From a03033e7432cb9130d3a343309f7eb9d5cec9e19 Mon Sep 17 00:00:00 2001
From: Andrew Pullin <pullin@berkeley.edu>
Date: Fri, 23 Jan 2026 11:28:58 -0800
Subject: [PATCH] Fix #1267: Allow wire logic connected to uwire port to have
 multiple drivers

TODO: Decide how resolved net types (tri0/tri1/triand/trior) should interact with uwire in a shared nexus.
---
 ivtest/ivltests/br_gh1267.v | 23 +++++++++++++++++++++++
 ivtest/regress-sv.list      |  1 +
 tgt-vvp/draw_net_input.c    | 21 +++++++++++++++++++--
 3 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 ivtest/ivltests/br_gh1267.v

diff --git a/ivtest/ivltests/br_gh1267.v b/ivtest/ivltests/br_gh1267.v
new file mode 100644
index 000000000..aa2ce8a5b
--- /dev/null
+++ b/ivtest/ivltests/br_gh1267.v
@@ -0,0 +1,23 @@
+// Test for GitHub issue #1267
+// Wire logic connected to uwire port should not trigger multi-driver error
+// The uwire semantics apply only to the uwire signal, not to wires connected to it.
+
+module a(input uwire logic a1);
+endmodule
+
+module b();
+  wire logic b1;
+
+  a b_inst(.a1(b1));
+  not not_inst(b1, b1);
+
+  assign b1 = 'b0;
+
+  initial begin
+    #1;
+    // b1 has multiple drivers, which is allowed for wire types
+    // The value will be X due to conflicting drivers
+    $display("b1 = %b (expected X due to conflicting drivers)", b1);
+    $display("PASSED");
+  end
+endmodule
diff --git a/ivtest/regress-sv.list b/ivtest/regress-sv.list
index 127f58fa5..89e4d7666 100644
--- a/ivtest/regress-sv.list
+++ b/ivtest/regress-sv.list
@@ -991,3 +991,4 @@ ipsupsel_real_idx	CE,-g2012		ivltests gold=ipsupsel_real_idx.gold
 real_edges		CE,-g2012		ivltests gold=real_edges.gold
 br_gh1112		CE,-g2009		ivltests gold=br_gh1112.gold
 br_gh670		normal,-g2009		ivltests
+br_gh1267		normal,-g2012		ivltests
diff --git a/tgt-vvp/draw_net_input.c b/tgt-vvp/draw_net_input.c
index d50eaaf38..fe0f0fc4d 100644
--- a/tgt-vvp/draw_net_input.c
+++ b/tgt-vvp/draw_net_input.c
@@ -30,6 +30,8 @@ static ivl_signal_type_t signal_type_of_nexus(ivl_nexus_t nex)
 {
       unsigned idx;
       ivl_signal_type_t out = IVL_SIT_TRI;
+      int has_tri = 0;
+      int has_uwire = 0;
 
       for (idx = 0 ;  idx < ivl_nexus_ptrs(nex) ;  idx += 1) {
 	    ivl_signal_type_t stype;
@@ -41,14 +43,29 @@ static ivl_signal_type_t signal_type_of_nexus(ivl_nexus_t nex)
 	    stype = ivl_signal_type(sig);
 	    if (stype == IVL_SIT_REG)
 		  continue;
-	    if (stype == IVL_SIT_TRI)
+	    if (stype == IVL_SIT_TRI) {
+		  has_tri = 1;
 		  continue;
+	    }
 	    if (stype == IVL_SIT_NONE)
 		  continue;
-	    if (stype == IVL_SIT_UWIRE) return IVL_SIT_UWIRE;
+	    if (stype == IVL_SIT_UWIRE) {
+		  has_uwire = 1;
+		  continue;
+	    }
 	    out = stype;
       }
 
+	/* If both TRI (wire) and UWIRE are in the nexus, return TRI
+	   because wire semantics allow multiple drivers. Only return
+	   UWIRE if no TRI signals are present. This fixes GitHub #1267
+	   where wire logic connected to uwire ports was incorrectly
+	   treated as requiring single-driver semantics.
+	   TODO: Decide how resolved net types (tri0/tri1/triand/trior)
+	         should interact with uwire in a shared nexus. */
+      if (has_uwire && !has_tri)
+	    return IVL_SIT_UWIRE;
+
       return out;
 }