//===- Andersens.cpp - Andersen's Interprocedural Alias Analysis ----------===// // // The LLVM Compiler Infrastructure // // This file was developed by the LLVM research group and is distributed under // the University of Illinois Open Source License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file defines a very simple implementation of Andersen's interprocedural // alias analysis. This implementation does not include any of the fancy // features that make Andersen's reasonably efficient (like cycle elimination or // variable substitution), but it should be useful for getting precision // numbers and can be extended in the future. // // In pointer analysis terms, this is a subset-based, flow-insensitive, // field-insensitive, and context-insensitive algorithm pointer algorithm. // // This algorithm is implemented as three stages: // 1. Object identification. // 2. Inclusion constraint identification. // 3. Inclusion constraint solving. // // The object identification stage identifies all of the memory objects in the // program, which includes globals, heap allocated objects, and stack allocated // objects. // // The inclusion constraint identification stage finds all inclusion constraints // in the program by scanning the program, looking for pointer assignments and // other statements that effect the points-to graph. For a statement like "A = // B", this statement is processed to indicate that A can point to anything that // B can point to. Constraints can handle copies, loads, and stores. // // The inclusion constraint solving phase iteratively propagates the inclusion // constraints until a fixed point is reached. This is an O(N^3) algorithm. // // In the initial pass, all indirect function calls are completely ignored. As // the analysis discovers new targets of function pointers, it iteratively // resolves a precise (and conservative) call graph. Also related, this // analysis initially assumes that all internal functions have known incoming // pointers. If we find that an internal function's address escapes outside of // the program, we update this assumption. // // Future Improvements: // This implementation of Andersen's algorithm is extremely slow. To make it // scale reasonably well, the inclusion constraints could be sorted (easy), // offline variable substitution would be a huge win (straight-forward), and // online cycle elimination (trickier) might help as well. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "anders-aa" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" #include "llvm/Instructions.h" #include "llvm/Module.h" #include "llvm/Pass.h" #include "llvm/Support/InstIterator.h" #include "llvm/Support/InstVisitor.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/Passes.h" #include "llvm/Support/Debug.h" #include "llvm/ADT/Statistic.h" #include #include using namespace llvm; namespace { Statistic<> NumIters("anders-aa", "Number of iterations to reach convergence"); Statistic<> NumConstraints("anders-aa", "Number of constraints"); Statistic<> NumNodes("anders-aa", "Number of nodes"); Statistic<> NumEscapingFunctions("anders-aa", "Number of internal functions that escape"); Statistic<> NumIndirectCallees("anders-aa", "Number of indirect callees found"); class Andersens : public ModulePass, public AliasAnalysis, private InstVisitor { /// Node class - This class is used to represent a memory object in the /// program, and is the primitive used to build the points-to graph. class Node { std::vector Pointees; Value *Val; public: Node() : Val(0) {} Node *setValue(Value *V) { assert(Val == 0 && "Value already set for this node!"); Val = V; return this; } /// getValue - Return the LLVM value corresponding to this node. /// Value *getValue() const { return Val; } typedef std::vector::const_iterator iterator; iterator begin() const { return Pointees.begin(); } iterator end() const { return Pointees.end(); } /// addPointerTo - Add a pointer to the list of pointees of this node, /// returning true if this caused a new pointer to be added, or false if /// we already knew about the points-to relation. bool addPointerTo(Node *N) { std::vector::iterator I = std::lower_bound(Pointees.begin(), Pointees.end(), N); if (I != Pointees.end() && *I == N) return false; Pointees.insert(I, N); return true; } /// intersects - Return true if the points-to set of this node intersects /// with the points-to set of the specified node. bool intersects(Node *N) const; /// intersectsIgnoring - Return true if the points-to set of this node /// intersects with the points-to set of the specified node on any nodes /// except for the specified node to ignore. bool intersectsIgnoring(Node *N, Node *Ignoring) const; // Constraint application methods. bool copyFrom(Node *N); bool loadFrom(Node *N); bool storeThrough(Node *N); }; /// GraphNodes - This vector is populated as part of the object /// identification stage of the analysis, which populates this vector with a /// node for each memory object and fills in the ValueNodes map. std::vector GraphNodes; /// ValueNodes - This map indicates the Node that a particular Value* is /// represented by. This contains entries for all pointers. std::map ValueNodes; /// ObjectNodes - This map contains entries for each memory object in the /// program: globals, alloca's and mallocs. std::map ObjectNodes; /// ReturnNodes - This map contains an entry for each function in the /// program that returns a value. std::map ReturnNodes; /// VarargNodes - This map contains the entry used to represent all pointers /// passed through the varargs portion of a function call for a particular /// function. An entry is not present in this map for functions that do not /// take variable arguments. std::map VarargNodes; /// Constraint - Objects of this structure are used to represent the various /// constraints identified by the algorithm. The constraints are 'copy', /// for statements like "A = B", 'load' for statements like "A = *B", and /// 'store' for statements like "*A = B". struct Constraint { enum ConstraintType { Copy, Load, Store } Type; Node *Dest, *Src; Constraint(ConstraintType Ty, Node *D, Node *S) : Type(Ty), Dest(D), Src(S) {} }; /// Constraints - This vector contains a list of all of the constraints /// identified by the program. std::vector Constraints; /// EscapingInternalFunctions - This set contains all of the internal /// functions that are found to escape from the program. If the address of /// an internal function is passed to an external function or otherwise /// escapes from the analyzed portion of the program, we must assume that /// any pointer arguments can alias the universal node. This set keeps /// track of those functions we are assuming to escape so far. std::set EscapingInternalFunctions; /// IndirectCalls - This contains a list of all of the indirect call sites /// in the program. Since the call graph is iteratively discovered, we may /// need to add constraints to our graph as we find new targets of function /// pointers. std::vector IndirectCalls; /// IndirectCallees - For each call site in the indirect calls list, keep /// track of the callees that we have discovered so far. As the analysis /// proceeds, more callees are discovered, until the call graph finally /// stabilizes. std::map > IndirectCallees; /// This enum defines the GraphNodes indices that correspond to important /// fixed sets. enum { UniversalSet = 0, NullPtr = 1, NullObject = 2, }; public: bool runOnModule(Module &M) { InitializeAliasAnalysis(this); IdentifyObjects(M); CollectConstraints(M); DEBUG(PrintConstraints()); SolveConstraints(); DEBUG(PrintPointsToGraph()); // Free the constraints list, as we don't need it to respond to alias // requests. ObjectNodes.clear(); ReturnNodes.clear(); VarargNodes.clear(); EscapingInternalFunctions.clear(); std::vector().swap(Constraints); return false; } void releaseMemory() { // FIXME: Until we have transitively required passes working correctly, // this cannot be enabled! Otherwise, using -count-aa with the pass // causes memory to be freed too early. :( #if 0 // The memory objects and ValueNodes data structures at the only ones that // are still live after construction. std::vector().swap(GraphNodes); ValueNodes.clear(); #endif } virtual void getAnalysisUsage(AnalysisUsage &AU) const { AliasAnalysis::getAnalysisUsage(AU); AU.setPreservesAll(); // Does not transform code } //------------------------------------------------ // Implement the AliasAnalysis API // AliasResult alias(const Value *V1, unsigned V1Size, const Value *V2, unsigned V2Size); ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); void getMustAliases(Value *P, std::vector &RetVals); bool pointsToConstantMemory(const Value *P); virtual void deleteValue(Value *V) { ValueNodes.erase(V); getAnalysis().deleteValue(V); } virtual void copyValue(Value *From, Value *To) { ValueNodes[To] = ValueNodes[From]; getAnalysis().copyValue(From, To); } private: /// getNode - Return the node corresponding to the specified pointer scalar. /// Node *getNode(Value *V) { if (Constant *C = dyn_cast(V)) if (!isa(C)) return getNodeForConstantPointer(C); std::map::iterator I = ValueNodes.find(V); if (I == ValueNodes.end()) { V->dump(); assert(I != ValueNodes.end() && "Value does not have a node in the points-to graph!"); } return &GraphNodes[I->second]; } /// getObject - Return the node corresponding to the memory object for the /// specified global or allocation instruction. Node *getObject(Value *V) { std::map::iterator I = ObjectNodes.find(V); assert(I != ObjectNodes.end() && "Value does not have an object in the points-to graph!"); return &GraphNodes[I->second]; } /// getReturnNode - Return the node representing the return value for the /// specified function. Node *getReturnNode(Function *F) { std::map::iterator I = ReturnNodes.find(F); assert(I != ReturnNodes.end() && "Function does not return a value!"); return &GraphNodes[I->second]; } /// getVarargNode - Return the node representing the variable arguments /// formal for the specified function. Node *getVarargNode(Function *F) { std::map::iterator I = VarargNodes.find(F); assert(I != VarargNodes.end() && "Function does not take var args!"); return &GraphNodes[I->second]; } /// getNodeValue - Get the node for the specified LLVM value and set the /// value for it to be the specified value. Node *getNodeValue(Value &V) { return getNode(&V)->setValue(&V); } void IdentifyObjects(Module &M); void CollectConstraints(Module &M); void SolveConstraints(); Node *getNodeForConstantPointer(Constant *C); Node *getNodeForConstantPointerTarget(Constant *C); void AddGlobalInitializerConstraints(Node *N, Constant *C); void AddConstraintsForNonInternalLinkage(Function *F); void AddConstraintsForCall(CallSite CS, Function *F); bool AddConstraintsForExternalCall(CallSite CS, Function *F); void PrintNode(Node *N); void PrintConstraints(); void PrintPointsToGraph(); //===------------------------------------------------------------------===// // Instruction visitation methods for adding constraints // friend class InstVisitor; void visitReturnInst(ReturnInst &RI); void visitInvokeInst(InvokeInst &II) { visitCallSite(CallSite(&II)); } void visitCallInst(CallInst &CI) { visitCallSite(CallSite(&CI)); } void visitCallSite(CallSite CS); void visitAllocationInst(AllocationInst &AI); void visitLoadInst(LoadInst &LI); void visitStoreInst(StoreInst &SI); void visitGetElementPtrInst(GetElementPtrInst &GEP); void visitPHINode(PHINode &PN); void visitCastInst(CastInst &CI); void visitSetCondInst(SetCondInst &SCI) {} // NOOP! void visitSelectInst(SelectInst &SI); void visitVAArg(VAArgInst &I); void visitInstruction(Instruction &I); }; RegisterOpt X("anders-aa", "Andersen's Interprocedural Alias Analysis"); RegisterAnalysisGroup Y; } ModulePass *llvm::createAndersensPass() { return new Andersens(); } //===----------------------------------------------------------------------===// // AliasAnalysis Interface Implementation //===----------------------------------------------------------------------===// AliasAnalysis::AliasResult Andersens::alias(const Value *V1, unsigned V1Size, const Value *V2, unsigned V2Size) { Node *N1 = getNode(const_cast(V1)); Node *N2 = getNode(const_cast(V2)); // Check to see if the two pointers are known to not alias. They don't alias // if their points-to sets do not intersect. if (!N1->intersectsIgnoring(N2, &GraphNodes[NullObject])) return NoAlias; return AliasAnalysis::alias(V1, V1Size, V2, V2Size); } AliasAnalysis::ModRefResult Andersens::getModRefInfo(CallSite CS, Value *P, unsigned Size) { // The only thing useful that we can contribute for mod/ref information is // when calling external function calls: if we know that memory never escapes // from the program, it cannot be modified by an external call. // // NOTE: This is not really safe, at least not when the entire program is not // available. The deal is that the external function could call back into the // program and modify stuff. We ignore this technical niggle for now. This // is, after all, a "research quality" implementation of Andersen's analysis. if (Function *F = CS.getCalledFunction()) if (F->isExternal()) { Node *N1 = getNode(P); bool PointsToUniversalSet = false; if (N1->begin() == N1->end()) return NoModRef; // P doesn't point to anything. // Get the first pointee. Node *FirstPointee = *N1->begin(); if (FirstPointee != &GraphNodes[UniversalSet]) return NoModRef; // P doesn't point to the universal set. } return AliasAnalysis::getModRefInfo(CS, P, Size); } /// getMustAlias - We can provide must alias information if we know that a /// pointer can only point to a specific function or the null pointer. /// Unfortunately we cannot determine must-alias information for global /// variables or any other memory memory objects because we do not track whether /// a pointer points to the beginning of an object or a field of it. void Andersens::getMustAliases(Value *P, std::vector &RetVals) { Node *N = getNode(P); Node::iterator I = N->begin(); if (I != N->end()) { // If there is exactly one element in the points-to set for the object... ++I; if (I == N->end()) { Node *Pointee = *N->begin(); // If a function is the only object in the points-to set, then it must be // the destination. Note that we can't handle global variables here, // because we don't know if the pointer is actually pointing to a field of // the global or to the beginning of it. if (Value *V = Pointee->getValue()) { if (Function *F = dyn_cast(V)) RetVals.push_back(F); } else { // If the object in the points-to set is the null object, then the null // pointer is a must alias. if (Pointee == &GraphNodes[NullObject]) RetVals.push_back(Constant::getNullValue(P->getType())); } } } AliasAnalysis::getMustAliases(P, RetVals); } /// pointsToConstantMemory - If we can determine that this pointer only points /// to constant memory, return true. In practice, this means that if the /// pointer can only point to constant globals, functions, or the null pointer, /// return true. /// bool Andersens::pointsToConstantMemory(const Value *P) { Node *N = getNode((Value*)P); for (Node::iterator I = N->begin(), E = N->end(); I != E; ++I) { if (Value *V = (*I)->getValue()) { if (!isa(V) || (isa(V) && !cast(V)->isConstant())) return AliasAnalysis::pointsToConstantMemory(P); } else { if (*I != &GraphNodes[NullObject]) return AliasAnalysis::pointsToConstantMemory(P); } } return true; } //===----------------------------------------------------------------------===// // Object Identification Phase //===----------------------------------------------------------------------===// /// IdentifyObjects - This stage scans the program, adding an entry to the /// GraphNodes list for each memory object in the program (global stack or /// heap), and populates the ValueNodes and ObjectNodes maps for these objects. /// void Andersens::IdentifyObjects(Module &M) { unsigned NumObjects = 0; // Object #0 is always the universal set: the object that we don't know // anything about. assert(NumObjects == UniversalSet && "Something changed!"); ++NumObjects; // Object #1 always represents the null pointer. assert(NumObjects == NullPtr && "Something changed!"); ++NumObjects; // Object #2 always represents the null object (the object pointed to by null) assert(NumObjects == NullObject && "Something changed!"); ++NumObjects; // Add all the globals first. for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I) { ObjectNodes[I] = NumObjects++; ValueNodes[I] = NumObjects++; } // Add nodes for all of the functions and the instructions inside of them. for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { // The function itself is a memory object. ValueNodes[F] = NumObjects++; ObjectNodes[F] = NumObjects++; if (isa(F->getFunctionType()->getReturnType())) ReturnNodes[F] = NumObjects++; if (F->getFunctionType()->isVarArg()) VarargNodes[F] = NumObjects++; // Add nodes for all of the incoming pointer arguments. for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) if (isa(I->getType())) ValueNodes[I] = NumObjects++; // Scan the function body, creating a memory object for each heap/stack // allocation in the body of the function and a node to represent all // pointer values defined by instructions and used as operands. for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) { // If this is an heap or stack allocation, create a node for the memory // object. if (isa(II->getType())) { ValueNodes[&*II] = NumObjects++; if (AllocationInst *AI = dyn_cast(&*II)) ObjectNodes[AI] = NumObjects++; } } } // Now that we know how many objects to create, make them all now! GraphNodes.resize(NumObjects); NumNodes += NumObjects; } //===----------------------------------------------------------------------===// // Constraint Identification Phase //===----------------------------------------------------------------------===// /// getNodeForConstantPointer - Return the node corresponding to the constant /// pointer itself. Andersens::Node *Andersens::getNodeForConstantPointer(Constant *C) { assert(isa(C->getType()) && "Not a constant pointer!"); if (isa(C) || isa(C)) return &GraphNodes[NullPtr]; else if (GlobalValue *GV = dyn_cast(C)) return getNode(GV); else if (ConstantExpr *CE = dyn_cast(C)) { switch (CE->getOpcode()) { case Instruction::GetElementPtr: return getNodeForConstantPointer(CE->getOperand(0)); case Instruction::Cast: if (isa(CE->getOperand(0)->getType())) return getNodeForConstantPointer(CE->getOperand(0)); else return &GraphNodes[UniversalSet]; default: std::cerr << "Constant Expr not yet handled: " << *CE << "\n"; assert(0); } } else { assert(0 && "Unknown constant pointer!"); } return 0; } /// getNodeForConstantPointerTarget - Return the node POINTED TO by the /// specified constant pointer. Andersens::Node *Andersens::getNodeForConstantPointerTarget(Constant *C) { assert(isa(C->getType()) && "Not a constant pointer!"); if (isa(C)) return &GraphNodes[NullObject]; else if (GlobalValue *GV = dyn_cast(C)) return getObject(GV); else if (ConstantExpr *CE = dyn_cast(C)) { switch (CE->getOpcode()) { case Instruction::GetElementPtr: return getNodeForConstantPointerTarget(CE->getOperand(0)); case Instruction::Cast: if (isa(CE->getOperand(0)->getType())) return getNodeForConstantPointerTarget(CE->getOperand(0)); else return &GraphNodes[UniversalSet]; default: std::cerr << "Constant Expr not yet handled: " << *CE << "\n"; assert(0); } } else { assert(0 && "Unknown constant pointer!"); } return 0; } /// AddGlobalInitializerConstraints - Add inclusion constraints for the memory /// object N, which contains values indicated by C. void Andersens::AddGlobalInitializerConstraints(Node *N, Constant *C) { if (C->getType()->isFirstClassType()) { if (isa(C->getType())) N->copyFrom(getNodeForConstantPointer(C)); } else if (C->isNullValue()) { N->addPointerTo(&GraphNodes[NullObject]); return; } else if (!isa(C)) { // If this is an array or struct, include constraints for each element. assert(isa(C) || isa(C)); for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) AddGlobalInitializerConstraints(N, cast(C->getOperand(i))); } } /// AddConstraintsForNonInternalLinkage - If this function does not have /// internal linkage, realize that we can't trust anything passed into or /// returned by this function. void Andersens::AddConstraintsForNonInternalLinkage(Function *F) { for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) if (isa(I->getType())) // If this is an argument of an externally accessible function, the // incoming pointer might point to anything. Constraints.push_back(Constraint(Constraint::Copy, getNode(I), &GraphNodes[UniversalSet])); } /// AddConstraintsForCall - If this is a call to a "known" function, add the /// constraints and return true. If this is a call to an unknown function, /// return false. bool Andersens::AddConstraintsForExternalCall(CallSite CS, Function *F) { assert(F->isExternal() && "Not an external function!"); // These functions don't induce any points-to constraints. if (F->getName() == "atoi" || F->getName() == "atof" || F->getName() == "atol" || F->getName() == "atoll" || F->getName() == "remove" || F->getName() == "unlink" || F->getName() == "rename" || F->getName() == "memcmp" || F->getName() == "llvm.memset.i32" || F->getName() == "llvm.memset.i64" || F->getName() == "strcmp" || F->getName() == "strncmp" || F->getName() == "execl" || F->getName() == "execlp" || F->getName() == "execle" || F->getName() == "execv" || F->getName() == "execvp" || F->getName() == "chmod" || F->getName() == "puts" || F->getName() == "write" || F->getName() == "open" || F->getName() == "create" || F->getName() == "truncate" || F->getName() == "chdir" || F->getName() == "mkdir" || F->getName() == "rmdir" || F->getName() == "read" || F->getName() == "pipe" || F->getName() == "wait" || F->getName() == "time" || F->getName() == "stat" || F->getName() == "fstat" || F->getName() == "lstat" || F->getName() == "strtod" || F->getName() == "strtof" || F->getName() == "strtold" || F->getName() == "fopen" || F->getName() == "fdopen" || F->getName() == "freopen" || F->getName() == "fflush" || F->getName() == "feof" || F->getName() == "fileno" || F->getName() == "clearerr" || F->getName() == "rewind" || F->getName() == "ftell" || F->getName() == "ferror" || F->getName() == "fgetc" || F->getName() == "fgetc" || F->getName() == "_IO_getc" || F->getName() == "fwrite" || F->getName() == "fread" || F->getName() == "fgets" || F->getName() == "ungetc" || F->getName() == "fputc" || F->getName() == "fputs" || F->getName() == "putc" || F->getName() == "ftell" || F->getName() == "rewind" || F->getName() == "_IO_putc" || F->getName() == "fseek" || F->getName() == "fgetpos" || F->getName() == "fsetpos" || F->getName() == "printf" || F->getName() == "fprintf" || F->getName() == "sprintf" || F->getName() == "vprintf" || F->getName() == "vfprintf" || F->getName() == "vsprintf" || F->getName() == "scanf" || F->getName() == "fscanf" || F->getName() == "sscanf" || F->getName() == "__assert_fail" || F->getName() == "modf") return true; // These functions do induce points-to edges. if (F->getName() == "llvm.memcpy.i32" || F->getName() == "llvm.memcpy.i64" || F->getName() == "llvm.memmove.i32" ||F->getName() == "llvm.memmove.i64" || F->getName() == "memmove") { // Note: this is a poor approximation, this says Dest = Src, instead of // *Dest = *Src. Constraints.push_back(Constraint(Constraint::Copy, getNode(CS.getArgument(0)), getNode(CS.getArgument(1)))); return true; } // Result = Arg0 if (F->getName() == "realloc" || F->getName() == "strchr" || F->getName() == "strrchr" || F->getName() == "strstr" || F->getName() == "strtok") { Constraints.push_back(Constraint(Constraint::Copy, getNode(CS.getInstruction()), getNode(CS.getArgument(0)))); return true; } return false; } /// CollectConstraints - This stage scans the program, adding a constraint to /// the Constraints list for each instruction in the program that induces a /// constraint, and setting up the initial points-to graph. /// void Andersens::CollectConstraints(Module &M) { // First, the universal set points to itself. GraphNodes[UniversalSet].addPointerTo(&GraphNodes[UniversalSet]); //Constraints.push_back(Constraint(Constraint::Load, &GraphNodes[UniversalSet], // &GraphNodes[UniversalSet])); Constraints.push_back(Constraint(Constraint::Store, &GraphNodes[UniversalSet], &GraphNodes[UniversalSet])); // Next, the null pointer points to the null object. GraphNodes[NullPtr].addPointerTo(&GraphNodes[NullObject]); // Next, add any constraints on global variables and their initializers. for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I) { // Associate the address of the global object as pointing to the memory for // the global: &G = Node *Object = getObject(I); Object->setValue(I); getNodeValue(*I)->addPointerTo(Object); if (I->hasInitializer()) { AddGlobalInitializerConstraints(Object, I->getInitializer()); } else { // If it doesn't have an initializer (i.e. it's defined in another // translation unit), it points to the universal set. Constraints.push_back(Constraint(Constraint::Copy, Object, &GraphNodes[UniversalSet])); } } for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { // Make the function address point to the function object. getNodeValue(*F)->addPointerTo(getObject(F)->setValue(F)); // Set up the return value node. if (isa(F->getFunctionType()->getReturnType())) getReturnNode(F)->setValue(F); if (F->getFunctionType()->isVarArg()) getVarargNode(F)->setValue(F); // Set up incoming argument nodes. for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) if (isa(I->getType())) getNodeValue(*I); if (!F->hasInternalLinkage()) AddConstraintsForNonInternalLinkage(F); if (!F->isExternal()) { // Scan the function body, creating a memory object for each heap/stack // allocation in the body of the function and a node to represent all // pointer values defined by instructions and used as operands. visit(F); } else { // External functions that return pointers return the universal set. if (isa(F->getFunctionType()->getReturnType())) Constraints.push_back(Constraint(Constraint::Copy, getReturnNode(F), &GraphNodes[UniversalSet])); // Any pointers that are passed into the function have the universal set // stored into them. for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) if (isa(I->getType())) { // Pointers passed into external functions could have anything stored // through them. Constraints.push_back(Constraint(Constraint::Store, getNode(I), &GraphNodes[UniversalSet])); // Memory objects passed into external function calls can have the // universal set point to them. Constraints.push_back(Constraint(Constraint::Copy, &GraphNodes[UniversalSet], getNode(I))); } // If this is an external varargs function, it can also store pointers // into any pointers passed through the varargs section. if (F->getFunctionType()->isVarArg()) Constraints.push_back(Constraint(Constraint::Store, getVarargNode(F), &GraphNodes[UniversalSet])); } } NumConstraints += Constraints.size(); } void Andersens::visitInstruction(Instruction &I) { #ifdef NDEBUG return; // This function is just a big assert. #endif if (isa(I)) return; // Most instructions don't have any effect on pointer values. switch (I.getOpcode()) { case Instruction::Br: case Instruction::Switch: case Instruction::Unwind: case Instruction::Unreachable: case Instruction::Free: case Instruction::Shl: case Instruction::Shr: return; default: // Is this something we aren't handling yet? std::cerr << "Unknown instruction: " << I; abort(); } } void Andersens::visitAllocationInst(AllocationInst &AI) { getNodeValue(AI)->addPointerTo(getObject(&AI)->setValue(&AI)); } void Andersens::visitReturnInst(ReturnInst &RI) { if (RI.getNumOperands() && isa(RI.getOperand(0)->getType())) // return V --> Constraints.push_back(Constraint(Constraint::Copy, getReturnNode(RI.getParent()->getParent()), getNode(RI.getOperand(0)))); } void Andersens::visitLoadInst(LoadInst &LI) { if (isa(LI.getType())) // P1 = load P2 --> Constraints.push_back(Constraint(Constraint::Load, getNodeValue(LI), getNode(LI.getOperand(0)))); } void Andersens::visitStoreInst(StoreInst &SI) { if (isa(SI.getOperand(0)->getType())) // store P1, P2 --> Constraints.push_back(Constraint(Constraint::Store, getNode(SI.getOperand(1)), getNode(SI.getOperand(0)))); } void Andersens::visitGetElementPtrInst(GetElementPtrInst &GEP) { // P1 = getelementptr P2, ... --> Constraints.push_back(Constraint(Constraint::Copy, getNodeValue(GEP), getNode(GEP.getOperand(0)))); } void Andersens::visitPHINode(PHINode &PN) { if (isa(PN.getType())) { Node *PNN = getNodeValue(PN); for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) // P1 = phi P2, P3 --> , , ... Constraints.push_back(Constraint(Constraint::Copy, PNN, getNode(PN.getIncomingValue(i)))); } } void Andersens::visitCastInst(CastInst &CI) { Value *Op = CI.getOperand(0); if (isa(CI.getType())) { if (isa(Op->getType())) { // P1 = cast P2 --> Constraints.push_back(Constraint(Constraint::Copy, getNodeValue(CI), getNode(CI.getOperand(0)))); } else { // P1 = cast int --> #if 0 Constraints.push_back(Constraint(Constraint::Copy, getNodeValue(CI), &GraphNodes[UniversalSet])); #else getNodeValue(CI); #endif } } else if (isa(Op->getType())) { // int = cast P1 --> #if 0 Constraints.push_back(Constraint(Constraint::Copy, &GraphNodes[UniversalSet], getNode(CI.getOperand(0)))); #else getNode(CI.getOperand(0)); #endif } } void Andersens::visitSelectInst(SelectInst &SI) { if (isa(SI.getType())) { Node *SIN = getNodeValue(SI); // P1 = select C, P2, P3 ---> , Constraints.push_back(Constraint(Constraint::Copy, SIN, getNode(SI.getOperand(1)))); Constraints.push_back(Constraint(Constraint::Copy, SIN, getNode(SI.getOperand(2)))); } } void Andersens::visitVAArg(VAArgInst &I) { assert(0 && "vaarg not handled yet!"); } /// AddConstraintsForCall - Add constraints for a call with actual arguments /// specified by CS to the function specified by F. Note that the types of /// arguments might not match up in the case where this is an indirect call and /// the function pointer has been casted. If this is the case, do something /// reasonable. void Andersens::AddConstraintsForCall(CallSite CS, Function *F) { // If this is a call to an external function, handle it directly to get some // taste of context sensitivity. if (F->isExternal() && AddConstraintsForExternalCall(CS, F)) return; if (isa(CS.getType())) { Node *CSN = getNode(CS.getInstruction()); if (isa(F->getFunctionType()->getReturnType())) { Constraints.push_back(Constraint(Constraint::Copy, CSN, getReturnNode(F))); } else { // If the function returns a non-pointer value, handle this just like we // treat a nonpointer cast to pointer. Constraints.push_back(Constraint(Constraint::Copy, CSN, &GraphNodes[UniversalSet])); } } else if (isa(F->getFunctionType()->getReturnType())) { Constraints.push_back(Constraint(Constraint::Copy, &GraphNodes[UniversalSet], getReturnNode(F))); } Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end(); CallSite::arg_iterator ArgI = CS.arg_begin(), ArgE = CS.arg_end(); for (; AI != AE && ArgI != ArgE; ++AI, ++ArgI) if (isa(AI->getType())) { if (isa((*ArgI)->getType())) { // Copy the actual argument into the formal argument. Constraints.push_back(Constraint(Constraint::Copy, getNode(AI), getNode(*ArgI))); } else { Constraints.push_back(Constraint(Constraint::Copy, getNode(AI), &GraphNodes[UniversalSet])); } } else if (isa((*ArgI)->getType())) { Constraints.push_back(Constraint(Constraint::Copy, &GraphNodes[UniversalSet], getNode(*ArgI))); } // Copy all pointers passed through the varargs section to the varargs node. if (F->getFunctionType()->isVarArg()) for (; ArgI != ArgE; ++ArgI) if (isa((*ArgI)->getType())) Constraints.push_back(Constraint(Constraint::Copy, getVarargNode(F), getNode(*ArgI))); // If more arguments are passed in than we track, just drop them on the floor. } void Andersens::visitCallSite(CallSite CS) { if (isa(CS.getType())) getNodeValue(*CS.getInstruction()); if (Function *F = CS.getCalledFunction()) { AddConstraintsForCall(CS, F); } else { // We don't handle indirect call sites yet. Keep track of them for when we // discover the call graph incrementally. IndirectCalls.push_back(CS); } } //===----------------------------------------------------------------------===// // Constraint Solving Phase //===----------------------------------------------------------------------===// /// intersects - Return true if the points-to set of this node intersects /// with the points-to set of the specified node. bool Andersens::Node::intersects(Node *N) const { iterator I1 = begin(), I2 = N->begin(), E1 = end(), E2 = N->end(); while (I1 != E1 && I2 != E2) { if (*I1 == *I2) return true; if (*I1 < *I2) ++I1; else ++I2; } return false; } /// intersectsIgnoring - Return true if the points-to set of this node /// intersects with the points-to set of the specified node on any nodes /// except for the specified node to ignore. bool Andersens::Node::intersectsIgnoring(Node *N, Node *Ignoring) const { iterator I1 = begin(), I2 = N->begin(), E1 = end(), E2 = N->end(); while (I1 != E1 && I2 != E2) { if (*I1 == *I2) { if (*I1 != Ignoring) return true; ++I1; ++I2; } else if (*I1 < *I2) ++I1; else ++I2; } return false; } // Copy constraint: all edges out of the source node get copied to the // destination node. This returns true if a change is made. bool Andersens::Node::copyFrom(Node *N) { // Use a mostly linear-time merge since both of the lists are sorted. bool Changed = false; iterator I = N->begin(), E = N->end(); unsigned i = 0; while (I != E && i != Pointees.size()) { if (Pointees[i] < *I) { ++i; } else if (Pointees[i] == *I) { ++i; ++I; } else { // We found a new element to copy over. Changed = true; Pointees.insert(Pointees.begin()+i, *I); ++i; ++I; } } if (I != E) { Pointees.insert(Pointees.end(), I, E); Changed = true; } return Changed; } bool Andersens::Node::loadFrom(Node *N) { bool Changed = false; for (iterator I = N->begin(), E = N->end(); I != E; ++I) Changed |= copyFrom(*I); return Changed; } bool Andersens::Node::storeThrough(Node *N) { bool Changed = false; for (iterator I = begin(), E = end(); I != E; ++I) Changed |= (*I)->copyFrom(N); return Changed; } /// SolveConstraints - This stage iteratively processes the constraints list /// propagating constraints (adding edges to the Nodes in the points-to graph) /// until a fixed point is reached. /// void Andersens::SolveConstraints() { bool Changed = true; unsigned Iteration = 0; while (Changed) { Changed = false; ++NumIters; DEBUG(std::cerr << "Starting iteration #" << Iteration++ << "!\n"); // Loop over all of the constraints, applying them in turn. for (unsigned i = 0, e = Constraints.size(); i != e; ++i) { Constraint &C = Constraints[i]; switch (C.Type) { case Constraint::Copy: Changed |= C.Dest->copyFrom(C.Src); break; case Constraint::Load: Changed |= C.Dest->loadFrom(C.Src); break; case Constraint::Store: Changed |= C.Dest->storeThrough(C.Src); break; default: assert(0 && "Unknown constraint!"); } } if (Changed) { // Check to see if any internal function's addresses have been passed to // external functions. If so, we have to assume that their incoming // arguments could be anything. If there are any internal functions in // the universal node that we don't know about, we must iterate. for (Node::iterator I = GraphNodes[UniversalSet].begin(), E = GraphNodes[UniversalSet].end(); I != E; ++I) if (Function *F = dyn_cast_or_null((*I)->getValue())) if (F->hasInternalLinkage() && EscapingInternalFunctions.insert(F).second) { // We found a function that is just now escaping. Mark it as if it // didn't have internal linkage. AddConstraintsForNonInternalLinkage(F); DEBUG(std::cerr << "Found escaping internal function: " << F->getName() << "\n"); ++NumEscapingFunctions; } // Check to see if we have discovered any new callees of the indirect call // sites. If so, add constraints to the analysis. for (unsigned i = 0, e = IndirectCalls.size(); i != e; ++i) { CallSite CS = IndirectCalls[i]; std::vector &KnownCallees = IndirectCallees[CS]; Node *CN = getNode(CS.getCalledValue()); for (Node::iterator NI = CN->begin(), E = CN->end(); NI != E; ++NI) if (Function *F = dyn_cast_or_null((*NI)->getValue())) { std::vector::iterator IP = std::lower_bound(KnownCallees.begin(), KnownCallees.end(), F); if (IP == KnownCallees.end() || *IP != F) { // Add the constraints for the call now. AddConstraintsForCall(CS, F); DEBUG(std::cerr << "Found actual callee '" << F->getName() << "' for call: " << *CS.getInstruction() << "\n"); ++NumIndirectCallees; KnownCallees.insert(IP, F); } } } } } } //===----------------------------------------------------------------------===// // Debugging Output //===----------------------------------------------------------------------===// void Andersens::PrintNode(Node *N) { if (N == &GraphNodes[UniversalSet]) { std::cerr << ""; return; } else if (N == &GraphNodes[NullPtr]) { std::cerr << ""; return; } else if (N == &GraphNodes[NullObject]) { std::cerr << ""; return; } assert(N->getValue() != 0 && "Never set node label!"); Value *V = N->getValue(); if (Function *F = dyn_cast(V)) { if (isa(F->getFunctionType()->getReturnType()) && N == getReturnNode(F)) { std::cerr << F->getName() << ":retval"; return; } else if (F->getFunctionType()->isVarArg() && N == getVarargNode(F)) { std::cerr << F->getName() << ":vararg"; return; } } if (Instruction *I = dyn_cast(V)) std::cerr << I->getParent()->getParent()->getName() << ":"; else if (Argument *Arg = dyn_cast(V)) std::cerr << Arg->getParent()->getName() << ":"; if (V->hasName()) std::cerr << V->getName(); else std::cerr << "(unnamed)"; if (isa(V) || isa(V)) if (N == getObject(V)) std::cerr << ""; } void Andersens::PrintConstraints() { std::cerr << "Constraints:\n"; for (unsigned i = 0, e = Constraints.size(); i != e; ++i) { std::cerr << " #" << i << ": "; Constraint &C = Constraints[i]; if (C.Type == Constraint::Store) std::cerr << "*"; PrintNode(C.Dest); std::cerr << " = "; if (C.Type == Constraint::Load) std::cerr << "*"; PrintNode(C.Src); std::cerr << "\n"; } } void Andersens::PrintPointsToGraph() { std::cerr << "Points-to graph:\n"; for (unsigned i = 0, e = GraphNodes.size(); i != e; ++i) { Node *N = &GraphNodes[i]; std::cerr << "[" << (N->end() - N->begin()) << "] "; PrintNode(N); std::cerr << "\t--> "; for (Node::iterator I = N->begin(), E = N->end(); I != E; ++I) { if (I != N->begin()) std::cerr << ", "; PrintNode(*I); } std::cerr << "\n"; } }