Move splitRef and mergeRef from LowerTypes to Utils

Make EmptyExpression part of WIR

1 files changed, 35 insertions, 0 deletions

diff --git a/src/main/scala/firrtl/Utils.scala b/src/main/scala/firrtl/Utils.scala
index 30dff01c..f54d8cd6 100644
--- a/src/main/scala/firrtl/Utils.scala
+++ b/src/main/scala/firrtl/Utils.scala
@@ -580,6 +580,41 @@ object Utils extends LazyLogging {
        case _ => NoInfo
     }}
 
+  /** Splits an Expression into root Ref and tail
+    *
+    * @example
+    *   Given:   SubField(SubIndex(SubField(Ref("a", UIntType(IntWidth(32))), "b"), 2), "c")
+    *   Returns: (Ref("a"), SubField(SubIndex(Ref("b"), 2), "c"))
+    *   a.b[2].c -> (a, b[2].c)
+    * @example
+    *   Given:   SubField(SubIndex(Ref("b"), 2), "c")
+    *   Returns: (Ref("b"), SubField(SubIndex(EmptyExpression, 2), "c"))
+    *   b[2].c -> (b, EMPTY[2].c)
+    * @note This function only supports WRef, WSubField, and WSubIndex
+    */
+  def splitRef(e: Expression): (WRef, Expression) = e match {
+    case e: WRef => (e, EmptyExpression)
+    case e: WSubIndex =>
+      val (root, tail) = splitRef(e.exp)
+      (root, WSubIndex(tail, e.value, e.tpe, e.gender))
+    case e: WSubField =>
+      val (root, tail) = splitRef(e.exp)
+      tail match {
+        case EmptyExpression => (root, WRef(e.name, e.tpe, root.kind, e.gender))
+        case exp => (root, WSubField(tail, e.name, e.tpe, e.gender))
+      }
+  }
+
+  /** Adds a root reference to some SubField/SubIndex chain */
+  def mergeRef(root: WRef, body: Expression): Expression = body match {
+    case e: WRef =>
+      WSubField(root, e.name, e.tpe, e.gender)
+    case e: WSubIndex =>
+      WSubIndex(mergeRef(root, e.exp), e.value, e.tpe, e.gender)
+    case e: WSubField =>
+      WSubField(mergeRef(root, e.exp), e.name, e.tpe, e.gender)
+    case EmptyExpression => root
+  }
 
 // =============== RECURISVE MAPPERS ===================
    def mapr (f: Width => Width, t:Type) : Type = {