Fix NBAs to unpacked arrays of unpacked structs (#5603)

This happened to work before #5516, by creating a whole shadow copy of
the entire array. Revert back to that behaviour for now, it will be
slow, but works still.

Fixes #5590

src/V3Delayed.cpp

@@ -251,10 +251,11 @@ class DelayedVisitor final : public VNVisitor {
         const AstNodeDType* const dtypep = vscp->dtypep()->skipRefp();
         // Unpacked arrays
         if (const AstUnpackArrayDType* const uaDTypep = VN_CAST(dtypep, UnpackArrayDType)) {
+            // Basic underlying type of elements, if any.
+            AstBasicDType* const basicp = uaDTypep->basicp();
             // If used in a loop, we must have a dynamic commit queue. (Also works in suspendables)
             if (vscpInfo.m_inLoop) {
                 // Arrays with compound element types are currently not supported in loops
-                AstBasicDType* const basicp = uaDTypep->basicp();
                 if (!basicp
                     || !(basicp->isIntegralOrPacked()  //
                          || basicp->isDouble()  //
@@ -266,8 +267,12 @@ class DelayedVisitor final : public VNVisitor {
             }
             // In a suspendable of fork, we must use the unique flag scheme, TODO: why?
             if (vscpInfo.m_inSuspOrFork) return Scheme::FlagUnique;
-            // Otherwise use the shared flag scheme
-            return Scheme::FlagShared;
+            // Otherwise if an array of packed/basic elements, use the shared flag scheme
+            if (basicp) return Scheme::FlagShared;
+            // Finally fall back on the shadow variable scheme, e.g. for
+            // arrays of unpacked structs. This will be slow.
+            // TODO: generic LHS scheme as discussed in #5092
+            return Scheme::ShadowVar;
         }
 
         // In a suspendable of fork, we must use the unique flag scheme, TODO: why?