Merge pull request #19886 from hvitved/rust/dataflow-caching

Rust: Cache `DataFlow::Node.{toString,getLocation}`

Author: hvitved

rust/ql/lib/codeql/rust/dataflow/internal/Node.qll

@@ -17,13 +17,19 @@ private import codeql.rust.dataflow.FlowSummary
 private import Node as Node
 private import DataFlowImpl
 private import FlowSummaryImpl as FlowSummaryImpl
+private import codeql.rust.internal.CachedStages
 
 /** An element, viewed as a node in a data flow graph. */
-abstract class NodePublic extends TNode {
+// It is important to not make this class `abstract`, as it otherwise results in
+// a needless charpred, which will result in recomputation of internal non-cached
+// predicates
+class NodePublic extends TNode {
   /** Gets the location of this node. */
+  cached
   abstract Location getLocation();
 
   /** Gets a textual representation of this node. */
+  cached
   abstract string toString();
 
   /**
@@ -55,17 +61,6 @@ abstract class Node extends NodePublic {
   CfgNode getCfgNode() { none() }
 }
 
-/** A node type that is not implemented. */
-final class NaNode extends Node {
-  NaNode() { none() }
-
-  override CfgScope getCfgScope() { none() }
-
-  override string toString() { result = "N/A" }
-
-  override Location getLocation() { none() }
-}
-
 /** A data flow node used to model flow summaries. */
 class FlowSummaryNode extends Node, TFlowSummaryNode {
   FlowSummaryImpl::Private::SummaryNode getSummaryNode() { this = TFlowSummaryNode(result) }
@@ -108,6 +103,7 @@ class FlowSummaryNode extends Node, TFlowSummaryNode {
   }
 
   override Location getLocation() {
+    Stages::DataFlowStage::ref() and
     exists(this.getSummarizedCallable()) and
     result instanceof EmptyLocation
     or
@@ -116,7 +112,10 @@ class FlowSummaryNode extends Node, TFlowSummaryNode {
     result = this.getSinkElement().getLocation()
   }
 
-  override string toString() { result = this.getSummaryNode().toString() }
+  override string toString() {
+    Stages::DataFlowStage::ref() and
+    result = this.getSummaryNode().toString()
+  }
 }
 
 /** A data flow node that corresponds directly to a CFG node for an AST node. */
@@ -440,9 +439,9 @@ private class CapturePostUpdateNode extends PostUpdateNode, CaptureNode {
   final override string toString() { result = PostUpdateNode.super.toString() }
 }
 
-final class CastNode = NaNode;
-
-private import codeql.rust.internal.CachedStages
+final class CastNode extends ExprNode {
+  CastNode() { none() }
+}
 
 cached
 newtype TNode =

rust/ql/lib/codeql/rust/internal/CachedStages.qll

@@ -186,7 +186,9 @@ module Stages {
     predicate backref() {
       1 = 1
       or
-      exists(Node n)
+      exists(any(Node n).toString())
+      or
+      exists(any(Node n).getLocation())
       or
       RustTaintTracking::defaultAdditionalTaintStep(_, _, _)
       or