Add Property expressions, starting with addition.

core/src/main/scala/chisel3/internal/firrtl/Converter.scala

@@ -100,6 +100,8 @@ private[chisel3] object Converter {
       fir.RWProbeExpr(convert(probe, ctx, info))
     case e @ ProbeRead(probe) =>
       fir.ProbeRead(convert(probe, ctx, info))
+    case PropExpr(info, tpe, op, args) =>
+      fir.PropExpr(convert(info), tpe, op, args.map(convert(_, ctx, info)))
     case other =>
       throw new InternalErrorException(s"Unexpected type in convert $other")
   }

core/src/main/scala/chisel3/internal/firrtl/IR.scala

@@ -186,6 +186,18 @@ private[chisel3] object ir {
     }
   }
 
+  /** Property expressions.
+    *
+    * Property expressions are conceptually similar to Nodes, but only exist as a tree of Args in-memory.
+    */
+  case class PropExpr(sourceInfo: SourceInfo, tpe: firrtlir.PropertyType, op: firrtlir.PropPrimOp, args: List[Arg])
+      extends Arg {
+    // PropExpr is different from other Args, because this is only used as an internal data structure, and we never name
+    // the Arg or use the name in textual FIRRTL. This is always expected to be the exp of a PropAssign, and it would be
+    // an internal error to request the name.
+    def name: String = throwException("Internal Error! PropExpr has no name")
+  }
+
   case class Ref(name: String) extends Arg
 
   /** Arg for ports of Modules

core/src/main/scala/chisel3/properties/Property.scala

@@ -7,6 +7,7 @@ import firrtl.{ir => fir}
 import firrtl.annotations.{InstanceTarget, IsMember, ModuleTarget, ReferenceTarget, Target}
 import chisel3.internal._
 import chisel3.internal.firrtl.{ir, Converter}
+import chisel3.internal.sourceinfo.SourceInfoTransform
 import chisel3.experimental.{prefix, requireIsHardware, Analog, SourceInfo}
 import chisel3.experimental.hierarchy.Instance
 import scala.reflect.runtime.universe.{typeOf, TypeTag}
@@ -228,7 +229,7 @@ sealed trait Property[T] extends Element { self =>
       }
   }
 
-  protected val tpe: PropertyType[_]
+  protected[properties] val tpe: PropertyType[_]
 
   private[chisel3] def _asUIntImpl(first: Boolean)(implicit sourceInfo: SourceInfo): chisel3.UInt = {
     Builder.error(s"${this._localErrorContext} does not support .asUInt.")
@@ -320,6 +321,8 @@ sealed trait Property[T] extends Element { self =>
     }
   }
 
+  final def +(that: Property[T])(implicit ev: PropertyArithmeticOps[Property[T]], sourceInfo: SourceInfo): Property[T] =
+    ev.add(this, that)
 }
 
 private[chisel3] sealed trait ClassTypeProvider[A] {
@@ -335,6 +338,67 @@ private[chisel3] object ClassTypeProvider {
   }
 }
 
+/** Typeclass for Property arithmetic.
+  */
+@implicitNotFound("arithmetic operations are not supported on Property type ${T}")
+sealed trait PropertyArithmeticOps[T] {
+  def add(lhs: T, rhs: T)(implicit sourceInfo: SourceInfo): T
+}
+
+object PropertyArithmeticOps {
+  // Type class instances for Property arithmetic.
+  implicit val intArithmeticOps: PropertyArithmeticOps[Property[Int]] =
+    new PropertyArithmeticOps[Property[Int]] {
+      def add(lhs: Property[Int], rhs: Property[Int])(implicit sourceInfo: SourceInfo) =
+        binOp(sourceInfo, fir.IntegerAddOp, lhs, rhs)
+    }
+
+  implicit val longArithmeticOps: PropertyArithmeticOps[Property[Long]] =
+    new PropertyArithmeticOps[Property[Long]] {
+      def add(lhs: Property[Long], rhs: Property[Long])(implicit sourceInfo: SourceInfo) =
+        binOp(sourceInfo, fir.IntegerAddOp, lhs, rhs)
+    }
+
+  implicit val bigIntArithmeticOps: PropertyArithmeticOps[Property[BigInt]] =
+    new PropertyArithmeticOps[Property[BigInt]] {
+      def add(lhs: Property[BigInt], rhs: Property[BigInt])(implicit sourceInfo: SourceInfo) =
+        binOp(sourceInfo, fir.IntegerAddOp, lhs, rhs)
+    }
+
+  // Helper function to create Property expression IR.
+  private def binOp[T: PropertyType](
+    sourceInfo: SourceInfo,
+    op:         fir.PropPrimOp,
+    lhs:        Property[T],
+    rhs:        Property[T]
+  ): Property[T] = {
+    implicit val info = sourceInfo
+
+    // Get the containing RawModule, or throw an error. We can only use the temporary Wire approach in RawModule, so at
+    // least give a decent error explaining this current shortcoming.
+    val currentModule = Builder.referenceUserContainer match {
+      case mod: RawModule => mod
+      case other =>
+        throwException(
+          sourceInfo.makeMessage(s => s"Property arithmetic is currently only supported in RawModules ${s}")
+        )
+    }
+
+    // Create a temporary Wire to assign the expression to. We currently don't support Nodes for Property types.
+    val wire = Wire(chiselTypeOf(lhs))
+    wire.autoSeed("_propExpr")
+
+    // Create a PropExpr with the correct type, operation, and operands.
+    val propExpr = ir.PropExpr(sourceInfo, lhs.tpe.getPropertyType(), op, List(lhs.ref, rhs.ref))
+
+    // Directly add a PropAssign command assigning the PropExpr to the Wire.
+    currentModule.addCommand(ir.PropAssign(sourceInfo, wire.lref, propExpr))
+
+    // Return the temporary Wire as the result.
+    wire.asInstanceOf[Property[T]]
+  }
+}
+
 /** Companion object for Property.
   */
 object Property {

docs/src/explanations/properties.md

@@ -114,3 +114,35 @@ class SequenceExample extends RawModule {
   outPort2 := Property(Seq(inPort, Property(789)))
 }
 ```
+
+### Property Expressions
+
+Expressions can be built out of `Property` values for certain `Property` types.
+This is useful for expressing design intent that is parameterized by input
+`Property` values.
+
+#### Integer Arithmetic
+
+The integral `Property` types, like `Property[Int]`, `Property[Long]` and 
+`Property[BigInt]`, can be used to build arithmetic expressions in terms of
+`Property` values.
+
+In the following example, an output `address` port of `Property[Int]` type is
+computed as the addition of an `offset` `Property[Int]` value relative to an 
+input `base` `Property[Int]` value.
+
+```scala mdoc:silent
+class IntegerArithmeticExample extends RawModule {
+  val base = IO(Input(Property[Int]()))
+  val address = IO(Output(Property[Int]()))
+  val offset = Property(1024)
+  address := base + offset
+}
+```
+
+The following table lists the possible arithmetic operators that are supported
+on integral `Property` typed values.
+
+| Operation | Description                                                |
+| --------- | -----------                                                |
+| `+`       | Perform addition as defined by FIRRTL spec section 25.1.1. |

firrtl/src/main/scala/firrtl/ir/IR.scala

@@ -257,6 +257,27 @@ case class PathPropertyLiteral(value: String) extends Expression with UseSeriali
 
 case class SequencePropertyValue(tpe: Type, values: Seq[Expression]) extends Expression with UseSerializer
 
+/** Property primitive operations.
+  */
+sealed abstract class PropPrimOp(name: String) {
+  override def toString: String = name
+}
+case object IntegerAddOp extends PropPrimOp("integer_add")
+
+/** Property expressions.
+  *
+  * Unlike other primitives, Property expressions serialize as a tree directly in their rvalue context.
+  */
+case class PropExpr(info: Info, tpe: Type, op: PropPrimOp, args: Seq[Expression])
+    extends Expression
+    with UseSerializer {
+  override def serialize: String = {
+    val serializedOp = op.toString()
+    val serializedArgs = args.map(_.serialize).mkString("(", ", ", ")")
+    serializedOp + serializedArgs
+  }
+}
+
 case class DoPrim(op: PrimOp, args: Seq[Expression], consts: Seq[BigInt], tpe: Type)
     extends Expression
     with UseSerializer

src/test/scala/chiselTests/properties/PropertySpec.scala

@@ -3,11 +3,12 @@
 package chiselTests.properties
 
 import chisel3._
-import chisel3.properties.{Class, Path, Property, PropertyType}
+import chisel3.properties.{Class, DynamicObject, Path, Property, PropertyType}
 import chiselTests.{ChiselFlatSpec, MatchesAndOmits}
 import circt.stage.ChiselStage
 import chisel3.properties.ClassType
 import chisel3.properties.AnyClassType
+import chisel3.util.experimental.BoringUtils
 
 class PropertySpec extends ChiselFlatSpec with MatchesAndOmits {
   behavior.of("Property")
@@ -617,4 +618,124 @@ class PropertySpec extends ChiselFlatSpec with MatchesAndOmits {
       lit.isLit shouldBe true
     })
   }
+
+  behavior.of("PropertyArithmeticOps")
+
+  it should "support expressions in temporaries, wires, and ports" in {
+    val chirrtl = ChiselStage.emitCHIRRTL(new RawModule {
+      val a = IO(Input(Property[Int]()))
+      val b = IO(Input(Property[Int]()))
+      val c = IO(Output(Property[Int]()))
+      val d = IO(Output(Property[Int]()))
+      val e = IO(Output(Property[Int]()))
+
+      val t = a + b
+
+      val w = WireInit(t)
+
+      c := t
+      d := t + a
+      e := w + (a + b)
+    })
+
+    matchesAndOmits(chirrtl)(
+      "wire t : Integer",
+      "propassign t, integer_add(a, b)",
+      "wire w : Integer",
+      "propassign w, t",
+      "propassign c, t",
+      "wire _d_propExpr : Integer",
+      "propassign _d_propExpr, integer_add(t, a)",
+      "propassign d, _d_propExpr",
+      "wire _e_propExpr",
+      "propassign _e_propExpr, integer_add(a, b)",
+      "wire _e_propExpr_1",
+      "propassign _e_propExpr_1, integer_add(w, _e_propExpr)",
+      "propassign e, _e_propExpr_1"
+    )()
+  }
+
+  it should "support boring from expressions" in {
+    val chirrtl = ChiselStage.emitCHIRRTL(new RawModule {
+      val child = Module(new RawModule {
+        val a = IO(Input(Property[Int]()))
+        val b = IO(Input(Property[Int]()))
+        val c = a + b
+      })
+
+      val a = IO(Input(Property[Int]()))
+      val b = IO(Input(Property[Int]()))
+      val c = IO(Output(Property[Int]()))
+
+      child.a := a
+      child.b := a
+      c := BoringUtils.bore(child.c)
+    })
+
+    matchesAndOmits(chirrtl)(
+      "output c_bore : Integer",
+      "wire c : Integer",
+      "propassign c, integer_add(a, b)",
+      "propassign c_bore, c",
+      "propassign c, child.c_bore"
+    )()
+  }
+
+  it should "support targeting the result of expressions" in {
+    val chirrtl = ChiselStage.emitCHIRRTL(new RawModule {
+      override def desiredName = "Top"
+
+      val mod = Module(new RawModule {
+        override def desiredName = "Foo"
+        val a = IO(Input(Property[Int]()))
+        val b = IO(Input(Property[Int]()))
+        val c = a + b
+      })
+
+      mod.c.toTarget.toString should equal("~Top|Foo>c")
+    })
+
+    matchesAndOmits(chirrtl)(
+      "wire c : Integer",
+      "propassign c, integer_add(a, b)"
+    )()
+  }
+
+  it should "not support expressions involving Property types that don't provide a typeclass instance" in {
+    assertTypeError("""
+      val a = Property[String]()
+      val b = Property[String]()
+      a + b
+    """)
+  }
+
+  it should "not support expressions in Classes, and give a nice error" in {
+    val e = the[ChiselException] thrownBy (ChiselStage.emitCHIRRTL(new RawModule {
+      DynamicObject(new Class {
+        val a = IO(Input(Property[BigInt]()))
+        val b = IO(Input(Property[BigInt]()))
+        val c = IO(Output(Property[BigInt]()))
+        c := a + b
+      })
+    }))
+
+    e.getMessage should include(
+      "Property arithmetic is currently only supported in RawModules @[src/test/scala/chiselTests/properties/PropertySpec.scala"
+    )
+  }
+
+  it should "support addition" in {
+    val chirrtl = ChiselStage.emitCHIRRTL(new RawModule {
+      val a = IO(Input(Property[BigInt]()))
+      val b = IO(Input(Property[BigInt]()))
+      val c = IO(Output(Property[BigInt]()))
+      c := a + b
+    })
+
+    matchesAndOmits(chirrtl)(
+      "wire _c_propExpr : Integer",
+      "propassign _c_propExpr, integer_add(a, b)",
+      "propassign c, _c_propExpr"
+    )()
+  }
 }