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/Instructions.h"
32 #include "llvm/Type.h"
33 #include "llvm/Target/TargetData.h"
36 // Register the AliasAnalysis interface, providing a nice name to refer to.
37 static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
38 char AliasAnalysis::ID = 0;
40 //===----------------------------------------------------------------------===//
41 // Default chaining methods
42 //===----------------------------------------------------------------------===//
44 AliasAnalysis::AliasResult
45 AliasAnalysis::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);
51 void 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);
56 bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
57 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
58 return AA->pointsToConstantMemory(P);
61 AliasAnalysis::ModRefBehavior
62 AliasAnalysis::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);
68 bool AliasAnalysis::hasNoModRefInfoForCalls() const {
69 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
70 return AA->hasNoModRefInfoForCalls();
73 void AliasAnalysis::deleteValue(Value *V) {
74 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
78 void AliasAnalysis::copyValue(Value *From, Value *To) {
79 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
80 AA->copyValue(From, To);
83 AliasAnalysis::ModRefResult
84 AliasAnalysis::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);
91 //===----------------------------------------------------------------------===//
92 // AliasAnalysis non-virtual helper method implementation
93 //===----------------------------------------------------------------------===//
95 AliasAnalysis::ModRefResult
96 AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
97 return alias(L->getOperand(0), TD->getTypeStoreSize(L->getType()),
98 P, Size) ? Ref : NoModRef;
101 AliasAnalysis::ModRefResult
102 AliasAnalysis::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))
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;
114 AliasAnalysis::ModRefBehavior
115 AliasAnalysis::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;
128 AliasAnalysis::ModRefBehavior
129 AliasAnalysis::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;
140 AliasAnalysis::ModRefResult
141 AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
142 ModRefResult Mask = ModRef;
143 ModRefBehavior MRB = getModRefBehavior(CS);
144 if (MRB == OnlyReadsMemory)
146 else if (MRB == DoesNotAccessMemory)
149 if (!AA) return Mask;
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);
156 return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size));
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!
164 AliasAnalysis::~AliasAnalysis() {}
166 /// InitializeAliasAnalysis - Subclasses must call this method to initialize the
167 /// AliasAnalysis interface before any other methods are called.
169 void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
170 TD = &P->getAnalysis<TargetData>();
171 AA = &P->getAnalysis<AliasAnalysis>();
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.
177 void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
178 AU.addRequired<TargetData>(); // All AA's need TargetData.
179 AU.addRequired<AliasAnalysis>(); // All AA's chain
182 /// canBasicBlockModify - Return true if it is possible for execution of the
183 /// specified basic block to modify the value pointed to by Ptr.
185 bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
186 const Value *Ptr, unsigned Size) {
187 return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
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.
195 bool 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.
204 for (; I != E; ++I) // Check every instruction in range
205 if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
210 /// isNoAliasCall - Return true if this pointer is returned by a noalias
212 bool 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);
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
226 bool llvm::isIdentifiedObject(const Value *V) {
227 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isNoAliasCall(V))
229 if (const Argument *A = dyn_cast<Argument>(V))
230 return A->hasNoAliasAttr() || A->hasByValAttr();
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.
238 DEFINING_FILE_FOR(AliasAnalysis)