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/Type.h"
31 #include "llvm/Target/TargetData.h"
35 // Register the AliasAnalysis interface, providing a nice name to refer to.
37 RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
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->getTypeSize(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), TD->getTypeSize(S->getOperand(0)->getType()),
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::ModRefResult
115 AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
116 ModRefResult Mask = ModRef;
117 if (Function *F = CS.getCalledFunction()) {
118 ModRefBehavior MRB = getModRefBehavior(F, CallSite());
119 if (MRB == OnlyReadsMemory)
121 else if (MRB == DoesNotAccessMemory)
125 if (!AA) return Mask;
127 // If P points to a constant memory location, the call definitely could not
128 // modify the memory location.
129 if ((Mask & Mod) && AA->pointsToConstantMemory(P))
130 Mask = ModRefResult(Mask & ~Mod);
132 return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size));
135 // AliasAnalysis destructor: DO NOT move this to the header file for
136 // AliasAnalysis or else clients of the AliasAnalysis class may not depend on
137 // the AliasAnalysis.o file in the current .a file, causing alias analysis
138 // support to not be included in the tool correctly!
140 AliasAnalysis::~AliasAnalysis() {}
142 /// setTargetData - Subclasses must call this method to initialize the
143 /// AliasAnalysis interface before any other methods are called.
145 void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
146 TD = &P->getAnalysis<TargetData>();
147 AA = &P->getAnalysis<AliasAnalysis>();
150 // getAnalysisUsage - All alias analysis implementations should invoke this
151 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
152 // TargetData is required by the pass.
153 void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
154 AU.addRequired<TargetData>(); // All AA's need TargetData.
155 AU.addRequired<AliasAnalysis>(); // All AA's chain
158 /// canBasicBlockModify - Return true if it is possible for execution of the
159 /// specified basic block to modify the value pointed to by Ptr.
161 bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
162 const Value *Ptr, unsigned Size) {
163 return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
166 /// canInstructionRangeModify - Return true if it is possible for the execution
167 /// of the specified instructions to modify the value pointed to by Ptr. The
168 /// instructions to consider are all of the instructions in the range of [I1,I2]
169 /// INCLUSIVE. I1 and I2 must be in the same basic block.
171 bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
172 const Instruction &I2,
173 const Value *Ptr, unsigned Size) {
174 assert(I1.getParent() == I2.getParent() &&
175 "Instructions not in same basic block!");
176 BasicBlock::iterator I = const_cast<Instruction*>(&I1);
177 BasicBlock::iterator E = const_cast<Instruction*>(&I2);
178 ++E; // Convert from inclusive to exclusive range.
180 for (; I != E; ++I) // Check every instruction in range
181 if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
186 // Because of the way .a files work, we must force the BasicAA implementation to
187 // be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
188 // the risk of AliasAnalysis being used, but the default implementation not
189 // being linked into the tool that uses it.
192 extern void BasicAAStub();
194 static IncludeFile INCLUDE_BASICAA_CPP((void*)&BasicAAStub);