Add --no-dce command-line option to skip DCE

2 files changed, 23 insertions, 4 deletions

diff --git a/src/main/scala/firrtl/transforms/DeadCodeElimination.scala b/src/main/scala/firrtl/transforms/DeadCodeElimination.scala
index 91a5dd5a..aa147733 100644
--- a/src/main/scala/firrtl/transforms/DeadCodeElimination.scala
+++ b/src/main/scala/firrtl/transforms/DeadCodeElimination.scala
@@ -286,7 +286,7 @@ class DeadCodeElimination extends Transform {
   }
 
   def execute(state: CircuitState): CircuitState = {
-    val (dontTouches: Seq[LogicNode], doTouchExtMods: Seq[String]) =
+    val (dontTouches: Seq[LogicNode], doTouchExtMods: Seq[String], noDCE: Option[Boolean]) =
       state.annotations match {
         case Some(aMap) =>
           // TODO Do with single walk over annotations
@@ -296,9 +296,17 @@ class DeadCodeElimination extends Transform {
           val optExtMods = aMap.annotations.collect {
             case OptimizableExtModuleAnnotation(ModuleName(name, _)) => name
           }
-          (dontTouches, optExtMods)
-        case None => (Seq.empty, Seq.empty)
+          val noDCE = aMap.annotations.collectFirst {
+            case NoDCEAnnotation() => true
+          }
+          (dontTouches, optExtMods, noDCE)
+        case None => (Seq.empty, Seq.empty, None)
       }
-    run(state, dontTouches, doTouchExtMods.toSet)
+    if (noDCE.getOrElse(false)) {
+      logger.info("Skipping DCE")
+      state
+    } else {
+      run(state, dontTouches, doTouchExtMods.toSet)
+    }
   }
 }
diff --git a/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala b/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
index 23723a60..2336710a 100644
--- a/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
+++ b/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
@@ -5,6 +5,17 @@ package transforms
 import firrtl.annotations._
 import firrtl.passes.PassException
 
+/** Indicate that DCE should not be run */
+object NoDCEAnnotation {
+  val marker = "noDCE!"
+  val transform = classOf[DeadCodeElimination]
+  def apply(): Annotation = Annotation(CircuitTopName, transform, marker)
+  def unapply(a: Annotation): Boolean = a match {
+    case Annotation(_, targetXform, value) if targetXform == transform && value == marker => true
+    case _ => false
+  }
+}
+
 /** A component that should be preserved
   *
   * DCE treats the component as a top-level sink of the circuit