gcc/tree-ssa-ifcombine.c

   1 /* Combining of if-expressions on trees.
   2    Copyright (C) 2007 Free Software Foundation, Inc.
   3    Contributed by Richard Guenther <rguenther@suse.de>
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GCC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License 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
  19 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  20 Boston, MA 02110-1301, USA.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tm.h"
  26 #include "tree.h"
  27 #include "basic-block.h"
  28 #include "timevar.h"
  29 #include "diagnostic.h"
  30 #include "tree-flow.h"
  31 #include "tree-pass.h"
  32 #include "tree-dump.h"
  33
  34 /* This pass combines COND_EXPRs to simplify control flow.  It
  35    currently recognizes bit tests and comparisons in chains that
  36    represent logical and or logical or of two COND_EXPRs.
  37
  38    It does so by walking basic blocks in a approximate reverse
  39    post-dominator order and trying to match CFG patterns that
  40    represent logical and or logical or of two COND_EXPRs.
  41    Transformations are done if the COND_EXPR conditions match
  42    either
  43
  44      1. two single bit tests X & (1 << Yn) (for logical and)
  45
  46      2. two bit tests X & Yn (for logical or)
  47
  48      3. two comparisons X OPn Y (for logical or)
  49
  50    To simplify this pass, removing basic blocks and dead code
  51    is left to CFG cleanup and DCE.  */
  52
  53
  54 /* Recognize a if-then-else CFG pattern starting to match with the
  55    COND_BB basic-block containing the COND_EXPR.  The recognized
  56    then end else blocks are stored to *THEN_BB and *ELSE_BB.  If
  57    *THEN_BB and/or *ELSE_BB are already set, they are required to
  58    match the then and else basic-blocks to make the pattern match.
  59    Returns true if the pattern matched, false otherwise.  */
  60
  61 static bool
  62 recognize_if_then_else (basic_block cond_bb,
  63                         basic_block *then_bb, basic_block *else_bb)
  64 {
  65   edge t, e;
  66
  67   if (EDGE_COUNT (cond_bb->succs) != 2)
  68     return false;
  69
  70   /* Find the then/else edges.  */
  71   t = EDGE_SUCC (cond_bb, 0);
  72   e = EDGE_SUCC (cond_bb, 1);
  73   if (!(t->flags & EDGE_TRUE_VALUE))
  74     {
  75       edge tmp = t;
  76       t = e;
  77       e = tmp;
  78     }
  79   if (!(t->flags & EDGE_TRUE_VALUE)
  80       || !(e->flags & EDGE_FALSE_VALUE))
  81     return false;
  82
  83   /* Check if the edge destinations point to the required block.  */
  84   if (*then_bb
  85       && t->dest != *then_bb)
  86     return false;
  87   if (*else_bb
  88       && e->dest != *else_bb)
  89     return false;
  90
  91   if (!*then_bb)
  92     *then_bb = t->dest;
  93   if (!*else_bb)
  94     *else_bb = e->dest;
  95
  96   return true;
  97 }
  98
  99 /* Verify if the basic block BB does not have side-effects.  Return
 100    true in this case, else false.  */
 101
 102 static bool
 103 bb_no_side_effects_p (basic_block bb)
 104 {
 105   block_stmt_iterator bsi;
 106
 107   for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
 108     {
 109       tree stmt = bsi_stmt (bsi);
 110       stmt_ann_t ann = stmt_ann (stmt);
 111
 112       if (ann->has_volatile_ops
 113           || !ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS))
 114         return false;
 115     }
 116
 117   return true;
 118 }
 119
 120 /* Verify if all PHI node arguments in DEST for edges from BB1 or
 121    BB2 to DEST are the same.  This makes the CFG merge point
 122    free from side-effects.  Return true in this case, else false.  */
 123
 124 static bool
 125 same_phi_args_p (basic_block bb1, basic_block bb2, basic_block dest)
 126 {
 127   edge e1 = find_edge (bb1, dest);
 128   edge e2 = find_edge (bb2, dest);
 129   tree phi;
 130
 131   for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi))
 132     if (!operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi, e1),
 133                           PHI_ARG_DEF_FROM_EDGE (phi, e2), 0))
 134       return false;
 135
 136   return true;
 137 }
 138
 139 /* Recognize a single bit test pattern in COND_EXPR and its defining
 140    statements.  Store the name being tested in *NAME and the bit
 141    in *BIT.  The COND_EXPR computes *NAME & (1 << *BIT).
 142    Returns true if the pattern matched, false otherwise.  */
 143
 144 static bool
 145 recognize_single_bit_test (tree cond_expr, tree *name, tree *bit)
 146 {
 147   tree t;
 148
 149   /* Get at the definition of the result of the bit test.  */
 150   t = TREE_OPERAND (cond_expr, 0);
 151   if (TREE_CODE (t) == NE_EXPR
 152       && integer_zerop (TREE_OPERAND (t, 1)))
 153     t = TREE_OPERAND (t, 0);
 154   if (TREE_CODE (t) != SSA_NAME)
 155     return false;
 156   t = SSA_NAME_DEF_STMT (t);
 157   if (TREE_CODE (t) != GIMPLE_MODIFY_STMT)
 158     return false;
 159   t = GIMPLE_STMT_OPERAND (t, 1);
 160
 161   /* Look at which bit is tested.  One form to recognize is
 162      D.1985_5 = state_3(D) >> control1_4(D);
 163      D.1986_6 = (int) D.1985_5;
 164      D.1987_7 = op0 & 1;
 165      if (D.1987_7 != 0)  */
 166   if (TREE_CODE (t) == BIT_AND_EXPR
 167       && integer_onep (TREE_OPERAND (t, 1))
 168       && TREE_CODE (TREE_OPERAND (t, 0)) == SSA_NAME)
 169     {
 170       tree orig_name = TREE_OPERAND (t, 0);
 171
 172       /* Look through copies and conversions to eventually
 173          find the stmt that computes the shift.  */
 174       t = orig_name;
 175       do {
 176         t = SSA_NAME_DEF_STMT (t);
 177         if (TREE_CODE (t) != GIMPLE_MODIFY_STMT)
 178           break;
 179         t = GIMPLE_STMT_OPERAND (t, 1);
 180         if (TREE_CODE (t) == NOP_EXPR
 181             || TREE_CODE (t) == CONVERT_EXPR)
 182           t = TREE_OPERAND (t, 0);
 183       } while (TREE_CODE (t) == SSA_NAME);
 184
 185       /* If we found such, decompose it.  */
 186       if (TREE_CODE (t) == RSHIFT_EXPR)
 187         {
 188           /* op0 & (1 << op1) */
 189           *bit = TREE_OPERAND (t, 1);
 190           *name = TREE_OPERAND (t, 0);
 191         }
 192       else
 193         {
 194           /* t & 1 */
 195           *bit = integer_zero_node;
 196           *name = orig_name;
 197         }
 198
 199       return true;
 200     }
 201
 202   /* Another form is
 203      D.1987_7 = op0 & (1 << CST)
 204      if (D.1987_7 != 0)  */
 205   if (TREE_CODE (t) == BIT_AND_EXPR
 206       && TREE_CODE (TREE_OPERAND (t, 0)) == SSA_NAME
 207       && integer_pow2p (TREE_OPERAND (t, 1)))
 208     {
 209       *name = TREE_OPERAND (t, 0);
 210       *bit = build_int_cst (integer_type_node,
 211                             tree_log2 (TREE_OPERAND (t, 1)));
 212       return true;
 213     }
 214
 215   /* Another form is
 216      D.1986_6 = 1 << control1_4(D)
 217      D.1987_7 = op0 & D.1986_6
 218      if (D.1987_7 != 0)  */
 219   if (TREE_CODE (t) == BIT_AND_EXPR
 220       && TREE_CODE (TREE_OPERAND (t, 0)) == SSA_NAME
 221       && TREE_CODE (TREE_OPERAND (t, 1)) == SSA_NAME)
 222     {
 223       tree tmp;
 224
 225       /* Both arguments of the BIT_AND_EXPR can be the single-bit
 226          specifying expression.  */
 227       tmp = SSA_NAME_DEF_STMT (TREE_OPERAND (t, 0));
 228       if (TREE_CODE (tmp) == GIMPLE_MODIFY_STMT
 229           && TREE_CODE (GIMPLE_STMT_OPERAND (tmp, 1)) == LSHIFT_EXPR
 230           && integer_onep (TREE_OPERAND (GIMPLE_STMT_OPERAND (tmp, 1), 0)))
 231         {
 232           *name = TREE_OPERAND (t, 1);
 233           *bit = TREE_OPERAND (GIMPLE_STMT_OPERAND (tmp, 1), 1);
 234           return true;
 235         }
 236
 237       tmp = SSA_NAME_DEF_STMT (TREE_OPERAND (t, 1));
 238       if (TREE_CODE (tmp) == GIMPLE_MODIFY_STMT
 239           && TREE_CODE (GIMPLE_STMT_OPERAND (tmp, 1)) == LSHIFT_EXPR
 240           && integer_onep (TREE_OPERAND (GIMPLE_STMT_OPERAND (tmp, 1), 0)))
 241         {
 242           *name = TREE_OPERAND (t, 0);
 243           *bit = TREE_OPERAND (GIMPLE_STMT_OPERAND (tmp, 1), 1);
 244           return true;
 245         }
 246     }
 247
 248   return false;
 249 }
 250
 251 /* Recognize a bit test pattern in COND_EXPR and its defining
 252    statements.  Store the name being tested in *NAME and the bits
 253    in *BITS.  The COND_EXPR computes *NAME & *BITS.
 254    Returns true if the pattern matched, false otherwise.  */
 255
 256 static bool
 257 recognize_bits_test (tree cond_expr, tree *name, tree *bits)
 258 {
 259   tree t;
 260
 261   /* Get at the definition of the result of the bit test.  */
 262   t = TREE_OPERAND (cond_expr, 0);
 263   if (TREE_CODE (t) == NE_EXPR
 264       && integer_zerop (TREE_OPERAND (t, 1)))
 265     t = TREE_OPERAND (t, 0);
 266   if (TREE_CODE (t) != SSA_NAME)
 267     return false;
 268   t = SSA_NAME_DEF_STMT (t);
 269   if (TREE_CODE (t) != GIMPLE_MODIFY_STMT)
 270     return false;
 271   t = GIMPLE_STMT_OPERAND (t, 1);
 272
 273   if (TREE_CODE (t) != BIT_AND_EXPR)
 274     return false;
 275
 276   *name = TREE_OPERAND (t, 0);
 277   *bits = TREE_OPERAND (t, 1);
 278
 279   return true;
 280 }
 281
 282 /* If-convert on a and pattern with a common else block.  The inner
 283    if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB.
 284    Returns true if the edges to the common else basic-block were merged.  */
 285
 286 static bool
 287 ifcombine_ifandif (basic_block inner_cond_bb, basic_block outer_cond_bb)
 288 {
 289   block_stmt_iterator bsi;
 290   tree inner_cond, outer_cond;
 291   tree name1, name2, bit1, bit2;
 292
 293   inner_cond = last_stmt (inner_cond_bb);
 294   if (!inner_cond
 295       || TREE_CODE (inner_cond) != COND_EXPR)
 296     return false;
 297
 298   outer_cond = last_stmt (outer_cond_bb);
 299   if (!outer_cond
 300       || TREE_CODE (outer_cond) != COND_EXPR)
 301     return false;
 302
 303   /* See if we test a single bit of the same name in both tests.  In
 304      that case remove the outer test, merging both else edges,
 305      and change the inner one to test for
 306      name & (bit1 | bit2) == (bit1 | bit2).  */
 307   if (recognize_single_bit_test (inner_cond, &name1, &bit1)
 308       && recognize_single_bit_test (outer_cond, &name2, &bit2)
 309       && name1 == name2)
 310     {
 311       tree t, t2;
 312
 313       /* Do it.  */
 314       bsi = bsi_for_stmt (inner_cond);
 315       t = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
 316                        build_int_cst (TREE_TYPE (name1), 1), bit1);
 317       t2 = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
 318                         build_int_cst (TREE_TYPE (name1), 1), bit2);
 319       t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), t, t2);
 320       t = force_gimple_operand_bsi (&bsi, t, true, NULL_TREE,
 321                                     true, BSI_SAME_STMT);
 322       t2 = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
 323       t2 = force_gimple_operand_bsi (&bsi, t2, true, NULL_TREE,
 324                                      true, BSI_SAME_STMT);
 325       COND_EXPR_COND (inner_cond) = fold_build2 (EQ_EXPR, boolean_type_node,
 326                                                  t2, t);
 327       update_stmt (inner_cond);
 328
 329       /* Leave CFG optimization to cfg_cleanup.  */
 330       COND_EXPR_COND (outer_cond) = boolean_true_node;
 331       update_stmt (outer_cond);
 332
 333       if (dump_file)
 334         {
 335           fprintf (dump_file, "optimizing double bit test to ");
 336           print_generic_expr (dump_file, name1, 0);
 337           fprintf (dump_file, " & T == T\nwith temporary T = (1 << ");
 338           print_generic_expr (dump_file, bit1, 0);
 339           fprintf (dump_file, ") | (1 << ");
 340           print_generic_expr (dump_file, bit2, 0);
 341           fprintf (dump_file, ")\n");
 342         }
 343
 344       return true;
 345     }
 346
 347   return false;
 348 }
 349
 350 /* If-convert on a or pattern with a common then block.  The inner
 351    if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB.
 352    Returns true, if the edges leading to the common then basic-block
 353    were merged.  */
 354
 355 static bool
 356 ifcombine_iforif (basic_block inner_cond_bb, basic_block outer_cond_bb)
 357 {
 358   tree inner_cond, outer_cond;
 359   tree name1, name2, bits1, bits2;
 360
 361   inner_cond = last_stmt (inner_cond_bb);
 362   if (!inner_cond
 363       || TREE_CODE (inner_cond) != COND_EXPR)
 364     return false;
 365
 366   outer_cond = last_stmt (outer_cond_bb);
 367   if (!outer_cond
 368       || TREE_CODE (outer_cond) != COND_EXPR)
 369     return false;
 370
 371   /* See if we have two bit tests of the same name in both tests.
 372      In that case remove the outer test and change the inner one to
 373      test for name & (bits1 | bits2) != 0.  */
 374   if (recognize_bits_test (inner_cond, &name1, &bits1)
 375       && recognize_bits_test (outer_cond, &name2, &bits2))
 376     {
 377       block_stmt_iterator bsi;
 378       tree t;
 379
 380       /* Find the common name which is bit-tested.  */
 381       if (name1 == name2)
 382         ;
 383       else if (bits1 == bits2)
 384         {
 385           t = name2;
 386           name2 = bits2;
 387           bits2 = t;
 388           t = name1;
 389           name1 = bits1;
 390           bits1 = t;
 391         }
 392       else if (name1 == bits2)
 393         {
 394           t = name2;
 395           name2 = bits2;
 396           bits2 = t;
 397         }
 398       else if (bits1 == name2)
 399         {
 400           t = name1;
 401           name1 = bits1;
 402           bits1 = t;
 403         }
 404       else
 405         return false;
 406
 407       /* Do it.  */
 408       bsi = bsi_for_stmt (inner_cond);
 409       t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), bits1, bits2);
 410       t = force_gimple_operand_bsi (&bsi, t, true, NULL_TREE,
 411                                     true, BSI_SAME_STMT);
 412       t = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
 413       t = force_gimple_operand_bsi (&bsi, t, true, NULL_TREE,
 414                                     true, BSI_SAME_STMT);
 415       COND_EXPR_COND (inner_cond) = fold_build2 (NE_EXPR, boolean_type_node, t,
 416                                                  build_int_cst (TREE_TYPE (t), 0));
 417       update_stmt (inner_cond);
 418
 419       /* Leave CFG optimization to cfg_cleanup.  */
 420       COND_EXPR_COND (outer_cond) = boolean_false_node;
 421       update_stmt (outer_cond);
 422
 423       if (dump_file)
 424         {
 425           fprintf (dump_file, "optimizing bits or bits test to ");
 426           print_generic_expr (dump_file, name1, 0);
 427           fprintf (dump_file, " & T != 0\nwith temporary T = ");
 428           print_generic_expr (dump_file, bits1, 0);
 429           fprintf (dump_file, " | ");
 430           print_generic_expr (dump_file, bits2, 0);
 431           fprintf (dump_file, "\n");
 432         }
 433
 434       return true;
 435     }
 436
 437   /* See if we have two comparisons that we can merge into one.
 438      This happens for C++ operator overloading where for example
 439      GE_EXPR is implemented as GT_EXPR || EQ_EXPR.  */
 440   else if (COMPARISON_CLASS_P (COND_EXPR_COND (inner_cond))
 441            && COMPARISON_CLASS_P (COND_EXPR_COND (outer_cond))
 442            && operand_equal_p (TREE_OPERAND (COND_EXPR_COND (inner_cond), 0),
 443                                TREE_OPERAND (COND_EXPR_COND (outer_cond), 0), 0)
 444            && operand_equal_p (TREE_OPERAND (COND_EXPR_COND (inner_cond), 1),
 445                                TREE_OPERAND (COND_EXPR_COND (outer_cond), 1), 0))
 446     {
 447       tree ccond1 = COND_EXPR_COND (inner_cond);
 448       tree ccond2 = COND_EXPR_COND (outer_cond);
 449       enum tree_code code1 = TREE_CODE (ccond1);
 450       enum tree_code code2 = TREE_CODE (ccond2);
 451       enum tree_code code;
 452       tree t;
 453
 454 #define CHK(a,b) ((code1 == a ## _EXPR && code2 == b ## _EXPR) \
 455                   || (code2 == a ## _EXPR && code1 == b ## _EXPR))
 456       /* Merge the two condition codes if possible.  */
 457       if (code1 == code2)
 458         code = code1;
 459       else if (CHK (EQ, LT))
 460         code = LE_EXPR;
 461       else if (CHK (EQ, GT))
 462         code = GE_EXPR;
 463       else if (CHK (LT, LE))
 464         code = LE_EXPR;
 465       else if (CHK (GT, GE))
 466         code = GE_EXPR;
 467       else if (INTEGRAL_TYPE_P (TREE_TYPE (TREE_OPERAND (ccond1, 0)))
 468                || flag_unsafe_math_optimizations)
 469         {
 470           if (CHK (LT, GT))
 471             code = NE_EXPR;
 472           else if (CHK (LT, NE))
 473             code = NE_EXPR;
 474           else if (CHK (GT, NE))
 475             code = NE_EXPR;
 476           else
 477             return false;
 478         }
 479       /* We could check for combinations leading to trivial true/false.  */
 480       else
 481         return false;
 482 #undef CHK
 483
 484       /* Do it.  */
 485       t = fold_build2 (code, boolean_type_node,
 486                        TREE_OPERAND (ccond2, 0), TREE_OPERAND (ccond2, 1));
 487       COND_EXPR_COND (inner_cond) = t;
 488       update_stmt (inner_cond);
 489
 490       /* Leave CFG optimization to cfg_cleanup.  */
 491       COND_EXPR_COND (outer_cond) = boolean_false_node;
 492       update_stmt (outer_cond);
 493
 494       if (dump_file)
 495         {
 496           fprintf (dump_file, "optimizing two comparisons to ");
 497           print_generic_expr (dump_file, t, 0);
 498           fprintf (dump_file, "\n");
 499         }
 500
 501       return true;
 502     }
 503
 504   return false;
 505 }
 506
 507 /* Recognize a CFG pattern and dispatch to the appropriate
 508    if-conversion helper.  We start with BB as the innermost
 509    worker basic-block.  Returns true if a transformation was done.  */
 510
 511 static bool
 512 tree_ssa_ifcombine_bb (basic_block inner_cond_bb)
 513 {
 514   basic_block then_bb = NULL, else_bb = NULL;
 515
 516   if (!recognize_if_then_else (inner_cond_bb, &then_bb, &else_bb))
 517     return false;
 518
 519   /* Recognize && and || of two conditions with a common
 520      then/else block which entry edges we can merge.  That is:
 521        if (a || b)
 522          ;
 523      and
 524        if (a && b)
 525          ;
 526      This requires a single predecessor of the inner cond_bb.  */
 527   if (single_pred_p (inner_cond_bb))
 528     {
 529       basic_block outer_cond_bb = single_pred (inner_cond_bb);
 530
 531       /* The && form is characterized by a common else_bb with
 532          the two edges leading to it mergable.  The latter is
 533          guaranteed by matching PHI arguments in the else_bb and
 534          the inner cond_bb having no side-effects.  */
 535       if (recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &else_bb)
 536           && same_phi_args_p (outer_cond_bb, inner_cond_bb, else_bb)
 537           && bb_no_side_effects_p (inner_cond_bb))
 538         {
 539           /* We have
 540                <outer_cond_bb>
 541                  if (q) goto inner_cond_bb; else goto else_bb;
 542                <inner_cond_bb>
 543                  if (p) goto ...; else goto else_bb;
 544                  ...
 545                <else_bb>
 546                  ...
 547            */
 548           return ifcombine_ifandif (inner_cond_bb, outer_cond_bb);
 549         }
 550
 551       /* The || form is characterized by a common then_bb with the
 552          two edges leading to it mergable.  The latter is guaranteed
 553          by matching PHI arguments in the then_bb and the inner cond_bb
 554          having no side-effects.  */
 555       if (recognize_if_then_else (outer_cond_bb, &then_bb, &inner_cond_bb)
 556           && same_phi_args_p (outer_cond_bb, inner_cond_bb, then_bb)
 557           && bb_no_side_effects_p (inner_cond_bb))
 558         {
 559           /* We have
 560                <outer_cond_bb>
 561                  if (q) goto then_bb; else goto inner_cond_bb;
 562                <inner_cond_bb>
 563                  if (q) goto then_bb; else goto ...;
 564                <then_bb>
 565                  ...
 566            */
 567           return ifcombine_iforif (inner_cond_bb, outer_cond_bb);
 568         }
 569     }
 570
 571   return false;
 572 }
 573
 574 /* Main entry for the tree if-conversion pass.  */
 575
 576 static unsigned int
 577 tree_ssa_ifcombine (void)
 578 {
 579   basic_block *bbs;
 580   bool cfg_changed = false;
 581   int i;
 582
 583   bbs = blocks_in_phiopt_order ();
 584
 585   for (i = 0; i < n_basic_blocks - NUM_FIXED_BLOCKS; ++i)
 586     {
 587       basic_block bb = bbs[i];
 588       tree stmt = last_stmt (bb);
 589
 590       if (stmt
 591           && TREE_CODE (stmt) == COND_EXPR)
 592         cfg_changed |= tree_ssa_ifcombine_bb (bb);
 593     }
 594
 595   free (bbs);
 596
 597   return cfg_changed ? TODO_cleanup_cfg : 0;
 598 }
 599
 600 static bool
 601 gate_ifcombine (void)
 602 {
 603   return 1;
 604 }
 605
 606 struct tree_opt_pass pass_tree_ifcombine = {
 607   "ifcombine",                  /* name */
 608   gate_ifcombine,               /* gate */
 609   tree_ssa_ifcombine,           /* execute */
 610   NULL,                         /* sub */
 611   NULL,                         /* next */
 612   0,                            /* static_pass_number */
 613   TV_TREE_IFCOMBINE,            /* tv_id */
 614   PROP_cfg | PROP_ssa,          /* properties_required */
 615   0,                            /* properties_provided */
 616   0,                            /* properties_destroyed */
 617   0,                            /* todo_flags_start */
 618   TODO_dump_func
 619   | TODO_ggc_collect
 620   | TODO_update_ssa
 621   | TODO_verify_ssa,            /* todo_flags_finish */
 622   0                             /* letter */
 623 };