Account node purity when checking if dynamic trigger is needed

src/V3Timing.cpp

@@ -578,8 +578,11 @@ class TimingControlVisitor final : public VNVisitor {
     // Returns true if we are under a class or the given tree has any references to locals. These
     // are cases where static, globally-evaluated triggers are not suitable.
     bool needDynamicTrigger(AstNode* const nodep) const {
-        return m_classp || nodep->exists([](const AstNodeVarRef* const refp) {
-            return refp->varp()->isFuncLocal();
+        return m_classp || nodep->exists([](AstNode* const nodep) {
+            if (AstNodeVarRef *varp = VN_CAST(nodep, NodeVarRef)) {
+                return varp->varp()->isFuncLocal();
+            }
+            return !nodep->isPure();
         });
     }
     // Returns true if the given trigger expression needs a destructive post update after trigger