1 files changed, 48 insertions, 0 deletions
diff --git a/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala b/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
new file mode 100644
index 00000000..23723a60
--- /dev/null
+++ b/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
@@ -0,0 +1,48 @@
+
+package firrtl
+package transforms
+
+import firrtl.annotations._
+import firrtl.passes.PassException
+
+/** A component that should be preserved
+  *
+  * DCE treats the component as a top-level sink of the circuit
+  */
+object DontTouchAnnotation {
+  private val marker = "DONTtouch!"
+  def apply(target: ComponentName): Annotation = Annotation(target, classOf[Transform], marker)
+
+  def unapply(a: Annotation): Option[ComponentName] = a match {
+    case Annotation(component: ComponentName, _, value) if value == marker => Some(component)
+    case _ => None
+  }
+
+  class DontTouchNotFoundException(module: String, component: String) extends PassException(
+    s"Component marked DONT Touch ($module.$component) not found!\n" +
+    "Perhaps it is an aggregate type? Currently only leaf components are supported.\n" +
+    "Otherwise it was probably accidentally deleted. Please check that your custom passes are not" +
+    "responsible and then file an issue on Github."
+  )
+
+  def errorNotFound(module: String, component: String) =
+    throw new DontTouchNotFoundException(module, component)
+}
+
+/** An [[firrtl.ir.ExtModule]] that can be optimized
+  *
+  * Firrtl does not know the semantics of an external module. This annotation provides some
+  * "greybox" information that the external module does not have any side effects. In particular,
+  * this means that the external module can be Dead Code Eliminated.
+  *
+  * @note Unlike [[DontTouchAnnotation]], we don't care if the annotation is deleted
+  */
+object OptimizableExtModuleAnnotation {
+  private val marker = "optimizableExtModule!"
+  def apply(target: ModuleName): Annotation = Annotation(target, classOf[Transform], marker)
+
+  def unapply(a: Annotation): Option[ModuleName] = a match {
+    case Annotation(component: ModuleName, _, value) if value == marker => Some(component)
+    case _ => None
+  }
+}