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**Type of issue**: bug report | feature request | other enhancement

**If the current behavior is a bug, please provide the steps to reproduce the problem:**
  * **If possible, please directly provide the FIRRTL file or a relevant fragment if the file is large**
  * **What is the current behavior?**
  * **What is the expected behavior?**
  * **Please tell us about your environment:**
    (examples)
    - version: `3.0-SNAPSHOT`
    - OS: `Linux knight 4.4.0-92-generic #115-Ubuntu SMP Thu Aug 10 09:04:33 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux`
    - verilator version (if relevant)

**What is the use case for changing the behavior?**

**Impact**: no functional change | API addition (no impact on existing code) | API modification | unknown

**Development Phase**: request | proposal

**Other information** (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. Stack Overflow, gitter, etc)