1 //===-- BranchFolding.cpp - Fold machine code branch instructions ---------===// 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 // This pass forwards branches to unconditional branches to make them branch 11 // directly to the target block. This pass often results in dead MBB's, which 12 // it then removes. 13 // 14 // Note that this pass must be run after register allocation, it cannot handle 15 // SSA form. 16 // 17 //===----------------------------------------------------------------------===// 18 19 #define DEBUG_TYPE "branchfolding" 20 #include "BranchFolding.h" 21 #include "llvm/Function.h" 22 #include "llvm/CodeGen/Passes.h" 23 #include "llvm/CodeGen/MachineModuleInfo.h" 24 #include "llvm/CodeGen/MachineFunctionPass.h" 25 #include "llvm/CodeGen/MachineJumpTableInfo.h" 26 #include "llvm/CodeGen/MachineRegisterInfo.h" 27 #include "llvm/CodeGen/RegisterScavenging.h" 28 #include "llvm/Target/TargetInstrInfo.h" 29 #include "llvm/Target/TargetMachine.h" 30 #include "llvm/Target/TargetRegisterInfo.h" 31 #include "llvm/Support/CommandLine.h" 32 #include "llvm/Support/Debug.h" 33 #include "llvm/Support/ErrorHandling.h" 34 #include "llvm/Support/raw_ostream.h" 35 #include "llvm/ADT/SmallSet.h" 36 #include "llvm/ADT/SetVector.h" 37 #include "llvm/ADT/Statistic.h" 38 #include "llvm/ADT/STLExtras.h" 39 #include <algorithm> 40 using namespace llvm; 41 42 STATISTIC(NumDeadBlocks, "Number of dead blocks removed"); 43 STATISTIC(NumBranchOpts, "Number of branches optimized"); 44 STATISTIC(NumTailMerge , "Number of block tails merged"); 45 STATISTIC(NumHoist , "Number of times common instructions are hoisted"); 46 47 static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge", 48 cl::init(cl::BOU_UNSET), cl::Hidden); 49 50 // Throttle for huge numbers of predecessors (compile speed problems) 51 static cl::opt<unsigned> 52 TailMergeThreshold("tail-merge-threshold", 53 cl::desc("Max number of predecessors to consider tail merging"), 54 cl::init(150), cl::Hidden); 55 56 // Heuristic for tail merging (and, inversely, tail duplication). 57 // TODO: This should be replaced with a target query. 58 static cl::opt<unsigned> 59 TailMergeSize("tail-merge-size", 60 cl::desc("Min number of instructions to consider tail merging"), 61 cl::init(3), cl::Hidden); 62 63 namespace { 64 /// BranchFolderPass - Wrap branch folder in a machine function pass. 65 class BranchFolderPass : public MachineFunctionPass { 66 public: 67 static char ID; 68 explicit BranchFolderPass(): MachineFunctionPass(ID) {} 69 70 virtual bool runOnMachineFunction(MachineFunction &MF); 71 72 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 73 AU.addRequired<TargetPassConfig>(); 74 MachineFunctionPass::getAnalysisUsage(AU); 75 } 76 }; 77 } 78 79 char BranchFolderPass::ID = 0; 80 char &llvm::BranchFolderPassID = BranchFolderPass::ID; 81 82 INITIALIZE_PASS(BranchFolderPass, "branch-folder", 83 "Control Flow Optimizer", false, false) 84 85 bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) { 86 TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>(); 87 BranchFolder Folder(PassConfig->getEnableTailMerge(), /*CommonHoist=*/true); 88 return Folder.OptimizeFunction(MF, 89 MF.getTarget().getInstrInfo(), 90 MF.getTarget().getRegisterInfo(), 91 getAnalysisIfAvailable<MachineModuleInfo>()); 92 } 93 94 95 BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist) { 96 switch (FlagEnableTailMerge) { 97 case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break; 98 case cl::BOU_TRUE: EnableTailMerge = true; break; 99 case cl::BOU_FALSE: EnableTailMerge = false; break; 100 } 101 102 EnableHoistCommonCode = CommonHoist; 103 } 104 105 /// RemoveDeadBlock - Remove the specified dead machine basic block from the 106 /// function, updating the CFG. 107 void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) { 108 assert(MBB->pred_empty() && "MBB must be dead!"); 109 DEBUG(dbgs() << "\nRemoving MBB: " << *MBB); 110 111 MachineFunction *MF = MBB->getParent(); 112 // drop all successors. 113 while (!MBB->succ_empty()) 114 MBB->removeSuccessor(MBB->succ_end()-1); 115 116 // Avoid matching if this pointer gets reused. 117 TriedMerging.erase(MBB); 118 119 // Remove the block. 120 MF->erase(MBB); 121 } 122 123 /// OptimizeImpDefsBlock - If a basic block is just a bunch of implicit_def 124 /// followed by terminators, and if the implicitly defined registers are not 125 /// used by the terminators, remove those implicit_def's. e.g. 126 /// BB1: 127 /// r0 = implicit_def 128 /// r1 = implicit_def 129 /// br 130 /// This block can be optimized away later if the implicit instructions are 131 /// removed. 132 bool BranchFolder::OptimizeImpDefsBlock(MachineBasicBlock *MBB) { 133 SmallSet<unsigned, 4> ImpDefRegs; 134 MachineBasicBlock::iterator I = MBB->begin(); 135 while (I != MBB->end()) { 136 if (!I->isImplicitDef()) 137 break; 138 unsigned Reg = I->getOperand(0).getReg(); 139 ImpDefRegs.insert(Reg); 140 for (const uint16_t *SubRegs = TRI->getSubRegisters(Reg); 141 unsigned SubReg = *SubRegs; ++SubRegs) 142 ImpDefRegs.insert(SubReg); 143 ++I; 144 } 145 if (ImpDefRegs.empty()) 146 return false; 147 148 MachineBasicBlock::iterator FirstTerm = I; 149 while (I != MBB->end()) { 150 if (!TII->isUnpredicatedTerminator(I)) 151 return false; 152 // See if it uses any of the implicitly defined registers. 153 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 154 MachineOperand &MO = I->getOperand(i); 155 if (!MO.isReg() || !MO.isUse()) 156 continue; 157 unsigned Reg = MO.getReg(); 158 if (ImpDefRegs.count(Reg)) 159 return false; 160 } 161 ++I; 162 } 163 164 I = MBB->begin(); 165 while (I != FirstTerm) { 166 MachineInstr *ImpDefMI = &*I; 167 ++I; 168 MBB->erase(ImpDefMI); 169 } 170 171 return true; 172 } 173 174 /// OptimizeFunction - Perhaps branch folding, tail merging and other 175 /// CFG optimizations on the given function. 176 bool BranchFolder::OptimizeFunction(MachineFunction &MF, 177 const TargetInstrInfo *tii, 178 const TargetRegisterInfo *tri, 179 MachineModuleInfo *mmi) { 180 if (!tii) return false; 181 182 TriedMerging.clear(); 183 184 TII = tii; 185 TRI = tri; 186 MMI = mmi; 187 RS = NULL; 188 189 // Use a RegScavenger to help update liveness when required. 190 MachineRegisterInfo &MRI = MF.getRegInfo(); 191 if (MRI.tracksLiveness() && TRI->requiresRegisterScavenging(MF)) 192 RS = new RegScavenger(); 193 else 194 MRI.invalidateLiveness(); 195 196 // Fix CFG. The later algorithms expect it to be right. 197 bool MadeChange = false; 198 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; I++) { 199 MachineBasicBlock *MBB = I, *TBB = 0, *FBB = 0; 200 SmallVector<MachineOperand, 4> Cond; 201 if (!TII->AnalyzeBranch(*MBB, TBB, FBB, Cond, true)) 202 MadeChange |= MBB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty()); 203 MadeChange |= OptimizeImpDefsBlock(MBB); 204 } 205 206 bool MadeChangeThisIteration = true; 207 while (MadeChangeThisIteration) { 208 MadeChangeThisIteration = TailMergeBlocks(MF); 209 MadeChangeThisIteration |= OptimizeBranches(MF); 210 if (EnableHoistCommonCode) 211 MadeChangeThisIteration |= HoistCommonCode(MF); 212 MadeChange |= MadeChangeThisIteration; 213 } 214 215 // See if any jump tables have become dead as the code generator 216 // did its thing. 217 MachineJumpTableInfo *JTI = MF.getJumpTableInfo(); 218 if (JTI == 0) { 219 delete RS; 220 return MadeChange; 221 } 222 223 // Walk the function to find jump tables that are live. 224 BitVector JTIsLive(JTI->getJumpTables().size()); 225 for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); 226 BB != E; ++BB) { 227 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); 228 I != E; ++I) 229 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) { 230 MachineOperand &Op = I->getOperand(op); 231 if (!Op.isJTI()) continue; 232 233 // Remember that this JT is live. 234 JTIsLive.set(Op.getIndex()); 235 } 236 } 237 238 // Finally, remove dead jump tables. This happens when the 239 // indirect jump was unreachable (and thus deleted). 240 for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i) 241 if (!JTIsLive.test(i)) { 242 JTI->RemoveJumpTable(i); 243 MadeChange = true; 244 } 245 246 delete RS; 247 return MadeChange; 248 } 249 250 //===----------------------------------------------------------------------===// 251 // Tail Merging of Blocks 252 //===----------------------------------------------------------------------===// 253 254 /// HashMachineInstr - Compute a hash value for MI and its operands. 255 static unsigned HashMachineInstr(const MachineInstr *MI) { 256 unsigned Hash = MI->getOpcode(); 257 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { 258 const MachineOperand &Op = MI->getOperand(i); 259 260 // Merge in bits from the operand if easy. 261 unsigned OperandHash = 0; 262 switch (Op.getType()) { 263 case MachineOperand::MO_Register: OperandHash = Op.getReg(); break; 264 case MachineOperand::MO_Immediate: OperandHash = Op.getImm(); break; 265 case MachineOperand::MO_MachineBasicBlock: 266 OperandHash = Op.getMBB()->getNumber(); 267 break; 268 case MachineOperand::MO_FrameIndex: 269 case MachineOperand::MO_ConstantPoolIndex: 270 case MachineOperand::MO_JumpTableIndex: 271 OperandHash = Op.getIndex(); 272 break; 273 case MachineOperand::MO_GlobalAddress: 274 case MachineOperand::MO_ExternalSymbol: 275 // Global address / external symbol are too hard, don't bother, but do 276 // pull in the offset. 277 OperandHash = Op.getOffset(); 278 break; 279 default: break; 280 } 281 282 Hash += ((OperandHash << 3) | Op.getType()) << (i&31); 283 } 284 return Hash; 285 } 286 287 /// HashEndOfMBB - Hash the last instruction in the MBB. 288 static unsigned HashEndOfMBB(const MachineBasicBlock *MBB) { 289 MachineBasicBlock::const_iterator I = MBB->end(); 290 if (I == MBB->begin()) 291 return 0; // Empty MBB. 292 293 --I; 294 // Skip debug info so it will not affect codegen. 295 while (I->isDebugValue()) { 296 if (I==MBB->begin()) 297 return 0; // MBB empty except for debug info. 298 --I; 299 } 300 301 return HashMachineInstr(I); 302 } 303 304 /// ComputeCommonTailLength - Given two machine basic blocks, compute the number 305 /// of instructions they actually have in common together at their end. Return 306 /// iterators for the first shared instruction in each block. 307 static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1, 308 MachineBasicBlock *MBB2, 309 MachineBasicBlock::iterator &I1, 310 MachineBasicBlock::iterator &I2) { 311 I1 = MBB1->end(); 312 I2 = MBB2->end(); 313 314 unsigned TailLen = 0; 315 while (I1 != MBB1->begin() && I2 != MBB2->begin()) { 316 --I1; --I2; 317 // Skip debugging pseudos; necessary to avoid changing the code. 318 while (I1->isDebugValue()) { 319 if (I1==MBB1->begin()) { 320 while (I2->isDebugValue()) { 321 if (I2==MBB2->begin()) 322 // I1==DBG at begin; I2==DBG at begin 323 return TailLen; 324 --I2; 325 } 326 ++I2; 327 // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin 328 return TailLen; 329 } 330 --I1; 331 } 332 // I1==first (untested) non-DBG preceding known match 333 while (I2->isDebugValue()) { 334 if (I2==MBB2->begin()) { 335 ++I1; 336 // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin 337 return TailLen; 338 } 339 --I2; 340 } 341 // I1, I2==first (untested) non-DBGs preceding known match 342 if (!I1->isIdenticalTo(I2) || 343 // FIXME: This check is dubious. It's used to get around a problem where 344 // people incorrectly expect inline asm directives to remain in the same 345 // relative order. This is untenable because normal compiler 346 // optimizations (like this one) may reorder and/or merge these 347 // directives. 348 I1->isInlineAsm()) { 349 ++I1; ++I2; 350 break; 351 } 352 ++TailLen; 353 } 354 // Back past possible debugging pseudos at beginning of block. This matters 355 // when one block differs from the other only by whether debugging pseudos 356 // are present at the beginning. (This way, the various checks later for 357 // I1==MBB1->begin() work as expected.) 358 if (I1 == MBB1->begin() && I2 != MBB2->begin()) { 359 --I2; 360 while (I2->isDebugValue()) { 361 if (I2 == MBB2->begin()) { 362 return TailLen; 363 } 364 --I2; 365 } 366 ++I2; 367 } 368 if (I2 == MBB2->begin() && I1 != MBB1->begin()) { 369 --I1; 370 while (I1->isDebugValue()) { 371 if (I1 == MBB1->begin()) 372 return TailLen; 373 --I1; 374 } 375 ++I1; 376 } 377 return TailLen; 378 } 379 380 void BranchFolder::MaintainLiveIns(MachineBasicBlock *CurMBB, 381 MachineBasicBlock *NewMBB) { 382 if (RS) { 383 RS->enterBasicBlock(CurMBB); 384 if (!CurMBB->empty()) 385 RS->forward(prior(CurMBB->end())); 386 BitVector RegsLiveAtExit(TRI->getNumRegs()); 387 RS->getRegsUsed(RegsLiveAtExit, false); 388 for (unsigned int i = 0, e = TRI->getNumRegs(); i != e; i++) 389 if (RegsLiveAtExit[i]) 390 NewMBB->addLiveIn(i); 391 } 392 } 393 394 /// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything 395 /// after it, replacing it with an unconditional branch to NewDest. 396 void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, 397 MachineBasicBlock *NewDest) { 398 MachineBasicBlock *CurMBB = OldInst->getParent(); 399 400 TII->ReplaceTailWithBranchTo(OldInst, NewDest); 401 402 // For targets that use the register scavenger, we must maintain LiveIns. 403 MaintainLiveIns(CurMBB, NewDest); 404 405 ++NumTailMerge; 406 } 407 408 /// SplitMBBAt - Given a machine basic block and an iterator into it, split the 409 /// MBB so that the part before the iterator falls into the part starting at the 410 /// iterator. This returns the new MBB. 411 MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, 412 MachineBasicBlock::iterator BBI1) { 413 if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1)) 414 return 0; 415 416 MachineFunction &MF = *CurMBB.getParent(); 417 418 // Create the fall-through block. 419 MachineFunction::iterator MBBI = &CurMBB; 420 MachineBasicBlock *NewMBB =MF.CreateMachineBasicBlock(CurMBB.getBasicBlock()); 421 CurMBB.getParent()->insert(++MBBI, NewMBB); 422 423 // Move all the successors of this block to the specified block. 424 NewMBB->transferSuccessors(&CurMBB); 425 426 // Add an edge from CurMBB to NewMBB for the fall-through. 427 CurMBB.addSuccessor(NewMBB); 428 429 // Splice the code over. 430 NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end()); 431 432 // For targets that use the register scavenger, we must maintain LiveIns. 433 MaintainLiveIns(&CurMBB, NewMBB); 434 435 return NewMBB; 436 } 437 438 /// EstimateRuntime - Make a rough estimate for how long it will take to run 439 /// the specified code. 440 static unsigned EstimateRuntime(MachineBasicBlock::iterator I, 441 MachineBasicBlock::iterator E) { 442 unsigned Time = 0; 443 for (; I != E; ++I) { 444 if (I->isDebugValue()) 445 continue; 446 if (I->isCall()) 447 Time += 10; 448 else if (I->mayLoad() || I->mayStore()) 449 Time += 2; 450 else 451 ++Time; 452 } 453 return Time; 454 } 455 456 // CurMBB needs to add an unconditional branch to SuccMBB (we removed these 457 // branches temporarily for tail merging). In the case where CurMBB ends 458 // with a conditional branch to the next block, optimize by reversing the 459 // test and conditionally branching to SuccMBB instead. 460 static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB, 461 const TargetInstrInfo *TII) { 462 MachineFunction *MF = CurMBB->getParent(); 463 MachineFunction::iterator I = llvm::next(MachineFunction::iterator(CurMBB)); 464 MachineBasicBlock *TBB = 0, *FBB = 0; 465 SmallVector<MachineOperand, 4> Cond; 466 DebugLoc dl; // FIXME: this is nowhere 467 if (I != MF->end() && 468 !TII->AnalyzeBranch(*CurMBB, TBB, FBB, Cond, true)) { 469 MachineBasicBlock *NextBB = I; 470 if (TBB == NextBB && !Cond.empty() && !FBB) { 471 if (!TII->ReverseBranchCondition(Cond)) { 472 TII->RemoveBranch(*CurMBB); 473 TII->InsertBranch(*CurMBB, SuccBB, NULL, Cond, dl); 474 return; 475 } 476 } 477 } 478 TII->InsertBranch(*CurMBB, SuccBB, NULL, 479 SmallVector<MachineOperand, 0>(), dl); 480 } 481 482 bool 483 BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const { 484 if (getHash() < o.getHash()) 485 return true; 486 else if (getHash() > o.getHash()) 487 return false; 488 else if (getBlock()->getNumber() < o.getBlock()->getNumber()) 489 return true; 490 else if (getBlock()->getNumber() > o.getBlock()->getNumber()) 491 return false; 492 else { 493 // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing 494 // an object with itself. 495 #ifndef _GLIBCXX_DEBUG 496 llvm_unreachable("Predecessor appears twice"); 497 #else 498 return false; 499 #endif 500 } 501 } 502 503 /// CountTerminators - Count the number of terminators in the given 504 /// block and set I to the position of the first non-terminator, if there 505 /// is one, or MBB->end() otherwise. 506 static unsigned CountTerminators(MachineBasicBlock *MBB, 507 MachineBasicBlock::iterator &I) { 508 I = MBB->end(); 509 unsigned NumTerms = 0; 510 for (;;) { 511 if (I == MBB->begin()) { 512 I = MBB->end(); 513 break; 514 } 515 --I; 516 if (!I->isTerminator()) break; 517 ++NumTerms; 518 } 519 return NumTerms; 520 } 521 522 /// ProfitableToMerge - Check if two machine basic blocks have a common tail 523 /// and decide if it would be profitable to merge those tails. Return the 524 /// length of the common tail and iterators to the first common instruction 525 /// in each block. 526 static bool ProfitableToMerge(MachineBasicBlock *MBB1, 527 MachineBasicBlock *MBB2, 528 unsigned minCommonTailLength, 529 unsigned &CommonTailLen, 530 MachineBasicBlock::iterator &I1, 531 MachineBasicBlock::iterator &I2, 532 MachineBasicBlock *SuccBB, 533 MachineBasicBlock *PredBB) { 534 CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2); 535 if (CommonTailLen == 0) 536 return false; 537 DEBUG(dbgs() << "Common tail length of BB#" << MBB1->getNumber() 538 << " and BB#" << MBB2->getNumber() << " is " << CommonTailLen 539 << '\n'); 540 541 // It's almost always profitable to merge any number of non-terminator 542 // instructions with the block that falls through into the common successor. 543 if (MBB1 == PredBB || MBB2 == PredBB) { 544 MachineBasicBlock::iterator I; 545 unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I); 546 if (CommonTailLen > NumTerms) 547 return true; 548 } 549 550 // If one of the blocks can be completely merged and happens to be in 551 // a position where the other could fall through into it, merge any number 552 // of instructions, because it can be done without a branch. 553 // TODO: If the blocks are not adjacent, move one of them so that they are? 554 if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin()) 555 return true; 556 if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin()) 557 return true; 558 559 // If both blocks have an unconditional branch temporarily stripped out, 560 // count that as an additional common instruction for the following 561 // heuristics. 562 unsigned EffectiveTailLen = CommonTailLen; 563 if (SuccBB && MBB1 != PredBB && MBB2 != PredBB && 564 !MBB1->back().isBarrier() && 565 !MBB2->back().isBarrier()) 566 ++EffectiveTailLen; 567 568 // Check if the common tail is long enough to be worthwhile. 569 if (EffectiveTailLen >= minCommonTailLength) 570 return true; 571 572 // If we are optimizing for code size, 2 instructions in common is enough if 573 // we don't have to split a block. At worst we will be introducing 1 new 574 // branch instruction, which is likely to be smaller than the 2 575 // instructions that would be deleted in the merge. 576 MachineFunction *MF = MBB1->getParent(); 577 if (EffectiveTailLen >= 2 && 578 MF->getFunction()->hasFnAttr(Attribute::OptimizeForSize) && 579 (I1 == MBB1->begin() || I2 == MBB2->begin())) 580 return true; 581 582 return false; 583 } 584 585 /// ComputeSameTails - Look through all the blocks in MergePotentials that have 586 /// hash CurHash (guaranteed to match the last element). Build the vector 587 /// SameTails of all those that have the (same) largest number of instructions 588 /// in common of any pair of these blocks. SameTails entries contain an 589 /// iterator into MergePotentials (from which the MachineBasicBlock can be 590 /// found) and a MachineBasicBlock::iterator into that MBB indicating the 591 /// instruction where the matching code sequence begins. 592 /// Order of elements in SameTails is the reverse of the order in which 593 /// those blocks appear in MergePotentials (where they are not necessarily 594 /// consecutive). 595 unsigned BranchFolder::ComputeSameTails(unsigned CurHash, 596 unsigned minCommonTailLength, 597 MachineBasicBlock *SuccBB, 598 MachineBasicBlock *PredBB) { 599 unsigned maxCommonTailLength = 0U; 600 SameTails.clear(); 601 MachineBasicBlock::iterator TrialBBI1, TrialBBI2; 602 MPIterator HighestMPIter = prior(MergePotentials.end()); 603 for (MPIterator CurMPIter = prior(MergePotentials.end()), 604 B = MergePotentials.begin(); 605 CurMPIter != B && CurMPIter->getHash() == CurHash; 606 --CurMPIter) { 607 for (MPIterator I = prior(CurMPIter); I->getHash() == CurHash ; --I) { 608 unsigned CommonTailLen; 609 if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(), 610 minCommonTailLength, 611 CommonTailLen, TrialBBI1, TrialBBI2, 612 SuccBB, PredBB)) { 613 if (CommonTailLen > maxCommonTailLength) { 614 SameTails.clear(); 615 maxCommonTailLength = CommonTailLen; 616 HighestMPIter = CurMPIter; 617 SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1)); 618 } 619 if (HighestMPIter == CurMPIter && 620 CommonTailLen == maxCommonTailLength) 621 SameTails.push_back(SameTailElt(I, TrialBBI2)); 622 } 623 if (I == B) 624 break; 625 } 626 } 627 return maxCommonTailLength; 628 } 629 630 /// RemoveBlocksWithHash - Remove all blocks with hash CurHash from 631 /// MergePotentials, restoring branches at ends of blocks as appropriate. 632 void BranchFolder::RemoveBlocksWithHash(unsigned CurHash, 633 MachineBasicBlock *SuccBB, 634 MachineBasicBlock *PredBB) { 635 MPIterator CurMPIter, B; 636 for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin(); 637 CurMPIter->getHash() == CurHash; 638 --CurMPIter) { 639 // Put the unconditional branch back, if we need one. 640 MachineBasicBlock *CurMBB = CurMPIter->getBlock(); 641 if (SuccBB && CurMBB != PredBB) 642 FixTail(CurMBB, SuccBB, TII); 643 if (CurMPIter == B) 644 break; 645 } 646 if (CurMPIter->getHash() != CurHash) 647 CurMPIter++; 648 MergePotentials.erase(CurMPIter, MergePotentials.end()); 649 } 650 651 /// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist 652 /// only of the common tail. Create a block that does by splitting one. 653 bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, 654 unsigned maxCommonTailLength, 655 unsigned &commonTailIndex) { 656 commonTailIndex = 0; 657 unsigned TimeEstimate = ~0U; 658 for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { 659 // Use PredBB if possible; that doesn't require a new branch. 660 if (SameTails[i].getBlock() == PredBB) { 661 commonTailIndex = i; 662 break; 663 } 664 // Otherwise, make a (fairly bogus) choice based on estimate of 665 // how long it will take the various blocks to execute. 666 unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(), 667 SameTails[i].getTailStartPos()); 668 if (t <= TimeEstimate) { 669 TimeEstimate = t; 670 commonTailIndex = i; 671 } 672 } 673 674 MachineBasicBlock::iterator BBI = 675 SameTails[commonTailIndex].getTailStartPos(); 676 MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); 677 678 // If the common tail includes any debug info we will take it pretty 679 // randomly from one of the inputs. Might be better to remove it? 680 DEBUG(dbgs() << "\nSplitting BB#" << MBB->getNumber() << ", size " 681 << maxCommonTailLength); 682 683 MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI); 684 if (!newMBB) { 685 DEBUG(dbgs() << "... failed!"); 686 return false; 687 } 688 689 SameTails[commonTailIndex].setBlock(newMBB); 690 SameTails[commonTailIndex].setTailStartPos(newMBB->begin()); 691 692 // If we split PredBB, newMBB is the new predecessor. 693 if (PredBB == MBB) 694 PredBB = newMBB; 695 696 return true; 697 } 698 699 // See if any of the blocks in MergePotentials (which all have a common single 700 // successor, or all have no successor) can be tail-merged. If there is a 701 // successor, any blocks in MergePotentials that are not tail-merged and 702 // are not immediately before Succ must have an unconditional branch to 703 // Succ added (but the predecessor/successor lists need no adjustment). 704 // The lone predecessor of Succ that falls through into Succ, 705 // if any, is given in PredBB. 706 707 bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB, 708 MachineBasicBlock *PredBB) { 709 bool MadeChange = false; 710 711 // Except for the special cases below, tail-merge if there are at least 712 // this many instructions in common. 713 unsigned minCommonTailLength = TailMergeSize; 714 715 DEBUG(dbgs() << "\nTryTailMergeBlocks: "; 716 for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) 717 dbgs() << "BB#" << MergePotentials[i].getBlock()->getNumber() 718 << (i == e-1 ? "" : ", "); 719 dbgs() << "\n"; 720 if (SuccBB) { 721 dbgs() << " with successor BB#" << SuccBB->getNumber() << '\n'; 722 if (PredBB) 723 dbgs() << " which has fall-through from BB#" 724 << PredBB->getNumber() << "\n"; 725 } 726 dbgs() << "Looking for common tails of at least " 727 << minCommonTailLength << " instruction" 728 << (minCommonTailLength == 1 ? "" : "s") << '\n'; 729 ); 730 731 // Sort by hash value so that blocks with identical end sequences sort 732 // together. 733 std::stable_sort(MergePotentials.begin(), MergePotentials.end()); 734 735 // Walk through equivalence sets looking for actual exact matches. 736 while (MergePotentials.size() > 1) { 737 unsigned CurHash = MergePotentials.back().getHash(); 738 739 // Build SameTails, identifying the set of blocks with this hash code 740 // and with the maximum number of instructions in common. 741 unsigned maxCommonTailLength = ComputeSameTails(CurHash, 742 minCommonTailLength, 743 SuccBB, PredBB); 744 745 // If we didn't find any pair that has at least minCommonTailLength 746 // instructions in common, remove all blocks with this hash code and retry. 747 if (SameTails.empty()) { 748 RemoveBlocksWithHash(CurHash, SuccBB, PredBB); 749 continue; 750 } 751 752 // If one of the blocks is the entire common tail (and not the entry 753 // block, which we can't jump to), we can treat all blocks with this same 754 // tail at once. Use PredBB if that is one of the possibilities, as that 755 // will not introduce any extra branches. 756 MachineBasicBlock *EntryBB = MergePotentials.begin()->getBlock()-> 757 getParent()->begin(); 758 unsigned commonTailIndex = SameTails.size(); 759 // If there are two blocks, check to see if one can be made to fall through 760 // into the other. 761 if (SameTails.size() == 2 && 762 SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) && 763 SameTails[1].tailIsWholeBlock()) 764 commonTailIndex = 1; 765 else if (SameTails.size() == 2 && 766 SameTails[1].getBlock()->isLayoutSuccessor( 767 SameTails[0].getBlock()) && 768 SameTails[0].tailIsWholeBlock()) 769 commonTailIndex = 0; 770 else { 771 // Otherwise just pick one, favoring the fall-through predecessor if 772 // there is one. 773 for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { 774 MachineBasicBlock *MBB = SameTails[i].getBlock(); 775 if (MBB == EntryBB && SameTails[i].tailIsWholeBlock()) 776 continue; 777 if (MBB == PredBB) { 778 commonTailIndex = i; 779 break; 780 } 781 if (SameTails[i].tailIsWholeBlock()) 782 commonTailIndex = i; 783 } 784 } 785 786 if (commonTailIndex == SameTails.size() || 787 (SameTails[commonTailIndex].getBlock() == PredBB && 788 !SameTails[commonTailIndex].tailIsWholeBlock())) { 789 // None of the blocks consist entirely of the common tail. 790 // Split a block so that one does. 791 if (!CreateCommonTailOnlyBlock(PredBB, 792 maxCommonTailLength, commonTailIndex)) { 793 RemoveBlocksWithHash(CurHash, SuccBB, PredBB); 794 continue; 795 } 796 } 797 798 MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); 799 // MBB is common tail. Adjust all other BB's to jump to this one. 800 // Traversal must be forwards so erases work. 801 DEBUG(dbgs() << "\nUsing common tail in BB#" << MBB->getNumber() 802 << " for "); 803 for (unsigned int i=0, e = SameTails.size(); i != e; ++i) { 804 if (commonTailIndex == i) 805 continue; 806 DEBUG(dbgs() << "BB#" << SameTails[i].getBlock()->getNumber() 807 << (i == e-1 ? "" : ", ")); 808 // Hack the end off BB i, making it jump to BB commonTailIndex instead. 809 ReplaceTailWithBranchTo(SameTails[i].getTailStartPos(), MBB); 810 // BB i is no longer a predecessor of SuccBB; remove it from the worklist. 811 MergePotentials.erase(SameTails[i].getMPIter()); 812 } 813 DEBUG(dbgs() << "\n"); 814 // We leave commonTailIndex in the worklist in case there are other blocks 815 // that match it with a smaller number of instructions. 816 MadeChange = true; 817 } 818 return MadeChange; 819 } 820 821 bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { 822 823 if (!EnableTailMerge) return false; 824 825 bool MadeChange = false; 826 827 // First find blocks with no successors. 828 MergePotentials.clear(); 829 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); 830 I != E && MergePotentials.size() < TailMergeThreshold; ++I) { 831 if (TriedMerging.count(I)) 832 continue; 833 if (I->succ_empty()) 834 MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I), I)); 835 } 836 837 // If this is a large problem, avoid visiting the same basic blocks 838 // multiple times. 839 if (MergePotentials.size() == TailMergeThreshold) 840 for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) 841 TriedMerging.insert(MergePotentials[i].getBlock()); 842 // See if we can do any tail merging on those. 843 if (MergePotentials.size() >= 2) 844 MadeChange |= TryTailMergeBlocks(NULL, NULL); 845 846 // Look at blocks (IBB) with multiple predecessors (PBB). 847 // We change each predecessor to a canonical form, by 848 // (1) temporarily removing any unconditional branch from the predecessor 849 // to IBB, and 850 // (2) alter conditional branches so they branch to the other block 851 // not IBB; this may require adding back an unconditional branch to IBB 852 // later, where there wasn't one coming in. E.g. 853 // Bcc IBB 854 // fallthrough to QBB 855 // here becomes 856 // Bncc QBB 857 // with a conceptual B to IBB after that, which never actually exists. 858 // With those changes, we see whether the predecessors' tails match, 859 // and merge them if so. We change things out of canonical form and 860 // back to the way they were later in the process. (OptimizeBranches 861 // would undo some of this, but we can't use it, because we'd get into 862 // a compile-time infinite loop repeatedly doing and undoing the same 863 // transformations.) 864 865 for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end(); 866 I != E; ++I) { 867 if (I->pred_size() >= 2) { 868 SmallPtrSet<MachineBasicBlock *, 8> UniquePreds; 869 MachineBasicBlock *IBB = I; 870 MachineBasicBlock *PredBB = prior(I); 871 MergePotentials.clear(); 872 for (MachineBasicBlock::pred_iterator P = I->pred_begin(), 873 E2 = I->pred_end(); 874 P != E2 && MergePotentials.size() < TailMergeThreshold; ++P) { 875 MachineBasicBlock *PBB = *P; 876 if (TriedMerging.count(PBB)) 877 continue; 878 // Skip blocks that loop to themselves, can't tail merge these. 879 if (PBB == IBB) 880 continue; 881 // Visit each predecessor only once. 882 if (!UniquePreds.insert(PBB)) 883 continue; 884 // Skip blocks which may jump to a landing pad. Can't tail merge these. 885 if (PBB->getLandingPadSuccessor()) 886 continue; 887 MachineBasicBlock *TBB = 0, *FBB = 0; 888 SmallVector<MachineOperand, 4> Cond; 889 if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond, true)) { 890 // Failing case: IBB is the target of a cbr, and 891 // we cannot reverse the branch. 892 SmallVector<MachineOperand, 4> NewCond(Cond); 893 if (!Cond.empty() && TBB == IBB) { 894 if (TII->ReverseBranchCondition(NewCond)) 895 continue; 896 // This is the QBB case described above 897 if (!FBB) 898 FBB = llvm::next(MachineFunction::iterator(PBB)); 899 } 900 // Failing case: the only way IBB can be reached from PBB is via 901 // exception handling. Happens for landing pads. Would be nice 902 // to have a bit in the edge so we didn't have to do all this. 903 if (IBB->isLandingPad()) { 904 MachineFunction::iterator IP = PBB; IP++; 905 MachineBasicBlock *PredNextBB = NULL; 906 if (IP != MF.end()) 907 PredNextBB = IP; 908 if (TBB == NULL) { 909 if (IBB != PredNextBB) // fallthrough 910 continue; 911 } else if (FBB) { 912 if (TBB != IBB && FBB != IBB) // cbr then ubr 913 continue; 914 } else if (Cond.empty()) { 915 if (TBB != IBB) // ubr 916 continue; 917 } else { 918 if (TBB != IBB && IBB != PredNextBB) // cbr 919 continue; 920 } 921 } 922 // Remove the unconditional branch at the end, if any. 923 if (TBB && (Cond.empty() || FBB)) { 924 DebugLoc dl; // FIXME: this is nowhere 925 TII->RemoveBranch(*PBB); 926 if (!Cond.empty()) 927 // reinsert conditional branch only, for now 928 TII->InsertBranch(*PBB, (TBB == IBB) ? FBB : TBB, 0, NewCond, dl); 929 } 930 MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB), *P)); 931 } 932 } 933 // If this is a large problem, avoid visiting the same basic blocks 934 // multiple times. 935 if (MergePotentials.size() == TailMergeThreshold) 936 for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) 937 TriedMerging.insert(MergePotentials[i].getBlock()); 938 if (MergePotentials.size() >= 2) 939 MadeChange |= TryTailMergeBlocks(IBB, PredBB); 940 // Reinsert an unconditional branch if needed. 941 // The 1 below can occur as a result of removing blocks in 942 // TryTailMergeBlocks. 943 PredBB = prior(I); // this may have been changed in TryTailMergeBlocks 944 if (MergePotentials.size() == 1 && 945 MergePotentials.begin()->getBlock() != PredBB) 946 FixTail(MergePotentials.begin()->getBlock(), IBB, TII); 947 } 948 } 949 return MadeChange; 950 } 951 952 //===----------------------------------------------------------------------===// 953 // Branch Optimization 954 //===----------------------------------------------------------------------===// 955 956 bool BranchFolder::OptimizeBranches(MachineFunction &MF) { 957 bool MadeChange = false; 958 959 // Make sure blocks are numbered in order 960 MF.RenumberBlocks(); 961 962 for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end(); 963 I != E; ) { 964 MachineBasicBlock *MBB = I++; 965 MadeChange |= OptimizeBlock(MBB); 966 967 // If it is dead, remove it. 968 if (MBB->pred_empty()) { 969 RemoveDeadBlock(MBB); 970 MadeChange = true; 971 ++NumDeadBlocks; 972 } 973 } 974 return MadeChange; 975 } 976 977 // Blocks should be considered empty if they contain only debug info; 978 // else the debug info would affect codegen. 979 static bool IsEmptyBlock(MachineBasicBlock *MBB) { 980 if (MBB->empty()) 981 return true; 982 for (MachineBasicBlock::iterator MBBI = MBB->begin(), MBBE = MBB->end(); 983 MBBI!=MBBE; ++MBBI) { 984 if (!MBBI->isDebugValue()) 985 return false; 986 } 987 return true; 988 } 989 990 // Blocks with only debug info and branches should be considered the same 991 // as blocks with only branches. 992 static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) { 993 MachineBasicBlock::iterator MBBI, MBBE; 994 for (MBBI = MBB->begin(), MBBE = MBB->end(); MBBI!=MBBE; ++MBBI) { 995 if (!MBBI->isDebugValue()) 996 break; 997 } 998 return (MBBI->isBranch()); 999 } 1000 1001 /// IsBetterFallthrough - Return true if it would be clearly better to 1002 /// fall-through to MBB1 than to fall through into MBB2. This has to return 1003 /// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will 1004 /// result in infinite loops. 1005 static bool IsBetterFallthrough(MachineBasicBlock *MBB1, 1006 MachineBasicBlock *MBB2) { 1007 // Right now, we use a simple heuristic. If MBB2 ends with a call, and 1008 // MBB1 doesn't, we prefer to fall through into MBB1. This allows us to 1009 // optimize branches that branch to either a return block or an assert block 1010 // into a fallthrough to the return. 1011 if (IsEmptyBlock(MBB1) || IsEmptyBlock(MBB2)) return false; 1012 1013 // If there is a clear successor ordering we make sure that one block 1014 // will fall through to the next 1015 if (MBB1->isSuccessor(MBB2)) return true; 1016 if (MBB2->isSuccessor(MBB1)) return false; 1017 1018 // Neither block consists entirely of debug info (per IsEmptyBlock check), 1019 // so we needn't test for falling off the beginning here. 1020 MachineBasicBlock::iterator MBB1I = --MBB1->end(); 1021 while (MBB1I->isDebugValue()) 1022 --MBB1I; 1023 MachineBasicBlock::iterator MBB2I = --MBB2->end(); 1024 while (MBB2I->isDebugValue()) 1025 --MBB2I; 1026 return MBB2I->isCall() && !MBB1I->isCall(); 1027 } 1028 1029 /// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch 1030 /// instructions on the block. Always use the DebugLoc of the first 1031 /// branching instruction found unless its absent, in which case use the 1032 /// DebugLoc of the second if present. 1033 static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) { 1034 MachineBasicBlock::iterator I = MBB.end(); 1035 if (I == MBB.begin()) 1036 return DebugLoc(); 1037 --I; 1038 while (I->isDebugValue() && I != MBB.begin()) 1039 --I; 1040 if (I->isBranch()) 1041 return I->getDebugLoc(); 1042 return DebugLoc(); 1043 } 1044 1045 /// OptimizeBlock - Analyze and optimize control flow related to the specified 1046 /// block. This is never called on the entry block. 1047 bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { 1048 bool MadeChange = false; 1049 MachineFunction &MF = *MBB->getParent(); 1050 ReoptimizeBlock: 1051 1052 MachineFunction::iterator FallThrough = MBB; 1053 ++FallThrough; 1054 1055 // If this block is empty, make everyone use its fall-through, not the block 1056 // explicitly. Landing pads should not do this since the landing-pad table 1057 // points to this block. Blocks with their addresses taken shouldn't be 1058 // optimized away. 1059 if (IsEmptyBlock(MBB) && !MBB->isLandingPad() && !MBB->hasAddressTaken()) { 1060 // Dead block? Leave for cleanup later. 1061 if (MBB->pred_empty()) return MadeChange; 1062 1063 if (FallThrough == MF.end()) { 1064 // TODO: Simplify preds to not branch here if possible! 1065 } else { 1066 // Rewrite all predecessors of the old block to go to the fallthrough 1067 // instead. 1068 while (!MBB->pred_empty()) { 1069 MachineBasicBlock *Pred = *(MBB->pred_end()-1); 1070 Pred->ReplaceUsesOfBlockWith(MBB, FallThrough); 1071 } 1072 // If MBB was the target of a jump table, update jump tables to go to the 1073 // fallthrough instead. 1074 if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo()) 1075 MJTI->ReplaceMBBInJumpTables(MBB, FallThrough); 1076 MadeChange = true; 1077 } 1078 return MadeChange; 1079 } 1080 1081 // Check to see if we can simplify the terminator of the block before this 1082 // one. 1083 MachineBasicBlock &PrevBB = *prior(MachineFunction::iterator(MBB)); 1084 1085 MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0; 1086 SmallVector<MachineOperand, 4> PriorCond; 1087 bool PriorUnAnalyzable = 1088 TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true); 1089 if (!PriorUnAnalyzable) { 1090 // If the CFG for the prior block has extra edges, remove them. 1091 MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB, 1092 !PriorCond.empty()); 1093 1094 // If the previous branch is conditional and both conditions go to the same 1095 // destination, remove the branch, replacing it with an unconditional one or 1096 // a fall-through. 1097 if (PriorTBB && PriorTBB == PriorFBB) { 1098 DebugLoc dl = getBranchDebugLoc(PrevBB); 1099 TII->RemoveBranch(PrevBB); 1100 PriorCond.clear(); 1101 if (PriorTBB != MBB) 1102 TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond, dl); 1103 MadeChange = true; 1104 ++NumBranchOpts; 1105 goto ReoptimizeBlock; 1106 } 1107 1108 // If the previous block unconditionally falls through to this block and 1109 // this block has no other predecessors, move the contents of this block 1110 // into the prior block. This doesn't usually happen when SimplifyCFG 1111 // has been used, but it can happen if tail merging splits a fall-through 1112 // predecessor of a block. 1113 // This has to check PrevBB->succ_size() because EH edges are ignored by 1114 // AnalyzeBranch. 1115 if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 && 1116 PrevBB.succ_size() == 1 && 1117 !MBB->hasAddressTaken() && !MBB->isLandingPad()) { 1118 DEBUG(dbgs() << "\nMerging into block: " << PrevBB 1119 << "From MBB: " << *MBB); 1120 // Remove redundant DBG_VALUEs first. 1121 if (PrevBB.begin() != PrevBB.end()) { 1122 MachineBasicBlock::iterator PrevBBIter = PrevBB.end(); 1123 --PrevBBIter; 1124 MachineBasicBlock::iterator MBBIter = MBB->begin(); 1125 // Check if DBG_VALUE at the end of PrevBB is identical to the 1126 // DBG_VALUE at the beginning of MBB. 1127 while (PrevBBIter != PrevBB.begin() && MBBIter != MBB->end() 1128 && PrevBBIter->isDebugValue() && MBBIter->isDebugValue()) { 1129 if (!MBBIter->isIdenticalTo(PrevBBIter)) 1130 break; 1131 MachineInstr *DuplicateDbg = MBBIter; 1132 ++MBBIter; -- PrevBBIter; 1133 DuplicateDbg->eraseFromParent(); 1134 } 1135 } 1136 PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end()); 1137 PrevBB.removeSuccessor(PrevBB.succ_begin()); 1138 assert(PrevBB.succ_empty()); 1139 PrevBB.transferSuccessors(MBB); 1140 MadeChange = true; 1141 return MadeChange; 1142 } 1143 1144 // If the previous branch *only* branches to *this* block (conditional or 1145 // not) remove the branch. 1146 if (PriorTBB == MBB && PriorFBB == 0) { 1147 TII->RemoveBranch(PrevBB); 1148 MadeChange = true; 1149 ++NumBranchOpts; 1150 goto ReoptimizeBlock; 1151 } 1152 1153 // If the prior block branches somewhere else on the condition and here if 1154 // the condition is false, remove the uncond second branch. 1155 if (PriorFBB == MBB) { 1156 DebugLoc dl = getBranchDebugLoc(PrevBB); 1157 TII->RemoveBranch(PrevBB); 1158 TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond, dl); 1159 MadeChange = true; 1160 ++NumBranchOpts; 1161 goto ReoptimizeBlock; 1162 } 1163 1164 // If the prior block branches here on true and somewhere else on false, and 1165 // if the branch condition is reversible, reverse the branch to create a 1166 // fall-through. 1167 if (PriorTBB == MBB) { 1168 SmallVector<MachineOperand, 4> NewPriorCond(PriorCond); 1169 if (!TII->ReverseBranchCondition(NewPriorCond)) { 1170 DebugLoc dl = getBranchDebugLoc(PrevBB); 1171 TII->RemoveBranch(PrevBB); 1172 TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond, dl); 1173 MadeChange = true; 1174 ++NumBranchOpts; 1175 goto ReoptimizeBlock; 1176 } 1177 } 1178 1179 // If this block has no successors (e.g. it is a return block or ends with 1180 // a call to a no-return function like abort or __cxa_throw) and if the pred 1181 // falls through into this block, and if it would otherwise fall through 1182 // into the block after this, move this block to the end of the function. 1183 // 1184 // We consider it more likely that execution will stay in the function (e.g. 1185 // due to loops) than it is to exit it. This asserts in loops etc, moving 1186 // the assert condition out of the loop body. 1187 if (MBB->succ_empty() && !PriorCond.empty() && PriorFBB == 0 && 1188 MachineFunction::iterator(PriorTBB) == FallThrough && 1189 !MBB->canFallThrough()) { 1190 bool DoTransform = true; 1191 1192 // We have to be careful that the succs of PredBB aren't both no-successor 1193 // blocks. If neither have successors and if PredBB is the second from 1194 // last block in the function, we'd just keep swapping the two blocks for 1195 // last. Only do the swap if one is clearly better to fall through than 1196 // the other. 1197 if (FallThrough == --MF.end() && 1198 !IsBetterFallthrough(PriorTBB, MBB)) 1199 DoTransform = false; 1200 1201 if (DoTransform) { 1202 // Reverse the branch so we will fall through on the previous true cond. 1203 SmallVector<MachineOperand, 4> NewPriorCond(PriorCond); 1204 if (!TII->ReverseBranchCondition(NewPriorCond)) { 1205 DEBUG(dbgs() << "\nMoving MBB: " << *MBB 1206 << "To make fallthrough to: " << *PriorTBB << "\n"); 1207 1208 DebugLoc dl = getBranchDebugLoc(PrevBB); 1209 TII->RemoveBranch(PrevBB); 1210 TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond, dl); 1211 1212 // Move this block to the end of the function. 1213 MBB->moveAfter(--MF.end()); 1214 MadeChange = true; 1215 ++NumBranchOpts; 1216 return MadeChange; 1217 } 1218 } 1219 } 1220 } 1221 1222 // Analyze the branch in the current block. 1223 MachineBasicBlock *CurTBB = 0, *CurFBB = 0; 1224 SmallVector<MachineOperand, 4> CurCond; 1225 bool CurUnAnalyzable= TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true); 1226 if (!CurUnAnalyzable) { 1227 // If the CFG for the prior block has extra edges, remove them. 1228 MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty()); 1229 1230 // If this is a two-way branch, and the FBB branches to this block, reverse 1231 // the condition so the single-basic-block loop is faster. Instead of: 1232 // Loop: xxx; jcc Out; jmp Loop 1233 // we want: 1234 // Loop: xxx; jncc Loop; jmp Out 1235 if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) { 1236 SmallVector<MachineOperand, 4> NewCond(CurCond); 1237 if (!TII->ReverseBranchCondition(NewCond)) { 1238 DebugLoc dl = getBranchDebugLoc(*MBB); 1239 TII->RemoveBranch(*MBB); 1240 TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond, dl); 1241 MadeChange = true; 1242 ++NumBranchOpts; 1243 goto ReoptimizeBlock; 1244 } 1245 } 1246 1247 // If this branch is the only thing in its block, see if we can forward 1248 // other blocks across it. 1249 if (CurTBB && CurCond.empty() && CurFBB == 0 && 1250 IsBranchOnlyBlock(MBB) && CurTBB != MBB && 1251 !MBB->hasAddressTaken()) { 1252 DebugLoc dl = getBranchDebugLoc(*MBB); 1253 // This block may contain just an unconditional branch. Because there can 1254 // be 'non-branch terminators' in the block, try removing the branch and 1255 // then seeing if the block is empty. 1256 TII->RemoveBranch(*MBB); 1257 // If the only things remaining in the block are debug info, remove these 1258 // as well, so this will behave the same as an empty block in non-debug 1259 // mode. 1260 if (!MBB->empty()) { 1261 bool NonDebugInfoFound = false; 1262 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); 1263 I != E; ++I) { 1264 if (!I->isDebugValue()) { 1265 NonDebugInfoFound = true; 1266 break; 1267 } 1268 } 1269 if (!NonDebugInfoFound) 1270 // Make the block empty, losing the debug info (we could probably 1271 // improve this in some cases.) 1272 MBB->erase(MBB->begin(), MBB->end()); 1273 } 1274 // If this block is just an unconditional branch to CurTBB, we can 1275 // usually completely eliminate the block. The only case we cannot 1276 // completely eliminate the block is when the block before this one 1277 // falls through into MBB and we can't understand the prior block's branch 1278 // condition. 1279 if (MBB->empty()) { 1280 bool PredHasNoFallThrough = !PrevBB.canFallThrough(); 1281 if (PredHasNoFallThrough || !PriorUnAnalyzable || 1282 !PrevBB.isSuccessor(MBB)) { 1283 // If the prior block falls through into us, turn it into an 1284 // explicit branch to us to make updates simpler. 1285 if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) && 1286 PriorTBB != MBB && PriorFBB != MBB) { 1287 if (PriorTBB == 0) { 1288 assert(PriorCond.empty() && PriorFBB == 0 && 1289 "Bad branch analysis"); 1290 PriorTBB = MBB; 1291 } else { 1292 assert(PriorFBB == 0 && "Machine CFG out of date!"); 1293 PriorFBB = MBB; 1294 } 1295 DebugLoc pdl = getBranchDebugLoc(PrevBB); 1296 TII->RemoveBranch(PrevBB); 1297 TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl); 1298 } 1299 1300 // Iterate through all the predecessors, revectoring each in-turn. 1301 size_t PI = 0; 1302 bool DidChange = false; 1303 bool HasBranchToSelf = false; 1304 while(PI != MBB->pred_size()) { 1305 MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI); 1306 if (PMBB == MBB) { 1307 // If this block has an uncond branch to itself, leave it. 1308 ++PI; 1309 HasBranchToSelf = true; 1310 } else { 1311 DidChange = true; 1312 PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB); 1313 // If this change resulted in PMBB ending in a conditional 1314 // branch where both conditions go to the same destination, 1315 // change this to an unconditional branch (and fix the CFG). 1316 MachineBasicBlock *NewCurTBB = 0, *NewCurFBB = 0; 1317 SmallVector<MachineOperand, 4> NewCurCond; 1318 bool NewCurUnAnalyzable = TII->AnalyzeBranch(*PMBB, NewCurTBB, 1319 NewCurFBB, NewCurCond, true); 1320 if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) { 1321 DebugLoc pdl = getBranchDebugLoc(*PMBB); 1322 TII->RemoveBranch(*PMBB); 1323 NewCurCond.clear(); 1324 TII->InsertBranch(*PMBB, NewCurTBB, 0, NewCurCond, pdl); 1325 MadeChange = true; 1326 ++NumBranchOpts; 1327 PMBB->CorrectExtraCFGEdges(NewCurTBB, 0, false); 1328 } 1329 } 1330 } 1331 1332 // Change any jumptables to go to the new MBB. 1333 if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo()) 1334 MJTI->ReplaceMBBInJumpTables(MBB, CurTBB); 1335 if (DidChange) { 1336 ++NumBranchOpts; 1337 MadeChange = true; 1338 if (!HasBranchToSelf) return MadeChange; 1339 } 1340 } 1341 } 1342 1343 // Add the branch back if the block is more than just an uncond branch. 1344 TII->InsertBranch(*MBB, CurTBB, 0, CurCond, dl); 1345 } 1346 } 1347 1348 // If the prior block doesn't fall through into this block, and if this 1349 // block doesn't fall through into some other block, see if we can find a 1350 // place to move this block where a fall-through will happen. 1351 if (!PrevBB.canFallThrough()) { 1352 1353 // Now we know that there was no fall-through into this block, check to 1354 // see if it has a fall-through into its successor. 1355 bool CurFallsThru = MBB->canFallThrough(); 1356 1357 if (!MBB->isLandingPad()) { 1358 // Check all the predecessors of this block. If one of them has no fall 1359 // throughs, move this block right after it. 1360 for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(), 1361 E = MBB->pred_end(); PI != E; ++PI) { 1362 // Analyze the branch at the end of the pred. 1363 MachineBasicBlock *PredBB = *PI; 1364 MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough; 1365 MachineBasicBlock *PredTBB = 0, *PredFBB = 0; 1366 SmallVector<MachineOperand, 4> PredCond; 1367 if (PredBB != MBB && !PredBB->canFallThrough() && 1368 !TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) 1369 && (!CurFallsThru || !CurTBB || !CurFBB) 1370 && (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) { 1371 // If the current block doesn't fall through, just move it. 1372 // If the current block can fall through and does not end with a 1373 // conditional branch, we need to append an unconditional jump to 1374 // the (current) next block. To avoid a possible compile-time 1375 // infinite loop, move blocks only backward in this case. 1376 // Also, if there are already 2 branches here, we cannot add a third; 1377 // this means we have the case 1378 // Bcc next 1379 // B elsewhere 1380 // next: 1381 if (CurFallsThru) { 1382 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB)); 1383 CurCond.clear(); 1384 TII->InsertBranch(*MBB, NextBB, 0, CurCond, DebugLoc()); 1385 } 1386 MBB->moveAfter(PredBB); 1387 MadeChange = true; 1388 goto ReoptimizeBlock; 1389 } 1390 } 1391 } 1392 1393 if (!CurFallsThru) { 1394 // Check all successors to see if we can move this block before it. 1395 for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(), 1396 E = MBB->succ_end(); SI != E; ++SI) { 1397 // Analyze the branch at the end of the block before the succ. 1398 MachineBasicBlock *SuccBB = *SI; 1399 MachineFunction::iterator SuccPrev = SuccBB; --SuccPrev; 1400 1401 // If this block doesn't already fall-through to that successor, and if 1402 // the succ doesn't already have a block that can fall through into it, 1403 // and if the successor isn't an EH destination, we can arrange for the 1404 // fallthrough to happen. 1405 if (SuccBB != MBB && &*SuccPrev != MBB && 1406 !SuccPrev->canFallThrough() && !CurUnAnalyzable && 1407 !SuccBB->isLandingPad()) { 1408 MBB->moveBefore(SuccBB); 1409 MadeChange = true; 1410 goto ReoptimizeBlock; 1411 } 1412 } 1413 1414 // Okay, there is no really great place to put this block. If, however, 1415 // the block before this one would be a fall-through if this block were 1416 // removed, move this block to the end of the function. 1417 MachineBasicBlock *PrevTBB = 0, *PrevFBB = 0; 1418 SmallVector<MachineOperand, 4> PrevCond; 1419 if (FallThrough != MF.end() && 1420 !TII->AnalyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) && 1421 PrevBB.isSuccessor(FallThrough)) { 1422 MBB->moveAfter(--MF.end()); 1423 MadeChange = true; 1424 return MadeChange; 1425 } 1426 } 1427 } 1428 1429 return MadeChange; 1430 } 1431 1432 //===----------------------------------------------------------------------===// 1433 // Hoist Common Code 1434 //===----------------------------------------------------------------------===// 1435 1436 /// HoistCommonCode - Hoist common instruction sequences at the start of basic 1437 /// blocks to their common predecessor. 1438 bool BranchFolder::HoistCommonCode(MachineFunction &MF) { 1439 bool MadeChange = false; 1440 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) { 1441 MachineBasicBlock *MBB = I++; 1442 MadeChange |= HoistCommonCodeInSuccs(MBB); 1443 } 1444 1445 return MadeChange; 1446 } 1447 1448 /// findFalseBlock - BB has a fallthrough. Find its 'false' successor given 1449 /// its 'true' successor. 1450 static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, 1451 MachineBasicBlock *TrueBB) { 1452 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), 1453 E = BB->succ_end(); SI != E; ++SI) { 1454 MachineBasicBlock *SuccBB = *SI; 1455 if (SuccBB != TrueBB) 1456 return SuccBB; 1457 } 1458 return NULL; 1459 } 1460 1461 /// findHoistingInsertPosAndDeps - Find the location to move common instructions 1462 /// in successors to. The location is ususally just before the terminator, 1463 /// however if the terminator is a conditional branch and its previous 1464 /// instruction is the flag setting instruction, the previous instruction is 1465 /// the preferred location. This function also gathers uses and defs of the 1466 /// instructions from the insertion point to the end of the block. The data is 1467 /// used by HoistCommonCodeInSuccs to ensure safety. 1468 static 1469 MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB, 1470 const TargetInstrInfo *TII, 1471 const TargetRegisterInfo *TRI, 1472 SmallSet<unsigned,4> &Uses, 1473 SmallSet<unsigned,4> &Defs) { 1474 MachineBasicBlock::iterator Loc = MBB->getFirstTerminator(); 1475 if (!TII->isUnpredicatedTerminator(Loc)) 1476 return MBB->end(); 1477 1478 for (unsigned i = 0, e = Loc->getNumOperands(); i != e; ++i) { 1479 const MachineOperand &MO = Loc->getOperand(i); 1480 if (!MO.isReg()) 1481 continue; 1482 unsigned Reg = MO.getReg(); 1483 if (!Reg) 1484 continue; 1485 if (MO.isUse()) { 1486 Uses.insert(Reg); 1487 for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) 1488 Uses.insert(*AS); 1489 } else if (!MO.isDead()) 1490 // Don't try to hoist code in the rare case the terminator defines a 1491 // register that is later used. 1492 return MBB->end(); 1493 } 1494 1495 if (Uses.empty()) 1496 return Loc; 1497 if (Loc == MBB->begin()) 1498 return MBB->end(); 1499 1500 // The terminator is probably a conditional branch, try not to separate the 1501 // branch from condition setting instruction. 1502 MachineBasicBlock::iterator PI = Loc; 1503 --PI; 1504 while (PI != MBB->begin() && Loc->isDebugValue()) 1505 --PI; 1506 1507 bool IsDef = false; 1508 for (unsigned i = 0, e = PI->getNumOperands(); !IsDef && i != e; ++i) { 1509 const MachineOperand &MO = PI->getOperand(i); 1510 // If PI has a regmask operand, it is probably a call. Separate away. 1511 if (MO.isRegMask()) 1512 return Loc; 1513 if (!MO.isReg() || MO.isUse()) 1514 continue; 1515 unsigned Reg = MO.getReg(); 1516 if (!Reg) 1517 continue; 1518 if (Uses.count(Reg)) 1519 IsDef = true; 1520 } 1521 if (!IsDef) 1522 // The condition setting instruction is not just before the conditional 1523 // branch. 1524 return Loc; 1525 1526 // Be conservative, don't insert instruction above something that may have 1527 // side-effects. And since it's potentially bad to separate flag setting 1528 // instruction from the conditional branch, just abort the optimization 1529 // completely. 1530 // Also avoid moving code above predicated instruction since it's hard to 1531 // reason about register liveness with predicated instruction. 1532 bool DontMoveAcrossStore = true; 1533 if (!PI->isSafeToMove(TII, 0, DontMoveAcrossStore) || 1534 TII->isPredicated(PI)) 1535 return MBB->end(); 1536 1537 1538 // Find out what registers are live. Note this routine is ignoring other live 1539 // registers which are only used by instructions in successor blocks. 1540 for (unsigned i = 0, e = PI->getNumOperands(); i != e; ++i) { 1541 const MachineOperand &MO = PI->getOperand(i); 1542 if (!MO.isReg()) 1543 continue; 1544 unsigned Reg = MO.getReg(); 1545 if (!Reg) 1546 continue; 1547 if (MO.isUse()) { 1548 Uses.insert(Reg); 1549 for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) 1550 Uses.insert(*AS); 1551 } else { 1552 if (Uses.count(Reg)) { 1553 Uses.erase(Reg); 1554 for (const uint16_t *SR = TRI->getSubRegisters(Reg); *SR; ++SR) 1555 Uses.erase(*SR); // Use getSubRegisters to be conservative 1556 } 1557 Defs.insert(Reg); 1558 for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) 1559 Defs.insert(*AS); 1560 } 1561 } 1562 1563 return PI; 1564 } 1565 1566 /// HoistCommonCodeInSuccs - If the successors of MBB has common instruction 1567 /// sequence at the start of the function, move the instructions before MBB 1568 /// terminator if it's legal. 1569 bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) { 1570 MachineBasicBlock *TBB = 0, *FBB = 0; 1571 SmallVector<MachineOperand, 4> Cond; 1572 if (TII->AnalyzeBranch(*MBB, TBB, FBB, Cond, true) || !TBB || Cond.empty()) 1573 return false; 1574 1575 if (!FBB) FBB = findFalseBlock(MBB, TBB); 1576 if (!FBB) 1577 // Malformed bcc? True and false blocks are the same? 1578 return false; 1579 1580 // Restrict the optimization to cases where MBB is the only predecessor, 1581 // it is an obvious win. 1582 if (TBB->pred_size() > 1 || FBB->pred_size() > 1) 1583 return false; 1584 1585 // Find a suitable position to hoist the common instructions to. Also figure 1586 // out which registers are used or defined by instructions from the insertion 1587 // point to the end of the block. 1588 SmallSet<unsigned, 4> Uses, Defs; 1589 MachineBasicBlock::iterator Loc = 1590 findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs); 1591 if (Loc == MBB->end()) 1592 return false; 1593 1594 bool HasDups = false; 1595 SmallVector<unsigned, 4> LocalDefs; 1596 SmallSet<unsigned, 4> LocalDefsSet; 1597 MachineBasicBlock::iterator TIB = TBB->begin(); 1598 MachineBasicBlock::iterator FIB = FBB->begin(); 1599 MachineBasicBlock::iterator TIE = TBB->end(); 1600 MachineBasicBlock::iterator FIE = FBB->end(); 1601 while (TIB != TIE && FIB != FIE) { 1602 // Skip dbg_value instructions. These do not count. 1603 if (TIB->isDebugValue()) { 1604 while (TIB != TIE && TIB->isDebugValue()) 1605 ++TIB; 1606 if (TIB == TIE) 1607 break; 1608 } 1609 if (FIB->isDebugValue()) { 1610 while (FIB != FIE && FIB->isDebugValue()) 1611 ++FIB; 1612 if (FIB == FIE) 1613 break; 1614 } 1615 if (!TIB->isIdenticalTo(FIB, MachineInstr::CheckKillDead)) 1616 break; 1617 1618 if (TII->isPredicated(TIB)) 1619 // Hard to reason about register liveness with predicated instruction. 1620 break; 1621 1622 bool IsSafe = true; 1623 for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) { 1624 MachineOperand &MO = TIB->getOperand(i); 1625 // Don't attempt to hoist instructions with register masks. 1626 if (MO.isRegMask()) { 1627 IsSafe = false; 1628 break; 1629 } 1630 if (!MO.isReg()) 1631 continue; 1632 unsigned Reg = MO.getReg(); 1633 if (!Reg) 1634 continue; 1635 if (MO.isDef()) { 1636 if (Uses.count(Reg)) { 1637 // Avoid clobbering a register that's used by the instruction at 1638 // the point of insertion. 1639 IsSafe = false; 1640 break; 1641 } 1642 1643 if (Defs.count(Reg) && !MO.isDead()) { 1644 // Don't hoist the instruction if the def would be clobber by the 1645 // instruction at the point insertion. FIXME: This is overly 1646 // conservative. It should be possible to hoist the instructions 1647 // in BB2 in the following example: 1648 // BB1: 1649 // r1, eflag = op1 r2, r3 1650 // brcc eflag 1651 // 1652 // BB2: 1653 // r1 = op2, ... 1654 // = op3, r1<kill> 1655 IsSafe = false; 1656 break; 1657 } 1658 } else if (!LocalDefsSet.count(Reg)) { 1659 if (Defs.count(Reg)) { 1660 // Use is defined by the instruction at the point of insertion. 1661 IsSafe = false; 1662 break; 1663 } 1664 1665 if (MO.isKill() && Uses.count(Reg)) 1666 // Kills a register that's read by the instruction at the point of 1667 // insertion. Remove the kill marker. 1668 MO.setIsKill(false); 1669 } 1670 } 1671 if (!IsSafe) 1672 break; 1673 1674 bool DontMoveAcrossStore = true; 1675 if (!TIB->isSafeToMove(TII, 0, DontMoveAcrossStore)) 1676 break; 1677 1678 // Remove kills from LocalDefsSet, these registers had short live ranges. 1679 for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) { 1680 MachineOperand &MO = TIB->getOperand(i); 1681 if (!MO.isReg() || !MO.isUse() || !MO.isKill()) 1682 continue; 1683 unsigned Reg = MO.getReg(); 1684 if (!Reg || !LocalDefsSet.count(Reg)) 1685 continue; 1686 for (const uint16_t *OR = TRI->getOverlaps(Reg); *OR; ++OR) 1687 LocalDefsSet.erase(*OR); 1688 } 1689 1690 // Track local defs so we can update liveins. 1691 for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) { 1692 MachineOperand &MO = TIB->getOperand(i); 1693 if (!MO.isReg() || !MO.isDef() || MO.isDead()) 1694 continue; 1695 unsigned Reg = MO.getReg(); 1696 if (!Reg) 1697 continue; 1698 LocalDefs.push_back(Reg); 1699 for (const uint16_t *OR = TRI->getOverlaps(Reg); *OR; ++OR) 1700 LocalDefsSet.insert(*OR); 1701 } 1702 1703 HasDups = true; 1704 ++TIB; 1705 ++FIB; 1706 } 1707 1708 if (!HasDups) 1709 return false; 1710 1711 MBB->splice(Loc, TBB, TBB->begin(), TIB); 1712 FBB->erase(FBB->begin(), FIB); 1713 1714 // Update livein's. 1715 for (unsigned i = 0, e = LocalDefs.size(); i != e; ++i) { 1716 unsigned Def = LocalDefs[i]; 1717 if (LocalDefsSet.count(Def)) { 1718 TBB->addLiveIn(Def); 1719 FBB->addLiveIn(Def); 1720 } 1721 } 1722 1723 ++NumHoist; 1724 return true; 1725 } 1726