gcc/gimple-low.c

   1 /* Tree lowering pass.  Lowers GIMPLE into unstructured form.
   2
   3    Copyright (C) 2003, 2005 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   gcc_assert (TREE_CODE (bind) == BIND_EXPR);
  73
  74   data.block = DECL_INITIAL (current_function_decl);
  75   BLOCK_SUBBLOCKS (data.block) = NULL_TREE;
  76   BLOCK_CHAIN (data.block) = NULL_TREE;
  77   TREE_ASM_WRITTEN (data.block) = 1;
  78
  79   data.return_statements = NULL_TREE;
  80
  81   *body_p = alloc_stmt_list ();
  82   i = tsi_start (*body_p);
  83   tsi_link_after (&i, bind, TSI_NEW_STMT);
  84   lower_bind_expr (&i, &data);
  85
  86   i = tsi_last (*body_p);
  87
  88   /* If the function falls off the end, we need a null return statement.
  89      If we've already got one in the return_statements list, we don't
  90      need to do anything special.  Otherwise build one by hand.  */
  91   if (block_may_fallthru (*body_p)
  92       && (data.return_statements == NULL
  93           || TREE_OPERAND (TREE_VALUE (data.return_statements), 0) != NULL))
  94     {
  95       x = build (RETURN_EXPR, void_type_node, NULL);
  96       SET_EXPR_LOCATION (x, cfun->function_end_locus);
  97       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
  98     }
  99
 100   /* If we lowered any return statements, emit the representative
 101      at the end of the function.  */
 102   for (t = data.return_statements ; t ; t = TREE_CHAIN (t))
 103     {
 104       x = build (LABEL_EXPR, void_type_node, TREE_PURPOSE (t));
 105       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
 106
 107       /* Remove the line number from the representative return statement.
 108          It now fills in for many such returns.  Failure to remove this
 109          will result in incorrect results for coverage analysis.  */
 110       x = TREE_VALUE (t);
 111 #ifdef USE_MAPPED_LOCATION
 112       SET_EXPR_LOCATION (x, UNKNOWN_LOCATION);
 113 #else
 114       SET_EXPR_LOCUS (x, NULL);
 115 #endif
 116       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
 117     }
 118
 119   gcc_assert (data.block == DECL_INITIAL (current_function_decl));
 120   BLOCK_SUBBLOCKS (data.block)
 121     = blocks_nreverse (BLOCK_SUBBLOCKS (data.block));
 122
 123   clear_block_marks (data.block);
 124 }
 125
 126 struct tree_opt_pass pass_lower_cf =
 127 {
 128   "lower",                              /* name */
 129   NULL,                                 /* gate */
 130   lower_function_body,                  /* execute */
 131   NULL,                                 /* sub */
 132   NULL,                                 /* next */
 133   0,                                    /* static_pass_number */
 134   0,                                    /* tv_id */
 135   PROP_gimple_any,                      /* properties_required */
 136   PROP_gimple_lcf,                      /* properties_provided */
 137   PROP_gimple_any,                      /* properties_destroyed */
 138   0,                                    /* todo_flags_start */
 139   TODO_dump_func,                       /* todo_flags_finish */
 140   0                                     /* letter */
 141 };
 142
 143
 144 /* Lowers the EXPR.  Unlike gimplification the statements are not relowered
 145    when they are changed -- if this has to be done, the lowering routine must
 146    do it explicitly.  DATA is passed through the recursion.  */
 147
 148 void
 149 lower_stmt_body (tree expr, struct lower_data *data)
 150 {
 151   tree_stmt_iterator tsi;
 152
 153   for (tsi = tsi_start (expr); !tsi_end_p (tsi); )
 154     lower_stmt (&tsi, data);
 155 }
 156
 157 /* Lowers statement TSI.  DATA is passed through the recursion.  */
 158
 159 static void
 160 lower_stmt (tree_stmt_iterator *tsi, struct lower_data *data)
 161 {
 162   tree stmt = tsi_stmt (*tsi);
 163
 164   if (EXPR_HAS_LOCATION (stmt) && data)
 165     TREE_BLOCK (stmt) = data->block;
 166
 167   switch (TREE_CODE (stmt))
 168     {
 169     case BIND_EXPR:
 170       lower_bind_expr (tsi, data);
 171       return;
 172     case COND_EXPR:
 173       lower_cond_expr (tsi, data);
 174       return;
 175     case RETURN_EXPR:
 176       lower_return_expr (tsi, data);
 177       return;
 178
 179     case TRY_FINALLY_EXPR:
 180     case TRY_CATCH_EXPR:
 181       lower_stmt_body (TREE_OPERAND (stmt, 0), data);
 182       lower_stmt_body (TREE_OPERAND (stmt, 1), data);
 183       break;
 184     case CATCH_EXPR:
 185       lower_stmt_body (CATCH_BODY (stmt), data);
 186       break;
 187     case EH_FILTER_EXPR:
 188       lower_stmt_body (EH_FILTER_FAILURE (stmt), data);
 189       break;
 190
 191     case NOP_EXPR:
 192     case ASM_EXPR:
 193     case MODIFY_EXPR:
 194     case CALL_EXPR:
 195     case GOTO_EXPR:
 196     case LABEL_EXPR:
 197     case SWITCH_EXPR:
 198       break;
 199
 200     default:
 201 #ifdef ENABLE_CHECKING
 202       print_node_brief (stderr, "", stmt, 0);
 203       internal_error ("unexpected node");
 204 #endif
 205     case COMPOUND_EXPR:
 206       gcc_unreachable ();
 207     }
 208
 209   tsi_next (tsi);
 210 }
 211
 212 /* Lowers a bind_expr TSI.  DATA is passed through the recursion.  */
 213
 214 static void
 215 lower_bind_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 216 {
 217   tree old_block = data->block;
 218   tree stmt = tsi_stmt (*tsi);
 219   tree new_block = BIND_EXPR_BLOCK (stmt);
 220
 221   if (new_block)
 222     {
 223       if (new_block == old_block)
 224         {
 225           /* The outermost block of the original function may not be the
 226              outermost statement chain of the gimplified function.  So we
 227              may see the outermost block just inside the function.  */
 228           gcc_assert (new_block == DECL_INITIAL (current_function_decl));
 229           new_block = NULL;
 230         }
 231       else
 232         {
 233           /* We do not expect to handle duplicate blocks.  */
 234           gcc_assert (!TREE_ASM_WRITTEN (new_block));
 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       gcc_assert (data->block == new_block);
 255
 256       BLOCK_SUBBLOCKS (new_block)
 257         = blocks_nreverse (BLOCK_SUBBLOCKS (new_block));
 258       data->block = old_block;
 259     }
 260
 261   /* The BIND_EXPR no longer carries any useful information -- kill it.  */
 262   tsi_link_before (tsi, BIND_EXPR_BODY (stmt), TSI_SAME_STMT);
 263   tsi_delink (tsi);
 264 }
 265
 266 /* Try to determine whether a TRY_CATCH expression can fall through.
 267    This is a subroutine of block_may_fallthru.  */
 268
 269 static bool
 270 try_catch_may_fallthru (tree stmt)
 271 {
 272   tree_stmt_iterator i;
 273
 274   /* If the TRY block can fall through, the whole TRY_CATCH can
 275      fall through.  */
 276   if (block_may_fallthru (TREE_OPERAND (stmt, 0)))
 277     return true;
 278
 279   i = tsi_start (TREE_OPERAND (stmt, 1));
 280   switch (TREE_CODE (tsi_stmt (i)))
 281     {
 282     case CATCH_EXPR:
 283       /* We expect to see a sequence of CATCH_EXPR trees, each with a
 284          catch expression and a body.  The whole TRY_CATCH may fall
 285          through iff any of the catch bodies falls through.  */
 286       for (; !tsi_end_p (i); tsi_next (&i))
 287         {
 288           if (block_may_fallthru (CATCH_BODY (tsi_stmt (i))))
 289             return true;
 290         }
 291       return false;
 292
 293     case EH_FILTER_EXPR:
 294       /* The exception filter expression only matters if there is an
 295          exception.  If the exception does not match EH_FILTER_TYPES,
 296          we will execute EH_FILTER_FAILURE, and we will fall through
 297          if that falls through.  If the exception does match
 298          EH_FILTER_TYPES, the stack unwinder will continue up the
 299          stack, so we will not fall through.  We don't know whether we
 300          will throw an exception which matches EH_FILTER_TYPES or not,
 301          so we just ignore EH_FILTER_TYPES and assume that we might
 302          throw an exception which doesn't match.  */
 303       return block_may_fallthru (EH_FILTER_FAILURE (tsi_stmt (i)));
 304
 305     default:
 306       /* This case represents statements to be executed when an
 307          exception occurs.  Those statements are implicitly followed
 308          by a RESX_EXPR to resume execution after the exception.  So
 309          in this case the TRY_CATCH never falls through.  */
 310       return false;
 311     }
 312 }
 313
 314 /* Try to determine if we can fall out of the bottom of BLOCK.  This guess
 315    need not be 100% accurate; simply be conservative and return true if we
 316    don't know.  This is used only to avoid stupidly generating extra code.
 317    If we're wrong, we'll just delete the extra code later.  */
 318
 319 bool
 320 block_may_fallthru (tree block)
 321 {
 322   tree stmt = expr_last (block);
 323
 324   switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)
 325     {
 326     case GOTO_EXPR:
 327     case RETURN_EXPR:
 328     case RESX_EXPR:
 329       /* Easy cases.  If the last statement of the block implies
 330          control transfer, then we can't fall through.  */
 331       return false;
 332
 333     case SWITCH_EXPR:
 334       /* If SWITCH_LABELS is set, this is lowered, and represents a
 335          branch to a selected label and hence can not fall through.
 336          Otherwise SWITCH_BODY is set, and the switch can fall
 337          through.  */
 338       return SWITCH_LABELS (stmt) == NULL_TREE;
 339
 340     case COND_EXPR:
 341       if (block_may_fallthru (COND_EXPR_THEN (stmt)))
 342         return true;
 343       return block_may_fallthru (COND_EXPR_ELSE (stmt));
 344
 345     case BIND_EXPR:
 346       return block_may_fallthru (BIND_EXPR_BODY (stmt));
 347
 348     case TRY_CATCH_EXPR:
 349       return try_catch_may_fallthru (stmt);
 350
 351     case TRY_FINALLY_EXPR:
 352       /* The finally clause is always executed after the try clause,
 353          so if it does not fall through, then the try-finally will not
 354          fall through.  Otherwise, if the try clause does not fall
 355          through, then when the finally clause falls through it will
 356          resume execution wherever the try clause was going.  So the
 357          whole try-finally will only fall through if both the try
 358          clause and the finally clause fall through.  */
 359       return (block_may_fallthru (TREE_OPERAND (stmt, 0))
 360               && block_may_fallthru (TREE_OPERAND (stmt, 1)));
 361
 362     case MODIFY_EXPR:
 363       if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
 364         stmt = TREE_OPERAND (stmt, 1);
 365       else
 366         return true;
 367       /* FALLTHRU */
 368
 369     case CALL_EXPR:
 370       /* Functions that do not return do not fall through.  */
 371       return (call_expr_flags (stmt) & ECF_NORETURN) == 0;
 372
 373     default:
 374       return true;
 375     }
 376 }
 377
 378 /* Lowers a cond_expr TSI.  DATA is passed through the recursion.  */
 379
 380 static void
 381 lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 382 {
 383   tree stmt = tsi_stmt (*tsi);
 384   bool then_is_goto, else_is_goto;
 385   tree then_branch, else_branch;
 386   tree then_goto, else_goto;
 387
 388   then_branch = COND_EXPR_THEN (stmt);
 389   else_branch = COND_EXPR_ELSE (stmt);
 390
 391   lower_stmt_body (then_branch, data);
 392   lower_stmt_body (else_branch, data);
 393
 394   then_goto = expr_only (then_branch);
 395   then_is_goto = then_goto && simple_goto_p (then_goto);
 396
 397   else_goto = expr_only (else_branch);
 398   else_is_goto = else_goto && simple_goto_p (else_goto);
 399
 400   if (!then_is_goto || !else_is_goto)
 401     {
 402       tree then_label, else_label, end_label, t;
 403
 404       then_label = NULL_TREE;
 405       else_label = NULL_TREE;
 406       end_label = NULL_TREE;
 407
 408       /* Replace the cond_expr with explicit gotos.  */
 409       if (!then_is_goto)
 410         {
 411           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 412           if (TREE_SIDE_EFFECTS (then_branch))
 413             then_label = t;
 414           else
 415             end_label = t;
 416           then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 417         }
 418
 419       if (!else_is_goto)
 420         {
 421           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 422           if (TREE_SIDE_EFFECTS (else_branch))
 423             else_label = t;
 424           else
 425             {
 426               /* Both THEN and ELSE can be no-ops if one or both contained an
 427                  empty BIND_EXPR that was associated with the toplevel block
 428                  of an inlined function.  In that case remove_useless_stmts
 429                  can't have cleaned things up for us; kill the whole
 430                  conditional now.  */
 431               if (end_label)
 432                 {
 433                   tsi_delink (tsi);
 434                   return;
 435                 }
 436               else
 437                 end_label = t;
 438             }
 439           else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 440         }
 441
 442       if (then_label)
 443         {
 444           bool may_fallthru = block_may_fallthru (then_branch);
 445
 446           tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);
 447           tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);
 448
 449           if (else_label && may_fallthru)
 450             {
 451               end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 452               t = build_and_jump (&LABEL_EXPR_LABEL (end_label));
 453               tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);
 454             }
 455         }
 456
 457       if (else_label)
 458         {
 459           tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);
 460           tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);
 461         }
 462
 463       if (end_label)
 464         tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);
 465     }
 466
 467   COND_EXPR_THEN (stmt) = then_goto;
 468   COND_EXPR_ELSE (stmt) = else_goto;
 469
 470   tsi_next (tsi);
 471 }
 472
 473 static void
 474 lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 475 {
 476   tree stmt = tsi_stmt (*tsi);
 477   tree value, t, label;
 478
 479   /* Extract the value being returned.  */
 480   value = TREE_OPERAND (stmt, 0);
 481   if (value && TREE_CODE (value) == MODIFY_EXPR)
 482     value = TREE_OPERAND (value, 1);
 483
 484   /* Match this up with an existing return statement that's been created.  */
 485   for (t = data->return_statements; t ; t = TREE_CHAIN (t))
 486     {
 487       tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);
 488       if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)
 489         tvalue = TREE_OPERAND (tvalue, 1);
 490
 491       if (value == tvalue)
 492         {
 493           label = TREE_PURPOSE (t);
 494           goto found;
 495         }
 496     }
 497
 498   /* Not found.  Create a new label and record the return statement.  */
 499   label = create_artificial_label ();
 500   data->return_statements = tree_cons (label, stmt, data->return_statements);
 501
 502   /* Generate a goto statement and remove the return statement.  */
 503  found:
 504   t = build (GOTO_EXPR, void_type_node, label);
 505   SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));
 506   tsi_link_before (tsi, t, TSI_SAME_STMT);
 507   tsi_delink (tsi);
 508 }
 509 \f
 510
 511 /* Record the variables in VARS.  */
 512
 513 void
 514 record_vars (tree vars)
 515 {
 516   for (; vars; vars = TREE_CHAIN (vars))
 517     {
 518       tree var = vars;
 519
 520       /* Nothing to do in this case.  */
 521       if (DECL_EXTERNAL (var))
 522         continue;
 523       if (TREE_CODE (var) == FUNCTION_DECL)
 524         continue;
 525
 526       /* Record the variable.  */
 527       cfun->unexpanded_var_list = tree_cons (NULL_TREE, var,
 528                                              cfun->unexpanded_var_list);
 529     }
 530 }
 531
 532 /* Check whether to expand a variable VAR.  */
 533
 534 static bool
 535 expand_var_p (tree var)
 536 {
 537   struct var_ann_d *ann;
 538
 539   if (TREE_CODE (var) != VAR_DECL)
 540     return true;
 541
 542   /* Leave statics and externals alone.  */
 543   if (TREE_STATIC (var) || DECL_EXTERNAL (var))
 544     return true;
 545
 546   /* Remove all unused local variables.  */
 547   ann = var_ann (var);
 548   if (!ann || !ann->used)
 549     return false;
 550
 551   return true;
 552 }
 553
 554 /* Throw away variables that are unused.  */
 555
 556 static void
 557 remove_useless_vars (void)
 558 {
 559   tree var, *cell;
 560   FILE *df = NULL;
 561
 562   if (dump_file && (dump_flags & TDF_DETAILS))
 563     {
 564       df = dump_file;
 565       fputs ("Discarding as unused:\n", df);
 566     }
 567
 568   for (cell = &cfun->unexpanded_var_list; *cell; )
 569     {
 570       var = TREE_VALUE (*cell);
 571
 572       if (!expand_var_p (var))
 573         {
 574           if (df)
 575             {
 576               fputs ("  ", df);
 577               print_generic_expr (df, var, dump_flags);
 578               fputc ('\n', df);
 579             }
 580
 581           *cell = TREE_CHAIN (*cell);
 582           continue;
 583         }
 584
 585       cell = &TREE_CHAIN (*cell);
 586     }
 587
 588   if (df)
 589     fputc ('\n', df);
 590 }
 591
 592 struct tree_opt_pass pass_remove_useless_vars =
 593 {
 594   "vars",                               /* name */
 595   NULL,                                 /* gate */
 596   remove_useless_vars,                  /* execute */
 597   NULL,                                 /* sub */
 598   NULL,                                 /* next */
 599   0,                                    /* static_pass_number */
 600   0,                                    /* tv_id */
 601   0,                                    /* properties_required */
 602   0,                                    /* properties_provided */
 603   0,                                    /* properties_destroyed */
 604   0,                                    /* todo_flags_start */
 605   TODO_dump_func,                       /* todo_flags_finish */
 606   0                                     /* letter */
 607 };
 608
 609 /* Mark BLOCK used if it has a used variable in it, then recurse over its
 610    subblocks.  */
 611
 612 static void
 613 mark_blocks_with_used_vars (tree block)
 614 {
 615   tree var;
 616   tree subblock;
 617
 618   if (!TREE_USED (block))
 619     {
 620       for (var = BLOCK_VARS (block);
 621            var;
 622            var = TREE_CHAIN (var))
 623         {
 624           if (TREE_USED (var))
 625             {
 626               TREE_USED (block) = true;
 627               break;
 628             }
 629         }
 630     }
 631   for (subblock = BLOCK_SUBBLOCKS (block);
 632        subblock;
 633        subblock = BLOCK_CHAIN (subblock))
 634     mark_blocks_with_used_vars (subblock);
 635 }
 636
 637 /* Mark the used attribute on blocks correctly.  */
 638
 639 static void
 640 mark_used_blocks (void)
 641 {
 642   mark_blocks_with_used_vars (DECL_INITIAL (current_function_decl));
 643 }
 644
 645
 646 struct tree_opt_pass pass_mark_used_blocks =
 647 {
 648   "blocks",                             /* name */
 649   NULL,                                 /* gate */
 650   mark_used_blocks,                     /* execute */
 651   NULL,                                 /* sub */
 652   NULL,                                 /* next */
 653   0,                                    /* static_pass_number */
 654   0,                                    /* tv_id */
 655   0,                                    /* properties_required */
 656   0,                                    /* properties_provided */
 657   0,                                    /* properties_destroyed */
 658   0,                                    /* todo_flags_start */
 659   TODO_dump_func,                       /* todo_flags_finish */
 660   0                                     /* letter */
 661 };