Fix soft cross-object constraint priority inversion (#7228) (#7233)

Emit nested constraint setup tasks in depth-first order (deepest first)
so outer-scope soft constraints get higher priority per IEEE 18.5.13.

src/V3Randomize.cpp

@@ -3959,18 +3959,14 @@ class RandomizeVisitor final : public VNVisitor {
         AstNodeExpr* beginValp = nullptr;
         AstVar* genp = getRandomGenerator(nodep);
         if (genp) {
+            // Phase 1: Process all constraints (create tasks, run ConstraintExprVisitor)
+            // Setup task refs are NOT added to setupAllTaskp here -- done in phase 2
             nodep->foreachMember([&](AstClass* const classp, AstConstraint* const constrp) {
                 AstTask* taskp = VN_AS(constrp->user2p(), Task);
                 if (!taskp) {
                     taskp = newSetupConstraintTask(classp, constrp->name());
                     constrp->user2p(taskp);
                 }
-                AstTaskRef* const setupTaskRefp = new AstTaskRef{constrp->fileline(), taskp};
-                setupTaskRefp->classOrPackagep(classp);
-
-                AstTask* const setupAllTaskp = getCreateConstraintSetupFunc(nodep);
-
-                setupAllTaskp->addStmtsp(setupTaskRefp->makeStmt());
 
                 if (AstTask* const resizeTaskp = VN_CAST(constrp->user3p(), Task)) {
                     AstTask* const resizeAllTaskp = getCreateAggrResizeTask(nodep);
@@ -3989,6 +3985,38 @@ class RandomizeVisitor final : public VNVisitor {
                         nodep, constrp, constrp->itemsp()->unlinkFrBackWithNext()));
                 }
             });
+
+            // Phase 2: Add setup task refs in depth order (deepest first = lowest priority)
+            // Ensures outer-scope soft constraints override inner-scope (IEEE 18.5.13)
+            {
+                // Count nesting depth by GLOBAL_CONSTRAINT_SEPARATOR occurrences
+                const auto constraintDepth = [](const AstConstraint* constrp) {
+                    int depth = 0;
+                    size_t pos = 0;
+                    while ((pos = constrp->name().find(GLOBAL_CONSTRAINT_SEPARATOR, pos))
+                           != std::string::npos) {
+                        ++depth;
+                        pos += std::strlen(GLOBAL_CONSTRAINT_SEPARATOR);
+                    }
+                    return depth;
+                };
+                int maxDepth = 0;
+                nodep->foreachMember([&](AstClass* const, AstConstraint* const constrp) {
+                    maxDepth = std::max(maxDepth, constraintDepth(constrp));
+                });
+                AstTask* const setupAllTaskp = getCreateConstraintSetupFunc(nodep);
+                for (int d = maxDepth; d >= 0; --d) {
+                    nodep->foreachMember(
+                        [&](AstClass* const classp, AstConstraint* const constrp) {
+                            if (constraintDepth(constrp) != d) return;
+                            AstTask* const taskp = VN_AS(constrp->user2p(), Task);
+                            AstTaskRef* const setupTaskRefp
+                                = new AstTaskRef{constrp->fileline(), taskp};
+                            setupTaskRefp->classOrPackagep(classp);
+                            setupAllTaskp->addStmtsp(setupTaskRefp->makeStmt());
+                        });
+                }
+            }
             // For derived classes: clone write_var calls from parent's randomize()
             if (nodep->extendsp()) {
                 AstClass* parentClassp = nodep->extendsp()->classp();

test_regress/t/t_randomize_soft_cross_object.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_randomize_soft_cross_object.v

@@ -0,0 +1,68 @@
+// 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
+`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
+
+// Test: Soft cross-object constraints should respect IEEE 1800-2023 18.5.13
+// outer-scope soft has higher priority than inner-scope soft.
+
+class sub_cfg_c;
+  rand int unsigned timeout;
+  rand bit enabled;
+  constraint soft_defaults {
+    soft timeout == 1000;
+    soft enabled == 0;
+  }
+endclass
+
+class parent_cfg_c;
+  rand bit enabled;
+  rand sub_cfg_c sub_a;
+  constraint soft_defaults { soft enabled == 0; }
+  constraint propagate_cons {
+    if (enabled) { sub_a.enabled == 1; }
+  }
+  function new();
+    sub_a = new();
+  endfunction
+endclass
+
+class top_test_c;
+  rand parent_cfg_c cfg;
+  rand sub_cfg_c extra_cfg;
+  constraint cfg_hard_cons { cfg.enabled == 1; }
+  constraint cfg_soft_cons {
+    soft cfg.sub_a.timeout == 5000;
+    soft extra_cfg.timeout == 9999;
+    soft extra_cfg.enabled == 1;
+  }
+  function new();
+    cfg = new();
+    extra_cfg = new();
+  endfunction
+endclass
+
+module t;
+  initial begin
+    static top_test_c obj = new();
+    repeat (10) begin
+      `checkd(obj.randomize(), 1)
+      // Two-level cross-object soft: parent's soft overrides child's
+      `checkd(obj.cfg.sub_a.timeout, 32'd5000)
+      // One-level cross-object soft: parent's soft overrides child's
+      `checkd(obj.extra_cfg.timeout, 32'd9999)
+      `checkd(obj.extra_cfg.enabled, 1'b1)
+      // Hard constraint propagation still works
+      `checkd(obj.cfg.enabled, 1'b1)
+      `checkd(obj.cfg.sub_a.enabled, 1'b1)
+    end
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule