BasicBlockUtils.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338
1//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==// 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 family of functions perform manipulations on basic blocks, and 11// instructions contained within basic blocks. 12// 13//===----------------------------------------------------------------------===// 14 15#include "llvm/Transforms/Utils/BasicBlockUtils.h" 16#include "llvm/Analysis/AliasAnalysis.h" 17#include "llvm/Analysis/CFG.h" 18#include "llvm/Analysis/LoopInfo.h" 19#include "llvm/Analysis/MemoryDependenceAnalysis.h" 20#include "llvm/IR/Constant.h" 21#include "llvm/IR/DataLayout.h" 22#include "llvm/IR/Dominators.h" 23#include "llvm/IR/Function.h" 24#include "llvm/IR/Instructions.h" 25#include "llvm/IR/IntrinsicInst.h" 26#include "llvm/IR/Type.h" 27#include "llvm/IR/ValueHandle.h" 28#include "llvm/Support/ErrorHandling.h" 29#include "llvm/Transforms/Scalar.h" 30#include "llvm/Transforms/Utils/Local.h" 31#include <algorithm> 32using namespace llvm; 33 34/// DeleteDeadBlock - Delete the specified block, which must have no 35/// predecessors. 36void llvm::DeleteDeadBlock(BasicBlock *BB) { 37 assert((pred_begin(BB) == pred_end(BB) || 38 // Can delete self loop. 39 BB->getSinglePredecessor() == BB) && "Block is not dead!"); 40 TerminatorInst *BBTerm = BB->getTerminator(); 41 42 // Loop through all of our successors and make sure they know that one 43 // of their predecessors is going away. 44 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) 45 BBTerm->getSuccessor(i)->removePredecessor(BB); 46 47 // Zap all the instructions in the block. 48 while (!BB->empty()) { 49 Instruction &I = BB->back(); 50 // If this instruction is used, replace uses with an arbitrary value. 51 // Because control flow can't get here, we don't care what we replace the 52 // value with. Note that since this block is unreachable, and all values 53 // contained within it must dominate their uses, that all uses will 54 // eventually be removed (they are themselves dead). 55 if (!I.use_empty()) 56 I.replaceAllUsesWith(UndefValue::get(I.getType())); 57 BB->getInstList().pop_back(); 58 } 59 60 // Zap the block! 61 BB->eraseFromParent(); 62} 63 64/// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are 65/// any single-entry PHI nodes in it, fold them away. This handles the case 66/// when all entries to the PHI nodes in a block are guaranteed equal, such as 67/// when the block has exactly one predecessor. 68void llvm::FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P) { 69 if (!isa<PHINode>(BB->begin())) return; 70 71 AliasAnalysis *AA = 0; 72 MemoryDependenceAnalysis *MemDep = 0; 73 if (P) { 74 AA = P->getAnalysisIfAvailable<AliasAnalysis>(); 75 MemDep = P->getAnalysisIfAvailable<MemoryDependenceAnalysis>(); 76 } 77 78 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 79 if (PN->getIncomingValue(0) != PN) 80 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 81 else 82 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 83 84 if (MemDep) 85 MemDep->removeInstruction(PN); // Memdep updates AA itself. 86 else if (AA && isa<PointerType>(PN->getType())) 87 AA->deleteValue(PN); 88 89 PN->eraseFromParent(); 90 } 91} 92 93 94/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it 95/// is dead. Also recursively delete any operands that become dead as 96/// a result. This includes tracing the def-use list from the PHI to see if 97/// it is ultimately unused or if it reaches an unused cycle. 98bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) { 99 // Recursively deleting a PHI may cause multiple PHIs to be deleted 100 // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete. 101 SmallVector<WeakVH, 8> PHIs; 102 for (BasicBlock::iterator I = BB->begin(); 103 PHINode *PN = dyn_cast<PHINode>(I); ++I) 104 PHIs.push_back(PN); 105 106 bool Changed = false; 107 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) 108 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*())) 109 Changed |= RecursivelyDeleteDeadPHINode(PN, TLI); 110 111 return Changed; 112} 113 114/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, 115/// if possible. The return value indicates success or failure. 116bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) { 117 // Don't merge away blocks who have their address taken. 118 if (BB->hasAddressTaken()) return false; 119 120 // Can't merge if there are multiple predecessors, or no predecessors. 121 BasicBlock *PredBB = BB->getUniquePredecessor(); 122 if (!PredBB) return false; 123 124 // Don't break self-loops. 125 if (PredBB == BB) return false; 126 // Don't break invokes. 127 if (isa<InvokeInst>(PredBB->getTerminator())) return false; 128 129 succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB)); 130 BasicBlock *OnlySucc = BB; 131 for (; SI != SE; ++SI) 132 if (*SI != OnlySucc) { 133 OnlySucc = 0; // There are multiple distinct successors! 134 break; 135 } 136 137 // Can't merge if there are multiple successors. 138 if (!OnlySucc) return false; 139 140 // Can't merge if there is PHI loop. 141 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) { 142 if (PHINode *PN = dyn_cast<PHINode>(BI)) { 143 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 144 if (PN->getIncomingValue(i) == PN) 145 return false; 146 } else 147 break; 148 } 149 150 // Begin by getting rid of unneeded PHIs. 151 if (isa<PHINode>(BB->front())) 152 FoldSingleEntryPHINodes(BB, P); 153 154 // Delete the unconditional branch from the predecessor... 155 PredBB->getInstList().pop_back(); 156 157 // Make all PHI nodes that referred to BB now refer to Pred as their 158 // source... 159 BB->replaceAllUsesWith(PredBB); 160 161 // Move all definitions in the successor to the predecessor... 162 PredBB->getInstList().splice(PredBB->end(), BB->getInstList()); 163 164 // Inherit predecessors name if it exists. 165 if (!PredBB->hasName()) 166 PredBB->takeName(BB); 167 168 // Finally, erase the old block and update dominator info. 169 if (P) { 170 if (DominatorTreeWrapperPass *DTWP = 171 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) { 172 DominatorTree &DT = DTWP->getDomTree(); 173 if (DomTreeNode *DTN = DT.getNode(BB)) { 174 DomTreeNode *PredDTN = DT.getNode(PredBB); 175 SmallVector<DomTreeNode*, 8> Children(DTN->begin(), DTN->end()); 176 for (SmallVectorImpl<DomTreeNode *>::iterator DI = Children.begin(), 177 DE = Children.end(); DI != DE; ++DI) 178 DT.changeImmediateDominator(*DI, PredDTN); 179 180 DT.eraseNode(BB); 181 } 182 183 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>()) 184 LI->removeBlock(BB); 185 186 if (MemoryDependenceAnalysis *MD = 187 P->getAnalysisIfAvailable<MemoryDependenceAnalysis>()) 188 MD->invalidateCachedPredecessors(); 189 } 190 } 191 192 BB->eraseFromParent(); 193 return true; 194} 195 196/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 197/// with a value, then remove and delete the original instruction. 198/// 199void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL, 200 BasicBlock::iterator &BI, Value *V) { 201 Instruction &I = *BI; 202 // Replaces all of the uses of the instruction with uses of the value 203 I.replaceAllUsesWith(V); 204 205 // Make sure to propagate a name if there is one already. 206 if (I.hasName() && !V->hasName()) 207 V->takeName(&I); 208 209 // Delete the unnecessary instruction now... 210 BI = BIL.erase(BI); 211} 212 213 214/// ReplaceInstWithInst - Replace the instruction specified by BI with the 215/// instruction specified by I. The original instruction is deleted and BI is 216/// updated to point to the new instruction. 217/// 218void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL, 219 BasicBlock::iterator &BI, Instruction *I) { 220 assert(I->getParent() == 0 && 221 "ReplaceInstWithInst: Instruction already inserted into basic block!"); 222 223 // Insert the new instruction into the basic block... 224 BasicBlock::iterator New = BIL.insert(BI, I); 225 226 // Replace all uses of the old instruction, and delete it. 227 ReplaceInstWithValue(BIL, BI, I); 228 229 // Move BI back to point to the newly inserted instruction 230 BI = New; 231} 232 233/// ReplaceInstWithInst - Replace the instruction specified by From with the 234/// instruction specified by To. 235/// 236void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) { 237 BasicBlock::iterator BI(From); 238 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To); 239} 240 241/// SplitEdge - Split the edge connecting specified block. Pass P must 242/// not be NULL. 243BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) { 244 unsigned SuccNum = GetSuccessorNumber(BB, Succ); 245 246 // If this is a critical edge, let SplitCriticalEdge do it. 247 TerminatorInst *LatchTerm = BB->getTerminator(); 248 if (SplitCriticalEdge(LatchTerm, SuccNum, P)) 249 return LatchTerm->getSuccessor(SuccNum); 250 251 // If the edge isn't critical, then BB has a single successor or Succ has a 252 // single pred. Split the block. 253 if (BasicBlock *SP = Succ->getSinglePredecessor()) { 254 // If the successor only has a single pred, split the top of the successor 255 // block. 256 assert(SP == BB && "CFG broken"); 257 SP = NULL; 258 return SplitBlock(Succ, Succ->begin(), P); 259 } 260 261 // Otherwise, if BB has a single successor, split it at the bottom of the 262 // block. 263 assert(BB->getTerminator()->getNumSuccessors() == 1 && 264 "Should have a single succ!"); 265 return SplitBlock(BB, BB->getTerminator(), P); 266} 267 268/// SplitBlock - Split the specified block at the specified instruction - every 269/// thing before SplitPt stays in Old and everything starting with SplitPt moves 270/// to a new block. The two blocks are joined by an unconditional branch and 271/// the loop info is updated. 272/// 273BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) { 274 BasicBlock::iterator SplitIt = SplitPt; 275 while (isa<PHINode>(SplitIt) || isa<LandingPadInst>(SplitIt)) 276 ++SplitIt; 277 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split"); 278 279 // The new block lives in whichever loop the old one did. This preserves 280 // LCSSA as well, because we force the split point to be after any PHI nodes. 281 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>()) 282 if (Loop *L = LI->getLoopFor(Old)) 283 L->addBasicBlockToLoop(New, LI->getBase()); 284 285 if (DominatorTreeWrapperPass *DTWP = 286 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) { 287 DominatorTree &DT = DTWP->getDomTree(); 288 // Old dominates New. New node dominates all other nodes dominated by Old. 289 if (DomTreeNode *OldNode = DT.getNode(Old)) { 290 std::vector<DomTreeNode *> Children; 291 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); 292 I != E; ++I) 293 Children.push_back(*I); 294 295 DomTreeNode *NewNode = DT.addNewBlock(New, Old); 296 for (std::vector<DomTreeNode *>::iterator I = Children.begin(), 297 E = Children.end(); I != E; ++I) 298 DT.changeImmediateDominator(*I, NewNode); 299 } 300 } 301 302 return New; 303} 304 305/// UpdateAnalysisInformation - Update DominatorTree, LoopInfo, and LCCSA 306/// analysis information. 307static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB, 308 ArrayRef<BasicBlock *> Preds, 309 Pass *P, bool &HasLoopExit) { 310 if (!P) return; 311 312 LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>(); 313 Loop *L = LI ? LI->getLoopFor(OldBB) : 0; 314 315 // If we need to preserve loop analyses, collect some information about how 316 // this split will affect loops. 317 bool IsLoopEntry = !!L; 318 bool SplitMakesNewLoopHeader = false; 319 if (LI) { 320 bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID); 321 for (ArrayRef<BasicBlock*>::iterator 322 i = Preds.begin(), e = Preds.end(); i != e; ++i) { 323 BasicBlock *Pred = *i; 324 325 // If we need to preserve LCSSA, determine if any of the preds is a loop 326 // exit. 327 if (PreserveLCSSA) 328 if (Loop *PL = LI->getLoopFor(Pred)) 329 if (!PL->contains(OldBB)) 330 HasLoopExit = true; 331 332 // If we need to preserve LoopInfo, note whether any of the preds crosses 333 // an interesting loop boundary. 334 if (!L) continue; 335 if (L->contains(Pred)) 336 IsLoopEntry = false; 337 else 338 SplitMakesNewLoopHeader = true; 339 } 340 } 341 342 // Update dominator tree if available. 343 if (DominatorTreeWrapperPass *DTWP = 344 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) 345 DTWP->getDomTree().splitBlock(NewBB); 346 347 if (!L) return; 348 349 if (IsLoopEntry) { 350 // Add the new block to the nearest enclosing loop (and not an adjacent 351 // loop). To find this, examine each of the predecessors and determine which 352 // loops enclose them, and select the most-nested loop which contains the 353 // loop containing the block being split. 354 Loop *InnermostPredLoop = 0; 355 for (ArrayRef<BasicBlock*>::iterator 356 i = Preds.begin(), e = Preds.end(); i != e; ++i) { 357 BasicBlock *Pred = *i; 358 if (Loop *PredLoop = LI->getLoopFor(Pred)) { 359 // Seek a loop which actually contains the block being split (to avoid 360 // adjacent loops). 361 while (PredLoop && !PredLoop->contains(OldBB)) 362 PredLoop = PredLoop->getParentLoop(); 363 364 // Select the most-nested of these loops which contains the block. 365 if (PredLoop && PredLoop->contains(OldBB) && 366 (!InnermostPredLoop || 367 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth())) 368 InnermostPredLoop = PredLoop; 369 } 370 } 371 372 if (InnermostPredLoop) 373 InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase()); 374 } else { 375 L->addBasicBlockToLoop(NewBB, LI->getBase()); 376 if (SplitMakesNewLoopHeader) 377 L->moveToHeader(NewBB); 378 } 379} 380 381/// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming 382/// from NewBB. This also updates AliasAnalysis, if available. 383static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB, 384 ArrayRef<BasicBlock*> Preds, BranchInst *BI, 385 Pass *P, bool HasLoopExit) { 386 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB. 387 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0; 388 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) { 389 PHINode *PN = cast<PHINode>(I++); 390 391 // Check to see if all of the values coming in are the same. If so, we 392 // don't need to create a new PHI node, unless it's needed for LCSSA. 393 Value *InVal = 0; 394 if (!HasLoopExit) { 395 InVal = PN->getIncomingValueForBlock(Preds[0]); 396 for (unsigned i = 1, e = Preds.size(); i != e; ++i) 397 if (InVal != PN->getIncomingValueForBlock(Preds[i])) { 398 InVal = 0; 399 break; 400 } 401 } 402 403 if (InVal) { 404 // If all incoming values for the new PHI would be the same, just don't 405 // make a new PHI. Instead, just remove the incoming values from the old 406 // PHI. 407 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 408 // Explicitly check the BB index here to handle duplicates in Preds. 409 int Idx = PN->getBasicBlockIndex(Preds[i]); 410 if (Idx >= 0) 411 PN->removeIncomingValue(Idx, false); 412 } 413 } else { 414 // If the values coming into the block are not the same, we need a PHI. 415 // Create the new PHI node, insert it into NewBB at the end of the block 416 PHINode *NewPHI = 417 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI); 418 if (AA) AA->copyValue(PN, NewPHI); 419 420 // Move all of the PHI values for 'Preds' to the new PHI. 421 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 422 Value *V = PN->removeIncomingValue(Preds[i], false); 423 NewPHI->addIncoming(V, Preds[i]); 424 } 425 426 InVal = NewPHI; 427 } 428 429 // Add an incoming value to the PHI node in the loop for the preheader 430 // edge. 431 PN->addIncoming(InVal, NewBB); 432 } 433} 434 435/// SplitBlockPredecessors - This method transforms BB by introducing a new 436/// basic block into the function, and moving some of the predecessors of BB to 437/// be predecessors of the new block. The new predecessors are indicated by the 438/// Preds array, which has NumPreds elements in it. The new block is given a 439/// suffix of 'Suffix'. 440/// 441/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, 442/// LoopInfo, and LCCSA but no other analyses. In particular, it does not 443/// preserve LoopSimplify (because it's complicated to handle the case where one 444/// of the edges being split is an exit of a loop with other exits). 445/// 446BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, 447 ArrayRef<BasicBlock*> Preds, 448 const char *Suffix, Pass *P) { 449 // Create new basic block, insert right before the original block. 450 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix, 451 BB->getParent(), BB); 452 453 // The new block unconditionally branches to the old block. 454 BranchInst *BI = BranchInst::Create(BB, NewBB); 455 456 // Move the edges from Preds to point to NewBB instead of BB. 457 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 458 // This is slightly more strict than necessary; the minimum requirement 459 // is that there be no more than one indirectbr branching to BB. And 460 // all BlockAddress uses would need to be updated. 461 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) && 462 "Cannot split an edge from an IndirectBrInst"); 463 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); 464 } 465 466 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI 467 // node becomes an incoming value for BB's phi node. However, if the Preds 468 // list is empty, we need to insert dummy entries into the PHI nodes in BB to 469 // account for the newly created predecessor. 470 if (Preds.size() == 0) { 471 // Insert dummy values as the incoming value. 472 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) 473 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB); 474 return NewBB; 475 } 476 477 // Update DominatorTree, LoopInfo, and LCCSA analysis information. 478 bool HasLoopExit = false; 479 UpdateAnalysisInformation(BB, NewBB, Preds, P, HasLoopExit); 480 481 // Update the PHI nodes in BB with the values coming from NewBB. 482 UpdatePHINodes(BB, NewBB, Preds, BI, P, HasLoopExit); 483 return NewBB; 484} 485 486/// SplitLandingPadPredecessors - This method transforms the landing pad, 487/// OrigBB, by introducing two new basic blocks into the function. One of those 488/// new basic blocks gets the predecessors listed in Preds. The other basic 489/// block gets the remaining predecessors of OrigBB. The landingpad instruction 490/// OrigBB is clone into both of the new basic blocks. The new blocks are given 491/// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. 492/// 493/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, 494/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular, 495/// it does not preserve LoopSimplify (because it's complicated to handle the 496/// case where one of the edges being split is an exit of a loop with other 497/// exits). 498/// 499void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB, 500 ArrayRef<BasicBlock*> Preds, 501 const char *Suffix1, const char *Suffix2, 502 Pass *P, 503 SmallVectorImpl<BasicBlock*> &NewBBs) { 504 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!"); 505 506 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert 507 // it right before the original block. 508 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(), 509 OrigBB->getName() + Suffix1, 510 OrigBB->getParent(), OrigBB); 511 NewBBs.push_back(NewBB1); 512 513 // The new block unconditionally branches to the old block. 514 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1); 515 516 // Move the edges from Preds to point to NewBB1 instead of OrigBB. 517 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 518 // This is slightly more strict than necessary; the minimum requirement 519 // is that there be no more than one indirectbr branching to BB. And 520 // all BlockAddress uses would need to be updated. 521 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) && 522 "Cannot split an edge from an IndirectBrInst"); 523 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1); 524 } 525 526 // Update DominatorTree, LoopInfo, and LCCSA analysis information. 527 bool HasLoopExit = false; 528 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, P, HasLoopExit); 529 530 // Update the PHI nodes in OrigBB with the values coming from NewBB1. 531 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, P, HasLoopExit); 532 533 // Move the remaining edges from OrigBB to point to NewBB2. 534 SmallVector<BasicBlock*, 8> NewBB2Preds; 535 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB); 536 i != e; ) { 537 BasicBlock *Pred = *i++; 538 if (Pred == NewBB1) continue; 539 assert(!isa<IndirectBrInst>(Pred->getTerminator()) && 540 "Cannot split an edge from an IndirectBrInst"); 541 NewBB2Preds.push_back(Pred); 542 e = pred_end(OrigBB); 543 } 544 545 BasicBlock *NewBB2 = 0; 546 if (!NewBB2Preds.empty()) { 547 // Create another basic block for the rest of OrigBB's predecessors. 548 NewBB2 = BasicBlock::Create(OrigBB->getContext(), 549 OrigBB->getName() + Suffix2, 550 OrigBB->getParent(), OrigBB); 551 NewBBs.push_back(NewBB2); 552 553 // The new block unconditionally branches to the old block. 554 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2); 555 556 // Move the remaining edges from OrigBB to point to NewBB2. 557 for (SmallVectorImpl<BasicBlock*>::iterator 558 i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i) 559 (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2); 560 561 // Update DominatorTree, LoopInfo, and LCCSA analysis information. 562 HasLoopExit = false; 563 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, P, HasLoopExit); 564 565 // Update the PHI nodes in OrigBB with the values coming from NewBB2. 566 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, P, HasLoopExit); 567 } 568 569 LandingPadInst *LPad = OrigBB->getLandingPadInst(); 570 Instruction *Clone1 = LPad->clone(); 571 Clone1->setName(Twine("lpad") + Suffix1); 572 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1); 573 574 if (NewBB2) { 575 Instruction *Clone2 = LPad->clone(); 576 Clone2->setName(Twine("lpad") + Suffix2); 577 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2); 578 579 // Create a PHI node for the two cloned landingpad instructions. 580 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad); 581 PN->addIncoming(Clone1, NewBB1); 582 PN->addIncoming(Clone2, NewBB2); 583 LPad->replaceAllUsesWith(PN); 584 LPad->eraseFromParent(); 585 } else { 586 // There is no second clone. Just replace the landing pad with the first 587 // clone. 588 LPad->replaceAllUsesWith(Clone1); 589 LPad->eraseFromParent(); 590 } 591} 592 593/// FoldReturnIntoUncondBranch - This method duplicates the specified return 594/// instruction into a predecessor which ends in an unconditional branch. If 595/// the return instruction returns a value defined by a PHI, propagate the 596/// right value into the return. It returns the new return instruction in the 597/// predecessor. 598ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 599 BasicBlock *Pred) { 600 Instruction *UncondBranch = Pred->getTerminator(); 601 // Clone the return and add it to the end of the predecessor. 602 Instruction *NewRet = RI->clone(); 603 Pred->getInstList().push_back(NewRet); 604 605 // If the return instruction returns a value, and if the value was a 606 // PHI node in "BB", propagate the right value into the return. 607 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end(); 608 i != e; ++i) { 609 Value *V = *i; 610 Instruction *NewBC = 0; 611 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) { 612 // Return value might be bitcasted. Clone and insert it before the 613 // return instruction. 614 V = BCI->getOperand(0); 615 NewBC = BCI->clone(); 616 Pred->getInstList().insert(NewRet, NewBC); 617 *i = NewBC; 618 } 619 if (PHINode *PN = dyn_cast<PHINode>(V)) { 620 if (PN->getParent() == BB) { 621 if (NewBC) 622 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred)); 623 else 624 *i = PN->getIncomingValueForBlock(Pred); 625 } 626 } 627 } 628 629 // Update any PHI nodes in the returning block to realize that we no 630 // longer branch to them. 631 BB->removePredecessor(Pred); 632 UncondBranch->eraseFromParent(); 633 return cast<ReturnInst>(NewRet); 634} 635 636/// SplitBlockAndInsertIfThen - Split the containing block at the 637/// specified instruction - everything before and including SplitBefore stays 638/// in the old basic block, and everything after SplitBefore is moved to a 639/// new block. The two blocks are connected by a conditional branch 640/// (with value of Cmp being the condition). 641/// Before: 642/// Head 643/// SplitBefore 644/// Tail 645/// After: 646/// Head 647/// if (Cond) 648/// ThenBlock 649/// SplitBefore 650/// Tail 651/// 652/// If Unreachable is true, then ThenBlock ends with 653/// UnreachableInst, otherwise it branches to Tail. 654/// Returns the NewBasicBlock's terminator. 655 656TerminatorInst *llvm::SplitBlockAndInsertIfThen(Value *Cond, 657 Instruction *SplitBefore, 658 bool Unreachable, 659 MDNode *BranchWeights) { 660 BasicBlock *Head = SplitBefore->getParent(); 661 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore); 662 TerminatorInst *HeadOldTerm = Head->getTerminator(); 663 LLVMContext &C = Head->getContext(); 664 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail); 665 TerminatorInst *CheckTerm; 666 if (Unreachable) 667 CheckTerm = new UnreachableInst(C, ThenBlock); 668 else 669 CheckTerm = BranchInst::Create(Tail, ThenBlock); 670 CheckTerm->setDebugLoc(SplitBefore->getDebugLoc()); 671 BranchInst *HeadNewTerm = 672 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond); 673 HeadNewTerm->setDebugLoc(SplitBefore->getDebugLoc()); 674 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights); 675 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm); 676 return CheckTerm; 677} 678 679/// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, 680/// but also creates the ElseBlock. 681/// Before: 682/// Head 683/// SplitBefore 684/// Tail 685/// After: 686/// Head 687/// if (Cond) 688/// ThenBlock 689/// else 690/// ElseBlock 691/// SplitBefore 692/// Tail 693void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, 694 TerminatorInst **ThenTerm, 695 TerminatorInst **ElseTerm, 696 MDNode *BranchWeights) { 697 BasicBlock *Head = SplitBefore->getParent(); 698 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore); 699 TerminatorInst *HeadOldTerm = Head->getTerminator(); 700 LLVMContext &C = Head->getContext(); 701 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail); 702 BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail); 703 *ThenTerm = BranchInst::Create(Tail, ThenBlock); 704 (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc()); 705 *ElseTerm = BranchInst::Create(Tail, ElseBlock); 706 (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc()); 707 BranchInst *HeadNewTerm = 708 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond); 709 HeadNewTerm->setDebugLoc(SplitBefore->getDebugLoc()); 710 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights); 711 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm); 712} 713 714 715/// GetIfCondition - Given a basic block (BB) with two predecessors, 716/// check to see if the merge at this block is due 717/// to an "if condition". If so, return the boolean condition that determines 718/// which entry into BB will be taken. Also, return by references the block 719/// that will be entered from if the condition is true, and the block that will 720/// be entered if the condition is false. 721/// 722/// This does no checking to see if the true/false blocks have large or unsavory 723/// instructions in them. 724Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 725 BasicBlock *&IfFalse) { 726 PHINode *SomePHI = dyn_cast<PHINode>(BB->begin()); 727 BasicBlock *Pred1 = NULL; 728 BasicBlock *Pred2 = NULL; 729 730 if (SomePHI) { 731 if (SomePHI->getNumIncomingValues() != 2) 732 return NULL; 733 Pred1 = SomePHI->getIncomingBlock(0); 734 Pred2 = SomePHI->getIncomingBlock(1); 735 } else { 736 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 737 if (PI == PE) // No predecessor 738 return NULL; 739 Pred1 = *PI++; 740 if (PI == PE) // Only one predecessor 741 return NULL; 742 Pred2 = *PI++; 743 if (PI != PE) // More than two predecessors 744 return NULL; 745 } 746 747 // We can only handle branches. Other control flow will be lowered to 748 // branches if possible anyway. 749 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator()); 750 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator()); 751 if (Pred1Br == 0 || Pred2Br == 0) 752 return 0; 753 754 // Eliminate code duplication by ensuring that Pred1Br is conditional if 755 // either are. 756 if (Pred2Br->isConditional()) { 757 // If both branches are conditional, we don't have an "if statement". In 758 // reality, we could transform this case, but since the condition will be 759 // required anyway, we stand no chance of eliminating it, so the xform is 760 // probably not profitable. 761 if (Pred1Br->isConditional()) 762 return 0; 763 764 std::swap(Pred1, Pred2); 765 std::swap(Pred1Br, Pred2Br); 766 } 767 768 if (Pred1Br->isConditional()) { 769 // The only thing we have to watch out for here is to make sure that Pred2 770 // doesn't have incoming edges from other blocks. If it does, the condition 771 // doesn't dominate BB. 772 if (Pred2->getSinglePredecessor() == 0) 773 return 0; 774 775 // If we found a conditional branch predecessor, make sure that it branches 776 // to BB and Pred2Br. If it doesn't, this isn't an "if statement". 777 if (Pred1Br->getSuccessor(0) == BB && 778 Pred1Br->getSuccessor(1) == Pred2) { 779 IfTrue = Pred1; 780 IfFalse = Pred2; 781 } else if (Pred1Br->getSuccessor(0) == Pred2 && 782 Pred1Br->getSuccessor(1) == BB) { 783 IfTrue = Pred2; 784 IfFalse = Pred1; 785 } else { 786 // We know that one arm of the conditional goes to BB, so the other must 787 // go somewhere unrelated, and this must not be an "if statement". 788 return 0; 789 } 790 791 return Pred1Br->getCondition(); 792 } 793 794 // Ok, if we got here, both predecessors end with an unconditional branch to 795 // BB. Don't panic! If both blocks only have a single (identical) 796 // predecessor, and THAT is a conditional branch, then we're all ok! 797 BasicBlock *CommonPred = Pred1->getSinglePredecessor(); 798 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor()) 799 return 0; 800 801 // Otherwise, if this is a conditional branch, then we can use it! 802 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator()); 803 if (BI == 0) return 0; 804 805 assert(BI->isConditional() && "Two successors but not conditional?"); 806 if (BI->getSuccessor(0) == Pred1) { 807 IfTrue = Pred1; 808 IfFalse = Pred2; 809 } else { 810 IfTrue = Pred2; 811 IfFalse = Pred1; 812 } 813 return BI->getCondition(); 814} 815