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[choice] Adds a means to declare a choice group without use #4554

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[choice] Adds a means to declare a choice group without use #4554

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7a2a62f
[choice] Adds a means to declare a choice group without use
davidbiancolin Dec 10, 2024
8dbb9b8
Update src/test/scala/chiselTests/ModuleChoiceSpec.scala
davidbiancolin Dec 10, 2024
a53063d
A slightly different implementation avoiding TypeTag
davidbiancolin Dec 10, 2024
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30 changes: 29 additions & 1 deletion core/src/main/scala/chisel3/choice/package.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,13 @@
package chisel3

import chisel3.experimental.{BaseModule, SourceInfo}
import chisel3.internal.Builder
import chisel3.util.simpleClassName

import scala.collection.mutable
import scala.reflect.runtime.universe._
import scala.reflect.runtime.{currentMirror => cm}
Comment on lines +10 to +11
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scala.reflect._ doesn't cross-compile with Scala 3, it needs to be put in core/src/main/scala-2/chisel3/


/** This package contains Chisel language definitions for describing configuration options and their accepted values.
*/
package object choice {
Expand All @@ -13,7 +18,7 @@ package object choice {
*
* @example
* {{{
* import chisel3.option.{Group, Case}
* import chisel3.choice.{Group, Case}
* object Platform extends Group {
* object FPGA extends Case
* object ASIC extends Case
Expand Down Expand Up @@ -47,4 +52,27 @@ package object choice {
*/
def ->[T](module: => T): (Case, () => T) = (this, () => module)
}

/** Registers all options in a group with the Builder.
* This lets Chisel know that this layer should be emitted into FIRRTL text.
*
* This API can be used to guarantee that a design will always have certain
* group defined. This is analagous in spirit to [[layer.addLayer]].
*/
def addGroup[T <: Group: TypeTag](group: T): Unit = {

val tpe = typeOf[T]
val classSymbol = tpe.typeSymbol.asClass
val classMirror = cm.reflectClass(classSymbol)

tpe.members.collect {
// Look only for inner objects. Note, this is not recursive.
case m: ModuleSymbol if m.isStatic =>
val instance = cm.reflectModule(m.asModule).instance
// Confirms the instance is a subtype of Case
if (cm.classSymbol(instance.getClass).toType <:< typeOf[Case]) {
Builder.options += instance.asInstanceOf[Case]
}
}
}
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This is clever reflection. 👍 However, it may be better to just make this information more easily accessible. Two changes would avoid the TypeTag (which is a Scala3 migration annoyance, I think) and any work in this function:

  1. Add a Builder member for storing groups and not just options.
  2. Add mutable.LinkedHashSet to Group that can be used to directly look up what Cases it supports. Then modify Case to insert into it.

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I started doing a (2) but wasn't sure when/how to finalize the set short of doing something either janky or switching the API in someway to use a different pattern.

But (1) seems really easy to do; the existing struct can probably just become a HashMap and we wouldn't need to reconstruct the the groups later.

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Ok i got rid of the type tag but i can't figure out how to avoid it altogether unless we change the API for defining these cases (so that they are not lazy initialized).

Alternatively, we could change the addGroup API to to instead take a one or more cases. For example addGroupHint(c: Case) would suffice to workaround my problem, but it seems rather hacky to not register the whole group and breaks the direct addLayer analogy.

However, I doubt breaking the Group API here is a big deal since no one should be using this? I'd change the Group` implementation to use a more factory like pattern that would force registration on the definition of the objects.

LMK

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Yeah, I think the laziness of the cases seems wrong. Laziness of groups seems fine. (You only get a group if you use it, but you get all of its cases.)

This would be a change to have the Builder register groups, have cases register that they are children of groups, and then pushing that change through to the converter.

However, all of this is independent of any change to the API. Given that, I will go ahead and approve this.

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I'm not sure if this reflection works in Scala 3 and as we are actively trying to get Scala 3 compilation into CI, I think we need to address it sooner rather than later. Can we do something similar to how Layers get the parents with an implicit rather than reflecting on the Group?

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Well, can i break the existing API? If so this is pretty straight forward. Otherwise i might need one of you guys (i.e., someone with more Scala foo than i) to do it. The crux of it is that the Cases are lazily constructed so something has to reference them to bind them to the group. If you're coming into the office today maybe we can chat about it?

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You can break it as much as you want. Just don't backport it to 6.x. This feature has no users and you won't be disturbing anyone.

}
21 changes: 20 additions & 1 deletion src/test/scala/chiselTests/ModuleChoiceSpec.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@
package chiselTests

import chisel3._
import chisel3.choice.{Case, Group, ModuleChoice}
import chisel3.choice.{addGroup, Case, Group, ModuleChoice}
import chiselTests.{ChiselFlatSpec, MatchesAndOmits, Utils}
import _root_.circt.stage.ChiselStage

Expand Down Expand Up @@ -129,3 +129,22 @@ class ModuleChoiceSpec extends ChiselFlatSpec with Utils with MatchesAndOmits {
}

}
class AddGroupSpec extends ChiselFlatSpec with Utils with MatchesAndOmits {
it should "emit options for a registered group even if there are no consumers" in {
class ModuleWithoutChoice extends Module {
addGroup(Platform)
val out = IO(UInt(8.W))
val in = IO(UInt(8.W))
out := in
}

val chirrtl = ChiselStage.emitCHIRRTL(new ModuleWithoutChoice, Array("--full-stacktrace"))
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Nit: Array("--full-stacktrace") can be dropped.


info("CHIRRTL emission looks correct")
matchesAndOmits(chirrtl)(
"option Platform :",
"FPGA",
"ASIC"
)()
}
}
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