//===- ExplodedGraph.cpp - Local, Path-Sens. "Exploded Graph" -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the template classes ExplodedNode and ExplodedGraph,
// which represent a path-sensitive, intra-procedural "exploded graph."
//
//===----------------------------------------------------------------------===//
#include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ParentMap.h"
#include "clang/AST/Stmt.h"
#include "clang/Analysis/ProgramPoint.h"
#include "clang/Analysis/Support/BumpVector.h"
#include "clang/Basic/LLVM.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState_Fwd.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Casting.h"
#include <cassert>
#include <memory>
using namespace clang;
using namespace ento;
//===----------------------------------------------------------------------===//
// Cleanup.
//===----------------------------------------------------------------------===//
ExplodedGraph::ExplodedGraph() = default;
ExplodedGraph::~ExplodedGraph() = default;
//===----------------------------------------------------------------------===//
// Node reclamation.
//===----------------------------------------------------------------------===//
bool ExplodedGraph::isInterestingLValueExpr(const Expr *Ex) {
if (!Ex->isLValue())
return false;
return isa<DeclRefExpr>(Ex) ||
isa<MemberExpr>(Ex) ||
isa<ObjCIvarRefExpr>(Ex);
}
bool ExplodedGraph::shouldCollect(const ExplodedNode *node) {
// First, we only consider nodes for reclamation of the following
// conditions apply:
//
// (1) 1 predecessor (that has one successor)
// (2) 1 successor (that has one predecessor)
//
// If a node has no successor it is on the "frontier", while a node
// with no predecessor is a root.
//
// After these prerequisites, we discard all "filler" nodes that
// are used only for intermediate processing, and are not essential
// for analyzer history:
//
// (a) PreStmtPurgeDeadSymbols
//
// We then discard all other nodes where *all* of the following conditions
// apply:
//
// (3) The ProgramPoint is for a PostStmt, but not a PostStore.
// (4) There is no 'tag' for the ProgramPoint.
// (5) The 'store' is the same as the predecessor.
// (6) The 'GDM' is the same as the predecessor.
// (7) The LocationContext is the same as the predecessor.
// (8) Expressions that are *not* lvalue expressions.
// (9) The PostStmt isn't for a non-consumed Stmt or Expr.
// (10) The successor is neither a CallExpr StmtPoint nor a CallEnter or
// PreImplicitCall (so that we would be able to find it when retrying a
// call with no inlining).
// FIXME: It may be safe to reclaim PreCall and PostCall nodes as well.
// Conditions 1 and 2.
if (node->pred_size() != 1 || node->succ_size() != 1)
return false;
const ExplodedNode *pred = *(node->pred_begin());
if (pred->succ_size() != 1)
return false;
const ExplodedNode *succ = *(node->succ_begin());
if (succ->pred_size() != 1)
return false;
// Now reclaim any nodes that are (by definition) not essential to
// analysis history and are not consulted by any client code.
ProgramPoint progPoint = node->getLocation();
if (progPoint.getAs<PreStmtPurgeDeadSymbols>())
return !progPoint.getTag();
// Condition 3.
if (!progPoint.getAs<PostStmt>() || progPoint.getAs<PostStore>())
return false;
// Condition 4.
if (progPoint.getTag())
return false;
// Conditions 5, 6, and 7.
ProgramStateRef state = node->getState();
ProgramStateRef pred_state = pred->getState();
if (state->store != pred_state->store || state->GDM != pred_state->GDM ||
progPoint.getLocationContext() != pred->getLocationContext())
return false;
// All further checks require expressions. As per #3, we know that we have
// a PostStmt.
const Expr *Ex = dyn_cast<Expr>(progPoint.castAs<PostStmt>().getStmt());
if (!Ex)
return false;
// Condition 8.
// Do not collect nodes for "interesting" lvalue expressions since they are
// used extensively for generating path diagnostics.
if (isInterestingLValueExpr(Ex))
return false;
// Condition 9.
// Do not collect nodes for non-consumed Stmt or Expr to ensure precise
// diagnostic generation; specifically, so that we could anchor arrows
// pointing to the beginning of statements (as written in code).
ParentMap &PM = progPoint.getLocationContext()->getParentMap();
if (!PM.isConsumedExpr(Ex))
return false;
// Condition 10.
const ProgramPoint SuccLoc = succ->getLocation();
if (Optional<StmtPoint> SP = SuccLoc.getAs<StmtPoint>())
if (CallEvent::isCallStmt(SP->getStmt()))
return false;
// Condition 10, continuation.
if (SuccLoc.getAs<CallEnter>() || SuccLoc.getAs<PreImplicitCall>())
return false;
return true;
}
void ExplodedGraph::collectNode(ExplodedNode *node) {
// Removing a node means:
// (a) changing the predecessors successor to the successor of this node
// (b) changing the successors predecessor to the predecessor of this node
// (c) Putting 'node' onto freeNodes.
assert(node->pred_size() == 1 || node->succ_size() == 1);
ExplodedNode *pred = *(node->pred_begin());
ExplodedNode *succ = *(node->succ_begin());
pred->replaceSuccessor(succ);
succ->replacePredecessor(pred);
FreeNodes.push_back(node);
Nodes.RemoveNode(node);
--NumNodes;
node->~ExplodedNode();
}
void ExplodedGraph::reclaimRecentlyAllocatedNodes() {
if (ChangedNodes.empty())
return;
// Only periodically reclaim nodes so that we can build up a set of
// nodes that meet the reclamation criteria. Freshly created nodes
// by definition have no successor, and thus cannot be reclaimed (see below).
assert(ReclaimCounter > 0);
if (--ReclaimCounter != 0)
return;
ReclaimCounter = ReclaimNodeInterval;
for (const auto node : ChangedNodes)
if (shouldCollect(node))
collectNode(node);
ChangedNodes.clear();
}
//===----------------------------------------------------------------------===//
// ExplodedNode.
//===----------------------------------------------------------------------===//
// An NodeGroup's storage type is actually very much like a TinyPtrVector:
// it can be either a pointer to a single ExplodedNode, or a pointer to a
// BumpVector allocated with the ExplodedGraph's allocator. This allows the
// common case of single-node NodeGroups to be implemented with no extra memory.
//
// Consequently, each of the NodeGroup methods have up to four cases to handle:
// 1. The flag is set and this group does not actually contain any nodes.
// 2. The group is empty, in which case the storage value is null.
// 3. The group contains a single node.
// 4. The group contains more than one node.
using ExplodedNodeVector = BumpVector<ExplodedNode *>;
using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>;
void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
assert(!V->isSink());
Preds.addNode(V, G);
V->Succs.addNode(this, G);
}
void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) {
assert(!getFlag());
GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
assert(Storage.is<ExplodedNode *>());
Storage = node;
assert(Storage.is<ExplodedNode *>());
}
void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) {
assert(!getFlag());
GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
if (Storage.isNull()) {
Storage = N;
assert(Storage.is<ExplodedNode *>());
return;
}
ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>();
if (!V) {
// Switch from single-node to multi-node representation.
ExplodedNode *Old = Storage.get<ExplodedNode *>();
BumpVectorContext &Ctx = G.getNodeAllocator();
V = G.getAllocator().Allocate<ExplodedNodeVector>();
new (V) ExplodedNodeVector(Ctx, 4);
V->push_back(Old, Ctx);
Storage = V;
assert(!getFlag());
assert(Storage.is<ExplodedNodeVector *>());
}
V->push_back(N, G.getNodeAllocator());
}
unsigned ExplodedNode::NodeGroup::size() const {
if (getFlag())
return 0;
const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
if (Storage.isNull())
return 0;
if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
return V->size();
return 1;
}
ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
if (getFlag())
return nullptr;
const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
if (Storage.isNull())
return nullptr;
if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
return V->begin();
return Storage.getAddrOfPtr1();
}
ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
if (getFlag())
return nullptr;
const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
if (Storage.isNull())
return nullptr;
if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
return V->end();
return Storage.getAddrOfPtr1() + 1;
}
int64_t ExplodedNode::getID(ExplodedGraph *G) const {
return G->getAllocator().identifyKnownAlignedObject<ExplodedNode>(this);
}
bool ExplodedNode::isTrivial() const {
return pred_size() == 1 && succ_size() == 1 &&
getFirstPred()->getState()->getID() == getState()->getID() &&
getFirstPred()->succ_size() == 1;
}
ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
ProgramStateRef State,
bool IsSink,
bool* IsNew) {
// Profile 'State' to determine if we already have an existing node.
llvm::FoldingSetNodeID profile;
void *InsertPos = nullptr;
NodeTy::Profile(profile, L, State, IsSink);
NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos);
if (!V) {
if (!FreeNodes.empty()) {
V = FreeNodes.back();
FreeNodes.pop_back();
}
else {
// Allocate a new node.
V = (NodeTy*) getAllocator().Allocate<NodeTy>();
}
new (V) NodeTy(L, State, IsSink);
if (ReclaimNodeInterval)
ChangedNodes.push_back(V);
// Insert the node into the node set and return it.
Nodes.InsertNode(V, InsertPos);
++NumNodes;
if (IsNew) *IsNew = true;
}
else
if (IsNew) *IsNew = false;
return V;
}
ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
ProgramStateRef State,
bool IsSink) {
NodeTy *V = (NodeTy *) getAllocator().Allocate<NodeTy>();
new (V) NodeTy(L, State, IsSink);
return V;
}
std::unique_ptr<ExplodedGraph>
ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks,
InterExplodedGraphMap *ForwardMap,
InterExplodedGraphMap *InverseMap) const {
if (Nodes.empty())
return nullptr;
using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
Pass1Ty Pass1;
using Pass2Ty = InterExplodedGraphMap;
InterExplodedGraphMap Pass2Scratch;
Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
SmallVector<const ExplodedNode*, 10> WL1, WL2;
// ===- Pass 1 (reverse DFS) -===
for (const auto Sink : Sinks)
if (Sink)
WL1.push_back(Sink);
// Process the first worklist until it is empty.
while (!WL1.empty()) {
const ExplodedNode *N = WL1.pop_back_val();
// Have we already visited this node? If so, continue to the next one.
if (!Pass1.insert(N).second)
continue;
// If this is a root enqueue it to the second worklist.
if (N->Preds.empty()) {
WL2.push_back(N);
continue;
}
// Visit our predecessors and enqueue them.
WL1.append(N->Preds.begin(), N->Preds.end());
}
// We didn't hit a root? Return with a null pointer for the new graph.
if (WL2.empty())
return nullptr;
// Create an empty graph.
std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph();
// ===- Pass 2 (forward DFS to construct the new graph) -===
while (!WL2.empty()) {
const ExplodedNode *N = WL2.pop_back_val();
// Skip this node if we have already processed it.
if (Pass2.find(N) != Pass2.end())
continue;
// Create the corresponding node in the new graph and record the mapping
// from the old node to the new node.
ExplodedNode *NewN = G->createUncachedNode(N->getLocation(), N->State, N->isSink());
Pass2[N] = NewN;
// Also record the reverse mapping from the new node to the old node.
if (InverseMap) (*InverseMap)[NewN] = N;
// If this node is a root, designate it as such in the graph.
if (N->Preds.empty())
G->addRoot(NewN);
// In the case that some of the intended predecessors of NewN have already
// been created, we should hook them up as predecessors.
// Walk through the predecessors of 'N' and hook up their corresponding
// nodes in the new graph (if any) to the freshly created node.
for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end();
I != E; ++I) {
Pass2Ty::iterator PI = Pass2.find(*I);
if (PI == Pass2.end())
continue;
NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *G);
}
// In the case that some of the intended successors of NewN have already
// been created, we should hook them up as successors. Otherwise, enqueue
// the new nodes from the original graph that should have nodes created
// in the new graph.
for (ExplodedNode::succ_iterator I = N->Succs.begin(), E = N->Succs.end();
I != E; ++I) {
Pass2Ty::iterator PI = Pass2.find(*I);
if (PI != Pass2.end()) {
const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G);
continue;
}
// Enqueue nodes to the worklist that were marked during pass 1.
if (Pass1.count(*I))
WL2.push_back(*I);
}
}
return G;
}
