From 57979136006b084411fd53bcd20e45128a154fce Mon Sep 17 00:00:00 2001
From: Yilou Wang <wangyilou123@gmail.com>
Date: Mon, 6 Jul 2026 20:14:24 +0200
Subject: [PATCH] Fix dist range bounds over rand variables failing
 randomization since #7802

---
 src/V3Randomize.cpp | 61 ++++++++++++++++++++++++++++++---------------
 1 file changed, 41 insertions(+), 20 deletions(-)

diff --git a/src/V3Randomize.cpp b/src/V3Randomize.cpp
index 2786ea305..da5d32b90 100644
--- a/src/V3Randomize.cpp
+++ b/src/V3Randomize.cpp
@@ -4571,31 +4571,47 @@ class RandomizeVisitor final : public VNVisitor {
                 continue;
             }
 
+            const auto boundRefsRandVarp = [](const AstNode* boundp) -> bool {
+                bool found = false;
+                boundp->foreach([&](const AstVarRef* vrefp) {
+                    if (vrefp->varp()->rand().isRandomizable()) found = true;
+                });
+                return found;
+            };
+
+            // (distExpr >= lo) && (distExpr <= hi); signed comparisons for signed vars
+            const auto rangeMembershipp = [&](const AstInsideRange* irp) -> AstNodeExpr* {
+                const bool isSigned = distp->exprp()->isSigned();
+                AstNodeExpr* const distExprGtep = distp->exprp()->cloneTreePure(false);
+                AstNodeExpr* const distExprLtep = distp->exprp()->cloneTreePure(false);
+                distExprGtep->user1(true);
+                distExprLtep->user1(true);
+                AstNodeExpr* const gep
+                    = isSigned
+                          ? static_cast<AstNodeExpr*>(
+                                new AstGteS{fl, distExprGtep, irp->lhsp()->cloneTreePure(false)})
+                          : static_cast<AstNodeExpr*>(
+                                new AstGte{fl, distExprGtep, irp->lhsp()->cloneTreePure(false)});
+                AstNodeExpr* const lep
+                    = isSigned
+                          ? static_cast<AstNodeExpr*>(
+                                new AstLteS{fl, distExprLtep, irp->rhsp()->cloneTreePure(false)})
+                          : static_cast<AstNodeExpr*>(
+                                new AstLte{fl, distExprLtep, irp->rhsp()->cloneTreePure(false)});
+                gep->user1(true);
+                lep->user1(true);
+                AstNodeExpr* const andp = new AstLogAnd{fl, gep, lep};
+                andp->user1(true);
+                return andp;
+            };
+
             // IEEE 1800-2023 18.5.3: values not in the distribution must never appear.
             // Build the union of all non-zero-weight ranges as a single hard ConstraintExpr
             AstNodeExpr* unionExprp = nullptr;
             for (const auto& bucket : buckets) {
                 AstNodeExpr* memberp;
                 if (const AstInsideRange* const irp = VN_CAST(bucket.rangep, InsideRange)) {
-                    // (distExpr >= lo) && (distExpr <= hi); signed comparisons for signed vars
-                    const bool isSigned = distp->exprp()->isSigned();
-                    AstNodeExpr* const distExprGtep = distp->exprp()->cloneTreePure(false);
-                    AstNodeExpr* const distExprLtep = distp->exprp()->cloneTreePure(false);
-                    distExprGtep->user1(true);
-                    distExprLtep->user1(true);
-                    AstNodeExpr* const gep
-                        = isSigned ? static_cast<AstNodeExpr*>(new AstGteS{
-                                         fl, distExprGtep, irp->lhsp()->cloneTreePure(false)})
-                                   : static_cast<AstNodeExpr*>(new AstGte{
-                                         fl, distExprGtep, irp->lhsp()->cloneTreePure(false)});
-                    AstNodeExpr* const lep
-                        = isSigned ? static_cast<AstNodeExpr*>(new AstLteS{
-                                         fl, distExprLtep, irp->rhsp()->cloneTreePure(false)})
-                                   : static_cast<AstNodeExpr*>(new AstLte{
-                                         fl, distExprLtep, irp->rhsp()->cloneTreePure(false)});
-                    gep->user1(true);
-                    lep->user1(true);
-                    memberp = new AstLogAnd{fl, gep, lep};
+                    memberp = rangeMembershipp(irp);
                 } else {
                     // distExpr == val
                     AstNodeExpr* const distExprCopyp = distp->exprp()->cloneTreePure(false);
@@ -4673,7 +4689,12 @@ class RandomizeVisitor final : public VNVisitor {
             AstNode* chainp = nullptr;
             for (int i = static_cast<int>(buckets.size()) - 1; i >= 0; --i) {
                 AstNodeExpr* constraintExprp;
-                if (const AstInsideRange* const irp = VN_CAST(buckets[i].rangep, InsideRange)) {
+                const AstInsideRange* const irp = VN_CAST(buckets[i].rangep, InsideRange);
+                if (irp && (boundRefsRandVarp(irp->lhsp()) || boundRefsRandVarp(irp->rhsp()))) {
+                    // Bounds solved concurrently cannot pin a pre-solve value; softly
+                    // prefer the symbolic range so the hard membership stays satisfiable
+                    constraintExprp = rangeMembershipp(irp);
+                } else if (irp) {
                     // Pick distExpr = lo + rand64() % (hi - lo + 1) for a uniform value in range
                     AstNodeExpr* const distExprCopyp = distp->exprp()->cloneTreePure(false);
                     distExprCopyp->user1(true);