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

6 files changed, 69 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
diff --git a/src/test/resources/features/HasDeadCode.fir b/src/test/resources/features/HasDeadCode.fir
new file mode 100644
index 00000000..db87ff7a
--- /dev/null
+++ b/src/test/resources/features/HasDeadCode.fir
@@ -0,0 +1,7 @@
+circuit HasDeadCode :
+  module HasDeadCode :
+    input i : UInt<1>
+    output o : UInt<1>
+    wire a : UInt<1>
+    a <= not(i)
+    o <= i
diff --git a/src/test/scala/firrtlTests/DCETests.scala b/src/test/scala/firrtlTests/DCETests.scala
index 129460e1..41edfa8b 100644
--- a/src/test/scala/firrtlTests/DCETests.scala
+++ b/src/test/scala/firrtlTests/DCETests.scala
@@ -9,6 +9,9 @@ import firrtl.transforms._
 import firrtl.annotations._
 import firrtl.passes.memlib.SimpleTransform
 
+import java.io.File
+import java.nio.file.Paths
+
 class DCETests extends FirrtlFlatSpec {
   // Not using executeTest because it is for positive testing, we need to check that stuff got
   // deleted
@@ -387,3 +390,27 @@ class DCETests extends FirrtlFlatSpec {
     exec(input, check)
   }
 }
+
+class DCECommandLineSpec extends FirrtlFlatSpec {
+
+  val testDir = createTestDirectory("dce")
+  val inputFile = Paths.get(getClass.getResource("/features/HasDeadCode.fir").toURI()).toFile()
+  val outFile = new File(testDir, "HasDeadCode.v")
+  val args = Array("-i", inputFile.getAbsolutePath, "-o", outFile.getAbsolutePath, "-X", "verilog")
+
+  "Dead Code Elimination" should "run by default" in {
+    firrtl.Driver.execute(args) match {
+      case FirrtlExecutionSuccess(_, verilog) =>
+        verilog should not include regex ("wire +a;")
+      case _ => fail("Unexpected compilation failure")
+    }
+  }
+
+  it should "not run when given --no-dce option" in {
+    firrtl.Driver.execute(args :+ "--no-dce") match {
+      case FirrtlExecutionSuccess(_, verilog) =>
+        verilog should include regex ("wire +a;")
+      case _ => fail("Unexpected compilation failure")
+    }
+  }
+}