GCC's bacl-end & assemble emission (42)

12.   Toolof genflags

This tool will output insn-flags, in which functions produced bygenemit will be declared, and a series HAVE_* macros containing the conditionaltemplate of define_insn and define_expand patterns.

 

233  int

234  main (int argc, char **argv)                                                                        ingenflags.c

235  {

236   rtx desc;

237   rtx dummy;

238   rtx *insns;

239   rtx *insn_ptr;

240 

241   progname= "genflags";

242   obstack_init (&obstack);

243 

244   /* We need to see all the possibilities.Elided insns may have

245      direct calls to their generators in Ccode.  */

246   insn_elision= 0;

247 

248   if (argc <= 1)

249     fatal ("no input file name");

250 

251   if (init_md_reader_args (argc, argv) != SUCCESS_EXIT_CODE)

252     return (FATAL_EXIT_CODE);

253 

254   puts ("/* Generated automatically by the program `genflags'");

255   puts ("   from the machinedescription file `md'.  */\n");

256   puts ("#ifndef GCC_INSN_FLAGS_H");

257   puts ("#define GCC_INSN_FLAGS_H\n");

258 

259   /* Read the machine description.  */

260 

261   while (1)

262   {

263     int line_no, insn_code_number = 0;

264 

265     desc = read_md_rtx (&line_no,&insn_code_number);

266     if (desc == NULL)

267       break;

268      if (GET_CODE (desc) ==DEFINE_INSN || GET_CODE (desc) == DEFINE_EXPAND)

269       gen_insn (desc);

270   }

271 

272   /* Print out the prototypes now.  */

273   dummy = (rtx) 0;

274   obstack_grow (&obstack, &dummy, sizeof(rtx));

275   insns = (rtx *) obstack_finish (&obstack);

276 

277    for(insn_ptr = insns; *insn_ptr; insn_ptr++)

278      gen_proto (*insn_ptr);

279 

280    puts("\n#endif /*GCC_INSN_FLAGS_H */");

281 

282   if (ferror (stdout) || fflush (stdout) || fclose (stdout))

283     return FATAL_EXIT_CODE;

284 

285   return SUCCESS_EXIT_CODE;

286  }

 

As we see from other sections, init_md_reader_args and read_md_rtx reads in patterns frommachine description file and creates corresponding rtx object referred bydesc.This object is handled by gen_insn.

 

192  static void

193  gen_insn (rtx insn)                                                                                     ingenflags.c

194  {

195   const char *name = XSTR (insn, 0);

196   const char *p;

197   int len;

198   int truth = maybe_eval_c_test (XSTR(insn, 2));

199 

200   /* Don't mention instructions whose names arethe null string

201      or begin with '*'. They are in the machinedescription just

202      to be recognized.  */

203   if (name[0] == 0 || name[0] == '*')

204     return;

205 

206   len = strlen (name);

207 

208   if (len > max_id_len)

209     max_id_len= len;

210 

211   if (truth == 0)

212     /* Emit nothing.  */;

213   else if (truth == 1)

214     printf ("#define HAVE_%s 1\n", name);

215   else

216   {

217     /* Write the macro definition, putting \'s atthe end of each line,

218        if more than one.  */

219     printf ("#define HAVE_%s (", name);

220      for(p = XSTR (insn, 2); *p; p++)

221     {

222       if (IS_VSPACE (*p))

223         fputs (" \\\n", stdout);

224       else

225         putchar (*p);

226     }

227     fputs (")\n", stdout);

228   }

229 

230   obstack_grow (&obstack, &insn, sizeof(rtx));

231  }

 

We have known that maybe_eval_c_test returns 1 for theexpression is known at compile time as true, 0 for the expression as false, and-1 for unknown. Notice that at line 203, patterns without name or namebeginning with ‘*’ will be ignored. And at line 230, the addresses of qualifiedrtx objects will be saved intoobstack.

Back to main, at line 275, a null rtx object isappended upon obstackto ensure FOR loop at line 277 willexit correctly. For every meaningful define_insn or define_expand pattern,gen_proto doesfollowing treatment.

 

129  static void

130  gen_proto (rtx insn)                                                                                   ingenflags.c

131  {

132   int num = num_operands (insn);

133   int i;

134   const char *name = XSTR (insn, 0);

135   int truth = maybe_eval_c_test (XSTR(insn, 2));

136 

137   /* Many md files don't refer to the last twooperands passed to the

138      call patterns. This means their generatorfunctions will be two

139      arguments too short. Instead of changingevery md file to touch

140      those operands, we wrap the prototypes inmacros that take the

141      correct number of arguments.  */

142   if (name[0] == 'c' || name[0] == 's')

143   {

144     if (!strcmp (name, "call")

145        || !strcmp (name, "call_pop")

146        || !strcmp (name, "sibcall")

147        || !strcmp (name, "sibcall_pop"))

148       gen_macro (name, num, 4);

149     else if (!strcmp (name, "call_value")

150            || !strcmp (name,"call_value_pop")

151            || !strcmp (name,"sibcall_value")

152            || !strcmp (name,"sibcall_value_pop"))

153       gen_macro (name, num, 5);

154   }

155 

156   if (truth != 0)

157     printf ("extern rtx       gen_%-*s (", max_id_len, name);

158   else

159     printf ("static inline rtx gen_%-*s (", max_id_len, name);

160 

161   if (num == 0)

162     fputs ("void", stdout);

163    else

164    {

165      for(i = 1; i < num; i++)

166        fputs ("rtx, ",stdout);

167 

168      fputs ("rtx", stdout);

169   }

170 

171   puts (");");

172 

173   /* Some back ends want to take the address ofgenerator functions,

174      so we cannot simply use #define for thesedummy definitions.  */

175   if (truth == 0)

176   {

177     printf ("static inline rtx\ngen_%s", name);

178     if (num > 0)

179      {

180        putchar ('(');

181        for(i = 0; i < num-1; i++)

182         printf ("rtx %cATTRIBUTE_UNUSED, ", 'a' + i);

183       printf ("rtx %c ATTRIBUTE_UNUSED)\n", 'a' + i);

184     }

185     else

186       puts ("(void)");

187     puts ("{\n  return0;\n}");

188   }

189 

190  }

 

Can see that patterns with name “call”, “call_pop”, “sibcall”,“sibcall_pop”, “call_value_pop”, “call_value”, “sibcall_value’, and“sibcall_value_pop” need further handle bygen_macro as following.

 

100  static void

101  gen_macro (const char *name, int real, intexpect)                                        ingenflags.c

102  {

103   int i;

104 

105   if (real > expect)

106     abort ();

107   if (real == 0)

108     abort ();

109 

110   /* #define GEN_CALL(A, B, C, D) gen_call((A),(B)) */

111    fputs ("#define GEN_",stdout);

112    for(i = 0; name[i]; i++)

113     putchar (TOUPPER (name[i]));

114 

115   putchar('(');

116   for (i = 0; i < expect - 1; i++)

117     printf ("%c, ", i + 'A');

118   printf ("%c) gen_%s (", i + 'A', name);

119 

120    for(i = 0; i < real - 1; i++)

121     printf ("(%c), ", i + 'A');

122   printf ("(%c))\n", i + 'A');

123  }

 

This function will generate a macro for corresponding functions forabove mentioned patterns. Back togen_proto, lines from 156 to 169, output theprototype of the functions. Notice that for conditional template of pattern ofcompile time known as false, the definition will be present in the insn-flagstoo - lines from 175 to 188 generate the functions return 0.