BasicBlockUtils.cpp revision fc2a3ed0c9e32cf7edaf5030fa0972b916cc5f0b
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/Function.h" 17#include "llvm/Instructions.h" 18#include "llvm/IntrinsicInst.h" 19#include "llvm/LLVMContext.h" 20#include "llvm/Constant.h" 21#include "llvm/Type.h" 22#include "llvm/Analysis/AliasAnalysis.h" 23#include "llvm/Analysis/LoopInfo.h" 24#include "llvm/Analysis/Dominators.h" 25#include "llvm/Target/TargetData.h" 26#include "llvm/Transforms/Utils/Local.h" 27#include "llvm/Support/ErrorHandling.h" 28#include "llvm/Support/ValueHandle.h" 29#include <algorithm> 30using namespace llvm; 31 32/// DeleteDeadBlock - Delete the specified block, which must have no 33/// predecessors. 34void llvm::DeleteDeadBlock(BasicBlock *BB) { 35 assert((pred_begin(BB) == pred_end(BB) || 36 // Can delete self loop. 37 BB->getSinglePredecessor() == BB) && "Block is not dead!"); 38 TerminatorInst *BBTerm = BB->getTerminator(); 39 40 // Loop through all of our successors and make sure they know that one 41 // of their predecessors is going away. 42 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) 43 BBTerm->getSuccessor(i)->removePredecessor(BB); 44 45 // Zap all the instructions in the block. 46 while (!BB->empty()) { 47 Instruction &I = BB->back(); 48 // If this instruction is used, replace uses with an arbitrary value. 49 // Because control flow can't get here, we don't care what we replace the 50 // value with. Note that since this block is unreachable, and all values 51 // contained within it must dominate their uses, that all uses will 52 // eventually be removed (they are themselves dead). 53 if (!I.use_empty()) 54 I.replaceAllUsesWith(BB->getContext().getUndef(I.getType())); 55 BB->getInstList().pop_back(); 56 } 57 58 // Zap the block! 59 BB->eraseFromParent(); 60} 61 62/// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are 63/// any single-entry PHI nodes in it, fold them away. This handles the case 64/// when all entries to the PHI nodes in a block are guaranteed equal, such as 65/// when the block has exactly one predecessor. 66void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) { 67 if (!isa<PHINode>(BB->begin())) 68 return; 69 70 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 71 if (PN->getIncomingValue(0) != PN) 72 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 73 else 74 PN->replaceAllUsesWith(BB->getContext().getUndef(PN->getType())); 75 PN->eraseFromParent(); 76 } 77} 78 79 80/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it 81/// is dead. Also recursively delete any operands that become dead as 82/// a result. This includes tracing the def-use list from the PHI to see if 83/// it is ultimately unused or if it reaches an unused cycle. 84void llvm::DeleteDeadPHIs(BasicBlock *BB) { 85 // Recursively deleting a PHI may cause multiple PHIs to be deleted 86 // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete. 87 SmallVector<WeakVH, 8> PHIs; 88 for (BasicBlock::iterator I = BB->begin(); 89 PHINode *PN = dyn_cast<PHINode>(I); ++I) 90 PHIs.push_back(PN); 91 92 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) 93 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*())) 94 RecursivelyDeleteDeadPHINode(PN); 95} 96 97/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, 98/// if possible. The return value indicates success or failure. 99bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) { 100 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); 101 // Can't merge the entry block. 102 if (pred_begin(BB) == pred_end(BB)) return false; 103 104 BasicBlock *PredBB = *PI++; 105 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same 106 if (*PI != PredBB) { 107 PredBB = 0; // There are multiple different predecessors... 108 break; 109 } 110 111 // Can't merge if there are multiple predecessors. 112 if (!PredBB) return false; 113 // Don't break self-loops. 114 if (PredBB == BB) return false; 115 // Don't break invokes. 116 if (isa<InvokeInst>(PredBB->getTerminator())) return false; 117 118 succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB)); 119 BasicBlock* OnlySucc = BB; 120 for (; SI != SE; ++SI) 121 if (*SI != OnlySucc) { 122 OnlySucc = 0; // There are multiple distinct successors! 123 break; 124 } 125 126 // Can't merge if there are multiple successors. 127 if (!OnlySucc) return false; 128 129 // Can't merge if there is PHI loop. 130 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) { 131 if (PHINode *PN = dyn_cast<PHINode>(BI)) { 132 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 133 if (PN->getIncomingValue(i) == PN) 134 return false; 135 } else 136 break; 137 } 138 139 // Begin by getting rid of unneeded PHIs. 140 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 141 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 142 BB->getInstList().pop_front(); // Delete the phi node... 143 } 144 145 // Delete the unconditional branch from the predecessor... 146 PredBB->getInstList().pop_back(); 147 148 // Move all definitions in the successor to the predecessor... 149 PredBB->getInstList().splice(PredBB->end(), BB->getInstList()); 150 151 // Make all PHI nodes that referred to BB now refer to Pred as their 152 // source... 153 BB->replaceAllUsesWith(PredBB); 154 155 // Inherit predecessors name if it exists. 156 if (!PredBB->hasName()) 157 PredBB->takeName(BB); 158 159 // Finally, erase the old block and update dominator info. 160 if (P) { 161 if (DominatorTree* DT = P->getAnalysisIfAvailable<DominatorTree>()) { 162 DomTreeNode* DTN = DT->getNode(BB); 163 DomTreeNode* PredDTN = DT->getNode(PredBB); 164 165 if (DTN) { 166 SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end()); 167 for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(), 168 DE = Children.end(); DI != DE; ++DI) 169 DT->changeImmediateDominator(*DI, PredDTN); 170 171 DT->eraseNode(BB); 172 } 173 } 174 } 175 176 BB->eraseFromParent(); 177 178 179 return true; 180} 181 182/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 183/// with a value, then remove and delete the original instruction. 184/// 185void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL, 186 BasicBlock::iterator &BI, Value *V) { 187 Instruction &I = *BI; 188 // Replaces all of the uses of the instruction with uses of the value 189 I.replaceAllUsesWith(V); 190 191 // Make sure to propagate a name if there is one already. 192 if (I.hasName() && !V->hasName()) 193 V->takeName(&I); 194 195 // Delete the unnecessary instruction now... 196 BI = BIL.erase(BI); 197} 198 199 200/// ReplaceInstWithInst - Replace the instruction specified by BI with the 201/// instruction specified by I. The original instruction is deleted and BI is 202/// updated to point to the new instruction. 203/// 204void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL, 205 BasicBlock::iterator &BI, Instruction *I) { 206 assert(I->getParent() == 0 && 207 "ReplaceInstWithInst: Instruction already inserted into basic block!"); 208 209 // Insert the new instruction into the basic block... 210 BasicBlock::iterator New = BIL.insert(BI, I); 211 212 // Replace all uses of the old instruction, and delete it. 213 ReplaceInstWithValue(BIL, BI, I); 214 215 // Move BI back to point to the newly inserted instruction 216 BI = New; 217} 218 219/// ReplaceInstWithInst - Replace the instruction specified by From with the 220/// instruction specified by To. 221/// 222void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) { 223 BasicBlock::iterator BI(From); 224 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To); 225} 226 227/// RemoveSuccessor - Change the specified terminator instruction such that its 228/// successor SuccNum no longer exists. Because this reduces the outgoing 229/// degree of the current basic block, the actual terminator instruction itself 230/// may have to be changed. In the case where the last successor of the block 231/// is deleted, a return instruction is inserted in its place which can cause a 232/// surprising change in program behavior if it is not expected. 233/// 234void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) { 235 assert(SuccNum < TI->getNumSuccessors() && 236 "Trying to remove a nonexistant successor!"); 237 238 // If our old successor block contains any PHI nodes, remove the entry in the 239 // PHI nodes that comes from this branch... 240 // 241 BasicBlock *BB = TI->getParent(); 242 TI->getSuccessor(SuccNum)->removePredecessor(BB); 243 244 TerminatorInst *NewTI = 0; 245 switch (TI->getOpcode()) { 246 case Instruction::Br: 247 // If this is a conditional branch... convert to unconditional branch. 248 if (TI->getNumSuccessors() == 2) { 249 cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum)); 250 } else { // Otherwise convert to a return instruction... 251 Value *RetVal = 0; 252 253 // Create a value to return... if the function doesn't return null... 254 if (BB->getParent()->getReturnType() != Type::VoidTy) 255 RetVal = TI->getContext().getNullValue( 256 BB->getParent()->getReturnType()); 257 258 // Create the return... 259 NewTI = ReturnInst::Create(RetVal); 260 } 261 break; 262 263 case Instruction::Invoke: // Should convert to call 264 case Instruction::Switch: // Should remove entry 265 default: 266 case Instruction::Ret: // Cannot happen, has no successors! 267 llvm_unreachable("Unhandled terminator instruction type in RemoveSuccessor!"); 268 } 269 270 if (NewTI) // If it's a different instruction, replace. 271 ReplaceInstWithInst(TI, NewTI); 272} 273 274/// SplitEdge - Split the edge connecting specified block. Pass P must 275/// not be NULL. 276BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) { 277 TerminatorInst *LatchTerm = BB->getTerminator(); 278 unsigned SuccNum = 0; 279#ifndef NDEBUG 280 unsigned e = LatchTerm->getNumSuccessors(); 281#endif 282 for (unsigned i = 0; ; ++i) { 283 assert(i != e && "Didn't find edge?"); 284 if (LatchTerm->getSuccessor(i) == Succ) { 285 SuccNum = i; 286 break; 287 } 288 } 289 290 // If this is a critical edge, let SplitCriticalEdge do it. 291 if (SplitCriticalEdge(BB->getTerminator(), SuccNum, P)) 292 return LatchTerm->getSuccessor(SuccNum); 293 294 // If the edge isn't critical, then BB has a single successor or Succ has a 295 // single pred. Split the block. 296 BasicBlock::iterator SplitPoint; 297 if (BasicBlock *SP = Succ->getSinglePredecessor()) { 298 // If the successor only has a single pred, split the top of the successor 299 // block. 300 assert(SP == BB && "CFG broken"); 301 SP = NULL; 302 return SplitBlock(Succ, Succ->begin(), P); 303 } else { 304 // Otherwise, if BB has a single successor, split it at the bottom of the 305 // block. 306 assert(BB->getTerminator()->getNumSuccessors() == 1 && 307 "Should have a single succ!"); 308 return SplitBlock(BB, BB->getTerminator(), P); 309 } 310} 311 312/// SplitBlock - Split the specified block at the specified instruction - every 313/// thing before SplitPt stays in Old and everything starting with SplitPt moves 314/// to a new block. The two blocks are joined by an unconditional branch and 315/// the loop info is updated. 316/// 317BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) { 318 BasicBlock::iterator SplitIt = SplitPt; 319 while (isa<PHINode>(SplitIt)) 320 ++SplitIt; 321 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split"); 322 323 // The new block lives in whichever loop the old one did. 324 if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>()) 325 if (Loop *L = LI->getLoopFor(Old)) 326 L->addBasicBlockToLoop(New, LI->getBase()); 327 328 if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) 329 { 330 // Old dominates New. New node domiantes all other nodes dominated by Old. 331 DomTreeNode *OldNode = DT->getNode(Old); 332 std::vector<DomTreeNode *> Children; 333 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); 334 I != E; ++I) 335 Children.push_back(*I); 336 337 DomTreeNode *NewNode = DT->addNewBlock(New,Old); 338 339 for (std::vector<DomTreeNode *>::iterator I = Children.begin(), 340 E = Children.end(); I != E; ++I) 341 DT->changeImmediateDominator(*I, NewNode); 342 } 343 344 if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>()) 345 DF->splitBlock(Old); 346 347 return New; 348} 349 350 351/// SplitBlockPredecessors - This method transforms BB by introducing a new 352/// basic block into the function, and moving some of the predecessors of BB to 353/// be predecessors of the new block. The new predecessors are indicated by the 354/// Preds array, which has NumPreds elements in it. The new block is given a 355/// suffix of 'Suffix'. 356/// 357/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and 358/// DominanceFrontier, but no other analyses. 359BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, 360 BasicBlock *const *Preds, 361 unsigned NumPreds, const char *Suffix, 362 Pass *P) { 363 // Create new basic block, insert right before the original block. 364 BasicBlock *NewBB = 365 BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB); 366 367 // The new block unconditionally branches to the old block. 368 BranchInst *BI = BranchInst::Create(BB, NewBB); 369 370 // Move the edges from Preds to point to NewBB instead of BB. 371 for (unsigned i = 0; i != NumPreds; ++i) 372 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); 373 374 // Update dominator tree and dominator frontier if available. 375 DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0; 376 if (DT) 377 DT->splitBlock(NewBB); 378 if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0) 379 DF->splitBlock(NewBB); 380 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0; 381 382 383 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI 384 // node becomes an incoming value for BB's phi node. However, if the Preds 385 // list is empty, we need to insert dummy entries into the PHI nodes in BB to 386 // account for the newly created predecessor. 387 if (NumPreds == 0) { 388 // Insert dummy values as the incoming value. 389 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) 390 cast<PHINode>(I)->addIncoming(BB->getContext().getUndef(I->getType()), 391 NewBB); 392 return NewBB; 393 } 394 395 // Otherwise, create a new PHI node in NewBB for each PHI node in BB. 396 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) { 397 PHINode *PN = cast<PHINode>(I++); 398 399 // Check to see if all of the values coming in are the same. If so, we 400 // don't need to create a new PHI node. 401 Value *InVal = PN->getIncomingValueForBlock(Preds[0]); 402 for (unsigned i = 1; i != NumPreds; ++i) 403 if (InVal != PN->getIncomingValueForBlock(Preds[i])) { 404 InVal = 0; 405 break; 406 } 407 408 if (InVal) { 409 // If all incoming values for the new PHI would be the same, just don't 410 // make a new PHI. Instead, just remove the incoming values from the old 411 // PHI. 412 for (unsigned i = 0; i != NumPreds; ++i) 413 PN->removeIncomingValue(Preds[i], false); 414 } else { 415 // If the values coming into the block are not the same, we need a PHI. 416 // Create the new PHI node, insert it into NewBB at the end of the block 417 PHINode *NewPHI = 418 PHINode::Create(PN->getType(), PN->getName()+".ph", BI); 419 if (AA) AA->copyValue(PN, NewPHI); 420 421 // Move all of the PHI values for 'Preds' to the new PHI. 422 for (unsigned i = 0; i != NumPreds; ++i) { 423 Value *V = PN->removeIncomingValue(Preds[i], false); 424 NewPHI->addIncoming(V, Preds[i]); 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 // Check to see if we can eliminate this phi node. 434 if (Value *V = PN->hasConstantValue(DT != 0)) { 435 Instruction *I = dyn_cast<Instruction>(V); 436 if (!I || DT == 0 || DT->dominates(I, PN)) { 437 PN->replaceAllUsesWith(V); 438 if (AA) AA->deleteValue(PN); 439 PN->eraseFromParent(); 440 } 441 } 442 } 443 444 return NewBB; 445} 446 447/// FindFunctionBackedges - Analyze the specified function to find all of the 448/// loop backedges in the function and return them. This is a relatively cheap 449/// (compared to computing dominators and loop info) analysis. 450/// 451/// The output is added to Result, as pairs of <from,to> edge info. 452void llvm::FindFunctionBackedges(const Function &F, 453 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) { 454 const BasicBlock *BB = &F.getEntryBlock(); 455 if (succ_begin(BB) == succ_end(BB)) 456 return; 457 458 SmallPtrSet<const BasicBlock*, 8> Visited; 459 SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack; 460 SmallPtrSet<const BasicBlock*, 8> InStack; 461 462 Visited.insert(BB); 463 VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); 464 InStack.insert(BB); 465 do { 466 std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back(); 467 const BasicBlock *ParentBB = Top.first; 468 succ_const_iterator &I = Top.second; 469 470 bool FoundNew = false; 471 while (I != succ_end(ParentBB)) { 472 BB = *I++; 473 if (Visited.insert(BB)) { 474 FoundNew = true; 475 break; 476 } 477 // Successor is in VisitStack, it's a back edge. 478 if (InStack.count(BB)) 479 Result.push_back(std::make_pair(ParentBB, BB)); 480 } 481 482 if (FoundNew) { 483 // Go down one level if there is a unvisited successor. 484 InStack.insert(BB); 485 VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); 486 } else { 487 // Go up one level. 488 InStack.erase(VisitStack.pop_back_val().first); 489 } 490 } while (!VisitStack.empty()); 491 492 493} 494 495 496 497/// AreEquivalentAddressValues - Test if A and B will obviously have the same 498/// value. This includes recognizing that %t0 and %t1 will have the same 499/// value in code like this: 500/// %t0 = getelementptr \@a, 0, 3 501/// store i32 0, i32* %t0 502/// %t1 = getelementptr \@a, 0, 3 503/// %t2 = load i32* %t1 504/// 505static bool AreEquivalentAddressValues(const Value *A, const Value *B) { 506 // Test if the values are trivially equivalent. 507 if (A == B) return true; 508 509 // Test if the values come form identical arithmetic instructions. 510 if (isa<BinaryOperator>(A) || isa<CastInst>(A) || 511 isa<PHINode>(A) || isa<GetElementPtrInst>(A)) 512 if (const Instruction *BI = dyn_cast<Instruction>(B)) 513 if (cast<Instruction>(A)->isIdenticalTo(BI)) 514 return true; 515 516 // Otherwise they may not be equivalent. 517 return false; 518} 519 520/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the 521/// instruction before ScanFrom) checking to see if we have the value at the 522/// memory address *Ptr locally available within a small number of instructions. 523/// If the value is available, return it. 524/// 525/// If not, return the iterator for the last validated instruction that the 526/// value would be live through. If we scanned the entire block and didn't find 527/// something that invalidates *Ptr or provides it, ScanFrom would be left at 528/// begin() and this returns null. ScanFrom could also be left 529/// 530/// MaxInstsToScan specifies the maximum instructions to scan in the block. If 531/// it is set to 0, it will scan the whole block. You can also optionally 532/// specify an alias analysis implementation, which makes this more precise. 533Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, 534 BasicBlock::iterator &ScanFrom, 535 unsigned MaxInstsToScan, 536 AliasAnalysis *AA) { 537 if (MaxInstsToScan == 0) MaxInstsToScan = ~0U; 538 539 // If we're using alias analysis to disambiguate get the size of *Ptr. 540 unsigned AccessSize = 0; 541 if (AA) { 542 const Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType(); 543 AccessSize = AA->getTypeStoreSize(AccessTy); 544 } 545 546 while (ScanFrom != ScanBB->begin()) { 547 // We must ignore debug info directives when counting (otherwise they 548 // would affect codegen). 549 Instruction *Inst = --ScanFrom; 550 if (isa<DbgInfoIntrinsic>(Inst)) 551 continue; 552 // We skip pointer-to-pointer bitcasts, which are NOPs. 553 // It is necessary for correctness to skip those that feed into a 554 // llvm.dbg.declare, as these are not present when debugging is off. 555 if (isa<BitCastInst>(Inst) && isa<PointerType>(Inst->getType())) 556 continue; 557 558 // Restore ScanFrom to expected value in case next test succeeds 559 ScanFrom++; 560 561 // Don't scan huge blocks. 562 if (MaxInstsToScan-- == 0) return 0; 563 564 --ScanFrom; 565 // If this is a load of Ptr, the loaded value is available. 566 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) 567 if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) 568 return LI; 569 570 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 571 // If this is a store through Ptr, the value is available! 572 if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) 573 return SI->getOperand(0); 574 575 // If Ptr is an alloca and this is a store to a different alloca, ignore 576 // the store. This is a trivial form of alias analysis that is important 577 // for reg2mem'd code. 578 if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) && 579 (isa<AllocaInst>(SI->getOperand(1)) || 580 isa<GlobalVariable>(SI->getOperand(1)))) 581 continue; 582 583 // If we have alias analysis and it says the store won't modify the loaded 584 // value, ignore the store. 585 if (AA && 586 (AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 587 continue; 588 589 // Otherwise the store that may or may not alias the pointer, bail out. 590 ++ScanFrom; 591 return 0; 592 } 593 594 // If this is some other instruction that may clobber Ptr, bail out. 595 if (Inst->mayWriteToMemory()) { 596 // If alias analysis claims that it really won't modify the load, 597 // ignore it. 598 if (AA && 599 (AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 600 continue; 601 602 // May modify the pointer, bail out. 603 ++ScanFrom; 604 return 0; 605 } 606 } 607 608 // Got to the start of the block, we didn't find it, but are done for this 609 // block. 610 return 0; 611} 612 613/// CopyPrecedingStopPoint - If I is immediately preceded by a StopPoint, 614/// make a copy of the stoppoint before InsertPos (presumably before copying 615/// or moving I). 616void llvm::CopyPrecedingStopPoint(Instruction *I, 617 BasicBlock::iterator InsertPos) { 618 if (I != I->getParent()->begin()) { 619 BasicBlock::iterator BBI = I; --BBI; 620 if (DbgStopPointInst *DSPI = dyn_cast<DbgStopPointInst>(BBI)) { 621 CallInst *newDSPI = DSPI->clone(I->getContext()); 622 newDSPI->insertBefore(InsertPos); 623 } 624 } 625} 626