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218 lines
7.7 KiB
C++
218 lines
7.7 KiB
C++
//===- DataStructureAA.cpp - Data Structure Based Alias Analysis ----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass uses the top-down data structure graphs to implement a simple
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// context sensitive alias analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Module.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Analysis/DataStructure/DataStructure.h"
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#include "llvm/Analysis/DataStructure/DSGraph.h"
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using namespace llvm;
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namespace {
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class DSAA : public ModulePass, public AliasAnalysis {
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TDDataStructures *TD;
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BUDataStructures *BU;
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public:
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DSAA() : TD(0) {}
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//------------------------------------------------
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// Implement the Pass API
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//
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// run - Build up the result graph, representing the pointer graph for the
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// program.
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//
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bool runOnModule(Module &M) {
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InitializeAliasAnalysis(this);
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TD = &getAnalysis<TDDataStructures>();
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BU = &getAnalysis<BUDataStructures>();
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return false;
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AliasAnalysis::getAnalysisUsage(AU);
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AU.setPreservesAll(); // Does not transform code
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AU.addRequiredTransitive<TDDataStructures>(); // Uses TD Datastructures
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AU.addRequiredTransitive<BUDataStructures>(); // Uses BU Datastructures
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}
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//------------------------------------------------
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// Implement the AliasAnalysis API
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//
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AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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void getMustAliases(Value *P, std::vector<Value*> &RetVals);
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ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
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ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
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return AliasAnalysis::getModRefInfo(CS1,CS2);
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}
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private:
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DSGraph *getGraphForValue(const Value *V);
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};
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// Register the pass...
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RegisterOpt<DSAA> X("ds-aa", "Data Structure Graph Based Alias Analysis");
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// Register as an implementation of AliasAnalysis
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RegisterAnalysisGroup<AliasAnalysis, DSAA> Y;
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}
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ModulePass *llvm::createDSAAPass() { return new DSAA(); }
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// getGraphForValue - Return the DSGraph to use for queries about the specified
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// value...
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//
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DSGraph *DSAA::getGraphForValue(const Value *V) {
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if (const Instruction *I = dyn_cast<Instruction>(V))
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return &TD->getDSGraph(*I->getParent()->getParent());
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else if (const Argument *A = dyn_cast<Argument>(V))
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return &TD->getDSGraph(*A->getParent());
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else if (const BasicBlock *BB = dyn_cast<BasicBlock>(V))
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return &TD->getDSGraph(*BB->getParent());
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return 0;
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}
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// isSinglePhysicalObject - For now, the only case that we know that there is
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// only one memory object in the node is when there is a single global in the
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// node, and the only composition bit set is Global.
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//
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static bool isSinglePhysicalObject(DSNode *N) {
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assert(N->isComplete() && "Can only tell if this is a complete object!");
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return N->isGlobalNode() && N->getGlobals().size() == 1 &&
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!N->isHeapNode() && !N->isAllocaNode() && !N->isUnknownNode();
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}
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// alias - This is the only method here that does anything interesting...
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AliasAnalysis::AliasResult DSAA::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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if (V1 == V2) return MustAlias;
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DSGraph *G1 = getGraphForValue(V1);
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DSGraph *G2 = getGraphForValue(V2);
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assert((!G1 || !G2 || G1 == G2) && "Alias query for 2 different functions?");
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// Get the graph to use...
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DSGraph &G = *(G1 ? G1 : (G2 ? G2 : &TD->getGlobalsGraph()));
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const DSGraph::ScalarMapTy &GSM = G.getScalarMap();
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DSGraph::ScalarMapTy::const_iterator I = GSM.find((Value*)V1);
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if (I == GSM.end()) return NoAlias;
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assert(I->second.getNode() && "Scalar map points to null node?");
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DSGraph::ScalarMapTy::const_iterator J = GSM.find((Value*)V2);
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if (J == GSM.end()) return NoAlias;
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assert(J->second.getNode() && "Scalar map points to null node?");
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DSNode *N1 = I->second.getNode(), *N2 = J->second.getNode();
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unsigned O1 = I->second.getOffset(), O2 = J->second.getOffset();
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// We can only make a judgment of one of the nodes is complete...
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if (N1->isComplete() || N2->isComplete()) {
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if (N1 != N2)
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return NoAlias; // Completely different nodes.
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#if 0 // This does not correctly handle arrays!
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// Both point to the same node and same offset, and there is only one
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// physical memory object represented in the node, return must alias.
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//
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// FIXME: This isn't correct because we do not handle array indexing
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// correctly.
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if (O1 == O2 && isSinglePhysicalObject(N1))
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return MustAlias; // Exactly the same object & offset
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#endif
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// See if they point to different offsets... if so, we may be able to
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// determine that they do not alias...
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if (O1 != O2) {
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if (O2 < O1) { // Ensure that O1 <= O2
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std::swap(V1, V2);
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std::swap(O1, O2);
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std::swap(V1Size, V2Size);
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}
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// FIXME: This is not correct because we do not handle array
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// indexing correctly with this check!
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//if (O1+V1Size <= O2) return NoAlias;
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}
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}
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// FIXME: we could improve on this by checking the globals graph for aliased
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// global queries...
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return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
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}
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/// getModRefInfo - does a callsite modify or reference a value?
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///
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AliasAnalysis::ModRefResult
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DSAA::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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Function *F = CS.getCalledFunction();
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if (!F) return pointsToConstantMemory(P) ? Ref : ModRef;
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if (F->isExternal()) return ModRef;
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// Clone the function TD graph, clearing off Mod/Ref flags
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const Function *csParent = CS.getInstruction()->getParent()->getParent();
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DSGraph TDGraph(TD->getDSGraph(*csParent));
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TDGraph.maskNodeTypes(0);
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// Insert the callee's BU graph into the TD graph
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const DSGraph &BUGraph = BU->getDSGraph(*F);
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TDGraph.mergeInGraph(TDGraph.getDSCallSiteForCallSite(CS),
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*F, BUGraph, 0);
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// Report the flags that have been added
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const DSNodeHandle &DSH = TDGraph.getNodeForValue(P);
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if (const DSNode *N = DSH.getNode())
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if (N->isModified())
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return N->isRead() ? ModRef : Mod;
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else
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return N->isRead() ? Ref : NoModRef;
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return NoModRef;
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}
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/// getMustAliases - If there are any pointers known that must alias this
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/// pointer, return them now. This allows alias-set based alias analyses to
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/// perform a form a value numbering (which is exposed by load-vn). If an alias
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/// analysis supports this, it should ADD any must aliased pointers to the
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/// specified vector.
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///
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void DSAA::getMustAliases(Value *P, std::vector<Value*> &RetVals) {
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#if 0 // This does not correctly handle arrays!
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// Currently the only must alias information we can provide is to say that
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// something is equal to a global value. If we already have a global value,
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// don't get worked up about it.
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if (!isa<GlobalValue>(P)) {
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DSGraph *G = getGraphForValue(P);
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if (!G) G = &TD->getGlobalsGraph();
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// The only must alias information we can currently determine occurs when
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// the node for P is a global node with only one entry.
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DSGraph::ScalarMapTy::const_iterator I = G->getScalarMap().find(P);
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if (I != G->getScalarMap().end()) {
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DSNode *N = I->second.getNode();
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if (N->isComplete() && isSinglePhysicalObject(N))
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RetVals.push_back(N->getGlobals()[0]);
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}
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}
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#endif
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return AliasAnalysis::getMustAliases(P, RetVals);
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}
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