Directions internals mega-refactor (#617)

Part 1 of mega-change in #578

Major notes:
- Input(...) and Output(...) now (effectively) recursively override their elements' directions
- Nodes given userDirection (Input, Output, Flip - what the user assigned to _that_ node) and actualDirection (Input, Output, None, but also Bidirectional and BidirectionalFlip for mostly Aggregates), because of the above (since a higher-level Input(...) can override the locally specified user direction).
- DataMirror (node reflection APIs) added to chisel3.experimental. This provides ways to query the user given direction of a node as well as the actual direction.
- checkSynthesizable replaced with requireIsHardware and requireIsChiselType and made available in chisel3.experimental.

Internal changes notes:
- toType moved into Emitter, this makes the implementation cleaner especially considering that Vec types can't be flipped in FIRRTL. This also more clearly separates Chisel frontend from FIRRTL emission.
- Direction separated from Bindings, both are now fields in Data, and all nodes are given hierarchical directions (Aggregates may be Bidirectional). The actualDirection at the Element (leaf) level should be the same as binding directions previously.
- Bindings are hierarchical, children (of a, for example, Bundle) have a ChildBinding that points to their parent. This is different than the previous scheme where Bindings only applied at the Element (leaf) level.
- Lots of small misc clean up.

Future PRs will address other parts of #578, including stricter direction checks that aren't a side-effect of this internal refactor, stricter checks and splitting of binding operations (Wire vs. WireInit), and node operations not introduced here (getType and deprecation of chiselCloneType). Since those shouldn't mess with internals, those should be much smaller.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/main/scala/chisel3/util/Decoupled.scala b/src/main/scala/chisel3/util/Decoupled.scala
index 5de24728..b9e1e7ed 100644
--- a/src/main/scala/chisel3/util/Decoupled.scala
+++ b/src/main/scala/chisel3/util/Decoupled.scala
@@ -6,6 +6,7 @@
 package chisel3.util
 
 import chisel3._
+import chisel3.experimental.{DataMirror, Direction}
 import chisel3.internal.naming._  // can't use chisel3_ version because of compile order
 
 /** An I/O Bundle containing 'valid' and 'ready' signals that handshake
@@ -88,7 +89,7 @@ object Decoupled
     */
   @chiselName
   def apply[T <: Data](irr: IrrevocableIO[T]): DecoupledIO[T] = {
-    require(irr.bits.flatten forall (_.dir == OUTPUT), "Only safe to cast produced Irrevocable bits to Decoupled.")
+    require(DataMirror.directionOf(irr.bits) == Direction.Output, "Only safe to cast produced Irrevocable bits to Decoupled.")
     val d = Wire(new DecoupledIO(irr.bits))
     d.bits := irr.bits
     d.valid := irr.valid
@@ -122,7 +123,7 @@ object Irrevocable
     * @note unsafe (and will error) on the consumer (output) side of an DecoupledIO
     */
   def apply[T <: Data](dec: DecoupledIO[T]): IrrevocableIO[T] = {
-    require(dec.bits.flatten forall (_.dir == INPUT), "Only safe to cast consumed Decoupled bits to Irrevocable.")
+    require(DataMirror.directionOf(dec.bits) == Direction.Input, "Only safe to cast consumed Decoupled bits to Irrevocable.")
     val i = Wire(new IrrevocableIO(dec.bits))
     dec.bits := i.bits
     dec.valid := i.valid