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, 21 insertions, 22 deletions

diff --git a/chiselFrontend/src/main/scala/chisel3/core/MonoConnect.scala b/chiselFrontend/src/main/scala/chisel3/core/MonoConnect.scala
index 80e96ce7..3c34785f 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/MonoConnect.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/MonoConnect.scala
@@ -120,24 +120,23 @@ object MonoConnect {
   // This function checks if element-level connection operation allowed.
   // Then it either issues it or throws the appropriate exception.
   def elemConnect(implicit sourceInfo: SourceInfo, connectCompileOptions: CompileOptions, sink: Element, source: Element, context_mod: UserModule): Unit = {
-    import Direction.{Input, Output} // Using extensively so import these
+    import BindingDirection.{Internal, Input, Output} // Using extensively so import these
     // If source has no location, assume in context module
     // This can occur if is a literal, unbound will error previously
     val sink_mod: BaseModule   = sink.binding.location.getOrElse(throw UnwritableSinkException)
     val source_mod: BaseModule = source.binding.location.getOrElse(context_mod)
 
-    val sink_direction: Option[Direction] = sink.binding.direction
-    val source_direction: Option[Direction] = source.binding.direction
-    // None means internal
+    val sink_direction = BindingDirection.from(sink.topBinding, sink.direction)
+    val source_direction = BindingDirection.from(source.topBinding, source.direction)
 
     // CASE: Context is same module that both left node and right node are in
     if( (context_mod == sink_mod) && (context_mod == source_mod) ) {
       ((sink_direction, source_direction): @unchecked) match {
         //    SINK          SOURCE
         //    CURRENT MOD   CURRENT MOD
-        case (Some(Output), _) => issueConnect(sink, source)
-        case (None,         _) => issueConnect(sink, source)
-        case (Some(Input),  _) => throw UnwritableSinkException
+        case (Output,       _) => issueConnect(sink, source)
+        case (Internal,     _) => issueConnect(sink, source)
+        case (Input,        _) => throw UnwritableSinkException
       }
     }
 
@@ -148,19 +147,19 @@ object MonoConnect {
       ((sink_direction, source_direction): @unchecked) match {
         //    SINK          SOURCE
         //    CURRENT MOD   CHILD MOD
-        case (None,         Some(Output)) => issueConnect(sink, source)
-        case (None,         Some(Input))  => issueConnect(sink, source)
-        case (Some(Output), Some(Output)) => issueConnect(sink, source)
-        case (Some(Output), Some(Input))  => issueConnect(sink, source)
-        case (_,            None) => {
+        case (Internal,     Output) => issueConnect(sink, source)
+        case (Internal,     Input)  => issueConnect(sink, source)
+        case (Output,       Output) => issueConnect(sink, source)
+        case (Output,       Input)  => issueConnect(sink, source)
+        case (_,            Internal) => {
           if (!(connectCompileOptions.dontAssumeDirectionality)) {
             issueConnect(sink, source)
           } else {
             throw UnreadableSourceException
           }
         }
-        case (Some(Input),  Some(Output)) if (!(connectCompileOptions.dontTryConnectionsSwapped)) => issueConnect(source, sink)
-        case (Some(Input),  _)    => throw UnwritableSinkException
+        case (Input,        Output) if (!(connectCompileOptions.dontTryConnectionsSwapped)) => issueConnect(source, sink)
+        case (Input,        _)    => throw UnwritableSinkException
       }
     }
 
@@ -171,9 +170,9 @@ object MonoConnect {
       ((sink_direction, source_direction): @unchecked) match {
         //    SINK          SOURCE
         //    CHILD MOD     CURRENT MOD
-        case (Some(Input),  _) => issueConnect(sink, source)
-        case (Some(Output), _) => throw UnwritableSinkException
-        case (None,         _) => throw UnwritableSinkException
+        case (Input,        _) => issueConnect(sink, source)
+        case (Output,       _) => throw UnwritableSinkException
+        case (Internal,     _) => throw UnwritableSinkException
       }
     }
 
@@ -187,17 +186,17 @@ object MonoConnect {
       ((sink_direction, source_direction): @unchecked) match {
         //    SINK          SOURCE
         //    CHILD MOD     CHILD MOD
-        case (Some(Input),  Some(Input))  => issueConnect(sink, source)
-        case (Some(Input),  Some(Output)) => issueConnect(sink, source)
-        case (Some(Output), _)            => throw UnwritableSinkException
-        case (_,            None) => {
+        case (Input,        Input)  => issueConnect(sink, source)
+        case (Input,        Output) => issueConnect(sink, source)
+        case (Output,       _)      => throw UnwritableSinkException
+        case (_,            Internal) => {
           if (!(connectCompileOptions.dontAssumeDirectionality)) {
             issueConnect(sink, source)
           } else {
             throw UnreadableSourceException
           }
         }
-        case (None,         _)            => throw UnwritableSinkException
+        case (Internal,     _)      => throw UnwritableSinkException
       }
     }