1 files changed, 35 insertions, 0 deletions
diff --git a/src/test/scala/firrtlTests/DCETests.scala b/src/test/scala/firrtlTests/DCETests.scala
index b8345093..a6def402 100644
--- a/src/test/scala/firrtlTests/DCETests.scala
+++ b/src/test/scala/firrtlTests/DCETests.scala
@@ -8,6 +8,7 @@ import firrtl.passes._
 import firrtl.transforms._
 import firrtl.annotations._
 import firrtl.passes.memlib.SimpleTransform
+import FirrtlCheckers._
 
 import java.io.File
 import java.nio.file.Paths
@@ -320,6 +321,40 @@ class DCETests extends FirrtlFlatSpec {
         """.stripMargin
     exec(input, input)
   }
+  "extmodules with no ports" should "NOT be deleted by default" in {
+    val input =
+      """circuit Top :
+        |  extmodule BlackBox :
+        |    defname = BlackBox
+        |  module Top :
+        |    input x : UInt<1>
+        |    output y : UInt<1>
+        |    inst blackBox of BlackBox
+        |    y <= x
+        |""".stripMargin
+    exec(input, input)
+  }
+  "extmodules with no ports marked optimizable" should "be deleted" in {
+    val input =
+      """circuit Top :
+        |  extmodule BlackBox :
+        |    defname = BlackBox
+        |  module Top :
+        |    input x : UInt<1>
+        |    output y : UInt<1>
+        |    inst blackBox of BlackBox
+        |    y <= x
+        |""".stripMargin
+    val check =
+      """circuit Top :
+        |  module Top :
+        |    input x : UInt<1>
+        |    output y : UInt<1>
+        |    y <= x
+        |""".stripMargin
+    val doTouchAnno = OptimizableExtModuleAnnotation(ModuleName("BlackBox", CircuitName("Top")))
+    exec(input, check, Seq(doTouchAnno))
+  }
   // bar.z is not used and thus is dead code, but foo.z is used so this code isn't eliminated
   "Module deduplication" should "should be preserved despite unused output of ONE instance" in {
     val input =