545 lines
18 KiB
C
545 lines
18 KiB
C
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//======- CFLGraph.h - Abstract stratified sets implementation. --------======//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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/// \file
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/// This file defines CFLGraph, an auxiliary data structure used by CFL-based
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/// alias analysis.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_CFLGRAPH_H
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#define LLVM_ANALYSIS_CFLGRAPH_H
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#include "AliasAnalysisSummary.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/IR/InstVisitor.h"
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#include "llvm/IR/Instructions.h"
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namespace llvm {
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namespace cflaa {
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/// \brief The Program Expression Graph (PEG) of CFL analysis
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/// CFLGraph is auxiliary data structure used by CFL-based alias analysis to
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/// describe flow-insensitive pointer-related behaviors. Given an LLVM function,
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/// the main purpose of this graph is to abstract away unrelated facts and
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/// translate the rest into a form that can be easily digested by CFL analyses.
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/// Each Node in the graph is an InstantiatedValue, and each edge represent a
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/// pointer assignment between InstantiatedValue. Pointer
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/// references/dereferences are not explicitly stored in the graph: we
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/// implicitly assume that for each node (X, I) it has a dereference edge to (X,
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/// I+1) and a reference edge to (X, I-1).
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class CFLGraph {
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public:
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typedef InstantiatedValue Node;
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struct Edge {
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Node Other;
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};
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typedef std::vector<Edge> EdgeList;
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struct NodeInfo {
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EdgeList Edges, ReverseEdges;
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AliasAttrs Attr;
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};
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class ValueInfo {
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std::vector<NodeInfo> Levels;
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public:
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bool addNodeToLevel(unsigned Level) {
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auto NumLevels = Levels.size();
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if (NumLevels > Level)
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return false;
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Levels.resize(Level + 1);
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return true;
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}
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NodeInfo &getNodeInfoAtLevel(unsigned Level) {
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assert(Level < Levels.size());
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return Levels[Level];
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}
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const NodeInfo &getNodeInfoAtLevel(unsigned Level) const {
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assert(Level < Levels.size());
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return Levels[Level];
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}
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unsigned getNumLevels() const { return Levels.size(); }
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};
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private:
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typedef DenseMap<Value *, ValueInfo> ValueMap;
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ValueMap ValueImpls;
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NodeInfo *getNode(Node N) {
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auto Itr = ValueImpls.find(N.Val);
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if (Itr == ValueImpls.end() || Itr->second.getNumLevels() <= N.DerefLevel)
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return nullptr;
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return &Itr->second.getNodeInfoAtLevel(N.DerefLevel);
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}
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public:
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typedef ValueMap::const_iterator const_value_iterator;
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bool addNode(Node N, AliasAttrs Attr = AliasAttrs()) {
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assert(N.Val != nullptr);
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auto &ValInfo = ValueImpls[N.Val];
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auto Changed = ValInfo.addNodeToLevel(N.DerefLevel);
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ValInfo.getNodeInfoAtLevel(N.DerefLevel).Attr |= Attr;
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return Changed;
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}
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void addAttr(Node N, AliasAttrs Attr) {
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auto *Info = getNode(N);
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assert(Info != nullptr);
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Info->Attr |= Attr;
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}
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void addEdge(Node From, Node To, int64_t Offset = 0) {
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auto *FromInfo = getNode(From);
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assert(FromInfo != nullptr);
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auto *ToInfo = getNode(To);
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assert(ToInfo != nullptr);
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FromInfo->Edges.push_back(Edge{To});
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ToInfo->ReverseEdges.push_back(Edge{From});
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}
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const NodeInfo *getNode(Node N) const {
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auto Itr = ValueImpls.find(N.Val);
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if (Itr == ValueImpls.end() || Itr->second.getNumLevels() <= N.DerefLevel)
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return nullptr;
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return &Itr->second.getNodeInfoAtLevel(N.DerefLevel);
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}
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AliasAttrs attrFor(Node N) const {
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auto *Info = getNode(N);
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assert(Info != nullptr);
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return Info->Attr;
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}
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iterator_range<const_value_iterator> value_mappings() const {
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return make_range<const_value_iterator>(ValueImpls.begin(),
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ValueImpls.end());
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}
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};
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///\brief A builder class used to create CFLGraph instance from a given function
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/// The CFL-AA that uses this builder must provide its own type as a template
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/// argument. This is necessary for interprocedural processing: CFLGraphBuilder
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/// needs a way of obtaining the summary of other functions when callinsts are
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/// encountered.
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/// As a result, we expect the said CFL-AA to expose a getAliasSummary() public
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/// member function that takes a Function& and returns the corresponding summary
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/// as a const AliasSummary*.
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template <typename CFLAA> class CFLGraphBuilder {
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// Input of the builder
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CFLAA &Analysis;
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const TargetLibraryInfo &TLI;
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// Output of the builder
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CFLGraph Graph;
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SmallVector<Value *, 4> ReturnedValues;
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// Helper class
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/// Gets the edges our graph should have, based on an Instruction*
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class GetEdgesVisitor : public InstVisitor<GetEdgesVisitor, void> {
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CFLAA &AA;
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const TargetLibraryInfo &TLI;
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CFLGraph &Graph;
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SmallVectorImpl<Value *> &ReturnValues;
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static bool hasUsefulEdges(ConstantExpr *CE) {
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// ConstantExpr doesn't have terminators, invokes, or fences, so only
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// needs
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// to check for compares.
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return CE->getOpcode() != Instruction::ICmp &&
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CE->getOpcode() != Instruction::FCmp;
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}
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// Returns possible functions called by CS into the given SmallVectorImpl.
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// Returns true if targets found, false otherwise.
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static bool getPossibleTargets(CallSite CS,
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SmallVectorImpl<Function *> &Output) {
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if (auto *Fn = CS.getCalledFunction()) {
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Output.push_back(Fn);
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return true;
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}
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// TODO: If the call is indirect, we might be able to enumerate all
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// potential
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// targets of the call and return them, rather than just failing.
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return false;
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}
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void addNode(Value *Val, AliasAttrs Attr = AliasAttrs()) {
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assert(Val != nullptr && Val->getType()->isPointerTy());
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if (auto GVal = dyn_cast<GlobalValue>(Val)) {
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if (Graph.addNode(InstantiatedValue{GVal, 0},
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getGlobalOrArgAttrFromValue(*GVal)))
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Graph.addNode(InstantiatedValue{GVal, 1}, getAttrUnknown());
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} else if (auto CExpr = dyn_cast<ConstantExpr>(Val)) {
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if (hasUsefulEdges(CExpr)) {
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if (Graph.addNode(InstantiatedValue{CExpr, 0}))
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visitConstantExpr(CExpr);
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}
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} else
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Graph.addNode(InstantiatedValue{Val, 0}, Attr);
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}
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void addAssignEdge(Value *From, Value *To, int64_t Offset = 0) {
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assert(From != nullptr && To != nullptr);
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if (!From->getType()->isPointerTy() || !To->getType()->isPointerTy())
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return;
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addNode(From);
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if (To != From) {
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addNode(To);
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Graph.addEdge(InstantiatedValue{From, 0}, InstantiatedValue{To, 0},
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Offset);
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}
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}
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void addDerefEdge(Value *From, Value *To, bool IsRead) {
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assert(From != nullptr && To != nullptr);
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if (!From->getType()->isPointerTy() || !To->getType()->isPointerTy())
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return;
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addNode(From);
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addNode(To);
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if (IsRead) {
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Graph.addNode(InstantiatedValue{From, 1});
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Graph.addEdge(InstantiatedValue{From, 1}, InstantiatedValue{To, 0});
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} else {
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Graph.addNode(InstantiatedValue{To, 1});
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Graph.addEdge(InstantiatedValue{From, 0}, InstantiatedValue{To, 1});
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}
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}
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void addLoadEdge(Value *From, Value *To) { addDerefEdge(From, To, true); }
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void addStoreEdge(Value *From, Value *To) { addDerefEdge(From, To, false); }
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public:
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GetEdgesVisitor(CFLGraphBuilder &Builder)
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: AA(Builder.Analysis), TLI(Builder.TLI), Graph(Builder.Graph),
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ReturnValues(Builder.ReturnedValues) {}
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void visitInstruction(Instruction &) {
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llvm_unreachable("Unsupported instruction encountered");
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}
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void visitReturnInst(ReturnInst &Inst) {
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if (auto RetVal = Inst.getReturnValue()) {
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if (RetVal->getType()->isPointerTy()) {
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addNode(RetVal);
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ReturnValues.push_back(RetVal);
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}
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}
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}
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void visitPtrToIntInst(PtrToIntInst &Inst) {
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auto *Ptr = Inst.getOperand(0);
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addNode(Ptr, getAttrEscaped());
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}
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void visitIntToPtrInst(IntToPtrInst &Inst) {
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auto *Ptr = &Inst;
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addNode(Ptr, getAttrUnknown());
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}
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void visitCastInst(CastInst &Inst) {
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auto *Src = Inst.getOperand(0);
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addAssignEdge(Src, &Inst);
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}
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void visitBinaryOperator(BinaryOperator &Inst) {
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auto *Op1 = Inst.getOperand(0);
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auto *Op2 = Inst.getOperand(1);
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addAssignEdge(Op1, &Inst);
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addAssignEdge(Op2, &Inst);
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}
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void visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = Inst.getNewValOperand();
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addStoreEdge(Val, Ptr);
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}
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void visitAtomicRMWInst(AtomicRMWInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = Inst.getValOperand();
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addStoreEdge(Val, Ptr);
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}
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void visitPHINode(PHINode &Inst) {
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for (Value *Val : Inst.incoming_values())
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addAssignEdge(Val, &Inst);
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}
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void visitGetElementPtrInst(GetElementPtrInst &Inst) {
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auto *Op = Inst.getPointerOperand();
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addAssignEdge(Op, &Inst);
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}
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void visitSelectInst(SelectInst &Inst) {
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// Condition is not processed here (The actual statement producing
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// the condition result is processed elsewhere). For select, the
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// condition is evaluated, but not loaded, stored, or assigned
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// simply as a result of being the condition of a select.
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auto *TrueVal = Inst.getTrueValue();
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auto *FalseVal = Inst.getFalseValue();
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addAssignEdge(TrueVal, &Inst);
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addAssignEdge(FalseVal, &Inst);
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}
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void visitAllocaInst(AllocaInst &Inst) { addNode(&Inst); }
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void visitLoadInst(LoadInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = &Inst;
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addLoadEdge(Ptr, Val);
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}
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void visitStoreInst(StoreInst &Inst) {
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auto *Ptr = Inst.getPointerOperand();
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auto *Val = Inst.getValueOperand();
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addStoreEdge(Val, Ptr);
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}
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void visitVAArgInst(VAArgInst &Inst) {
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// We can't fully model va_arg here. For *Ptr = Inst.getOperand(0), it
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// does
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// two things:
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// 1. Loads a value from *((T*)*Ptr).
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// 2. Increments (stores to) *Ptr by some target-specific amount.
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// For now, we'll handle this like a landingpad instruction (by placing
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// the
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// result in its own group, and having that group alias externals).
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addNode(&Inst, getAttrUnknown());
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}
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static bool isFunctionExternal(Function *Fn) {
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return !Fn->hasExactDefinition();
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}
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bool tryInterproceduralAnalysis(CallSite CS,
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const SmallVectorImpl<Function *> &Fns) {
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assert(Fns.size() > 0);
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if (CS.arg_size() > MaxSupportedArgsInSummary)
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return false;
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// Exit early if we'll fail anyway
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for (auto *Fn : Fns) {
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if (isFunctionExternal(Fn) || Fn->isVarArg())
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return false;
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// Fail if the caller does not provide enough arguments
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assert(Fn->arg_size() <= CS.arg_size());
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if (!AA.getAliasSummary(*Fn))
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return false;
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}
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for (auto *Fn : Fns) {
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auto Summary = AA.getAliasSummary(*Fn);
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assert(Summary != nullptr);
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auto &RetParamRelations = Summary->RetParamRelations;
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for (auto &Relation : RetParamRelations) {
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auto IRelation = instantiateExternalRelation(Relation, CS);
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if (IRelation.hasValue()) {
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Graph.addNode(IRelation->From);
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Graph.addNode(IRelation->To);
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Graph.addEdge(IRelation->From, IRelation->To);
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}
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}
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auto &RetParamAttributes = Summary->RetParamAttributes;
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for (auto &Attribute : RetParamAttributes) {
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auto IAttr = instantiateExternalAttribute(Attribute, CS);
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if (IAttr.hasValue())
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Graph.addNode(IAttr->IValue, IAttr->Attr);
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}
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}
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return true;
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}
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void visitCallSite(CallSite CS) {
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auto Inst = CS.getInstruction();
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// Make sure all arguments and return value are added to the graph first
|
||
|
|
for (Value *V : CS.args())
|
||
|
|
if (V->getType()->isPointerTy())
|
||
|
|
addNode(V);
|
||
|
|
if (Inst->getType()->isPointerTy())
|
||
|
|
addNode(Inst);
|
||
|
|
|
||
|
|
// Check if Inst is a call to a library function that
|
||
|
|
// allocates/deallocates
|
||
|
|
// on the heap. Those kinds of functions do not introduce any aliases.
|
||
|
|
// TODO: address other common library functions such as realloc(),
|
||
|
|
// strdup(),
|
||
|
|
// etc.
|
||
|
|
if (isMallocLikeFn(Inst, &TLI) || isCallocLikeFn(Inst, &TLI) ||
|
||
|
|
isFreeCall(Inst, &TLI))
|
||
|
|
return;
|
||
|
|
|
||
|
|
// TODO: Add support for noalias args/all the other fun function
|
||
|
|
// attributes
|
||
|
|
// that we can tack on.
|
||
|
|
SmallVector<Function *, 4> Targets;
|
||
|
|
if (getPossibleTargets(CS, Targets))
|
||
|
|
if (tryInterproceduralAnalysis(CS, Targets))
|
||
|
|
return;
|
||
|
|
|
||
|
|
// Because the function is opaque, we need to note that anything
|
||
|
|
// could have happened to the arguments (unless the function is marked
|
||
|
|
// readonly or readnone), and that the result could alias just about
|
||
|
|
// anything, too (unless the result is marked noalias).
|
||
|
|
if (!CS.onlyReadsMemory())
|
||
|
|
for (Value *V : CS.args()) {
|
||
|
|
if (V->getType()->isPointerTy()) {
|
||
|
|
// The argument itself escapes.
|
||
|
|
Graph.addAttr(InstantiatedValue{V, 0}, getAttrEscaped());
|
||
|
|
// The fate of argument memory is unknown. Note that since
|
||
|
|
// AliasAttrs is transitive with respect to dereference, we only
|
||
|
|
// need to specify it for the first-level memory.
|
||
|
|
Graph.addNode(InstantiatedValue{V, 1}, getAttrUnknown());
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
if (Inst->getType()->isPointerTy()) {
|
||
|
|
auto *Fn = CS.getCalledFunction();
|
||
|
|
if (Fn == nullptr || !Fn->doesNotAlias(0))
|
||
|
|
// No need to call addNode() since we've added Inst at the
|
||
|
|
// beginning of this function and we know it is not a global.
|
||
|
|
Graph.addAttr(InstantiatedValue{Inst, 0}, getAttrUnknown());
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/// Because vectors/aggregates are immutable and unaddressable, there's
|
||
|
|
/// nothing we can do to coax a value out of them, other than calling
|
||
|
|
/// Extract{Element,Value}. We can effectively treat them as pointers to
|
||
|
|
/// arbitrary memory locations we can store in and load from.
|
||
|
|
void visitExtractElementInst(ExtractElementInst &Inst) {
|
||
|
|
auto *Ptr = Inst.getVectorOperand();
|
||
|
|
auto *Val = &Inst;
|
||
|
|
addLoadEdge(Ptr, Val);
|
||
|
|
}
|
||
|
|
|
||
|
|
void visitInsertElementInst(InsertElementInst &Inst) {
|
||
|
|
auto *Vec = Inst.getOperand(0);
|
||
|
|
auto *Val = Inst.getOperand(1);
|
||
|
|
addAssignEdge(Vec, &Inst);
|
||
|
|
addStoreEdge(Val, &Inst);
|
||
|
|
}
|
||
|
|
|
||
|
|
void visitLandingPadInst(LandingPadInst &Inst) {
|
||
|
|
// Exceptions come from "nowhere", from our analysis' perspective.
|
||
|
|
// So we place the instruction its own group, noting that said group may
|
||
|
|
// alias externals
|
||
|
|
addNode(&Inst, getAttrUnknown());
|
||
|
|
}
|
||
|
|
|
||
|
|
void visitInsertValueInst(InsertValueInst &Inst) {
|
||
|
|
auto *Agg = Inst.getOperand(0);
|
||
|
|
auto *Val = Inst.getOperand(1);
|
||
|
|
addAssignEdge(Agg, &Inst);
|
||
|
|
addStoreEdge(Val, &Inst);
|
||
|
|
}
|
||
|
|
|
||
|
|
void visitExtractValueInst(ExtractValueInst &Inst) {
|
||
|
|
auto *Ptr = Inst.getAggregateOperand();
|
||
|
|
addLoadEdge(Ptr, &Inst);
|
||
|
|
}
|
||
|
|
|
||
|
|
void visitShuffleVectorInst(ShuffleVectorInst &Inst) {
|
||
|
|
auto *From1 = Inst.getOperand(0);
|
||
|
|
auto *From2 = Inst.getOperand(1);
|
||
|
|
addAssignEdge(From1, &Inst);
|
||
|
|
addAssignEdge(From2, &Inst);
|
||
|
|
}
|
||
|
|
|
||
|
|
void visitConstantExpr(ConstantExpr *CE) {
|
||
|
|
switch (CE->getOpcode()) {
|
||
|
|
default:
|
||
|
|
llvm_unreachable("Unknown instruction type encountered!");
|
||
|
|
// Build the switch statement using the Instruction.def file.
|
||
|
|
#define HANDLE_INST(NUM, OPCODE, CLASS) \
|
||
|
|
case Instruction::OPCODE: \
|
||
|
|
this->visit##OPCODE(*(CLASS *)CE); \
|
||
|
|
break;
|
||
|
|
#include "llvm/IR/Instruction.def"
|
||
|
|
}
|
||
|
|
}
|
||
|
|
};
|
||
|
|
|
||
|
|
// Helper functions
|
||
|
|
|
||
|
|
// Determines whether or not we an instruction is useless to us (e.g.
|
||
|
|
// FenceInst)
|
||
|
|
static bool hasUsefulEdges(Instruction *Inst) {
|
||
|
|
bool IsNonInvokeRetTerminator = isa<TerminatorInst>(Inst) &&
|
||
|
|
!isa<InvokeInst>(Inst) &&
|
||
|
|
!isa<ReturnInst>(Inst);
|
||
|
|
return !isa<CmpInst>(Inst) && !isa<FenceInst>(Inst) &&
|
||
|
|
!IsNonInvokeRetTerminator;
|
||
|
|
}
|
||
|
|
|
||
|
|
void addArgumentToGraph(Argument &Arg) {
|
||
|
|
if (Arg.getType()->isPointerTy()) {
|
||
|
|
Graph.addNode(InstantiatedValue{&Arg, 0},
|
||
|
|
getGlobalOrArgAttrFromValue(Arg));
|
||
|
|
// Pointees of a formal parameter is known to the caller
|
||
|
|
Graph.addNode(InstantiatedValue{&Arg, 1}, getAttrCaller());
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Given an Instruction, this will add it to the graph, along with any
|
||
|
|
// Instructions that are potentially only available from said Instruction
|
||
|
|
// For example, given the following line:
|
||
|
|
// %0 = load i16* getelementptr ([1 x i16]* @a, 0, 0), align 2
|
||
|
|
// addInstructionToGraph would add both the `load` and `getelementptr`
|
||
|
|
// instructions to the graph appropriately.
|
||
|
|
void addInstructionToGraph(GetEdgesVisitor &Visitor, Instruction &Inst) {
|
||
|
|
if (!hasUsefulEdges(&Inst))
|
||
|
|
return;
|
||
|
|
|
||
|
|
Visitor.visit(Inst);
|
||
|
|
}
|
||
|
|
|
||
|
|
// Builds the graph needed for constructing the StratifiedSets for the given
|
||
|
|
// function
|
||
|
|
void buildGraphFrom(Function &Fn) {
|
||
|
|
GetEdgesVisitor Visitor(*this);
|
||
|
|
|
||
|
|
for (auto &Bb : Fn.getBasicBlockList())
|
||
|
|
for (auto &Inst : Bb.getInstList())
|
||
|
|
addInstructionToGraph(Visitor, Inst);
|
||
|
|
|
||
|
|
for (auto &Arg : Fn.args())
|
||
|
|
addArgumentToGraph(Arg);
|
||
|
|
}
|
||
|
|
|
||
|
|
public:
|
||
|
|
CFLGraphBuilder(CFLAA &Analysis, const TargetLibraryInfo &TLI, Function &Fn)
|
||
|
|
: Analysis(Analysis), TLI(TLI) {
|
||
|
|
buildGraphFrom(Fn);
|
||
|
|
}
|
||
|
|
|
||
|
|
const CFLGraph &getCFLGraph() const { return Graph; }
|
||
|
|
const SmallVector<Value *, 4> &getReturnValues() const {
|
||
|
|
return ReturnedValues;
|
||
|
|
}
|
||
|
|
};
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif
|