Do Shr constant propagation in Legalize

This uses the foldShiftRight method of the ConstantPropagation
Transform when legalizing Shr PrimOps. This has the effect of removing
literals with bit extracts from the MinimumVerilogCompiler.

This makes the formerly private foldShiftRight method of a public
method of the ConstantPropagation companion object.

Tests in the MimimumVerilogCompilerSpec are updated to check that Shr
is handled as intended.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

1 files changed, 11 insertions, 11 deletions

diff --git a/src/main/scala/firrtl/transforms/ConstantPropagation.scala b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
index 54338719..6618312a 100644
--- a/src/main/scala/firrtl/transforms/ConstantPropagation.scala
+++ b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
@@ -45,6 +45,17 @@ object ConstantPropagation {
       case _ => e
     }
   }
+
+  def foldShiftRight(e: DoPrim) = e.consts.head.toInt match {
+    case 0 => e.args.head
+    case x => e.args.head match {
+      // TODO when amount >= x.width, return a zero-width wire
+      case UIntLiteral(v, IntWidth(w)) => UIntLiteral(v >> x, IntWidth((w - x) max 1))
+      // take sign bit if shift amount is larger than arg width
+      case SIntLiteral(v, IntWidth(w)) => SIntLiteral(v >> x, IntWidth((w - x) max 1))
+      case _ => e
+    }
+  }
 }
 
 class ConstantPropagation extends Transform with ResolvedAnnotationPaths {
@@ -144,17 +155,6 @@ class ConstantPropagation extends Transform with ResolvedAnnotationPaths {
     case _ => e
   }
 
-  private def foldShiftRight(e: DoPrim) = e.consts.head.toInt match {
-    case 0 => e.args.head
-    case x => e.args.head match {
-      // TODO when amount >= x.width, return a zero-width wire
-      case UIntLiteral(v, IntWidth(w)) => UIntLiteral(v >> x, IntWidth((w - x) max 1))
-      // take sign bit if shift amount is larger than arg width
-      case SIntLiteral(v, IntWidth(w)) => SIntLiteral(v >> x, IntWidth((w - x) max 1))
-      case _ => e
-    }
-  }
-
   private def foldDynamicShiftRight(e: DoPrim) = e.args.last match {
     case UIntLiteral(v, IntWidth(w)) =>
       val shr = DoPrim(Shr, Seq(e.args.head), Seq(v), UnknownType)