Make it a warning to have too-wide literal values in Bundle Literals (#…

…4093) (#4095)

(cherry picked from commit 4f33bf6)

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

core/src/main/scala/chisel3/Aggregate.scala

@@ -1118,7 +1118,7 @@ abstract class Record extends Aggregate {
     * )
     * }}}
     */
-  private[chisel3] def _makeLit(elems: (this.type => (Data, Data))*): this.type = {
+  private[chisel3] def _makeLit(elems: (this.type => (Data, Data))*)(implicit sourceInfo: SourceInfo): this.type = {
 
     requireIsChiselType(this, "bundle literal constructor model")
     val clone = cloneType
@@ -1222,6 +1222,8 @@ abstract class Record extends Aggregate {
             // TODO make this a warning then an error, but for older versions, just truncate.
             val valuex = if (widthValue < value.width.get) {
               // Mask the value to the width of the field.
+              val msg = s"Literal value $value is too wide for field ${cloneFields(field)} with width $widthValue"
+              Builder.warning(Warning(WarningID.BundleLiteralValueTooWide, msg))
               val mask = (BigInt(1) << widthValue) - 1
               value.cloneWithValue(value.num & mask).cloneWithWidth(width)
             } else if (widthValue > value.width.get) value.cloneWithWidth(width)

core/src/main/scala/chisel3/internal/Warning.scala

@@ -19,6 +19,7 @@ private[chisel3] object WarningID extends Enumeration {
   val DynamicIndexTooWide = Value(4)
   val DynamicIndexTooNarrow = Value(5)
   val ExtractFromVecSizeZero = Value(6)
+  val BundleLiteralValueTooWide = Value(7)
 }
 import WarningID.WarningID
 

docs/src/explanations/warnings.md

@@ -143,3 +143,10 @@ It can be fixed as described in the [Cookbook](../cookbooks/cookbook#how-do-i-re
 
 This warning occurs when indexing a `Vec` with no elements.
 It can be fixed by removing the indexing operation for the size zero `Vec` (perhaps via guarding with an `if-else` or `Option.when`).
+
+### [W007] Bundle literal value too wide
+
+This warning occurs when creating a [Bundle Literal](../appendix/experimental-features#bundle-literals) where the literal value for a
+field is wider than the Bundle field's width.
+It can be fixed by reducing the width of the literal (perhaps choosing a different value if it is impossible to encode the value in the
+field's width).

src/test/scala/chiselTests/BundleLiteralSpec.scala

@@ -344,15 +344,17 @@ class BundleLiteralSpec extends ChiselFlatSpec with Utils {
     exc.getMessage should include(".c")
   }
 
-  "bundle literals with too-wide of literal values" should "truncate" in {
+  "bundle literals with too-wide of literal values" should "warn and truncate" in {
     class SimpleBundle extends Bundle {
       val a = UInt(4.W)
       val b = UInt(4.W)
     }
-    val chirrtl = ChiselStage.emitCHIRRTL(new RawModule {
+    val (stdout, _, chirrtl) = grabStdOutErr(ChiselStage.emitCHIRRTL(new RawModule {
       val lit = (new SimpleBundle).Lit(_.a -> 0xde.U, _.b -> 0xad.U)
       val x = lit.asUInt
-    })
+    }))
+    stdout should include("[W007] Literal value ULit(222,) is too wide for field _.a with width 4")
+    stdout should include("[W007] Literal value ULit(173,) is too wide for field _.b with width 4")
     chirrtl should include("node x = cat(UInt<4>(0he), UInt<4>(0hd))")
   }
 

src/test/scala/chiselTests/VecLiteralSpec.scala

@@ -436,17 +436,16 @@ class VecLiteralSpec extends ChiselFreeSpec with Utils {
 
   class VecExample extends RawModule {
     val out = IO(Output(Vec(2, new SubBundle)))
-    // Note that 22.U is too wide for bar so gets truncated below.
     val bundle = Vec(2, new SubBundle).Lit(
-      0 -> (new SubBundle).Lit(_.foo -> 42.U, _.bar -> 22.U),
+      0 -> (new SubBundle).Lit(_.foo -> 42.U, _.bar -> 0xd.U),
       1 -> (new SubBundle).Lit(_.foo -> 7.U, _.bar -> 3.U)
     )
     out := bundle
   }
 
   "vec literals can contain bundles and should not be bulk connected" in {
     val chirrtl = ChiselStage.emitCHIRRTL(new VecExample)
-    chirrtl should include("""connect out[0].bar, UInt<4>(0h6)""")
+    chirrtl should include("""connect out[0].bar, UInt<4>(0hd)""")
     chirrtl should include("""connect out[0].foo, UInt<8>(0h2a)""")
     chirrtl should include("""connect out[1].bar, UInt<4>(0h3)""")
     chirrtl should include("""connect out[1].foo, UInt<8>(0h7)""")