gcc/hw-doloop.c

   1 /* Code to analyze doloop loops in order for targets to perform late
   2    optimizations converting doloops to other forms of hardware loops.
   3    Copyright (C) 2011-2013 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 3, 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 COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "rtl.h"
  26 #include "flags.h"
  27 #include "expr.h"
  28 #include "hard-reg-set.h"
  29 #include "regs.h"
  30 #include "basic-block.h"
  31 #include "tm_p.h"
  32 #include "df.h"
  33 #include "cfgloop.h"
  34 #include "recog.h"
  35 #include "target.h"
  36 #include "hw-doloop.h"
  37 #include "dumpfile.h"
  38
  39 #ifdef HAVE_doloop_end
  40
  41 /* Dump information collected in LOOPS.  */
  42 static void
  43 dump_hwloops (hwloop_info loops)
  44 {
  45   hwloop_info loop;
  46
  47   for (loop = loops; loop; loop = loop->next)
  48     {
  49       hwloop_info i;
  50       basic_block b;
  51       unsigned ix;
  52
  53       fprintf (dump_file, ";; loop %d: ", loop->loop_no);
  54       if (loop->bad)
  55         fprintf (dump_file, "(bad) ");
  56       fprintf (dump_file, "{head:%d, depth:%d, reg:%u}",
  57                loop->head == NULL ? -1 : loop->head->index,
  58                loop->depth, REGNO (loop->iter_reg));
  59
  60       fprintf (dump_file, " blocks: [ ");
  61       for (ix = 0; loop->blocks.iterate (ix, &b); ix++)
  62         fprintf (dump_file, "%d ", b->index);
  63       fprintf (dump_file, "] ");
  64
  65       fprintf (dump_file, " inner loops: [ ");
  66       for (ix = 0; loop->loops.iterate (ix, &i); ix++)
  67         fprintf (dump_file, "%d ", i->loop_no);
  68       fprintf (dump_file, "]\n");
  69     }
  70   fprintf (dump_file, "\n");
  71 }
  72
  73 /* Return true if BB is part of LOOP.  */
  74 static bool
  75 bb_in_loop_p (hwloop_info loop, basic_block bb)
  76 {
  77   return bitmap_bit_p (loop->block_bitmap, bb->index);
  78 }
  79
  80 /* Scan the blocks of LOOP (and its inferiors), and record things such as
  81    hard registers set, jumps out of and within the loop.  */
  82 static void
  83 scan_loop (hwloop_info loop)
  84 {
  85   unsigned ix;
  86   basic_block bb;
  87
  88   if (loop->bad)
  89     return;
  90
  91   if (REGNO_REG_SET_P (df_get_live_in (loop->successor),
  92                        REGNO (loop->iter_reg)))
  93     loop->iter_reg_used_outside = true;
  94
  95   for (ix = 0; loop->blocks.iterate (ix, &bb); ix++)
  96     {
  97       rtx insn;
  98       edge e;
  99       edge_iterator ei;
 100
 101       if (bb != loop->tail)
 102         FOR_EACH_EDGE (e, ei, bb->succs)
 103           {
 104             if (bb_in_loop_p (loop, e->dest))
 105               {
 106                 if (!(e->flags & EDGE_FALLTHRU))
 107                   loop->jumps_within = true;
 108               }
 109             else
 110               {
 111                 loop->jumps_outof = true;
 112                 if (!loop->bad)
 113                   gcc_assert (!REGNO_REG_SET_P (df_get_live_in (e->dest),
 114                                                 REGNO (loop->iter_reg)));
 115               }
 116           }
 117
 118       for (insn = BB_HEAD (bb);
 119            insn != NEXT_INSN (BB_END (bb));
 120            insn = NEXT_INSN (insn))
 121         {
 122           df_ref *def_rec;
 123           HARD_REG_SET set_this_insn;
 124
 125           if (!NONDEBUG_INSN_P (insn))
 126             continue;
 127
 128           if (recog_memoized (insn) < 0
 129               && (GET_CODE (PATTERN (insn)) == ASM_INPUT
 130                   || asm_noperands (PATTERN (insn)) >= 0))
 131             loop->has_asm = true;
 132
 133           CLEAR_HARD_REG_SET (set_this_insn);
 134           for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
 135             {
 136               rtx dreg = DF_REF_REG (*def_rec);
 137
 138               if (!REG_P (dreg))
 139                 continue;
 140
 141               add_to_hard_reg_set (&set_this_insn, GET_MODE (dreg),
 142                                    REGNO (dreg));
 143             }
 144
 145           if (insn == loop->loop_end)
 146             CLEAR_HARD_REG_BIT (set_this_insn, REGNO (loop->iter_reg));
 147           else if (reg_mentioned_p (loop->iter_reg, PATTERN (insn)))
 148             loop->iter_reg_used = true;
 149           IOR_HARD_REG_SET (loop->regs_set_in_loop, set_this_insn);
 150         }
 151     }
 152 }
 153
 154 /* Compute the incoming_dest and incoming_src members of LOOP by
 155    identifying the edges that jump into the loop.  If there is more
 156    than one block that jumps into the loop, incoming_src will be set
 157    to NULL; likewise, if there is more than one block in the loop that
 158    is the destination of an incoming edge, incoming_dest will be NULL.
 159
 160    Return true if either of these two fields is nonnull, false
 161    otherwise.  */
 162 static bool
 163 process_incoming_edges (hwloop_info loop)
 164 {
 165   edge e;
 166   edge_iterator ei;
 167   bool first = true;
 168
 169   FOR_EACH_EDGE (e, ei, loop->incoming)
 170     {
 171       if (first)
 172         {
 173           loop->incoming_src = e->src;
 174           loop->incoming_dest = e->dest;
 175           first = false;
 176         }
 177       else
 178         {
 179           if (e->dest != loop->incoming_dest)
 180             loop->incoming_dest = NULL;
 181           if (e->src != loop->incoming_src)
 182             loop->incoming_src = NULL;
 183         }
 184     }
 185   if (loop->incoming_src == NULL && loop->incoming_dest == NULL)
 186     return false;
 187
 188   return true;
 189 }
 190
 191 /* Try to identify a forwarder block that jump into LOOP, and add it to
 192    the set of blocks in the loop, updating the vector of incoming blocks as
 193    well.  This transformation gives a second chance to loops we couldn't
 194    otherwise handle by increasing the chance that we'll end up with one
 195    incoming_src block.
 196    Return true if we made a change, false otherwise.  */
 197 static bool
 198 add_forwarder_blocks (hwloop_info loop)
 199 {
 200   edge e;
 201   edge_iterator ei;
 202
 203   FOR_EACH_EDGE (e, ei, loop->incoming)
 204     {
 205       if (forwarder_block_p (e->src))
 206         {
 207           edge e2;
 208           edge_iterator ei2;
 209
 210           if (dump_file)
 211             fprintf (dump_file,
 212                      ";; Adding forwarder block %d to loop %d and retrying\n",
 213                      e->src->index, loop->loop_no);
 214           loop->blocks.safe_push (e->src);
 215           bitmap_set_bit (loop->block_bitmap, e->src->index);
 216           FOR_EACH_EDGE (e2, ei2, e->src->preds)
 217             vec_safe_push (loop->incoming, e2);
 218           loop->incoming->unordered_remove (ei.index);
 219           return true;
 220         }
 221     }
 222   return false;
 223 }
 224
 225 /* Called from reorg_loops when a potential loop end is found.  LOOP is
 226    a newly set up structure describing the loop, it is this function's
 227    responsibility to fill most of it.  TAIL_BB and TAIL_INSN point to the
 228    loop_end insn and its enclosing basic block.  REG is the loop counter
 229    register.
 230    For our purposes, a loop is defined by the set of blocks reachable from
 231    the loop head in which the loop counter register is live.  This matches
 232    the expected use; targets that call into this code usually replace the
 233    loop counter with a different special register.  */
 234 static void
 235 discover_loop (hwloop_info loop, basic_block tail_bb, rtx tail_insn, rtx reg)
 236 {
 237   bool found_tail;
 238   unsigned dwork = 0;
 239   basic_block bb;
 240   vec<basic_block> works;
 241
 242   loop->tail = tail_bb;
 243   loop->loop_end = tail_insn;
 244   loop->iter_reg = reg;
 245   vec_alloc (loop->incoming, 2);
 246   loop->start_label = JUMP_LABEL (tail_insn);
 247
 248   if (EDGE_COUNT (tail_bb->succs) != 2)
 249     {
 250       loop->bad = true;
 251       return;
 252     }
 253   loop->head = BRANCH_EDGE (tail_bb)->dest;
 254   loop->successor = FALLTHRU_EDGE (tail_bb)->dest;
 255
 256   works.create (20);
 257   works.safe_push (loop->head);
 258
 259   found_tail = false;
 260   for (dwork = 0; works.iterate (dwork, &bb); dwork++)
 261     {
 262       edge e;
 263       edge_iterator ei;
 264       if (bb == EXIT_BLOCK_PTR)
 265         {
 266           /* We've reached the exit block.  The loop must be bad. */
 267           if (dump_file)
 268             fprintf (dump_file,
 269                      ";; Loop is bad - reached exit block while scanning\n");
 270           loop->bad = true;
 271           break;
 272         }
 273
 274       if (bitmap_bit_p (loop->block_bitmap, bb->index))
 275         continue;
 276
 277       /* We've not seen this block before.  Add it to the loop's
 278          list and then add each successor to the work list.  */
 279
 280       loop->blocks.safe_push (bb);
 281       bitmap_set_bit (loop->block_bitmap, bb->index);
 282
 283       if (bb == tail_bb)
 284         found_tail = true;
 285       else
 286         {
 287           FOR_EACH_EDGE (e, ei, bb->succs)
 288             {
 289               basic_block succ = EDGE_SUCC (bb, ei.index)->dest;
 290               if (REGNO_REG_SET_P (df_get_live_in (succ),
 291                                    REGNO (loop->iter_reg)))
 292                 works.safe_push (succ);
 293             }
 294         }
 295     }
 296
 297   if (!found_tail)
 298     loop->bad = true;
 299
 300   /* Find the predecessor, and make sure nothing else jumps into this loop.  */
 301   if (!loop->bad)
 302     {
 303       FOR_EACH_VEC_ELT (loop->blocks, dwork, bb)
 304         {
 305           edge e;
 306           edge_iterator ei;
 307           FOR_EACH_EDGE (e, ei, bb->preds)
 308             {
 309               basic_block pred = e->src;
 310
 311               if (!bb_in_loop_p (loop, pred))
 312                 {
 313                   if (dump_file)
 314                     fprintf (dump_file, ";; Loop %d: incoming edge %d -> %d\n",
 315                              loop->loop_no, pred->index,
 316                              e->dest->index);
 317                   vec_safe_push (loop->incoming, e);
 318                 }
 319             }
 320         }
 321
 322       if (!process_incoming_edges (loop))
 323         {
 324           if (dump_file)
 325             fprintf (dump_file,
 326                      ";; retrying loop %d with forwarder blocks\n",
 327                      loop->loop_no);
 328           if (!add_forwarder_blocks (loop))
 329             {
 330               if (dump_file)
 331                 fprintf (dump_file, ";; No forwarder blocks found\n");
 332               loop->bad = true;
 333             }
 334           else if (!process_incoming_edges (loop))
 335             {
 336               if (dump_file)
 337                 fprintf (dump_file,
 338                          ";; can't find suitable entry for loop %d\n",
 339                          loop->loop_no);
 340             }
 341         }
 342     }
 343
 344   works.release ();
 345 }
 346
 347 /* Analyze the structure of the loops in the current function.  Use
 348    LOOP_STACK for bitmap allocations.  Returns all the valid candidates for
 349    hardware loops found in this function.  HOOKS is the argument
 350    passed to reorg_loops, used here to find the iteration registers
 351    from a loop_end pattern.  */
 352 static hwloop_info
 353 discover_loops (bitmap_obstack *loop_stack, struct hw_doloop_hooks *hooks)
 354 {
 355   hwloop_info loops = NULL;
 356   hwloop_info loop;
 357   basic_block bb;
 358   int nloops = 0;
 359
 360   /* Find all the possible loop tails.  This means searching for every
 361      loop_end instruction.  For each one found, create a hwloop_info
 362      structure and add the head block to the work list. */
 363   FOR_EACH_BB (bb)
 364     {
 365       rtx tail = BB_END (bb);
 366       rtx insn, reg;
 367
 368       while (tail && NOTE_P (tail) && tail != BB_HEAD (bb))
 369         tail = PREV_INSN (tail);
 370
 371       if (tail == NULL_RTX)
 372         continue;
 373
 374       if (!JUMP_P (tail))
 375         continue;
 376       reg = hooks->end_pattern_reg (tail);
 377       if (reg == NULL_RTX)
 378         continue;
 379
 380       /* A possible loop end */
 381
 382       /* There's a degenerate case we can handle - an empty loop consisting
 383          of only a back branch.  Handle that by deleting the branch.  */
 384       insn = JUMP_LABEL (tail);
 385       while (insn && !NONDEBUG_INSN_P (insn))
 386         insn = NEXT_INSN (insn);
 387       if (insn == tail)
 388         {
 389           basic_block succ = FALLTHRU_EDGE (bb)->dest;
 390           if (dump_file)
 391             {
 392               fprintf (dump_file, ";; degenerate loop ending at\n");
 393               print_rtl_single (dump_file, tail);
 394             }
 395           if (!REGNO_REG_SET_P (df_get_live_in (succ), REGNO (reg)))
 396             {
 397               if (dump_file)
 398                 fprintf (dump_file, ";; deleting it\n");
 399               delete_insn_and_edges (tail);
 400               continue;
 401             }
 402         }
 403
 404       loop = XCNEW (struct hwloop_info_d);
 405       loop->next = loops;
 406       loops = loop;
 407       loop->loop_no = nloops++;
 408       loop->blocks.create (20);
 409       loop->block_bitmap = BITMAP_ALLOC (loop_stack);
 410
 411       if (dump_file)
 412         {
 413           fprintf (dump_file, ";; potential loop %d ending at\n",
 414                    loop->loop_no);
 415           print_rtl_single (dump_file, tail);
 416         }
 417
 418       discover_loop (loop, bb, tail, reg);
 419     }
 420
 421   /* Compute loop nestings.  Given two loops A and B, either the sets
 422      of their blocks don't intersect at all, or one is the subset of
 423      the other, or the blocks don't form a good nesting structure.  */
 424   for (loop = loops; loop; loop = loop->next)
 425     {
 426       hwloop_info other;
 427
 428       if (loop->bad)
 429         continue;
 430
 431       for (other = loops; other; other = other->next)
 432         {
 433           if (other->bad)
 434             continue;
 435
 436           if (!bitmap_intersect_p (other->block_bitmap, loop->block_bitmap))
 437             continue;
 438           if (!bitmap_intersect_compl_p (other->block_bitmap,
 439                                          loop->block_bitmap))
 440             loop->loops.safe_push (other);
 441           else if (!bitmap_intersect_compl_p (loop->block_bitmap,
 442                                               other->block_bitmap))
 443             other->loops.safe_push (loop);
 444           else
 445             {
 446               if (dump_file)
 447                 fprintf (dump_file,
 448                          ";; can't find suitable nesting for loops %d and %d\n",
 449                          loop->loop_no, other->loop_no);
 450               loop->bad = other->bad = true;
 451             }
 452         }
 453     }
 454
 455   if (dump_file)
 456     dump_hwloops (loops);
 457
 458   return loops;
 459 }
 460
 461 /* Free up the loop structures in LOOPS.  */
 462 static void
 463 free_loops (hwloop_info loops)
 464 {
 465   while (loops)
 466     {
 467       hwloop_info loop = loops;
 468       loops = loop->next;
 469       loop->loops.release ();
 470       loop->blocks.release ();
 471       BITMAP_FREE (loop->block_bitmap);
 472       XDELETE (loop);
 473     }
 474 }
 475
 476 #define BB_AUX_INDEX(BB) ((intptr_t) (BB)->aux)
 477
 478 /* Initialize the aux fields to give ascending indices to basic blocks.  */
 479 static void
 480 set_bb_indices (void)
 481 {
 482   basic_block bb;
 483   intptr_t index;
 484
 485   index = 0;
 486   FOR_EACH_BB (bb)
 487     bb->aux = (void *) index++;
 488 }
 489
 490 /* The taken-branch edge from the loop end can actually go forward.
 491    If the target's hardware loop support requires that the loop end be
 492    after the loop start, try to reorder a loop's basic blocks when we
 493    find such a case.
 494    This is not very aggressive; it only moves at most one block.  It
 495    does not introduce new branches into loops; it may remove them, or
 496    it may switch fallthru/jump edges.  */
 497 static void
 498 reorder_loops (hwloop_info loops)
 499 {
 500   basic_block bb;
 501   hwloop_info loop;
 502
 503   cfg_layout_initialize (0);
 504
 505   set_bb_indices ();
 506
 507   for (loop = loops; loop; loop = loop->next)
 508     {
 509       edge e;
 510       edge_iterator ei;
 511
 512       if (loop->bad)
 513         continue;
 514
 515       if (BB_AUX_INDEX (loop->head) <= BB_AUX_INDEX (loop->tail))
 516         continue;
 517
 518       FOR_EACH_EDGE (e, ei, loop->head->succs)
 519         {
 520           if (bitmap_bit_p (loop->block_bitmap, e->dest->index)
 521               && BB_AUX_INDEX (e->dest) < BB_AUX_INDEX (loop->tail))
 522             {
 523               basic_block start_bb = e->dest;
 524               basic_block start_prev_bb = start_bb->prev_bb;
 525
 526               if (dump_file)
 527                 fprintf (dump_file, ";; Moving block %d before block %d\n",
 528                          loop->head->index, start_bb->index);
 529               loop->head->prev_bb->next_bb = loop->head->next_bb;
 530               loop->head->next_bb->prev_bb = loop->head->prev_bb;
 531
 532               loop->head->prev_bb = start_prev_bb;
 533               loop->head->next_bb = start_bb;
 534               start_prev_bb->next_bb = start_bb->prev_bb = loop->head;
 535
 536               set_bb_indices ();
 537               break;
 538             }
 539         }
 540       loops = loops->next;
 541     }
 542
 543   FOR_EACH_BB (bb)
 544     {
 545       if (bb->next_bb != EXIT_BLOCK_PTR)
 546         bb->aux = bb->next_bb;
 547       else
 548         bb->aux = NULL;
 549     }
 550   cfg_layout_finalize ();
 551   clear_aux_for_blocks ();
 552   df_analyze ();
 553 }
 554
 555 /* Call the OPT function for LOOP and all of its sub-loops.  This is
 556    done in a depth-first search; innermost loops are visited first.
 557    OPTIMIZE and FAIL are the functions passed to reorg_loops by the
 558    target's reorg pass.  */
 559 static void
 560 optimize_loop (hwloop_info loop, struct hw_doloop_hooks *hooks)
 561 {
 562   int ix;
 563   hwloop_info inner;
 564   int inner_depth = 0;
 565
 566   if (loop->visited)
 567     return;
 568
 569   loop->visited = 1;
 570
 571   if (loop->bad)
 572     {
 573       if (dump_file)
 574         fprintf (dump_file, ";; loop %d bad when found\n", loop->loop_no);
 575       goto bad_loop;
 576     }
 577
 578   /* Every loop contains in its list of inner loops every loop nested inside
 579      it, even if there are intermediate loops.  This works because we're doing
 580      a depth-first search here and never visit a loop more than once.
 581      Recursion depth is effectively limited by the number of available
 582      hardware registers.  */
 583   for (ix = 0; loop->loops.iterate (ix, &inner); ix++)
 584     {
 585       optimize_loop (inner, hooks);
 586
 587       if (!inner->bad && inner_depth < inner->depth)
 588         inner_depth = inner->depth;
 589       /* The set of registers may be changed while optimizing the inner
 590          loop.  */
 591       IOR_HARD_REG_SET (loop->regs_set_in_loop, inner->regs_set_in_loop);
 592     }
 593
 594   loop->depth = inner_depth + 1;
 595
 596   if (hooks->opt (loop))
 597     return;
 598
 599  bad_loop:
 600   if (dump_file)
 601     fprintf (dump_file, ";; loop %d is bad\n", loop->loop_no);
 602
 603   loop->bad = true;
 604   hooks->fail (loop);
 605 }
 606
 607 /* This function can be used from a port's machine_dependent_reorg to
 608    find and analyze loops that end in loop_end instructions.  It uses
 609    a set of function pointers in HOOKS to call back into the
 610    target-specific functions to perform the actual machine-specific
 611    transformations.
 612
 613    Such transformations typically involve additional set-up
 614    instructions before the loop, to define loop bounds or set up a
 615    special loop counter register.
 616
 617    DO_REORDER should be set to true if we should try to use the
 618    reorder_loops function to ensure the loop end occurs after the loop
 619    start.  This is for use by targets where the loop hardware requires
 620    this condition.
 621
 622    HOOKS is used to pass in target specific hooks; see
 623    hw-doloop.h.  */
 624 void
 625 reorg_loops (bool do_reorder, struct hw_doloop_hooks *hooks)
 626 {
 627   hwloop_info loops = NULL;
 628   hwloop_info loop;
 629   bitmap_obstack loop_stack;
 630
 631   df_live_add_problem ();
 632   df_live_set_all_dirty ();
 633   df_analyze ();
 634
 635   bitmap_obstack_initialize (&loop_stack);
 636
 637   if (dump_file)
 638     fprintf (dump_file, ";; Find loops, first pass\n\n");
 639
 640   loops = discover_loops (&loop_stack, hooks);
 641
 642   if (do_reorder)
 643     {
 644       reorder_loops (loops);
 645       free_loops (loops);
 646
 647       if (dump_file)
 648         fprintf (dump_file, ";; Find loops, second pass\n\n");
 649
 650       loops = discover_loops (&loop_stack, hooks);
 651     }
 652
 653   for (loop = loops; loop; loop = loop->next)
 654     scan_loop (loop);
 655
 656   /* Now apply the optimizations.  */
 657   for (loop = loops; loop; loop = loop->next)
 658     optimize_loop (loop, hooks);
 659
 660   if (dump_file)
 661     {
 662       fprintf (dump_file, ";; After hardware loops optimization:\n\n");
 663       dump_hwloops (loops);
 664     }
 665
 666   free_loops (loops);
 667
 668   if (dump_file)
 669     print_rtl (dump_file, get_insns ());
 670 }
 671 #endif