From 506cfc1c6fd1600308d208a65861c4df40b44328 Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@koefferlein.de>
Date: Mon, 30 Sep 2019 20:58:55 +0200
Subject: [PATCH] WIP: attempt to retain nets which don't have active elements
 but pins. This is supposed to simplify debugging in case of fake pins. When
 removing those nets, the pin is very difficult to find.

---
 src/db/db/dbCircuit.cc                      |  2 +-
 src/db/db/dbNetlist.cc                      | 10 +++++++++-
 src/db/unit_tests/dbLayoutToNetlistTests.cc |  2 +-
 src/db/unit_tests/dbNetlistTests.cc         |  2 +-
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/db/db/dbCircuit.cc b/src/db/db/dbCircuit.cc
index f608a9f77..35cd1ca6e 100644
--- a/src/db/db/dbCircuit.cc
+++ b/src/db/db/dbCircuit.cc
@@ -545,7 +545,7 @@ void Circuit::purge_nets ()
 {
   std::vector<db::Net *> nets_to_be_purged;
   for (net_iterator n = begin_nets (); n != end_nets (); ++n) {
-    if (n->is_floating ()) {
+    if (n->is_floating () && n->pin_count () == 0) {
       nets_to_be_purged.push_back (n.operator-> ());
     }
   }
diff --git a/src/db/db/dbNetlist.cc b/src/db/db/dbNetlist.cc
index 429ea8b7d..56d4befdd 100644
--- a/src/db/db/dbNetlist.cc
+++ b/src/db/db/dbNetlist.cc
@@ -485,8 +485,16 @@ void Netlist::purge ()
 
     Circuit *circuit = c.operator-> ();
 
+    //  purge floating, disconnected nets
     circuit->purge_nets ();
-    if (circuit->begin_nets () == circuit->end_nets () && ! circuit->dont_purge ()) {
+
+    //  if only floating net - connected to a pin - are left, consider this circuit for purging
+    bool purge_candidate = ! circuit->dont_purge ();
+    for (db::Circuit::net_iterator n = circuit->begin_nets (); n != circuit->end_nets () && purge_candidate; ++n) {
+      purge_candidate = n->is_floating ();
+    }
+
+    if (purge_candidate) {
 
       //  No nets left: delete the subcircuits that refer to us and finally delete the circuit
       while (circuit->begin_refs () != circuit->end_refs ()) {
diff --git a/src/db/unit_tests/dbLayoutToNetlistTests.cc b/src/db/unit_tests/dbLayoutToNetlistTests.cc
index c4b7ca373..011322222 100644
--- a/src/db/unit_tests/dbLayoutToNetlistTests.cc
+++ b/src/db/unit_tests/dbLayoutToNetlistTests.cc
@@ -1096,7 +1096,7 @@ TEST(3_GlobalNetConnections)
     "  subcircuit INV2 $1 ($1=$I1,IN=$I3,$3=$I7,OUT=$I4,VSS=$I5,VDD=$I6,BULK=BULK);\n"
     "  subcircuit INV2 $2 ($1=$I1,IN=$I4,$3=$I8,OUT=$I2,VSS=$I5,VDD=$I6,BULK=BULK);\n"
     "end;\n"
-    "circuit INV2 ($1=(null),IN=IN,$3=$3,OUT=OUT,VSS=VSS,VDD=VDD,BULK=(null));\n"
+    "circuit INV2 ($1=$1,IN=IN,$3=$3,OUT=OUT,VSS=VSS,VDD=VDD,BULK=BULK);\n"
     "  device PMOS $1 (S=$3,G=IN,D=VDD) (L=0.25,W=0.95,AS=0.49875,AD=0.26125,PS=2.95,PD=1.5);\n"
     "  device PMOS $2 (S=VDD,G=$3,D=OUT) (L=0.25,W=0.95,AS=0.26125,AD=0.49875,PS=1.5,PD=2.95);\n"
     "  device NMOS $3 (S=$3,G=IN,D=VSS) (L=0.25,W=0.95,AS=0.49875,AD=0.26125,PS=2.95,PD=1.5);\n"
diff --git a/src/db/unit_tests/dbNetlistTests.cc b/src/db/unit_tests/dbNetlistTests.cc
index 9de025763..38cb3d709 100644
--- a/src/db/unit_tests/dbNetlistTests.cc
+++ b/src/db/unit_tests/dbNetlistTests.cc
@@ -1380,7 +1380,7 @@ TEST(22_BlankCircuit)
   nl2.purge ();
 
   EXPECT_EQ (nl2.to_string (),
-    "circuit RINGO (IN=(null),OSC=OSC,VSS=VSS,VDD=VDD);\n"
+    "circuit RINGO (IN=IN,OSC=OSC,VSS=VSS,VDD=VDD);\n"
     "  subcircuit INV2 INV2_SC1 (IN=$I8,$2=FB,OUT=OSC,$4=VSS,$5=VDD);\n"
     "  subcircuit INV2 INV2_SC2 (IN=FB,$2=(null),OUT=$I8,$4=VSS,$5=VDD);\n"
     "end;\n"