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

4 files changed, 35 insertions, 7 deletions

diff --git a/src/main/scala/firrtl/Driver.scala b/src/main/scala/firrtl/Driver.scala
index 6c4c450b..264ba44c 100644
--- a/src/main/scala/firrtl/Driver.scala
+++ b/src/main/scala/firrtl/Driver.scala
@@ -12,7 +12,7 @@ import logger.Logger
 import Parser.{IgnoreInfo, InfoMode}
 import annotations._
 import firrtl.annotations.AnnotationYamlProtocol._
-import firrtl.transforms.{BlackBoxSourceHelper, BlackBoxTargetDir, DontCheckCombLoopsAnnotation}
+import firrtl.transforms._
 import Utils.throwInternalError
 
 
@@ -167,7 +167,8 @@ object Driver {
 
     // Should these and outputAnnos be moved to loadAnnotations?
     val globalAnnos = Seq(TargetDirAnnotation(optionsManager.targetDirName)) ++
-      (if (firrtlConfig.dontCheckCombLoops) Seq(DontCheckCombLoopsAnnotation()) else Seq())
+      (if (firrtlConfig.dontCheckCombLoops) Seq(DontCheckCombLoopsAnnotation()) else Seq()) ++
+      (if (firrtlConfig.noDCE) Seq(NoDCEAnnotation()) else Seq())
 
     val finalState = firrtlConfig.compiler.compile(
       CircuitState(parsedInput,
diff --git a/src/main/scala/firrtl/ExecutionOptionsManager.scala b/src/main/scala/firrtl/ExecutionOptionsManager.scala
index ebe27a7d..8aa23f70 100644
--- a/src/main/scala/firrtl/ExecutionOptionsManager.scala
+++ b/src/main/scala/firrtl/ExecutionOptionsManager.scala
@@ -157,7 +157,8 @@ case class FirrtlExecutionOptions(
     annotationFileNameOverride: String = "",
     forceAppendAnnoFile:    Boolean = false,
     emitOneFilePerModule:   Boolean = false,
-    dontCheckCombLoops:     Boolean = false)
+    dontCheckCombLoops:     Boolean = false,
+    noDCE:                  Boolean = false)
   extends ComposableOptions {
 
   require(!(emitOneFilePerModule && outputFileNameOverride.nonEmpty),
@@ -420,6 +421,13 @@ trait HasFirrtlOptions {
       "Do NOT check for combinational loops (not recommended)"
     }
 
+  parser.opt[Unit]("no-dce")
+    .foreach { _ =>
+      firrtlOptions = firrtlOptions.copy(noDCE = true)
+    }.text {
+      "Do NOT run dead code elimination"
+    }
+
   parser.note("")
 }
 
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