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+//===- 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/CFGStmtMap.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).
+ const 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;
+}
+
+bool ExplodedNode::isTrivial() const {
+ return pred_size() == 1 && succ_size() == 1 &&
+ getFirstPred()->getState()->getID() == getState()->getID() &&
+ getFirstPred()->succ_size() == 1;
+}
+
+const CFGBlock *ExplodedNode::getCFGBlock() const {
+ ProgramPoint P = getLocation();
+ if (auto BEP = P.getAs<BlockEntrance>())
+ return BEP->getBlock();
+
+ // Find the node's current statement in the CFG.
+ // FIXME: getStmtForDiagnostics() does nasty things in order to provide
+ // a valid statement for body farms, do we need this behavior here?
+ if (const Stmt *S = getStmtForDiagnostics())
+ return getLocationContext()
+ ->getAnalysisDeclContext()
+ ->getCFGStmtMap()
+ ->getBlock(S);
+
+ return nullptr;
+}
+
+static const LocationContext *
+findTopAutosynthesizedParentContext(const LocationContext *LC) {
+ assert(LC->getAnalysisDeclContext()->isBodyAutosynthesized());
+ const LocationContext *ParentLC = LC->getParent();
+ assert(ParentLC && "We don't start analysis from autosynthesized code");
+ while (ParentLC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
+ LC = ParentLC;
+ ParentLC = LC->getParent();
+ assert(ParentLC && "We don't start analysis from autosynthesized code");
+ }
+ return LC;
+}
+
+const Stmt *ExplodedNode::getStmtForDiagnostics() const {
+ // We cannot place diagnostics on autosynthesized code.
+ // Put them onto the call site through which we jumped into autosynthesized
+ // code for the first time.
+ const LocationContext *LC = getLocationContext();
+ if (LC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
+ // It must be a stack frame because we only autosynthesize functions.
+ return cast<StackFrameContext>(findTopAutosynthesizedParentContext(LC))
+ ->getCallSite();
+ }
+ // Otherwise, see if the node's program point directly points to a statement.
+ // FIXME: Refactor into a ProgramPoint method?
+ ProgramPoint P = getLocation();
+ if (auto SP = P.getAs<StmtPoint>())
+ return SP->getStmt();
+ if (auto BE = P.getAs<BlockEdge>())
+ return BE->getSrc()->getTerminatorStmt();
+ if (auto CE = P.getAs<CallEnter>())
+ return CE->getCallExpr();
+ if (auto CEE = P.getAs<CallExitEnd>())
+ return CEE->getCalleeContext()->getCallSite();
+ if (auto PIPP = P.getAs<PostInitializer>())
+ return PIPP->getInitializer()->getInit();
+ if (auto CEB = P.getAs<CallExitBegin>())
+ return CEB->getReturnStmt();
+ if (auto FEP = P.getAs<FunctionExitPoint>())
+ return FEP->getStmt();
+
+ return nullptr;
+}
+
+const Stmt *ExplodedNode::getNextStmtForDiagnostics() const {
+ for (const ExplodedNode *N = getFirstSucc(); N; N = N->getFirstSucc()) {
+ if (const Stmt *S = N->getStmtForDiagnostics()) {
+ // Check if the statement is '?' or '&&'/'||'. These are "merges",
+ // not actual statement points.
+ switch (S->getStmtClass()) {
+ case Stmt::ChooseExprClass:
+ case Stmt::BinaryConditionalOperatorClass:
+ case Stmt::ConditionalOperatorClass:
+ continue;
+ case Stmt::BinaryOperatorClass: {
+ BinaryOperatorKind Op = cast<BinaryOperator>(S)->getOpcode();
+ if (Op == BO_LAnd || Op == BO_LOr)
+ continue;
+ break;
+ }
+ default:
+ break;
+ }
+ // We found the statement, so return it.
+ return S;
+ }
+ }
+
+ return nullptr;
+}
+
+const Stmt *ExplodedNode::getPreviousStmtForDiagnostics() const {
+ for (const ExplodedNode *N = getFirstPred(); N; N = N->getFirstPred())
+ if (const Stmt *S = N->getStmtForDiagnostics())
+ return S;
+
+ return nullptr;
+}
+
+const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const {
+ if (const Stmt *S = getStmtForDiagnostics())
+ return S;
+
+ return getPreviousStmtForDiagnostics();
+}
+
+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>();
+ }
+
+ ++NumNodes;
+ new (V) NodeTy(L, State, NumNodes, IsSink);
+
+ if (ReclaimNodeInterval)
+ ChangedNodes.push_back(V);
+
+ // Insert the node into the node set and return it.
+ Nodes.InsertNode(V, InsertPos);
+
+ if (IsNew) *IsNew = true;
+ }
+ else
+ if (IsNew) *IsNew = false;
+
+ return V;
+}
+
+ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
+ ProgramStateRef State,
+ int64_t Id,
+ bool IsSink) {
+ NodeTy *V = (NodeTy *) getAllocator().Allocate<NodeTy>();
+ new (V) NodeTy(L, State, Id, 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->getID(), 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;
+}
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.