Preserve literals across .asUInt (#4148)

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

@@ -105,8 +105,14 @@ sealed abstract class Aggregate extends Data {
   // This means we need the `first` argument so that we can preserve this behavior of Aggregates while still allowing subclasses
   // to override .asUInt behavior
   override private[chisel3] def _asUIntImpl(first: Boolean)(implicit sourceInfo: SourceInfo): UInt = {
-    val elts = this.getElements.map(_._asUIntImpl(false))
-    if (elts.isEmpty && !first) 0.U(0.W) else SeqUtils.do_asUInt(elts)
+    checkingLitOption(checkForDontCares = false) match {
+      case Some(value) =>
+        // Using UInt.Lit instead of .U so we can use Width argument which may be Unknown
+        UInt.Lit(value, this.width)
+      case None =>
+        val elts = this.getElements.map(_._asUIntImpl(false))
+        if (elts.isEmpty && !first) 0.U(0.W) else SeqUtils.do_asUInt(elts)
+    }
   }
 
   private[chisel3] override def connectFromBits(

core/src/main/scala/chisel3/Bits.scala

@@ -1023,9 +1023,22 @@ sealed class SInt private[chisel3] (width: Width) extends Bits(width) with Num[S
   override def do_>>(that: UInt)(implicit sourceInfo: SourceInfo): SInt =
     binop(sourceInfo, SInt(this.width), DynamicShiftRightOp, that)
 
-  override private[chisel3] def _asUIntImpl(first: Boolean)(implicit sourceInfo: SourceInfo): UInt = pushOp(
-    DefPrim(sourceInfo, UInt(this.width), AsUIntOp, ref)
-  )
+  override private[chisel3] def _asUIntImpl(first: Boolean)(implicit sourceInfo: SourceInfo): UInt =
+    this.litOption match {
+      case Some(value) =>
+        // This is a reinterpretation of raw bits
+        val posValue =
+          if (value.signum == -1) {
+            (BigInt(1) << this.width.get) + value
+          } else {
+            value
+          }
+        // Using UInt.Lit instead of .U so we can use Width argument which may be Unknown
+        UInt.Lit(posValue, this.width)
+      case None =>
+        pushOp(DefPrim(sourceInfo, UInt(this.width), AsUIntOp, ref))
+    }
+
   override def do_asSInt(implicit sourceInfo: SourceInfo): SInt = this
 
   private[chisel3] override def connectFromBits(

src/test/scala/chiselTests/BundleLiteralSpec.scala

@@ -3,6 +3,7 @@
 package chiselTests
 
 import chisel3._
+import chisel3.util.Cat
 import circt.stage.ChiselStage
 import chisel3.testers.BasicTester
 import chisel3.experimental.BundleLiterals._
@@ -28,6 +29,15 @@ class BundleLiteralSpec extends ChiselFlatSpec with Utils {
     val c = UInt(16.W)
   }
 
+  class ChildBundle extends Bundle {
+    val foo = UInt(4.W)
+  }
+  class ComplexBundle(w: Int) extends Bundle {
+    val a = Vec(2, new ChildBundle)
+    val b = UInt(w.W)
+    val c = UInt(4.W)
+  }
+
   "bundle literals" should "pack" in {
     assertTesterPasses {
       new BasicTester {
@@ -351,7 +361,7 @@ class BundleLiteralSpec extends ChiselFlatSpec with Utils {
     }
     val (stdout, _, chirrtl) = grabStdOutErr(ChiselStage.emitCHIRRTL(new RawModule {
       val lit = (new SimpleBundle).Lit(_.a -> 0xde.U, _.b -> 0xad.U)
-      val x = lit.asUInt
+      val x = Cat(lit.a, lit.b)
     }))
     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")
@@ -366,7 +376,7 @@ class BundleLiteralSpec extends ChiselFlatSpec with Utils {
     val chirrtl = ChiselStage.emitCHIRRTL(
       new RawModule {
         val lit = (new SimpleBundle).Lit(_.a -> 5.U, _.b -> 0.U)
-        val x = lit.asUInt
+        val x = Cat(lit.a, lit.b)
       },
       args = Array("--warnings-as-errors")
     )
@@ -407,8 +417,50 @@ class BundleLiteralSpec extends ChiselFlatSpec with Utils {
       val lit = (new SimpleBundle).Lit(_.a -> 0x3.U, _.b -> 0x3.U(3.W))
       lit.a.getWidth should be(4)
       lit.b.getWidth should be(4)
-      val cat = lit.asUInt
+      val cat = Cat(lit.a, lit.b)
     })
     chirrtl should include("node cat = cat(UInt<4>(0h3), UInt<4>(0h3))")
   }
+
+  "Calling .asUInt on a Bundle literal" should "return a UInt literal and work outside of elaboration" in {
+    val blit = (new MyBundle).Lit(_.a -> 42.U, _.b -> true.B, _.c -> MyEnum.sB)
+    val ulit = blit.asUInt
+    ulit.litOption should be(Some(171))
+
+    assertTesterPasses {
+      new BasicTester {
+        // Check that it gives the same value as the generated hardware
+        val wire = WireInit(blit).asUInt
+        chisel3.assert(ulit.litValue.U === wire)
+        stop()
+      }
+    }
+  }
+
+  "Calling .asUInt on a Bundle literal with DontCare fields" should "NOT return a UInt literal" in {
+    ChiselStage.emitCHIRRTL(new RawModule {
+      val blit = (new MyBundle).Lit(_.a -> 42.U, _.c -> MyEnum.sB)
+      val ulit = blit.asUInt
+      ulit.litOption should be(None)
+    })
+  }
+
+  "Calling .asUInt on a Bundle literal with zero-width fields" should "return a UInt literal and work outside of elaboration" in {
+    import chisel3.experimental.VecLiterals._
+
+    val vlit = Vec.Lit((new ChildBundle).Lit(_.foo -> 0xa.U), (new ChildBundle).Lit(_.foo -> 0xb.U))
+    val blit = (new ComplexBundle(0)).Lit(_.a -> vlit, _.b -> 0.U(0.W), _.c -> 0xc.U)
+    val ulit = blit.asUInt
+    ulit.litOption should be(Some(0xbac))
+
+    assertTesterPasses {
+      new BasicTester {
+        // Check that it gives the same value as the generated hardware
+        val wire = WireInit(blit).asUInt
+        chisel3.assert(ulit.litValue.U === wire)
+        stop()
+      }
+    }
+  }
+
 }

src/test/scala/chiselTests/SIntOps.scala

@@ -219,4 +219,32 @@ class SIntOpsSpec extends ChiselPropSpec with Utils with ShiftRightWidthBehavior
     val verilog = ChiselStage.emitSystemVerilog(new TestModule, args)
     verilog should include(" widthcheck = in[7];")
   }
+
+  property("Calling .asUInt on an SInt literal should maintain the literal value") {
+    val s0 = 3.S
+    val u0 = s0.asUInt
+    u0.litValue should be(3)
+
+    val s1 = -3.S
+    val u1 = s1.asUInt
+    u1.litValue should be(5)
+
+    val s2 = -3.S(8.W)
+    val u2 = s2.asUInt
+    u2.litValue should be(0xfd)
+
+    assertTesterPasses {
+      new BasicTester {
+        // Check that it gives the same value as the generated hardware
+        val wire0 = WireInit(s0).asUInt
+        chisel3.assert(u0.litValue.U === wire0)
+        val wire1 = WireInit(s1).asUInt
+        chisel3.assert(u1.litValue.U === wire1)
+        val wire2 = WireInit(s2).asUInt
+        chisel3.assert(u2.litValue.U === wire2)
+
+        stop()
+      }
+    }
+  }
 }

src/test/scala/chiselTests/UIntOps.scala

@@ -607,4 +607,8 @@ class UIntOpsSpec extends ChiselPropSpec with Matchers with Utils with ShiftRigh
     val e = the[IllegalArgumentException] thrownBy (UInt(-8.W))
     e.getMessage should include("Widths must be non-negative, got -8")
   }
+
+  property("Calling .asUInt on a UInt literal should maintain the literal value") {
+    3.U.asUInt.litValue should be(3)
+  }
 }

src/test/scala/chiselTests/VecLiteralSpec.scala

@@ -3,6 +3,7 @@
 package chiselTests
 
 import chisel3._
+import chisel3.util.Cat
 import chisel3.experimental.BundleLiterals.AddBundleLiteralConstructor
 import chisel3.experimental.VecLiterals._
 import chisel3.experimental.VecLiteralException
@@ -537,13 +538,43 @@ class VecLiteralSpec extends ChiselFreeSpec with Utils {
       val lit0 = (Vec(2, UInt(4.W))).Lit(0 -> 0x3.U, 1 -> 0x2.U(3.W))
       lit0(0).getWidth should be(4)
       lit0(1).getWidth should be(4)
-      val uint0 = lit0.asUInt
+      val uint0 = Cat(lit0(1), lit0(0))
       val lit1 = Vec.Lit(0x3.U, 0x2.U(4.W))
       lit1(0).getWidth should be(4)
       lit1(1).getWidth should be(4)
-      val uint1 = lit1.asUInt
+      val uint1 = Cat(lit1(1), lit1(0))
     })
     chirrtl should include("node uint0 = cat(UInt<4>(0h2), UInt<4>(0h3))")
     chirrtl should include("node uint1 = cat(UInt<4>(0h2), UInt<4>(0h3))")
   }
+
+  "Calling .asUInt on a Vec literal should return a UInt literal and work outside of elaboration" in {
+    val vlit0 = Vec(2, UInt(4.W)).Lit(0 -> 0x3.U, 1 -> 0x2.U(3.W))
+    val ulit0 = vlit0.asUInt
+    ulit0.litOption should be(Some(0x23))
+
+    val vlit1 = Vec.Lit(0x3.U, 0x2.U(4.W))
+    val ulit1 = vlit1.asUInt
+    ulit1.litOption should be(Some(0x23))
+
+    assertTesterPasses {
+      new BasicTester {
+        // Check that it gives the same value as the generated hardware
+        val wire0 = WireInit(vlit0).asUInt
+        chisel3.assert(ulit0.litValue.U === wire0)
+        val wire1 = WireInit(vlit1).asUInt
+        chisel3.assert(ulit1.litValue.U === wire1)
+
+        stop()
+      }
+    }
+  }
+
+  "Calling .asUInt on a Vec literal with DontCare fields should NOT return a UInt literal" in {
+    ChiselStage.emitCHIRRTL(new RawModule {
+      val vlit = Vec(2, UInt(4.W)).Lit(1 -> 0x2.U(3.W))
+      val ulit = vlit.asUInt
+      ulit.litOption should be(None)
+    })
+  }
 }