1 //===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source 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/BasicBlock.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/Target/TargetData.h"
34 // Register the AliasAnalysis interface, providing a nice name to refer to.
36 RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
39 //===----------------------------------------------------------------------===//
40 // Default chaining methods
41 //===----------------------------------------------------------------------===//
43 AliasAnalysis::AliasResult
44 AliasAnalysis::alias(const Value *V1, unsigned V1Size,
45 const Value *V2, unsigned V2Size) {
46 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
47 return AA->alias(V1, V1Size, V2, V2Size);
50 void AliasAnalysis::getMustAliases(Value *P, std::vector<Value*> &RetVals) {
51 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
52 return AA->getMustAliases(P, RetVals);
55 bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
56 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
57 return AA->pointsToConstantMemory(P);
60 AliasAnalysis::ModRefBehavior
61 AliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
62 std::vector<PointerAccessInfo> *Info) {
63 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
64 return AA->getModRefBehavior(F, CS, Info);
67 bool AliasAnalysis::hasNoModRefInfoForCalls() const {
68 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
69 return AA->hasNoModRefInfoForCalls();
72 void AliasAnalysis::deleteValue(Value *V) {
73 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
77 void AliasAnalysis::copyValue(Value *From, Value *To) {
78 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
79 AA->copyValue(From, To);
82 AliasAnalysis::ModRefResult
83 AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
84 // FIXME: we can do better.
85 assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
86 return AA->getModRefInfo(CS1, CS2);
90 //===----------------------------------------------------------------------===//
91 // AliasAnalysis non-virtual helper method implementation
92 //===----------------------------------------------------------------------===//
94 AliasAnalysis::ModRefResult
95 AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
96 return alias(L->getOperand(0), TD->getTypeSize(L->getType()),
97 P, Size) ? Ref : NoModRef;
100 AliasAnalysis::ModRefResult
101 AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
102 // If the stored address cannot alias the pointer in question, then the
103 // pointer cannot be modified by the store.
104 if (!alias(S->getOperand(1), TD->getTypeSize(S->getOperand(0)->getType()),
108 // If the pointer is a pointer to constant memory, then it could not have been
109 // modified by this store.
110 return pointsToConstantMemory(P) ? NoModRef : Mod;
113 AliasAnalysis::ModRefResult
114 AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
115 ModRefResult Mask = ModRef;
116 if (Function *F = CS.getCalledFunction())
117 if (onlyReadsMemory(F)) {
118 if (doesNotAccessMemory(F)) return NoModRef;
122 if (!AA) return Mask;
124 // If P points to a constant memory location, the call definitely could not
125 // modify the memory location.
126 if ((Mask & Mod) && AA->pointsToConstantMemory(P))
129 return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size));
132 // AliasAnalysis destructor: DO NOT move this to the header file for
133 // AliasAnalysis or else clients of the AliasAnalysis class may not depend on
134 // the AliasAnalysis.o file in the current .a file, causing alias analysis
135 // support to not be included in the tool correctly!
137 AliasAnalysis::~AliasAnalysis() {}
139 /// setTargetData - Subclasses must call this method to initialize the
140 /// AliasAnalysis interface before any other methods are called.
142 void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
143 TD = &P->getAnalysis<TargetData>();
144 AA = &P->getAnalysis<AliasAnalysis>();
147 // getAnalysisUsage - All alias analysis implementations should invoke this
148 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
149 // TargetData is required by the pass.
150 void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
151 AU.addRequired<TargetData>(); // All AA's need TargetData.
152 AU.addRequired<AliasAnalysis>(); // All AA's chain
155 /// canBasicBlockModify - Return true if it is possible for execution of the
156 /// specified basic block to modify the value pointed to by Ptr.
158 bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
159 const Value *Ptr, unsigned Size) {
160 return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
163 /// canInstructionRangeModify - Return true if it is possible for the execution
164 /// of the specified instructions to modify the value pointed to by Ptr. The
165 /// instructions to consider are all of the instructions in the range of [I1,I2]
166 /// INCLUSIVE. I1 and I2 must be in the same basic block.
168 bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
169 const Instruction &I2,
170 const Value *Ptr, unsigned Size) {
171 assert(I1.getParent() == I2.getParent() &&
172 "Instructions not in same basic block!");
173 BasicBlock::iterator I = const_cast<Instruction*>(&I1);
174 BasicBlock::iterator E = const_cast<Instruction*>(&I2);
175 ++E; // Convert from inclusive to exclusive range.
177 for (; I != E; ++I) // Check every instruction in range
178 if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
183 // Because of the way .a files work, we must force the BasicAA implementation to
184 // be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
185 // the risk of AliasAnalysis being used, but the default implementation not
186 // being linked into the tool that uses it.
189 extern void BasicAAStub();
191 static IncludeFile INCLUDE_BASICAA_CPP((void*)&BasicAAStub);