and DestB is set and isCond is true, then the block ends with a 489 // conditional branch followed by an unconditional branch. DestA is the 490 // 'true' destination and DestB is the 'false' destination. 491 492 bool MadeChange = false; 493 bool AddedFallThrough = false; 494 495 MachineFunction::iterator FallThru = 496 llvm::next(MachineFunction::iterator(this)); 497 498 if (isCond) { 499 // If this block ends with a conditional branch that falls through to its 500 // successor, set DestB as the successor. 501 if (DestB == 0 && FallThru != getParent()->end()) { 502 DestB = FallThru; 503 AddedFallThrough = true; 504 } 505 } else { 506 // If this is an unconditional branch with no explicit dest, it must just be 507 // a fallthrough into DestA. 508 if (DestA == 0 && FallThru != getParent()->end()) { 509 DestA = FallThru; 510 AddedFallThrough = true; 511 } 512 } 513 514 MachineBasicBlock::succ_iterator SI = succ_begin(); 515 MachineBasicBlock *OrigDestA = DestA, *OrigDestB = DestB; 516 while (SI != succ_end()) { 517 const MachineBasicBlock *MBB = *SI; 518 if (MBB == DestA) { 519 DestA = 0; 520 ++SI; 521 } else if (MBB == DestB) { 522 DestB = 0; 523 ++SI; 524 } else if (MBB->isLandingPad() && 525 MBB != OrigDestA && MBB != OrigDestB) { 526 ++SI; 527 } else { 528 // Otherwise, this is a superfluous edge, remove it. 529 SI = removeSuccessor(SI); 530 MadeChange = true; 531 } 532 } 533 534 if (!AddedFallThrough) 535 assert(DestA == 0 && DestB == 0 && "MachineCFG is missing edges!"); 536 else if (isCond) 537 assert(DestA == 0 && "MachineCFG is missing edges!"); 538 539 return MadeChange; 540} 541 542/// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping 543/// any DEBUG_VALUE instructions. Return UnknownLoc if there is none. 544DebugLoc 545MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) { 546 DebugLoc DL; 547 MachineBasicBlock::iterator E = end(); 548 if (MBBI != E) { 549 // Skip debug declarations, we don't want a DebugLoc from them. 550 MachineBasicBlock::iterator MBBI2 = MBBI; 551 while (MBBI2 != E && MBBI2->isDebugValue()) 552 MBBI2++; 553 if (MBBI2 != E) 554 DL = MBBI2->getDebugLoc(); 555 } 556 return DL; 557} 558 559void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB, 560 bool t) { 561 OS << "BB#" << MBB->getNumber(); 562} 563 564