MachineBasicBlock.cpp revision 1e60b69d6816cb2ab7aaa6524d1b92358200f640
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/ADT/SmallPtrSet.h" 27#include "llvm/Support/Debug.h" 28#include "llvm/Support/LeakDetector.h" 29#include "llvm/Support/raw_ostream.h" 30#include <algorithm> 31using namespace llvm; 32 33MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb) 34 : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false), 35 AddressTaken(false) { 36 Insts.Parent = this; 37} 38 39MachineBasicBlock::~MachineBasicBlock() { 40 LeakDetector::removeGarbageObject(this); 41} 42 43/// getSymbol - Return the MCSymbol for this basic block. 44/// 45MCSymbol *MachineBasicBlock::getSymbol() const { 46 const MachineFunction *MF = getParent(); 47 MCContext &Ctx = MF->getContext(); 48 const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix(); 49 return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" + 50 Twine(MF->getFunctionNumber()) + "_" + 51 Twine(getNumber())); 52} 53 54 55raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) { 56 MBB.print(OS); 57 return OS; 58} 59 60/// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the 61/// parent pointer of the MBB, the MBB numbering, and any instructions in the 62/// MBB to be on the right operand list for registers. 63/// 64/// MBBs start out as #-1. When a MBB is added to a MachineFunction, it 65/// gets the next available unique MBB number. If it is removed from a 66/// MachineFunction, it goes back to being #-1. 67void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) { 68 MachineFunction &MF = *N->getParent(); 69 N->Number = MF.addToMBBNumbering(N); 70 71 // Make sure the instructions have their operands in the reginfo lists. 72 MachineRegisterInfo &RegInfo = MF.getRegInfo(); 73 for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I) 74 I->AddRegOperandsToUseLists(RegInfo); 75 76 LeakDetector::removeGarbageObject(N); 77} 78 79void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) { 80 N->getParent()->removeFromMBBNumbering(N->Number); 81 N->Number = -1; 82 LeakDetector::addGarbageObject(N); 83} 84 85 86/// addNodeToList (MI) - When we add an instruction to a basic block 87/// list, we update its parent pointer and add its operands from reg use/def 88/// lists if appropriate. 89void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) { 90 assert(N->getParent() == 0 && "machine instruction already in a basic block"); 91 N->setParent(Parent); 92 93 // Add the instruction's register operands to their corresponding 94 // use/def lists. 95 MachineFunction *MF = Parent->getParent(); 96 N->AddRegOperandsToUseLists(MF->getRegInfo()); 97 98 LeakDetector::removeGarbageObject(N); 99} 100 101/// removeNodeFromList (MI) - When we remove an instruction from a basic block 102/// list, we update its parent pointer and remove its operands from reg use/def 103/// lists if appropriate. 104void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) { 105 assert(N->getParent() != 0 && "machine instruction not in a basic block"); 106 107 // Remove from the use/def lists. 108 N->RemoveRegOperandsFromUseLists(); 109 110 N->setParent(0); 111 112 LeakDetector::addGarbageObject(N); 113} 114 115/// transferNodesFromList (MI) - When moving a range of instructions from one 116/// MBB list to another, we need to update the parent pointers and the use/def 117/// lists. 118void ilist_traits<MachineInstr>:: 119transferNodesFromList(ilist_traits<MachineInstr> &fromList, 120 MachineBasicBlock::iterator first, 121 MachineBasicBlock::iterator last) { 122 assert(Parent->getParent() == fromList.Parent->getParent() && 123 "MachineInstr parent mismatch!"); 124 125 // Splice within the same MBB -> no change. 126 if (Parent == fromList.Parent) return; 127 128 // If splicing between two blocks within the same function, just update the 129 // parent pointers. 130 for (; first != last; ++first) 131 first->setParent(Parent); 132} 133 134void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) { 135 assert(!MI->getParent() && "MI is still in a block!"); 136 Parent->getParent()->DeleteMachineInstr(MI); 137} 138 139MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() { 140 iterator I = end(); 141 while (I != begin() && (--I)->getDesc().isTerminator()) 142 ; /*noop */ 143 if (I != end() && !I->getDesc().isTerminator()) ++I; 144 return I; 145} 146 147void MachineBasicBlock::dump() const { 148 print(dbgs()); 149} 150 151static inline void OutputReg(raw_ostream &os, unsigned RegNo, 152 const TargetRegisterInfo *TRI = 0) { 153 if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) { 154 if (TRI) 155 os << " %" << TRI->get(RegNo).Name; 156 else 157 os << " %physreg" << RegNo; 158 } else 159 os << " %reg" << RegNo; 160} 161 162StringRef MachineBasicBlock::getName() const { 163 if (const BasicBlock *LBB = getBasicBlock()) 164 return LBB->getName(); 165 else 166 return "(null)"; 167} 168 169void MachineBasicBlock::print(raw_ostream &OS) const { 170 const MachineFunction *MF = getParent(); 171 if (!MF) { 172 OS << "Can't print out MachineBasicBlock because parent MachineFunction" 173 << " is null\n"; 174 return; 175 } 176 177 if (Alignment) { OS << "Alignment " << Alignment << "\n"; } 178 179 OS << "BB#" << getNumber() << ": "; 180 181 const char *Comma = ""; 182 if (const BasicBlock *LBB = getBasicBlock()) { 183 OS << Comma << "derived from LLVM BB "; 184 WriteAsOperand(OS, LBB, /*PrintType=*/false); 185 Comma = ", "; 186 } 187 if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; } 188 if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; } 189 OS << '\n'; 190 191 const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo(); 192 if (!livein_empty()) { 193 OS << " Live Ins:"; 194 for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I) 195 OutputReg(OS, *I, TRI); 196 OS << '\n'; 197 } 198 // Print the preds of this block according to the CFG. 199 if (!pred_empty()) { 200 OS << " Predecessors according to CFG:"; 201 for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI) 202 OS << " BB#" << (*PI)->getNumber(); 203 OS << '\n'; 204 } 205 206 for (const_iterator I = begin(); I != end(); ++I) { 207 OS << '\t'; 208 I->print(OS, &getParent()->getTarget()); 209 } 210 211 // Print the successors of this block according to the CFG. 212 if (!succ_empty()) { 213 OS << " Successors according to CFG:"; 214 for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI) 215 OS << " BB#" << (*SI)->getNumber(); 216 OS << '\n'; 217 } 218} 219 220void MachineBasicBlock::removeLiveIn(unsigned Reg) { 221 std::vector<unsigned>::iterator I = 222 std::find(LiveIns.begin(), LiveIns.end(), Reg); 223 assert(I != LiveIns.end() && "Not a live in!"); 224 LiveIns.erase(I); 225} 226 227bool MachineBasicBlock::isLiveIn(unsigned Reg) const { 228 livein_iterator I = std::find(livein_begin(), livein_end(), Reg); 229 return I != livein_end(); 230} 231 232void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) { 233 getParent()->splice(NewAfter, this); 234} 235 236void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) { 237 MachineFunction::iterator BBI = NewBefore; 238 getParent()->splice(++BBI, this); 239} 240 241void MachineBasicBlock::updateTerminator() { 242 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 243 // A block with no successors has no concerns with fall-through edges. 244 if (this->succ_empty()) return; 245 246 MachineBasicBlock *TBB = 0, *FBB = 0; 247 SmallVector<MachineOperand, 4> Cond; 248 bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond); 249 (void) B; 250 assert(!B && "UpdateTerminators requires analyzable predecessors!"); 251 if (Cond.empty()) { 252 if (TBB) { 253 // The block has an unconditional branch. If its successor is now 254 // its layout successor, delete the branch. 255 if (isLayoutSuccessor(TBB)) 256 TII->RemoveBranch(*this); 257 } else { 258 // The block has an unconditional fallthrough. If its successor is not 259 // its layout successor, insert a branch. 260 TBB = *succ_begin(); 261 if (!isLayoutSuccessor(TBB)) 262 TII->InsertBranch(*this, TBB, 0, Cond); 263 } 264 } else { 265 if (FBB) { 266 // The block has a non-fallthrough conditional branch. If one of its 267 // successors is its layout successor, rewrite it to a fallthrough 268 // conditional branch. 269 if (isLayoutSuccessor(TBB)) { 270 if (TII->ReverseBranchCondition(Cond)) 271 return; 272 TII->RemoveBranch(*this); 273 TII->InsertBranch(*this, FBB, 0, Cond); 274 } else if (isLayoutSuccessor(FBB)) { 275 TII->RemoveBranch(*this); 276 TII->InsertBranch(*this, TBB, 0, Cond); 277 } 278 } else { 279 // The block has a fallthrough conditional branch. 280 MachineBasicBlock *MBBA = *succ_begin(); 281 MachineBasicBlock *MBBB = *llvm::next(succ_begin()); 282 if (MBBA == TBB) std::swap(MBBB, MBBA); 283 if (isLayoutSuccessor(TBB)) { 284 if (TII->ReverseBranchCondition(Cond)) { 285 // We can't reverse the condition, add an unconditional branch. 286 Cond.clear(); 287 TII->InsertBranch(*this, MBBA, 0, Cond); 288 return; 289 } 290 TII->RemoveBranch(*this); 291 TII->InsertBranch(*this, MBBA, 0, Cond); 292 } else if (!isLayoutSuccessor(MBBA)) { 293 TII->RemoveBranch(*this); 294 TII->InsertBranch(*this, TBB, MBBA, Cond); 295 } 296 } 297 } 298} 299 300void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) { 301 Successors.push_back(succ); 302 succ->addPredecessor(this); 303} 304 305void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) { 306 succ->removePredecessor(this); 307 succ_iterator I = std::find(Successors.begin(), Successors.end(), succ); 308 assert(I != Successors.end() && "Not a current successor!"); 309 Successors.erase(I); 310} 311 312MachineBasicBlock::succ_iterator 313MachineBasicBlock::removeSuccessor(succ_iterator I) { 314 assert(I != Successors.end() && "Not a current successor!"); 315 (*I)->removePredecessor(this); 316 return Successors.erase(I); 317} 318 319void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) { 320 Predecessors.push_back(pred); 321} 322 323void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) { 324 std::vector<MachineBasicBlock *>::iterator I = 325 std::find(Predecessors.begin(), Predecessors.end(), pred); 326 assert(I != Predecessors.end() && "Pred is not a predecessor of this block!"); 327 Predecessors.erase(I); 328} 329 330void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) { 331 if (this == fromMBB) 332 return; 333 334 for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(), 335 E = fromMBB->succ_end(); I != E; ++I) 336 addSuccessor(*I); 337 338 while (!fromMBB->succ_empty()) 339 fromMBB->removeSuccessor(fromMBB->succ_begin()); 340} 341 342bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const { 343 std::vector<MachineBasicBlock *>::const_iterator I = 344 std::find(Successors.begin(), Successors.end(), MBB); 345 return I != Successors.end(); 346} 347 348bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const { 349 MachineFunction::const_iterator I(this); 350 return llvm::next(I) == MachineFunction::const_iterator(MBB); 351} 352 353bool MachineBasicBlock::canFallThrough() { 354 MachineFunction::iterator Fallthrough = this; 355 ++Fallthrough; 356 // If FallthroughBlock is off the end of the function, it can't fall through. 357 if (Fallthrough == getParent()->end()) 358 return false; 359 360 // If FallthroughBlock isn't a successor, no fallthrough is possible. 361 if (!isSuccessor(Fallthrough)) 362 return false; 363 364 // Analyze the branches, if any, at the end of the block. 365 MachineBasicBlock *TBB = 0, *FBB = 0; 366 SmallVector<MachineOperand, 4> Cond; 367 const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo(); 368 if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) { 369 // If we couldn't analyze the branch, examine the last instruction. 370 // If the block doesn't end in a known control barrier, assume fallthrough 371 // is possible. The isPredicable check is needed because this code can be 372 // called during IfConversion, where an instruction which is normally a 373 // Barrier is predicated and thus no longer an actual control barrier. This 374 // is over-conservative though, because if an instruction isn't actually 375 // predicated we could still treat it like a barrier. 376 return empty() || !back().getDesc().isBarrier() || 377 back().getDesc().isPredicable(); 378 } 379 380 // If there is no branch, control always falls through. 381 if (TBB == 0) return true; 382 383 // If there is some explicit branch to the fallthrough block, it can obviously 384 // reach, even though the branch should get folded to fall through implicitly. 385 if (MachineFunction::iterator(TBB) == Fallthrough || 386 MachineFunction::iterator(FBB) == Fallthrough) 387 return true; 388 389 // If it's an unconditional branch to some block not the fall through, it 390 // doesn't fall through. 391 if (Cond.empty()) return false; 392 393 // Otherwise, if it is conditional and has no explicit false block, it falls 394 // through. 395 return FBB == 0; 396} 397 398/// removeFromParent - This method unlinks 'this' from the containing function, 399/// and returns it, but does not delete it. 400MachineBasicBlock *MachineBasicBlock::removeFromParent() { 401 assert(getParent() && "Not embedded in a function!"); 402 getParent()->remove(this); 403 return this; 404} 405 406 407/// eraseFromParent - This method unlinks 'this' from the containing function, 408/// and deletes it. 409void MachineBasicBlock::eraseFromParent() { 410 assert(getParent() && "Not embedded in a function!"); 411 getParent()->erase(this); 412} 413 414 415/// ReplaceUsesOfBlockWith - Given a machine basic block that branched to 416/// 'Old', change the code and CFG so that it branches to 'New' instead. 417void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old, 418 MachineBasicBlock *New) { 419 assert(Old != New && "Cannot replace self with self!"); 420 421 MachineBasicBlock::iterator I = end(); 422 while (I != begin()) { 423 --I; 424 if (!I->getDesc().isTerminator()) break; 425 426 // Scan the operands of this machine instruction, replacing any uses of Old 427 // with New. 428 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 429 if (I->getOperand(i).isMBB() && 430 I->getOperand(i).getMBB() == Old) 431 I->getOperand(i).setMBB(New); 432 } 433 434 // Update the successor information. 435 removeSuccessor(Old); 436 addSuccessor(New); 437} 438 439/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the 440/// CFG to be inserted. If we have proven that MBB can only branch to DestA and 441/// DestB, remove any other MBB successors from the CFG. DestA and DestB can be 442/// null. 443/// 444/// Besides DestA and DestB, retain other edges leading to LandingPads 445/// (currently there can be only one; we don't check or require that here). 446/// Note it is possible that DestA and/or DestB are LandingPads. 447bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA, 448 MachineBasicBlock *DestB, 449 bool isCond) { 450 // The values of DestA and DestB frequently come from a call to the 451 // 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial 452 // values from there. 453 // 454 // 1. If both DestA and DestB are null, then the block ends with no branches 455 // (it falls through to its successor). 456 // 2. If DestA is set, DestB is null, and isCond is false, then the block ends 457 // with only an unconditional branch. 458 // 3. If DestA is set, DestB is null, and isCond is true, then the block ends 459 // with a conditional branch that falls through to a successor (DestB). 460 // 4. If DestA and DestB is set and isCond is true, then the block ends with a 461 // conditional branch followed by an unconditional branch. DestA is the 462 // 'true' destination and DestB is the 'false' destination. 463 464 bool Changed = false; 465 466 MachineFunction::iterator FallThru = 467 llvm::next(MachineFunction::iterator(this)); 468 469 if (DestA == 0 && DestB == 0) { 470 // Block falls through to successor. 471 DestA = FallThru; 472 DestB = FallThru; 473 } else if (DestA != 0 && DestB == 0) { 474 if (isCond) 475 // Block ends in conditional jump that falls through to successor. 476 DestB = FallThru; 477 } else { 478 assert(DestA && DestB && isCond && 479 "CFG in a bad state. Cannot correct CFG edges"); 480 } 481 482 // Remove superfluous edges. I.e., those which aren't destinations of this 483 // basic block, duplicate edges, or landing pads. 484 SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs; 485 MachineBasicBlock::succ_iterator SI = succ_begin(); 486 while (SI != succ_end()) { 487 const MachineBasicBlock *MBB = *SI; 488 if (!SeenMBBs.insert(MBB) || 489 (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) { 490 // This is a superfluous edge, remove it. 491 SI = removeSuccessor(SI); 492 Changed = true; 493 } else { 494 ++SI; 495 } 496 } 497 498 return Changed; 499} 500 501/// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping 502/// any DBG_VALUE instructions. Return UnknownLoc if there is none. 503DebugLoc 504MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) { 505 DebugLoc DL; 506 MachineBasicBlock::iterator E = end(); 507 if (MBBI != E) { 508 // Skip debug declarations, we don't want a DebugLoc from them. 509 MachineBasicBlock::iterator MBBI2 = MBBI; 510 while (MBBI2 != E && MBBI2->isDebugValue()) 511 MBBI2++; 512 if (MBBI2 != E) 513 DL = MBBI2->getDebugLoc(); 514 } 515 return DL; 516} 517 518void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB, 519 bool t) { 520 OS << "BB#" << MBB->getNumber(); 521} 522 523