AliasAnalysis.cpp revision a5f81bba4ab18d6129774d4d67495f14b6f64375
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/Instructions.h" 32#include "llvm/Type.h" 33#include "llvm/Target/TargetData.h" 34using namespace llvm; 35 36// Register the AliasAnalysis interface, providing a nice name to refer to. 37static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis"); 38char AliasAnalysis::ID = 0; 39 40//===----------------------------------------------------------------------===// 41// Default chaining methods 42//===----------------------------------------------------------------------===// 43 44AliasAnalysis::AliasResult 45AliasAnalysis::alias(const Value *V1, unsigned V1Size, 46 const Value *V2, unsigned V2Size) { 47 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 48 return AA->alias(V1, V1Size, V2, V2Size); 49} 50 51void AliasAnalysis::getMustAliases(Value *P, std::vector<Value*> &RetVals) { 52 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 53 return AA->getMustAliases(P, RetVals); 54} 55 56bool AliasAnalysis::pointsToConstantMemory(const Value *P) { 57 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 58 return AA->pointsToConstantMemory(P); 59} 60 61AliasAnalysis::ModRefBehavior 62AliasAnalysis::getModRefBehavior(Function *F, CallSite CS, 63 std::vector<PointerAccessInfo> *Info) { 64 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 65 return AA->getModRefBehavior(F, CS, Info); 66} 67 68bool AliasAnalysis::hasNoModRefInfoForCalls() const { 69 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 70 return AA->hasNoModRefInfoForCalls(); 71} 72 73void AliasAnalysis::deleteValue(Value *V) { 74 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 75 AA->deleteValue(V); 76} 77 78void AliasAnalysis::copyValue(Value *From, Value *To) { 79 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 80 AA->copyValue(From, To); 81} 82 83AliasAnalysis::ModRefResult 84AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) { 85 // FIXME: we can do better. 86 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); 87 return AA->getModRefInfo(CS1, CS2); 88} 89 90 91//===----------------------------------------------------------------------===// 92// AliasAnalysis non-virtual helper method implementation 93//===----------------------------------------------------------------------===// 94 95AliasAnalysis::ModRefResult 96AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) { 97 return alias(L->getOperand(0), TD->getTypeStoreSize(L->getType()), 98 P, Size) ? Ref : NoModRef; 99} 100 101AliasAnalysis::ModRefResult 102AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) { 103 // If the stored address cannot alias the pointer in question, then the 104 // pointer cannot be modified by the store. 105 if (!alias(S->getOperand(1), 106 TD->getTypeStoreSize(S->getOperand(0)->getType()), P, Size)) 107 return NoModRef; 108 109 // If the pointer is a pointer to constant memory, then it could not have been 110 // modified by this store. 111 return pointsToConstantMemory(P) ? NoModRef : Mod; 112} 113 114AliasAnalysis::ModRefBehavior 115AliasAnalysis::getModRefBehavior(CallSite CS, 116 std::vector<PointerAccessInfo> *Info) { 117 if (CS.doesNotAccessMemory()) 118 // Can't do better than this. 119 return DoesNotAccessMemory; 120 ModRefBehavior MRB = UnknownModRefBehavior; 121 if (Function *F = CS.getCalledFunction()) 122 MRB = getModRefBehavior(F, CS, Info); 123 if (MRB != DoesNotAccessMemory && CS.onlyReadsMemory()) 124 return OnlyReadsMemory; 125 return MRB; 126} 127 128AliasAnalysis::ModRefBehavior 129AliasAnalysis::getModRefBehavior(Function *F, 130 std::vector<PointerAccessInfo> *Info) { 131 if (F->doesNotAccessMemory()) 132 // Can't do better than this. 133 return DoesNotAccessMemory; 134 ModRefBehavior MRB = getModRefBehavior(F, CallSite(), Info); 135 if (MRB != DoesNotAccessMemory && F->onlyReadsMemory()) 136 return OnlyReadsMemory; 137 return MRB; 138} 139 140AliasAnalysis::ModRefResult 141AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { 142 ModRefResult Mask = ModRef; 143 ModRefBehavior MRB = getModRefBehavior(CS); 144 if (MRB == OnlyReadsMemory) 145 Mask = Ref; 146 else if (MRB == DoesNotAccessMemory) 147 return NoModRef; 148 149 if (!AA) return Mask; 150 151 // If P points to a constant memory location, the call definitely could not 152 // modify the memory location. 153 if ((Mask & Mod) && AA->pointsToConstantMemory(P)) 154 Mask = ModRefResult(Mask & ~Mod); 155 156 return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size)); 157} 158 159// AliasAnalysis destructor: DO NOT move this to the header file for 160// AliasAnalysis or else clients of the AliasAnalysis class may not depend on 161// the AliasAnalysis.o file in the current .a file, causing alias analysis 162// support to not be included in the tool correctly! 163// 164AliasAnalysis::~AliasAnalysis() {} 165 166/// InitializeAliasAnalysis - Subclasses must call this method to initialize the 167/// AliasAnalysis interface before any other methods are called. 168/// 169void AliasAnalysis::InitializeAliasAnalysis(Pass *P) { 170 TD = &P->getAnalysis<TargetData>(); 171 AA = &P->getAnalysis<AliasAnalysis>(); 172} 173 174// getAnalysisUsage - All alias analysis implementations should invoke this 175// directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that 176// TargetData is required by the pass. 177void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 178 AU.addRequired<TargetData>(); // All AA's need TargetData. 179 AU.addRequired<AliasAnalysis>(); // All AA's chain 180} 181 182/// canBasicBlockModify - Return true if it is possible for execution of the 183/// specified basic block to modify the value pointed to by Ptr. 184/// 185bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB, 186 const Value *Ptr, unsigned Size) { 187 return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size); 188} 189 190/// canInstructionRangeModify - Return true if it is possible for the execution 191/// of the specified instructions to modify the value pointed to by Ptr. The 192/// instructions to consider are all of the instructions in the range of [I1,I2] 193/// INCLUSIVE. I1 and I2 must be in the same basic block. 194/// 195bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1, 196 const Instruction &I2, 197 const Value *Ptr, unsigned Size) { 198 assert(I1.getParent() == I2.getParent() && 199 "Instructions not in same basic block!"); 200 BasicBlock::iterator I = const_cast<Instruction*>(&I1); 201 BasicBlock::iterator E = const_cast<Instruction*>(&I2); 202 ++E; // Convert from inclusive to exclusive range. 203 204 for (; I != E; ++I) // Check every instruction in range 205 if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod) 206 return true; 207 return false; 208} 209 210/// isNoAliasCall - Return true if this pointer is returned by a noalias 211/// function. 212bool llvm::isNoAliasCall(const Value *V) { 213 if (isa<CallInst>(V) || isa<InvokeInst>(V)) 214 return CallSite(const_cast<Instruction*>(cast<Instruction>(V))) 215 .paramHasAttr(0, Attribute::NoAlias); 216 return false; 217} 218 219/// isIdentifiedObject - Return true if this pointer refers to a distinct and 220/// identifiable object. This returns true for: 221/// Global Variables and Functions 222/// Allocas and Mallocs 223/// ByVal and NoAlias Arguments 224/// NoAlias returns 225/// 226bool llvm::isIdentifiedObject(const Value *V) { 227 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isNoAliasCall(V)) 228 return true; 229 if (const Argument *A = dyn_cast<Argument>(V)) 230 return A->hasNoAliasAttr() || A->hasByValAttr(); 231 return false; 232} 233 234// Because of the way .a files work, we must force the BasicAA implementation to 235// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run 236// the risk of AliasAnalysis being used, but the default implementation not 237// being linked into the tool that uses it. 238DEFINING_FILE_FOR(AliasAnalysis) 239