Support FST tracing in hierarchical verilation (#3251)

* Rename t_hier_block_trace -> t_hier_block_trace_vcd

* Add t_hir_block_trace_fst test

* Support FST dump with hierarchical verilation

src/V3ProtectLib.cpp

@@ -410,9 +410,9 @@ private:
                                   + "_protectlib_trace(void* vhandlep__V, void* tfp, int levels, "
                                     "int options) {\n");
             castPtr(fl, txtp);
-            txtp->addText(
-                fl,
-                /**/ "handlep__V->trace(static_cast<VerilatedVcdC*>(tfp), levels, options);\n");
+            txtp->addText(fl,
+                          /**/ "handlep__V->trace(static_cast<" + v3Global.opt.traceClassBase()
+                              + "C*>(tfp), levels, options);\n");
             txtp->addText(fl, "}\n\n");
         }
 

test_regress/t/t_hier_block_trace_fst.pl

@@ -0,0 +1,35 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+scenarios(vlt_all => 1);
+
+top_filename("t/t_hier_block.v");
+
+# CI environment offers 2 VCPUs, 2 thread setting causes the following warning.
+# %Warning-UNOPTTHREADS: Thread scheduler is unable to provide requested parallelism; consider asking for fewer threads.
+# So use 6 threads here though it's not optimal in performace wise, but ok.
+
+compile(
+    v_flags2 => ['t/t_hier_block.cpp'],
+    verilator_flags2 => [($Self->{vltmt} ? ' --threads 6' : ''),
+                         '--hierarchical',
+                         '--Wno-TIMESCALEMOD',
+                         '--trace-fst',
+                         '--no-trace-underscore',  # To avoid handle mismatches
+    ],
+    );
+
+execute(
+    check_finished => 1,
+    );
+
+fst_identical($Self->trace_filename, $Self->{golden_filename});
+
+ok(1);
+1;