//===- 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/Compiler.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 <algorithm>
#include <set>
using namespace llvm;
STATISTIC(NumIters , "Number of iterations to reach convergence");
STATISTIC(NumConstraints , "Number of constraints");
STATISTIC(NumNodes , "Number of nodes");
STATISTIC(NumEscapingFunctions, "Number of internal functions that escape");
STATISTIC(NumIndirectCallees , "Number of indirect callees found");
namespace {
class VISIBILITY_HIDDEN Andersens : public ModulePass, public AliasAnalysis,
private InstVisitor<Andersens> {
public:
static char ID; // Class identification, replacement for typeinfo
Andersens() : ModulePass((intptr_t)&ID) {}
private:
/// 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<Node*> Pointees;
Value *Val;
public:
static const unsigned ID; // Pass identification, replacement for typeid
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<Node*>::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<Node*>::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<Node> GraphNodes;
/// ValueNodes - This map indicates the Node that a particular Value* is
/// represented by. This contains entries for all pointers.
std::map<Value*, unsigned> ValueNodes;
/// ObjectNodes - This map contains entries for each memory object in the
/// program: globals, alloca's and mallocs.
std::map<Value*, unsigned> ObjectNodes;
/// ReturnNodes - This map contains an entry for each function in the
/// program that returns a value.
std::map<Function*, unsigned> 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<Function*, unsigned> 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<Constraint> 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<Function*> 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<CallSite> 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<CallSite, std::vector<Function*> > 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<Constraint>().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<Node>().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);
virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
void getMustAliases(Value *P, std::vector<Value*> &RetVals);
bool pointsToConstantMemory(const Value *P);
virtual void deleteValue(Value *V) {
ValueNodes.erase(V);
getAnalysis<AliasAnalysis>().deleteValue(V);
}
virtual void copyValue(Value *From, Value *To) {
ValueNodes[To] = ValueNodes[From];
getAnalysis<AliasAnalysis>().copyValue(From, To);
}
private:
/// getNode - Return the node corresponding to the specified pointer scalar.
///
Node *getNode(Value *V) {
if (Constant *C = dyn_cast<Constant>(V))
if (!isa<GlobalValue>(C))
return getNodeForConstantPointer(C);
std::map<Value*, unsigned>::iterator I = ValueNodes.find(V);
if (I == ValueNodes.end()) {
#ifndef NDEBUG
V->dump();
#endif
assert(0 && "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<Value*, unsigned>::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<Function*, unsigned>::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<Function*, unsigned>::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<Andersens>;
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 visitICmpInst(ICmpInst &ICI) {} // NOOP!
void visitFCmpInst(FCmpInst &ICI) {} // NOOP!
void visitSelectInst(SelectInst &SI);
void visitVAArg(VAArgInst &I);
void visitInstruction(Instruction &I);
};
char Andersens::ID = 0;
RegisterPass<Andersens> X("anders-aa",
"Andersen's Interprocedural Alias Analysis");
RegisterAnalysisGroup<AliasAnalysis> Y(X);
}
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<Value*>(V1));
Node *N2 = getNode(const_cast<Value*>(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->isDeclaration()) {
Node *N1 = getNode(P);
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);
}
AliasAnalysis::ModRefResult
Andersens::getModRefInfo(CallSite CS1, CallSite CS2) {
return AliasAnalysis::getModRefInfo(CS1,CS2);
}
/// 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<Value*> &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<Function>(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<GlobalValue>(V) || (isa<GlobalVariable>(V) &&
!cast<GlobalVariable>(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<PointerType>(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<PointerType>(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<PointerType>(II->getType())) {
ValueNodes[&*II] = NumObjects++;
if (AllocationInst *AI = dyn_cast<AllocationInst>(&*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<PointerType>(C->getType()) && "Not a constant pointer!");
if (isa<ConstantPointerNull>(C) || isa<UndefValue>(C))
return &GraphNodes[NullPtr];
else if (GlobalValue *GV = dyn_cast<GlobalValue>(C))
return getNode(GV);
else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
switch (CE->getOpcode()) {
case Instruction::GetElementPtr:
return getNodeForConstantPointer(CE->getOperand(0));
case Instruction::IntToPtr:
return &GraphNodes[UniversalSet];
case Instruction::BitCast:
return getNodeForConstantPointer(CE->getOperand(0));
default:
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<PointerType>(C->getType()) && "Not a constant pointer!");
if (isa<ConstantPointerNull>(C))
return &GraphNodes[NullObject];
else if (GlobalValue *GV = dyn_cast<GlobalValue>(C))
return getObject(GV);
else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
switch (CE->getOpcode()) {
case Instruction::GetElementPtr:
return getNodeForConstantPointerTarget(CE->getOperand(0));
case Instruction::IntToPtr:
return &GraphNodes[UniversalSet];
case Instruction::BitCast:
return getNodeForConstantPointerTarget(CE->getOperand(0));
default:
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<PointerType>(C->getType()))
N->copyFrom(getNodeForConstantPointer(C));
} else if (C->isNullValue()) {
N->addPointerTo(&GraphNodes[NullObject]);
return;
} else if (!isa<UndefValue>(C)) {
// If this is an array or struct, include constraints for each element.
assert(isa<ConstantArray>(C) || isa<ConstantStruct>(C));
for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
AddGlobalInitializerConstraints(N, cast<Constant>(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<PointerType>(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->isDeclaration() && "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 = <G memory>
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<PointerType>(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<PointerType>(I->getType()))
getNodeValue(*I);
if (!F->hasInternalLinkage())
AddConstraintsForNonInternalLinkage(F);
if (!F->isDeclaration()) {
// 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<PointerType>(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<PointerType>(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<BinaryOperator>(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::ICmp:
case Instruction::FCmp:
return;
default:
// Is this something we aren't handling yet?
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<PointerType>(RI.getOperand(0)->getType()))
// return V --> <Copy/retval{F}/v>
Constraints.push_back(Constraint(Constraint::Copy,
getReturnNode(RI.getParent()->getParent()),
getNode(RI.getOperand(0))));
}
void Andersens::visitLoadInst(LoadInst &LI) {
if (isa<PointerType>(LI.getType()))
// P1 = load P2 --> <Load/P1/P2>
Constraints.push_back(Constraint(Constraint::Load, getNodeValue(LI),
getNode(LI.getOperand(0))));
}
void Andersens::visitStoreInst(StoreInst &SI) {
if (isa<PointerType>(SI.getOperand(0)->getType()))
// store P1, P2 --> <Store/P2/P1>
Constraints.push_back(Constraint(Constraint::Store,
getNode(SI.getOperand(1)),
getNode(SI.getOperand(0))));
}
void Andersens::visitGetElementPtrInst(GetElementPtrInst &GEP) {
// P1 = getelementptr P2, ... --> <Copy/P1/P2>
Constraints.push_back(Constraint(Constraint::Copy, getNodeValue(GEP),
getNode(GEP.getOperand(0))));
}
void Andersens::visitPHINode(PHINode &PN) {
if (isa<PointerType>(PN.getType())) {
Node *PNN = getNodeValue(PN);
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
// P1 = phi P2, P3 --> <Copy/P1/P2>, <Copy/P1/P3>, ...
Constraints.push_back(Constraint(Constraint::Copy, PNN,
getNode(PN.getIncomingValue(i))));
}
}
void Andersens::visitCastInst(CastInst &CI) {
Value *Op = CI.getOperand(0);
if (isa<PointerType>(CI.getType())) {
if (isa<PointerType>(Op->getType())) {
// P1 = cast P2 --> <Copy/P1/P2>
Constraints.push_back(Constraint(Constraint::Copy, getNodeValue(CI),
getNode(CI.getOperand(0))));
} else {
// P1 = cast int --> <Copy/P1/Univ>
#if 0
Constraints.push_back(Constraint(Constraint::Copy, getNodeValue(CI),
&GraphNodes[UniversalSet]));
#else
getNodeValue(CI);
#endif
}
} else if (isa<PointerType>(Op->getType())) {
// int = cast P1 --> <Copy/Univ/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<PointerType>(SI.getType())) {
Node *SIN = getNodeValue(SI);
// P1 = select C, P2, P3 ---> <Copy/P1/P2>, <Copy/P1/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->isDeclaration() && AddConstraintsForExternalCall(CS, F))
return;
if (isa<PointerType>(CS.getType())) {
Node *CSN = getNode(CS.getInstruction());
if (isa<PointerType>(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<PointerType>(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<PointerType>(AI->getType())) {
if (isa<PointerType>((*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<PointerType>((*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<PointerType>((*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<PointerType>(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;
DOUT << "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<Function>((*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);
DOUT << "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<Function*> &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<Function>((*NI)->getValue())) {
std::vector<Function*>::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);
DOUT << "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]) {
cerr << "<universal>";
return;
} else if (N == &GraphNodes[NullPtr]) {
cerr << "<nullptr>";
return;
} else if (N == &GraphNodes[NullObject]) {
cerr << "<null>";
return;
}
assert(N->getValue() != 0 && "Never set node label!");
Value *V = N->getValue();
if (Function *F = dyn_cast<Function>(V)) {
if (isa<PointerType>(F->getFunctionType()->getReturnType()) &&
N == getReturnNode(F)) {
cerr << F->getName() << ":retval";
return;
} else if (F->getFunctionType()->isVarArg() && N == getVarargNode(F)) {
cerr << F->getName() << ":vararg";
return;
}
}
if (Instruction *I = dyn_cast<Instruction>(V))
cerr << I->getParent()->getParent()->getName() << ":";
else if (Argument *Arg = dyn_cast<Argument>(V))
cerr << Arg->getParent()->getName() << ":";
if (V->hasName())
cerr << V->getName();
else
cerr << "(unnamed)";
if (isa<GlobalValue>(V) || isa<AllocationInst>(V))
if (N == getObject(V))
cerr << "<mem>";
}
void Andersens::PrintConstraints() {
cerr << "Constraints:\n";
for (unsigned i = 0, e = Constraints.size(); i != e; ++i) {
cerr << " #" << i << ": ";
Constraint &C = Constraints[i];
if (C.Type == Constraint::Store)
cerr << "*";
PrintNode(C.Dest);
cerr << " = ";
if (C.Type == Constraint::Load)
cerr << "*";
PrintNode(C.Src);
cerr << "\n";
}
}
void Andersens::PrintPointsToGraph() {
cerr << "Points-to graph:\n";
for (unsigned i = 0, e = GraphNodes.size(); i != e; ++i) {
Node *N = &GraphNodes[i];
cerr << "[" << (N->end() - N->begin()) << "] ";
PrintNode(N);
cerr << "\t--> ";
for (Node::iterator I = N->begin(), E = N->end(); I != E; ++I) {
if (I != N->begin()) cerr << ", ";
PrintNode(*I);
}
cerr << "\n";
}
}
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