Fix object randomization skipped by an unrelated global constraint

src/V3Randomize.cpp

@@ -3776,6 +3776,25 @@ class RandomizeVisitor final : public VNVisitor {
             return VN_IS(dtypep, ClassRefDType);
         });
     }
+    // True if this class has a constraint reaching into a sub-object (a global
+    // constraint): a member-select chain rooted at a rand class-typed handle.
+    // Such a class basic-randomizes first and lets the solver override the
+    // constrained leaves afterwards, so a leaf shared with a standalone
+    // randomize() of the sub-object's type is still basic-randomized there.
+    bool classOwnsGlobalConstraint(AstClass* classp) {
+        return classp->existsMember([](const AstClass*, const AstConstraint* constrp) {
+            bool owns = false;
+            constrp->foreach([&](const AstMemberSel* memberSelp) {
+                const AstNode* rootp = memberSelp->fromp();
+                while (const AstMemberSel* const sp = VN_CAST(rootp, MemberSel))
+                    rootp = sp->fromp();
+                if (const AstVarRef* const refp = VN_CAST(rootp, VarRef)) {
+                    if (VN_IS(refp->varp()->dtypep()->skipRefp(), ClassRefDType)) owns = true;
+                }
+            });
+            return owns;
+        });
+    }
     // Get or create __VrandCb_pre/__VrandCb_post task for nested callbacks
     AstTask* getCreateNestedCallbackTask(AstClass* classp, const string& suffix) {
         const string name = "__VrandCb_" + suffix;
@@ -4561,6 +4580,10 @@ class RandomizeVisitor final : public VNVisitor {
         UINFO(9, "Define randomize() for " << nodep);
         nodep->baseMostClassp()->needRNG(true);
 
+        // Detect global-constraint ownership BEFORE the constraint items are
+        // unlinked into setup tasks below (after that the member-selects are gone).
+        const bool basicFirst = classOwnsGlobalConstraint(nodep);
+
         FileLine* fl = nodep->fileline();
         AstFunc* const randomizep = V3Randomize::newRandomizeFunc(m_memberMap, nodep);
         AstVar* const fvarp = VN_AS(randomizep->fvarp(), Var);
@@ -4857,8 +4880,20 @@ class RandomizeVisitor final : public VNVisitor {
             beginValp = new AstConst{fl, AstConst::WidthedValue{}, 32, 1};
         }
 
+        AstFunc* const basicRandomizep
+            = V3Randomize::newRandomizeFunc(m_memberMap, nodep, BASIC_RANDOMIZE_FUNC_NAME);
+        addBasicRandomizeBody(basicRandomizep, nodep, randModeVarp);
+        // A class that owns a global constraint (basicFirst, detected above)
+        // basic-randomizes FIRST and lets the solver override the constrained
+        // leaves afterwards.  This way a leaf that is only globally constrained
+        // (not user3) is still basic-randomized when its type is randomized
+        // standalone, while the owner's solver result wins.  This assumes such an
+        // owner has no size-constrained arrays of its own (needsSizePhase): a
+        // global constraint cannot reach an array element, so the two are mutually
+        // exclusive today and basic randomization stays before the solver.
         AstVarRef* const fvarRefp = new AstVarRef{fl, fvarp, VAccess::WRITE};
-        randomizep->addStmtsp(new AstAssign{fl, fvarRefp, beginValp});
+        randomizep->addStmtsp(new AstAssign{
+            fl, fvarRefp, basicFirst ? new AstFuncRef{fl, basicRandomizep} : beginValp});
 
         const auto sizeArraysIt = m_sizeConstrainedArrays.find(nodep);
         const bool needsSizePhase
@@ -4874,12 +4909,10 @@ class RandomizeVisitor final : public VNVisitor {
         AstVarRef* const fvarRefReadp = fvarRefp->cloneTree(false);
         fvarRefReadp->access(VAccess::READ);
 
-        AstFunc* const basicRandomizep
-            = V3Randomize::newRandomizeFunc(m_memberMap, nodep, BASIC_RANDOMIZE_FUNC_NAME);
-        addBasicRandomizeBody(basicRandomizep, nodep, randModeVarp);
-        AstFuncRef* const basicRandomizeCallp = new AstFuncRef{fl, basicRandomizep};
+        AstNodeExpr* const secondHalfp
+            = basicFirst ? beginValp : new AstFuncRef{fl, basicRandomizep};
         randomizep->addStmtsp(new AstAssign{fl, fvarRefp->cloneTree(false),
-                                            new AstAnd{fl, fvarRefReadp, basicRandomizeCallp}});
+                                            new AstAnd{fl, fvarRefReadp, secondHalfp}});
 
         // Call nested post_randomize on rand class-type members (IEEE 18.4.1)
         if (classHasRandClassMembers(nodep)) {
@@ -5405,15 +5438,30 @@ public:
     explicit RandomizeVisitor(AstNetlist* nodep)
         : m_inlineUniqueNames{"__Vrandwith"} {
         createRandomizeClassVars(nodep);
-        // Mark variables in global constraints
-        // These should not be randomized in nested class's __VBasicRand
-        nodep->foreach([&](AstConstraint* constrp) {
-            constrp->foreach([&](AstMemberSel* memberSelp) {
-                // Only mark if this MemberSel was created during constraint cloning
-                if (memberSelp->user2p()) {
+        // Mark variables solved by a global constraint so the owning class's
+        // __VBasicRand does not also randomize them.  This must run before any
+        // class is lowered, otherwise a constrained variable whose class is
+        // lowered before its constraint's owner would be basic-randomized too.
+        // Only constraints whose enclosing class is actually randomized count: a
+        // constraint living in a class that is never randomized through this
+        // object must not flag a shared rand variable, or a standalone
+        // randomize() of the sub-object's type stops randomizing it (issue
+        // #7833).  And only the leaf data field is solved -- an intermediate
+        // class-typed sub-object must still be basic-randomized so its own
+        // unconstrained members are randomized.
+        nodep->foreach([&](AstClass* const classp) {
+            if (!classp->user1()) return;
+            classp->foreachMember([&](AstClass* const ownerClassp, AstConstraint* const constrp) {
+                constrp->foreach([&](AstMemberSel* const memberSelp) {
                     AstVar* const varp = memberSelp->varp();
+                    if (VN_IS(varp->dtypep()->skipRefp(), ClassRefDType)) return;
+                    // Only a LOCAL constraint (leaf owned by the constraint's own
+                    // class) flags the leaf as solver-owned.  A leaf reached through
+                    // a global constraint is left to basic randomization; the owning
+                    // class basic-randomizes first and the solver overrides it.
+                    if (VN_AS(varp->user2p(), NodeModule) != ownerClassp) return;
                     if (!varp->user3()) varp->user3(true);
-                }
+                });
             });
         });
 

test_regress/t/t_constraint_global_subobj_combined.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_subobj_combined.v

@@ -0,0 +1,81 @@
+// 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
+
+class C;
+  rand int x;
+  rand int y;
+endclass
+
+class B;
+  rand C c;
+  function new();
+    c = new();
+  endfunction
+endclass
+
+class A;
+  rand B b;
+  constraint c_foo {b.c.x == 123;}
+  function new();
+    b = new();
+  endfunction
+endclass
+
+module t_constraint_global_subobj_combined;
+  B b;
+  A a;
+  int px, py;
+  bit xvar, yvar;
+
+  initial begin
+    // Same compilation randomizes BOTH the sub-object holder B standalone AND the
+    // global-constraint owner A.  A leaf (C::x) is therefore solver-owned for A
+    // but must be freely randomized for B; both have to work at once (issue
+    // #7833).
+    b = new();
+    if (b.randomize() != 1) $stop;
+    px = b.c.x;
+    py = b.c.y;
+    xvar = 0;
+    yvar = 0;
+    for (int i = 0; i < 20; i++) begin
+      if (b.randomize() != 1) $stop;
+      if (b.c.x != px) xvar = 1;
+      if (b.c.y != py) yvar = 1;
+      px = b.c.x;
+      py = b.c.y;
+    end
+    if (!xvar) begin
+      $display("ERROR: standalone b.c.x not randomized (stuck)");
+      $stop;
+    end
+    if (!yvar) begin
+      $display("ERROR: standalone b.c.y not randomized (stuck)");
+      $stop;
+    end
+
+    a = new();
+    if (a.randomize() != 1) $stop;
+    py = a.b.c.y;
+    yvar = 0;
+    for (int i = 0; i < 20; i++) begin
+      if (a.randomize() != 1) $stop;
+      if (a.b.c.x != 123) begin
+        $display("ERROR: global constraint b.c.x == 123 not applied, got %0d", a.b.c.x);
+        $stop;
+      end
+      if (a.b.c.y != py) yvar = 1;
+      py = a.b.c.y;
+    end
+    if (!yvar) begin
+      $display("ERROR: a.b.c.y not randomized (stuck)");
+      $stop;
+    end
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule

test_regress/t/t_constraint_global_subobj_standalone.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_subobj_standalone.v

@@ -0,0 +1,63 @@
+// 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
+
+class C;
+  rand int x;
+  rand int y;
+endclass
+
+class B;
+  rand C c;
+  function new();
+    c = new();
+  endfunction
+endclass
+
+class A;
+  rand B b;
+  constraint c_foo {b.c.x == 123;}
+  function new();
+    b = new();
+  endfunction
+endclass
+
+module t_constraint_global_subobj_standalone;
+  B b;
+  int px, py;
+  bit xvar, yvar;
+
+  initial begin
+    // Issue #7833: a standalone randomize() of B must randomize the nested
+    // sub-object fields c.x and c.y.  Class A holds a global constraint that
+    // references type C through b.c.x, which used to flag C's fields as solved
+    // and skip them in B's basic randomization even though A is never
+    // randomized here.
+    b = new();
+    if (b.randomize() != 1) $stop;
+    px = b.c.x;
+    py = b.c.y;
+    xvar = 0;
+    yvar = 0;
+    for (int i = 0; i < 20; i++) begin
+      if (b.randomize() != 1) $stop;
+      if (b.c.x != px) xvar = 1;
+      if (b.c.y != py) yvar = 1;
+      px = b.c.x;
+      py = b.c.y;
+    end
+    if (!xvar) begin
+      $display("ERROR: b.c.x not randomized (stuck)");
+      $stop;
+    end
+    if (!yvar) begin
+      $display("ERROR: b.c.y not randomized (stuck)");
+      $stop;
+    end
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule