Fix NBAs to unpacked arrays of unpacked structs

This happened to work before verilator#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 verilator#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?

test_regress/t/t_nba_struct_array.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 by Wilson Snyder. 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-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile()
+
+test.execute(check_finished=True)
+
+test.passes()

test_regress/t/t_nba_struct_array.v

@@ -0,0 +1,93 @@
+
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2024 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+`define stop $stop
+`define checkh(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got='h%x exp='h%x\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0)
+
+module t(clk);
+  input clk;
+
+  logic [31:0] cyc = 0;
+  always @(posedge clk) begin
+    cyc <= cyc + 1;
+    if (cyc == 99) begin
+      $write("*-* All Finished *-*\n");
+      $finish;
+    end
+  end
+
+`define at_posedge_clk_on_cycle(n) always @(posedge clk) if (cyc == n)
+
+  struct {
+    int foo;
+    int bar;
+  } arr [2];
+
+  initial begin
+    arr[0].foo = 0;
+    arr[0].bar = 100;
+    arr[1].foo = 0;
+    arr[1].bar = 100;
+  end
+
+  `at_posedge_clk_on_cycle(0) begin
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo, 0);
+      `checkh(arr[i].bar, 100);
+    end
+  end
+  `at_posedge_clk_on_cycle(1) begin
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo, 0);
+      `checkh(arr[i].bar, 100);
+    end
+    arr[0].foo <=  0;
+    arr[0].bar <= -0;
+    arr[1].foo <=  1;
+    arr[1].bar <= -1;
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo, 0);
+      `checkh(arr[i].bar, 100);
+    end
+  end
+  `at_posedge_clk_on_cycle(2) begin
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo,  i);
+      `checkh(arr[i].bar, -i);
+    end
+    arr[0].foo <= ~0;
+    arr[0].bar <=  0;
+    arr[1].foo <= ~1;
+    arr[1].bar <=  1;
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo,  i);
+      `checkh(arr[i].bar, -i);
+    end
+  end
+  `at_posedge_clk_on_cycle(3) begin
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo, ~i);
+      `checkh(arr[i].bar,  i);
+    end
+    arr[0].foo <= -1;
+    arr[0].bar <= -2;
+    arr[1].foo <= -1;
+    arr[1].bar <= -2;
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo, ~i);
+      `checkh(arr[i].bar,  i);
+    end
+  end
+  `at_posedge_clk_on_cycle(4) begin
+    for (int i = 0; i < 2; ++i) begin
+      `checkh(arr[i].foo, -1);
+      `checkh(arr[i].bar, -2);
+    end
+  end
+
+
+endmodule