Studying note of GCC-3.4.6 source (18)

3.        Preparation According to Parsing Options

3.1. Hooks for Langauges

Back to toplev_main, as we mentioned before, it’s appreciate that front-end can make new language introducation easy. In GCC, the front-end provides the famework for language, all language related treatments are designed as callback. It also bundles all these callbacks into a structure as following.

212  struct lang_hooks                                                                                in langhooks.h

213  {

214   

215    const char *name;

216 

217   

219    size_t identifier_size;

220 

221   

224    size_t (*tree_size) (enum tree_code);

225 

226   

229    unsigned int (*init_options) (unsigned int argc, const char **argv);

230 

231   

233    void (*initialize_diagnostics) (struct diagnostic_context *);

234 

235   

244    int (*handle_option) (size_t code, const char *arg, int value);

245 

246   

248    bool (*missing_argument) (const char *opt, size_t code);

249 

250   

258    bool (*post_options) (const char **);

259 

260   

263    bool (*init) (void);

264 

265   

266    void (*finish) (void);

267 

268   

270    void (*parse_file) (int);

271 

272   

273    void (*clear_binding_stack) (void);

274 

275   

277    HOST_WIDE_INT (*get_alias_set) (tree);

278 

279   

282    tree (*expand_constant) (tree);

283 

284   

286    rtx (*expand_expr) (tree, rtx, enum machine_mode, int, rtx *);

287 

288   

299    tree (*truthvalue_conversion) (tree);

300 

301   

308    int (*safe_from_p) (rtx, tree);

309 

310   

312    void (*finish_incomplete_decl) (tree);

313 

314   

317    int (*unsafe_for_reeval) (tree);

318 

319   

322    bool (*mark_addressable) (tree);

323 

324   

325    int (*staticp) (tree);

326 

327   

329    void (*dup_lang_specific_decl) (tree);

330 

331   

334    tree (*unsave_expr_now) (tree);

335 

336   

338    tree (*maybe_build_cleanup) (tree);

339 

340   

345    void (*set_decl_assembler_name) (tree);

346 

347   

349    bool (*can_use_bit_fields_p) (void);

350 

351   

352    bool honor_readonly;

353 

354   

357    bool no_body_blocks;

358 

359   

361    void (*print_statistics) (void);

362 

363   

365    lang_print_tree_hook print_xnode;

366 

367   

369    lang_print_tree_hook print_decl;

370    lang_print_tree_hook print_type;

371    lang_print_tree_hook print_identifier;

372 

373   

379    const char *(*decl_printable_name) (tree decl, int verbosity);

380 

381   

382    tree (*lang_get_callee_fndecl) (tree);

383 

384   

385    void (*print_error_function) (struct diagnostic_context *, const char *);

386 

387   

391    tree (*expr_size) (tree);

392 

393   

395    bool (*decl_uninit) (tree);

396 

397   

402    const struct attribute_spec *attribute_table;

403    const struct attribute_spec *common_attribute_table;

404    const struct attribute_spec *format_attribute_table;

405 

406   

407    struct lang_hooks_for_functions function;

408 

409    struct lang_hooks_for_tree_inlining tree_inlining;

410 

411    struct lang_hooks_for_callgraph callgraph;

412 

413    struct lang_hooks_for_tree_dump tree_dump;

414 

415    struct lang_hooks_for_decls decls;

416 

417    struct lang_hooks_for_types types;

418 

419    struct lang_hooks_for_rtl_expansion rtl_expand;

420 

421   

423  };

It is a big and complex but important data structure; it has a global instance lang_hooks. Every front-end needs set this structure. It is initialized by macro LANG_HOOKS_INITIALIZER.  Front-end doesn’t need provide the whole definition, for part front-end doesn’t define, default operation is assumed (commonly is harmless empty operation or returns false value). Following, with C++ front-end, we will see the functionality one by one.

3.2. Initialization source reader

No doubt different language has different compilation options set, and their processing is front-end dependent. Routine decode_options processes compilation options for the language. Note that the function can be invoked by all front-ends.

479  void

480  decode_options (unsigned int argc, const char **argv)                                          in opts.c

481  {

482    unsigned int i, lang_mask;

483 

484   

485    lang_mask = (*lang_hooks.init_options) (argc, argv);

486 

487    lang_hooks.initialize_diagnostics (global_dc);

For C/C++, they share the same init_options operation. It’s c_common_init_options. Its major work is to create a reader for source files for scanning program.

188  unsigned int

189  c_common_init_options (unsigned int argc, const char **argv)                       in c-opts.c

190  {

191    static const unsigned int lang_flags[] = {CL_C, CL_ObjC, CL_CXX, CL_ObjCXX};

192    unsigned int i, result;

193 

194   

196    if (c_dialect_cxx ())

197    {

198     

200      diagnostic_line_cutoff (global_dc) = 80;

201     

203      diagnostic_prefixing_rule (global_dc) = DIAGNOSTICS_SHOW_PREFIX_ONCE;

204    }

205 

206    parse_in = cpp_create_reader (c_dialect_cxx () ? CLK_GNUCXX: CLK_GNUC89,

207                       ident_hash);

c_dialect_cxx at line 195 is a very simple macro to check if it is C++ dialect.

254  #define c_dialect_cxx()         (c_language & clk_cxx)                            in c-common.h

c_language is an instance of an enum type of c_language_kind. It is initialized by front-end, for example, in C++ front-end, it is set as clk_cxx.

241  typedef enum c_language_kind                                                             in c-common.h

242  {

243    clk_c          = 0,       

244    clk_objc      = 1,       

245    clk_cxx       = 2,       

246    clk_objcxx  = 3        

247  }

248  c_language_kind;

249 

250 

252  extern c_language_kind c_language;                                                      in c-common.h