Add --main to generate main() C++ (previously was experimental only) (#3265).

Changes

@@ -20,6 +20,7 @@ Verilator 4.227 devel
 **Minor:**
 
 * Support IEEE constant signal strengths (#3601). [Ryszard Rozak/Antmicro]
+* Add --main to generate main() C++ (previously was experimental only).
 * Fix thread saftey in SystemC VL_ASSIGN_SBW/WSB (#3494) (#3513). [Mladen Slijepcevic]
 * Fix crash in gate optimization of circular logic (#3543). [Bill Flynn]
 * Fix arguments in non-static method call (#3547) (#3582). [Gustav Svensk]

bin/verilator

@@ -343,6 +343,7 @@ detailed descriptions of these arguments.
     --lint-only                 Lint, but do not make output
     --make <build-tool>         Generate scripts for specified build tool
      -MAKEFLAGS <flags>         Arguments to pass to make during --build
+    --main                      Generate C++ main()
     --max-num-width <value>     Maximum number width (default: 64K)
     --Mdir <directory>          Name of output object directory
     --MMD                       Create .d dependency files

docs/guide/exe_verilator.rst

@@ -709,6 +709,15 @@ Summary:
    (e.g. ``-MAKEFLAGS -l -MAKEFLAGS -k``). Use of this option should not be
    required for simple builds using the host toolchain.
 
+.. option:: --main
+
+   Generates a top-level C++ main() file that supports parsing arguments,
+   but does not drive any inputs.  This is sufficient to use for top-level
+   SystemVerilog designs that has no inputs, and does not need the C++ to
+   do any time advancement.
+
+   Implies :vlopt:`--cc` if no other output mode was provided.
+
 .. option:: --max-num-width <value>
 
    Set the maximum number literal width (e.g. in 1024'd22 this it the

src/V3Options.cpp

@@ -435,6 +435,11 @@ string V3Options::allArgsStringForHierBlock(bool forTop) const {
     return out;
 }
 
+void V3Options::ccSet() {  // --cc
+    m_outFormatOk = true;
+    m_systemC = false;
+}
+
 //######################################################################
 // File searching
 
@@ -719,9 +724,10 @@ bool V3Options::systemCFound() {
 // V3 Options notification methods
 
 void V3Options::notify() {
-    FileLine* const cmdfl = new FileLine(FileLine::commandLineFilename());
-
     // Notify that all arguments have been passed and final modification can be made.
+    FileLine* const cmdfl = new FileLine{FileLine::commandLineFilename()};
+
+    if (!outFormatOk() && v3Global.opt.main()) ccSet();  // --main implies --cc if not provided
     if (!outFormatOk() && !cdc() && !dpiHdrOnly() && !lintOnly() && !preprocOnly() && !xmlOnly()) {
         v3fatal("verilator: Need --cc, --sc, --cdc, --dpi-hdr-only, --lint-only, "
                 "--xml-only or --E option");
@@ -1002,10 +1008,7 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc, char
     DECL_OPTION("-build", Set, &m_build);
 
     DECL_OPTION("-CFLAGS", CbVal, callStrSetter(&V3Options::addCFlags));
-    DECL_OPTION("-cc", CbCall, [this]() {
-        m_outFormatOk = true;
-        m_systemC = false;
-    });
+    DECL_OPTION("-cc", CbCall, [this]() { ccSet(); });
     DECL_OPTION("-cdc", OnOff, &m_cdc);
     DECL_OPTION("-clk", CbVal, callStrSetter(&V3Options::addClocker));
     DECL_OPTION("-no-clk", CbVal, callStrSetter(&V3Options::addNoClocker));
@@ -1175,7 +1178,7 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc, char
         m_makeDir = valp;
         addIncDirFallback(m_makeDir);  // Need to find generated files there too
     });
-    DECL_OPTION("-main", OnOff, &m_main).undocumented();  // Future
+    DECL_OPTION("-main", OnOff, &m_main);
     DECL_OPTION("-make", CbVal, [this, fl](const char* valp) {
         if (!strcmp(valp, "cmake")) {
             m_cmake = true;

src/V3Options.h

@@ -410,8 +410,9 @@ public:
     void addNoClocker(const string& signame);
     void addVFile(const string& filename);
     void addForceInc(const string& filename);
-    void notify();
     bool available() const { return m_available; }
+    void ccSet();
+    void notify();
 
     // ACCESSORS (options)
     bool preprocOnly() const { return m_preprocOnly; }

test_regress/t/t_flag_main.pl

@@ -11,6 +11,9 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(simulator => 1);
 
 compile(
+    verilator_flags => [# Custom as don't want -cc
+                        "-Mdir $Self->{obj_dir}",
+                        "--debug-check", ],
     verilator_flags2 => ['--exe --build --main'],
     verilator_make_cmake => 0,
     verilator_make_gmake => 0,