Combinational Dependency Annotation (#809)

2 files changed, 47 insertions, 4 deletions

diff --git a/src/main/scala/firrtl/transforms/CheckCombLoops.scala b/src/main/scala/firrtl/transforms/CheckCombLoops.scala
index e1e6cf63..98033a2f 100644
--- a/src/main/scala/firrtl/transforms/CheckCombLoops.scala
+++ b/src/main/scala/firrtl/transforms/CheckCombLoops.scala
@@ -24,6 +24,14 @@ object CheckCombLoops {
 
 case object DontCheckCombLoopsAnnotation extends NoTargetAnnotation
 
+case class CombinationalPath(sink: ComponentName, sources: Seq[ComponentName]) extends Annotation {
+  override def update(renames: RenameMap): Seq[Annotation] = {
+    val newSources = sources.flatMap { s => renames.get(s).getOrElse(Seq(s)) }
+    val newSinks = renames.get(sink).getOrElse(Seq(sink))
+    newSinks.map(snk => CombinationalPath(snk, newSources))
+  }
+}
+
 /** Finds and detects combinational logic loops in a circuit, if any
   * exist. Returns the input circuit with no modifications.
   * 
@@ -181,7 +189,7 @@ class CheckCombLoops extends Transform {
    * and only if it combinationally depends on input Y. Associate this
    * reduced graph with the module for future use.
    */
-  private def run(c: Circuit): Circuit = {
+  private def run(c: Circuit): (Circuit, Seq[Annotation]) = {
     val errors = new Errors()
     /* TODO(magyar): deal with exmodules! No pass warnings currently
      *  exist. Maybe warn when iterating through modules.
@@ -211,8 +219,14 @@ class CheckCombLoops extends Transform {
         errors.append(new CombLoopException(m.info, m.name, expandedCycle))
       }
     }
+    val mn = ModuleName(c.main, CircuitName(c.main))
+    val annos = simplifiedModuleGraphs(c.main).getEdgeMap.collect { case (from, tos) if tos.nonEmpty =>
+      val sink = ComponentName(from.name, mn)
+      val sources = tos.map(x => ComponentName(x.name, mn))
+      CombinationalPath(sink, sources.toSeq)
+    }
     errors.trigger()
-    c
+    (c, annos.toSeq)
   }
 
   def execute(state: CircuitState): CircuitState = {
@@ -221,8 +235,8 @@ class CheckCombLoops extends Transform {
       logger.warn("Skipping Combinational Loop Detection")
       state
     } else {
-      val result = run(state.circuit)
-      CircuitState(result, outputForm, state.annotations, state.renames)
+      val (result, annos) = run(state.circuit)
+      CircuitState(result, outputForm, state.annotations ++ annos, state.renames)
     }
   }
 }
diff --git a/src/test/scala/firrtlTests/CheckCombLoopsSpec.scala b/src/test/scala/firrtlTests/CheckCombLoopsSpec.scala
index d09b4d06..ed498180 100644
--- a/src/test/scala/firrtlTests/CheckCombLoopsSpec.scala
+++ b/src/test/scala/firrtlTests/CheckCombLoopsSpec.scala
@@ -189,6 +189,35 @@ class CheckCombLoopsSpec extends SimpleTransformSpec {
       compile(CircuitState(parse(input), ChirrtlForm), writer)
     }
   }
+
+  "Circuit" should "create an annotation" in {
+    val input = """circuit hasnoloops :
+                  |  module thru :
+                  |    input in1 : UInt<1>
+                  |    input in2 : UInt<1>
+                  |    output out1 : UInt<1>
+                  |    output out2 : UInt<1>
+                  |    out1 <= in1
+                  |    out2 <= in2
+                  |  module hasnoloops :
+                  |    input clk : Clock
+                  |    input a : UInt<1>
+                  |    output b : UInt<1>
+                  |    wire x : UInt<1>
+                  |    inst inner of thru
+                  |    inner.in1 <= a
+                  |    x <= inner.out1
+                  |    inner.in2 <= x
+                  |    b <= inner.out2
+                  |""".stripMargin
+
+    val writer = new java.io.StringWriter
+    val cs = compile(CircuitState(parse(input), ChirrtlForm), writer)
+    val mn = ModuleName("hasnoloops", CircuitName("hasnoloops"))
+    cs.annotations.collect {
+      case c @ CombinationalPath(ComponentName("b", `mn`), Seq(ComponentName("a", `mn`))) => c
+    }.nonEmpty should be (true)
+  }
 }
 
 class CheckCombLoopsCommandLineSpec extends FirrtlFlatSpec {