gcc/ipa-pure-const.c

   1 /* Callgraph based analysis of static variables.
   2    Copyright (C) 2004, 2005, 2007 Free Software Foundation, Inc.
   3    Contributed by Kenneth Zadeck <zadeck@naturalbridge.com>
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 3, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 /* This file mark functions as being either const (TREE_READONLY) or
  22    pure (DECL_IS_PURE).
  23
  24    This must be run after inlining decisions have been made since
  25    otherwise, the local sets will not contain information that is
  26    consistent with post inlined state.  The global sets are not prone
  27    to this problem since they are by definition transitive.  */
  28
  29 /* The code in this module is called by the ipa pass manager. It
  30    should be one of the later passes since it's information is used by
  31    the rest of the compilation. */
  32
  33 #include "config.h"
  34 #include "system.h"
  35 #include "coretypes.h"
  36 #include "tm.h"
  37 #include "tree.h"
  38 #include "tree-flow.h"
  39 #include "tree-inline.h"
  40 #include "tree-pass.h"
  41 #include "langhooks.h"
  42 #include "pointer-set.h"
  43 #include "ggc.h"
  44 #include "ipa-utils.h"
  45 #include "c-common.h"
  46 #include "tree-gimple.h"
  47 #include "cgraph.h"
  48 #include "output.h"
  49 #include "flags.h"
  50 #include "timevar.h"
  51 #include "diagnostic.h"
  52 #include "langhooks.h"
  53 #include "target.h"
  54
  55 static struct pointer_set_t *visited_nodes;
  56
  57 /* Lattice values for const and pure functions.  Everything starts out
  58    being const, then may drop to pure and then neither depending on
  59    what is found.  */
  60 enum pure_const_state_e
  61 {
  62   IPA_CONST,
  63   IPA_PURE,
  64   IPA_NEITHER
  65 };
  66
  67 /* Holder inserted into the ipa_dfs_info aux field to hold the
  68    const_state.  */
  69 struct funct_state_d
  70 {
  71   enum pure_const_state_e pure_const_state;
  72   bool state_set_in_source;
  73 };
  74
  75 typedef struct funct_state_d * funct_state;
  76
  77 /* Return the function state from NODE.  */
  78
  79 static inline funct_state
  80 get_function_state (struct cgraph_node *node)
  81 {
  82   struct ipa_dfs_info * info = (struct ipa_dfs_info *) node->aux;
  83   return (funct_state) info->aux;
  84 }
  85
  86 /* Check to see if the use (or definition when CHECHING_WRITE is true)
  87    variable T is legal in a function that is either pure or const.  */
  88
  89 static inline void
  90 check_decl (funct_state local,
  91             tree t, bool checking_write)
  92 {
  93   /* If the variable has the "used" attribute, treat it as if it had a
  94      been touched by the devil.  */
  95   if (lookup_attribute ("used", DECL_ATTRIBUTES (t)))
  96     {
  97       local->pure_const_state = IPA_NEITHER;
  98       return;
  99     }
 100
 101   /* Do not want to do anything with volatile except mark any
 102      function that uses one to be not const or pure.  */
 103   if (TREE_THIS_VOLATILE (t))
 104     {
 105       local->pure_const_state = IPA_NEITHER;
 106       return;
 107     }
 108
 109   /* Do not care about a local automatic that is not static.  */
 110   if (!TREE_STATIC (t) && !DECL_EXTERNAL (t))
 111     return;
 112
 113   /* Since we have dealt with the locals and params cases above, if we
 114      are CHECKING_WRITE, this cannot be a pure or constant
 115      function.  */
 116   if (checking_write)
 117     {
 118       local->pure_const_state = IPA_NEITHER;
 119       return;
 120     }
 121
 122   if (DECL_EXTERNAL (t) || TREE_PUBLIC (t))
 123     {
 124       /* If the front end set the variable to be READONLY and
 125          constant, we can allow this variable in pure or const
 126          functions but the scope is too large for our analysis to set
 127          these bits ourselves.  */
 128
 129       if (TREE_READONLY (t)
 130           && DECL_INITIAL (t)
 131           && is_gimple_min_invariant (DECL_INITIAL (t)))
 132         ; /* Read of a constant, do not change the function state.  */
 133       else
 134         {
 135           /* Just a regular read.  */
 136           if (local->pure_const_state == IPA_CONST)
 137             local->pure_const_state = IPA_PURE;
 138         }
 139     }
 140
 141   /* Compilation level statics can be read if they are readonly
 142      variables.  */
 143   if (TREE_READONLY (t))
 144     return;
 145
 146   /* Just a regular read.  */
 147   if (local->pure_const_state == IPA_CONST)
 148     local->pure_const_state = IPA_PURE;
 149 }
 150
 151 /* If T is a VAR_DECL check to see if it is an allowed reference.  */
 152
 153 static void
 154 check_operand (funct_state local,
 155                tree t, bool checking_write)
 156 {
 157   if (!t) return;
 158
 159   if (TREE_CODE (t) == VAR_DECL)
 160     check_decl (local, t, checking_write);
 161 }
 162
 163 /* Examine tree T for references.  */
 164
 165 static void
 166 check_tree (funct_state local, tree t, bool checking_write)
 167 {
 168   if ((TREE_CODE (t) == EXC_PTR_EXPR) || (TREE_CODE (t) == FILTER_EXPR)
 169       || TREE_CODE (t) == SSA_NAME)
 170     return;
 171
 172   /* Any tree which is volatile disqualifies thie function from being
 173      const or pure. */
 174   if (TREE_THIS_VOLATILE (t))
 175     {
 176       local->pure_const_state = IPA_NEITHER;
 177       return;
 178     }
 179
 180   while (TREE_CODE (t) == REALPART_EXPR
 181          || TREE_CODE (t) == IMAGPART_EXPR
 182          || handled_component_p (t))
 183     {
 184       if (TREE_CODE (t) == ARRAY_REF)
 185         check_operand (local, TREE_OPERAND (t, 1), false);
 186       t = TREE_OPERAND (t, 0);
 187     }
 188
 189   /* The bottom of an indirect reference can only be read, not
 190      written.  */
 191   if (INDIRECT_REF_P (t))
 192     {
 193       check_tree (local, TREE_OPERAND (t, 0), false);
 194
 195       /* Any indirect reference that occurs on the lhs
 196          disqualifies the function from being pure or const. Any
 197          indirect reference that occurs on the rhs disqualifies the
 198          function from being const.  */
 199       if (checking_write)
 200         {
 201           local->pure_const_state = IPA_NEITHER;
 202           return;
 203         }
 204       else if (local->pure_const_state == IPA_CONST)
 205         local->pure_const_state = IPA_PURE;
 206     }
 207
 208   if (SSA_VAR_P (t))
 209     check_operand (local, t, checking_write);
 210 }
 211
 212 /* Scan tree T to see if there are any addresses taken in within T.  */
 213
 214 static void
 215 look_for_address_of (funct_state local, tree t)
 216 {
 217   if (TREE_CODE (t) == ADDR_EXPR)
 218     {
 219       tree x = get_base_var (t);
 220       if (TREE_CODE (x) == VAR_DECL)
 221         {
 222           check_decl (local, x, false);
 223
 224           /* Taking the address of something appears to be reasonable
 225              in PURE code.  Not allowed in const.  */
 226           if (local->pure_const_state == IPA_CONST)
 227             local->pure_const_state = IPA_PURE;
 228         }
 229     }
 230 }
 231
 232 /* Check to see if T is a read or address of operation on a var we are
 233    interested in analyzing.  LOCAL is passed in to get access to its
 234    bit vectors.  */
 235
 236 static void
 237 check_rhs_var (funct_state local, tree t)
 238 {
 239   look_for_address_of (local, t);
 240
 241   /* Memcmp and strlen can both trap and they are declared pure.  */
 242   if (tree_could_trap_p (t)
 243       && local->pure_const_state == IPA_CONST)
 244     local->pure_const_state = IPA_PURE;
 245
 246   check_tree(local, t, false);
 247 }
 248
 249 /* Check to see if T is an assignment to a var we are interested in
 250    analyzing.  LOCAL is passed in to get access to its bit vectors. */
 251
 252 static void
 253 check_lhs_var (funct_state local, tree t)
 254 {
 255   /* Memcmp and strlen can both trap and they are declared pure.
 256      Which seems to imply that we can apply the same rule here.  */
 257   if (tree_could_trap_p (t)
 258       && local->pure_const_state == IPA_CONST)
 259     local->pure_const_state = IPA_PURE;
 260
 261   check_tree(local, t, true);
 262 }
 263
 264 /* This is a scaled down version of get_asm_expr_operands from
 265    tree_ssa_operands.c.  The version there runs much later and assumes
 266    that aliasing information is already available. Here we are just
 267    trying to find if the set of inputs and outputs contain references
 268    or address of operations to local static variables.  STMT is the
 269    actual asm statement.  */
 270
 271 static void
 272 get_asm_expr_operands (funct_state local, tree stmt)
 273 {
 274   int noutputs = list_length (ASM_OUTPUTS (stmt));
 275   const char **oconstraints
 276     = (const char **) alloca ((noutputs) * sizeof (const char *));
 277   int i;
 278   tree link;
 279   const char *constraint;
 280   bool allows_mem, allows_reg, is_inout;
 281
 282   for (i=0, link = ASM_OUTPUTS (stmt); link; ++i, link = TREE_CHAIN (link))
 283     {
 284       oconstraints[i] = constraint
 285         = TREE_STRING_POINTER (TREE_VALUE (TREE_PURPOSE (link)));
 286       parse_output_constraint (&constraint, i, 0, 0,
 287                                &allows_mem, &allows_reg, &is_inout);
 288
 289       check_lhs_var (local, TREE_VALUE (link));
 290     }
 291
 292   for (link = ASM_INPUTS (stmt); link; link = TREE_CHAIN (link))
 293     {
 294       constraint
 295         = TREE_STRING_POINTER (TREE_VALUE (TREE_PURPOSE (link)));
 296       parse_input_constraint (&constraint, 0, 0, noutputs, 0,
 297                               oconstraints, &allows_mem, &allows_reg);
 298
 299       check_rhs_var (local, TREE_VALUE (link));
 300     }
 301
 302   for (link = ASM_CLOBBERS (stmt); link; link = TREE_CHAIN (link))
 303     if (simple_cst_equal(TREE_VALUE (link), memory_identifier_string) == 1)
 304       /* Abandon all hope, ye who enter here. */
 305       local->pure_const_state = IPA_NEITHER;
 306
 307   if (ASM_VOLATILE_P (stmt))
 308     local->pure_const_state = IPA_NEITHER;
 309 }
 310
 311 /* Check the parameters of a function call to CALL_EXPR to see if
 312    there are any references in the parameters that are not allowed for
 313    pure or const functions.  Also check to see if this is either an
 314    indirect call, a call outside the compilation unit, or has special
 315    attributes that may also effect the purity.  The CALL_EXPR node for
 316    the entire call expression.  */
 317
 318 static void
 319 check_call (funct_state local, tree call_expr)
 320 {
 321   int flags = call_expr_flags (call_expr);
 322   tree operand;
 323   call_expr_arg_iterator iter;
 324   tree callee_t = get_callee_fndecl (call_expr);
 325   struct cgraph_node* callee;
 326   enum availability avail = AVAIL_NOT_AVAILABLE;
 327
 328   FOR_EACH_CALL_EXPR_ARG (operand, iter, call_expr)
 329     check_rhs_var (local, operand);
 330
 331   /* The const and pure flags are set by a variety of places in the
 332      compiler (including here).  If someone has already set the flags
 333      for the callee, (such as for some of the builtins) we will use
 334      them, otherwise we will compute our own information.
 335
 336      Const and pure functions have less clobber effects than other
 337      functions so we process these first.  Otherwise if it is a call
 338      outside the compilation unit or an indirect call we punt.  This
 339      leaves local calls which will be processed by following the call
 340      graph.  */
 341   if (callee_t)
 342     {
 343       callee = cgraph_node(callee_t);
 344       avail = cgraph_function_body_availability (callee);
 345
 346       /* When bad things happen to bad functions, they cannot be const
 347          or pure.  */
 348       if (setjmp_call_p (callee_t))
 349         local->pure_const_state = IPA_NEITHER;
 350
 351       if (DECL_BUILT_IN_CLASS (callee_t) == BUILT_IN_NORMAL)
 352         switch (DECL_FUNCTION_CODE (callee_t))
 353           {
 354           case BUILT_IN_LONGJMP:
 355           case BUILT_IN_NONLOCAL_GOTO:
 356             local->pure_const_state = IPA_NEITHER;
 357             break;
 358           default:
 359             break;
 360           }
 361     }
 362
 363   /* The callee is either unknown (indirect call) or there is just no
 364      scannable code for it (external call) .  We look to see if there
 365      are any bits available for the callee (such as by declaration or
 366      because it is builtin) and process solely on the basis of those
 367      bits. */
 368   if (avail == AVAIL_NOT_AVAILABLE || avail == AVAIL_OVERWRITABLE)
 369     {
 370       if (flags & ECF_PURE)
 371         {
 372           if (local->pure_const_state == IPA_CONST)
 373             local->pure_const_state = IPA_PURE;
 374         }
 375       else
 376         local->pure_const_state = IPA_NEITHER;
 377     }
 378   else
 379     {
 380       /* We have the code and we will scan it for the effects. */
 381       if (flags & ECF_PURE)
 382         {
 383           if (local->pure_const_state == IPA_CONST)
 384             local->pure_const_state = IPA_PURE;
 385         }
 386     }
 387 }
 388
 389 /* TP is the part of the tree currently under the microscope.
 390    WALK_SUBTREES is part of the walk_tree api but is unused here.
 391    DATA is cgraph_node of the function being walked.  */
 392
 393 /* FIXME: When this is converted to run over SSA form, this code
 394    should be converted to use the operand scanner.  */
 395
 396 static tree
 397 scan_function (tree *tp,
 398                       int *walk_subtrees,
 399                       void *data)
 400 {
 401   struct cgraph_node *fn = (struct cgraph_node *) data;
 402   tree t = *tp;
 403   funct_state local = get_function_state (fn);
 404
 405   switch (TREE_CODE (t))
 406     {
 407     case VAR_DECL:
 408       if (DECL_INITIAL (t))
 409         walk_tree (&DECL_INITIAL (t), scan_function, fn, visited_nodes);
 410       *walk_subtrees = 0;
 411       break;
 412
 413     case GIMPLE_MODIFY_STMT:
 414       {
 415         /* First look on the lhs and see what variable is stored to */
 416         tree lhs = GIMPLE_STMT_OPERAND (t, 0);
 417         tree rhs = GIMPLE_STMT_OPERAND (t, 1);
 418         check_lhs_var (local, lhs);
 419
 420         /* For the purposes of figuring out what the cast affects */
 421
 422         /* Next check the operands on the rhs to see if they are ok. */
 423         switch (TREE_CODE_CLASS (TREE_CODE (rhs)))
 424           {
 425           case tcc_binary:
 426             {
 427               tree op0 = TREE_OPERAND (rhs, 0);
 428               tree op1 = TREE_OPERAND (rhs, 1);
 429               check_rhs_var (local, op0);
 430               check_rhs_var (local, op1);
 431             }
 432             break;
 433           case tcc_unary:
 434             {
 435               tree op0 = TREE_OPERAND (rhs, 0);
 436               check_rhs_var (local, op0);
 437             }
 438
 439             break;
 440           case tcc_reference:
 441             check_rhs_var (local, rhs);
 442             break;
 443           case tcc_declaration:
 444             check_rhs_var (local, rhs);
 445             break;
 446           case tcc_expression:
 447             switch (TREE_CODE (rhs))
 448               {
 449               case ADDR_EXPR:
 450                 check_rhs_var (local, rhs);
 451                 break;
 452               default:
 453                 break;
 454               }
 455             break;
 456           case tcc_vl_exp:
 457             switch (TREE_CODE (rhs))
 458               {
 459               case CALL_EXPR:
 460                 check_call (local, rhs);
 461                 break;
 462               default:
 463                 break;
 464               }
 465             break;
 466           default:
 467             break;
 468           }
 469         *walk_subtrees = 0;
 470       }
 471       break;
 472
 473     case ADDR_EXPR:
 474       /* This case is here to find addresses on rhs of constructors in
 475          decl_initial of static variables. */
 476       check_rhs_var (local, t);
 477       *walk_subtrees = 0;
 478       break;
 479
 480     case LABEL_EXPR:
 481       if (DECL_NONLOCAL (TREE_OPERAND (t, 0)))
 482         /* Target of long jump. */
 483         local->pure_const_state = IPA_NEITHER;
 484       break;
 485
 486     case CALL_EXPR:
 487       check_call (local, t);
 488       *walk_subtrees = 0;
 489       break;
 490
 491     case ASM_EXPR:
 492       get_asm_expr_operands (local, t);
 493       *walk_subtrees = 0;
 494       break;
 495
 496     default:
 497       break;
 498     }
 499   return NULL;
 500 }
 501
 502 /* This is the main routine for finding the reference patterns for
 503    global variables within a function FN.  */
 504
 505 static void
 506 analyze_function (struct cgraph_node *fn)
 507 {
 508   funct_state l = XCNEW (struct funct_state_d);
 509   tree decl = fn->decl;
 510   struct ipa_dfs_info * w_info = (struct ipa_dfs_info *) fn->aux;
 511
 512   w_info->aux = l;
 513
 514   l->pure_const_state = IPA_CONST;
 515   l->state_set_in_source = false;
 516
 517   /* If this function does not return normally or does not bind local,
 518      do not touch this unless it has been marked as const or pure by the
 519      front end.  */
 520   if (TREE_THIS_VOLATILE (decl)
 521       || !targetm.binds_local_p (decl))
 522     {
 523       l->pure_const_state = IPA_NEITHER;
 524       return;
 525     }
 526
 527   if (TREE_READONLY (decl))
 528     {
 529       l->pure_const_state = IPA_CONST;
 530       l->state_set_in_source = true;
 531     }
 532   if (DECL_IS_PURE (decl))
 533     {
 534       l->pure_const_state = IPA_PURE;
 535       l->state_set_in_source = true;
 536     }
 537
 538   if (dump_file)
 539     {
 540       fprintf (dump_file, "\n local analysis of %s with initial value = %d\n ",
 541                cgraph_node_name (fn),
 542                l->pure_const_state);
 543     }
 544
 545   if (!l->state_set_in_source)
 546     {
 547       struct function *this_cfun = DECL_STRUCT_FUNCTION (decl);
 548       basic_block this_block;
 549
 550       FOR_EACH_BB_FN (this_block, this_cfun)
 551         {
 552           block_stmt_iterator bsi;
 553           for (bsi = bsi_start (this_block); !bsi_end_p (bsi); bsi_next (&bsi))
 554             {
 555               walk_tree (bsi_stmt_ptr (bsi), scan_function,
 556                          fn, visited_nodes);
 557               if (l->pure_const_state == IPA_NEITHER)
 558                 goto end;
 559             }
 560         }
 561
 562       if (l->pure_const_state != IPA_NEITHER)
 563         {
 564           tree old_decl = current_function_decl;
 565           /* Const functions cannot have back edges (an
 566              indication of possible infinite loop side
 567              effect.  */
 568
 569           current_function_decl = fn->decl;
 570
 571           /* The C++ front end, has a tendency to some times jerk away
 572              a function after it has created it.  This should have
 573              been fixed.  */
 574           gcc_assert (DECL_STRUCT_FUNCTION (fn->decl));
 575
 576           push_cfun (DECL_STRUCT_FUNCTION (fn->decl));
 577
 578           if (mark_dfs_back_edges ())
 579             l->pure_const_state = IPA_NEITHER;
 580
 581           current_function_decl = old_decl;
 582           pop_cfun ();
 583         }
 584     }
 585
 586 end:
 587   if (dump_file)
 588     {
 589       fprintf (dump_file, "after local analysis of %s with initial value = %d\n ",
 590                cgraph_node_name (fn),
 591                l->pure_const_state);
 592     }
 593 }
 594
 595 \f
 596 /* Produce the global information by preforming a transitive closure
 597    on the local information that was produced by ipa_analyze_function
 598    and ipa_analyze_variable.  */
 599
 600 static unsigned int
 601 static_execute (void)
 602 {
 603   struct cgraph_node *node;
 604   struct cgraph_node *w;
 605   struct cgraph_node **order =
 606     XCNEWVEC (struct cgraph_node *, cgraph_n_nodes);
 607   int order_pos = ipa_utils_reduced_inorder (order, true, false);
 608   int i;
 609   struct ipa_dfs_info * w_info;
 610
 611   if (!memory_identifier_string)
 612     memory_identifier_string = build_string(7, "memory");
 613
 614   /* There are some shared nodes, in particular the initializers on
 615      static declarations.  We do not need to scan them more than once
 616      since all we would be interested in are the addressof
 617      operations.  */
 618   visited_nodes = pointer_set_create ();
 619
 620   /* Process all of the functions.
 621
 622      We do not want to process any of the clones so we check that this
 623      is a master clone.  However, we do NOT process any
 624      AVAIL_OVERWRITABLE functions (these are never clones) we cannot
 625      guarantee that what we learn about the one we see will be true
 626      for the one that overriders it.
 627   */
 628   for (node = cgraph_nodes; node; node = node->next)
 629     if (node->analyzed && cgraph_is_master_clone (node))
 630       analyze_function (node);
 631
 632   pointer_set_destroy (visited_nodes);
 633   visited_nodes = NULL;
 634   if (dump_file)
 635     {
 636       dump_cgraph (dump_file);
 637       ipa_utils_print_order(dump_file, "reduced", order, order_pos);
 638     }
 639
 640   /* Propagate the local information thru the call graph to produce
 641      the global information.  All the nodes within a cycle will have
 642      the same info so we collapse cycles first.  Then we can do the
 643      propagation in one pass from the leaves to the roots.  */
 644   for (i = 0; i < order_pos; i++ )
 645     {
 646       enum pure_const_state_e pure_const_state = IPA_CONST;
 647       node = order[i];
 648
 649       /* Find the worst state for any node in the cycle.  */
 650       w = node;
 651       while (w)
 652         {
 653           funct_state w_l = get_function_state (w);
 654           if (pure_const_state < w_l->pure_const_state)
 655             pure_const_state = w_l->pure_const_state;
 656
 657           if (pure_const_state == IPA_NEITHER)
 658             break;
 659
 660           if (!w_l->state_set_in_source)
 661             {
 662               struct cgraph_edge *e;
 663               for (e = w->callees; e; e = e->next_callee)
 664                 {
 665                   struct cgraph_node *y = e->callee;
 666                   /* Only look at the master nodes and skip external nodes.  */
 667                   y = cgraph_master_clone (y);
 668                   if (y)
 669                     {
 670                       funct_state y_l = get_function_state (y);
 671                       if (pure_const_state < y_l->pure_const_state)
 672                         pure_const_state = y_l->pure_const_state;
 673                       if (pure_const_state == IPA_NEITHER)
 674                         break;
 675                     }
 676                 }
 677             }
 678           w_info = (struct ipa_dfs_info *) w->aux;
 679           w = w_info->next_cycle;
 680         }
 681
 682       /* Copy back the region's pure_const_state which is shared by
 683          all nodes in the region.  */
 684       w = node;
 685       while (w)
 686         {
 687           funct_state w_l = get_function_state (w);
 688
 689           /* All nodes within a cycle share the same info.  */
 690           if (!w_l->state_set_in_source)
 691             {
 692               w_l->pure_const_state = pure_const_state;
 693               switch (pure_const_state)
 694                 {
 695                 case IPA_CONST:
 696                   TREE_READONLY (w->decl) = 1;
 697                   if (dump_file)
 698                     fprintf (dump_file, "Function found to be const: %s\n",
 699                              lang_hooks.decl_printable_name(w->decl, 2));
 700                   break;
 701
 702                 case IPA_PURE:
 703                   DECL_IS_PURE (w->decl) = 1;
 704                   if (dump_file)
 705                     fprintf (dump_file, "Function found to be pure: %s\n",
 706                              lang_hooks.decl_printable_name(w->decl, 2));
 707                   break;
 708
 709                 default:
 710                   break;
 711                 }
 712             }
 713           w_info = (struct ipa_dfs_info *) w->aux;
 714           w = w_info->next_cycle;
 715         }
 716     }
 717
 718   /* Cleanup. */
 719   for (node = cgraph_nodes; node; node = node->next)
 720     /* Get rid of the aux information.  */
 721     if (node->aux)
 722       {
 723         w_info = (struct ipa_dfs_info *) node->aux;
 724         if (w_info->aux)
 725           free (w_info->aux);
 726         free (node->aux);
 727         node->aux = NULL;
 728       }
 729
 730   free (order);
 731   return 0;
 732 }
 733
 734 static bool
 735 gate_pure_const (void)
 736 {
 737   return (flag_unit_at_a_time != 0 && flag_ipa_pure_const
 738           /* Don't bother doing anything if the program has errors.  */
 739           && !(errorcount || sorrycount));
 740 }
 741
 742 struct tree_opt_pass pass_ipa_pure_const =
 743 {
 744   "pure-const",                         /* name */
 745   gate_pure_const,                      /* gate */
 746   static_execute,                       /* execute */
 747   NULL,                                 /* sub */
 748   NULL,                                 /* next */
 749   0,                                    /* static_pass_number */
 750   TV_IPA_PURE_CONST,                    /* tv_id */
 751   0,                                    /* properties_required */
 752   0,                                    /* properties_provided */
 753   0,                                    /* properties_destroyed */
 754   0,                                    /* todo_flags_start */
 755   0,                                    /* todo_flags_finish */
 756   0                                     /* letter */
 757 };
 758
 759