Add support for dynamic indexing on Vec identity views (#2298)

2 files changed, 33 insertions, 3 deletions

diff --git a/core/src/main/scala/chisel3/Aggregate.scala b/core/src/main/scala/chisel3/Aggregate.scala
index 6c6d89c3..dbde7068 100644
--- a/core/src/main/scala/chisel3/Aggregate.scala
+++ b/core/src/main/scala/chisel3/Aggregate.scala
@@ -3,7 +3,7 @@
 package chisel3
 
 import chisel3.experimental.VecLiterals.AddVecLiteralConstructor
-import chisel3.experimental.dataview.{InvalidViewException, isView}
+import chisel3.experimental.dataview.{InvalidViewException, isView, reifySingleData}
 
 import scala.collection.immutable.{SeqMap, VectorMap}
 import scala.collection.mutable.{HashSet, LinkedHashMap}
@@ -258,9 +258,20 @@ sealed class Vec[T <: Data] private[chisel3] (gen: => T, val length: Int)
   def do_apply(p: UInt)(implicit compileOptions: CompileOptions): T = {
     requireIsHardware(this, "vec")
     requireIsHardware(p, "vec index")
+
+    // Special handling for views
     if (isView(this)) {
-      throw InvalidViewException("Dynamic indexing of Views is not yet supported")
+      reifySingleData(this) match {
+        // Views complicate things a bit, but views that correspond exactly to an identical Vec can just forward the
+        // dynamic indexing to the target Vec
+        // In theory, we could still do this forwarding if the sample element were different by deriving a DataView
+        case Some(target: Vec[T @unchecked]) if this.length == target.length &&
+                                                this.sample_element.typeEquivalent(target.sample_element) =>
+          return target.do_apply(p)
+        case _ => throw InvalidViewException("Dynamic indexing of Views is not yet supported")
+      }
     }
+
     val port = gen
 
     // Reconstruct the resolvedDirection (in Aggregate.bind), since it's not stored.
diff --git a/src/test/scala/chiselTests/experimental/DataView.scala b/src/test/scala/chiselTests/experimental/DataView.scala
index 399b0cbc..7c5d170b 100644
--- a/src/test/scala/chiselTests/experimental/DataView.scala
+++ b/src/test/scala/chiselTests/experimental/DataView.scala
@@ -313,8 +313,26 @@ class DataViewSpec extends ChiselFlatSpec {
     verilog should include ("assign z = d;")
   }
 
-  it should "error if you try to dynamically index a Vec view" in {
+  it should "support dynamic indexing for Vec identity views" in {
+    class MyModule extends Module {
+      val dataIn = IO(Input(UInt(8.W)))
+      val addr = IO(Input(UInt(2.W)))
+      val dataOut = IO(Output(UInt(8.W)))
+
+      val vec = RegInit(0.U.asTypeOf(Vec(4, UInt(8.W))))
+      val view = vec.viewAs[Vec[UInt]]
+      // Dynamic indexing is more of a "generator" in Chisel3 than an individual node
+      // This style is not recommended, this is just testing the behavior
+      val selected = view(addr)
+      selected := dataIn
+      dataOut := selected
+    }
+    val chirrtl = ChiselStage.emitChirrtl(new MyModule)
+    chirrtl should include ("vec[addr] <= dataIn")
+    chirrtl should include ("dataOut <= vec[addr]")
+  }
 
+  it should "error if you try to dynamically index a Vec view that does not correspond to a Vec target" in {
     class MyModule extends Module {
       val inA, inB = IO(Input(UInt(8.W)))
       val outA, outB = IO(Output(UInt(8.W)))
@@ -323,6 +341,7 @@ class DataViewSpec extends ChiselFlatSpec {
       val a, b, c, d = RegInit(0.U)
 
       // Dynamic indexing is more of a "generator" in Chisel3 than an individual node
+      // This style is not recommended, this is just testing the behavior
       val selected = Seq((a, b), (c, d)).apply(idx)
       selected := (inA, inB)
       (outA, outB) := selected