AliasAnalysis.cpp revision 5753a4a0033da4add45f2e9930a4e1159d92a869
1//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==// 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 file implements the generic AliasAnalysis interface which is used as the 11// common interface used by all clients and implementations of alias analysis. 12// 13// This file also implements the default version of the AliasAnalysis interface 14// that is to be used when no other implementation is specified. This does some 15// simple tests that detect obvious cases: two different global pointers cannot 16// alias, a global cannot alias a malloc, two different mallocs cannot alias, 17// etc. 18// 19// This alias analysis implementation really isn't very good for anything, but 20// it is very fast, and makes a nice clean default implementation. Because it 21// handles lots of little corner cases, other, more complex, alias analysis 22// implementations may choose to rely on this pass to resolve these simple and 23// easy cases. 24// 25//===----------------------------------------------------------------------===// 26 27#include "llvm/Analysis/AliasAnalysis.h" 28#include "llvm/Pass.h" 29#include "llvm/BasicBlock.h" 30#include "llvm/Function.h" 31#include "llvm/IntrinsicInst.h" 32#include "llvm/Instructions.h" 33#include "llvm/Type.h" 34#include "llvm/Target/TargetData.h" 35using namespace llvm; 36 37// Register the AliasAnalysis interface, providing a nice name to refer to. 38static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis"); 39char AliasAnalysis::ID = 0; 40 41//===----------------------------------------------------------------------===// 42// Default chaining methods 43//===----------------------------------------------------------------------===// 44 45AliasAnalysis::AliasResult 46AliasAnalysis::alias(const Value *V1, unsigned V1Size, 47 const Value *V2, unsigned V2Size) { 48 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 49 return AA->alias(V1, V1Size, V2, V2Size); 50} 51 52void AliasAnalysis::getMustAliases(Value *P, std::vector<Value*> &RetVals) { 53 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 54 return AA->getMustAliases(P, RetVals); 55} 56 57bool AliasAnalysis::pointsToConstantMemory(const Value *P) { 58 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 59 return AA->pointsToConstantMemory(P); 60} 61 62bool AliasAnalysis::hasNoModRefInfoForCalls() const { 63 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 64 return AA->hasNoModRefInfoForCalls(); 65} 66 67void AliasAnalysis::deleteValue(Value *V) { 68 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 69 AA->deleteValue(V); 70} 71 72void AliasAnalysis::copyValue(Value *From, Value *To) { 73 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 74 AA->copyValue(From, To); 75} 76 77AliasAnalysis::ModRefResult 78AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) { 79 // FIXME: we can do better. 80 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 81 return AA->getModRefInfo(CS1, CS2); 82} 83 84 85//===----------------------------------------------------------------------===// 86// AliasAnalysis non-virtual helper method implementation 87//===----------------------------------------------------------------------===// 88 89AliasAnalysis::ModRefResult 90AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) { 91 return alias(L->getOperand(0), getTypeStoreSize(L->getType()), 92 P, Size) ? Ref : NoModRef; 93} 94 95AliasAnalysis::ModRefResult 96AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) { 97 // If the stored address cannot alias the pointer in question, then the 98 // pointer cannot be modified by the store. 99 if (!alias(S->getOperand(1), 100 getTypeStoreSize(S->getOperand(0)->getType()), P, Size)) 101 return NoModRef; 102 103 // If the pointer is a pointer to constant memory, then it could not have been 104 // modified by this store. 105 return pointsToConstantMemory(P) ? NoModRef : Mod; 106} 107 108AliasAnalysis::ModRefBehavior 109AliasAnalysis::getModRefBehavior(CallSite CS, 110 std::vector<PointerAccessInfo> *Info) { 111 if (CS.doesNotAccessMemory()) 112 // Can't do better than this. 113 return DoesNotAccessMemory; 114 ModRefBehavior MRB = getModRefBehavior(CS.getCalledFunction(), Info); 115 if (MRB != DoesNotAccessMemory && CS.onlyReadsMemory()) 116 return OnlyReadsMemory; 117 return MRB; 118} 119 120AliasAnalysis::ModRefBehavior 121AliasAnalysis::getModRefBehavior(Function *F, 122 std::vector<PointerAccessInfo> *Info) { 123 if (F) { 124 if (F->doesNotAccessMemory()) 125 // Can't do better than this. 126 return DoesNotAccessMemory; 127 if (F->onlyReadsMemory()) 128 return OnlyReadsMemory; 129 if (unsigned id = F->getIntrinsicID()) { 130#define GET_INTRINSIC_MODREF_BEHAVIOR 131#include "llvm/Intrinsics.gen" 132#undef GET_INTRINSIC_MODREF_BEHAVIOR 133 } 134 } 135 return UnknownModRefBehavior; 136} 137 138AliasAnalysis::ModRefResult 139AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { 140 ModRefResult Mask = ModRef; 141 ModRefBehavior MRB = getModRefBehavior(CS); 142 if (MRB == DoesNotAccessMemory) 143 return NoModRef; 144 else if (MRB == OnlyReadsMemory) 145 Mask = Ref; 146 else if (MRB == AliasAnalysis::AccessesArguments) { 147 bool doesAlias = false; 148 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end(); 149 AI != AE; ++AI) 150 if (alias(*AI, ~0U, P, Size) != NoAlias) { 151 doesAlias = true; 152 break; 153 } 154 155 if (!doesAlias) 156 return NoModRef; 157 } 158 159 if (!AA) return Mask; 160 161 // If P points to a constant memory location, the call definitely could not 162 // modify the memory location. 163 if ((Mask & Mod) && AA->pointsToConstantMemory(P)) 164 Mask = ModRefResult(Mask & ~Mod); 165 166 return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size)); 167} 168 169// AliasAnalysis destructor: DO NOT move this to the header file for 170// AliasAnalysis or else clients of the AliasAnalysis class may not depend on 171// the AliasAnalysis.o file in the current .a file, causing alias analysis 172// support to not be included in the tool correctly! 173// 174AliasAnalysis::~AliasAnalysis() {} 175 176/// InitializeAliasAnalysis - Subclasses must call this method to initialize the 177/// AliasAnalysis interface before any other methods are called. 178/// 179void AliasAnalysis::InitializeAliasAnalysis(Pass *P) { 180 TD = P->getAnalysisIfAvailable<TargetData>(); 181 AA = &P->getAnalysis<AliasAnalysis>(); 182} 183 184// getAnalysisUsage - All alias analysis implementations should invoke this 185// directly (using AliasAnalysis::getAnalysisUsage(AU)). 186void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 187 AU.addRequired<AliasAnalysis>(); // All AA's chain 188} 189 190/// getTypeStoreSize - Return the TargetData store size for the given type, 191/// if known, or a conservative value otherwise. 192/// 193unsigned AliasAnalysis::getTypeStoreSize(const Type *Ty) { 194 return TD ? TD->getTypeStoreSize(Ty) : ~0u; 195} 196 197/// canBasicBlockModify - Return true if it is possible for execution of the 198/// specified basic block to modify the value pointed to by Ptr. 199/// 200bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB, 201 const Value *Ptr, unsigned Size) { 202 return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size); 203} 204 205/// canInstructionRangeModify - Return true if it is possible for the execution 206/// of the specified instructions to modify the value pointed to by Ptr. The 207/// instructions to consider are all of the instructions in the range of [I1,I2] 208/// INCLUSIVE. I1 and I2 must be in the same basic block. 209/// 210bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1, 211 const Instruction &I2, 212 const Value *Ptr, unsigned Size) { 213 assert(I1.getParent() == I2.getParent() && 214 "Instructions not in same basic block!"); 215 BasicBlock::iterator I = const_cast<Instruction*>(&I1); 216 BasicBlock::iterator E = const_cast<Instruction*>(&I2); 217 ++E; // Convert from inclusive to exclusive range. 218 219 for (; I != E; ++I) // Check every instruction in range 220 if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod) 221 return true; 222 return false; 223} 224 225/// isNoAliasCall - Return true if this pointer is returned by a noalias 226/// function. 227bool llvm::isNoAliasCall(const Value *V) { 228 if (isa<CallInst>(V) || isa<InvokeInst>(V)) 229 return CallSite(const_cast<Instruction*>(cast<Instruction>(V))) 230 .paramHasAttr(0, Attribute::NoAlias); 231 return false; 232} 233 234/// isIdentifiedObject - Return true if this pointer refers to a distinct and 235/// identifiable object. This returns true for: 236/// Global Variables and Functions (but not Global Aliases) 237/// Allocas and Mallocs 238/// ByVal and NoAlias Arguments 239/// NoAlias returns 240/// 241bool llvm::isIdentifiedObject(const Value *V) { 242 if (isa<AllocationInst>(V) || isNoAliasCall(V)) 243 return true; 244 if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V)) 245 return true; 246 if (const Argument *A = dyn_cast<Argument>(V)) 247 return A->hasNoAliasAttr() || A->hasByValAttr(); 248 return false; 249} 250 251// Because of the way .a files work, we must force the BasicAA implementation to 252// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run 253// the risk of AliasAnalysis being used, but the default implementation not 254// being linked into the tool that uses it. 255DEFINING_FILE_FOR(AliasAnalysis) 256