gcc/gimple-low.c

   1 /* Tree lowering pass.  Lowers GIMPLE into unstructured form.
   2
   3    Copyright (C) 2003 Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 2, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING.  If not, write to the Free
  19 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
  20 02111-1307, USA.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tm.h"
  26 #include "tree.h"
  27 #include "rtl.h"
  28 #include "errors.h"
  29 #include "varray.h"
  30 #include "tree-gimple.h"
  31 #include "tree-inline.h"
  32 #include "diagnostic.h"
  33 #include "langhooks.h"
  34 #include "langhooks-def.h"
  35 #include "tree-flow.h"
  36 #include "timevar.h"
  37 #include "except.h"
  38 #include "hashtab.h"
  39 #include "flags.h"
  40 #include "function.h"
  41 #include "expr.h"
  42 #include "toplev.h"
  43 #include "tree-pass.h"
  44
  45 struct lower_data
  46 {
  47   /* Block the current statement belongs to.  */
  48   tree block;
  49
  50   /* A TREE_LIST of label and return statements to be moved to the end
  51      of the function.  */
  52   tree return_statements;
  53 };
  54
  55 static void lower_stmt (tree_stmt_iterator *, struct lower_data *);
  56 static void lower_bind_expr (tree_stmt_iterator *, struct lower_data *);
  57 static void lower_cond_expr (tree_stmt_iterator *, struct lower_data *);
  58 static void lower_return_expr (tree_stmt_iterator *, struct lower_data *);
  59 static bool expand_var_p (tree);
  60
  61 /* Lowers the body of current_function_decl.  */
  62
  63 static void
  64 lower_function_body (void)
  65 {
  66   struct lower_data data;
  67   tree *body_p = &DECL_SAVED_TREE (current_function_decl);
  68   tree bind = *body_p;
  69   tree_stmt_iterator i;
  70   tree t, x;
  71
  72   if (TREE_CODE (bind) != BIND_EXPR)
  73     abort ();
  74
  75   data.block = DECL_INITIAL (current_function_decl);
  76   BLOCK_SUBBLOCKS (data.block) = NULL_TREE;
  77   BLOCK_CHAIN (data.block) = NULL_TREE;
  78   TREE_ASM_WRITTEN (data.block) = 1;
  79
  80   data.return_statements = NULL_TREE;
  81
  82   *body_p = alloc_stmt_list ();
  83   i = tsi_start (*body_p);
  84   tsi_link_after (&i, bind, TSI_NEW_STMT);
  85   lower_bind_expr (&i, &data);
  86
  87   i = tsi_last (*body_p);
  88
  89   /* If the function falls off the end, we need a null return statement.
  90      If we've already got one in the return_statements list, we don't
  91      need to do anything special.  Otherwise build one by hand.  */
  92   if (block_may_fallthru (*body_p)
  93       && (data.return_statements == NULL
  94           || TREE_OPERAND (TREE_VALUE (data.return_statements), 0) != NULL))
  95     {
  96       x = build (RETURN_EXPR, void_type_node, NULL);
  97       SET_EXPR_LOCATION (x, cfun->function_end_locus);
  98       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
  99     }
 100
 101   /* If we lowered any return statements, emit the representative
 102      at the end of the function.  */
 103   for (t = data.return_statements ; t ; t = TREE_CHAIN (t))
 104     {
 105       x = build (LABEL_EXPR, void_type_node, TREE_PURPOSE (t));
 106       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
 107
 108       /* Remove the line number from the representative return statement.
 109          It now fills in for many such returns.  Failure to remove this
 110          will result in incorrect results for coverage analysis.  */
 111       x = TREE_VALUE (t);
 112 #ifdef USE_MAPPED_LOCATION
 113       SET_EXPR_LOCATION (x, UNKNOWN_LOCATION);
 114 #else
 115       SET_EXPR_LOCUS (x, NULL);
 116 #endif
 117       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
 118     }
 119
 120   if (data.block != DECL_INITIAL (current_function_decl))
 121     abort ();
 122   BLOCK_SUBBLOCKS (data.block)
 123     = blocks_nreverse (BLOCK_SUBBLOCKS (data.block));
 124
 125   clear_block_marks (data.block);
 126 }
 127
 128 struct tree_opt_pass pass_lower_cf =
 129 {
 130   "lower",                              /* name */
 131   NULL,                                 /* gate */
 132   lower_function_body,                  /* execute */
 133   NULL,                                 /* sub */
 134   NULL,                                 /* next */
 135   0,                                    /* static_pass_number */
 136   0,                                    /* tv_id */
 137   PROP_gimple_any,                      /* properties_required */
 138   PROP_gimple_lcf,                      /* properties_provided */
 139   PROP_gimple_any,                      /* properties_destroyed */
 140   0,                                    /* todo_flags_start */
 141   TODO_dump_func                        /* todo_flags_finish */
 142 };
 143
 144
 145 /* Lowers the EXPR.  Unlike gimplification the statements are not relowered
 146    when they are changed -- if this has to be done, the lowering routine must
 147    do it explicitly.  DATA is passed through the recursion.  */
 148
 149 void
 150 lower_stmt_body (tree expr, struct lower_data *data)
 151 {
 152   tree_stmt_iterator tsi;
 153
 154   for (tsi = tsi_start (expr); !tsi_end_p (tsi); )
 155     lower_stmt (&tsi, data);
 156 }
 157
 158 /* Lowers statement TSI.  DATA is passed through the recursion.  */
 159
 160 static void
 161 lower_stmt (tree_stmt_iterator *tsi, struct lower_data *data)
 162 {
 163   tree stmt = tsi_stmt (*tsi);
 164
 165   if (EXPR_HAS_LOCATION (stmt) && data)
 166     TREE_BLOCK (stmt) = data->block;
 167
 168   switch (TREE_CODE (stmt))
 169     {
 170     case BIND_EXPR:
 171       lower_bind_expr (tsi, data);
 172       return;
 173     case COND_EXPR:
 174       lower_cond_expr (tsi, data);
 175       return;
 176     case RETURN_EXPR:
 177       lower_return_expr (tsi, data);
 178       return;
 179
 180     case TRY_FINALLY_EXPR:
 181     case TRY_CATCH_EXPR:
 182       lower_stmt_body (TREE_OPERAND (stmt, 0), data);
 183       lower_stmt_body (TREE_OPERAND (stmt, 1), data);
 184       break;
 185     case CATCH_EXPR:
 186       lower_stmt_body (CATCH_BODY (stmt), data);
 187       break;
 188     case EH_FILTER_EXPR:
 189       lower_stmt_body (EH_FILTER_FAILURE (stmt), data);
 190       break;
 191
 192     case NOP_EXPR:
 193     case ASM_EXPR:
 194     case MODIFY_EXPR:
 195     case CALL_EXPR:
 196     case GOTO_EXPR:
 197     case LABEL_EXPR:
 198     case SWITCH_EXPR:
 199       break;
 200
 201     default:
 202       print_node_brief (stderr, "", stmt, 0);
 203     case COMPOUND_EXPR:
 204       abort ();
 205     }
 206
 207   tsi_next (tsi);
 208 }
 209
 210 /* Lowers a bind_expr TSI.  DATA is passed through the recursion.  */
 211
 212 static void
 213 lower_bind_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 214 {
 215   tree old_block = data->block;
 216   tree stmt = tsi_stmt (*tsi);
 217   tree new_block = BIND_EXPR_BLOCK (stmt);
 218
 219   if (new_block)
 220     {
 221       if (new_block == old_block)
 222         {
 223           /* The outermost block of the original function may not be the
 224              outermost statement chain of the gimplified function.  So we
 225              may see the outermost block just inside the function.  */
 226           if (new_block != DECL_INITIAL (current_function_decl))
 227             abort ();
 228           new_block = NULL;
 229         }
 230       else
 231         {
 232           /* We do not expect to handle duplicate blocks.  */
 233           if (TREE_ASM_WRITTEN (new_block))
 234             abort ();
 235           TREE_ASM_WRITTEN (new_block) = 1;
 236
 237           /* Block tree may get clobbered by inlining.  Normally this would
 238              be fixed in rest_of_decl_compilation using block notes, but
 239              since we are not going to emit them, it is up to us.  */
 240           BLOCK_CHAIN (new_block) = BLOCK_SUBBLOCKS (old_block);
 241           BLOCK_SUBBLOCKS (old_block) = new_block;
 242           BLOCK_SUBBLOCKS (new_block) = NULL_TREE;
 243           BLOCK_SUPERCONTEXT (new_block) = old_block;
 244
 245           data->block = new_block;
 246         }
 247     }
 248
 249   record_vars (BIND_EXPR_VARS (stmt));
 250   lower_stmt_body (BIND_EXPR_BODY (stmt), data);
 251
 252   if (new_block)
 253     {
 254       if (data->block != new_block)
 255         abort ();
 256
 257       BLOCK_SUBBLOCKS (new_block)
 258         = blocks_nreverse (BLOCK_SUBBLOCKS (new_block));
 259       data->block = old_block;
 260     }
 261
 262   /* The BIND_EXPR no longer carries any useful information -- kill it.  */
 263   tsi_link_before (tsi, BIND_EXPR_BODY (stmt), TSI_SAME_STMT);
 264   tsi_delink (tsi);
 265 }
 266
 267 /* Try to determine if we can fall out of the bottom of BLOCK.  This guess
 268    need not be 100% accurate; simply be conservative and return true if we
 269    don't know.  This is used only to avoid stupidly generating extra code.
 270    If we're wrong, we'll just delete the extra code later.  */
 271
 272 bool
 273 block_may_fallthru (tree block)
 274 {
 275   tree stmt = expr_last (block);
 276
 277   switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)
 278     {
 279     case GOTO_EXPR:
 280     case RETURN_EXPR:
 281     case RESX_EXPR:
 282     case SWITCH_EXPR:
 283       /* Easy cases.  If the last statement of the block implies
 284          control transfer, then we can't fall through.  */
 285       return false;
 286
 287     case COND_EXPR:
 288       if (block_may_fallthru (COND_EXPR_THEN (stmt)))
 289         return true;
 290       return block_may_fallthru (COND_EXPR_ELSE (stmt));
 291
 292     case BIND_EXPR:
 293       return block_may_fallthru (BIND_EXPR_BODY (stmt));
 294
 295     case TRY_FINALLY_EXPR:
 296       return block_may_fallthru (TREE_OPERAND (stmt, 1));
 297
 298     case MODIFY_EXPR:
 299       if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
 300         stmt = TREE_OPERAND (stmt, 1);
 301       else
 302         return true;
 303       /* FALLTHRU */
 304
 305     case CALL_EXPR:
 306       /* Functions that do not return do not fall through.  */
 307       return (call_expr_flags (stmt) & ECF_NORETURN) == 0;
 308
 309     default:
 310       return true;
 311     }
 312 }
 313
 314 /* Lowers a cond_expr TSI.  DATA is passed through the recursion.  */
 315
 316 static void
 317 lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 318 {
 319   tree stmt = tsi_stmt (*tsi);
 320   bool then_is_goto, else_is_goto;
 321   tree then_branch, else_branch;
 322   tree then_goto, else_goto;
 323
 324   then_branch = COND_EXPR_THEN (stmt);
 325   else_branch = COND_EXPR_ELSE (stmt);
 326
 327   lower_stmt_body (then_branch, data);
 328   lower_stmt_body (else_branch, data);
 329
 330   then_goto = expr_only (then_branch);
 331   then_is_goto = then_goto && simple_goto_p (then_goto);
 332
 333   else_goto = expr_only (else_branch);
 334   else_is_goto = else_goto && simple_goto_p (else_goto);
 335
 336   if (!then_is_goto || !else_is_goto)
 337     {
 338       tree then_label, else_label, end_label, t;
 339
 340       then_label = NULL_TREE;
 341       else_label = NULL_TREE;
 342       end_label = NULL_TREE;
 343
 344       /* Replace the cond_expr with explicit gotos.  */
 345       if (!then_is_goto)
 346         {
 347           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 348           if (TREE_SIDE_EFFECTS (then_branch))
 349             then_label = t;
 350           else
 351             end_label = t;
 352           then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 353         }
 354
 355       if (!else_is_goto)
 356         {
 357           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 358           if (TREE_SIDE_EFFECTS (else_branch))
 359             else_label = t;
 360           else
 361             {
 362               /* Both THEN and ELSE can be no-ops if one or both contained an
 363                  empty BIND_EXPR that was associated with the toplevel block
 364                  of an inlined function.  In that case remove_useless_stmts
 365                  can't have cleaned things up for us; kill the whole
 366                  conditional now.  */
 367               if (end_label)
 368                 {
 369                   tsi_delink (tsi);
 370                   return;
 371                 }
 372               else
 373                 end_label = t;
 374             }
 375           else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 376         }
 377
 378       if (then_label)
 379         {
 380           bool may_fallthru = block_may_fallthru (then_branch);
 381
 382           tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);
 383           tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);
 384
 385           if (else_label && may_fallthru)
 386             {
 387               end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 388               t = build_and_jump (&LABEL_EXPR_LABEL (end_label));
 389               tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);
 390             }
 391         }
 392
 393       if (else_label)
 394         {
 395           tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);
 396           tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);
 397         }
 398
 399       if (end_label)
 400         tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);
 401     }
 402
 403   COND_EXPR_THEN (stmt) = then_goto;
 404   COND_EXPR_ELSE (stmt) = else_goto;
 405
 406   tsi_next (tsi);
 407 }
 408
 409 static void
 410 lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 411 {
 412   tree stmt = tsi_stmt (*tsi);
 413   tree value, t, label;
 414
 415   /* Extract the value being returned.  */
 416   value = TREE_OPERAND (stmt, 0);
 417   if (value && TREE_CODE (value) == MODIFY_EXPR)
 418     value = TREE_OPERAND (value, 1);
 419
 420   /* Match this up with an existing return statement that's been created.  */
 421   for (t = data->return_statements; t ; t = TREE_CHAIN (t))
 422     {
 423       tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);
 424       if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)
 425         tvalue = TREE_OPERAND (tvalue, 1);
 426
 427       if (value == tvalue)
 428         {
 429           label = TREE_PURPOSE (t);
 430           goto found;
 431         }
 432     }
 433
 434   /* Not found.  Create a new label and record the return statement.  */
 435   label = create_artificial_label ();
 436   data->return_statements = tree_cons (label, stmt, data->return_statements);
 437
 438   /* Generate a goto statement and remove the return statement.  */
 439  found:
 440   t = build (GOTO_EXPR, void_type_node, label);
 441   SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));
 442   tsi_link_before (tsi, t, TSI_SAME_STMT);
 443   tsi_delink (tsi);
 444 }
 445 \f
 446
 447 /* Record the variables in VARS.  */
 448
 449 void
 450 record_vars (tree vars)
 451 {
 452   for (; vars; vars = TREE_CHAIN (vars))
 453     {
 454       tree var = vars;
 455
 456       /* Nothing to do in this case.  */
 457       if (DECL_EXTERNAL (var))
 458         continue;
 459       if (TREE_CODE (var) == FUNCTION_DECL)
 460         continue;
 461
 462       /* Record the variable.  */
 463       cfun->unexpanded_var_list = tree_cons (NULL_TREE, var,
 464                                              cfun->unexpanded_var_list);
 465     }
 466 }
 467
 468 /* Check whether to expand a variable VAR.  */
 469
 470 static bool
 471 expand_var_p (tree var)
 472 {
 473   struct var_ann_d *ann;
 474
 475   if (TREE_CODE (var) != VAR_DECL)
 476     return true;
 477
 478   /* Leave statics and externals alone.  */
 479   if (TREE_STATIC (var) || DECL_EXTERNAL (var))
 480     return true;
 481
 482   /* Remove all unused local variables.  */
 483   ann = var_ann (var);
 484   if (!ann || !ann->used)
 485     return false;
 486
 487   return true;
 488 }
 489
 490 /* Throw away variables that are unused.  */
 491
 492 static void
 493 remove_useless_vars (void)
 494 {
 495   tree var, *cell;
 496   FILE *df = NULL;
 497
 498   if (dump_file && (dump_flags & TDF_DETAILS))
 499     {
 500       df = dump_file;
 501       fputs ("Discarding as unused:\n", df);
 502     }
 503
 504   for (cell = &cfun->unexpanded_var_list; *cell; )
 505     {
 506       var = TREE_VALUE (*cell);
 507
 508       if (!expand_var_p (var))
 509         {
 510           if (df)
 511             {
 512               fputs ("  ", df);
 513               print_generic_expr (df, var, dump_flags);
 514               fputc ('\n', df);
 515             }
 516
 517           *cell = TREE_CHAIN (*cell);
 518           continue;
 519         }
 520
 521       cell = &TREE_CHAIN (*cell);
 522     }
 523
 524   if (df)
 525     fputc ('\n', df);
 526 }
 527
 528 struct tree_opt_pass pass_remove_useless_vars =
 529 {
 530   "vars",                               /* name */
 531   NULL,                                 /* gate */
 532   remove_useless_vars,                  /* execute */
 533   NULL,                                 /* sub */
 534   NULL,                                 /* next */
 535   0,                                    /* static_pass_number */
 536   0,                                    /* tv_id */
 537   0,                                    /* properties_required */
 538   0,                                    /* properties_provided */
 539   0,                                    /* properties_destroyed */
 540   0,                                    /* todo_flags_start */
 541   TODO_dump_func                        /* todo_flags_finish */
 542 };