gcc/tree-ssa-phiopt.c

   1 /* Optimization of PHI nodes by converting them into straightline code.
   2    Copyright (C) 2004, 2005 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it
   7 under the terms of the GNU General Public License as published by the
   8 Free Software Foundation; either version 2, or (at your option) any
   9 later version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT
  12 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING.  If not, write to the Free
  18 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
  19 02111-1307, USA.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "errors.h"
  26 #include "ggc.h"
  27 #include "tree.h"
  28 #include "rtl.h"
  29 #include "flags.h"
  30 #include "tm_p.h"
  31 #include "basic-block.h"
  32 #include "timevar.h"
  33 #include "diagnostic.h"
  34 #include "tree-flow.h"
  35 #include "tree-pass.h"
  36 #include "tree-dump.h"
  37 #include "langhooks.h"
  38
  39 static void tree_ssa_phiopt (void);
  40 static bool conditional_replacement (basic_block, basic_block, basic_block,
  41                                      edge, edge, tree, tree, tree);
  42 static bool value_replacement (basic_block, basic_block, basic_block,
  43                                edge, edge, tree, tree, tree);
  44 static bool abs_replacement (basic_block, basic_block, basic_block,
  45                              edge, edge, tree, tree, tree);
  46 static void replace_phi_edge_with_variable (basic_block, basic_block, edge,
  47                                             tree, tree);
  48
  49 /* This pass eliminates PHI nodes which can be trivially implemented as
  50    an assignment from a conditional expression.  i.e. if we have something
  51    like:
  52
  53      bb0:
  54       if (cond) goto bb2; else goto bb1;
  55      bb1:
  56      bb2:
  57       x = PHI (0 (bb1), 1 (bb0)
  58
  59    We can rewrite that as:
  60
  61      bb0:
  62      bb1:
  63      bb2:
  64       x = cond;
  65
  66    bb1 will become unreachable and bb0 and bb2 will almost always
  67    be merged into a single block.  This occurs often due to gimplification
  68     of conditionals.
  69
  70    Also done is the following optimization:
  71
  72      bb0:
  73       if (a != b) goto bb2; else goto bb1;
  74      bb1:
  75      bb2:
  76       x = PHI (a (bb1), b (bb0))
  77
  78    We can rewrite that as:
  79
  80      bb0:
  81      bb1:
  82      bb2:
  83       x = b;
  84
  85    This can sometimes occur as a result of other optimizations.  A
  86    similar transformation is done by the ifcvt RTL optimizer.
  87
  88    This pass also eliminates PHI nodes which are really absolute
  89    values.  i.e. if we have something like:
  90
  91      bb0:
  92       if (a >= 0) goto bb2; else goto bb1;
  93      bb1:
  94       x = -a;
  95      bb2:
  96       x = PHI (x (bb1), a (bb0));
  97
  98    We can rewrite that as:
  99
 100      bb0:
 101      bb1:
 102      bb2:
 103       x = ABS_EXPR< a >;
 104
 105    bb1 will become unreachable and bb0 and bb2 will almost always be merged
 106    into a single block.  Similar transformations are done by the ifcvt
 107    RTL optimizer.  */
 108
 109 static void
 110 tree_ssa_phiopt (void)
 111 {
 112   basic_block bb;
 113   bool removed_phis = false;
 114
 115   /* Search every basic block for COND_EXPR we may be able to optimize
 116      in reverse order so we can find more.  */
 117   FOR_EACH_BB_REVERSE (bb)
 118     {
 119       tree cond_expr;
 120       tree phi;
 121       basic_block bb1, bb2;
 122       edge e1, e2;
 123
 124       cond_expr = last_stmt (bb);
 125       /* Check to see if the last statement is a COND_EXPR.  */
 126       if (!cond_expr
 127           || TREE_CODE (cond_expr) != COND_EXPR)
 128         continue;
 129
 130       e1 = EDGE_SUCC (bb, 0);
 131       bb1 = e1->dest;
 132       e2 = EDGE_SUCC (bb, 1);
 133       bb2 = e2->dest;
 134
 135       /* We cannot do the optimization on abnormal edges.  */
 136       if ((e1->flags & EDGE_ABNORMAL) != 0
 137           || (e2->flags & EDGE_ABNORMAL) != 0)
 138        continue;
 139
 140       /* If either bb1's succ or bb2 or bb2's succ is non NULL.  */
 141       if (EDGE_COUNT (bb1->succs) < 1
 142           || bb2 == NULL
 143           || EDGE_COUNT (bb2->succs) < 1)
 144         continue;
 145
 146       /* Find the bb which is the fall through to the other.  */
 147       if (EDGE_SUCC (bb1, 0)->dest == bb2)
 148         ;
 149       else if (EDGE_SUCC (bb2, 0)->dest == bb1)
 150         {
 151           basic_block bb_tmp = bb1;
 152           edge e_tmp = e1;
 153           bb1 = bb2;
 154           bb2 = bb_tmp;
 155           e1 = e2;
 156           e2 = e_tmp;
 157         }
 158       else
 159         continue;
 160
 161       e1 = EDGE_SUCC (bb1, 0);
 162
 163       /* Make sure that bb1 is just a fall through.  */
 164       if (EDGE_COUNT (bb1->succs) > 1
 165           || (e1->flags & EDGE_FALLTHRU) == 0)
 166         continue;
 167
 168       /* Also make that bb1 only have one pred and it is bb.  */
 169       if (EDGE_COUNT (bb1->preds) > 1
 170           || EDGE_PRED (bb1, 0)->src != bb)
 171         continue;
 172
 173       phi = phi_nodes (bb2);
 174
 175       /* Check to make sure that there is only one PHI node.
 176          TODO: we could do it with more than one iff the other PHI nodes
 177          have the same elements for these two edges.  */
 178       if (phi && PHI_CHAIN (phi) == NULL)
 179         {
 180           tree arg0 = NULL, arg1 = NULL;
 181
 182           arg0 = PHI_ARG_DEF_TREE (phi, e1->dest_idx);
 183           arg1 = PHI_ARG_DEF_TREE (phi, e2->dest_idx);
 184
 185           /* We know something is wrong if we cannot find the edges in the PHI
 186              node.  */
 187           gcc_assert (arg0 != NULL && arg1 != NULL);
 188
 189           /* Do the replacement of conditional if it can be done.  */
 190           if (conditional_replacement (bb, bb1, bb2, e1, e2, phi, arg0, arg1)
 191               || value_replacement (bb, bb1, bb2, e1, e2, phi, arg0, arg1)
 192               || abs_replacement (bb, bb1, bb2, e1, e2, phi, arg0, arg1))
 193             {
 194               /* We have done the replacement so we need to rebuild the
 195                  cfg when this pass is complete.  */
 196               removed_phis = true;
 197             }
 198         }
 199     }
 200 }
 201
 202 /* Return TRUE if block BB has no executable statements, otherwise return
 203    FALSE.  */
 204 bool
 205 empty_block_p (basic_block bb)
 206 {
 207   block_stmt_iterator bsi;
 208
 209   /* BB must have no executable statements.  */
 210   bsi = bsi_start (bb);
 211   while (!bsi_end_p (bsi)
 212           && (TREE_CODE (bsi_stmt (bsi)) == LABEL_EXPR
 213               || IS_EMPTY_STMT (bsi_stmt (bsi))))
 214     bsi_next (&bsi);
 215
 216   if (!bsi_end_p (bsi))
 217     return false;
 218
 219   return true;
 220 }
 221
 222 /* Replace PHI node element whoes edge is E in block BB with variable NEW.
 223    Remove the edge from COND_BLOCK which does not lead to BB (COND_BLOCK
 224    is known to have two edges, one of which must reach BB).  */
 225
 226 static void
 227 replace_phi_edge_with_variable (basic_block cond_block, basic_block bb,
 228                                 edge e, tree phi, tree new)
 229 {
 230   basic_block block_to_remove;
 231   block_stmt_iterator bsi;
 232
 233   /* Change the PHI argument to new.  */
 234   PHI_ARG_DEF_TREE (phi, e->dest_idx) = new;
 235
 236   /* Remove the empty basic block.  */
 237   if (EDGE_SUCC (cond_block, 0)->dest == bb)
 238     {
 239       EDGE_SUCC (cond_block, 0)->flags |= EDGE_FALLTHRU;
 240       EDGE_SUCC (cond_block, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
 241
 242       block_to_remove = EDGE_SUCC (cond_block, 1)->dest;
 243     }
 244   else
 245     {
 246       EDGE_SUCC (cond_block, 1)->flags |= EDGE_FALLTHRU;
 247       EDGE_SUCC (cond_block, 1)->flags
 248         &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
 249
 250       block_to_remove = EDGE_SUCC (cond_block, 0)->dest;
 251     }
 252   delete_basic_block (block_to_remove);
 253
 254   /* Eliminate the COND_EXPR at the end of COND_BLOCK.  */
 255   bsi = bsi_last (cond_block);
 256   bsi_remove (&bsi);
 257
 258   if (dump_file && (dump_flags & TDF_DETAILS))
 259     fprintf (dump_file,
 260               "COND_EXPR in block %d and PHI in block %d converted to straightline code.\n",
 261               cond_block->index,
 262               bb->index);
 263 }
 264
 265 /*  The function conditional_replacement does the main work of doing the
 266     conditional replacement.  Return true if the replacement is done.
 267     Otherwise return false.
 268     BB is the basic block where the replacement is going to be done on.  ARG0
 269     is argument 0 from PHI.  Likewise for ARG1.  */
 270
 271 static bool
 272 conditional_replacement (basic_block cond_bb, basic_block middle_bb,
 273                          basic_block phi_bb, edge e0, edge e1, tree phi,
 274                          tree arg0, tree arg1)
 275 {
 276   tree result;
 277   tree old_result = NULL;
 278   tree new, cond;
 279   block_stmt_iterator bsi;
 280   edge true_edge, false_edge;
 281   tree new_var = NULL;
 282   tree new_var1;
 283
 284   /* The PHI arguments have the constants 0 and 1, then convert
 285      it to the conditional.  */
 286   if ((integer_zerop (arg0) && integer_onep (arg1))
 287       || (integer_zerop (arg1) && integer_onep (arg0)))
 288     ;
 289   else
 290     return false;
 291
 292   if (!empty_block_p (middle_bb))
 293     return false;
 294
 295   /* If the condition is not a naked SSA_NAME and its type does not
 296      match the type of the result, then we have to create a new
 297      variable to optimize this case as it would likely create
 298      non-gimple code when the condition was converted to the
 299      result's type.  */
 300   cond = COND_EXPR_COND (last_stmt (cond_bb));
 301   result = PHI_RESULT (phi);
 302   if (TREE_CODE (cond) != SSA_NAME
 303       && !lang_hooks.types_compatible_p (TREE_TYPE (cond), TREE_TYPE (result)))
 304     {
 305       new_var = make_rename_temp (TREE_TYPE (cond), NULL);
 306       old_result = cond;
 307       cond = new_var;
 308     }
 309
 310   /* If the condition was a naked SSA_NAME and the type is not the
 311      same as the type of the result, then convert the type of the
 312      condition.  */
 313   if (!lang_hooks.types_compatible_p (TREE_TYPE (cond), TREE_TYPE (result)))
 314     cond = fold_convert (TREE_TYPE (result), cond);
 315
 316   /* We need to know which is the true edge and which is the false
 317      edge so that we know when to invert the condition below.  */
 318   extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
 319
 320   /* Insert our new statement at the end of conditional block before the
 321      COND_EXPR.  */
 322   bsi = bsi_last (cond_bb);
 323   bsi_insert_before (&bsi, build_empty_stmt (), BSI_NEW_STMT);
 324
 325   if (old_result)
 326     {
 327       tree new1;
 328       if (!COMPARISON_CLASS_P (old_result))
 329         return false;
 330
 331       new1 = build (TREE_CODE (old_result), TREE_TYPE (old_result),
 332                     TREE_OPERAND (old_result, 0),
 333                     TREE_OPERAND (old_result, 1));
 334
 335       new1 = build (MODIFY_EXPR, TREE_TYPE (old_result), new_var, new1);
 336       bsi_insert_after (&bsi, new1, BSI_NEW_STMT);
 337     }
 338
 339   new_var1 = duplicate_ssa_name (PHI_RESULT (phi), NULL);
 340
 341
 342   /* At this point we know we have a COND_EXPR with two successors.
 343      One successor is BB, the other successor is an empty block which
 344      falls through into BB.
 345
 346      There is a single PHI node at the join point (BB) and its arguments
 347      are constants (0, 1).
 348
 349      So, given the condition COND, and the two PHI arguments, we can
 350      rewrite this PHI into non-branching code:
 351
 352        dest = (COND) or dest = COND'
 353
 354      We use the condition as-is if the argument associated with the
 355      true edge has the value one or the argument associated with the
 356      false edge as the value zero.  Note that those conditions are not
 357      the same since only one of the outgoing edges from the COND_EXPR
 358      will directly reach BB and thus be associated with an argument.  */
 359   if ((e0 == true_edge && integer_onep (arg0))
 360       || (e0 == false_edge && integer_zerop (arg0))
 361       || (e1 == true_edge && integer_onep (arg1))
 362       || (e1 == false_edge && integer_zerop (arg1)))
 363     {
 364       new = build (MODIFY_EXPR, TREE_TYPE (new_var1), new_var1, cond);
 365     }
 366   else
 367     {
 368       tree cond1 = invert_truthvalue (cond);
 369
 370       cond = cond1;
 371       /* If what we get back is a conditional expression, there is no
 372           way that it can be gimple.  */
 373       if (TREE_CODE (cond) == COND_EXPR)
 374         {
 375           release_ssa_name (new_var1);
 376           return false;
 377         }
 378
 379       /* If what we get back is not gimple try to create it as gimple by
 380          using a temporary variable.  */
 381       if (is_gimple_cast (cond)
 382           && !is_gimple_val (TREE_OPERAND (cond, 0)))
 383         {
 384           tree temp = TREE_OPERAND (cond, 0);
 385           tree new_var_1 = make_rename_temp (TREE_TYPE (temp), NULL);
 386           new = build (MODIFY_EXPR, TREE_TYPE (new_var_1), new_var_1, temp);
 387           bsi_insert_after (&bsi, new, BSI_NEW_STMT);
 388           cond = fold_convert (TREE_TYPE (result), new_var_1);
 389         }
 390
 391       if (TREE_CODE (cond) == TRUTH_NOT_EXPR
 392           &&  !is_gimple_val (TREE_OPERAND (cond, 0)))
 393         {
 394           release_ssa_name (new_var1);
 395           return false;
 396         }
 397
 398       new = build (MODIFY_EXPR, TREE_TYPE (new_var1), new_var1, cond);
 399     }
 400
 401   bsi_insert_after (&bsi, new, BSI_NEW_STMT);
 402
 403   SSA_NAME_DEF_STMT (new_var1) = new;
 404
 405   replace_phi_edge_with_variable (cond_bb, phi_bb, e1, phi, new_var1);
 406
 407   /* Note that we optimized this PHI.  */
 408   return true;
 409 }
 410
 411 /*  The function value_replacement does the main work of doing the value
 412     replacement.  Return true if the replacement is done.  Otherwise return
 413     false.
 414     BB is the basic block where the replacement is going to be done on.  ARG0
 415     is argument 0 from the PHI.  Likewise for ARG1.  */
 416
 417 static bool
 418 value_replacement (basic_block cond_bb, basic_block middle_bb,
 419                    basic_block phi_bb, edge e0, edge e1, tree phi,
 420                    tree arg0, tree arg1)
 421 {
 422   tree result;
 423   tree cond;
 424   edge true_edge, false_edge;
 425
 426   /* If the type says honor signed zeros we cannot do this
 427      optimization.  */
 428   if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (arg1))))
 429     return false;
 430
 431   if (!empty_block_p (middle_bb))
 432     return false;
 433
 434   cond = COND_EXPR_COND (last_stmt (cond_bb));
 435   result = PHI_RESULT (phi);
 436
 437   /* This transformation is only valid for equality comparisons.  */
 438   if (TREE_CODE (cond) != NE_EXPR && TREE_CODE (cond) != EQ_EXPR)
 439     return false;
 440
 441   /* We need to know which is the true edge and which is the false
 442       edge so that we know if have abs or negative abs.  */
 443   extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
 444
 445   /* At this point we know we have a COND_EXPR with two successors.
 446      One successor is BB, the other successor is an empty block which
 447      falls through into BB.
 448
 449      The condition for the COND_EXPR is known to be NE_EXPR or EQ_EXPR.
 450
 451      There is a single PHI node at the join point (BB) with two arguments.
 452
 453      We now need to verify that the two arguments in the PHI node match
 454      the two arguments to the equality comparison.  */
 455
 456   if ((operand_equal_for_phi_arg_p (arg0, TREE_OPERAND (cond, 0))
 457        && operand_equal_for_phi_arg_p (arg1, TREE_OPERAND (cond, 1)))
 458       || (operand_equal_for_phi_arg_p (arg1, TREE_OPERAND (cond, 0))
 459           && operand_equal_for_phi_arg_p (arg0, TREE_OPERAND (cond, 1))))
 460     {
 461       edge e;
 462       tree arg;
 463
 464       /* For NE_EXPR, we want to build an assignment result = arg where
 465          arg is the PHI argument associated with the true edge.  For
 466          EQ_EXPR we want the PHI argument associated with the false edge.  */
 467       e = (TREE_CODE (cond) == NE_EXPR ? true_edge : false_edge);
 468
 469       /* Unfortunately, E may not reach BB (it may instead have gone to
 470          OTHER_BLOCK).  If that is the case, then we want the single outgoing
 471          edge from OTHER_BLOCK which reaches BB and represents the desired
 472          path from COND_BLOCK.  */
 473       if (e->dest == middle_bb)
 474         e = EDGE_SUCC (e->dest, 0);
 475
 476       /* Now we know the incoming edge to BB that has the argument for the
 477          RHS of our new assignment statement.  */
 478       if (e0 == e)
 479         arg = arg0;
 480       else
 481         arg = arg1;
 482
 483       replace_phi_edge_with_variable (cond_bb, phi_bb, e1, phi, arg);
 484
 485       /* Note that we optimized this PHI.  */
 486       return true;
 487     }
 488   return false;
 489 }
 490
 491 /*  The function absolute_replacement does the main work of doing the absolute
 492     replacement.  Return true if the replacement is done.  Otherwise return
 493     false.
 494     bb is the basic block where the replacement is going to be done on.  arg0
 495     is argument 0 from the phi.  Likewise for arg1.  */
 496
 497 static bool
 498 abs_replacement (basic_block cond_bb, basic_block middle_bb,
 499                  basic_block phi_bb, edge e0 ATTRIBUTE_UNUSED, edge e1,
 500                  tree phi, tree arg0, tree arg1)
 501 {
 502   tree result;
 503   tree new, cond;
 504   block_stmt_iterator bsi;
 505   edge true_edge, false_edge;
 506   tree assign = NULL;
 507   edge e;
 508   tree rhs = NULL, lhs = NULL;
 509   bool negate;
 510   enum tree_code cond_code;
 511
 512   /* If the type says honor signed zeros we cannot do this
 513      optimization.  */
 514   if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (arg1))))
 515     return false;
 516
 517   /* OTHER_BLOCK must have only one executable statement which must have the
 518      form arg0 = -arg1 or arg1 = -arg0.  */
 519   bsi = bsi_start (middle_bb);
 520   while (!bsi_end_p (bsi))
 521     {
 522       tree stmt = bsi_stmt (bsi);
 523
 524       /* Empty statements and labels are uninteresting.  */
 525       if (TREE_CODE (stmt) == LABEL_EXPR
 526           || IS_EMPTY_STMT (stmt))
 527         {
 528           bsi_next (&bsi);
 529           continue;
 530         }
 531
 532       /* If we found the assignment, but it was not the only executable
 533          statement in OTHER_BLOCK, then we can not optimize.  */
 534       if (assign)
 535         return false;
 536
 537       /* If we got here, then we have found the first executable statement
 538          in OTHER_BLOCK.  If it is anything other than arg = -arg1 or
 539          arg1 = -arg0, then we can not optimize.  */
 540       if (TREE_CODE (stmt) == MODIFY_EXPR)
 541         {
 542           lhs = TREE_OPERAND (stmt, 0);
 543           rhs = TREE_OPERAND (stmt, 1);
 544
 545           if (TREE_CODE (rhs) == NEGATE_EXPR)
 546             {
 547               rhs = TREE_OPERAND (rhs, 0);
 548
 549               /* The assignment has to be arg0 = -arg1 or arg1 = -arg0.  */
 550               if ((lhs == arg0 && rhs == arg1)
 551                   || (lhs == arg1 && rhs == arg0))
 552                 {
 553                   assign = stmt;
 554                   bsi_next (&bsi);
 555                 }
 556               else
 557                 return false;
 558             }
 559           else
 560             return false;
 561         }
 562       else
 563         return false;
 564     }
 565
 566   /* If we did not find the proper negation assignment, then we can not
 567      optimize.  */
 568   if (assign == NULL)
 569     return false;
 570
 571   cond = COND_EXPR_COND (last_stmt (cond_bb));
 572   result = PHI_RESULT (phi);
 573
 574   /* Only relationals comparing arg[01] against zero are interesting.  */
 575   cond_code = TREE_CODE (cond);
 576   if (cond_code != GT_EXPR && cond_code != GE_EXPR
 577       && cond_code != LT_EXPR && cond_code != LE_EXPR)
 578     return false;
 579
 580   /* Make sure the conditional is arg[01] OP y.  */
 581   if (TREE_OPERAND (cond, 0) != rhs)
 582     return false;
 583
 584   if (FLOAT_TYPE_P (TREE_TYPE (TREE_OPERAND (cond, 1)))
 585                ? real_zerop (TREE_OPERAND (cond, 1))
 586                : integer_zerop (TREE_OPERAND (cond, 1)))
 587     ;
 588   else
 589     return false;
 590
 591   /* We need to know which is the true edge and which is the false
 592      edge so that we know if have abs or negative abs.  */
 593   extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
 594
 595   /* For GT_EXPR/GE_EXPR, if the true edge goes to OTHER_BLOCK, then we
 596      will need to negate the result.  Similarly for LT_EXPR/LE_EXPR if
 597      the false edge goes to OTHER_BLOCK.  */
 598   if (cond_code == GT_EXPR || cond_code == GE_EXPR)
 599     e = true_edge;
 600   else
 601     e = false_edge;
 602
 603   if (e->dest == middle_bb)
 604     negate = true;
 605   else
 606     negate = false;
 607
 608   result = duplicate_ssa_name (result, NULL);
 609
 610   if (negate)
 611     lhs = make_rename_temp (TREE_TYPE (result), NULL);
 612   else
 613     lhs = result;
 614
 615   /* Build the modify expression with abs expression.  */
 616   new = build (MODIFY_EXPR, TREE_TYPE (lhs),
 617                lhs, build1 (ABS_EXPR, TREE_TYPE (lhs), rhs));
 618
 619   bsi = bsi_last (cond_bb);
 620   bsi_insert_before (&bsi, new, BSI_NEW_STMT);
 621
 622   if (negate)
 623     {
 624       /* Get the right BSI.  We want to insert after the recently
 625          added ABS_EXPR statement (which we know is the first statement
 626          in the block.  */
 627       new = build (MODIFY_EXPR, TREE_TYPE (result),
 628                    result, build1 (NEGATE_EXPR, TREE_TYPE (lhs), lhs));
 629
 630       bsi_insert_after (&bsi, new, BSI_NEW_STMT);
 631     }
 632
 633   SSA_NAME_DEF_STMT (result) = new;
 634   replace_phi_edge_with_variable (cond_bb, phi_bb, e1, phi, result);
 635
 636   /* Note that we optimized this PHI.  */
 637   return true;
 638 }
 639
 640
 641 /* Always do these optimizations if we have SSA
 642    trees to work on.  */
 643 static bool
 644 gate_phiopt (void)
 645 {
 646   return 1;
 647 }
 648
 649 struct tree_opt_pass pass_phiopt =
 650 {
 651   "phiopt",                             /* name */
 652   gate_phiopt,                          /* gate */
 653   tree_ssa_phiopt,                      /* execute */
 654   NULL,                                 /* sub */
 655   NULL,                                 /* next */
 656   0,                                    /* static_pass_number */
 657   TV_TREE_PHIOPT,                       /* tv_id */
 658   PROP_cfg | PROP_ssa | PROP_alias,     /* properties_required */
 659   0,                                    /* properties_provided */
 660   0,                                    /* properties_destroyed */
 661   0,                                    /* todo_flags_start */
 662   TODO_cleanup_cfg | TODO_dump_func | TODO_ggc_collect  /* todo_flags_finish */
 663     | TODO_verify_ssa | TODO_rename_vars
 664     | TODO_verify_flow | TODO_verify_stmts,
 665   0                                     /* letter */
 666 };