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//===- DataStructureAA.cpp - Data Structure Based Alias Analysis ----------===//
//
// This pass uses the top-down data structure graphs to implement a simple
// context sensitive alias analysis.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/DataStructure.h"
#include "llvm/Analysis/DSGraph.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Module.h"
namespace {
class DSAA : public Pass, public AliasAnalysis {
TDDataStructures *TD;
public:
DSAA() : TD(0) {}
//------------------------------------------------
// Implement the Pass API
//
// run - Build up the result graph, representing the pointer graph for the
// program.
//
bool run(Module &M) {
InitializeAliasAnalysis(this);
TD = &getAnalysis<TDDataStructures>();
return false;
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AliasAnalysis::getAnalysisUsage(AU);
AU.setPreservesAll(); // Does not transform code...
AU.addRequired<TDDataStructures>(); // Uses TD Datastructures
AU.addRequired<AliasAnalysis>(); // Chains to another AA impl...
}
//------------------------------------------------
// Implement the AliasAnalysis API
//
// alias - This is the only method here that does anything interesting...
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
};
// Register the pass...
RegisterOpt<DSAA> X("ds-aa", "Data Structure Graph Based Alias Analysis");
// Register as an implementation of AliasAnalysis
RegisterAnalysisGroup<AliasAnalysis, DSAA> Y;
}
// getValueFunction - return the function containing the specified value if
// available, or null otherwise.
//
static const Function *getValueFunction(const Value *V) {
if (const Instruction *I = dyn_cast<Instruction>(V))
return I->getParent()->getParent();
else if (const Argument *A = dyn_cast<Argument>(V))
return A->getParent();
else if (const BasicBlock *BB = dyn_cast<BasicBlock>(V))
return BB->getParent();
return 0;
}
// alias - This is the only method here that does anything interesting...
AliasAnalysis::AliasResult DSAA::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
if (V1 == V2) return MustAlias;
const Function *F1 = getValueFunction(V1);
const Function *F2 = getValueFunction(V2);
assert((!F1 || !F2 || F1 == F2) && "Alias query for 2 different functions?");
if (F2) F1 = F2;
if (F1) {
// Get the graph for a function...
DSGraph &G = TD->getDSGraph(*F1);
hash_map<Value*, DSNodeHandle> &GSM = G.getScalarMap();
hash_map<Value*, DSNodeHandle>::iterator I = GSM.find((Value*)V1);
if (I != GSM.end()) {
assert(I->second.getNode() && "Scalar map points to null node?");
hash_map<Value*, DSNodeHandle>::iterator J = GSM.find((Value*)V2);
if (J != GSM.end()) {
assert(J->second.getNode() && "Scalar map points to null node?");
DSNode *N1 = I->second.getNode(), *N2 = J->second.getNode();
unsigned O1 = I->second.getOffset(), O2 = J->second.getOffset();
// We can only make a judgement of one of the nodes is complete...
if (!N1->isIncomplete() || !N2->isIncomplete()) {
if (N1 != N2)
return NoAlias; // Completely different nodes.
// Both point to the same node and same offset, and there is only one
// physical memory object represented in the node, return must alias.
if (O1 == O2 && !N1->isMultiObject())
return MustAlias; // Exactly the same object & offset
// See if they point to different offsets... if so, we may be able to
// determine that they do not alias...
if (O1 != O2) {
if (O2 < O1) { // Ensure that O1 <= O2
std::swap(V1, V2);
std::swap(O1, O2);
std::swap(V1Size, V2Size);
}
// FIXME: This is not correct because we do not handle array
// indexing correctly with this check!
//if (O1+V1Size <= O2) return NoAlias;
}
}
}
}
}
// FIXME: we could improve on this by checking the globals graph for aliased
// global queries...
return getAnalysis<AliasAnalysis>().alias(V1, V1Size, V2, V2Size);
}
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