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
  71   if (TREE_CODE (bind) != BIND_EXPR)
  72     abort ();
  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   /* If we lowered any return statements, emit the representative at the
  87      end of the function.  */
  88   if (data.return_statements)
  89     {
  90       tree t, x;
  91       i = tsi_last (*body_p);
  92
  93       for (t = data.return_statements; t ; t = TREE_CHAIN (t))
  94         {
  95           x = build (LABEL_EXPR, void_type_node, TREE_PURPOSE (t));
  96           tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
  97
  98           /* Remove the line number from the representative return statement.
  99              It now fills in for many such returns.  Failure to remove this
 100              will result in incorrect results for coverage analysis.  */
 101           x = TREE_VALUE (t);
 102           SET_EXPR_LOCUS (x, NULL);
 103           tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
 104         }
 105     }
 106
 107   if (data.block != DECL_INITIAL (current_function_decl))
 108     abort ();
 109   BLOCK_SUBBLOCKS (data.block)
 110     = blocks_nreverse (BLOCK_SUBBLOCKS (data.block));
 111
 112   clear_block_marks (data.block);
 113
 114   /* Avoid producing notes for blocks.  */
 115   cfun->dont_emit_block_notes = 1;
 116   reset_block_changes ();
 117 }
 118
 119 struct tree_opt_pass pass_lower_cf =
 120 {
 121   "lower",                              /* name */
 122   NULL,                                 /* gate */
 123   lower_function_body,                  /* execute */
 124   NULL,                                 /* sub */
 125   NULL,                                 /* next */
 126   0,                                    /* static_pass_number */
 127   0,                                    /* tv_id */
 128   PROP_gimple_any,                      /* properties_required */
 129   PROP_gimple_lcf,                      /* properties_provided */
 130   PROP_gimple_any,                      /* properties_destroyed */
 131   0,                                    /* todo_flags_start */
 132   TODO_dump_func                        /* todo_flags_finish */
 133 };
 134
 135
 136 /* Lowers the EXPR.  Unlike gimplification the statements are not relowered
 137    when they are changed -- if this has to be done, the lowering routine must
 138    do it explicitly.  DATA is passed through the recursion.  */
 139
 140 void
 141 lower_stmt_body (tree expr, struct lower_data *data)
 142 {
 143   tree_stmt_iterator tsi;
 144
 145   for (tsi = tsi_start (expr); !tsi_end_p (tsi); )
 146     lower_stmt (&tsi, data);
 147 }
 148
 149 /* Lowers statement TSI.  DATA is passed through the recursion.  */
 150
 151 static void
 152 lower_stmt (tree_stmt_iterator *tsi, struct lower_data *data)
 153 {
 154   tree stmt = tsi_stmt (*tsi);
 155
 156   if (EXPR_HAS_LOCATION (stmt) && data)
 157     TREE_BLOCK (stmt) = data->block;
 158
 159   switch (TREE_CODE (stmt))
 160     {
 161     case BIND_EXPR:
 162       lower_bind_expr (tsi, data);
 163       return;
 164     case COND_EXPR:
 165       lower_cond_expr (tsi, data);
 166       return;
 167     case RETURN_EXPR:
 168       lower_return_expr (tsi, data);
 169       return;
 170
 171     case TRY_FINALLY_EXPR:
 172     case TRY_CATCH_EXPR:
 173       lower_stmt_body (TREE_OPERAND (stmt, 0), data);
 174       lower_stmt_body (TREE_OPERAND (stmt, 1), data);
 175       break;
 176     case CATCH_EXPR:
 177       lower_stmt_body (CATCH_BODY (stmt), data);
 178       break;
 179     case EH_FILTER_EXPR:
 180       lower_stmt_body (EH_FILTER_FAILURE (stmt), data);
 181       break;
 182
 183     case NOP_EXPR:
 184     case ASM_EXPR:
 185     case MODIFY_EXPR:
 186     case CALL_EXPR:
 187     case GOTO_EXPR:
 188     case LABEL_EXPR:
 189     case VA_ARG_EXPR:
 190     case SWITCH_EXPR:
 191       break;
 192
 193     default:
 194       print_node_brief (stderr, "", stmt, 0);
 195     case COMPOUND_EXPR:
 196       abort ();
 197     }
 198
 199   tsi_next (tsi);
 200 }
 201
 202 /* Lowers a bind_expr TSI.  DATA is passed through the recursion.  */
 203
 204 static void
 205 lower_bind_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 206 {
 207   tree old_block = data->block;
 208   tree stmt = tsi_stmt (*tsi);
 209   tree new_block = BIND_EXPR_BLOCK (stmt);
 210
 211   if (new_block)
 212     {
 213       if (new_block == old_block)
 214         {
 215           /* The outermost block of the original function may not be the
 216              outermost statement chain of the gimplified function.  So we
 217              may see the outermost block just inside the function.  */
 218           if (new_block != DECL_INITIAL (current_function_decl))
 219             abort ();
 220           new_block = NULL;
 221         }
 222       else
 223         {
 224           /* We do not expect to handle duplicate blocks.  */
 225           if (TREE_ASM_WRITTEN (new_block))
 226             abort ();
 227           TREE_ASM_WRITTEN (new_block) = 1;
 228
 229           /* Block tree may get clobbered by inlining.  Normally this would
 230              be fixed in rest_of_decl_compilation using block notes, but
 231              since we are not going to emit them, it is up to us.  */
 232           BLOCK_CHAIN (new_block) = BLOCK_SUBBLOCKS (old_block);
 233           BLOCK_SUBBLOCKS (old_block) = new_block;
 234           BLOCK_SUBBLOCKS (new_block) = NULL_TREE;
 235           BLOCK_SUPERCONTEXT (new_block) = old_block;
 236
 237           data->block = new_block;
 238         }
 239     }
 240
 241   record_vars (BIND_EXPR_VARS (stmt));
 242   lower_stmt_body (BIND_EXPR_BODY (stmt), data);
 243
 244   if (new_block)
 245     {
 246       if (data->block != new_block)
 247         abort ();
 248
 249       BLOCK_SUBBLOCKS (new_block)
 250         = blocks_nreverse (BLOCK_SUBBLOCKS (new_block));
 251       data->block = old_block;
 252     }
 253
 254   /* The BIND_EXPR no longer carries any useful information -- kill it.  */
 255   tsi_link_before (tsi, BIND_EXPR_BODY (stmt), TSI_SAME_STMT);
 256   tsi_delink (tsi);
 257 }
 258
 259 /* Try to determine if we can fall out of the bottom of BLOCK.  This guess
 260    need not be 100% accurate; simply be conservative and return true if we
 261    don't know.  This is used only to avoid stupidly generating extra code.
 262    If we're wrong, we'll just delete the extra code later.  */
 263
 264 bool
 265 block_may_fallthru (tree block)
 266 {
 267   tree stmt = expr_last (block);
 268
 269   switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)
 270     {
 271     case GOTO_EXPR:
 272     case RETURN_EXPR:
 273     case RESX_EXPR:
 274     case SWITCH_EXPR:
 275       /* Easy cases.  If the last statement of the block implies
 276          control transfer, then we can't fall through.  */
 277       return false;
 278
 279     case COND_EXPR:
 280       if (block_may_fallthru (COND_EXPR_THEN (stmt)))
 281         return true;
 282       return block_may_fallthru (COND_EXPR_ELSE (stmt));
 283
 284     case BIND_EXPR:
 285       return block_may_fallthru (BIND_EXPR_BODY (stmt));
 286
 287     case TRY_FINALLY_EXPR:
 288       return block_may_fallthru (TREE_OPERAND (stmt, 1));
 289
 290     case MODIFY_EXPR:
 291       if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
 292         stmt = TREE_OPERAND (stmt, 1);
 293       else
 294         return true;
 295       /* FALLTHRU */
 296
 297     case CALL_EXPR:
 298       /* Functions that do not return do not fall through.  */
 299       return (call_expr_flags (stmt) & ECF_NORETURN) == 0;
 300
 301     default:
 302       return true;
 303     }
 304 }
 305
 306 /* Lowers a cond_expr TSI.  DATA is passed through the recursion.  */
 307
 308 static void
 309 lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 310 {
 311   tree stmt = tsi_stmt (*tsi);
 312   bool then_is_goto, else_is_goto;
 313   tree then_branch, else_branch;
 314   tree then_goto, else_goto;
 315
 316   then_branch = COND_EXPR_THEN (stmt);
 317   else_branch = COND_EXPR_ELSE (stmt);
 318
 319   lower_stmt_body (then_branch, data);
 320   lower_stmt_body (else_branch, data);
 321
 322   then_goto = expr_only (then_branch);
 323   then_is_goto = then_goto && simple_goto_p (then_goto);
 324
 325   else_goto = expr_only (else_branch);
 326   else_is_goto = else_goto && simple_goto_p (else_goto);
 327
 328   if (!then_is_goto || !else_is_goto)
 329     {
 330       tree then_label, else_label, end_label, t;
 331
 332       then_label = NULL_TREE;
 333       else_label = NULL_TREE;
 334       end_label = NULL_TREE;
 335
 336       /* Replace the cond_expr with explicit gotos.  */
 337       if (!then_is_goto)
 338         {
 339           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 340           if (TREE_SIDE_EFFECTS (then_branch))
 341             then_label = t;
 342           else
 343             end_label = t;
 344           then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 345         }
 346
 347       if (!else_is_goto)
 348         {
 349           t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 350           if (TREE_SIDE_EFFECTS (else_branch))
 351             else_label = t;
 352           else
 353             {
 354               /* Both THEN and ELSE can be no-ops if one or both contained an
 355                  empty BIND_EXPR that was associated with the toplevel block
 356                  of an inlined function.  In that case remove_useless_stmts
 357                  can't have cleaned things up for us; kill the whole
 358                  conditional now.  */
 359               if (end_label)
 360                 {
 361                   tsi_delink (tsi);
 362                   return;
 363                 }
 364               else
 365                 end_label = t;
 366             }
 367           else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
 368         }
 369
 370       if (then_label)
 371         {
 372           bool may_fallthru = block_may_fallthru (then_branch);
 373
 374           tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);
 375           tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);
 376
 377           if (else_label && may_fallthru)
 378             {
 379               end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
 380               t = build_and_jump (&LABEL_EXPR_LABEL (end_label));
 381               tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);
 382             }
 383         }
 384
 385       if (else_label)
 386         {
 387           tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);
 388           tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);
 389         }
 390
 391       if (end_label)
 392         tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);
 393     }
 394
 395   COND_EXPR_THEN (stmt) = then_goto;
 396   COND_EXPR_ELSE (stmt) = else_goto;
 397
 398   tsi_next (tsi);
 399 }
 400
 401 static void
 402 lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)
 403 {
 404   tree stmt = tsi_stmt (*tsi);
 405   tree value, t, label;
 406
 407   /* Extract the value being returned.  */
 408   value = TREE_OPERAND (stmt, 0);
 409   if (value && TREE_CODE (value) == MODIFY_EXPR)
 410     value = TREE_OPERAND (value, 1);
 411
 412   /* Match this up with an existing return statement that's been created.  */
 413   for (t = data->return_statements; t ; t = TREE_CHAIN (t))
 414     {
 415       tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);
 416       if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)
 417         tvalue = TREE_OPERAND (tvalue, 1);
 418
 419       if (value == tvalue)
 420         {
 421           label = TREE_PURPOSE (t);
 422           goto found;
 423         }
 424     }
 425
 426   /* Not found.  Create a new label and record the return statement.  */
 427   label = create_artificial_label ();
 428   data->return_statements = tree_cons (label, stmt, data->return_statements);
 429
 430   /* Generate a goto statement and remove the return statement.  */
 431  found:
 432   t = build (GOTO_EXPR, void_type_node, label);
 433   SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));
 434   tsi_link_before (tsi, t, TSI_SAME_STMT);
 435   tsi_delink (tsi);
 436 }
 437 \f
 438
 439 /* Record the variables in VARS.  */
 440
 441 void
 442 record_vars (tree vars)
 443 {
 444   for (; vars; vars = TREE_CHAIN (vars))
 445     {
 446       tree var = vars;
 447
 448       /* Nothing to do in this case.  */
 449       if (DECL_EXTERNAL (var))
 450         continue;
 451       if (TREE_CODE (var) == FUNCTION_DECL)
 452         continue;
 453
 454       /* Record the variable.  */
 455       cfun->unexpanded_var_list = tree_cons (NULL_TREE, var,
 456                                              cfun->unexpanded_var_list);
 457     }
 458 }
 459
 460 /* Check whether to expand a variable VAR.  */
 461
 462 static bool
 463 expand_var_p (tree var)
 464 {
 465   struct var_ann_d *ann;
 466
 467   if (TREE_CODE (var) != VAR_DECL)
 468     return true;
 469
 470   ann = var_ann (var);
 471
 472   /* Remove all unused, unaliased temporaries.  Also remove unused, unaliased
 473      local variables during highly optimizing compilations.  */
 474   ann = var_ann (var);
 475   if (ann
 476       && ! ann->may_aliases
 477       && ! ann->used
 478       && ! ann->has_hidden_use
 479       && ! TREE_ADDRESSABLE (var)
 480       && ! TREE_THIS_VOLATILE (var)
 481       && (DECL_ARTIFICIAL (var) || optimize >= 2))
 482     return false;
 483
 484   return true;
 485 }
 486
 487 /* Throw away variables that are unused.  */
 488
 489 static void
 490 remove_useless_vars (void)
 491 {
 492   tree var, *cell;
 493
 494   for (cell = &cfun->unexpanded_var_list; *cell; )
 495     {
 496       var = TREE_VALUE (*cell);
 497
 498       if (!expand_var_p (var))
 499         {
 500           *cell = TREE_CHAIN (*cell);
 501           continue;
 502         }
 503
 504       cell = &TREE_CHAIN (*cell);
 505     }
 506 }
 507
 508 /* Expand variables in the unexpanded_var_list.  */
 509
 510 void
 511 expand_used_vars (void)
 512 {
 513   tree cell;
 514
 515   cfun->unexpanded_var_list = nreverse (cfun->unexpanded_var_list);
 516
 517   for (cell = cfun->unexpanded_var_list; cell; cell = TREE_CHAIN (cell))
 518     expand_var (TREE_VALUE (cell));
 519
 520   cfun->unexpanded_var_list = NULL_TREE;
 521 }
 522
 523 struct tree_opt_pass pass_remove_useless_vars =
 524 {
 525   "vars",                               /* name */
 526   NULL,                                 /* gate */
 527   remove_useless_vars,                  /* execute */
 528   NULL,                                 /* sub */
 529   NULL,                                 /* next */
 530   0,                                    /* static_pass_number */
 531   0,                                    /* tv_id */
 532   0,                                    /* properties_required */
 533   0,                                    /* properties_provided */
 534   0,                                    /* properties_destroyed */
 535   0,                                    /* todo_flags_start */
 536   TODO_dump_func                        /* todo_flags_finish */
 537 };