From 0c93a121c109c3e167d80173dbfe8c2e355b30ef Mon Sep 17 00:00:00 2001
From: Jack Koenig
Date: Tue, 10 Apr 2018 21:24:49 -0700
Subject: Fix bug in Constant Propagation for registers propped to zero (#787)

It wasn't properly padding the width of the constant zero.
Also add a test that shows the buggy behavior.---
 src/main/scala/firrtl/transforms/ConstantPropagation.scala | 3 ++-
 1 file changed, 2 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 2def130c..c417357b 100644
--- a/src/main/scala/firrtl/transforms/ConstantPropagation.scala
+++ b/src/main/scala/firrtl/transforms/ConstantPropagation.scala
@@ -379,7 +379,8 @@ class ConstantPropagation extends Transform {
           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)
+            val zero = passes.RemoveValidIf.getGroundZero(ltpe)
+            nodeMap(lname) = constPropExpression(nodeMap, instMap, constSubOutputs)(pad(zero, ltpe))
           case _ =>
         }
         // Mark instance inputs connected to a constant
-- 
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