1 files changed, 16 insertions, 2 deletions
diff --git a/src/main/scala/firrtl/transforms/ReplaceTruncatingArithmetic.scala b/src/main/scala/firrtl/transforms/ReplaceTruncatingArithmetic.scala
index 1fe9a723..8aa1553a 100644
--- a/src/main/scala/firrtl/transforms/ReplaceTruncatingArithmetic.scala
+++ b/src/main/scala/firrtl/transforms/ReplaceTruncatingArithmetic.scala
@@ -1,3 +1,5 @@
+// See LICENSE for license details.
+
 package firrtl
 package transforms
 
@@ -24,10 +26,22 @@ object ReplaceTruncatingArithmetic {
     */
   def onExpr(netlist: Netlist)(expr: Expression): Expression =
     expr.map(onExpr(netlist)) match {
+      // If an unsigned wrapping add/sub
       case orig @ DoPrim(Tail, Seq(e), SeqBIOne, tailtpe) =>
         netlist.getOrElse(we(e), e) match {
-          case DoPrim(Add, args, cs, _) => DoPrim(Addw, args, cs, tailtpe)
-          case DoPrim(Sub, args, cs, _) => DoPrim(Subw, args, cs, tailtpe)
+          case DoPrim(Add, args, cs, u: UIntType) => DoPrim(Addw, args, cs, tailtpe)
+          case DoPrim(Sub, args, cs, u: UIntType) => DoPrim(Subw, args, cs, tailtpe)
+          case _ => orig // Not a candidate
+        }
+      // If a signed wrapping add/sub, there should be a cast
+      case orig @ DoPrim(AsSInt, Seq(x), _, casttpe) =>
+        netlist.getOrElse(we(x), x) match {
+          case DoPrim(Tail, Seq(e), SeqBIOne, tailtpe) =>
+            netlist.getOrElse(we(e), e) match {
+              case DoPrim(Add, args, cs, s: SIntType) => DoPrim(Addw, args, cs, casttpe)
+              case DoPrim(Sub, args, cs, s: SIntType) => DoPrim(Subw, args, cs, casttpe)
+              case _ => orig // Not a candidate
+            }
           case _ => orig // Not a candidate
         }
       case other => other // Not a candidate