aboutsummaryrefslogtreecommitdiff
path: root/gcc/tree-ssa-ifcombine.c
blob: 459c60a305705e46953f0c74382ec38a4c7b0835 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
/* Combining of if-expressions on trees.
   Copyright (C) 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
   Contributed by Richard Guenther <rguenther@suse.de>

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "basic-block.h"
#include "timevar.h"
#include "tree-pretty-print.h"
#include "tree-flow.h"
#include "tree-pass.h"
#include "tree-dump.h"

/* This pass combines COND_EXPRs to simplify control flow.  It
   currently recognizes bit tests and comparisons in chains that
   represent logical and or logical or of two COND_EXPRs.

   It does so by walking basic blocks in a approximate reverse
   post-dominator order and trying to match CFG patterns that
   represent logical and or logical or of two COND_EXPRs.
   Transformations are done if the COND_EXPR conditions match
   either

     1. two single bit tests X & (1 << Yn) (for logical and)

     2. two bit tests X & Yn (for logical or)

     3. two comparisons X OPn Y (for logical or)

   To simplify this pass, removing basic blocks and dead code
   is left to CFG cleanup and DCE.  */


/* Recognize a if-then-else CFG pattern starting to match with the
   COND_BB basic-block containing the COND_EXPR.  The recognized
   then end else blocks are stored to *THEN_BB and *ELSE_BB.  If
   *THEN_BB and/or *ELSE_BB are already set, they are required to
   match the then and else basic-blocks to make the pattern match.
   Returns true if the pattern matched, false otherwise.  */

static bool
recognize_if_then_else (basic_block cond_bb,
			basic_block *then_bb, basic_block *else_bb)
{
  edge t, e;

  if (EDGE_COUNT (cond_bb->succs) != 2)
    return false;

  /* Find the then/else edges.  */
  t = EDGE_SUCC (cond_bb, 0);
  e = EDGE_SUCC (cond_bb, 1);
  if (!(t->flags & EDGE_TRUE_VALUE))
    {
      edge tmp = t;
      t = e;
      e = tmp;
    }
  if (!(t->flags & EDGE_TRUE_VALUE)
      || !(e->flags & EDGE_FALSE_VALUE))
    return false;

  /* Check if the edge destinations point to the required block.  */
  if (*then_bb
      && t->dest != *then_bb)
    return false;
  if (*else_bb
      && e->dest != *else_bb)
    return false;

  if (!*then_bb)
    *then_bb = t->dest;
  if (!*else_bb)
    *else_bb = e->dest;

  return true;
}

/* Verify if the basic block BB does not have side-effects.  Return
   true in this case, else false.  */

static bool
bb_no_side_effects_p (basic_block bb)
{
  gimple_stmt_iterator gsi;

  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
    {
      gimple stmt = gsi_stmt (gsi);

      if (gimple_has_side_effects (stmt)
	  || gimple_vuse (stmt))
	return false;
    }

  return true;
}

/* Verify if all PHI node arguments in DEST for edges from BB1 or
   BB2 to DEST are the same.  This makes the CFG merge point
   free from side-effects.  Return true in this case, else false.  */

static bool
same_phi_args_p (basic_block bb1, basic_block bb2, basic_block dest)
{
  edge e1 = find_edge (bb1, dest);
  edge e2 = find_edge (bb2, dest);
  gimple_stmt_iterator gsi;
  gimple phi;

  for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
    {
      phi = gsi_stmt (gsi);
      if (!operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi, e1),
			    PHI_ARG_DEF_FROM_EDGE (phi, e2), 0))
        return false;
    }

  return true;
}

/* Return the best representative SSA name for CANDIDATE which is used
   in a bit test.  */

static tree
get_name_for_bit_test (tree candidate)
{
  /* Skip single-use names in favor of using the name from a
     non-widening conversion definition.  */
  if (TREE_CODE (candidate) == SSA_NAME
      && has_single_use (candidate))
    {
      gimple def_stmt = SSA_NAME_DEF_STMT (candidate);
      if (is_gimple_assign (def_stmt)
	  && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt)))
	{
	  if (TYPE_PRECISION (TREE_TYPE (candidate))
	      <= TYPE_PRECISION (TREE_TYPE (gimple_assign_rhs1 (def_stmt))))
	    return gimple_assign_rhs1 (def_stmt);
	}
    }

  return candidate;
}

/* Recognize a single bit test pattern in GIMPLE_COND and its defining
   statements.  Store the name being tested in *NAME and the bit
   in *BIT.  The GIMPLE_COND computes *NAME & (1 << *BIT).
   Returns true if the pattern matched, false otherwise.  */

static bool
recognize_single_bit_test (gimple cond, tree *name, tree *bit)
{
  gimple stmt;

  /* Get at the definition of the result of the bit test.  */
  if (gimple_cond_code (cond) != NE_EXPR
      || TREE_CODE (gimple_cond_lhs (cond)) != SSA_NAME
      || !integer_zerop (gimple_cond_rhs (cond)))
    return false;
  stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond));
  if (!is_gimple_assign (stmt))
    return false;

  /* Look at which bit is tested.  One form to recognize is
     D.1985_5 = state_3(D) >> control1_4(D);
     D.1986_6 = (int) D.1985_5;
     D.1987_7 = op0 & 1;
     if (D.1987_7 != 0)  */
  if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
      && integer_onep (gimple_assign_rhs2 (stmt))
      && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME)
    {
      tree orig_name = gimple_assign_rhs1 (stmt);

      /* Look through copies and conversions to eventually
	 find the stmt that computes the shift.  */
      stmt = SSA_NAME_DEF_STMT (orig_name);

      while (is_gimple_assign (stmt)
	     && ((CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (stmt))
		  && (TYPE_PRECISION (TREE_TYPE (gimple_assign_lhs (stmt)))
		      <= TYPE_PRECISION (TREE_TYPE (gimple_assign_rhs1 (stmt)))))
		 || gimple_assign_ssa_name_copy_p (stmt)))
	stmt = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmt));

      /* If we found such, decompose it.  */
      if (is_gimple_assign (stmt)
	  && gimple_assign_rhs_code (stmt) == RSHIFT_EXPR)
	{
	  /* op0 & (1 << op1) */
	  *bit = gimple_assign_rhs2 (stmt);
	  *name = gimple_assign_rhs1 (stmt);
	}
      else
	{
	  /* t & 1 */
	  *bit = integer_zero_node;
	  *name = get_name_for_bit_test (orig_name);
	}

      return true;
    }

  /* Another form is
     D.1987_7 = op0 & (1 << CST)
     if (D.1987_7 != 0)  */
  if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
      && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
      && integer_pow2p (gimple_assign_rhs2 (stmt)))
    {
      *name = gimple_assign_rhs1 (stmt);
      *bit = build_int_cst (integer_type_node,
			    tree_log2 (gimple_assign_rhs2 (stmt)));
      return true;
    }

  /* Another form is
     D.1986_6 = 1 << control1_4(D)
     D.1987_7 = op0 & D.1986_6
     if (D.1987_7 != 0)  */
  if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
      && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
      && TREE_CODE (gimple_assign_rhs2 (stmt)) == SSA_NAME)
    {
      gimple tmp;

      /* Both arguments of the BIT_AND_EXPR can be the single-bit
	 specifying expression.  */
      tmp = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmt));
      if (is_gimple_assign (tmp)
	  && gimple_assign_rhs_code (tmp) == LSHIFT_EXPR
	  && integer_onep (gimple_assign_rhs1 (tmp)))
	{
	  *name = gimple_assign_rhs2 (stmt);
	  *bit = gimple_assign_rhs2 (tmp);
	  return true;
	}

      tmp = SSA_NAME_DEF_STMT (gimple_assign_rhs2 (stmt));
      if (is_gimple_assign (tmp)
	  && gimple_assign_rhs_code (tmp) == LSHIFT_EXPR
	  && integer_onep (gimple_assign_rhs1 (tmp)))
	{
	  *name = gimple_assign_rhs1 (stmt);
	  *bit = gimple_assign_rhs2 (tmp);
	  return true;
	}
    }

  return false;
}

/* Recognize a bit test pattern in a GIMPLE_COND and its defining
   statements.  Store the name being tested in *NAME and the bits
   in *BITS.  The COND_EXPR computes *NAME & *BITS.
   Returns true if the pattern matched, false otherwise.  */

static bool
recognize_bits_test (gimple cond, tree *name, tree *bits)
{
  gimple stmt;

  /* Get at the definition of the result of the bit test.  */
  if (gimple_cond_code (cond) != NE_EXPR
      || TREE_CODE (gimple_cond_lhs (cond)) != SSA_NAME
      || !integer_zerop (gimple_cond_rhs (cond)))
    return false;
  stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond));
  if (!is_gimple_assign (stmt)
      || gimple_assign_rhs_code (stmt) != BIT_AND_EXPR)
    return false;

  *name = get_name_for_bit_test (gimple_assign_rhs1 (stmt));
  *bits = gimple_assign_rhs2 (stmt);

  return true;
}

/* If-convert on a and pattern with a common else block.  The inner
   if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB.
   Returns true if the edges to the common else basic-block were merged.  */

static bool
ifcombine_ifandif (basic_block inner_cond_bb, basic_block outer_cond_bb)
{
  gimple_stmt_iterator gsi;
  gimple inner_cond, outer_cond;
  tree name1, name2, bit1, bit2;

  inner_cond = last_stmt (inner_cond_bb);
  if (!inner_cond
      || gimple_code (inner_cond) != GIMPLE_COND)
    return false;

  outer_cond = last_stmt (outer_cond_bb);
  if (!outer_cond
      || gimple_code (outer_cond) != GIMPLE_COND)
    return false;

  /* See if we test a single bit of the same name in both tests.  In
     that case remove the outer test, merging both else edges,
     and change the inner one to test for
     name & (bit1 | bit2) == (bit1 | bit2).  */
  if (recognize_single_bit_test (inner_cond, &name1, &bit1)
      && recognize_single_bit_test (outer_cond, &name2, &bit2)
      && name1 == name2)
    {
      tree t, t2;

      /* Do it.  */
      gsi = gsi_for_stmt (inner_cond);
      t = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
		       build_int_cst (TREE_TYPE (name1), 1), bit1);
      t2 = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
		        build_int_cst (TREE_TYPE (name1), 1), bit2);
      t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), t, t2);
      t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
				    true, GSI_SAME_STMT);
      t2 = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
      t2 = force_gimple_operand_gsi (&gsi, t2, true, NULL_TREE,
				     true, GSI_SAME_STMT);
      t = fold_build2 (EQ_EXPR, boolean_type_node, t2, t);
      t = canonicalize_cond_expr_cond (t);
      if (!t)
	return false;
      gimple_cond_set_condition_from_tree (inner_cond, t);
      update_stmt (inner_cond);

      /* Leave CFG optimization to cfg_cleanup.  */
      gimple_cond_set_condition_from_tree (outer_cond, boolean_true_node);
      update_stmt (outer_cond);

      if (dump_file)
	{
	  fprintf (dump_file, "optimizing double bit test to ");
	  print_generic_expr (dump_file, name1, 0);
	  fprintf (dump_file, " & T == T\nwith temporary T = (1 << ");
	  print_generic_expr (dump_file, bit1, 0);
	  fprintf (dump_file, ") | (1 << ");
	  print_generic_expr (dump_file, bit2, 0);
	  fprintf (dump_file, ")\n");
	}

      return true;
    }

  /* See if we have two comparisons that we can merge into one.  */
  else if (TREE_CODE_CLASS (gimple_cond_code (inner_cond)) == tcc_comparison
	   && TREE_CODE_CLASS (gimple_cond_code (outer_cond)) == tcc_comparison)
    {
      tree t;

      if (!(t = maybe_fold_and_comparisons (gimple_cond_code (inner_cond),
					    gimple_cond_lhs (inner_cond),
					    gimple_cond_rhs (inner_cond),
					    gimple_cond_code (outer_cond),
					    gimple_cond_lhs (outer_cond),
					    gimple_cond_rhs (outer_cond))))
	return false;
      t = canonicalize_cond_expr_cond (t);
      if (!t)
	return false;
      gimple_cond_set_condition_from_tree (inner_cond, t);
      update_stmt (inner_cond);

      /* Leave CFG optimization to cfg_cleanup.  */
      gimple_cond_set_condition_from_tree (outer_cond, boolean_true_node);
      update_stmt (outer_cond);

      if (dump_file)
	{
	  fprintf (dump_file, "optimizing two comparisons to ");
	  print_generic_expr (dump_file, t, 0);
	  fprintf (dump_file, "\n");
	}

      return true;
    }

  return false;
}

/* If-convert on a or pattern with a common then block.  The inner
   if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB.
   Returns true, if the edges leading to the common then basic-block
   were merged.  */

static bool
ifcombine_iforif (basic_block inner_cond_bb, basic_block outer_cond_bb)
{
  gimple inner_cond, outer_cond;
  tree name1, name2, bits1, bits2;

  inner_cond = last_stmt (inner_cond_bb);
  if (!inner_cond
      || gimple_code (inner_cond) != GIMPLE_COND)
    return false;

  outer_cond = last_stmt (outer_cond_bb);
  if (!outer_cond
      || gimple_code (outer_cond) != GIMPLE_COND)
    return false;

  /* See if we have two bit tests of the same name in both tests.
     In that case remove the outer test and change the inner one to
     test for name & (bits1 | bits2) != 0.  */
  if (recognize_bits_test (inner_cond, &name1, &bits1)
      && recognize_bits_test (outer_cond, &name2, &bits2))
    {
      gimple_stmt_iterator gsi;
      tree t;

      /* Find the common name which is bit-tested.  */
      if (name1 == name2)
	;
      else if (bits1 == bits2)
	{
	  t = name2;
	  name2 = bits2;
	  bits2 = t;
	  t = name1;
	  name1 = bits1;
	  bits1 = t;
	}
      else if (name1 == bits2)
	{
	  t = name2;
	  name2 = bits2;
	  bits2 = t;
	}
      else if (bits1 == name2)
	{
	  t = name1;
	  name1 = bits1;
	  bits1 = t;
	}
      else
	return false;

      /* As we strip non-widening conversions in finding a common
         name that is tested make sure to end up with an integral
	 type for building the bit operations.  */
      if (TYPE_PRECISION (TREE_TYPE (bits1))
	  >= TYPE_PRECISION (TREE_TYPE (bits2)))
	{
	  bits1 = fold_convert (unsigned_type_for (TREE_TYPE (bits1)), bits1);
	  name1 = fold_convert (TREE_TYPE (bits1), name1);
	  bits2 = fold_convert (unsigned_type_for (TREE_TYPE (bits2)), bits2);
	  bits2 = fold_convert (TREE_TYPE (bits1), bits2);
	}
      else
	{
	  bits2 = fold_convert (unsigned_type_for (TREE_TYPE (bits2)), bits2);
	  name1 = fold_convert (TREE_TYPE (bits2), name1);
	  bits1 = fold_convert (unsigned_type_for (TREE_TYPE (bits1)), bits1);
	  bits1 = fold_convert (TREE_TYPE (bits2), bits1);
	}

      /* Do it.  */
      gsi = gsi_for_stmt (inner_cond);
      t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), bits1, bits2);
      t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
				    true, GSI_SAME_STMT);
      t = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
      t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
				    true, GSI_SAME_STMT);
      t = fold_build2 (NE_EXPR, boolean_type_node, t,
		       build_int_cst (TREE_TYPE (t), 0));
      t = canonicalize_cond_expr_cond (t);
      if (!t)
	return false;
      gimple_cond_set_condition_from_tree (inner_cond, t);
      update_stmt (inner_cond);

      /* Leave CFG optimization to cfg_cleanup.  */
      gimple_cond_set_condition_from_tree (outer_cond, boolean_false_node);
      update_stmt (outer_cond);

      if (dump_file)
	{
	  fprintf (dump_file, "optimizing bits or bits test to ");
	  print_generic_expr (dump_file, name1, 0);
	  fprintf (dump_file, " & T != 0\nwith temporary T = ");
	  print_generic_expr (dump_file, bits1, 0);
	  fprintf (dump_file, " | ");
	  print_generic_expr (dump_file, bits2, 0);
	  fprintf (dump_file, "\n");
	}

      return true;
    }

  /* See if we have two comparisons that we can merge into one.
     This happens for C++ operator overloading where for example
     GE_EXPR is implemented as GT_EXPR || EQ_EXPR.  */
    else if (TREE_CODE_CLASS (gimple_cond_code (inner_cond)) == tcc_comparison
	   && TREE_CODE_CLASS (gimple_cond_code (outer_cond)) == tcc_comparison)
    {
      tree t;

      if (!(t = maybe_fold_or_comparisons (gimple_cond_code (inner_cond),
					   gimple_cond_lhs (inner_cond),
					   gimple_cond_rhs (inner_cond),
					   gimple_cond_code (outer_cond),
					   gimple_cond_lhs (outer_cond),
					   gimple_cond_rhs (outer_cond))))
	return false;
      t = canonicalize_cond_expr_cond (t);
      if (!t)
	return false;
      gimple_cond_set_condition_from_tree (inner_cond, t);
      update_stmt (inner_cond);

      /* Leave CFG optimization to cfg_cleanup.  */
      gimple_cond_set_condition_from_tree (outer_cond, boolean_false_node);
      update_stmt (outer_cond);

      if (dump_file)
	{
	  fprintf (dump_file, "optimizing two comparisons to ");
	  print_generic_expr (dump_file, t, 0);
	  fprintf (dump_file, "\n");
	}

      return true;
    }

  return false;
}

/* Recognize a CFG pattern and dispatch to the appropriate
   if-conversion helper.  We start with BB as the innermost
   worker basic-block.  Returns true if a transformation was done.  */

static bool
tree_ssa_ifcombine_bb (basic_block inner_cond_bb)
{
  basic_block then_bb = NULL, else_bb = NULL;

  if (!recognize_if_then_else (inner_cond_bb, &then_bb, &else_bb))
    return false;

  /* Recognize && and || of two conditions with a common
     then/else block which entry edges we can merge.  That is:
       if (a || b)
	 ;
     and
       if (a && b)
	 ;
     This requires a single predecessor of the inner cond_bb.  */
  if (single_pred_p (inner_cond_bb))
    {
      basic_block outer_cond_bb = single_pred (inner_cond_bb);

      /* The && form is characterized by a common else_bb with
	 the two edges leading to it mergable.  The latter is
	 guaranteed by matching PHI arguments in the else_bb and
	 the inner cond_bb having no side-effects.  */
      if (recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &else_bb)
	  && same_phi_args_p (outer_cond_bb, inner_cond_bb, else_bb)
	  && bb_no_side_effects_p (inner_cond_bb))
	{
	  /* We have
	       <outer_cond_bb>
		 if (q) goto inner_cond_bb; else goto else_bb;
	       <inner_cond_bb>
		 if (p) goto ...; else goto else_bb;
		 ...
	       <else_bb>
		 ...
	   */
	  return ifcombine_ifandif (inner_cond_bb, outer_cond_bb);
	}

      /* The || form is characterized by a common then_bb with the
	 two edges leading to it mergable.  The latter is guaranteed
         by matching PHI arguments in the then_bb and the inner cond_bb
	 having no side-effects.  */
      if (recognize_if_then_else (outer_cond_bb, &then_bb, &inner_cond_bb)
	  && same_phi_args_p (outer_cond_bb, inner_cond_bb, then_bb)
	  && bb_no_side_effects_p (inner_cond_bb))
	{
	  /* We have
	       <outer_cond_bb>
		 if (q) goto then_bb; else goto inner_cond_bb;
	       <inner_cond_bb>
		 if (q) goto then_bb; else goto ...;
	       <then_bb>
		 ...
	   */
	  return ifcombine_iforif (inner_cond_bb, outer_cond_bb);
	}
    }

  return false;
}

/* Main entry for the tree if-conversion pass.  */

static unsigned int
tree_ssa_ifcombine (void)
{
  basic_block *bbs;
  bool cfg_changed = false;
  int i;

  bbs = blocks_in_phiopt_order ();
  calculate_dominance_info (CDI_DOMINATORS);

  for (i = 0; i < n_basic_blocks - NUM_FIXED_BLOCKS; ++i)
    {
      basic_block bb = bbs[i];
      gimple stmt = last_stmt (bb);

      if (stmt
	  && gimple_code (stmt) == GIMPLE_COND)
	cfg_changed |= tree_ssa_ifcombine_bb (bb);
    }

  free (bbs);

  return cfg_changed ? TODO_cleanup_cfg : 0;
}

static bool
gate_ifcombine (void)
{
  return 1;
}

struct gimple_opt_pass pass_tree_ifcombine =
{
 {
  GIMPLE_PASS,
  "ifcombine",			/* name */
  gate_ifcombine,		/* gate */
  tree_ssa_ifcombine,		/* execute */
  NULL,				/* sub */
  NULL,				/* next */
  0,				/* static_pass_number */
  TV_TREE_IFCOMBINE,		/* tv_id */
  PROP_cfg | PROP_ssa,		/* properties_required */
  0,				/* properties_provided */
  0,				/* properties_destroyed */
  0,				/* todo_flags_start */
  TODO_ggc_collect
  | TODO_update_ssa
  | TODO_verify_ssa		/* todo_flags_finish */
 }
};