@specs-feup/clava/src-api/clava/graphs/cfg/CfgBuilder.ts

A C/C++ source-to-source compiler written in Typescript

import { debug } from "@specs-feup/lara/api/lara/core/LaraCore.js";
import Graphs from "@specs-feup/lara/api/lara/graphs/Graphs.js";
import cytoscape from "cytoscape";
import Query from "@specs-feup/lara/api/weaver/Query.js";
import {
  Break,
  Continue,
  FunctionJp,
  LabelDecl,
  LabelStmt,
  Loop,
  Scope,
  Statement,
  Switch,
} from "../../../Joinpoints.js";
import ClavaJoinPoints from "../../ClavaJoinPoints.js";
import CfgEdge from "./CfgEdge.js";
import CfgEdgeType from "./CfgEdgeType.js";
import CfgNodeData from "./CfgNodeData.js";
import CfgNodeType from "./CfgNodeType.js";
import CfgUtils from "./CfgUtils.js";
import NextCfgNode from "./NextCfgNode.js";
import CaseData from "./nodedata/CaseData.js";
import DataFactory from "./nodedata/DataFactory.js";
import HeaderData from "./nodedata/HeaderData.js";
import IfData from "./nodedata/IfData.js";
import InstListNodeData from "./nodedata/InstListNodeData.js";
import LoopData from "./nodedata/LoopData.js";
import ScopeNodeData from "./nodedata/ScopeNodeData.js";
import SwitchData from "./nodedata/SwitchData.js";
import GotoData from "./nodedata/GotoData.js";
import LabelData from "./nodedata/LabelData.js";
import { LaraJoinPoint } from "@specs-feup/lara/api/LaraJoinPoint.js";

export default class CfgBuilder {
  /**
   * AST node to process
   */
  private jp: Statement;

  /**
   * Graph being built
   */
  private graph: cytoscape.Core;

  /**
   * Maps stmts to graph nodes
   */
  private nodes: Map<string, cytoscape.NodeSingular>;

  /**
   * The start node of the graph
   */
  private startNode: cytoscape.NodeSingular;

  /**
   * The end node of the graph
   */
  private endNode: cytoscape.NodeSingular;

  /**
   * Maps the astId to the corresponding temporary statement
   */
  private temporaryStmts: Record<string, Statement>;

  /**
   * If true, uses deterministic ids for the graph ids (e.g. id_0, id_1...). Otherwise, uses $jp.astId whenever possible.
   */
  private deterministicIds: boolean;

  /**
   * Current id, in case deterministic ids are used
   */
  private currentId: number;

  /**
   * An instance of DataFactory, for creating graph node data
   */
  private dataFactory: DataFactory;

  /**
   * Calculates what node is unconditionally executed after a given statement
   */
  private nextNodes: NextCfgNode;

  /**
   * If true, each instruction list should be split
   */
  private splitInstList: boolean;

  /**
   * If true, the goto nodes should be excluded from the graph
   */
  private removeGotoNodes: boolean;

  /**
   * If true, the label nodes should be excluded from the graph
   */
  private removeLabelNodes: boolean;

  /**
   * If true, the temporary scope statements should not be removed from the graph
   */
  private keepTemporaryScopeStmts: boolean;

  /**
   * Creates a new instance of the CfgBuilder class
   * @param $jp -
   * @param deterministicIds - If true, uses deterministic ids for the graph ids (e.g. id_0, id_1...). Otherwise, uses $jp.astId whenever possible
   * @param options - An object containing configuration options for the cfg
   */
  constructor(
    $jp: Statement,
    deterministicIds: boolean = false,
    options = {
      /**
       * If true, statements of each instruction list must be split
       */
      splitInstList: false,
      /**
       * If true, the nodes that correspond to goto statements will be excluded from the resulting graph
       */
      removeGotoNodes: false,
      /**
       * If true, the nodes that correspond to label statements will be excluded from the resulting graph
       */
      removeLabelNodes: false,
      /**
       * If true, the temporary scope statements will be kept in the resulting graph
       */
      keepTemporaryScopeStmts: false,
    }
  ) {
    this.jp = $jp;
    this.splitInstList = options.splitInstList ?? false;
    this.removeGotoNodes = options.removeGotoNodes ?? false;
    this.removeLabelNodes = options.removeLabelNodes ?? false;
    this.keepTemporaryScopeStmts = options.keepTemporaryScopeStmts ?? false;
    this.deterministicIds = deterministicIds;
    this.currentId = 0;
    this.dataFactory = new DataFactory(this.jp);
    this.graph = Graphs.newGraph();
    this.nodes = new Map();

    // Create start and end nodes
    // Do not add them to #nodes, since they have no associated statements
    this.startNode = Graphs.addNode(
      this.graph,
      this.dataFactory.newData(
        CfgNodeType.START,
        undefined,
        "start",
        this.splitInstList
      )
    );

    this.endNode = Graphs.addNode(
      this.graph,
      this.dataFactory.newData(
        CfgNodeType.END,
        undefined,
        "end",
        this.splitInstList
      )
    );

    this.temporaryStmts = {};
    this.nextNodes = new NextCfgNode(this.jp, this.nodes, this.endNode);
  }

  /**
   * Returns the next id that will be used to identify a graph node
   */
  private nextId() {
    const nextId = "id_" + this.currentId;
    this.currentId++;
    return nextId;
  }

  /**
   * Connects two nodes using a directed edge
   * @param source - Starting point from which the edge originates
   * @param target - Destination point to which the edge points
   * @param edgeType - The edge label that connects
   */
  private addEdge(
    source: cytoscape.NodeSingular,
    target: cytoscape.NodeSingular,
    edgeType: CfgEdgeType
  ) {
    Graphs.addEdge(this.graph, source, target, new CfgEdge(edgeType));
  }

  /**
   * Builds the control flow graph
   * @returns An array that includes the built graph, the nodes, the start and end nodes
   */
  build(): [
    cytoscape.Core,
    Map<string, cytoscape.NodeSingular>,
    cytoscape.NodeSingular,
    cytoscape.NodeSingular,
  ] {
    this.addAuxComments();
    this.createNodes();

    //this._fillNodes();
    this.connectNodes();

    this.cleanCfg();

    // TODO: Check graph invariants
    // 1. Each node has either one unconditional outgoing edge,
    // or two outgoing edges that must be a pair true/false,
    // or if there is no outgoing edge must be the end node

    return [this.graph, this.nodes, this.startNode, this.endNode];
  }

  /**
   * Inserts comments that specify the beginning and end of a scope
   */
  protected addAuxComments() {
    for (const $currentJp of this.jp.descendants) {
      if ($currentJp instanceof Scope) {
        const $scopeStart = $currentJp.insertBegin(
          ClavaJoinPoints.comment("SCOPE_START")
        ) as Statement;
        this.temporaryStmts[$scopeStart.astId] = $scopeStart;

        const $scopeEnd = $currentJp.insertEnd(
          ClavaJoinPoints.comment("SCOPE_END")
        ) as Statement;
        this.temporaryStmts[$scopeEnd.astId] = $scopeEnd;
      }
    }
  }

  /**
   * Creates all nodes (except start and end), with only the leader statement
   */
  protected createNodes() {
    // Test all statements for leadership
    // If they are leaders, create node
    for (const $stmt of Query.searchFromInclusive(this.jp, Statement)) {
      if (CfgUtils.isLeader($stmt)) {
        if (
          this.splitInstList &&
          CfgUtils.getNodeType($stmt) === CfgNodeType.INST_LIST
        ) {
          this.getOrAddNode($stmt, true, CfgNodeType.INST_LIST);

          for (const $rightJp of $stmt.siblingsRight) {
            const $right = $rightJp as Statement;
            if (!CfgUtils.isLeader($right))
              this.getOrAddNode($right, true, CfgNodeType.INST_LIST);
            else break;
          }
        } else this.getOrAddNode($stmt, true);
      }
    }

    // Special case: if starting node is a statement and a graph node was not created for it (e.g. creating a graph starting from an arbitrary statement),
    // create one with the type INST_LIST
    if (
      this.jp instanceof Statement &&
      this.nodes.get(this.jp.astId) === undefined
    ) {
      this.getOrAddNode(this.jp, true, CfgNodeType.INST_LIST);
    }
  }

  /**
   * Connects a node associated with a statement that is an instance of a "if" statement.
   * @param node - Node whose type is "IF"
   */
  private connectIfNode(node: cytoscape.NodeSingular) {
    const ifStmt = (node.data() as IfData).if;

    if (ifStmt === undefined) {
      throw new Error("If statement is undefined");
    }

    const thenStmt = ifStmt.then;

    if (thenStmt === undefined) {
      throw new Error("Then statement is undefined");
    }

    const thenNode = this.nodes.get(thenStmt.astId);

    if (thenNode === undefined) {
      throw new Error(
        "Node for then statement is undefined: " + thenStmt.astId
      );
    }

    this.addEdge(node, thenNode, CfgEdgeType.TRUE);

    const elseStmt = ifStmt.else;

    if (elseStmt !== undefined) {
      const elseNode = this.nodes.get(elseStmt.astId);

      if (elseNode === undefined) {
        throw new Error(
          "Node for else statement is undefined: " + elseStmt.astId
        );
      }

      this.addEdge(node, elseNode, CfgEdgeType.FALSE);
    } else {
      // Usually there should always be a sibling, because of inserted comments
      // However, if an arbitary statement is given as the starting point,
      // sometimes there might not be nothing after. In this case, connect to the
      // end node.
      const afterNode = this.nextNodes.nextExecutedNode(ifStmt);

      // Add edge
      this.addEdge(node, afterNode, CfgEdgeType.FALSE);
    }
  }

  /**
   * Connects a node associated with a statement that is an instance of a "loop" statement.
   * @param node - Node whose type is "LOOP"
   */
  private connectLoopNode(node: cytoscape.NodeSingular) {
    const $loop = (node.data() as LoopData).loop;

    if ($loop === undefined) {
      throw new Error("Loop statement is undefined");
    }

    let afterStmt = undefined;

    switch ($loop.kind) {
      case "for":
        afterStmt = $loop.init;
        break;
      case "while":
        afterStmt = $loop.cond;
        break;
      case "dowhile":
        afterStmt = $loop.body;
        break;
      default:
        throw new Error("Case not defined for loops of kind " + $loop.kind);
    }

    const afterNode = this.nodes.get(afterStmt.astId) ?? this.endNode;

    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * Connects a node associated with a statement that is part of a loop header and corresponds to the loop condition
   * @param node - Node whose type is "COND"
   */
  private connectCondNode(node: cytoscape.NodeSingular) {
    // Get kind of loop
    const $condStmt = (node.data() as HeaderData).nodeStmt;

    if ($condStmt === undefined) {
      throw new Error("Cond statement is undefined");
    }

    const $loop = $condStmt.parent;

    if ($loop === undefined) {
      throw new Error("Loop is undefined");
    }

    if (!($loop instanceof Loop)) {
      throw new Error("$loop is not an instance of Loop");
    }

    // True - first stmt of the loop body
    const trueNode = this.nodes.get($loop.body.astId) ?? this.endNode;
    this.addEdge(node, trueNode, CfgEdgeType.TRUE);

    // False - next stmt of the loop
    const falseNode = this.nextNodes.nextExecutedNode($loop);

    // Create edge
    this.addEdge(node, falseNode, CfgEdgeType.FALSE);
  }

  /**
   * Connects a node associated with a statement that is an instance of a "break" statement.
   * @param node - Node whose type is "BREAK"
   */
  private connectBreakNode(node: cytoscape.NodeSingular) {
    const $breakStmt = (node.data() as CfgNodeData<Break>).nodeStmt;

    if ($breakStmt === undefined) {
      throw new Error("Break statement is undefined");
    }

    const $enclosingStmt = $breakStmt.enclosingStmt;
    const afterNode = this.nextNodes.nextExecutedNode($enclosingStmt);

    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * Connects a node associated with a statement that is an instance of a "continue" statement.
   * @param node - Node whose type is "CONTINUE"
   */
  private connectContinueNode(node: cytoscape.NodeSingular) {
    const $continueStmt = (node.data() as CfgNodeData<Continue>).nodeStmt;

    if ($continueStmt === undefined) {
      throw new Error("Continue statement is undefined");
    }

    const $loop = $continueStmt.getAncestor("loop") as Loop | undefined;

    if ($loop === undefined) {
      throw new Error("Loop is undefined");
    }

    const $afterStmt = $loop.kind === "for" ? $loop.step : $loop.cond;
    const afterNode = this.nodes.get($afterStmt.astId) ?? this.endNode;

    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * Connects a node associated with a statement that is an instance of a "switch" statement.
   * @param node - Node whose type is "SWITCH"
   */
  private connectSwitchNode(node: cytoscape.NodeSingular) {
    const $switchStmt = (node.data() as SwitchData).switch;

    if ($switchStmt === undefined) {
      throw new Error("Switch statement is undefined");
    }

    let firstReachedCase = undefined;

    // The first reached case is the first non-default case.
    // If the switch only has one case statement, and it is the default case, then this default case will be the first reached case
    for (const $case of $switchStmt.cases) {
      firstReachedCase = this.nodes.get($case.astId);

      if (!$case.isDefault) {
        break;
      }
    }

    if (firstReachedCase) {
      this.addEdge(node, firstReachedCase, CfgEdgeType.UNCONDITIONAL);
    }
  }

  /**
   * Connects a node associated with a statement that is an instance of a "case" statement.
   * @param node - Node whose type is "CASE"
   */
  private connectCaseNode(node: cytoscape.NodeSingular) {
    const $caseStmt = (node.data() as CaseData).case;

    if ($caseStmt === undefined) {
      throw new Error("Case statement is undefined");
    }

    const $switchStmt = $caseStmt.getAncestor("switch") as Switch | undefined;

    if ($switchStmt === undefined) {
      throw new Error("Switch statement is undefined");
    }

    const numCases = $switchStmt.cases.length;
    const hasIntermediateDefault =
      $switchStmt.hasDefaultCase && !$switchStmt.cases[numCases - 1].isDefault;

    // Connect the node to the first instruction to be executed
    const firstExecutedInst = this.nextNodes.nextExecutedNode($caseStmt);
    if ($caseStmt.isDefault)
      this.addEdge(node, firstExecutedInst, CfgEdgeType.UNCONDITIONAL);
    else this.addEdge(node, firstExecutedInst, CfgEdgeType.TRUE);

    let falseNode = undefined;
    if ($caseStmt.nextCase !== undefined) {
      // Not the last case

      // If the next case is an intermediate default case, the node should be connected to the CASE node following the default case
      if (hasIntermediateDefault && $caseStmt.nextCase.isDefault)
        falseNode = this.nodes.get($caseStmt.nextCase.nextCase.astId);
      else if (!$caseStmt.isDefault)
        // Else, if it is not an intermediate default case, it should be connected to the next case
        falseNode = this.nodes.get($caseStmt.nextCase.astId);
    } else if (!$caseStmt.isDefault) {
      // Last case but not a default case

      // If switch statement has an intermediate default case, connect the current statement to the default case
      if (hasIntermediateDefault)
        falseNode = this.nodes.get($switchStmt.getDefaultCase.astId);
      // Else, connect it to the statement following the switch
      else falseNode = this.nextNodes.nextExecutedNode($switchStmt);
    }

    if (falseNode !== undefined)
      this.addEdge(node, falseNode, CfgEdgeType.FALSE);
  }

  /**
   * Connects a node associated with a statement that is part of a loop header and corresponds to the loop initialization
   * @param node - Node whose type is "INIT"
   */
  private connectInitNode(node: cytoscape.NodeSingular) {
    const $initStmt = (node.data() as HeaderData).nodeStmt;

    if ($initStmt === undefined) {
      throw new Error("Init statement is undefined");
    }

    const $loop = $initStmt.parent;

    if ($loop === undefined) {
      throw new Error("Loop is undefined");
    }

    if (!($loop instanceof Loop)) {
      throw new Error("$loop is not an instance of Loop");
    }

    if ($loop.kind !== "for") {
      throw new Error("Not implemented for loops of kind " + $loop.kind);
    }

    const $condStmt = $loop.cond;
    if ($condStmt === undefined) {
      throw new Error(
        "Not implemented when for loops do not have a condition statement"
      );
    }

    const afterNode = this.nodes.get($condStmt.astId) ?? this.endNode;
    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * Connects a node associated with a statement that is part of a loop header and corresponds to the loop step
   * @param node - Node whose type is "STEP"
   */
  private connectStepNode(node: cytoscape.NodeSingular) {
    // Get loop
    const $stepStmt = (node.data() as HeaderData).nodeStmt;

    if ($stepStmt === undefined) {
      throw new Error("Step statement is undefined");
    }

    const $loop = $stepStmt.parent;

    if ($loop === undefined) {
      throw new Error("Loop is undefined");
    }

    if (!($loop instanceof Loop)) {
      throw new Error("$loop is not an instance of Loop");
    }

    if ($loop.kind !== "for") {
      throw new Error("Not implemented for loops of kind " + $loop.kind);
    }

    const $condStmt = $loop.cond;
    if ($condStmt === undefined) {
      throw new Error(
        "Not implemented when for loops do not have a condition statement"
      );
    }

    const afterNode = this.nodes.get($condStmt.astId) ?? this.endNode;
    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * @param node - Node whose type is "INST_LIST"
   */
  private connectInstListNode(node: cytoscape.NodeSingular) {
    const $lastStmt = (node.data() as InstListNodeData).getLastStmt();

    if ($lastStmt === undefined) {
      throw new Error("Last statement is undefined");
    }

    const afterNode = this.nextNodes.nextExecutedNode($lastStmt);
    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * @param node - Node whose type is "GOTO"
   */
  private connectGotoNode(node: cytoscape.NodeSingular) {
    const $gotoStmt = (node.data() as GotoData).nodeStmt;

    if ($gotoStmt === undefined) {
      throw new Error("Goto statement is undefined");
    }

    const labelName = $gotoStmt.label.name;
    const $labelStmt = Query.searchFromInclusive(this.jp, LabelStmt, {
      decl: (decl: LaraJoinPoint) => (decl as LabelDecl).name == labelName,
    }).first();

    if ($labelStmt === undefined) {
      throw new Error("Label statement is undefined");
    }

    const afterNode = this.nodes.get($labelStmt.astId);
    if (afterNode === undefined) {
      throw new Error(
        "Node for label statement is undefined: " + $labelStmt.astId
      );
    }

    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * @param node - Node whose type is "LABEL"
   */
  private connectLabelNode(node: cytoscape.NodeSingular) {
    const $labelStmt = (node.data() as LabelData).nodeStmt;

    if ($labelStmt === undefined) {
      throw new Error("Label statement is undefined");
    }

    const afterNode = this.nextNodes.nextExecutedNode($labelStmt);
    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * Connects a node associated with a statement that is an instance of a "return" statement.
   * @param node - Node whose type is "RETURN"
   */
  private connectReturnNode(node: cytoscape.NodeSingular) {
    this.addEdge(node, this.endNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * Connects a node associated with a statement that is an instance of a "scope" statement.
   * @param node - Node whose type is "SCOPE", "THEN" or "ELSE"
   */
  private connectScopeNode(node: cytoscape.NodeSingular) {
    const $scope = (node.data() as ScopeNodeData).scope;

    // Scope connects to its own first statement that will be an INST_LIST
    const afterNode = this.nodes.get($scope.firstStmt.astId);

    if (afterNode === undefined) {
      throw new Error(
        "Node for first statement of scope is undefined: " +
          $scope.firstStmt.astId
      );
    }

    this.addEdge(node, afterNode, CfgEdgeType.UNCONDITIONAL);
  }

  /**
   * Connects the leader statement nodes according to their type
   */
  protected connectNodes() {
    // Connect start
    let startAstNode = this.jp;
    if (startAstNode instanceof FunctionJp) {
      startAstNode = startAstNode.body;
    }

    if (!(startAstNode instanceof Statement)) {
      throw new Error(
        "Not defined how to connect the Start node to an AST node of type " +
          this.jp.joinPointType
      );
    }

    const afterNode = this.nodes.get(startAstNode.astId);

    if (afterNode === undefined) {
      throw new Error(
        "Node for first statement of scope is undefined: " + startAstNode.astId
      );
    }

    // Add edge
    this.addEdge(this.startNode, afterNode, CfgEdgeType.UNCONDITIONAL);

    for (const astId of this.nodes.keys()) {
      const node = this.nodes.get(astId);

      if (node === undefined) {
        throw new Error("Node is undefined for astId " + astId);
      }

      const nodeData = node.data() as CfgNodeData;
      const nodeStmt = nodeData.nodeStmt;

      if (nodeStmt === undefined) {
        throw new Error("Node statement is undefined");
      }

      // Only add connections for astIds of leader statements
      if (nodeStmt.astId !== astId) {
        continue;
      }

      const nodeType = nodeData.type;

      if (nodeType === undefined) {
        throw new Error("Node type is undefined: ");
      }

      switch (nodeType) {
        case CfgNodeType.IF:
          this.connectIfNode(node);
          break;
        case CfgNodeType.LOOP:
          this.connectLoopNode(node);
          break;
        case CfgNodeType.COND:
          this.connectCondNode(node);
          break;
        case CfgNodeType.BREAK:
          this.connectBreakNode(node);
          break;
        case CfgNodeType.CONTINUE:
          this.connectContinueNode(node);
          break;
        case CfgNodeType.SWITCH:
          this.connectSwitchNode(node);
          break;
        case CfgNodeType.CASE:
          this.connectCaseNode(node);
          break;
        case CfgNodeType.INIT:
          this.connectInitNode(node);
          break;
        case CfgNodeType.STEP:
          this.connectStepNode(node);
          break;
        case CfgNodeType.INST_LIST:
          this.connectInstListNode(node);
          break;
        case CfgNodeType.GOTO:
          this.connectGotoNode(node);
          break;
        case CfgNodeType.LABEL:
          this.connectLabelNode(node);
          break;
        case CfgNodeType.RETURN:
          this.connectReturnNode(node);
          break;
        case CfgNodeType.SCOPE:
        case CfgNodeType.THEN:
        case CfgNodeType.ELSE:
          this.connectScopeNode(node);
          break;
      }
    }
  }

  protected cleanCfg() {
    // Remove temporary instructions from the code
    if (!this.keepTemporaryScopeStmts) {
      for (const stmtId in this.temporaryStmts) {
        this.temporaryStmts[stmtId].detach();
      }
    }

    // Remove temporary instructions from the instList nodes and this.nodes
    for (const node of this.nodes.values()) {
      const nodeData = node.data() as InstListNodeData;

      // Only inst lists need to be cleaned
      if (nodeData.type !== CfgNodeType.INST_LIST) {
        const tempStmts = nodeData.stmts.filter(
          ($stmt) => this.temporaryStmts[$stmt.astId] !== undefined
        );
        if (tempStmts.length > 0) {
          console.log(
            "Node '" +
              nodeData.type.toString() +
              "' has temporary stmts: " +
              tempStmts.toString()
          );
        }
        continue;
      }

      // Filter stmts that are temporary statements
      if (this.keepTemporaryScopeStmts) {
        continue;
      }

      const filteredStmts = [];
      for (const $stmt of nodeData.stmts) {
        // If not a temporary stmt, add to filtered list
        if (this.temporaryStmts[$stmt.astId] === undefined) {
          filteredStmts.push($stmt);
        }
        // Otherwise, remove from this.nodes
        else {
          this.nodes.delete($stmt.astId);
        }
      }

      if (filteredStmts.length !== nodeData.stmts.length) {
        nodeData.stmts = filteredStmts;
      }
    }

    // Remove empty instList CFG nodes
    for (const node of this.graph.nodes()) {
      const nodeData = node.data() as CfgNodeData;

      // Only nodes that are inst lists
      if (nodeData.type !== CfgNodeType.INST_LIST) {
        continue;
      }

      // Only empty nodes
      if (nodeData.stmts.length > 0) {
        continue;
      }

      // Remove node, replacing the connections with a new connection of the same type and the incoming edge
      // of the node being removed
      Graphs.removeNode(
        this.graph,
        node,
        (incoming) => new CfgEdge((incoming.data() as CfgEdge).type)
      );
    }

    // Remove label nodes
    if (this.removeLabelNodes) {
      for (const node of this.graph.nodes()) {
        const nodeData = node.data() as CfgNodeData;

        // Only nodes whose type is "LABEL"
        if (nodeData.type !== CfgNodeType.LABEL) continue;

        Graphs.removeNode(
          this.graph,
          node,
          (incoming) => new CfgEdge((incoming.data() as CfgEdge).type)
        );

        if (nodeData.nodeStmt === undefined) {
          throw new Error("Node statement is undefined");
        }
        this.nodes.delete(nodeData.nodeStmt.astId);
      }
    }

    // Remove goto nodes
    if (this.removeGotoNodes) {
      for (const node of this.graph.nodes()) {
        const nodeData = node.data() as CfgNodeData;

        // Only nodes whose type is "GOTO"
        if (nodeData.type !== CfgNodeType.GOTO) continue;

        Graphs.removeNode(
          this.graph,
          node,
          (incoming) => new CfgEdge((incoming.data() as CfgEdge).type)
        );

        if (nodeData.nodeStmt === undefined) {
          throw new Error("Node statement is undefined");
        }
        this.nodes.delete(nodeData.nodeStmt.astId);
      }
    }

    // Remove nodes that have no incoming edge and are not start
    for (const node of this.graph.nodes()) {
      const nodeData = node.data() as CfgNodeData;

      // Only nodes that are not start
      if (nodeData.type === CfgNodeType.START) {
        continue;
      }

      // Ignore nodes with incoming edges
      if (node.incomers().length > 0) {
        continue;
      }

      // Remove node
      debug(
        "[CfgBuilder] Removing statement that is not executed (e.g. is after a return): " +
          nodeData.stmts.toString()
      );

      // Removes nodes. As there are no incoming edges, the edge handler is a dummy as it is not called
      Graphs.removeNode(
        this.graph,
        node,
        () => new CfgEdge(CfgEdgeType.UNCONDITIONAL)
      );
    }
  }

  /**
   * Returns the node corresponding to this statement, or creates a new one if one does not exist yet.
   */
  protected getOrAddNode(
    $stmt: Statement,
    create: boolean = false,
    forceNodeType?: CfgNodeType
  ) {
    let node = this.nodes.get($stmt.astId);

    // If there is not yet a node for this statement, create
    if (node === undefined && create) {
      const nodeType = forceNodeType ?? CfgUtils.getNodeType($stmt);

      if (nodeType === undefined) {
        throw new Error(
          "Node type is undefined for statement at line " + $stmt.line
        );
      }

      const nodeId = this.deterministicIds ? this.nextId() : undefined;

      node = Graphs.addNode(
        this.graph,
        this.dataFactory.newData(nodeType, $stmt, nodeId, this.splitInstList)
      );

      // Associate all statements of graph node
      for (const $nodeStmt of (node.data() as CfgNodeData).stmts) {
        // Check if it has not been already added
        if (this.nodes.get($nodeStmt.astId) !== undefined) {
          throw new Error(
            "Adding mapping twice for statement " +
              $nodeStmt.astId +
              "@" +
              $nodeStmt.location
          );
        }

        this.nodes.set($nodeStmt.astId, node);
      }
    } else {
      throw new Error("No node for statement at line " + $stmt.line);
    }

    return node;
  }
}