gcc/loop-doloop.c

   1 /* Perform doloop optimizations
   2    Copyright (C) 2004, 2005, 2006, 2007, 2008 Free Software Foundation,
   3    Inc.
   4    Based on code by Michael P. Hayes (m.hayes@elec.canterbury.ac.nz)
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it under
   9 the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 3, or (at your option) any later
  11 version.
  12
  13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  16 for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with GCC; see the file COPYING3.  If not see
  20 <http://www.gnu.org/licenses/>.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tm.h"
  26 #include "rtl.h"
  27 #include "flags.h"
  28 #include "expr.h"
  29 #include "hard-reg-set.h"
  30 #include "basic-block.h"
  31 #include "toplev.h"
  32 #include "tm_p.h"
  33 #include "cfgloop.h"
  34 #include "output.h"
  35 #include "params.h"
  36 #include "target.h"
  37
  38 /* This module is used to modify loops with a determinable number of
  39    iterations to use special low-overhead looping instructions.
  40
  41    It first validates whether the loop is well behaved and has a
  42    determinable number of iterations (either at compile or run-time).
  43    It then modifies the loop to use a low-overhead looping pattern as
  44    follows:
  45
  46    1. A pseudo register is allocated as the loop iteration counter.
  47
  48    2. The number of loop iterations is calculated and is stored
  49       in the loop counter.
  50
  51    3. At the end of the loop, the jump insn is replaced by the
  52       doloop_end pattern.  The compare must remain because it might be
  53       used elsewhere.  If the loop-variable or condition register are
  54       used elsewhere, they will be eliminated by flow.
  55
  56    4. An optional doloop_begin pattern is inserted at the top of the
  57       loop.
  58
  59    TODO The optimization should only performed when either the biv used for exit
  60    condition is unused at all except for the exit test, or if we do not have to
  61    change its value, since otherwise we have to add a new induction variable,
  62    which usually will not pay up (unless the cost of the doloop pattern is
  63    somehow extremely lower than the cost of compare & jump, or unless the bct
  64    register cannot be used for anything else but doloop -- ??? detect these
  65    cases).  */
  66
  67 #ifdef HAVE_doloop_end
  68
  69 /* Return the loop termination condition for PATTERN or zero
  70    if it is not a decrement and branch jump insn.  */
  71
  72 rtx
  73 doloop_condition_get (rtx doloop_pat)
  74 {
  75   rtx cmp;
  76   rtx inc;
  77   rtx reg;
  78   rtx inc_src;
  79   rtx condition;
  80   rtx pattern;
  81
  82   /* The canonical doloop pattern we expect has one of the following
  83      forms:
  84
  85      1)  (parallel [(set (pc) (if_then_else (condition)
  86                                             (label_ref (label))
  87                                             (pc)))
  88                      (set (reg) (plus (reg) (const_int -1)))
  89                      (additional clobbers and uses)])
  90
  91      The branch must be the first entry of the parallel (also required
  92      by jump.c), and the second entry of the parallel must be a set of
  93      the loop counter register.  Some targets (IA-64) wrap the set of
  94      the loop counter in an if_then_else too.
  95
  96      2)  (set (reg) (plus (reg) (const_int -1))
  97          (set (pc) (if_then_else (reg != 0)
  98                                  (label_ref (label))
  99                                  (pc))).  */
 100
 101   pattern = PATTERN (doloop_pat);
 102
 103   if (GET_CODE (pattern) != PARALLEL)
 104     {
 105       rtx cond;
 106
 107       /* We expect the decrement to immediately precede the branch.  */
 108
 109       if ((PREV_INSN (doloop_pat) == NULL_RTX)
 110           || !INSN_P (PREV_INSN (doloop_pat)))
 111         return 0;
 112
 113       cmp = pattern;
 114       inc = PATTERN (PREV_INSN (doloop_pat));
 115       /* We expect the condition to be of the form (reg != 0)  */
 116       cond = XEXP (SET_SRC (cmp), 0);
 117       if (GET_CODE (cond) != NE || XEXP (cond, 1) != const0_rtx)
 118         return 0;
 119
 120     }
 121   else
 122     {
 123       cmp = XVECEXP (pattern, 0, 0);
 124       inc = XVECEXP (pattern, 0, 1);
 125     }
 126
 127   /* Check for (set (reg) (something)).  */
 128   if (GET_CODE (inc) != SET)
 129     return 0;
 130   reg = SET_DEST (inc);
 131   if (! REG_P (reg))
 132     return 0;
 133
 134   /* Check if something = (plus (reg) (const_int -1)).
 135      On IA-64, this decrement is wrapped in an if_then_else.  */
 136   inc_src = SET_SRC (inc);
 137   if (GET_CODE (inc_src) == IF_THEN_ELSE)
 138     inc_src = XEXP (inc_src, 1);
 139   if (GET_CODE (inc_src) != PLUS
 140       || XEXP (inc_src, 0) != reg
 141       || XEXP (inc_src, 1) != constm1_rtx)
 142     return 0;
 143
 144   /* Check for (set (pc) (if_then_else (condition)
 145                                        (label_ref (label))
 146                                        (pc))).  */
 147   if (GET_CODE (cmp) != SET
 148       || SET_DEST (cmp) != pc_rtx
 149       || GET_CODE (SET_SRC (cmp)) != IF_THEN_ELSE
 150       || GET_CODE (XEXP (SET_SRC (cmp), 1)) != LABEL_REF
 151       || XEXP (SET_SRC (cmp), 2) != pc_rtx)
 152     return 0;
 153
 154   /* Extract loop termination condition.  */
 155   condition = XEXP (SET_SRC (cmp), 0);
 156
 157   /* We expect a GE or NE comparison with 0 or 1.  */
 158   if ((GET_CODE (condition) != GE
 159        && GET_CODE (condition) != NE)
 160       || (XEXP (condition, 1) != const0_rtx
 161           && XEXP (condition, 1) != const1_rtx))
 162     return 0;
 163
 164   if ((XEXP (condition, 0) == reg)
 165       || (GET_CODE (XEXP (condition, 0)) == PLUS
 166                    && XEXP (XEXP (condition, 0), 0) == reg))
 167    {
 168      if (GET_CODE (pattern) != PARALLEL)
 169      /*  The second form we expect:
 170
 171          (set (reg) (plus (reg) (const_int -1))
 172          (set (pc) (if_then_else (reg != 0)
 173                                  (label_ref (label))
 174                                  (pc))).
 175
 176          is equivalent to the following:
 177
 178          (parallel [(set (pc) (if_then_else (reg != 1)
 179                                             (label_ref (label))
 180                                             (pc)))
 181                      (set (reg) (plus (reg) (const_int -1)))
 182                      (additional clobbers and uses)])
 183
 184          So we return that form instead.
 185      */
 186         condition = gen_rtx_fmt_ee (NE, VOIDmode, inc_src, const1_rtx);
 187
 188     return condition;
 189    }
 190
 191   /* ??? If a machine uses a funny comparison, we could return a
 192      canonicalized form here.  */
 193
 194   return 0;
 195 }
 196
 197 /* Return nonzero if the loop specified by LOOP is suitable for
 198    the use of special low-overhead looping instructions.  DESC
 199    describes the number of iterations of the loop.  */
 200
 201 static bool
 202 doloop_valid_p (struct loop *loop, struct niter_desc *desc)
 203 {
 204   basic_block *body = get_loop_body (loop), bb;
 205   rtx insn;
 206   unsigned i;
 207   bool result = true;
 208
 209   /* Check for loops that may not terminate under special conditions.  */
 210   if (!desc->simple_p
 211       || desc->assumptions
 212       || desc->infinite)
 213     {
 214       /* There are some cases that would require a special attention.
 215          For example if the comparison is LEU and the comparison value
 216          is UINT_MAX then the loop will not terminate.  Similarly, if the
 217          comparison code is GEU and the comparison value is 0, the
 218          loop will not terminate.
 219
 220          If the absolute increment is not 1, the loop can be infinite
 221          even with LTU/GTU, e.g. for (i = 3; i > 0; i -= 2)
 222
 223          ??? We could compute these conditions at run-time and have a
 224          additional jump around the loop to ensure an infinite loop.
 225          However, it is very unlikely that this is the intended
 226          behavior of the loop and checking for these rare boundary
 227          conditions would pessimize all other code.
 228
 229          If the loop is executed only a few times an extra check to
 230          restart the loop could use up most of the benefits of using a
 231          count register loop.  Note however, that normally, this
 232          restart branch would never execute, so it could be predicted
 233          well by the CPU.  We should generate the pessimistic code by
 234          default, and have an option, e.g. -funsafe-loops that would
 235          enable count-register loops in this case.  */
 236       if (dump_file)
 237         fprintf (dump_file, "Doloop: Possible infinite iteration case.\n");
 238       result = false;
 239       goto cleanup;
 240     }
 241
 242   for (i = 0; i < loop->num_nodes; i++)
 243     {
 244       bb = body[i];
 245
 246       for (insn = BB_HEAD (bb);
 247            insn != NEXT_INSN (BB_END (bb));
 248            insn = NEXT_INSN (insn))
 249         {
 250           /* Different targets have different necessities for low-overhead
 251              looping.  Call the back end for each instruction within the loop
 252              to let it decide whether the insn prohibits a low-overhead loop.
 253              It will then return the cause for it to emit to the dump file.  */
 254           const char * invalid = targetm.invalid_within_doloop (insn);
 255           if (invalid)
 256             {
 257               if (dump_file)
 258                 fprintf (dump_file, "Doloop: %s\n", invalid);
 259               result = false;
 260               goto cleanup;
 261             }
 262         }
 263     }
 264   result = true;
 265
 266 cleanup:
 267   free (body);
 268
 269   return result;
 270 }
 271
 272 /* Adds test of COND jumping to DEST on edge *E and set *E to the new fallthru
 273    edge.  If the condition is always false, do not do anything.  If it is always
 274    true, redirect E to DEST and return false.  In all other cases, true is
 275    returned.  */
 276
 277 static bool
 278 add_test (rtx cond, edge *e, basic_block dest)
 279 {
 280   rtx seq, jump, label;
 281   enum machine_mode mode;
 282   rtx op0 = XEXP (cond, 0), op1 = XEXP (cond, 1);
 283   enum rtx_code code = GET_CODE (cond);
 284   basic_block bb;
 285
 286   mode = GET_MODE (XEXP (cond, 0));
 287   if (mode == VOIDmode)
 288     mode = GET_MODE (XEXP (cond, 1));
 289
 290   start_sequence ();
 291   op0 = force_operand (op0, NULL_RTX);
 292   op1 = force_operand (op1, NULL_RTX);
 293   label = block_label (dest);
 294   do_compare_rtx_and_jump (op0, op1, code, 0, mode, NULL_RTX, NULL_RTX, label);
 295
 296   jump = get_last_insn ();
 297   if (!jump || !JUMP_P (jump))
 298     {
 299       /* The condition is always false and the jump was optimized out.  */
 300       end_sequence ();
 301       return true;
 302     }
 303
 304   seq = get_insns ();
 305   end_sequence ();
 306
 307   /* There always is at least the jump insn in the sequence.  */
 308   gcc_assert (seq != NULL_RTX);
 309
 310   bb = split_edge_and_insert (*e, seq);
 311   *e = single_succ_edge (bb);
 312
 313   if (any_uncondjump_p (jump))
 314     {
 315       /* The condition is always true.  */
 316       delete_insn (jump);
 317       redirect_edge_and_branch_force (*e, dest);
 318       return false;
 319     }
 320
 321   JUMP_LABEL (jump) = label;
 322
 323   /* The jump is supposed to handle an unlikely special case.  */
 324   add_reg_note (jump, REG_BR_PROB, const0_rtx);
 325
 326   LABEL_NUSES (label)++;
 327
 328   make_edge (bb, dest, (*e)->flags & ~EDGE_FALLTHRU);
 329   return true;
 330 }
 331
 332 /* Modify the loop to use the low-overhead looping insn where LOOP
 333    describes the loop, DESC describes the number of iterations of the
 334    loop, and DOLOOP_INSN is the low-overhead looping insn to emit at the
 335    end of the loop.  CONDITION is the condition separated from the
 336    DOLOOP_SEQ.  COUNT is the number of iterations of the LOOP.
 337    ZERO_EXTEND_P says to zero extend COUNT after the increment of it to
 338    word_mode.  */
 339
 340 static void
 341 doloop_modify (struct loop *loop, struct niter_desc *desc,
 342                rtx doloop_seq, rtx condition, rtx count, bool zero_extend_p)
 343 {
 344   rtx counter_reg;
 345   rtx tmp, noloop = NULL_RTX;
 346   rtx sequence;
 347   rtx jump_insn;
 348   rtx jump_label;
 349   int nonneg = 0;
 350   bool increment_count;
 351   basic_block loop_end = desc->out_edge->src;
 352   enum machine_mode mode;
 353   rtx true_prob_val;
 354
 355   jump_insn = BB_END (loop_end);
 356
 357   if (dump_file)
 358     {
 359       fprintf (dump_file, "Doloop: Inserting doloop pattern (");
 360       if (desc->const_iter)
 361         fprintf (dump_file, HOST_WIDEST_INT_PRINT_DEC, desc->niter);
 362       else
 363         fputs ("runtime", dump_file);
 364       fputs (" iterations).\n", dump_file);
 365     }
 366
 367   /* Get the probability of the original branch. If it exists we would
 368      need to update REG_BR_PROB of the new jump_insn.  */
 369   true_prob_val = find_reg_note (jump_insn, REG_BR_PROB, NULL_RTX);
 370
 371   /* Discard original jump to continue loop.  The original compare
 372      result may still be live, so it cannot be discarded explicitly.  */
 373   delete_insn (jump_insn);
 374
 375   counter_reg = XEXP (condition, 0);
 376   if (GET_CODE (counter_reg) == PLUS)
 377     counter_reg = XEXP (counter_reg, 0);
 378   mode = GET_MODE (counter_reg);
 379
 380   increment_count = false;
 381   switch (GET_CODE (condition))
 382     {
 383     case NE:
 384       /* Currently only NE tests against zero and one are supported.  */
 385       noloop = XEXP (condition, 1);
 386       if (noloop != const0_rtx)
 387         {
 388           gcc_assert (noloop == const1_rtx);
 389           increment_count = true;
 390         }
 391       break;
 392
 393     case GE:
 394       /* Currently only GE tests against zero are supported.  */
 395       gcc_assert (XEXP (condition, 1) == const0_rtx);
 396
 397       noloop = constm1_rtx;
 398
 399       /* The iteration count does not need incrementing for a GE test.  */
 400       increment_count = false;
 401
 402       /* Determine if the iteration counter will be non-negative.
 403          Note that the maximum value loaded is iterations_max - 1.  */
 404       if (desc->niter_max
 405           <= ((unsigned HOST_WIDEST_INT) 1
 406               << (GET_MODE_BITSIZE (mode) - 1)))
 407         nonneg = 1;
 408       break;
 409
 410       /* Abort if an invalid doloop pattern has been generated.  */
 411     default:
 412       gcc_unreachable ();
 413     }
 414
 415   if (increment_count)
 416     count = simplify_gen_binary (PLUS, mode, count, const1_rtx);
 417
 418   if (zero_extend_p)
 419     count = simplify_gen_unary (ZERO_EXTEND, word_mode,
 420                                 count, mode);
 421
 422   /* Insert initialization of the count register into the loop header.  */
 423   start_sequence ();
 424   tmp = force_operand (count, counter_reg);
 425   convert_move (counter_reg, tmp, 1);
 426   sequence = get_insns ();
 427   end_sequence ();
 428   emit_insn_after (sequence, BB_END (loop_preheader_edge (loop)->src));
 429
 430   if (desc->noloop_assumptions)
 431     {
 432       rtx ass = copy_rtx (desc->noloop_assumptions);
 433       basic_block preheader = loop_preheader_edge (loop)->src;
 434       basic_block set_zero
 435               = split_edge (loop_preheader_edge (loop));
 436       basic_block new_preheader
 437               = split_edge (loop_preheader_edge (loop));
 438       edge te;
 439
 440       /* Expand the condition testing the assumptions and if it does not pass,
 441          reset the count register to 0.  */
 442       redirect_edge_and_branch_force (single_succ_edge (preheader), new_preheader);
 443       set_immediate_dominator (CDI_DOMINATORS, new_preheader, preheader);
 444
 445       set_zero->count = 0;
 446       set_zero->frequency = 0;
 447
 448       te = single_succ_edge (preheader);
 449       for (; ass; ass = XEXP (ass, 1))
 450         if (!add_test (XEXP (ass, 0), &te, set_zero))
 451           break;
 452
 453       if (ass)
 454         {
 455           /* We reached a condition that is always true.  This is very hard to
 456              reproduce (such a loop does not roll, and thus it would most
 457              likely get optimized out by some of the preceding optimizations).
 458              In fact, I do not have any testcase for it.  However, it would
 459              also be very hard to show that it is impossible, so we must
 460              handle this case.  */
 461           set_zero->count = preheader->count;
 462           set_zero->frequency = preheader->frequency;
 463         }
 464
 465       if (EDGE_COUNT (set_zero->preds) == 0)
 466         {
 467           /* All the conditions were simplified to false, remove the
 468              unreachable set_zero block.  */
 469           delete_basic_block (set_zero);
 470         }
 471       else
 472         {
 473           /* Reset the counter to zero in the set_zero block.  */
 474           start_sequence ();
 475           convert_move (counter_reg, noloop, 0);
 476           sequence = get_insns ();
 477           end_sequence ();
 478           emit_insn_after (sequence, BB_END (set_zero));
 479
 480           set_immediate_dominator (CDI_DOMINATORS, set_zero,
 481                                    recompute_dominator (CDI_DOMINATORS,
 482                                                         set_zero));
 483         }
 484
 485       set_immediate_dominator (CDI_DOMINATORS, new_preheader,
 486                                recompute_dominator (CDI_DOMINATORS,
 487                                                     new_preheader));
 488     }
 489
 490   /* Some targets (eg, C4x) need to initialize special looping
 491      registers.  */
 492 #ifdef HAVE_doloop_begin
 493   {
 494     rtx init;
 495     unsigned level = get_loop_level (loop) + 1;
 496     init = gen_doloop_begin (counter_reg,
 497                              desc->const_iter ? desc->niter_expr : const0_rtx,
 498                              GEN_INT (desc->niter_max),
 499                              GEN_INT (level));
 500     if (init)
 501       {
 502         start_sequence ();
 503         emit_insn (init);
 504         sequence = get_insns ();
 505         end_sequence ();
 506         emit_insn_after (sequence, BB_END (loop_preheader_edge (loop)->src));
 507       }
 508   }
 509 #endif
 510
 511   /* Insert the new low-overhead looping insn.  */
 512   emit_jump_insn_after (doloop_seq, BB_END (loop_end));
 513   jump_insn = BB_END (loop_end);
 514   jump_label = block_label (desc->in_edge->dest);
 515   JUMP_LABEL (jump_insn) = jump_label;
 516   LABEL_NUSES (jump_label)++;
 517
 518   /* Ensure the right fallthru edge is marked, for case we have reversed
 519      the condition.  */
 520   desc->in_edge->flags &= ~EDGE_FALLTHRU;
 521   desc->out_edge->flags |= EDGE_FALLTHRU;
 522
 523   /* Add a REG_NONNEG note if the actual or estimated maximum number
 524      of iterations is non-negative.  */
 525   if (nonneg)
 526     add_reg_note (jump_insn, REG_NONNEG, NULL_RTX);
 527
 528   /* Update the REG_BR_PROB note.  */
 529   if (true_prob_val)
 530     {
 531       /* Seems safer to use the branch probability.  */
 532       add_reg_note (jump_insn, REG_BR_PROB,
 533                     GEN_INT (desc->in_edge->probability));
 534     }
 535 }
 536
 537 /* Process loop described by LOOP validating that the loop is suitable for
 538    conversion to use a low overhead looping instruction, replacing the jump
 539    insn where suitable.  Returns true if the loop was successfully
 540    modified.  */
 541
 542 static bool
 543 doloop_optimize (struct loop *loop)
 544 {
 545   enum machine_mode mode;
 546   rtx doloop_seq, doloop_pat, doloop_reg;
 547   rtx iterations, count;
 548   rtx iterations_max;
 549   rtx start_label;
 550   rtx condition;
 551   unsigned level, est_niter;
 552   int max_cost;
 553   struct niter_desc *desc;
 554   unsigned word_mode_size;
 555   unsigned HOST_WIDE_INT word_mode_max;
 556   bool zero_extend_p = false;
 557
 558   if (dump_file)
 559     fprintf (dump_file, "Doloop: Processing loop %d.\n", loop->num);
 560
 561   iv_analysis_loop_init (loop);
 562
 563   /* Find the simple exit of a LOOP.  */
 564   desc = get_simple_loop_desc (loop);
 565
 566   /* Check that loop is a candidate for a low-overhead looping insn.  */
 567   if (!doloop_valid_p (loop, desc))
 568     {
 569       if (dump_file)
 570         fprintf (dump_file,
 571                  "Doloop: The loop is not suitable.\n");
 572       return false;
 573     }
 574   mode = desc->mode;
 575
 576   est_niter = 3;
 577   if (desc->const_iter)
 578     est_niter = desc->niter;
 579   /* If the estimate on number of iterations is reliable (comes from profile
 580      feedback), use it.  Do not use it normally, since the expected number
 581      of iterations of an unrolled loop is 2.  */
 582   if (loop->header->count)
 583     est_niter = expected_loop_iterations (loop);
 584
 585   if (est_niter < 3)
 586     {
 587       if (dump_file)
 588         fprintf (dump_file,
 589                  "Doloop: Too few iterations (%u) to be profitable.\n",
 590                  est_niter);
 591       return false;
 592     }
 593
 594   max_cost
 595     = COSTS_N_INSNS (PARAM_VALUE (PARAM_MAX_ITERATIONS_COMPUTATION_COST));
 596   if (rtx_cost (desc->niter_expr, SET, optimize_loop_for_speed_p (loop))
 597       > max_cost)
 598     {
 599       if (dump_file)
 600         fprintf (dump_file,
 601                  "Doloop: number of iterations too costly to compute.\n");
 602       return false;
 603     }
 604
 605   count = copy_rtx (desc->niter_expr);
 606   iterations = desc->const_iter ? desc->niter_expr : const0_rtx;
 607   iterations_max = GEN_INT (desc->niter_max);
 608   level = get_loop_level (loop) + 1;
 609
 610   /* Generate looping insn.  If the pattern FAILs then give up trying
 611      to modify the loop since there is some aspect the back-end does
 612      not like.  */
 613   start_label = block_label (desc->in_edge->dest);
 614   doloop_reg = gen_reg_rtx (mode);
 615   doloop_seq = gen_doloop_end (doloop_reg, iterations, iterations_max,
 616                                GEN_INT (level), start_label);
 617
 618   word_mode_size = GET_MODE_BITSIZE (word_mode);
 619   word_mode_max
 620           = ((unsigned HOST_WIDE_INT) 1 << (word_mode_size - 1) << 1) - 1;
 621   if (! doloop_seq
 622       && mode != word_mode
 623       /* Before trying mode different from the one in that # of iterations is
 624          computed, we must be sure that the number of iterations fits into
 625          the new mode.  */
 626       && (word_mode_size >= GET_MODE_BITSIZE (mode)
 627           || desc->niter_max <= word_mode_max))
 628     {
 629       if (word_mode_size > GET_MODE_BITSIZE (mode))
 630         {
 631           zero_extend_p = true;
 632           iterations = simplify_gen_unary (ZERO_EXTEND, word_mode,
 633                                            iterations, mode);
 634           iterations_max = simplify_gen_unary (ZERO_EXTEND, word_mode,
 635                                                iterations_max, mode);
 636         }
 637       else
 638         {
 639           count = lowpart_subreg (word_mode, count, mode);
 640           iterations = lowpart_subreg (word_mode, iterations, mode);
 641           iterations_max = lowpart_subreg (word_mode, iterations_max, mode);
 642         }
 643       PUT_MODE (doloop_reg, word_mode);
 644       doloop_seq = gen_doloop_end (doloop_reg, iterations, iterations_max,
 645                                    GEN_INT (level), start_label);
 646     }
 647   if (! doloop_seq)
 648     {
 649       if (dump_file)
 650         fprintf (dump_file,
 651                  "Doloop: Target unwilling to use doloop pattern!\n");
 652       return false;
 653     }
 654
 655   /* If multiple instructions were created, the last must be the
 656      jump instruction.  Also, a raw define_insn may yield a plain
 657      pattern.  */
 658   doloop_pat = doloop_seq;
 659   if (INSN_P (doloop_pat))
 660     {
 661       while (NEXT_INSN (doloop_pat) != NULL_RTX)
 662         doloop_pat = NEXT_INSN (doloop_pat);
 663       if (!JUMP_P (doloop_pat))
 664         doloop_pat = NULL_RTX;
 665     }
 666
 667   if (! doloop_pat
 668       || ! (condition = doloop_condition_get (doloop_pat)))
 669     {
 670       if (dump_file)
 671         fprintf (dump_file, "Doloop: Unrecognizable doloop pattern!\n");
 672       return false;
 673     }
 674
 675   doloop_modify (loop, desc, doloop_seq, condition, count, zero_extend_p);
 676   return true;
 677 }
 678
 679 /* This is the main entry point.  Process all loops using doloop_optimize.  */
 680
 681 void
 682 doloop_optimize_loops (void)
 683 {
 684   loop_iterator li;
 685   struct loop *loop;
 686
 687   FOR_EACH_LOOP (li, loop, 0)
 688     {
 689       doloop_optimize (loop);
 690     }
 691
 692   iv_analysis_done ();
 693
 694 #ifdef ENABLE_CHECKING
 695   verify_dominators (CDI_DOMINATORS);
 696   verify_loop_structure ();
 697 #endif
 698 }
 699 #endif /* HAVE_doloop_end */
 700