gcc/tree-ssa-phiprop.c

   1 /* Backward propagation of indirect loads through PHIs.
   2    Copyright (C) 2007-2015 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 3, 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 COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "hash-set.h"
  26 #include "machmode.h"
  27 #include "vec.h"
  28 #include "double-int.h"
  29 #include "input.h"
  30 #include "alias.h"
  31 #include "symtab.h"
  32 #include "wide-int.h"
  33 #include "inchash.h"
  34 #include "tree.h"
  35 #include "fold-const.h"
  36 #include "tm_p.h"
  37 #include "predict.h"
  38 #include "hard-reg-set.h"
  39 #include "input.h"
  40 #include "function.h"
  41 #include "dominance.h"
  42 #include "cfg.h"
  43 #include "basic-block.h"
  44 #include "gimple-pretty-print.h"
  45 #include "tree-ssa-alias.h"
  46 #include "internal-fn.h"
  47 #include "tree-eh.h"
  48 #include "gimple-expr.h"
  49 #include "is-a.h"
  50 #include "gimple.h"
  51 #include "gimplify.h"
  52 #include "gimple-iterator.h"
  53 #include "gimple-ssa.h"
  54 #include "tree-phinodes.h"
  55 #include "ssa-iterators.h"
  56 #include "stringpool.h"
  57 #include "tree-ssanames.h"
  58 #include "tree-pass.h"
  59 #include "langhooks.h"
  60 #include "flags.h"
  61
  62 /* This pass propagates indirect loads through the PHI node for its
  63    address to make the load source possibly non-addressable and to
  64    allow for PHI optimization to trigger.
  65
  66    For example the pass changes
  67
  68      # addr_1 = PHI <&a, &b>
  69      tmp_1 = *addr_1;
  70
  71    to
  72
  73      # tmp_1 = PHI <a, b>
  74
  75    but also handles more complex scenarios like
  76
  77      D.2077_2 = &this_1(D)->a1;
  78      ...
  79
  80      # b_12 = PHI <&c(2), D.2077_2(3)>
  81      D.2114_13 = *b_12;
  82      ...
  83
  84      # b_15 = PHI <b_12(4), &b(5)>
  85      D.2080_5 = &this_1(D)->a0;
  86      ...
  87
  88      # b_18 = PHI <D.2080_5(6), &c(7)>
  89      ...
  90
  91      # b_21 = PHI <b_15(8), b_18(9)>
  92      D.2076_8 = *b_21;
  93
  94    where the addresses loaded are defined by PHIs itself.
  95    The above happens for
  96
  97      std::max(std::min(a0, c), std::min(std::max(a1, c), b))
  98
  99    where this pass transforms it to a form later PHI optimization
 100    recognizes and transforms it to the simple
 101
 102      D.2109_10 = this_1(D)->a1;
 103      D.2110_11 = c;
 104      D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
 105      D.2115_14 = b;
 106      D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
 107      D.2119_16 = this_1(D)->a0;
 108      D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
 109      D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;
 110
 111    The pass does a dominator walk processing loads using a basic-block
 112    local analysis and stores the result for use by transformations on
 113    dominated basic-blocks.  */
 114
 115
 116 /* Structure to keep track of the value of a dereferenced PHI result
 117    and the virtual operand used for that dereference.  */
 118
 119 struct phiprop_d
 120 {
 121   tree value;
 122   tree vuse;
 123 };
 124
 125 /* Verify if the value recorded for NAME in PHIVN is still valid at
 126    the start of basic block BB.  */
 127
 128 static bool
 129 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
 130 {
 131   tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
 132   gimple use_stmt;
 133   imm_use_iterator ui2;
 134   bool ok = true;
 135
 136   /* The def stmts of the virtual uses need to be dominated by bb.  */
 137   gcc_assert (vuse != NULL_TREE);
 138
 139   FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
 140     {
 141       /* If BB does not dominate a VDEF, the value is invalid.  */
 142       if ((gimple_vdef (use_stmt) != NULL_TREE
 143            || gimple_code (use_stmt) == GIMPLE_PHI)
 144           && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
 145         {
 146           ok = false;
 147           BREAK_FROM_IMM_USE_STMT (ui2);
 148         }
 149     }
 150
 151   return ok;
 152 }
 153
 154 /* Insert a new phi node for the dereference of PHI at basic_block
 155    BB with the virtual operands from USE_STMT.  */
 156
 157 static tree
 158 phiprop_insert_phi (basic_block bb, gphi *phi, gimple use_stmt,
 159                     struct phiprop_d *phivn, size_t n)
 160 {
 161   tree res;
 162   gphi *new_phi;
 163   edge_iterator ei;
 164   edge e;
 165
 166   gcc_assert (is_gimple_assign (use_stmt)
 167               && gimple_assign_rhs_code (use_stmt) == MEM_REF);
 168
 169   /* Build a new PHI node to replace the definition of
 170      the indirect reference lhs.  */
 171   res = gimple_assign_lhs (use_stmt);
 172   new_phi = create_phi_node (res, bb);
 173
 174   if (dump_file && (dump_flags & TDF_DETAILS))
 175     {
 176       fprintf (dump_file, "Inserting PHI for result of load ");
 177       print_gimple_stmt (dump_file, use_stmt, 0, 0);
 178     }
 179
 180   /* Add PHI arguments for each edge inserting loads of the
 181      addressable operands.  */
 182   FOR_EACH_EDGE (e, ei, bb->preds)
 183     {
 184       tree old_arg, new_var;
 185       gassign *tmp;
 186       source_location locus;
 187
 188       old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
 189       locus = gimple_phi_arg_location_from_edge (phi, e);
 190       while (TREE_CODE (old_arg) == SSA_NAME
 191              && (SSA_NAME_VERSION (old_arg) >= n
 192                  || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
 193         {
 194           gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
 195           old_arg = gimple_assign_rhs1 (def_stmt);
 196           locus = gimple_location (def_stmt);
 197         }
 198
 199       if (TREE_CODE (old_arg) == SSA_NAME)
 200         {
 201           if (dump_file && (dump_flags & TDF_DETAILS))
 202             {
 203               fprintf (dump_file, "  for edge defining ");
 204               print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
 205               fprintf (dump_file, " reusing PHI result ");
 206               print_generic_expr (dump_file,
 207                                   phivn[SSA_NAME_VERSION (old_arg)].value, 0);
 208               fprintf (dump_file, "\n");
 209             }
 210           /* Reuse a formerly created dereference.  */
 211           new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
 212         }
 213       else
 214         {
 215           tree rhs = gimple_assign_rhs1 (use_stmt);
 216           gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
 217           new_var = make_ssa_name (TREE_TYPE (rhs));
 218           if (!is_gimple_min_invariant (old_arg))
 219             old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
 220           else
 221             old_arg = unshare_expr (old_arg);
 222           tmp = gimple_build_assign (new_var,
 223                                      fold_build2 (MEM_REF, TREE_TYPE (rhs),
 224                                                   old_arg,
 225                                                   TREE_OPERAND (rhs, 1)));
 226           gimple_set_location (tmp, locus);
 227
 228           gsi_insert_on_edge (e, tmp);
 229           update_stmt (tmp);
 230
 231           if (dump_file && (dump_flags & TDF_DETAILS))
 232             {
 233               fprintf (dump_file, "  for edge defining ");
 234               print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
 235               fprintf (dump_file, " inserting load ");
 236               print_gimple_stmt (dump_file, tmp, 0, 0);
 237             }
 238         }
 239
 240       add_phi_arg (new_phi, new_var, e, locus);
 241     }
 242
 243   update_stmt (new_phi);
 244
 245   if (dump_file && (dump_flags & TDF_DETAILS))
 246     print_gimple_stmt (dump_file, new_phi, 0, 0);
 247
 248   return res;
 249 }
 250
 251 /* Propagate between the phi node arguments of PHI in BB and phi result
 252    users.  For now this matches
 253         # p_2 = PHI <&x, &y>
 254       <Lx>:;
 255         p_3 = p_2;
 256         z_2 = *p_3;
 257    and converts it to
 258         # z_2 = PHI <x, y>
 259       <Lx>:;
 260    Returns true if a transformation was done and edge insertions
 261    need to be committed.  Global data PHIVN and N is used to track
 262    past transformation results.  We need to be especially careful here
 263    with aliasing issues as we are moving memory reads.  */
 264
 265 static bool
 266 propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn,
 267                     size_t n)
 268 {
 269   tree ptr = PHI_RESULT (phi);
 270   gimple use_stmt;
 271   tree res = NULL_TREE;
 272   gimple_stmt_iterator gsi;
 273   imm_use_iterator ui;
 274   use_operand_p arg_p, use;
 275   ssa_op_iter i;
 276   bool phi_inserted;
 277   tree type = NULL_TREE;
 278
 279   if (!POINTER_TYPE_P (TREE_TYPE (ptr))
 280       || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
 281     return false;
 282
 283   /* Check if we can "cheaply" dereference all phi arguments.  */
 284   FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
 285     {
 286       tree arg = USE_FROM_PTR (arg_p);
 287       /* Walk the ssa chain until we reach a ssa name we already
 288          created a value for or we reach a definition of the form
 289          ssa_name_n = &var;  */
 290       while (TREE_CODE (arg) == SSA_NAME
 291              && !SSA_NAME_IS_DEFAULT_DEF (arg)
 292              && (SSA_NAME_VERSION (arg) >= n
 293                  || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
 294         {
 295           gimple def_stmt = SSA_NAME_DEF_STMT (arg);
 296           if (!gimple_assign_single_p (def_stmt))
 297             return false;
 298           arg = gimple_assign_rhs1 (def_stmt);
 299         }
 300       if (TREE_CODE (arg) != ADDR_EXPR
 301           && !(TREE_CODE (arg) == SSA_NAME
 302                && SSA_NAME_VERSION (arg) < n
 303                && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
 304                && (!type
 305                    || types_compatible_p
 306                        (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
 307                && phivn_valid_p (phivn, arg, bb)))
 308         return false;
 309       if (!type
 310           && TREE_CODE (arg) == SSA_NAME)
 311         type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
 312     }
 313
 314   /* Find a dereferencing use.  First follow (single use) ssa
 315      copy chains for ptr.  */
 316   while (single_imm_use (ptr, &use, &use_stmt)
 317          && gimple_assign_ssa_name_copy_p (use_stmt))
 318     ptr = gimple_assign_lhs (use_stmt);
 319
 320   /* Replace the first dereference of *ptr if there is one and if we
 321      can move the loads to the place of the ptr phi node.  */
 322   phi_inserted = false;
 323   FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
 324     {
 325       gimple def_stmt;
 326       tree vuse;
 327
 328       /* Only replace loads in blocks that post-dominate the PHI node.  That
 329          makes sure we don't end up speculating loads.  */
 330       if (!dominated_by_p (CDI_POST_DOMINATORS,
 331                            bb, gimple_bb (use_stmt)))
 332         continue;
 333
 334       /* Check whether this is a load of *ptr.  */
 335       if (!(is_gimple_assign (use_stmt)
 336             && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
 337             && gimple_assign_rhs_code (use_stmt) == MEM_REF
 338             && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
 339             && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
 340             && (!type
 341                 || types_compatible_p
 342                      (TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
 343             /* We cannot replace a load that may throw or is volatile.  */
 344             && !stmt_can_throw_internal (use_stmt)))
 345         continue;
 346
 347       /* Check if we can move the loads.  The def stmt of the virtual use
 348          needs to be in a different basic block dominating bb.  */
 349       vuse = gimple_vuse (use_stmt);
 350       def_stmt = SSA_NAME_DEF_STMT (vuse);
 351       if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
 352           && (gimple_bb (def_stmt) == bb
 353               || !dominated_by_p (CDI_DOMINATORS,
 354                                   bb, gimple_bb (def_stmt))))
 355         goto next;
 356
 357       /* Found a proper dereference.  Insert a phi node if this
 358          is the first load transformation.  */
 359       if (!phi_inserted)
 360         {
 361           res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
 362           type = TREE_TYPE (res);
 363
 364           /* Remember the value we created for *ptr.  */
 365           phivn[SSA_NAME_VERSION (ptr)].value = res;
 366           phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;
 367
 368           /* Remove old stmt.  The phi is taken care of by DCE, if we
 369              want to delete it here we also have to delete all intermediate
 370              copies.  */
 371           gsi = gsi_for_stmt (use_stmt);
 372           gsi_remove (&gsi, true);
 373
 374           phi_inserted = true;
 375         }
 376       else
 377         {
 378           /* Further replacements are easy, just make a copy out of the
 379              load.  */
 380           gimple_assign_set_rhs1 (use_stmt, res);
 381           update_stmt (use_stmt);
 382         }
 383
 384 next:;
 385       /* Continue searching for a proper dereference.  */
 386     }
 387
 388   return phi_inserted;
 389 }
 390
 391 /* Main entry for phiprop pass.  */
 392
 393 namespace {
 394
 395 const pass_data pass_data_phiprop =
 396 {
 397   GIMPLE_PASS, /* type */
 398   "phiprop", /* name */
 399   OPTGROUP_NONE, /* optinfo_flags */
 400   TV_TREE_PHIPROP, /* tv_id */
 401   ( PROP_cfg | PROP_ssa ), /* properties_required */
 402   0, /* properties_provided */
 403   0, /* properties_destroyed */
 404   0, /* todo_flags_start */
 405   TODO_update_ssa, /* todo_flags_finish */
 406 };
 407
 408 class pass_phiprop : public gimple_opt_pass
 409 {
 410 public:
 411   pass_phiprop (gcc::context *ctxt)
 412     : gimple_opt_pass (pass_data_phiprop, ctxt)
 413   {}
 414
 415   /* opt_pass methods: */
 416   virtual bool gate (function *) { return flag_tree_phiprop; }
 417   virtual unsigned int execute (function *);
 418
 419 }; // class pass_phiprop
 420
 421 unsigned int
 422 pass_phiprop::execute (function *fun)
 423 {
 424   vec<basic_block> bbs;
 425   struct phiprop_d *phivn;
 426   bool did_something = false;
 427   basic_block bb;
 428   gphi_iterator gsi;
 429   unsigned i;
 430   size_t n;
 431
 432   calculate_dominance_info (CDI_DOMINATORS);
 433   calculate_dominance_info (CDI_POST_DOMINATORS);
 434
 435   n = num_ssa_names;
 436   phivn = XCNEWVEC (struct phiprop_d, n);
 437
 438   /* Walk the dominator tree in preorder.  */
 439   bbs = get_all_dominated_blocks (CDI_DOMINATORS,
 440                                   single_succ (ENTRY_BLOCK_PTR_FOR_FN (fun)));
 441   FOR_EACH_VEC_ELT (bbs, i, bb)
 442     for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
 443       did_something |= propagate_with_phi (bb, gsi.phi (), phivn, n);
 444
 445   if (did_something)
 446     gsi_commit_edge_inserts ();
 447
 448   bbs.release ();
 449   free (phivn);
 450
 451   free_dominance_info (CDI_POST_DOMINATORS);
 452
 453   return 0;
 454 }
 455
 456 } // anon namespace
 457
 458 gimple_opt_pass *
 459 make_pass_phiprop (gcc::context *ctxt)
 460 {
 461   return new pass_phiprop (ctxt);
 462 }