Support this.randomize() with constraints (#6634)

src/V3Randomize.cpp

@@ -914,7 +914,22 @@ class ConstraintExprVisitor final : public VNVisitor {
         if (nodep->user1()) {
             nodep->v3warn(CONSTRAINTIGN, "Global constraints ignored (unsupported)");
         }
-        editFormat(nodep);
+        // Handle MemberSel references created by captureRefByThis()
+        if (VN_IS(nodep->fromp(), VarRef)
+            && nodep->fromp()->user1()  // Depending on a randomized variable
+            && nodep->user2p()  // Pointer to containing module
+            && VN_AS(nodep->user2p(), NodeModule) == nodep->varp()->user2p()) {
+            // Convert to VarRef
+            AstVarRef* const varRefp
+                = new AstVarRef{nodep->fileline(), nodep->varp(), VAccess::READ};
+            varRefp->user1(nodep->varp()->rand().isRandomizable());
+            varRefp->classOrPackagep(VN_AS(nodep->user2p(), NodeModule));
+            nodep->replaceWith(varRefp);
+            VL_DO_DANGLING(pushDeletep(nodep), nodep);
+            visit(varRefp);
+        } else {
+            editFormat(nodep);
+        }
     }
     void visit(AstSFormatF* nodep) override {}
     void visit(AstStmtExpr* nodep) override {}

test_regress/t/t_randomize_this_with.py

@@ -0,0 +1,21 @@
+#!/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
+
+if not test.have_solver:
+    test.skip("No constraint solver installed")
+
+test.scenarios('simulator')
+
+test.compile()
+
+test.execute()
+
+test.passes()

test_regress/t/t_randomize_this_with.v

@@ -0,0 +1,28 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Antmicro.
+// SPDX-License-Identifier: CC0-1.0
+
+`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);
+
+class Cls;
+  rand int v_rand;
+  int v_norand;
+  task body;
+    int x;
+    v_norand = 42;
+    x = this.randomize() with {v_rand==0;};
+    `checkd(v_rand, 0);
+    `checkd(v_norand, 42);
+  endtask
+endclass
+
+module t;
+  initial begin
+    Cls c = new;
+    c.body();
+    $finish;
+  end
+endmodule