2 files changed, 12 insertions, 7 deletions
diff --git a/src/main/scala/firrtl/transforms/ConstantPropagation.scala b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
index ca48cbb5..b767ef65 100644
--- a/src/main/scala/firrtl/transforms/ConstantPropagation.scala
+++ b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
@@ -407,8 +407,13 @@ class ConstantPropagation extends Transform {
       mod.module -> children.map(i => i.name -> i.module).toMap
     })
 
-    // Module name to number of instances
-    val instCount: Map[String, Int] = iGraph.getVertices.groupBy(_.module).mapValues(_.size)
+    // This is a *relative* instance count, ie. how many there are when you visit each Module once
+    // (even if it is instantiated multiple times)
+    val instCount: Map[String, Int] = iGraph.getEdgeMap.foldLeft(Map(c.main -> 1)) {
+      case (cs, (_, values)) => values.foldLeft(cs) {
+        case (counts, value) => counts.updated(value.module, counts.getOrElse(value.module, 0) + 1)
+      }
+    }
 
     // DiGraph using Module names as nodes, destination of edge is a parent Module
     val parentGraph: DiGraph[String] = iGraph.reverse.transformNodes(_.module)
diff --git a/src/test/scala/firrtlTests/ConstantPropagationTests.scala b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
index 06e24b97..2aad4f21 100644
--- a/src/test/scala/firrtlTests/ConstantPropagationTests.scala
+++ b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
@@ -67,9 +67,9 @@ s"""circuit Top :
     out <= in
   module Child :
     output out : UInt<1>
-    inst b of Bottom
-    b.in <= UInt(1)
-    out <= b.out
+    inst b0 of Bottom
+    b0.in <= UInt(1)
+    out <= b0.out
   module Top :
     input x : UInt<1>
     output z : UInt<1>
@@ -91,8 +91,8 @@ s"""circuit Top :
     out <= UInt(1)
   module Child :
     output out : UInt<1>
-    inst b of Bottom
-    b.in <= UInt(1)
+    inst b0 of Bottom
+    b0.in <= UInt(1)
     out <= UInt(1)
   module Top :
     input x : UInt<1>