gcc/c-iterate.c

   1 /* Build expressions with type checking for C compiler.
   2    Copyright (C) 1987, 1988, 1989, 1992 Free Software Foundation, Inc.
   3
   4 This file is part of GNU CC.
   5
   6 GNU CC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU CC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU CC; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20
  21 /* This file is part of the C front end.
  22    It is responsible for implementing iterators,
  23    both their declarations and the expansion of statements using them.  */
  24
  25 #include "config.h"
  26 #include <stdio.h>
  27 #include "tree.h"
  28 #include "c-tree.h"
  29 #include "flags.h"
  30 #include "obstack.h"
  31 #include "rtl.h"
  32
  33 static void expand_stmt_with_iterators_1 ();
  34 static tree collect_iterators();
  35 static void iterator_loop_prologue ();
  36 static void iterator_loop_epilogue ();
  37 static void add_ixpansion ();
  38 static void delete_ixpansion();
  39 static int top_level_ixpansion_p ();
  40 static void istack_sublevel_to_current ();
  41
  42 /* A special obstack, and a pointer to the start of
  43    all the data in it (so we can free everything easily).  */
  44 static struct obstack ixp_obstack;
  45 static char *ixp_firstobj;
  46 \f
  47 /*
  48                 KEEPING TRACK OF EXPANSIONS
  49
  50    In order to clean out expansions corresponding to statements inside
  51    "{(...)}" constructs we have to keep track of all expansions.  The
  52    cleanup is needed when an automatic, or implicit, expansion on
  53    iterator, say X, happens to a statement which contains a {(...)}
  54    form with a statement already expanded on X.  In this case we have
  55    to go back and cleanup the inner expansion.  This can be further
  56    complicated by the fact that {(...)} can be nested.
  57
  58    To make this cleanup possible, we keep lists of all expansions, and
  59    to make it work for nested constructs, we keep a stack.  The list at
  60    the top of the stack (ITER_STACK.CURRENT_LEVEL) corresponds to the
  61    currently parsed level.  All expansions of the levels below the
  62    current one are kept in one list whose head is pointed to by
  63    ITER_STACK.SUBLEVEL_FIRST (SUBLEVEL_LAST is there for making merges
  64    easy).  The process works as follows:
  65
  66    -- On "({"  a new node is added to the stack by PUSH_ITERATOR_STACK.
  67                The sublevel list is not changed at this point.
  68
  69    -- On "})" the list for the current level is appended to the sublevel
  70               list.
  71
  72    -- On ";"  sublevel lists are appended to the current level lists.
  73               The reason is this: if they have not been superseded by the
  74               expansion at the current level, they still might be
  75               superseded later by the expansion on the higher level.
  76               The levels do not have to distinguish levels below, so we
  77               can merge the lists together.  */
  78
  79 struct  ixpansion
  80 {
  81   tree ixdecl;                  /* Iterator decl */
  82   rtx  ixprologue_start;        /* First insn of epilogue. NULL means */
  83   /* explicit (FOR) expansion*/
  84   rtx  ixprologue_end;
  85   rtx  ixepilogue_start;
  86   rtx  ixepilogue_end;
  87   struct ixpansion *next;       /* Next in the list */
  88 };
  89
  90 struct iter_stack_node
  91 {
  92   struct ixpansion *first;      /* Head of list of ixpansions */
  93   struct ixpansion *last;       /* Last node in list  of ixpansions */
  94   struct iter_stack_node *next; /* Next level iterator stack node  */
  95 };
  96
  97 struct iter_stack_node *iter_stack;
  98
  99 struct iter_stack_node sublevel_ixpansions;
 100 \f
 101 /* Initialize our obstack once per compilation.  */
 102
 103 void
 104 init_iterators ()
 105 {
 106   gcc_obstack_init (&ixp_obstack);
 107   ixp_firstobj = (char *) obstack_alloc (&ixp_obstack, 0);
 108 }
 109
 110 /* Handle the start of an explicit `for' loop for iterator IDECL.  */
 111
 112 void
 113 iterator_for_loop_start (idecl)
 114      tree idecl;
 115 {
 116   ITERATOR_BOUND_P (idecl) = 1;
 117   add_ixpansion (idecl, 0, 0, 0, 0);
 118   iterator_loop_prologue (idecl, 0, 0);
 119 }
 120
 121 /* Handle the end of an explicit `for' loop for iterator IDECL.  */
 122
 123 void
 124 iterator_for_loop_end (idecl)
 125      tree idecl;
 126 {
 127   iterator_loop_epilogue (idecl, 0, 0);
 128   ITERATOR_BOUND_P (idecl) = 0;
 129 }
 130 \f
 131 /*
 132                 ITERATOR RTL EXPANSIONS
 133
 134    Expanding simple statements with iterators is straightforward:
 135    collect the list of all free iterators in the statement, and
 136    generate a loop for each of them.
 137
 138    An iterator is "free" if it has not been "bound" by a FOR
 139    operator.  The DECL_RTL of the iterator is the loop counter.  */
 140
 141 /* Expand a statement STMT, possibly containing iterator usage, into RTL.  */
 142
 143 void
 144 iterator_expand (stmt)
 145     tree stmt;
 146 {
 147   tree iter_list = collect_iterators (stmt, NULL_TREE);
 148   expand_stmt_with_iterators_1 (stmt, iter_list);
 149   istack_sublevel_to_current ();
 150 }
 151
 152
 153 static void
 154 expand_stmt_with_iterators_1 (stmt, iter_list)
 155      tree stmt, iter_list;
 156 {
 157   if (iter_list == 0)
 158     expand_expr_stmt (stmt);
 159   else
 160     {
 161       tree current_iterator = TREE_VALUE (iter_list);
 162       tree iter_list_tail   = TREE_CHAIN (iter_list);
 163       rtx p_start, p_end, e_start, e_end;
 164
 165       iterator_loop_prologue (current_iterator, &p_start, &p_end);
 166       expand_stmt_with_iterators_1 (stmt, iter_list_tail);
 167       iterator_loop_epilogue (current_iterator, &e_start, &e_end);
 168
 169       /** Delete all inner expansions based on current_iterator **/
 170       /** before adding the outer one. **/
 171
 172       delete_ixpansion (current_iterator);
 173       add_ixpansion (current_iterator, p_start, p_end, e_start, e_end);
 174     }
 175 }
 176
 177
 178 /* Return a list containing all the free (i.e. not bound by a
 179    containing `for' statement) iterators mentioned in EXP, plus those
 180    in LIST.  Do not add duplicate entries to the list.  */
 181
 182 static tree
 183 collect_iterators (exp, list)
 184      tree exp, list;
 185 {
 186   if (exp == 0) return list;
 187
 188   switch (TREE_CODE (exp))
 189     {
 190     case VAR_DECL:
 191       if (! ITERATOR_P (exp) || ITERATOR_BOUND_P (exp))
 192         return list;
 193       if (value_member (exp, list))
 194         return list;
 195       return tree_cons (NULL_TREE, exp, list);
 196
 197     case TREE_LIST:
 198       {
 199         tree tail;
 200         for (tail = exp; tail; tail = TREE_CHAIN (tail))
 201           list = collect_iterators (TREE_VALUE (tail), list);
 202         return list;
 203       }
 204
 205       /* we do not automatically iterate blocks -- one must */
 206       /* use the FOR construct to do that */
 207
 208     case BLOCK:
 209       return list;
 210
 211     default:
 212       switch (TREE_CODE_CLASS (TREE_CODE (exp)))
 213         {
 214         case '1':
 215         case '2':
 216         case '<':
 217         case 'e':
 218         case 'r':
 219           {
 220             int num_args = tree_code_length[TREE_CODE (exp)];
 221             int i;
 222
 223             for (i = 0; i < num_args; i++)
 224               list = collect_iterators (TREE_OPERAND (exp, i), list);
 225             return list;
 226           }
 227         default:
 228           return list;
 229         }
 230     }
 231 }
 232 \f
 233 /* Emit rtl for the start of a loop for iterator IDECL.
 234
 235    If necessary, create loop counter rtx and store it as DECL_RTL of IDECL.
 236
 237    The prologue normally starts and ends with notes, which are returned
 238    by this function in *START_NOTE and *END_NODE.
 239    If START_NOTE and END_NODE are 0, we don't make those notes.  */
 240
 241 static void
 242 iterator_loop_prologue (idecl, start_note, end_note)
 243      tree idecl;
 244      rtx *start_note, *end_note;
 245 {
 246   /* Force the save_expr in DECL_INITIAL to be calculated
 247      if it hasn't been calculated yet.  */
 248   expand_expr (DECL_INITIAL (idecl), 0, VOIDmode, 0);
 249
 250   if (DECL_RTL (idecl) == 0)
 251     expand_decl (idecl);
 252
 253   if (start_note)
 254     *start_note = emit_note (0, NOTE_INSN_DELETED);
 255   /* Initialize counter.  */
 256   expand_expr (build (MODIFY_EXPR, TREE_TYPE (idecl),
 257                       idecl, integer_zero_node),
 258                0, VOIDmode, 0);
 259
 260   expand_start_loop_continue_elsewhere (1);
 261
 262   ITERATOR_BOUND_P (idecl) = 1;
 263
 264   if (end_note)
 265     *end_note = emit_note (0, NOTE_INSN_DELETED);
 266 }
 267
 268 /* Similar to the previous function, but for the end of the loop.
 269
 270    DECL_RTL is zeroed unless we are inside "({...})". The reason for that is
 271    described below.
 272
 273    When we create two (or more) loops based on the same IDECL, and
 274    both inside the same "({...})"  construct, we must be prepared to
 275    delete both of the loops and create a single one on the level
 276    above, i.e.  enclosing the "({...})". The new loop has to use the
 277    same counter rtl because the references to the iterator decl
 278    (IDECL) have already been expanded as references to the counter
 279    rtl.
 280
 281    It is incorrect to use the same counter reg in different functions,
 282    and it is desirable to use different counters in disjoint loops
 283    when we know there's no need to combine them (because then they can
 284    get allocated separately).  */
 285
 286 static void
 287 iterator_loop_epilogue (idecl, start_note, end_note)
 288      tree idecl;
 289      rtx *start_note, *end_note;
 290 {
 291   tree test, incr;
 292
 293   if (start_note)
 294     *start_note = emit_note (0, NOTE_INSN_DELETED);
 295   expand_loop_continue_here ();
 296   incr = build_binary_op (PLUS_EXPR, idecl, integer_one_node, 0);
 297   expand_expr (build (MODIFY_EXPR, TREE_TYPE (idecl), idecl, incr),
 298                0, VOIDmode, 0);
 299   test = build_binary_op (LT_EXPR, idecl, DECL_INITIAL (idecl), 0);
 300   expand_exit_loop_if_false (0, test);
 301   expand_end_loop ();
 302
 303   ITERATOR_BOUND_P (idecl) = 0;
 304   /* we can reset rtl since there is not chance that this expansion */
 305   /* would be superceded by a higher level one */
 306   if (top_level_ixpansion_p ())
 307     DECL_RTL (idecl) = 0;
 308   if (end_note)
 309     *end_note = emit_note (0, NOTE_INSN_DELETED);
 310 }
 311 \f
 312 /* Return true if we are not currently inside a "({...})" construct.  */
 313
 314 static int
 315 top_level_ixpansion_p ()
 316 {
 317   return iter_stack == 0;
 318 }
 319
 320 /* Given two chains of iter_stack_nodes,
 321    append the nodes in X into Y.  */
 322
 323 static void
 324 isn_append (x, y)
 325      struct iter_stack_node *x, *y;
 326 {
 327   if (x->first == 0)
 328     return;
 329
 330   if (y->first == 0)
 331     {
 332       y->first = x->first;
 333       y->last  = x->last;
 334     }
 335   else
 336     {
 337       y->last->next = x->first;
 338       y->last = x->last;
 339     }
 340 }
 341
 342 /** Make X empty **/
 343
 344 #define ISN_ZERO(X) (X).first=(X).last=0
 345 \f
 346 /* Move the ixpansions in sublevel_ixpansions into the current
 347    node on the iter_stack, or discard them if the iter_stack is empty.
 348    We do this at the end of a statement.  */
 349
 350 static void
 351 istack_sublevel_to_current ()
 352 {
 353   /* At the top level we can throw away sublevel's expansions  **/
 354   /* because there is nobody above us to ask for a cleanup **/
 355   if (iter_stack != 0)
 356     /** Merging with empty sublevel list is a no-op **/
 357     if (sublevel_ixpansions.last)
 358       isn_append (&sublevel_ixpansions, iter_stack);
 359
 360   if (iter_stack == 0)
 361     obstack_free (&ixp_obstack, ixp_firstobj);
 362
 363   ISN_ZERO (sublevel_ixpansions);
 364 }
 365
 366 /* Push a new node on the iter_stack, when we enter a ({...}).  */
 367
 368 void
 369 push_iterator_stack ()
 370 {
 371   struct iter_stack_node *new_top
 372     = (struct iter_stack_node*)
 373       obstack_alloc (&ixp_obstack, sizeof (struct iter_stack_node));
 374
 375   new_top->first = 0;
 376   new_top->last = 0;
 377   new_top->next = iter_stack;
 378   iter_stack = new_top;
 379 }
 380
 381 /* Pop iter_stack, moving the ixpansions in the node being popped
 382    into sublevel_ixpansions.  */
 383
 384 void
 385 pop_iterator_stack ()
 386 {
 387   if (iter_stack == 0)
 388     abort ();
 389
 390   isn_append (iter_stack, &sublevel_ixpansions);
 391   /** Pop current level node: */
 392   iter_stack = iter_stack->next;
 393 }
 394 \f
 395
 396 /* Record an iterator expansion ("ixpansion") for IDECL.
 397    The remaining paramters are the notes in the loop entry
 398    and exit rtl.  */
 399
 400 static void
 401 add_ixpansion (idecl, pro_start, pro_end, epi_start, epi_end)
 402      tree idecl;
 403      rtx pro_start, pro_end, epi_start, epi_end;
 404 {
 405   struct ixpansion* newix;
 406
 407   /* Do nothing if we are not inside "({...})",
 408      as in that case this expansion can't need subsequent RTL modification.  */
 409   if (iter_stack == 0)
 410     return;
 411
 412   newix = (struct ixpansion*) obstack_alloc (&ixp_obstack,
 413                                              sizeof (struct ixpansion));
 414   newix->ixdecl = idecl;
 415   newix->ixprologue_start = pro_start;
 416   newix->ixprologue_end   = pro_end;
 417   newix->ixepilogue_start = epi_start;
 418   newix->ixepilogue_end   = epi_end;
 419
 420   newix->next = iter_stack->first;
 421   iter_stack->first = newix;
 422   if (iter_stack->last == 0)
 423     iter_stack->last = newix;
 424 }
 425
 426 /* Delete the RTL for all ixpansions for iterator IDECL
 427    in our sublevels.  We do this when we make a larger
 428    containing expansion for IDECL.  */
 429
 430 static void
 431 delete_ixpansion (idecl)
 432      tree idecl;
 433 {
 434   struct ixpansion* previx = 0, *ix;
 435
 436   for (ix = sublevel_ixpansions.first; ix; ix = ix->next)
 437     if (ix->ixdecl == idecl)
 438       {
 439         /** zero means that this is a mark for FOR -- **/
 440         /** we do not delete anything, just issue an error. **/
 441
 442         if (ix->ixprologue_start == 0)
 443           error_with_decl (idecl,
 444                            "`for (%s)' appears within implicit iteration");
 445         else
 446           {
 447             rtx insn;
 448             /* We delete all insns, including notes because leaving loop */
 449             /* notes and barriers produced by iterator expansion would */
 450             /* be misleading to other phases */
 451
 452             for (insn = NEXT_INSN (ix->ixprologue_start);
 453                  insn != ix->ixprologue_end;
 454                  insn = NEXT_INSN (insn))
 455               delete_insn (insn);
 456             for (insn = NEXT_INSN (ix->ixepilogue_start);
 457                  insn != ix->ixepilogue_end;
 458                  insn = NEXT_INSN (insn))
 459               delete_insn (insn);
 460           }
 461
 462         /* Delete this ixpansion from sublevel_ixpansions.  */
 463         if (previx)
 464           previx->next = ix->next;
 465         else
 466           sublevel_ixpansions.first = ix->next;
 467         if (sublevel_ixpansions.last == ix)
 468           sublevel_ixpansions.last = previx;
 469       }
 470     else
 471       previx = ix;
 472 }
 473 \f
 474 #ifdef DEBUG_ITERATORS
 475
 476 /* The functions below are for use from source level debugger.
 477    They print short forms of iterator lists and the iterator stack.  */
 478
 479 /* Print the name of the iterator D.  */
 480
 481 void
 482 prdecl (d)
 483      tree d;
 484 {
 485   if (d)
 486     {
 487       if (TREE_CODE (d) == VAR_DECL)
 488         {
 489           tree tname = DECL_NAME (d);
 490           char *dname = IDENTIFIER_POINTER (tname);
 491           fprintf (stderr, dname);
 492         }
 493       else
 494         fprintf (stderr, "<<Not a Decl!!!>>");
 495     }
 496   else
 497     fprintf (stderr, "<<NULL!!>>");
 498 }
 499
 500 /* Print Iterator List -- names only */
 501
 502 tree
 503 pil (head)
 504      tree head;
 505 {
 506   tree current, next;
 507   for (current = head; current; current = next)
 508     {
 509       tree node = TREE_VALUE (current);
 510       prdecl (node);
 511       next = TREE_CHAIN (current);
 512       if (next) fprintf (stderr, ",");
 513     }
 514   fprintf (stderr, "\n");
 515 }
 516
 517 /* Print IXpansion List */
 518
 519 struct ixpansion *
 520 pixl (head)
 521      struct ixpansion *head;
 522 {
 523   struct ixpansion *current, *next;
 524   fprintf (stderr, "> ");
 525   if (head == 0)
 526     fprintf (stderr, "(empty)");
 527
 528   for (current=head; current; current = next)
 529     {
 530       tree node = current->ixdecl;
 531       prdecl (node);
 532       next = current->next;
 533       if (next)
 534         fprintf (stderr, ",");
 535     }
 536   fprintf (stderr, "\n");
 537   return head;
 538 }
 539
 540 /* Print Iterator Stack*/
 541
 542 void
 543 pis ()
 544 {
 545   struct iter_stack_node *stack_node;
 546
 547   fprintf (stderr, "--SubLevel: ");
 548   pixl (sublevel_ixpansions.first);
 549   fprintf (stderr, "--Stack:--\n");
 550   for (stack_node = iter_stack;
 551        stack_node;
 552        stack_node = stack_node->next)
 553     pixl (stack_node->first);
 554 }
 555
 556 #endif /* DEBUG_ITERATORS */