From fd8feb55cfa55e2c270d11c1a6ae60ba1950be59 Mon Sep 17 00:00:00 2001
From: Jack Koenig
Date: Wed, 28 Mar 2018 10:48:54 -0700
Subject: Replace unconnected registers with 0 in Constant Propagation (#776)

Moved from RemoveValidIf

Also Make RemoveValidIf.getGroundZero public and support Fixed
---
 src/main/scala/firrtl/transforms/ConstantPropagation.scala | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'src/main/scala/firrtl/transforms')

diff --git a/src/main/scala/firrtl/transforms/ConstantPropagation.scala b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
index 8217a9bd..2def130c 100644
--- a/src/main/scala/firrtl/transforms/ConstantPropagation.scala
+++ b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
@@ -378,6 +378,8 @@ class ConstantPropagation extends Transform {
             nodeMap(lname) = constPropExpression(nodeMap, instMap, constSubOutputs)(pad(fval, ltpe))
           case Mux(_, tval: Literal, fval: WRef, _) if weq(lref, fval) =>
             nodeMap(lname) = constPropExpression(nodeMap, instMap, constSubOutputs)(pad(tval, ltpe))
+          case WRef(`lname`, _,_,_) => // If a register is connected to itself, propagate zero
+            nodeMap(lname) = passes.RemoveValidIf.getGroundZero(ltpe)
           case _ =>
         }
         // Mark instance inputs connected to a constant
-- 
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