1 //===- DataStructureAA.cpp - Data Structure Based Alias Analysis ----------===//
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 pass uses the top-down data structure graphs to implement a simple
11 // context sensitive alias analysis.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Module.h"
16 #include "llvm/Analysis/AliasAnalysis.h"
17 #include "llvm/Analysis/Passes.h"
18 #include "llvm/Analysis/DataStructure/DataStructure.h"
19 #include "llvm/Analysis/DataStructure/DSGraph.h"
23 class DSAA : public ModulePass, public AliasAnalysis {
29 //------------------------------------------------
30 // Implement the Pass API
33 // run - Build up the result graph, representing the pointer graph for the
36 bool runOnModule(Module &M) {
37 InitializeAliasAnalysis(this);
38 TD = &getAnalysis<TDDataStructures>();
39 BU = &getAnalysis<BUDataStructures>();
43 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
44 AliasAnalysis::getAnalysisUsage(AU);
45 AU.setPreservesAll(); // Does not transform code
46 AU.addRequiredTransitive<TDDataStructures>(); // Uses TD Datastructures
47 AU.addRequiredTransitive<BUDataStructures>(); // Uses BU Datastructures
50 //------------------------------------------------
51 // Implement the AliasAnalysis API
54 AliasResult alias(const Value *V1, unsigned V1Size,
55 const Value *V2, unsigned V2Size);
57 void getMustAliases(Value *P, std::vector<Value*> &RetVals);
59 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
60 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
61 return AliasAnalysis::getModRefInfo(CS1,CS2);
65 DSGraph *getGraphForValue(const Value *V);
68 // Register the pass...
69 RegisterOpt<DSAA> X("ds-aa", "Data Structure Graph Based Alias Analysis");
71 // Register as an implementation of AliasAnalysis
72 RegisterAnalysisGroup<AliasAnalysis, DSAA> Y;
75 ModulePass *llvm::createDSAAPass() { return new DSAA(); }
77 // getGraphForValue - Return the DSGraph to use for queries about the specified
80 DSGraph *DSAA::getGraphForValue(const Value *V) {
81 if (const Instruction *I = dyn_cast<Instruction>(V))
82 return &TD->getDSGraph(*I->getParent()->getParent());
83 else if (const Argument *A = dyn_cast<Argument>(V))
84 return &TD->getDSGraph(*A->getParent());
85 else if (const BasicBlock *BB = dyn_cast<BasicBlock>(V))
86 return &TD->getDSGraph(*BB->getParent());
90 // isSinglePhysicalObject - For now, the only case that we know that there is
91 // only one memory object in the node is when there is a single global in the
92 // node, and the only composition bit set is Global.
94 static bool isSinglePhysicalObject(DSNode *N) {
95 assert(N->isComplete() && "Can only tell if this is a complete object!");
96 return N->isGlobalNode() && N->getGlobals().size() == 1 &&
97 !N->isHeapNode() && !N->isAllocaNode() && !N->isUnknownNode();
100 // alias - This is the only method here that does anything interesting...
101 AliasAnalysis::AliasResult DSAA::alias(const Value *V1, unsigned V1Size,
102 const Value *V2, unsigned V2Size) {
103 if (V1 == V2) return MustAlias;
105 DSGraph *G1 = getGraphForValue(V1);
106 DSGraph *G2 = getGraphForValue(V2);
107 assert((!G1 || !G2 || G1 == G2) && "Alias query for 2 different functions?");
109 // Get the graph to use...
110 DSGraph &G = *(G1 ? G1 : (G2 ? G2 : &TD->getGlobalsGraph()));
112 const DSGraph::ScalarMapTy &GSM = G.getScalarMap();
113 DSGraph::ScalarMapTy::const_iterator I = GSM.find((Value*)V1);
114 if (I == GSM.end()) return NoAlias;
116 assert(I->second.getNode() && "Scalar map points to null node?");
117 DSGraph::ScalarMapTy::const_iterator J = GSM.find((Value*)V2);
118 if (J == GSM.end()) return NoAlias;
120 assert(J->second.getNode() && "Scalar map points to null node?");
122 DSNode *N1 = I->second.getNode(), *N2 = J->second.getNode();
123 unsigned O1 = I->second.getOffset(), O2 = J->second.getOffset();
125 // We can only make a judgment of one of the nodes is complete...
126 if (N1->isComplete() || N2->isComplete()) {
128 return NoAlias; // Completely different nodes.
130 #if 0 // This does not correctly handle arrays!
131 // Both point to the same node and same offset, and there is only one
132 // physical memory object represented in the node, return must alias.
134 // FIXME: This isn't correct because we do not handle array indexing
137 if (O1 == O2 && isSinglePhysicalObject(N1))
138 return MustAlias; // Exactly the same object & offset
141 // See if they point to different offsets... if so, we may be able to
142 // determine that they do not alias...
144 if (O2 < O1) { // Ensure that O1 <= O2
147 std::swap(V1Size, V2Size);
150 // FIXME: This is not correct because we do not handle array
151 // indexing correctly with this check!
152 //if (O1+V1Size <= O2) return NoAlias;
156 // FIXME: we could improve on this by checking the globals graph for aliased
158 return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
161 /// getModRefInfo - does a callsite modify or reference a value?
163 AliasAnalysis::ModRefResult
164 DSAA::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
165 Function *F = CS.getCalledFunction();
166 if (!F) return pointsToConstantMemory(P) ? Ref : ModRef;
167 if (F->isExternal()) return ModRef;
169 // Clone the function TD graph, clearing off Mod/Ref flags
170 const Function *csParent = CS.getInstruction()->getParent()->getParent();
171 DSGraph TDGraph(TD->getDSGraph(*csParent));
172 TDGraph.maskNodeTypes(0);
174 // Insert the callee's BU graph into the TD graph
175 const DSGraph &BUGraph = BU->getDSGraph(*F);
176 TDGraph.mergeInGraph(TDGraph.getDSCallSiteForCallSite(CS),
179 // Report the flags that have been added
180 const DSNodeHandle &DSH = TDGraph.getNodeForValue(P);
181 if (const DSNode *N = DSH.getNode())
183 return N->isRead() ? ModRef : Mod;
185 return N->isRead() ? Ref : NoModRef;
190 /// getMustAliases - If there are any pointers known that must alias this
191 /// pointer, return them now. This allows alias-set based alias analyses to
192 /// perform a form a value numbering (which is exposed by load-vn). If an alias
193 /// analysis supports this, it should ADD any must aliased pointers to the
194 /// specified vector.
196 void DSAA::getMustAliases(Value *P, std::vector<Value*> &RetVals) {
197 #if 0 // This does not correctly handle arrays!
198 // Currently the only must alias information we can provide is to say that
199 // something is equal to a global value. If we already have a global value,
200 // don't get worked up about it.
201 if (!isa<GlobalValue>(P)) {
202 DSGraph *G = getGraphForValue(P);
203 if (!G) G = &TD->getGlobalsGraph();
205 // The only must alias information we can currently determine occurs when
206 // the node for P is a global node with only one entry.
207 DSGraph::ScalarMapTy::const_iterator I = G->getScalarMap().find(P);
208 if (I != G->getScalarMap().end()) {
209 DSNode *N = I->second.getNode();
210 if (N->isComplete() && isSinglePhysicalObject(N))
211 RetVals.push_back(N->getGlobals()[0]);
215 return AliasAnalysis::getMustAliases(P, RetVals);