Avoid silently truncating BigInt to Int

- Introduce internal helper `castToInt`, which issues an error when the input
BigInt can't be represented as Int.

- Use `castToInt` wherever we were using `toInt` in a potentially unsafe way.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/main/scala/chisel3/internal/firrtl/Converter.scala b/src/main/scala/chisel3/internal/firrtl/Converter.scala
index ee9d3a99..9366bea2 100644
--- a/src/main/scala/chisel3/internal/firrtl/Converter.scala
+++ b/src/main/scala/chisel3/internal/firrtl/Converter.scala
@@ -6,7 +6,7 @@ import chisel3.core.{SpecifiedDirection, EnumType}
 import chisel3.experimental._
 import chisel3.internal.sourceinfo.{NoSourceInfo, SourceLine, SourceInfo}
 import firrtl.{ir => fir}
-import chisel3.internal.throwException
+import chisel3.internal.{castToInt, throwException}
 
 import scala.annotation.tailrec
 import scala.collection.immutable.{Queue}
@@ -50,7 +50,7 @@ private[chisel3] object Converter {
     case Slot(imm, name) =>
       fir.SubField(convert(imm, ctx), name, fir.UnknownType)
     case Index(imm, ILit(idx)) =>
-      fir.SubIndex(convert(imm, ctx), idx.toInt, fir.UnknownType)
+      fir.SubIndex(convert(imm, ctx), castToInt(idx, "Index"), fir.UnknownType)
     case Index(imm, value) =>
       fir.SubAccess(convert(imm, ctx), convert(value, ctx), fir.UnknownType)
     case ModuleIO(mod, name) =>