Fix sign extension issue in Emitter (#1785)

* add sign-extend const-prop test

* Emitter: don't wrap Neg operand in concat

2 files changed, 11 insertions, 1 deletions

diff --git a/src/main/scala/firrtl/Emitter.scala b/src/main/scala/firrtl/Emitter.scala
index fdfda3e6..850c8ca1 100644
--- a/src/main/scala/firrtl/Emitter.scala
+++ b/src/main/scala/firrtl/Emitter.scala
@@ -398,7 +398,7 @@ class VerilogEmitter extends SeqTransform with Emitter {
          error("Verilog emitter does not support SHIFT_RIGHT >= arg width")
        case Shr if c0 == (bitWidth(a0.tpe)-1) => Seq(a0,"[", bitWidth(a0.tpe) - 1, "]")
        case Shr => Seq(a0,"[", bitWidth(a0.tpe) - 1, ":", c0, "]")
-       case Neg => Seq("-{", cast(a0), "}")
+       case Neg => Seq("-", cast(a0))
        case Cvt => a0.tpe match {
          case (_: UIntType) => Seq("{1'b0,", cast(a0), "}")
          case (_: SIntType) => Seq(cast(a0))
diff --git a/src/test/scala/firrtlTests/ConstantPropagationTests.scala b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
index 653653d6..efe85e48 100644
--- a/src/test/scala/firrtlTests/ConstantPropagationTests.scala
+++ b/src/test/scala/firrtlTests/ConstantPropagationTests.scala
@@ -1651,4 +1651,14 @@ class ConstantPropagationEquivalenceSpec extends FirrtlFlatSpec {
           |""".stripMargin
      firrtlEquivalenceTest(input, transforms)
    }
+
+  "propagation of signed expressions" should "have the correct signs" in {
+    val input =
+      s"""circuit SignTester :
+         |  module SignTester :
+         |    output ref : SInt<3>
+         |    ref <= mux(UInt<1>("h0"), SInt<3>("h0"), neg(UInt<2>("h3")))
+         |""".stripMargin
+    firrtlEquivalenceTest(input, transforms)
+  }
 }