fix rand_mode subobj case

src/V3Randomize.cpp

@@ -742,6 +742,17 @@ class ConstraintExprVisitor final : public VNVisitor {
                                            // (shared across all constraints)
     std::set<AstVar*>* m_sizeConstrainedArraysp = nullptr;  // Arrays with size+element constraints
 
+    // Walk extends chain to find __Vrandmode variable (user2p on AstClass)
+    static AstVar* findRandModeVar(AstNodeModule* classp) {
+        while (classp) {
+            if (classp->user2p()) return VN_AS(classp->user2p(), Var);
+            AstClass* const cp = VN_CAST(classp, Class);
+            if (!cp || !cp->extendsp()) return nullptr;
+            classp = cp->extendsp()->classp();
+        }
+        return nullptr;
+    }
+
     // Build full path for a MemberSel chain (e.g., "obj.l2.l3.l4")
     std::string buildMemberPath(const AstMemberSel* const memberSelp) {
         const AstNode* fromp = memberSelp->fromp();
@@ -1085,7 +1096,7 @@ class ConstraintExprVisitor final : public VNVisitor {
             AstNodeExpr* randModeAccess;
             if (membersel) {
                 AstNodeModule* const varClassp = VN_AS(varp->user2p(), NodeModule);
-                AstVar* const effectiveRandModeVarp = VN_AS(varClassp->user2p(), Var);
+                AstVar* const effectiveRandModeVarp = findRandModeVar(varClassp);
                 if (effectiveRandModeVarp) {
                     // Member's class has randmode, use it
                     AstNodeExpr* parentAccess = membersel->fromp()->cloneTree(false);
@@ -1353,7 +1364,7 @@ class ConstraintExprVisitor final : public VNVisitor {
                 initTaskp->addStmtsp(methodp->makeStmt());
                 if (isGlobalConstrained && membersel && randMode.usesMode) {
                     AstNodeModule* const varClassp = VN_AS(varp->user2p(), NodeModule);
-                    AstVar* const subRandModeVarp = VN_AS(varClassp->user2p(), Var);
+                    AstVar* const subRandModeVarp = findRandModeVar(varClassp);
                     if (subRandModeVarp) {
                         AstNodeExpr* const parentAccess = membersel->fromp()->cloneTree(false);
                         AstMemberSel* const randModeSel

test_regress/t/t_constraint_global_randmode_subobj.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# 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-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+if not test.have_solver:
+    test.skip("No constraint solver installed")
+
+test.compile()
+
+test.execute()
+
+test.passes()

test_regress/t/t_constraint_global_randmode_subobj.v

@@ -0,0 +1,116 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2026 PlanV GmbH
+// SPDX-License-Identifier: CC0-1.0
+// verilog_format: off
+
+typedef logic [31:0] uvm_reg_data_t;
+
+class uvm_object;
+endclass
+
+class uvm_reg_field extends uvm_object;
+  rand uvm_reg_data_t value;
+  int unsigned m_size;
+
+  function uvm_reg_data_t get;
+    return value;
+  endfunction
+
+  function void set_rand_mode(bit rand_mode);
+    value.rand_mode(rand_mode);
+    uvm_reg_field_valid.constraint_mode(rand_mode);
+  endfunction
+
+  function bit get_rand_mode();
+    return bit'(value.rand_mode());
+  endfunction
+
+  constraint uvm_reg_field_valid {
+    if (64'd64 > {32'd0, m_size}) {
+      {32'd0, value} < (64'd1 << m_size);
+    }
+  }
+
+  function void configure(int unsigned size);
+    m_size = size;
+  endfunction
+endclass
+
+class uvm_reg extends uvm_object;
+  virtual function void build();
+  endfunction
+endclass
+
+class regA extends uvm_reg;
+  rand uvm_reg_field fA1;
+  rand uvm_reg_field fA2;
+
+  virtual function void build();
+    this.fA1 = new;
+    this.fA2 = new;
+    this.fA1.configure(16);
+    this.fA2.configure(16);
+  endfunction
+endclass
+
+class test extends uvm_object;
+  regA rg;
+
+  function new;
+    rg = new;
+    rg.build();
+  endfunction
+
+  task run_test;
+    uvm_reg_data_t pre_fA1;
+    uvm_reg_data_t pre_fA2;
+    int rand_ok;
+
+    // Disable fA1, enable fA2
+    rg.fA1.set_rand_mode(0);
+    rg.fA2.set_rand_mode(1);
+
+    if (rg.fA1.get_rand_mode() != 0) $stop;
+    if (rg.fA2.get_rand_mode() != 1) $stop;
+
+    pre_fA1 = rg.fA1.value;
+
+    rand_ok = rg.randomize();
+    if (rand_ok != 0) begin
+      // fA1 should be unchanged
+      if (rg.fA1.get() !== pre_fA1) begin
+        $display("%%Error: fA1 changed: got=%0h exp=%0h", rg.fA1.get(), pre_fA1);
+        $stop;
+      end
+    end
+
+    // Re-enable fA1, disable fA2
+    rg.fA1.set_rand_mode(1);
+    rg.fA2.set_rand_mode(0);
+
+    pre_fA2 = rg.fA2.value;
+
+    rand_ok = rg.randomize();
+    if (rand_ok != 0) begin
+      // fA2 should be unchanged
+      if (rg.fA2.get() !== pre_fA2) begin
+        $display("%%Error: fA2 changed: got=%0h exp=%0h", rg.fA2.get(), pre_fA2);
+        $stop;
+      end
+    end
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  endtask
+
+endclass
+
+module top;
+  initial begin
+    test t;
+    t = new;
+    t.run_test();
+  end
+endmodule