mask bits when propagating bitwise ops (#1745)

* ConstProp: test bitwise op of signed literals

* ConstProp: use bit mask for FoldOr/FoldXor

* handle and also

* add UIntLiteral.masked helper

Co-authored-by: Jack Koenig <koenig@sifive.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/main/scala/firrtl/ir/IR.scala b/src/main/scala/firrtl/ir/IR.scala
index 275cbe51..023f53fd 100644
--- a/src/main/scala/firrtl/ir/IR.scala
+++ b/src/main/scala/firrtl/ir/IR.scala
@@ -297,6 +297,15 @@ case class UIntLiteral(value: BigInt, width: Width) extends Literal {
 object UIntLiteral {
   def minWidth(value: BigInt): Width = IntWidth(math.max(value.bitLength, 1))
   def apply(value: BigInt): UIntLiteral = new UIntLiteral(value, minWidth(value))
+
+  /** Utility to construct UIntLiterals masked by the width
+    *
+    * This supports truncating negative values as well as values that are too wide for the width
+    */
+  def masked(value: BigInt, width: IntWidth): UIntLiteral = {
+    val mask = (BigInt(1) << width.width.toInt) - 1
+    UIntLiteral(value & mask, width)
+  }
 }
 case class SIntLiteral(value: BigInt, width: Width) extends Literal {
   def tpe = SIntType(width)