//==- CoreEngine.cpp - Path-Sensitive Dataflow Engine ------------*- C++ -*-//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines a generic engine for intraprocedural, path-sensitive,
// dataflow analysis via graph reachability engine.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "CoreEngine"
#include "clang/StaticAnalyzer/Core/PathSensitive/CoreEngine.h"
#include "clang/AST/Expr.h"
#include "clang/AST/StmtCXX.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Casting.h"
using namespace clang;
using namespace ento;
STATISTIC(NumSteps,
"The # of steps executed.");
STATISTIC(NumReachedMaxSteps,
"The # of times we reached the max number of steps.");
STATISTIC(NumPathsExplored,
"The # of paths explored by the analyzer.");
//===----------------------------------------------------------------------===//
// Worklist classes for exploration of reachable states.
//===----------------------------------------------------------------------===//
WorkList::Visitor::~Visitor() {}
namespace {
class DFS : public WorkList {
SmallVector<WorkListUnit,20> Stack;
public:
virtual bool hasWork() const {
return !Stack.empty();
}
virtual void enqueue(const WorkListUnit& U) {
Stack.push_back(U);
}
virtual WorkListUnit dequeue() {
assert (!Stack.empty());
const WorkListUnit& U = Stack.back();
Stack.pop_back(); // This technically "invalidates" U, but we are fine.
return U;
}
virtual bool visitItemsInWorkList(Visitor &V) {
for (SmallVectorImpl<WorkListUnit>::iterator
I = Stack.begin(), E = Stack.end(); I != E; ++I) {
if (V.visit(*I))
return true;
}
return false;
}
};
class BFS : public WorkList {
std::deque<WorkListUnit> Queue;
public:
virtual bool hasWork() const {
return !Queue.empty();
}
virtual void enqueue(const WorkListUnit& U) {
Queue.push_back(U);
}
virtual WorkListUnit dequeue() {
WorkListUnit U = Queue.front();
Queue.pop_front();
return U;
}
virtual bool visitItemsInWorkList(Visitor &V) {
for (std::deque<WorkListUnit>::iterator
I = Queue.begin(), E = Queue.end(); I != E; ++I) {
if (V.visit(*I))
return true;
}
return false;
}
};
} // end anonymous namespace
// Place the dstor for WorkList here because it contains virtual member
// functions, and we the code for the dstor generated in one compilation unit.
WorkList::~WorkList() {}
WorkList *WorkList::makeDFS() { return new DFS(); }
WorkList *WorkList::makeBFS() { return new BFS(); }
namespace {
class BFSBlockDFSContents : public WorkList {
std::deque<WorkListUnit> Queue;
SmallVector<WorkListUnit,20> Stack;
public:
virtual bool hasWork() const {
return !Queue.empty() || !Stack.empty();
}
virtual void enqueue(const WorkListUnit& U) {
if (U.getNode()->getLocation().getAs<BlockEntrance>())
Queue.push_front(U);
else
Stack.push_back(U);
}
virtual WorkListUnit dequeue() {
// Process all basic blocks to completion.
if (!Stack.empty()) {
const WorkListUnit& U = Stack.back();
Stack.pop_back(); // This technically "invalidates" U, but we are fine.
return U;
}
assert(!Queue.empty());
// Don't use const reference. The subsequent pop_back() might make it
// unsafe.
WorkListUnit U = Queue.front();
Queue.pop_front();
return U;
}
virtual bool visitItemsInWorkList(Visitor &V) {
for (SmallVectorImpl<WorkListUnit>::iterator
I = Stack.begin(), E = Stack.end(); I != E; ++I) {
if (V.visit(*I))
return true;
}
for (std::deque<WorkListUnit>::iterator
I = Queue.begin(), E = Queue.end(); I != E; ++I) {
if (V.visit(*I))
return true;
}
return false;
}
};
} // end anonymous namespace
WorkList* WorkList::makeBFSBlockDFSContents() {
return new BFSBlockDFSContents();
}
//===----------------------------------------------------------------------===//
// Core analysis engine.
//===----------------------------------------------------------------------===//
/// ExecuteWorkList - Run the worklist algorithm for a maximum number of steps.
bool CoreEngine::ExecuteWorkList(const LocationContext *L, unsigned Steps,
ProgramStateRef InitState) {
if (G->num_roots() == 0) { // Initialize the analysis by constructing
// the root if none exists.
const CFGBlock *Entry = &(L->getCFG()->getEntry());
assert (Entry->empty() &&
"Entry block must be empty.");
assert (Entry->succ_size() == 1 &&
"Entry block must have 1 successor.");
// Mark the entry block as visited.
FunctionSummaries->markVisitedBasicBlock(Entry->getBlockID(),
L->getDecl(),
L->getCFG()->getNumBlockIDs());
// Get the solitary successor.
const CFGBlock *Succ = *(Entry->succ_begin());
// Construct an edge representing the
// starting location in the function.
BlockEdge StartLoc(Entry, Succ, L);
// Set the current block counter to being empty.
WList->setBlockCounter(BCounterFactory.GetEmptyCounter());
if (!InitState)
// Generate the root.
generateNode(StartLoc, SubEng.getInitialState(L), 0);
else
generateNode(StartLoc, InitState, 0);
}
// Check if we have a steps limit
bool UnlimitedSteps = Steps == 0;
while (WList->hasWork()) {
if (!UnlimitedSteps) {
if (Steps == 0) {
NumReachedMaxSteps++;
break;
}
--Steps;
}
NumSteps++;
const WorkListUnit& WU = WList->dequeue();
// Set the current block counter.
WList->setBlockCounter(WU.getBlockCounter());
// Retrieve the node.
ExplodedNode *Node = WU.getNode();
dispatchWorkItem(Node, Node->getLocation(), WU);
}
SubEng.processEndWorklist(hasWorkRemaining());
return WList->hasWork();
}
void CoreEngine::dispatchWorkItem(ExplodedNode* Pred, ProgramPoint Loc,
const WorkListUnit& WU) {
// Dispatch on the location type.
switch (Loc.getKind()) {
case ProgramPoint::BlockEdgeKind:
HandleBlockEdge(Loc.castAs<BlockEdge>(), Pred);
break;
case ProgramPoint::BlockEntranceKind:
HandleBlockEntrance(Loc.castAs<BlockEntrance>(), Pred);
break;
case ProgramPoint::BlockExitKind:
assert (false && "BlockExit location never occur in forward analysis.");
break;
case ProgramPoint::CallEnterKind: {
CallEnter CEnter = Loc.castAs<CallEnter>();
SubEng.processCallEnter(CEnter, Pred);
break;
}
case ProgramPoint::CallExitBeginKind:
SubEng.processCallExit(Pred);
break;
case ProgramPoint::EpsilonKind: {
assert(Pred->hasSinglePred() &&
"Assume epsilon has exactly one predecessor by construction");
ExplodedNode *PNode = Pred->getFirstPred();
dispatchWorkItem(Pred, PNode->getLocation(), WU);
break;
}
default:
assert(Loc.getAs<PostStmt>() ||
Loc.getAs<PostInitializer>() ||
Loc.getAs<PostImplicitCall>() ||
Loc.getAs<CallExitEnd>());
HandlePostStmt(WU.getBlock(), WU.getIndex(), Pred);
break;
}
}
bool CoreEngine::ExecuteWorkListWithInitialState(const LocationContext *L,
unsigned Steps,
ProgramStateRef InitState,
ExplodedNodeSet &Dst) {
bool DidNotFinish = ExecuteWorkList(L, Steps, InitState);
for (ExplodedGraph::eop_iterator I = G->eop_begin(),
E = G->eop_end(); I != E; ++I) {
Dst.Add(*I);
}
return DidNotFinish;
}
void CoreEngine::HandleBlockEdge(const BlockEdge &L, ExplodedNode *Pred) {
const CFGBlock *Blk = L.getDst();
NodeBuilderContext BuilderCtx(*this, Blk, Pred);
// Mark this block as visited.
const LocationContext *LC = Pred->getLocationContext();
FunctionSummaries->markVisitedBasicBlock(Blk->getBlockID(),
LC->getDecl(),
LC->getCFG()->getNumBlockIDs());
// Check if we are entering the EXIT block.
if (Blk == &(L.getLocationContext()->getCFG()->getExit())) {
assert (L.getLocationContext()->getCFG()->getExit().size() == 0
&& "EXIT block cannot contain Stmts.");
// Process the final state transition.
SubEng.processEndOfFunction(BuilderCtx, Pred);
// This path is done. Don't enqueue any more nodes.
return;
}
// Call into the SubEngine to process entering the CFGBlock.
ExplodedNodeSet dstNodes;
BlockEntrance BE(Blk, Pred->getLocationContext());
NodeBuilderWithSinks nodeBuilder(Pred, dstNodes, BuilderCtx, BE);
SubEng.processCFGBlockEntrance(L, nodeBuilder, Pred);
// Auto-generate a node.
if (!nodeBuilder.hasGeneratedNodes()) {
nodeBuilder.generateNode(Pred->State, Pred);
}
// Enqueue nodes onto the worklist.
enqueue(dstNodes);
}
void CoreEngine::HandleBlockEntrance(const BlockEntrance &L,
ExplodedNode *Pred) {
// Increment the block counter.
const LocationContext *LC = Pred->getLocationContext();
unsigned BlockId = L.getBlock()->getBlockID();
BlockCounter Counter = WList->getBlockCounter();
Counter = BCounterFactory.IncrementCount(Counter, LC->getCurrentStackFrame(),
BlockId);
WList->setBlockCounter(Counter);
// Process the entrance of the block.
if (Optional<CFGElement> E = L.getFirstElement()) {
NodeBuilderContext Ctx(*this, L.getBlock(), Pred);
SubEng.processCFGElement(*E, Pred, 0, &Ctx);
}
else
HandleBlockExit(L.getBlock(), Pred);
}
void CoreEngine::HandleBlockExit(const CFGBlock * B, ExplodedNode *Pred) {
if (const Stmt *Term = B->getTerminator()) {
switch (Term->getStmtClass()) {
default:
llvm_unreachable("Analysis for this terminator not implemented.");
// Model static initializers.
case Stmt::DeclStmtClass:
HandleStaticInit(cast<DeclStmt>(Term), B, Pred);
return;
case Stmt::BinaryOperatorClass: // '&&' and '||'
HandleBranch(cast<BinaryOperator>(Term)->getLHS(), Term, B, Pred);
return;
case Stmt::BinaryConditionalOperatorClass:
case Stmt::ConditionalOperatorClass:
HandleBranch(cast<AbstractConditionalOperator>(Term)->getCond(),
Term, B, Pred);
return;
// FIXME: Use constant-folding in CFG construction to simplify this
// case.
case Stmt::ChooseExprClass:
HandleBranch(cast<ChooseExpr>(Term)->getCond(), Term, B, Pred);
return;
case Stmt::CXXTryStmtClass: {
// Generate a node for each of the successors.
// Our logic for EH analysis can certainly be improved.
for (CFGBlock::const_succ_iterator it = B->succ_begin(),
et = B->succ_end(); it != et; ++it) {
if (const CFGBlock *succ = *it) {
generateNode(BlockEdge(B, succ, Pred->getLocationContext()),
Pred->State, Pred);
}
}
return;
}
case Stmt::DoStmtClass:
HandleBranch(cast<DoStmt>(Term)->getCond(), Term, B, Pred);
return;
case Stmt::CXXForRangeStmtClass:
HandleBranch(cast<CXXForRangeStmt>(Term)->getCond(), Term, B, Pred);
return;
case Stmt::ForStmtClass:
HandleBranch(cast<ForStmt>(Term)->getCond(), Term, B, Pred);
return;
case Stmt::ContinueStmtClass:
case Stmt::BreakStmtClass:
case Stmt::GotoStmtClass:
break;
case Stmt::IfStmtClass:
HandleBranch(cast<IfStmt>(Term)->getCond(), Term, B, Pred);
return;
case Stmt::IndirectGotoStmtClass: {
// Only 1 successor: the indirect goto dispatch block.
assert (B->succ_size() == 1);
IndirectGotoNodeBuilder
builder(Pred, B, cast<IndirectGotoStmt>(Term)->getTarget(),
*(B->succ_begin()), this);
SubEng.processIndirectGoto(builder);
return;
}
case Stmt::ObjCForCollectionStmtClass: {
// In the case of ObjCForCollectionStmt, it appears twice in a CFG:
//
// (1) inside a basic block, which represents the binding of the
// 'element' variable to a value.
// (2) in a terminator, which represents the branch.
//
// For (1), subengines will bind a value (i.e., 0 or 1) indicating
// whether or not collection contains any more elements. We cannot
// just test to see if the element is nil because a container can
// contain nil elements.
HandleBranch(Term, Term, B, Pred);
return;
}
case Stmt::SwitchStmtClass: {
SwitchNodeBuilder builder(Pred, B, cast<SwitchStmt>(Term)->getCond(),
this);
SubEng.processSwitch(builder);
return;
}
case Stmt::WhileStmtClass:
HandleBranch(cast<WhileStmt>(Term)->getCond(), Term, B, Pred);
return;
}
}
assert (B->succ_size() == 1 &&
"Blocks with no terminator should have at most 1 successor.");
generateNode(BlockEdge(B, *(B->succ_begin()), Pred->getLocationContext()),
Pred->State, Pred);
}
void CoreEngine::HandleBranch(const Stmt *Cond, const Stmt *Term,
const CFGBlock * B, ExplodedNode *Pred) {
assert(B->succ_size() == 2);
NodeBuilderContext Ctx(*this, B, Pred);
ExplodedNodeSet Dst;
SubEng.processBranch(Cond, Term, Ctx, Pred, Dst,
*(B->succ_begin()), *(B->succ_begin()+1));
// Enqueue the new frontier onto the worklist.
enqueue(Dst);
}
void CoreEngine::HandleStaticInit(const DeclStmt *DS, const CFGBlock *B,
ExplodedNode *Pred) {
assert(B->succ_size() == 2);
NodeBuilderContext Ctx(*this, B, Pred);
ExplodedNodeSet Dst;
SubEng.processStaticInitializer(DS, Ctx, Pred, Dst,
*(B->succ_begin()), *(B->succ_begin()+1));
// Enqueue the new frontier onto the worklist.
enqueue(Dst);
}
void CoreEngine::HandlePostStmt(const CFGBlock *B, unsigned StmtIdx,
ExplodedNode *Pred) {
assert(B);
assert(!B->empty());
if (StmtIdx == B->size())
HandleBlockExit(B, Pred);
else {
NodeBuilderContext Ctx(*this, B, Pred);
SubEng.processCFGElement((*B)[StmtIdx], Pred, StmtIdx, &Ctx);
}
}
/// generateNode - Utility method to generate nodes, hook up successors,
/// and add nodes to the worklist.
void CoreEngine::generateNode(const ProgramPoint &Loc,
ProgramStateRef State,
ExplodedNode *Pred) {
bool IsNew;
ExplodedNode *Node = G->getNode(Loc, State, false, &IsNew);
if (Pred)
Node->addPredecessor(Pred, *G); // Link 'Node' with its predecessor.
else {
assert (IsNew);
G->addRoot(Node); // 'Node' has no predecessor. Make it a root.
}
// Only add 'Node' to the worklist if it was freshly generated.
if (IsNew) WList->enqueue(Node);
}
void CoreEngine::enqueueStmtNode(ExplodedNode *N,
const CFGBlock *Block, unsigned Idx) {
assert(Block);
assert (!N->isSink());
// Check if this node entered a callee.
if (N->getLocation().getAs<CallEnter>()) {
// Still use the index of the CallExpr. It's needed to create the callee
// StackFrameContext.
WList->enqueue(N, Block, Idx);
return;
}
// Do not create extra nodes. Move to the next CFG element.
if (N->getLocation().getAs<PostInitializer>() ||
N->getLocation().getAs<PostImplicitCall>()) {
WList->enqueue(N, Block, Idx+1);
return;
}
if (N->getLocation().getAs<EpsilonPoint>()) {
WList->enqueue(N, Block, Idx);
return;
}
// At this point, we know we're processing a normal statement.
CFGStmt CS = (*Block)[Idx].castAs<CFGStmt>();
PostStmt Loc(CS.getStmt(), N->getLocationContext());
if (Loc == N->getLocation()) {
// Note: 'N' should be a fresh node because otherwise it shouldn't be
// a member of Deferred.
WList->enqueue(N, Block, Idx+1);
return;
}
bool IsNew;
ExplodedNode *Succ = G->getNode(Loc, N->getState(), false, &IsNew);
Succ->addPredecessor(N, *G);
if (IsNew)
WList->enqueue(Succ, Block, Idx+1);
}
ExplodedNode *CoreEngine::generateCallExitBeginNode(ExplodedNode *N) {
// Create a CallExitBegin node and enqueue it.
const StackFrameContext *LocCtx
= cast<StackFrameContext>(N->getLocationContext());
// Use the callee location context.
CallExitBegin Loc(LocCtx);
bool isNew;
ExplodedNode *Node = G->getNode(Loc, N->getState(), false, &isNew);
Node->addPredecessor(N, *G);
return isNew ? Node : 0;
}
void CoreEngine::enqueue(ExplodedNodeSet &Set) {
for (ExplodedNodeSet::iterator I = Set.begin(),
E = Set.end(); I != E; ++I) {
WList->enqueue(*I);
}
}
void CoreEngine::enqueue(ExplodedNodeSet &Set,
const CFGBlock *Block, unsigned Idx) {
for (ExplodedNodeSet::iterator I = Set.begin(),
E = Set.end(); I != E; ++I) {
enqueueStmtNode(*I, Block, Idx);
}
}
void CoreEngine::enqueueEndOfFunction(ExplodedNodeSet &Set) {
for (ExplodedNodeSet::iterator I = Set.begin(), E = Set.end(); I != E; ++I) {
ExplodedNode *N = *I;
// If we are in an inlined call, generate CallExitBegin node.
if (N->getLocationContext()->getParent()) {
N = generateCallExitBeginNode(N);
if (N)
WList->enqueue(N);
} else {
// TODO: We should run remove dead bindings here.
G->addEndOfPath(N);
NumPathsExplored++;
}
}
}
void NodeBuilder::anchor() { }
ExplodedNode* NodeBuilder::generateNodeImpl(const ProgramPoint &Loc,
ProgramStateRef State,
ExplodedNode *FromN,
bool MarkAsSink) {
HasGeneratedNodes = true;
bool IsNew;
ExplodedNode *N = C.Eng.G->getNode(Loc, State, MarkAsSink, &IsNew);
N->addPredecessor(FromN, *C.Eng.G);
Frontier.erase(FromN);
if (!IsNew)
return 0;
if (!MarkAsSink)
Frontier.Add(N);
return N;
}
void NodeBuilderWithSinks::anchor() { }
StmtNodeBuilder::~StmtNodeBuilder() {
if (EnclosingBldr)
for (ExplodedNodeSet::iterator I = Frontier.begin(),
E = Frontier.end(); I != E; ++I )
EnclosingBldr->addNodes(*I);
}
void BranchNodeBuilder::anchor() { }
ExplodedNode *BranchNodeBuilder::generateNode(ProgramStateRef State,
bool branch,
ExplodedNode *NodePred) {
// If the branch has been marked infeasible we should not generate a node.
if (!isFeasible(branch))
return NULL;
ProgramPoint Loc = BlockEdge(C.Block, branch ? DstT:DstF,
NodePred->getLocationContext());
ExplodedNode *Succ = generateNodeImpl(Loc, State, NodePred);
return Succ;
}
ExplodedNode*
IndirectGotoNodeBuilder::generateNode(const iterator &I,
ProgramStateRef St,
bool IsSink) {
bool IsNew;
ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, I.getBlock(),
Pred->getLocationContext()), St,
IsSink, &IsNew);
Succ->addPredecessor(Pred, *Eng.G);
if (!IsNew)
return 0;
if (!IsSink)
Eng.WList->enqueue(Succ);
return Succ;
}
ExplodedNode*
SwitchNodeBuilder::generateCaseStmtNode(const iterator &I,
ProgramStateRef St) {
bool IsNew;
ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, I.getBlock(),
Pred->getLocationContext()), St,
false, &IsNew);
Succ->addPredecessor(Pred, *Eng.G);
if (!IsNew)
return 0;
Eng.WList->enqueue(Succ);
return Succ;
}
ExplodedNode*
SwitchNodeBuilder::generateDefaultCaseNode(ProgramStateRef St,
bool IsSink) {
// Get the block for the default case.
assert(Src->succ_rbegin() != Src->succ_rend());
CFGBlock *DefaultBlock = *Src->succ_rbegin();
// Sanity check for default blocks that are unreachable and not caught
// by earlier stages.
if (!DefaultBlock)
return NULL;
bool IsNew;
ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, DefaultBlock,
Pred->getLocationContext()), St,
IsSink, &IsNew);
Succ->addPredecessor(Pred, *Eng.G);
if (!IsNew)
return 0;
if (!IsSink)
Eng.WList->enqueue(Succ);
return Succ;
}