Fix width of constant propagation of SInt with zero (#2120)

2 files changed, 15 insertions, 1 deletions

diff --git a/src/main/scala/firrtl/transforms/ConstantPropagation.scala b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
index 0523082d..7106c699 100644
--- a/src/main/scala/firrtl/transforms/ConstantPropagation.scala
+++ b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
@@ -230,7 +230,7 @@ class ConstantPropagation extends Transform with DependencyAPIMigration {
     }
     def simplify(e: Expression, lhs: Literal, rhs: Expression) = lhs match {
       case UIntLiteral(v, _) if v == BigInt(0)                                            => rhs
-      case SIntLiteral(v, _) if v == BigInt(0)                                            => asUInt(rhs, e.tpe)
+      case SIntLiteral(v, _) if v == BigInt(0)                                            => asUInt(pad(rhs, e.tpe), e.tpe)
       case UIntLiteral(v, IntWidth(w)) if v == (BigInt(1) << bitWidth(rhs.tpe).toInt) - 1 => lhs
       case _                                                                              => e
     }
diff --git a/src/test/scala/firrtlTests/ConstantPropagationTests.scala b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
index 28c1d823..60cf1b8b 100644
--- a/src/test/scala/firrtlTests/ConstantPropagationTests.scala
+++ b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
@@ -1638,6 +1638,20 @@ class ConstantPropagationEquivalenceSpec extends FirrtlFlatSpec {
     firrtlEquivalenceTest(input, transforms)
   }
 
+  // https://github.com/chipsalliance/firrtl/issues/2034
+  "SInt OR with constant zero" should "have the correct widths" in {
+    val input =
+      s"""circuit WidthsOrSInt :
+         |  module WidthsOrSInt :
+         |    input in : SInt<1>
+         |    input in2 : SInt<4>
+         |    output out : UInt<8>
+         |    output out2 : UInt<8>
+         |    out <= or(in, SInt<8>(0))
+         |    out2 <= or(in2, SInt<8>(0))""".stripMargin
+    firrtlEquivalenceTest(input, transforms)
+  }
+
   "addition by zero width wires" should "have the correct widths" in {
     val input =
       s"""circuit ZeroWidthAdd: