Add NoConstantPropagationAnnotation to disable constatnt propagation (#2150)

* add --no-constant-propagation to disable constant propagation

* add test

* deprecate DisableFold.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

5 files changed, 32 insertions, 3 deletions

diff --git a/src/main/resources/META-INF/services/firrtl.options.RegisteredTransform b/src/main/resources/META-INF/services/firrtl.options.RegisteredTransform
index bb72d45c..9304c39a 100644
--- a/src/main/resources/META-INF/services/firrtl.options.RegisteredTransform
+++ b/src/main/resources/META-INF/services/firrtl.options.RegisteredTransform
@@ -3,3 +3,4 @@ firrtl.transforms.CheckCombLoops
 firrtl.passes.InlineInstances
 firrtl.passes.clocklist.ClockListTransform
 firrtl.transforms.formal.AssertSubmoduleAssumptions
+firrtl.transforms.ConstantPropagation
diff --git a/src/main/scala/firrtl/stage/FirrtlAnnotations.scala b/src/main/scala/firrtl/stage/FirrtlAnnotations.scala
index 26655efd..44c88418 100644
--- a/src/main/scala/firrtl/stage/FirrtlAnnotations.scala
+++ b/src/main/scala/firrtl/stage/FirrtlAnnotations.scala
@@ -291,6 +291,7 @@ case object PrettyNoExprInlining extends NoTargetAnnotation with FirrtlOption wi
   */
 case class DisableFold(op: ir.PrimOp) extends NoTargetAnnotation with FirrtlOption
 
+@deprecated("will be removed and merged into ConstantPropagation in 1.5", "1.4")
 object DisableFold extends HasShellOptions {
 
   private val mapping: Map[String, ir.PrimOp] = PrimOps.builtinPrimOps.map { case op => op.toString -> op }.toMap
diff --git a/src/main/scala/firrtl/transforms/ConstantPropagation.scala b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
index 7106c699..5610c7e7 100644
--- a/src/main/scala/firrtl/transforms/ConstantPropagation.scala
+++ b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
@@ -13,7 +13,7 @@ import firrtl.PrimOps._
 import firrtl.graph.DiGraph
 import firrtl.analyses.InstanceKeyGraph
 import firrtl.annotations.TargetToken.Ref
-import firrtl.options.Dependency
+import firrtl.options.{Dependency, RegisteredTransform, ShellOption}
 import firrtl.stage.DisableFold
 
 import annotation.tailrec
@@ -101,7 +101,7 @@ object ConstantPropagation {
 
 }
 
-class ConstantPropagation extends Transform with DependencyAPIMigration {
+class ConstantPropagation extends Transform with RegisteredTransform with DependencyAPIMigration {
   import ConstantPropagation._
 
   override def prerequisites =
@@ -124,6 +124,14 @@ class ConstantPropagation extends Transform with DependencyAPIMigration {
     case _                      => false
   }
 
+  val options = Seq(
+    new ShellOption[Unit](
+      longOption = "no-constant-propagation",
+      toAnnotationSeq = _ => Seq(NoConstantPropagationAnnotation),
+      helpText = "Disable constant propagation elimination"
+    )
+  )
+
   sealed trait SimplifyBinaryOp {
     def matchingArgsValue(e: DoPrim, arg: Expression): Expression
     def apply(e: DoPrim): Expression = {
@@ -869,6 +877,11 @@ class ConstantPropagation extends Transform with DependencyAPIMigration {
 
     val disabledOps = state.annotations.collect { case DisableFold(op) => op }.toSet
 
-    state.copy(circuit = run(state.circuit, dontTouchMap, disabledOps))
+    if (state.annotations.contains(NoConstantPropagationAnnotation)) {
+      logger.info("Skipping Constant Propagation")
+      state
+    } else {
+      state.copy(circuit = run(state.circuit, dontTouchMap, disabledOps))
+    }
   }
 }
diff --git a/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala b/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
index 10163b72..e817571a 100644
--- a/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
+++ b/src/main/scala/firrtl/transforms/OptimizationAnnotations.scala
@@ -9,6 +9,9 @@ import firrtl.passes.PassException
 /** Indicate that DCE should not be run */
 case object NoDCEAnnotation extends NoTargetAnnotation
 
+/** Indicate that ConstantPropagation should not be run */
+case object NoConstantPropagationAnnotation extends NoTargetAnnotation
+
 /** Lets an annotation mark its ReferenceTarget members as DontTouch
   *
   * This permits a transform to run and remove its associated annotations,
diff --git a/src/test/scala/firrtlTests/ConstantPropagationTests.scala b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
index 60cf1b8b..bc7f92e6 100644
--- a/src/test/scala/firrtlTests/ConstantPropagationTests.scala
+++ b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
@@ -908,6 +908,17 @@ class ConstantPropagationIntegrationSpec extends LowTransformSpec {
     execute(input, check, Seq(dontTouch("Child.in1")))
   }
 
+  it should "NOT optimize if no-constant-propagation is enabled" in {
+    val input =
+      """circuit Foo:
+        |  module Foo:
+        |    input a: UInt<1>
+        |    output b: UInt<1>
+        |    b <= and(UInt<1>(0), a)""".stripMargin
+    val check = parse(input).serialize
+    execute(input, check, Seq(NoConstantPropagationAnnotation))
+  }
+
   it should "still propagate constants even when there is name swapping" in {
     val input =
       """circuit Top :