BasicBlockUtils.cpp revision a7235ea7245028a0723e8ab7fd011386b3900777
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(UndefValue::get(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(UndefValue::get(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 = Constant::getNullValue(BB->getParent()->getReturnType()); 256 257 // Create the return... 258 NewTI = ReturnInst::Create(RetVal); 259 } 260 break; 261 262 case Instruction::Invoke: // Should convert to call 263 case Instruction::Switch: // Should remove entry 264 default: 265 case Instruction::Ret: // Cannot happen, has no successors! 266 llvm_unreachable("Unhandled terminator instruction type in RemoveSuccessor!"); 267 } 268 269 if (NewTI) // If it's a different instruction, replace. 270 ReplaceInstWithInst(TI, NewTI); 271} 272 273/// SplitEdge - Split the edge connecting specified block. Pass P must 274/// not be NULL. 275BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) { 276 TerminatorInst *LatchTerm = BB->getTerminator(); 277 unsigned SuccNum = 0; 278#ifndef NDEBUG 279 unsigned e = LatchTerm->getNumSuccessors(); 280#endif 281 for (unsigned i = 0; ; ++i) { 282 assert(i != e && "Didn't find edge?"); 283 if (LatchTerm->getSuccessor(i) == Succ) { 284 SuccNum = i; 285 break; 286 } 287 } 288 289 // If this is a critical edge, let SplitCriticalEdge do it. 290 if (SplitCriticalEdge(BB->getTerminator(), SuccNum, P)) 291 return LatchTerm->getSuccessor(SuccNum); 292 293 // If the edge isn't critical, then BB has a single successor or Succ has a 294 // single pred. Split the block. 295 BasicBlock::iterator SplitPoint; 296 if (BasicBlock *SP = Succ->getSinglePredecessor()) { 297 // If the successor only has a single pred, split the top of the successor 298 // block. 299 assert(SP == BB && "CFG broken"); 300 SP = NULL; 301 return SplitBlock(Succ, Succ->begin(), P); 302 } else { 303 // Otherwise, if BB has a single successor, split it at the bottom of the 304 // block. 305 assert(BB->getTerminator()->getNumSuccessors() == 1 && 306 "Should have a single succ!"); 307 return SplitBlock(BB, BB->getTerminator(), P); 308 } 309} 310 311/// SplitBlock - Split the specified block at the specified instruction - every 312/// thing before SplitPt stays in Old and everything starting with SplitPt moves 313/// to a new block. The two blocks are joined by an unconditional branch and 314/// the loop info is updated. 315/// 316BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) { 317 BasicBlock::iterator SplitIt = SplitPt; 318 while (isa<PHINode>(SplitIt)) 319 ++SplitIt; 320 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split"); 321 322 // The new block lives in whichever loop the old one did. 323 if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>()) 324 if (Loop *L = LI->getLoopFor(Old)) 325 L->addBasicBlockToLoop(New, LI->getBase()); 326 327 if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) 328 { 329 // Old dominates New. New node domiantes all other nodes dominated by Old. 330 DomTreeNode *OldNode = DT->getNode(Old); 331 std::vector<DomTreeNode *> Children; 332 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); 333 I != E; ++I) 334 Children.push_back(*I); 335 336 DomTreeNode *NewNode = DT->addNewBlock(New,Old); 337 338 for (std::vector<DomTreeNode *>::iterator I = Children.begin(), 339 E = Children.end(); I != E; ++I) 340 DT->changeImmediateDominator(*I, NewNode); 341 } 342 343 if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>()) 344 DF->splitBlock(Old); 345 346 return New; 347} 348 349 350/// SplitBlockPredecessors - This method transforms BB by introducing a new 351/// basic block into the function, and moving some of the predecessors of BB to 352/// be predecessors of the new block. The new predecessors are indicated by the 353/// Preds array, which has NumPreds elements in it. The new block is given a 354/// suffix of 'Suffix'. 355/// 356/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and 357/// DominanceFrontier, but no other analyses. 358BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, 359 BasicBlock *const *Preds, 360 unsigned NumPreds, const char *Suffix, 361 Pass *P) { 362 // Create new basic block, insert right before the original block. 363 BasicBlock *NewBB = 364 BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB); 365 366 // The new block unconditionally branches to the old block. 367 BranchInst *BI = BranchInst::Create(BB, NewBB); 368 369 // Move the edges from Preds to point to NewBB instead of BB. 370 for (unsigned i = 0; i != NumPreds; ++i) 371 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); 372 373 // Update dominator tree and dominator frontier if available. 374 DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0; 375 if (DT) 376 DT->splitBlock(NewBB); 377 if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0) 378 DF->splitBlock(NewBB); 379 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0; 380 381 382 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI 383 // node becomes an incoming value for BB's phi node. However, if the Preds 384 // list is empty, we need to insert dummy entries into the PHI nodes in BB to 385 // account for the newly created predecessor. 386 if (NumPreds == 0) { 387 // Insert dummy values as the incoming value. 388 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) 389 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB); 390 return NewBB; 391 } 392 393 // Otherwise, create a new PHI node in NewBB for each PHI node in BB. 394 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) { 395 PHINode *PN = cast<PHINode>(I++); 396 397 // Check to see if all of the values coming in are the same. If so, we 398 // don't need to create a new PHI node. 399 Value *InVal = PN->getIncomingValueForBlock(Preds[0]); 400 for (unsigned i = 1; i != NumPreds; ++i) 401 if (InVal != PN->getIncomingValueForBlock(Preds[i])) { 402 InVal = 0; 403 break; 404 } 405 406 if (InVal) { 407 // If all incoming values for the new PHI would be the same, just don't 408 // make a new PHI. Instead, just remove the incoming values from the old 409 // PHI. 410 for (unsigned i = 0; i != NumPreds; ++i) 411 PN->removeIncomingValue(Preds[i], false); 412 } else { 413 // If the values coming into the block are not the same, we need a PHI. 414 // Create the new PHI node, insert it into NewBB at the end of the block 415 PHINode *NewPHI = 416 PHINode::Create(PN->getType(), PN->getName()+".ph", BI); 417 if (AA) AA->copyValue(PN, NewPHI); 418 419 // Move all of the PHI values for 'Preds' to the new PHI. 420 for (unsigned i = 0; i != NumPreds; ++i) { 421 Value *V = PN->removeIncomingValue(Preds[i], false); 422 NewPHI->addIncoming(V, Preds[i]); 423 } 424 InVal = NewPHI; 425 } 426 427 // Add an incoming value to the PHI node in the loop for the preheader 428 // edge. 429 PN->addIncoming(InVal, NewBB); 430 431 // Check to see if we can eliminate this phi node. 432 if (Value *V = PN->hasConstantValue(DT != 0)) { 433 Instruction *I = dyn_cast<Instruction>(V); 434 if (!I || DT == 0 || DT->dominates(I, PN)) { 435 PN->replaceAllUsesWith(V); 436 if (AA) AA->deleteValue(PN); 437 PN->eraseFromParent(); 438 } 439 } 440 } 441 442 return NewBB; 443} 444 445/// FindFunctionBackedges - Analyze the specified function to find all of the 446/// loop backedges in the function and return them. This is a relatively cheap 447/// (compared to computing dominators and loop info) analysis. 448/// 449/// The output is added to Result, as pairs of <from,to> edge info. 450void llvm::FindFunctionBackedges(const Function &F, 451 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) { 452 const BasicBlock *BB = &F.getEntryBlock(); 453 if (succ_begin(BB) == succ_end(BB)) 454 return; 455 456 SmallPtrSet<const BasicBlock*, 8> Visited; 457 SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack; 458 SmallPtrSet<const BasicBlock*, 8> InStack; 459 460 Visited.insert(BB); 461 VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); 462 InStack.insert(BB); 463 do { 464 std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back(); 465 const BasicBlock *ParentBB = Top.first; 466 succ_const_iterator &I = Top.second; 467 468 bool FoundNew = false; 469 while (I != succ_end(ParentBB)) { 470 BB = *I++; 471 if (Visited.insert(BB)) { 472 FoundNew = true; 473 break; 474 } 475 // Successor is in VisitStack, it's a back edge. 476 if (InStack.count(BB)) 477 Result.push_back(std::make_pair(ParentBB, BB)); 478 } 479 480 if (FoundNew) { 481 // Go down one level if there is a unvisited successor. 482 InStack.insert(BB); 483 VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); 484 } else { 485 // Go up one level. 486 InStack.erase(VisitStack.pop_back_val().first); 487 } 488 } while (!VisitStack.empty()); 489 490 491} 492 493 494 495/// AreEquivalentAddressValues - Test if A and B will obviously have the same 496/// value. This includes recognizing that %t0 and %t1 will have the same 497/// value in code like this: 498/// %t0 = getelementptr \@a, 0, 3 499/// store i32 0, i32* %t0 500/// %t1 = getelementptr \@a, 0, 3 501/// %t2 = load i32* %t1 502/// 503static bool AreEquivalentAddressValues(const Value *A, const Value *B) { 504 // Test if the values are trivially equivalent. 505 if (A == B) return true; 506 507 // Test if the values come form identical arithmetic instructions. 508 if (isa<BinaryOperator>(A) || isa<CastInst>(A) || 509 isa<PHINode>(A) || isa<GetElementPtrInst>(A)) 510 if (const Instruction *BI = dyn_cast<Instruction>(B)) 511 if (cast<Instruction>(A)->isIdenticalTo(BI)) 512 return true; 513 514 // Otherwise they may not be equivalent. 515 return false; 516} 517 518/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the 519/// instruction before ScanFrom) checking to see if we have the value at the 520/// memory address *Ptr locally available within a small number of instructions. 521/// If the value is available, return it. 522/// 523/// If not, return the iterator for the last validated instruction that the 524/// value would be live through. If we scanned the entire block and didn't find 525/// something that invalidates *Ptr or provides it, ScanFrom would be left at 526/// begin() and this returns null. ScanFrom could also be left 527/// 528/// MaxInstsToScan specifies the maximum instructions to scan in the block. If 529/// it is set to 0, it will scan the whole block. You can also optionally 530/// specify an alias analysis implementation, which makes this more precise. 531Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, 532 BasicBlock::iterator &ScanFrom, 533 unsigned MaxInstsToScan, 534 AliasAnalysis *AA) { 535 if (MaxInstsToScan == 0) MaxInstsToScan = ~0U; 536 537 // If we're using alias analysis to disambiguate get the size of *Ptr. 538 unsigned AccessSize = 0; 539 if (AA) { 540 const Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType(); 541 AccessSize = AA->getTypeStoreSize(AccessTy); 542 } 543 544 while (ScanFrom != ScanBB->begin()) { 545 // We must ignore debug info directives when counting (otherwise they 546 // would affect codegen). 547 Instruction *Inst = --ScanFrom; 548 if (isa<DbgInfoIntrinsic>(Inst)) 549 continue; 550 // We skip pointer-to-pointer bitcasts, which are NOPs. 551 // It is necessary for correctness to skip those that feed into a 552 // llvm.dbg.declare, as these are not present when debugging is off. 553 if (isa<BitCastInst>(Inst) && isa<PointerType>(Inst->getType())) 554 continue; 555 556 // Restore ScanFrom to expected value in case next test succeeds 557 ScanFrom++; 558 559 // Don't scan huge blocks. 560 if (MaxInstsToScan-- == 0) return 0; 561 562 --ScanFrom; 563 // If this is a load of Ptr, the loaded value is available. 564 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) 565 if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) 566 return LI; 567 568 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 569 // If this is a store through Ptr, the value is available! 570 if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) 571 return SI->getOperand(0); 572 573 // If Ptr is an alloca and this is a store to a different alloca, ignore 574 // the store. This is a trivial form of alias analysis that is important 575 // for reg2mem'd code. 576 if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) && 577 (isa<AllocaInst>(SI->getOperand(1)) || 578 isa<GlobalVariable>(SI->getOperand(1)))) 579 continue; 580 581 // If we have alias analysis and it says the store won't modify the loaded 582 // value, ignore the store. 583 if (AA && 584 (AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 585 continue; 586 587 // Otherwise the store that may or may not alias the pointer, bail out. 588 ++ScanFrom; 589 return 0; 590 } 591 592 // If this is some other instruction that may clobber Ptr, bail out. 593 if (Inst->mayWriteToMemory()) { 594 // If alias analysis claims that it really won't modify the load, 595 // ignore it. 596 if (AA && 597 (AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 598 continue; 599 600 // May modify the pointer, bail out. 601 ++ScanFrom; 602 return 0; 603 } 604 } 605 606 // Got to the start of the block, we didn't find it, but are done for this 607 // block. 608 return 0; 609} 610 611/// CopyPrecedingStopPoint - If I is immediately preceded by a StopPoint, 612/// make a copy of the stoppoint before InsertPos (presumably before copying 613/// or moving I). 614void llvm::CopyPrecedingStopPoint(Instruction *I, 615 BasicBlock::iterator InsertPos) { 616 if (I != I->getParent()->begin()) { 617 BasicBlock::iterator BBI = I; --BBI; 618 if (DbgStopPointInst *DSPI = dyn_cast<DbgStopPointInst>(BBI)) { 619 CallInst *newDSPI = DSPI->clone(I->getContext()); 620 newDSPI->insertBefore(InsertPos); 621 } 622 } 623} 624