From f2e05bc0b7b744e401c0cd1f9c9b59849f6d5f3f Mon Sep 17 00:00:00 2001
From: Jonathan Drolet <jonathan.drolet@gmail.com>
Date: Thu, 27 Nov 2025 14:17:18 -0500
Subject: [PATCH] Support unpacked struct in localparam (#6053 partial) (#6708)

---
 src/V3Const.cpp                           | 32 ++++++++++++
 test_regress/t/t_struct_unpacked_param.py | 18 +++++++
 test_regress/t/t_struct_unpacked_param.v  | 59 +++++++++++++++++++++++
 3 files changed, 109 insertions(+)
 create mode 100755 test_regress/t/t_struct_unpacked_param.py
 create mode 100644 test_regress/t/t_struct_unpacked_param.v

diff --git a/src/V3Const.cpp b/src/V3Const.cpp
index bb0d69434..a058746d1 100644
--- a/src/V3Const.cpp
+++ b/src/V3Const.cpp
@@ -2931,6 +2931,31 @@ class ConstVisitor final : public VNVisitor {
         replaceWithSimulation(nodep);
     }
 
+    void visit(AstStructSel* nodep) override {
+        iterateChildren(nodep);
+
+        if (VN_IS(nodep->fromp(), ConsPackUOrStruct)) {
+            const AstConsPackUOrStruct* const consp = VN_AS(nodep->fromp(), ConsPackUOrStruct);
+            for (AstConsPackMember* memberp = consp->membersp(); memberp;
+                 memberp = VN_AS(memberp->nextp(), ConsPackMember)) {
+
+                if (memberp->dtypep() && memberp->dtypep()->name() == nodep->name()) {
+                    AstNode* const valuep = memberp->rhsp();
+
+                    if (VN_IS(valuep, Const)) {
+                        const V3Number& num = VN_AS(valuep, Const)->num();
+                        VL_DO_DANGLING(replaceNum(nodep, num), nodep);
+                    } else {
+                        AstNode* const newp = valuep->cloneTree(false);
+                        nodep->replaceWith(newp);
+                        VL_DO_DANGLING(pushDeletep(nodep), nodep);
+                    }
+                    break;
+                }
+            }
+        }
+    }
+
     void visit(AstCAwait* nodep) override {
         m_hasJumpDelay = true;
         iterateChildren(nodep);
@@ -2976,6 +3001,11 @@ class ConstVisitor final : public VNVisitor {
                     nodep->replaceWithKeepDType(newp);
                     VL_DO_DANGLING(pushDeletep(nodep), nodep);
                     did = true;
+                } else if (m_params && VN_IS(valuep, ConsPackUOrStruct)) {
+                    AstNode* const newp = valuep->cloneTree(false);
+                    nodep->replaceWithKeepDType(newp);
+                    VL_DO_DANGLING(pushDeletep(nodep), nodep);
+                    did = true;
                 } else if (nodep->varp()->isParam() && VN_IS(valuep, Unbounded)) {
                     AstNode* const newp = valuep->cloneTree(false);
                     nodep->replaceWithKeepDType(newp);
@@ -3654,6 +3684,8 @@ class ConstVisitor final : public VNVisitor {
     }
 
     void visit(AstInitArray* nodep) override { iterateChildren(nodep); }
+    void visit(AstConsPackUOrStruct* nodep) override { iterateChildren(nodep); }
+    void visit(AstConsPackMember* nodep) override { iterateChildren(nodep); }
     void visit(AstInitItem* nodep) override { iterateChildren(nodep); }
     void visit(AstUnbounded* nodep) override { iterateChildren(nodep); }
     // These are converted by V3Param.  Don't constify as we don't want the
diff --git a/test_regress/t/t_struct_unpacked_param.py b/test_regress/t/t_struct_unpacked_param.py
new file mode 100755
index 000000000..c39e83d77
--- /dev/null
+++ b/test_regress/t/t_struct_unpacked_param.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios("simulator")
+
+test.compile()
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_struct_unpacked_param.v b/test_regress/t/t_struct_unpacked_param.v
new file mode 100644
index 000000000..634f3bc1b
--- /dev/null
+++ b/test_regress/t/t_struct_unpacked_param.v
@@ -0,0 +1,59 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2025 by Jonathan Drolet.
+// SPDX-License-Identifier: CC0-1.0
+
+// verilog_format: off
+`define stop $stop
+`define checkd(gotv, expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0d exp=%0d\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0);
+// verilog_format: on
+
+module t;
+
+  typedef struct {
+    int a;
+    int b;
+    int c;
+  } subsubstruct_t;
+
+  typedef struct {
+    int a;
+    int b;
+    subsubstruct_t subsub;
+    int c;
+  } substruct_t;
+
+  typedef substruct_t substruct_t_t;
+
+  typedef struct {
+    int a;
+    int b;
+    substruct_t_t sub;
+    int c;
+  } struct_t;
+
+  // Constant value unpacked struct support is limited at the moment.
+  // Only localparams are supported, returning constant unpacked structure
+  // from function or passing unpacked structure as parameters is not
+  // (yet) supported
+  localparam struct_t MY_STRUCT = '{a: 10, b: 5, c: 20, sub: '{a: 100, b: 200, c: 150, subsub: '{default: 10}}};
+
+  // Make standalone localparam to ensure MY_STRUCT is const
+  localparam int C = MY_STRUCT.c;
+  localparam int S_A = MY_STRUCT.sub.a;
+  localparam int SS_B = MY_STRUCT.sub.subsub.b;
+
+  initial begin
+    `checkd(MY_STRUCT.a, 10);
+    `checkd(MY_STRUCT.b, 5);
+    `checkd(MY_STRUCT.c, 20);
+    `checkd(MY_STRUCT.sub.c, 150);
+    `checkd(C, 20);
+    `checkd(S_A, 100);
+    `checkd(SS_B, 10);
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+
+endmodule