MachineBasicBlock.cpp revision e4454320b3cfffe926a487c33fbeb454366de2f8
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 146void MachineBasicBlock::dump() const { 147 print(dbgs()); 148} 149 150static inline void OutputReg(raw_ostream &os, unsigned RegNo, 151 const TargetRegisterInfo *TRI = 0) { 152 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) { 153 if (TRI) 154 os << " %" << TRI->get(RegNo).Name; 155 else 156 os << " %physreg" << RegNo; 157 } else 158 os << " %reg" << RegNo; 159} 160 161StringRef MachineBasicBlock::getName() const { 162 if (const BasicBlock *LBB = getBasicBlock()) 163 return LBB->getName(); 164 else 165 return "(null)"; 166} 167 168void MachineBasicBlock::print(raw_ostream &OS) const { 169 const MachineFunction *MF = getParent(); 170 if (!MF) { 171 OS << "Can't print out MachineBasicBlock because parent MachineFunction" 172 << " is null\n"; 173 return; 174 } 175 176 if (Alignment) { OS << "Alignment " << Alignment << "\n"; } 177 178 OS << "BB#" << getNumber() << ": "; 179 180 const char *Comma = ""; 181 if (const BasicBlock *LBB = getBasicBlock()) { 182 OS << Comma << "derived from LLVM BB "; 183 WriteAsOperand(OS, LBB, /*PrintType=*/false); 184 Comma = ", "; 185 } 186 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; } 187 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; } 188 OS << '\n'; 189 190 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo(); 191 if (!livein_empty()) { 192 OS << " Live Ins:"; 193 for (const_livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I) 194 OutputReg(OS, *I, TRI); 195 OS << '\n'; 196 } 197 // Print the preds of this block according to the CFG. 198 if (!pred_empty()) { 199 OS << " Predecessors according to CFG:"; 200 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI) 201 OS << " BB#" << (*PI)->getNumber(); 202 OS << '\n'; 203 } 204 205 for (const_iterator I = begin(); I != end(); ++I) { 206 OS << '\t'; 207 I->print(OS, &getParent()->getTarget()); 208 } 209 210 // Print the successors of this block according to the CFG. 211 if (!succ_empty()) { 212 OS << " Successors according to CFG:"; 213 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI) 214 OS << " BB#" << (*SI)->getNumber(); 215 OS << '\n'; 216 } 217} 218 219void MachineBasicBlock::removeLiveIn(unsigned Reg) { 220 livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 221 assert(I != livein_end() && "Not a live in!"); 222 LiveIns.erase(I); 223} 224 225bool MachineBasicBlock::isLiveIn(unsigned Reg) const { 226 const_livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 227 return I != livein_end(); 228} 229 230void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) { 231 getParent()->splice(NewAfter, this); 232} 233 234void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) { 235 MachineFunction::iterator BBI = NewBefore; 236 getParent()->splice(++BBI, this); 237} 238 239void MachineBasicBlock::updateTerminator() { 240 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 241 // A block with no successors has no concerns with fall-through edges. 242 if (this->succ_empty()) return; 243 244 MachineBasicBlock *TBB = 0, *FBB = 0; 245 SmallVector<MachineOperand, 4> Cond; 246 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond); 247 (void) B; 248 assert(!B && "UpdateTerminators requires analyzable predecessors!"); 249 if (Cond.empty()) { 250 if (TBB) { 251 // The block has an unconditional branch. If its successor is now 252 // its layout successor, delete the branch. 253 if (isLayoutSuccessor(TBB)) 254 TII->RemoveBranch(*this); 255 } else { 256 // The block has an unconditional fallthrough. If its successor is not 257 // its layout successor, insert a branch. 258 TBB = *succ_begin(); 259 if (!isLayoutSuccessor(TBB)) 260 TII->InsertBranch(*this, TBB, 0, Cond); 261 } 262 } else { 263 if (FBB) { 264 // The block has a non-fallthrough conditional branch. If one of its 265 // successors is its layout successor, rewrite it to a fallthrough 266 // conditional branch. 267 if (isLayoutSuccessor(TBB)) { 268 if (TII->ReverseBranchCondition(Cond)) 269 return; 270 TII->RemoveBranch(*this); 271 TII->InsertBranch(*this, FBB, 0, Cond); 272 } else if (isLayoutSuccessor(FBB)) { 273 TII->RemoveBranch(*this); 274 TII->InsertBranch(*this, TBB, 0, Cond); 275 } 276 } else { 277 // The block has a fallthrough conditional branch. 278 MachineBasicBlock *MBBA = *succ_begin(); 279 MachineBasicBlock *MBBB = *llvm::next(succ_begin()); 280 if (MBBA == TBB) std::swap(MBBB, MBBA); 281 if (isLayoutSuccessor(TBB)) { 282 if (TII->ReverseBranchCondition(Cond)) { 283 // We can't reverse the condition, add an unconditional branch. 284 Cond.clear(); 285 TII->InsertBranch(*this, MBBA, 0, Cond); 286 return; 287 } 288 TII->RemoveBranch(*this); 289 TII->InsertBranch(*this, MBBA, 0, Cond); 290 } else if (!isLayoutSuccessor(MBBA)) { 291 TII->RemoveBranch(*this); 292 TII->InsertBranch(*this, TBB, MBBA, Cond); 293 } 294 } 295 } 296} 297 298void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) { 299 Successors.push_back(succ); 300 succ->addPredecessor(this); 301} 302 303void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) { 304 succ->removePredecessor(this); 305 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ); 306 assert(I != Successors.end() && "Not a current successor!"); 307 Successors.erase(I); 308} 309 310MachineBasicBlock::succ_iterator 311MachineBasicBlock::removeSuccessor(succ_iterator I) { 312 assert(I != Successors.end() && "Not a current successor!"); 313 (*I)->removePredecessor(this); 314 return Successors.erase(I); 315} 316 317void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) { 318 Predecessors.push_back(pred); 319} 320 321void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) { 322 std::vector<MachineBasicBlock *>::iterator I = 323 std::find(Predecessors.begin(), Predecessors.end(), pred); 324 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!"); 325 Predecessors.erase(I); 326} 327 328void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) { 329 if (this == fromMBB) 330 return; 331 332 for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(), 333 E = fromMBB->succ_end(); I != E; ++I) 334 addSuccessor(*I); 335 336 while (!fromMBB->succ_empty()) 337 fromMBB->removeSuccessor(fromMBB->succ_begin()); 338} 339 340bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const { 341 std::vector<MachineBasicBlock *>::const_iterator I = 342 std::find(Successors.begin(), Successors.end(), MBB); 343 return I != Successors.end(); 344} 345 346bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const { 347 MachineFunction::const_iterator I(this); 348 return llvm::next(I) == MachineFunction::const_iterator(MBB); 349} 350 351bool MachineBasicBlock::canFallThrough() { 352 MachineFunction::iterator Fallthrough = this; 353 ++Fallthrough; 354 // If FallthroughBlock is off the end of the function, it can't fall through. 355 if (Fallthrough == getParent()->end()) 356 return false; 357 358 // If FallthroughBlock isn't a successor, no fallthrough is possible. 359 if (!isSuccessor(Fallthrough)) 360 return false; 361 362 // Analyze the branches, if any, at the end of the block. 363 MachineBasicBlock *TBB = 0, *FBB = 0; 364 SmallVector<MachineOperand, 4> Cond; 365 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 366 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) { 367 // If we couldn't analyze the branch, examine the last instruction. 368 // If the block doesn't end in a known control barrier, assume fallthrough 369 // is possible. The isPredicable check is needed because this code can be 370 // called during IfConversion, where an instruction which is normally a 371 // Barrier is predicated and thus no longer an actual control barrier. This 372 // is over-conservative though, because if an instruction isn't actually 373 // predicated we could still treat it like a barrier. 374 return empty() || !back().getDesc().isBarrier() || 375 back().getDesc().isPredicable(); 376 } 377 378 // If there is no branch, control always falls through. 379 if (TBB == 0) return true; 380 381 // If there is some explicit branch to the fallthrough block, it can obviously 382 // reach, even though the branch should get folded to fall through implicitly. 383 if (MachineFunction::iterator(TBB) == Fallthrough || 384 MachineFunction::iterator(FBB) == Fallthrough) 385 return true; 386 387 // If it's an unconditional branch to some block not the fall through, it 388 // doesn't fall through. 389 if (Cond.empty()) return false; 390 391 // Otherwise, if it is conditional and has no explicit false block, it falls 392 // through. 393 return FBB == 0; 394} 395 396/// removeFromParent - This method unlinks 'this' from the containing function, 397/// and returns it, but does not delete it. 398MachineBasicBlock *MachineBasicBlock::removeFromParent() { 399 assert(getParent() && "Not embedded in a function!"); 400 getParent()->remove(this); 401 return this; 402} 403 404 405/// eraseFromParent - This method unlinks 'this' from the containing function, 406/// and deletes it. 407void MachineBasicBlock::eraseFromParent() { 408 assert(getParent() && "Not embedded in a function!"); 409 getParent()->erase(this); 410} 411 412 413/// ReplaceUsesOfBlockWith - Given a machine basic block that branched to 414/// 'Old', change the code and CFG so that it branches to 'New' instead. 415void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old, 416 MachineBasicBlock *New) { 417 assert(Old != New && "Cannot replace self with self!"); 418 419 MachineBasicBlock::iterator I = end(); 420 while (I != begin()) { 421 --I; 422 if (!I->getDesc().isTerminator()) break; 423 424 // Scan the operands of this machine instruction, replacing any uses of Old 425 // with New. 426 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 427 if (I->getOperand(i).isMBB() && 428 I->getOperand(i).getMBB() == Old) 429 I->getOperand(i).setMBB(New); 430 } 431 432 // Update the successor information. 433 removeSuccessor(Old); 434 addSuccessor(New); 435} 436 437/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the 438/// CFG to be inserted. If we have proven that MBB can only branch to DestA and 439/// DestB, remove any other MBB successors from the CFG. DestA and DestB can be 440/// null. 441/// 442/// Besides DestA and DestB, retain other edges leading to LandingPads 443/// (currently there can be only one; we don't check or require that here). 444/// Note it is possible that DestA and/or DestB are LandingPads. 445bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA, 446 MachineBasicBlock *DestB, 447 bool isCond) { 448 // The values of DestA and DestB frequently come from a call to the 449 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial 450 // values from there. 451 // 452 // 1. If both DestA and DestB are null, then the block ends with no branches 453 // (it falls through to its successor). 454 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends 455 // with only an unconditional branch. 456 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends 457 // with a conditional branch that falls through to a successor (DestB). 458 // 4. If DestA and DestB is set and isCond is true, then the block ends with a 459 // conditional branch followed by an unconditional branch. DestA is the 460 // 'true' destination and DestB is the 'false' destination. 461 462 bool MadeChange = false; 463 bool AddedFallThrough = false; 464 465 MachineFunction::iterator FallThru = 466 llvm::next(MachineFunction::iterator(this)); 467 468 if (isCond) { 469 // If this block ends with a conditional branch that falls through to its 470 // successor, set DestB as the successor. 471 if (DestB == 0 && FallThru != getParent()->end()) { 472 DestB = FallThru; 473 AddedFallThrough = true; 474 } 475 } else { 476 // If this is an unconditional branch with no explicit dest, it must just be 477 // a fallthrough into DestA. 478 if (DestA == 0 && FallThru != getParent()->end()) { 479 DestA = FallThru; 480 AddedFallThrough = true; 481 } 482 } 483 484 MachineBasicBlock::succ_iterator SI = succ_begin(); 485 MachineBasicBlock *OrigDestA = DestA, *OrigDestB = DestB; 486 while (SI != succ_end()) { 487 const MachineBasicBlock *MBB = *SI; 488 if (MBB == DestA) { 489 DestA = 0; 490 ++SI; 491 } else if (MBB == DestB) { 492 DestB = 0; 493 ++SI; 494 } else if (MBB->isLandingPad() && 495 MBB != OrigDestA && MBB != OrigDestB) { 496 ++SI; 497 } else { 498 // Otherwise, this is a superfluous edge, remove it. 499 SI = removeSuccessor(SI); 500 MadeChange = true; 501 } 502 } 503 504 if (!AddedFallThrough) 505 assert(DestA == 0 && DestB == 0 && "MachineCFG is missing edges!"); 506 else if (isCond) 507 assert(DestA == 0 && "MachineCFG is missing edges!"); 508 509 return MadeChange; 510} 511 512/// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping 513/// any DBG_VALUE instructions. Return UnknownLoc if there is none. 514DebugLoc 515MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) { 516 DebugLoc DL; 517 MachineBasicBlock::iterator E = end(); 518 if (MBBI != E) { 519 // Skip debug declarations, we don't want a DebugLoc from them. 520 MachineBasicBlock::iterator MBBI2 = MBBI; 521 while (MBBI2 != E && MBBI2->isDebugValue()) 522 MBBI2++; 523 if (MBBI2 != E) 524 DL = MBBI2->getDebugLoc(); 525 } 526 return DL; 527} 528 529void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB, 530 bool t) { 531 OS << "BB#" << MBB->getNumber(); 532} 533 534