Add warning that timing controls in DPI exports are unsupported (#4238)

Signed-off-by: Krzysztof Bieganski <kbieganski@antmicro.com>

src/V3Timing.cpp

@@ -568,17 +568,25 @@ private:
     }
     void visit(AstCFunc* nodep) override {
         iterateChildren(nodep);
-        if (nodep->user2()) {
-            nodep->rtnType("VlCoroutine");
-            // If in a class, create a shared pointer to 'this'
-            if (m_classp) nodep->addInitsp(new AstCStmt{nodep->fileline(), "VL_KEEP_THIS;\n"});
-            if (!nodep->exists([](AstCAwait*) { return true; })) {
-                // It's a coroutine but has no awaits (a class method that overrides/is
-                // overridden by a suspendable, but doesn't have any awaits itself). Add a
-                // co_return at the end (either that or a co_await is required in a
-                // coroutine)
-                nodep->addStmtsp(new AstCStmt{nodep->fileline(), "co_return;\n"});
-            }
+        if (!nodep->user2()) return;
+        nodep->rtnType("VlCoroutine");
+        // If in a class, create a shared pointer to 'this'
+        if (m_classp) nodep->addInitsp(new AstCStmt{nodep->fileline(), "VL_KEEP_THIS;\n"});
+        AstNode* firstCoStmtp = nullptr;  // First co_* statement in the function
+        nodep->exists([&](AstCAwait* const awaitp) -> bool { return (firstCoStmtp = awaitp); });
+        if (!firstCoStmtp) {
+            // It's a coroutine but has no awaits (a class method that overrides/is
+            // overridden by a suspendable, but doesn't have any awaits itself). Add a
+            // co_return at the end (either that or a co_await is required in a
+            // coroutine)
+            firstCoStmtp = new AstCStmt{nodep->fileline(), "co_return;\n"};
+            nodep->addStmtsp(firstCoStmtp);
+        }
+        if (nodep->dpiExportImpl()) {
+            // A DPI-exported coroutine won't be able to block the calling code
+            // Error on the await node; fall back to the function node
+            firstCoStmtp->v3warn(E_UNSUPPORTED,
+                                 "Unsupported: Timing controls inside DPI-exported tasks");
         }
     }
     void visit(AstNodeCCall* nodep) override {

test_regress/t/t_timing_dpi.pl

@@ -1,28 +0,0 @@
-#!/usr/bin/env perl
-if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
-# DESCRIPTION: Verilator: Verilog Test driver/expect definition
-#
-# This file ONLY is placed under the Creative Commons Public Domain, for
-# any use, without warranty, 2023 by Toru Niina.
-# SPDX-License-Identifier: CC0-1.0
-
-
-scenarios(vlt => 1);
-
-if (!$Self->have_coroutines) {
-    skip("No coroutine support")
-}
-else {
-    compile(
-        v_flags2 => ["t/t_timing_dpi.cpp"],
-        verilator_flags2 => ["--exe --main --timing"],
-        make_main => 0,
-        );
-
-    execute(
-        check_finished => 1,
-        );
-}
-
-ok(1);
-1

test_regress/t/t_timing_dpi_unsup.out

@@ -0,0 +1,5 @@
+%Error-UNSUPPORTED: t/t_timing_dpi_unsup.v:28:19: Unsupported: Timing controls inside DPI-exported tasks
+   28 |         repeat(n) @(negedge clk);
+      |                   ^
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: Exiting due to

test_regress/t/t_timing_dpi_unsup.pl

@@ -0,0 +1,22 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2023 by Antmicro Ltd. 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
+
+scenarios(linter => 1);
+
+top_filename("t/t_timing_dpi_unsup.v");
+
+lint(
+    verilator_flags2 => ["--timing"],
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;

test_regress/t/t_timing_dpi_unsup.v

@@ -24,19 +24,19 @@ module t;
 
     export "DPI-C" task tb_sv_wait;
     task automatic tb_sv_wait(input int n);
-        `WRITE_VERBOSE("tb_sv_wait start...");
+        `WRITE_VERBOSE("tb_sv_wait start...\n");
         repeat(n) @(negedge clk);
-        `WRITE_VERBOSE("tb_sv_wait done!");
+        `WRITE_VERBOSE("tb_sv_wait done!\n");
     endtask
 
     always #halfcycle clk = ~clk;
 
     initial begin
-        `WRITE_VERBOSE("test start");
+        `WRITE_VERBOSE("test start\n");
         repeat(10) @(posedge clk);
-        `WRITE_VERBOSE("calling tb_c_wait...");
+        `WRITE_VERBOSE("calling tb_c_wait...\n");
         tb_c_wait();
-        `WRITE_VERBOSE("tb_c_wait finish");
+        `WRITE_VERBOSE("tb_c_wait finish\n");
         repeat(10) @(posedge clk);
         $write("*-* All Finished *-*\n");
         $finish;