From 2d52f525c57f8c7d6170c993b24e123241415f4d Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Sat, 7 Mar 2020 10:51:06 -0500
Subject: [PATCH] Add --structs-packed for forward compatibility, #1541.

---
 Changes           | 2 ++
 bin/verilator     | 7 +++++++
 src/V3Options.cpp | 2 ++
 src/V3Options.h   | 2 ++
 src/V3Width.cpp   | 3 +++
 5 files changed, 16 insertions(+)

diff --git a/Changes b/Changes
index 4c0ace434..671649dd1 100644
--- a/Changes
+++ b/Changes
@@ -15,6 +15,8 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 ***   Add check for assertOn for asserts, #2162. [Tobias Wölfel]
 
+***   Add --structs-packed for forward compatibility.
+
 ***   Fix genblk naming with directly nested generate blocks, #2176. [Alexander Grobman]
 
 ****  Implement $displayb/o/h, $writeb/o/h, etc, #1637.
diff --git a/bin/verilator b/bin/verilator
index 57ae1c283..b321db9e7 100755
--- a/bin/verilator
+++ b/bin/verilator
@@ -1344,6 +1344,13 @@ Creates more detailed statistics, including a list of all the variables by
 size (plain --stats just gives a count).  See --stats, which is implied by
 this.
 
+=item --structs-packed
+
+Converts all unpacked structures to packed structures and issues a UNPACKED
+warning.  Currently this is the default and --no-structs-packed will not
+work.  Specifying this option allows for forward compatibility when a
+future version of Verilator no longer always packs unpacked structures.
+
 =item -sv
 
 Specifies SystemVerilog language features should be enabled; equivalent to
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index eb56d87b2..724fc37e4 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -786,6 +786,7 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc, char
             else if ( onoffb(sw, "-skip-identical", bflag/*ref*/))   { m_skipIdentical = bflag; }
             else if ( onoff (sw, "-stats", flag/*ref*/))             { m_stats = flag; }
             else if ( onoff (sw, "-stats-vars", flag/*ref*/))        { m_statsVars = flag; m_stats |= flag; }
+            else if ( onoff (sw, "-structs-unpacked", flag/*ref*/))  { m_structsPacked = flag; }
             else if (!strcmp(sw, "-sv"))                             { m_defaultLanguage = V3LangCode::L1800_2005; }
             else if ( onoff (sw, "-threads-coarsen", flag/*ref*/))   { m_threadsCoarsen = flag; }  // Undocumented, debug
             else if ( onoff (sw, "-trace", flag/*ref*/))             { m_trace = flag; }
@@ -1489,6 +1490,7 @@ V3Options::V3Options() {
     m_savable = false;
     m_stats = false;
     m_statsVars = false;
+    m_structsPacked = true;
     m_systemC = false;
     m_threads = 0;
     m_threadsDpiPure = true;
diff --git a/src/V3Options.h b/src/V3Options.h
index f89ab5a45..339349fdc 100644
--- a/src/V3Options.h
+++ b/src/V3Options.h
@@ -184,6 +184,7 @@ class V3Options {
     bool        m_relativeIncludes; // main switch: --relative-includes
     bool        m_reportUnoptflat; // main switch: --report-unoptflat
     bool        m_savable;      // main switch: --savable
+    bool        m_structsPacked;  // main switch: --structs-packed
     bool        m_systemC;      // main switch: --sc: System C instead of simple C++
     bool        m_stats;        // main switch: --stats
     bool        m_statsVars;    // main switch: --stats-vars
@@ -322,6 +323,7 @@ class V3Options {
     bool savable() const { return m_savable; }
     bool stats() const { return m_stats; }
     bool statsVars() const { return m_statsVars; }
+    bool structsPacked() const { return m_structsPacked; }
     bool assertOn() const { return m_assert; }  // assertOn as __FILE__ may be defined
     bool autoflush() const { return m_autoflush; }
     bool bboxSys() const { return m_bboxSys; }
diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index 8283ce30c..485dbd7e0 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -1745,6 +1745,9 @@ private:
         //if (debug()>=9) nodep->dumpTree("-class-in--");
         if (!nodep->packed()) {
             nodep->v3warn(UNPACKED, "Unsupported: Unpacked struct/union");
+            if (!v3Global.opt.structsPacked()) {
+                nodep->v3warn(UNPACKED, "Unsupported: --no-structs-packed");
+            }
         }
         userIterateChildren(nodep, NULL);  // First size all members
         nodep->repairMemberCache();