1 //===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
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,
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
25 //===----------------------------------------------------------------------===//
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"
37 // Register the AliasAnalysis interface, providing a nice name to refer to.
38 static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
39 char AliasAnalysis::ID = 0;
41 //===----------------------------------------------------------------------===//
42 // Default chaining methods
43 //===----------------------------------------------------------------------===//
45 AliasAnalysis::AliasResult
46 AliasAnalysis::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);
52 bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
53 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
54 return AA->pointsToConstantMemory(P);
57 void AliasAnalysis::deleteValue(Value *V) {
58 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
62 void AliasAnalysis::copyValue(Value *From, Value *To) {
63 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
64 AA->copyValue(From, To);
67 AliasAnalysis::ModRefResult
68 AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
69 // FIXME: we can do better.
70 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
71 return AA->getModRefInfo(CS1, CS2);
75 //===----------------------------------------------------------------------===//
76 // AliasAnalysis non-virtual helper method implementation
77 //===----------------------------------------------------------------------===//
79 AliasAnalysis::ModRefResult
80 AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
81 return alias(L->getOperand(0), getTypeStoreSize(L->getType()),
82 P, Size) ? Ref : NoModRef;
85 AliasAnalysis::ModRefResult
86 AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
87 // If the stored address cannot alias the pointer in question, then the
88 // pointer cannot be modified by the store.
89 if (!alias(S->getOperand(1),
90 getTypeStoreSize(S->getOperand(0)->getType()), P, Size))
93 // If the pointer is a pointer to constant memory, then it could not have been
94 // modified by this store.
95 return pointsToConstantMemory(P) ? NoModRef : Mod;
98 AliasAnalysis::ModRefBehavior
99 AliasAnalysis::getModRefBehavior(CallSite CS,
100 std::vector<PointerAccessInfo> *Info) {
101 if (CS.doesNotAccessMemory())
102 // Can't do better than this.
103 return DoesNotAccessMemory;
104 ModRefBehavior MRB = getModRefBehavior(CS.getCalledFunction(), Info);
105 if (MRB != DoesNotAccessMemory && CS.onlyReadsMemory())
106 return OnlyReadsMemory;
110 AliasAnalysis::ModRefBehavior
111 AliasAnalysis::getModRefBehavior(Function *F,
112 std::vector<PointerAccessInfo> *Info) {
114 if (F->doesNotAccessMemory())
115 // Can't do better than this.
116 return DoesNotAccessMemory;
117 if (F->onlyReadsMemory())
118 return OnlyReadsMemory;
119 if (unsigned id = F->getIntrinsicID()) {
120 #define GET_INTRINSIC_MODREF_BEHAVIOR
121 #include "llvm/Intrinsics.gen"
122 #undef GET_INTRINSIC_MODREF_BEHAVIOR
125 return UnknownModRefBehavior;
128 AliasAnalysis::ModRefResult
129 AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
130 ModRefBehavior MRB = getModRefBehavior(CS);
131 if (MRB == DoesNotAccessMemory)
134 ModRefResult Mask = ModRef;
135 if (MRB == OnlyReadsMemory)
137 else if (MRB == AliasAnalysis::AccessesArguments) {
138 bool doesAlias = false;
139 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
141 if (!isNoAlias(*AI, ~0U, P, Size)) {
150 if (!AA) return Mask;
152 // If P points to a constant memory location, the call definitely could not
153 // modify the memory location.
154 if ((Mask & Mod) && AA->pointsToConstantMemory(P))
155 Mask = ModRefResult(Mask & ~Mod);
157 return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size));
160 // AliasAnalysis destructor: DO NOT move this to the header file for
161 // AliasAnalysis or else clients of the AliasAnalysis class may not depend on
162 // the AliasAnalysis.o file in the current .a file, causing alias analysis
163 // support to not be included in the tool correctly!
165 AliasAnalysis::~AliasAnalysis() {}
167 /// InitializeAliasAnalysis - Subclasses must call this method to initialize the
168 /// AliasAnalysis interface before any other methods are called.
170 void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
171 TD = P->getAnalysisIfAvailable<TargetData>();
172 AA = &P->getAnalysis<AliasAnalysis>();
175 // getAnalysisUsage - All alias analysis implementations should invoke this
176 // directly (using AliasAnalysis::getAnalysisUsage(AU)).
177 void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
178 AU.addRequired<AliasAnalysis>(); // All AA's chain
181 /// getTypeStoreSize - Return the TargetData store size for the given type,
182 /// if known, or a conservative value otherwise.
184 unsigned AliasAnalysis::getTypeStoreSize(const Type *Ty) {
185 return TD ? TD->getTypeStoreSize(Ty) : ~0u;
188 /// canBasicBlockModify - Return true if it is possible for execution of the
189 /// specified basic block to modify the value pointed to by Ptr.
191 bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
192 const Value *Ptr, unsigned Size) {
193 return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
196 /// canInstructionRangeModify - Return true if it is possible for the execution
197 /// of the specified instructions to modify the value pointed to by Ptr. The
198 /// instructions to consider are all of the instructions in the range of [I1,I2]
199 /// INCLUSIVE. I1 and I2 must be in the same basic block.
201 bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
202 const Instruction &I2,
203 const Value *Ptr, unsigned Size) {
204 assert(I1.getParent() == I2.getParent() &&
205 "Instructions not in same basic block!");
206 BasicBlock::iterator I = const_cast<Instruction*>(&I1);
207 BasicBlock::iterator E = const_cast<Instruction*>(&I2);
208 ++E; // Convert from inclusive to exclusive range.
210 for (; I != E; ++I) // Check every instruction in range
211 if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
216 /// isNoAliasCall - Return true if this pointer is returned by a noalias
218 bool llvm::isNoAliasCall(const Value *V) {
219 if (isa<CallInst>(V) || isa<InvokeInst>(V))
220 return CallSite(const_cast<Instruction*>(cast<Instruction>(V)))
221 .paramHasAttr(0, Attribute::NoAlias);
225 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
226 /// identifiable object. This returns true for:
227 /// Global Variables and Functions (but not Global Aliases)
228 /// Allocas and Mallocs
229 /// ByVal and NoAlias Arguments
232 bool llvm::isIdentifiedObject(const Value *V) {
233 if (isa<AllocaInst>(V) || isNoAliasCall(V))
235 if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
237 if (const Argument *A = dyn_cast<Argument>(V))
238 return A->hasNoAliasAttr() || A->hasByValAttr();
242 // Because of the way .a files work, we must force the BasicAA implementation to
243 // be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
244 // the risk of AliasAnalysis being used, but the default implementation not
245 // being linked into the tool that uses it.
246 DEFINING_FILE_FOR(AliasAnalysis)