2 files changed, 28 insertions, 0 deletions
diff --git a/src/main/scala/firrtl/analyses/InstanceGraph.scala b/src/main/scala/firrtl/analyses/InstanceGraph.scala
index b8b40065..7b60b110 100644
--- a/src/main/scala/firrtl/analyses/InstanceGraph.scala
+++ b/src/main/scala/firrtl/analyses/InstanceGraph.scala
@@ -140,6 +140,16 @@ class InstanceGraph(c: Circuit) {
   def getChildrenInstanceMap: collection.Map[OfModule, collection.Map[Instance, OfModule]] =
     childInstances.map(kv => kv._1.OfModule -> asOrderedMap(kv._2, (i: WDefInstance) => i.toTokens))
 
+  /** The set of all modules in the circuit */
+  lazy val modules: collection.Set[OfModule] = graph.getVertices.map(_.OfModule)
+
+  /** The set of all modules in the circuit reachable from the top module */
+  lazy val reachableModules: collection.Set[OfModule] =
+    mutable.LinkedHashSet(trueTopInstance.OfModule) ++ graph.reachableFrom(trueTopInstance).map(_.OfModule)
+
+  /** The set of all modules *not* reachable in the circuit */
+  lazy val unreachableModules: collection.Set[OfModule] = modules diff reachableModules
+
 }
 
 object InstanceGraph {
diff --git a/src/test/scala/firrtlTests/analyses/InstanceGraphTests.scala b/src/test/scala/firrtlTests/analyses/InstanceGraphTests.scala
index ee6ecd5f..8f748732 100644
--- a/src/test/scala/firrtlTests/analyses/InstanceGraphTests.scala
+++ b/src/test/scala/firrtlTests/analyses/InstanceGraphTests.scala
@@ -244,4 +244,22 @@ circuit Top :
                              OfModule("Bar") -> 0)
     iGraph.staticInstanceCount should be (expectedCounts)
   }
+
+  behavior of "Reachable/Unreachable helper methods"
+
+  they should "report correct reachable/unreachable counts" in {
+    val input =
+      """|circuit Top:
+         |  module Unreachable:
+         |    skip
+         |  module Reachable:
+         |    skip
+         |  module Top:
+         |    inst reachable of Reachable
+         |""".stripMargin
+    val iGraph = new InstanceGraph(ToWorkingIR.run(parse(input)))
+    iGraph.modules should contain theSameElementsAs Seq(OfModule("Top"), OfModule("Reachable"), OfModule("Unreachable"))
+    iGraph.reachableModules should contain theSameElementsAs Seq(OfModule("Top"), OfModule("Reachable"))
+    iGraph.unreachableModules should contain theSameElementsAs Seq(OfModule("Unreachable"))
+  }
 }