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, 51 Franklin Street, Fifth Floor, Boston, MA
  20 02110-1301, 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 "varray.h"
  29 #include "tree-gimple.h"
  30 #include "tree-inline.h"
  31 #include "diagnostic.h"
  32 #include "langhooks.h"
  33 #include "langhooks-def.h"
  34 #include "tree-flow.h"
  35 #include "timevar.h"
  36 #include "except.h"
  37 #include "hashtab.h"
  38 #include "flags.h"
  39 #include "function.h"
  40 #include "expr.h"
  41 #include "toplev.h"
  42 #include "tree-pass.h"
  43
  44 struct lower_data
  45 {
  46   /* Block the current statement belongs to.  */
  47   tree block;
  48
  49   /* A TREE_LIST of label and return statements to be moved to the end
  50      of the function.  */
  51   tree return_statements;
  52 };
  53
  54 static void lower_stmt (tree_stmt_iterator *, struct lower_data *);
  55 static void lower_bind_expr (tree_stmt_iterator *, struct lower_data *);
  56 static void lower_cond_expr (tree_stmt_iterator *, struct lower_data *);
  57 static void lower_return_expr (tree_stmt_iterator *, struct lower_data *);
  58 static bool expand_var_p (tree);
  59
  60 /* Lowers the body of current_function_decl.  */
  61
  62 static void
  63 lower_function_body (void)
  64 {
  65   struct lower_data data;
  66   tree *body_p = &DECL_SAVED_TREE (current_function_decl);
  67   tree bind = *body_p;
  68   tree_stmt_iterator i;
  69   tree t, x;
  70
  71   gcc_assert (TREE_CODE (bind) == BIND_EXPR);
  72
  73   data.block = DECL_INITIAL (current_function_decl);
  74   BLOCK_SUBBLOCKS (data.block) = NULL_TREE;
  75   BLOCK_CHAIN (data.block) = NULL_TREE;
  76   TREE_ASM_WRITTEN (data.block) = 1;
  77
  78   data.return_statements = NULL_TREE;
  79
  80   *body_p = alloc_stmt_list ();
  81   i = tsi_start (*body_p);
  82   tsi_link_after (&i, bind, TSI_NEW_STMT);
  83   lower_bind_expr (&i, &data);
  84
  85   i = tsi_last (*body_p);
  86
  87   /* If the function falls off the end, we need a null return statement.
  88      If we've already got one in the return_statements list, we don't
  89      need to do anything special.  Otherwise build one by hand.  */
  90   if (block_may_fallthru (*body_p)
  91       && (data.return_statements == NULL
  92           || TREE_OPERAND (TREE_VALUE (data.return_statements), 0) != NULL))
  93     {
  94       x = build (RETURN_EXPR, void_type_node, NULL);
  95       SET_EXPR_LOCATION (x, cfun->function_end_locus);
  96       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
  97     }
  98
  99   /* If we lowered any return statements, emit the representative
 100      at the end of the function.  */
 101   for (t = data.return_statements ; t ; t = TREE_CHAIN (t))
 102     {
 103       x = build (LABEL_EXPR, void_type_node, TREE_PURPOSE (t));
 104       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
 105
 106       /* Remove the line number from the representative return statement.
 107          It now fills in for many such returns.  Failure to remove this
 108          will result in incorrect results for coverage analysis.  */
 109       x = TREE_VALUE (t);
 110 #ifdef USE_MAPPED_LOCATION
 111       SET_EXPR_LOCATION (x, UNKNOWN_LOCATION);
 112 #else
 113       SET_EXPR_LOCUS (x, NULL);
 114 #endif
 115       tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
 116     }
 117
 118   gcc_assert (data.block == DECL_INITIAL (current_function_decl));
 119   BLOCK_SUBBLOCKS (data.block)
 120     = blocks_nreverse (BLOCK_SUBBLOCKS (data.block));
 121
 122   clear_block_marks (data.block);
 123 }
 124
 125 struct tree_opt_pass pass_lower_cf =
 126 {
 127   "lower",                              /* name */
 128   NULL,                                 /* gate */
 129   lower_function_body,                  /* execute */
 130   NULL,                                 /* sub */
 131   NULL,                                 /* next */
 132   0,                                    /* static_pass_number */
 133   0,                                    /* tv_id */
 134   PROP_gimple_any,                      /* properties_required */
 135   PROP_gimple_lcf,                      /* properties_provided */
 136   PROP_gimple_any,                      /* properties_destroyed */
 137   0,                                    /* todo_flags_start */
 138   TODO_dump_func,                       /* todo_flags_finish */
 139   0                                     /* letter */
 140 };
 141
 142
 143 /* Lowers the EXPR.  Unlike gimplification the statements are not relowered
 144    when they are changed -- if this has to be done, the lowering routine must
 145    do it explicitly.  DATA is passed through the recursion.  */
 146
 147 static void
 148 lower_stmt_body (tree expr, struct lower_data *data)
 149 {
 150   tree_stmt_iterator tsi;
 151
 152   for (tsi = tsi_start (expr); !tsi_end_p (tsi); )
 153     lower_stmt (&tsi, data);
 154 }
 155
 156 /* Lowers statement TSI.  DATA is passed through the recursion.  */
 157
 158 static void
 159 lower_stmt (tree_stmt_iterator *tsi, struct lower_data *data)
 160 {
 161   tree stmt = tsi_stmt (*tsi);
 162
 163   if (EXPR_HAS_LOCATION (stmt) && data)
 164     TREE_BLOCK (stmt) = data->block;
 165
 166   switch (TREE_CODE (stmt))
 167     {
 168     case BIND_EXPR:
 169       lower_bind_expr (tsi, data);
 170       return;
 171     case COND_EXPR:
 172       lower_cond_expr (tsi, data);
 173       return;
 174     case RETURN_EXPR:
 175       lower_return_expr (tsi, data);
 176       return;
 177
 178     case TRY_FINALLY_EXPR:
 179     case TRY_CATCH_EXPR:
 180       lower_stmt_body (TREE_OPERAND (stmt, 0), data);
 181       lower_stmt_body (TREE_OPERAND (stmt, 1), data);
 182       break;
 183     case CATCH_EXPR:
 184       lower_stmt_body (CATCH_BODY (stmt), data);
 185       break;
 186     case EH_FILTER_EXPR:
 187       lower_stmt_body (EH_FILTER_FAILURE (stmt), data);
 188       break;
 189
 190     case NOP_EXPR:
 191     case ASM_EXPR:
 192     case MODIFY_EXPR:
 193     case CALL_EXPR:
 194     case GOTO_EXPR:
 195     case LABEL_EXPR:
 196     case SWITCH_EXPR:
 197       break;
 198
 199     default:
 200 #ifdef ENABLE_CHECKING
 201       print_node_brief (stderr, "", stmt, 0);
 202       internal_error ("unexpected node");
 203 #endif
 204     case COMPOUND_EXPR:
 205       gcc_unreachable ();
 206     }
 207
 208   tsi_next (tsi);
 209 }
 210
 211 /* Lowers a bind_expr TSI.  DATA is passed through the recursion.  */
 212
 213 static void
 214 lower_bind_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 215 {
 216   tree old_block = data->block;
 217   tree stmt = tsi_stmt (*tsi);
 218   tree new_block = BIND_EXPR_BLOCK (stmt);
 219
 220   if (new_block)
 221     {
 222       if (new_block == old_block)
 223         {
 224           /* The outermost block of the original function may not be the
 225              outermost statement chain of the gimplified function.  So we
 226              may see the outermost block just inside the function.  */
 227           gcc_assert (new_block == DECL_INITIAL (current_function_decl));
 228           new_block = NULL;
 229         }
 230       else
 231         {
 232           /* We do not expect to handle duplicate blocks.  */
 233           gcc_assert (!TREE_ASM_WRITTEN (new_block));
 234           TREE_ASM_WRITTEN (new_block) = 1;
 235
 236           /* Block tree may get clobbered by inlining.  Normally this would
 237              be fixed in rest_of_decl_compilation using block notes, but
 238              since we are not going to emit them, it is up to us.  */
 239           BLOCK_CHAIN (new_block) = BLOCK_SUBBLOCKS (old_block);
 240           BLOCK_SUBBLOCKS (old_block) = new_block;
 241           BLOCK_SUBBLOCKS (new_block) = NULL_TREE;
 242           BLOCK_SUPERCONTEXT (new_block) = old_block;
 243
 244           data->block = new_block;
 245         }
 246     }
 247
 248   record_vars (BIND_EXPR_VARS (stmt));
 249   lower_stmt_body (BIND_EXPR_BODY (stmt), data);
 250
 251   if (new_block)
 252     {
 253       gcc_assert (data->block == new_block);
 254
 255       BLOCK_SUBBLOCKS (new_block)
 256         = blocks_nreverse (BLOCK_SUBBLOCKS (new_block));
 257       data->block = old_block;
 258     }
 259
 260   /* The BIND_EXPR no longer carries any useful information -- kill it.  */
 261   tsi_link_before (tsi, BIND_EXPR_BODY (stmt), TSI_SAME_STMT);
 262   tsi_delink (tsi);
 263 }
 264
 265 /* Try to determine whether a TRY_CATCH expression can fall through.
 266    This is a subroutine of block_may_fallthru.  */
 267
 268 static bool
 269 try_catch_may_fallthru (tree stmt)
 270 {
 271   tree_stmt_iterator i;
 272
 273   /* If the TRY block can fall through, the whole TRY_CATCH can
 274      fall through.  */
 275   if (block_may_fallthru (TREE_OPERAND (stmt, 0)))
 276     return true;
 277
 278   i = tsi_start (TREE_OPERAND (stmt, 1));
 279   switch (TREE_CODE (tsi_stmt (i)))
 280     {
 281     case CATCH_EXPR:
 282       /* We expect to see a sequence of CATCH_EXPR trees, each with a
 283          catch expression and a body.  The whole TRY_CATCH may fall
 284          through iff any of the catch bodies falls through.  */
 285       for (; !tsi_end_p (i); tsi_next (&i))
 286         {
 287           if (block_may_fallthru (CATCH_BODY (tsi_stmt (i))))
 288             return true;
 289         }
 290       return false;
 291
 292     case EH_FILTER_EXPR:
 293       /* The exception filter expression only matters if there is an
 294          exception.  If the exception does not match EH_FILTER_TYPES,
 295          we will execute EH_FILTER_FAILURE, and we will fall through
 296          if that falls through.  If the exception does match
 297          EH_FILTER_TYPES, the stack unwinder will continue up the
 298          stack, so we will not fall through.  We don't know whether we
 299          will throw an exception which matches EH_FILTER_TYPES or not,
 300          so we just ignore EH_FILTER_TYPES and assume that we might
 301          throw an exception which doesn't match.  */
 302       return block_may_fallthru (EH_FILTER_FAILURE (tsi_stmt (i)));
 303
 304     default:
 305       /* This case represents statements to be executed when an
 306          exception occurs.  Those statements are implicitly followed
 307          by a RESX_EXPR to resume execution after the exception.  So
 308          in this case the TRY_CATCH never falls through.  */
 309       return false;
 310     }
 311 }
 312
 313 /* Try to determine if we can fall out of the bottom of BLOCK.  This guess
 314    need not be 100% accurate; simply be conservative and return true if we
 315    don't know.  This is used only to avoid stupidly generating extra code.
 316    If we're wrong, we'll just delete the extra code later.  */
 317
 318 bool
 319 block_may_fallthru (tree block)
 320 {
 321   tree stmt = expr_last (block);
 322
 323   switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)
 324     {
 325     case GOTO_EXPR:
 326     case RETURN_EXPR:
 327     case RESX_EXPR:
 328       /* Easy cases.  If the last statement of the block implies
 329          control transfer, then we can't fall through.  */
 330       return false;
 331
 332     case SWITCH_EXPR:
 333       /* If SWITCH_LABELS is set, this is lowered, and represents a
 334          branch to a selected label and hence can not fall through.
 335          Otherwise SWITCH_BODY is set, and the switch can fall
 336          through.  */
 337       return SWITCH_LABELS (stmt) == NULL_TREE;
 338
 339     case COND_EXPR:
 340       if (block_may_fallthru (COND_EXPR_THEN (stmt)))
 341         return true;
 342       return block_may_fallthru (COND_EXPR_ELSE (stmt));
 343
 344     case BIND_EXPR:
 345       return block_may_fallthru (BIND_EXPR_BODY (stmt));
 346
 347     case TRY_CATCH_EXPR:
 348       return try_catch_may_fallthru (stmt);
 349
 350     case TRY_FINALLY_EXPR:
 351       /* The finally clause is always executed after the try clause,
 352          so if it does not fall through, then the try-finally will not
 353          fall through.  Otherwise, if the try clause does not fall
 354          through, then when the finally clause falls through it will
 355          resume execution wherever the try clause was going.  So the
 356          whole try-finally will only fall through if both the try
 357          clause and the finally clause fall through.  */
 358       return (block_may_fallthru (TREE_OPERAND (stmt, 0))
 359               && block_may_fallthru (TREE_OPERAND (stmt, 1)));
 360
 361     case MODIFY_EXPR:
 362       if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
 363         stmt = TREE_OPERAND (stmt, 1);
 364       else
 365         return true;
 366       /* FALLTHRU */
 367
 368     case CALL_EXPR:
 369       /* Functions that do not return do not fall through.  */
 370       return (call_expr_flags (stmt) & ECF_NORETURN) == 0;
 371
 372     default:
 373       return true;
 374     }
 375 }
 376
 377 /* Lowers a cond_expr TSI.  DATA is passed through the recursion.  */
 378
 379 static void
 380 lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 381 {
 382   tree stmt = tsi_stmt (*tsi);
 383   bool then_is_goto, else_is_goto;
 384   tree then_branch, else_branch;
 385   tree then_goto, else_goto;
 386
 387   then_branch = COND_EXPR_THEN (stmt);
 388   else_branch = COND_EXPR_ELSE (stmt);
 389
 390   lower_stmt_body (then_branch, data);
 391   lower_stmt_body (else_branch, data);
 392
 393   then_goto = expr_only (then_branch);
 394   then_is_goto = then_goto && simple_goto_p (then_goto);
 395
 396   else_goto = expr_only (else_branch);
 397   else_is_goto = else_goto && simple_goto_p (else_goto);
 398
 399   if (!then_is_goto || !else_is_goto)
 400     {
 401       tree then_label, else_label, end_label, t;
 402
 403       then_label = NULL_TREE;
 404       else_label = NULL_TREE;
 405       end_label = NULL_TREE;
 406
 407       /* Replace the cond_expr with explicit gotos.  */
 408       if (!then_is_goto)
 409         {
 410           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 411           if (TREE_SIDE_EFFECTS (then_branch))
 412             then_label = t;
 413           else
 414             end_label = t;
 415           then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 416         }
 417
 418       if (!else_is_goto)
 419         {
 420           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 421           if (TREE_SIDE_EFFECTS (else_branch))
 422             else_label = t;
 423           else
 424             {
 425               /* Both THEN and ELSE can be no-ops if one or both contained an
 426                  empty BIND_EXPR that was associated with the toplevel block
 427                  of an inlined function.  In that case remove_useless_stmts
 428                  can't have cleaned things up for us; kill the whole
 429                  conditional now.  */
 430               if (end_label)
 431                 {
 432                   tsi_delink (tsi);
 433                   return;
 434                 }
 435               else
 436                 end_label = t;
 437             }
 438           else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 439         }
 440
 441       if (then_label)
 442         {
 443           bool may_fallthru = block_may_fallthru (then_branch);
 444
 445           tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);
 446           tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);
 447
 448           if (else_label && may_fallthru)
 449             {
 450               end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 451               t = build_and_jump (&LABEL_EXPR_LABEL (end_label));
 452               tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);
 453             }
 454         }
 455
 456       if (else_label)
 457         {
 458           tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);
 459           tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);
 460         }
 461
 462       if (end_label)
 463         tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);
 464     }
 465
 466   COND_EXPR_THEN (stmt) = then_goto;
 467   COND_EXPR_ELSE (stmt) = else_goto;
 468
 469   tsi_next (tsi);
 470 }
 471
 472 static void
 473 lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 474 {
 475   tree stmt = tsi_stmt (*tsi);
 476   tree value, t, label;
 477
 478   /* Extract the value being returned.  */
 479   value = TREE_OPERAND (stmt, 0);
 480   if (value && TREE_CODE (value) == MODIFY_EXPR)
 481     value = TREE_OPERAND (value, 1);
 482
 483   /* Match this up with an existing return statement that's been created.  */
 484   for (t = data->return_statements; t ; t = TREE_CHAIN (t))
 485     {
 486       tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);
 487       if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)
 488         tvalue = TREE_OPERAND (tvalue, 1);
 489
 490       if (value == tvalue)
 491         {
 492           label = TREE_PURPOSE (t);
 493           goto found;
 494         }
 495     }
 496
 497   /* Not found.  Create a new label and record the return statement.  */
 498   label = create_artificial_label ();
 499   data->return_statements = tree_cons (label, stmt, data->return_statements);
 500
 501   /* Generate a goto statement and remove the return statement.  */
 502  found:
 503   t = build (GOTO_EXPR, void_type_node, label);
 504   SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));
 505   tsi_link_before (tsi, t, TSI_SAME_STMT);
 506   tsi_delink (tsi);
 507 }
 508 \f
 509
 510 /* Record the variables in VARS.  */
 511
 512 void
 513 record_vars (tree vars)
 514 {
 515   for (; vars; vars = TREE_CHAIN (vars))
 516     {
 517       tree var = vars;
 518
 519       /* BIND_EXPRs contains also function/type/constant declarations
 520          we don't need to care about.  */
 521       if (TREE_CODE (var) != VAR_DECL)
 522         continue;
 523       /* Nothing to do in this case.  */
 524       if (DECL_EXTERNAL (var))
 525         continue;
 526
 527       /* Record the variable.  */
 528       cfun->unexpanded_var_list = tree_cons (NULL_TREE, var,
 529                                              cfun->unexpanded_var_list);
 530     }
 531 }
 532
 533 /* Check whether to expand a variable VAR.  */
 534
 535 static bool
 536 expand_var_p (tree var)
 537 {
 538   struct var_ann_d *ann;
 539
 540   if (TREE_CODE (var) != VAR_DECL)
 541     return true;
 542
 543   /* Leave statics and externals alone.  */
 544   if (TREE_STATIC (var) || DECL_EXTERNAL (var))
 545     return true;
 546
 547   /* Remove all unused local variables.  */
 548   ann = var_ann (var);
 549   if (!ann || !ann->used)
 550     return false;
 551
 552   return true;
 553 }
 554
 555 /* Throw away variables that are unused.  */
 556
 557 static void
 558 remove_useless_vars (void)
 559 {
 560   tree var, *cell;
 561   FILE *df = NULL;
 562
 563   if (dump_file && (dump_flags & TDF_DETAILS))
 564     {
 565       df = dump_file;
 566       fputs ("Discarding as unused:\n", df);
 567     }
 568
 569   for (cell = &cfun->unexpanded_var_list; *cell; )
 570     {
 571       var = TREE_VALUE (*cell);
 572
 573       if (!expand_var_p (var))
 574         {
 575           if (df)
 576             {
 577               fputs ("  ", df);
 578               print_generic_expr (df, var, dump_flags);
 579               fputc ('\n', df);
 580             }
 581
 582           *cell = TREE_CHAIN (*cell);
 583           continue;
 584         }
 585
 586       cell = &TREE_CHAIN (*cell);
 587     }
 588
 589   if (df)
 590     fputc ('\n', df);
 591 }
 592
 593 struct tree_opt_pass pass_remove_useless_vars =
 594 {
 595   "vars",                               /* name */
 596   NULL,                                 /* gate */
 597   remove_useless_vars,                  /* execute */
 598   NULL,                                 /* sub */
 599   NULL,                                 /* next */
 600   0,                                    /* static_pass_number */
 601   0,                                    /* tv_id */
 602   0,                                    /* properties_required */
 603   0,                                    /* properties_provided */
 604   0,                                    /* properties_destroyed */
 605   0,                                    /* todo_flags_start */
 606   TODO_dump_func,                       /* todo_flags_finish */
 607   0                                     /* letter */
 608 };
 609
 610 /* Mark BLOCK used if it has a used variable in it, then recurse over its
 611    subblocks.  */
 612
 613 static void
 614 mark_blocks_with_used_vars (tree block)
 615 {
 616   tree var;
 617   tree subblock;
 618
 619   if (!TREE_USED (block))
 620     {
 621       for (var = BLOCK_VARS (block);
 622            var;
 623            var = TREE_CHAIN (var))
 624         {
 625           if (TREE_USED (var))
 626             {
 627               TREE_USED (block) = true;
 628               break;
 629             }
 630         }
 631     }
 632   for (subblock = BLOCK_SUBBLOCKS (block);
 633        subblock;
 634        subblock = BLOCK_CHAIN (subblock))
 635     mark_blocks_with_used_vars (subblock);
 636 }
 637
 638 /* Mark the used attribute on blocks correctly.  */
 639
 640 static void
 641 mark_used_blocks (void)
 642 {
 643   mark_blocks_with_used_vars (DECL_INITIAL (current_function_decl));
 644 }
 645
 646
 647 struct tree_opt_pass pass_mark_used_blocks =
 648 {
 649   "blocks",                             /* name */
 650   NULL,                                 /* gate */
 651   mark_used_blocks,                     /* execute */
 652   NULL,                                 /* sub */
 653   NULL,                                 /* next */
 654   0,                                    /* static_pass_number */
 655   0,                                    /* tv_id */
 656   0,                                    /* properties_required */
 657   0,                                    /* properties_provided */
 658   0,                                    /* properties_destroyed */
 659   0,                                    /* todo_flags_start */
 660   TODO_dump_func,                       /* todo_flags_finish */
 661   0                                     /* letter */
 662 };