From 878204db73d67b5e6a6ec5f583019c8ba3c85a45 Mon Sep 17 00:00:00 2001
From: Geza Lore <gezalore@gmail.com>
Date: Sat, 16 Mar 2024 10:35:56 +0000
Subject: [PATCH] Do not feed any empty logic into scheduling (#4972)

---
 src/V3ActiveTop.cpp       | 15 +++++++++++++++
 src/V3OrderCFuncEmitter.h |  3 ++-
 src/V3Sched.cpp           |  9 +--------
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/src/V3ActiveTop.cpp b/src/V3ActiveTop.cpp
index 2f4e63bd6..de1f11d43 100644
--- a/src/V3ActiveTop.cpp
+++ b/src/V3ActiveTop.cpp
@@ -77,6 +77,21 @@ class ActiveTopVisitor final : public VNVisitor {
             VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
             return;
         }
+
+        // Delete empty procedures
+        for (AstNode *stmtp = nodep->stmtsp(), *nextp; stmtp; stmtp = nextp) {
+            nextp = stmtp->nextp();
+            if (AstNodeProcedure* const procp = VN_CAST(stmtp, NodeProcedure)) {
+                if (!procp->stmtsp()) VL_DO_DANGLING(pushDeletep(procp->unlinkFrBack()), stmtp);
+            }
+        }
+
+        // Delete empty actives
+        if (!nodep->stmtsp()) {
+            VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
+            return;
+        }
+
         // Move the SENTREE for each active up to the global level.
         // This way we'll easily see what clock domains are identical
         AstSenTree* const wantp = m_finder.getSenTree(sensesp);
diff --git a/src/V3OrderCFuncEmitter.h b/src/V3OrderCFuncEmitter.h
index ed0c0d4db..37cda41f3 100644
--- a/src/V3OrderCFuncEmitter.h
+++ b/src/V3OrderCFuncEmitter.h
@@ -116,7 +116,8 @@ public:
         AstNode* const headp = [&]() -> AstNode* {
             if (!procp) return logicp;  // Not a procedure, handle as a unit
             AstNode* const stmtsp = procp->stmtsp();
-            if (stmtsp) stmtsp->unlinkFrBackWithNext();
+            UASSERT_OBJ(stmtsp, procp, "Empty process should have been deleted earlier");
+            stmtsp->unlinkFrBackWithNext();
             // Procedure is no longer needed and can be deleted right now
             VL_DO_DANGLING(procp->deleteTree(), procp);
             return stmtsp;
diff --git a/src/V3Sched.cpp b/src/V3Sched.cpp
index 5e471ce8d..b00c68d34 100644
--- a/src/V3Sched.cpp
+++ b/src/V3Sched.cpp
@@ -355,14 +355,9 @@ LogicClasses gatherLogicClasses(AstNetlist* netlistp) {
     LogicClasses result;
 
     netlistp->foreach([&](AstScope* scopep) {
-        std::vector<AstActive*> empty;
-
         scopep->foreach([&](AstActive* activep) {
             AstSenTree* const senTreep = activep->sensesp();
-            if (!activep->stmtsp()) {
-                // Some AstActives might be empty due to previous optimizations
-                empty.push_back(activep);
-            } else if (senTreep->hasStatic()) {
+            if (senTreep->hasStatic()) {
                 UASSERT_OBJ(!senTreep->sensesp()->nextp(), activep,
                             "static initializer with additional sensitivities");
                 result.m_static.emplace_back(scopep, activep);
@@ -393,8 +388,6 @@ LogicClasses gatherLogicClasses(AstNetlist* netlistp) {
                 }
             }
         });
-
-        for (AstActive* const activep : empty) activep->unlinkFrBack()->deleteTree();
     });
 
     return result;