From 65454f5ff1a370d66202a073e18cdcd40180f051 Mon Sep 17 00:00:00 2001
From: Jack Koenig
Date: Tue, 27 Mar 2018 10:58:45 -0700
Subject: Const prop improvement (#772)

Improve constant propagation of connections to references

[skip formal checks]

LEC fails on this PR because this PR actually changes the circuit. The
change is that it constant propagates some additional registers. This is
really just extending #621 to work on more registers that it was
supposed to be propagating anyway.
---
 src/main/scala/firrtl/transforms/ConstantPropagation.scala | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

(limited to 'src/main')

diff --git a/src/main/scala/firrtl/transforms/ConstantPropagation.scala b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
index 57b88890..8217a9bd 100644
--- a/src/main/scala/firrtl/transforms/ConstantPropagation.scala
+++ b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
@@ -358,6 +358,7 @@ class ConstantPropagation extends Transform {
 
     def constPropStmt(s: Statement): Statement = {
       val stmtx = s map constPropStmt map constPropExpression(nodeMap, instMap, constSubOutputs)
+      // Record things that should be propagated
       stmtx match {
         case x: DefNode if !dontTouches.contains(x.name) => propagateRef(x.name, x.value)
         case Connect(_, WRef(wname, wtpe, WireKind, _), expr: Literal) if !dontTouches.contains(wname) =>
@@ -387,7 +388,13 @@ class ConstantPropagation extends Transform {
           portsMap(port) = paddedLit +: portsMap.getOrElse(port, List.empty)
         case _ =>
       }
-      stmtx
+      // Actually transform some statements
+      stmtx match {
+        // Propagate connections to references
+        case Connect(info, lhs, rref @ WRef(rname, _, NodeKind, _)) if !dontTouches.contains(rname) =>
+          Connect(info, lhs, nodeMap(rname))
+        case other => other
+      }
     }
 
     val modx = m.copy(body = backPropStmt(constPropStmt(m.body)))
-- 
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