Using IdentityHashSet in EOG pass to remove superfluous EOG nodes (#…

…1275)

* EOG pass speedup

There was an issue that massivly slowed down the EOG pass for programs that a LOT (>500.000) EOG nodes. Now we are using an identity hash set instead of a regular hash set to store the set of unique EOG nodes.

* Add some comments

* revert js change

---------

Co-authored-by: Alexander Kuechler <[email protected]>

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/passes/EvaluationOrderGraphPass.kt

@@ -37,6 +37,7 @@ import de.fraunhofer.aisec.cpg.graph.scopes.*
 import de.fraunhofer.aisec.cpg.graph.statements.*
 import de.fraunhofer.aisec.cpg.graph.statements.expressions.*
 import de.fraunhofer.aisec.cpg.graph.types.Type
+import de.fraunhofer.aisec.cpg.helpers.IdentitySet
 import de.fraunhofer.aisec.cpg.helpers.SubgraphWalker
 import de.fraunhofer.aisec.cpg.helpers.Util
 import de.fraunhofer.aisec.cpg.passes.order.DependsOn
@@ -177,28 +178,34 @@ open class EvaluationOrderGraphPass(ctx: TranslationContext) : TranslationUnitPa
 
     /**
      * Removes EOG edges by first building the negative set of nodes that cannot be visited and then
-     * remove there outgoing edges.In contrast to truncateLooseEdges this also removes cycles.
+     * remove there outgoing edges. This also removes cycles.
      */
     protected fun removeUnreachableEOGEdges(tu: TranslationUnitDeclaration) {
-        val eognodes =
-            SubgraphWalker.flattenAST(tu)
-                .filter { it.prevEOG.isNotEmpty() || it.nextEOG.isNotEmpty() }
-                .toMutableList()
+        // All nodes which have an eog edge
+        val eogNodes = IdentitySet<Node>()
+        eogNodes.addAll(
+            SubgraphWalker.flattenAST(tu).filter {
+                it.prevEOG.isNotEmpty() || it.nextEOG.isNotEmpty()
+            }
+        )
+        // only eog entry points
         var validStarts =
-            eognodes
+            eogNodes
                 .filter { node ->
                     node is FunctionDeclaration ||
                         node is RecordDeclaration ||
                         node is NamespaceDeclaration ||
                         node is TranslationUnitDeclaration
                 }
                 .toSet()
+        // Remove all nodes from eogNodes which are reachable from validStarts and transitively.
         while (validStarts.isNotEmpty()) {
-            eognodes.removeAll(validStarts)
-            validStarts = validStarts.flatMap { it.nextEOG }.filter { it in eognodes }.toSet()
+            eogNodes.removeAll(validStarts)
+            validStarts = validStarts.flatMap { it.nextEOG }.filter { it in eogNodes }.toSet()
         }
-        // remaining eognodes were not visited and have to be removed from the EOG
-        for (unvisitedNode in eognodes) {
+        // The remaining nodes are unreachable from the entry points. We delete their outgoing EOG
+        // edges.
+        for (unvisitedNode in eogNodes) {
             unvisitedNode.nextEOGEdges.forEach { next ->
                 next.end.removePrevEOGEntry(unvisitedNode)
             }