gcc/gimple-ssa-evrp.c

   1 /* Support routines for Value Range Propagation (VRP).
   2    Copyright (C) 2005-2019 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
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 3, or (at your option)
   9 any later version.
  10
  11 GCC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "backend.h"
  24 #include "tree.h"
  25 #include "gimple.h"
  26 #include "tree-pass.h"
  27 #include "ssa.h"
  28 #include "gimple-pretty-print.h"
  29 #include "cfganal.h"
  30 #include "gimple-fold.h"
  31 #include "tree-eh.h"
  32 #include "gimple-iterator.h"
  33 #include "tree-cfg.h"
  34 #include "tree-ssa-loop-manip.h"
  35 #include "tree-ssa-loop.h"
  36 #include "cfgloop.h"
  37 #include "tree-scalar-evolution.h"
  38 #include "tree-ssa-propagate.h"
  39 #include "alloc-pool.h"
  40 #include "domwalk.h"
  41 #include "tree-cfgcleanup.h"
  42 #include "vr-values.h"
  43 #include "gimple-ssa-evrp-analyze.h"
  44
  45 class evrp_folder : public substitute_and_fold_engine
  46 {
  47  public:
  48   tree get_value (tree) FINAL OVERRIDE;
  49   evrp_folder (class vr_values *vr_values_) : vr_values (vr_values_) { }
  50   bool simplify_stmt_using_ranges (gimple_stmt_iterator *gsi)
  51     { return vr_values->simplify_stmt_using_ranges (gsi); }
  52   class vr_values *vr_values;
  53
  54  private:
  55   DISABLE_COPY_AND_ASSIGN (evrp_folder);
  56 };
  57
  58 tree
  59 evrp_folder::get_value (tree op)
  60 {
  61   return vr_values->op_with_constant_singleton_value_range (op);
  62 }
  63
  64 /* evrp_dom_walker visits the basic blocks in the dominance order and set
  65    the Value Ranges (VR) for SSA_NAMEs in the scope.  Use this VR to
  66    discover more VRs.  */
  67
  68 class evrp_dom_walker : public dom_walker
  69 {
  70 public:
  71   evrp_dom_walker ()
  72     : dom_walker (CDI_DOMINATORS),
  73       evrp_range_analyzer (true),
  74       evrp_folder (evrp_range_analyzer.get_vr_values ())
  75     {
  76       need_eh_cleanup = BITMAP_ALLOC (NULL);
  77     }
  78   ~evrp_dom_walker ()
  79     {
  80       BITMAP_FREE (need_eh_cleanup);
  81     }
  82   virtual edge before_dom_children (basic_block);
  83   virtual void after_dom_children (basic_block);
  84   void cleanup (void);
  85
  86  private:
  87   DISABLE_COPY_AND_ASSIGN (evrp_dom_walker);
  88   bitmap need_eh_cleanup;
  89   auto_vec<gimple *> stmts_to_fixup;
  90   auto_vec<gimple *> stmts_to_remove;
  91
  92   class evrp_range_analyzer evrp_range_analyzer;
  93   class evrp_folder evrp_folder;
  94 };
  95
  96 edge
  97 evrp_dom_walker::before_dom_children (basic_block bb)
  98 {
  99   if (dump_file && (dump_flags & TDF_DETAILS))
 100     fprintf (dump_file, "Visiting BB%d\n", bb->index);
 101
 102   evrp_range_analyzer.enter (bb);
 103
 104   for (gphi_iterator gpi = gsi_start_phis (bb);
 105        !gsi_end_p (gpi); gsi_next (&gpi))
 106     {
 107       gphi *phi = gpi.phi ();
 108       tree lhs = PHI_RESULT (phi);
 109       if (virtual_operand_p (lhs))
 110         continue;
 111
 112       value_range *vr = evrp_range_analyzer.get_value_range (lhs);
 113       /* Mark PHIs whose lhs we fully propagate for removal.  */
 114       tree val = value_range_constant_singleton (vr);
 115       if (val && may_propagate_copy (lhs, val))
 116         {
 117           stmts_to_remove.safe_push (phi);
 118           continue;
 119         }
 120     }
 121
 122   edge taken_edge = NULL;
 123
 124   /* Visit all other stmts and discover any new VRs possible.  */
 125   for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
 126        !gsi_end_p (gsi); gsi_next (&gsi))
 127     {
 128       gimple *stmt = gsi_stmt (gsi);
 129       tree output = NULL_TREE;
 130       gimple *old_stmt = stmt;
 131       bool was_noreturn = (is_gimple_call (stmt)
 132                            && gimple_call_noreturn_p (stmt));
 133
 134       if (dump_file && (dump_flags & TDF_DETAILS))
 135         {
 136           fprintf (dump_file, "Visiting stmt ");
 137           print_gimple_stmt (dump_file, stmt, 0);
 138         }
 139
 140       evrp_range_analyzer.record_ranges_from_stmt (stmt, false);
 141
 142       if (gcond *cond = dyn_cast <gcond *> (stmt))
 143         {
 144           evrp_range_analyzer.vrp_visit_cond_stmt (cond, &taken_edge);
 145           if (taken_edge)
 146             {
 147               if (taken_edge->flags & EDGE_TRUE_VALUE)
 148                 gimple_cond_make_true (cond);
 149               else if (taken_edge->flags & EDGE_FALSE_VALUE)
 150                 gimple_cond_make_false (cond);
 151               else
 152                 gcc_unreachable ();
 153               update_stmt (stmt);
 154             }
 155         }
 156       else if (stmt_interesting_for_vrp (stmt))
 157         {
 158           output = get_output_for_vrp (stmt);
 159           if (output)
 160             {
 161               tree val;
 162               value_range *vr = evrp_range_analyzer.get_value_range (output);
 163
 164               /* Mark stmts whose output we fully propagate for removal.  */
 165               if ((val = value_range_constant_singleton (vr))
 166                   && may_propagate_copy (output, val)
 167                   && !stmt_could_throw_p (cfun, stmt)
 168                   && !gimple_has_side_effects (stmt))
 169                 {
 170                   stmts_to_remove.safe_push (stmt);
 171                   continue;
 172                 }
 173             }
 174         }
 175
 176       /* Try folding stmts with the VR discovered.  */
 177       bool did_replace = evrp_folder.replace_uses_in (stmt);
 178       gimple_stmt_iterator prev_gsi = gsi;
 179       gsi_prev (&prev_gsi);
 180       if (fold_stmt (&gsi, follow_single_use_edges)
 181           || did_replace)
 182         {
 183           stmt = gsi_stmt (gsi);
 184           update_stmt (stmt);
 185           did_replace = true;
 186         }
 187       if (evrp_folder.simplify_stmt_using_ranges (&gsi))
 188         {
 189           stmt = gsi_stmt (gsi);
 190           update_stmt (stmt);
 191           did_replace = true;
 192         }
 193
 194       if (did_replace)
 195         {
 196           /* If we wound up generating new stmts during folding
 197              drop all their defs to VARYING.  We can't easily
 198              process them because we've already instantiated
 199              ranges on uses on STMT that only hold after it.  */
 200           if (gsi_end_p (prev_gsi))
 201             prev_gsi = gsi_start_bb (bb);
 202           else
 203             gsi_next (&prev_gsi);
 204           while (gsi_stmt (prev_gsi) != gsi_stmt (gsi))
 205             {
 206               evrp_range_analyzer.get_vr_values ()
 207                 ->set_defs_to_varying (gsi_stmt (prev_gsi));
 208               gsi_next (&prev_gsi);
 209             }
 210
 211           /* If we cleaned up EH information from the statement,
 212              remove EH edges.  */
 213           if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
 214             bitmap_set_bit (need_eh_cleanup, bb->index);
 215
 216           /* If we turned a not noreturn call into a noreturn one
 217              schedule it for fixup.  */
 218           if (!was_noreturn
 219               && is_gimple_call (stmt)
 220               && gimple_call_noreturn_p (stmt))
 221             stmts_to_fixup.safe_push (stmt);
 222
 223           if (gimple_assign_single_p (stmt))
 224             {
 225               tree rhs = gimple_assign_rhs1 (stmt);
 226               if (TREE_CODE (rhs) == ADDR_EXPR)
 227                 recompute_tree_invariant_for_addr_expr (rhs);
 228             }
 229         }
 230     }
 231
 232   /* Visit BB successor PHI nodes and replace PHI args.  */
 233   edge e;
 234   edge_iterator ei;
 235   FOR_EACH_EDGE (e, ei, bb->succs)
 236     {
 237       for (gphi_iterator gpi = gsi_start_phis (e->dest);
 238            !gsi_end_p (gpi); gsi_next (&gpi))
 239         {
 240           gphi *phi = gpi.phi ();
 241           use_operand_p use_p = PHI_ARG_DEF_PTR_FROM_EDGE (phi, e);
 242           tree arg = USE_FROM_PTR (use_p);
 243           if (TREE_CODE (arg) != SSA_NAME
 244               || virtual_operand_p (arg))
 245             continue;
 246           value_range *vr = evrp_range_analyzer.get_value_range (arg);
 247           tree val = value_range_constant_singleton (vr);
 248           if (val && may_propagate_copy (arg, val))
 249             propagate_value (use_p, val);
 250         }
 251     }
 252
 253   return taken_edge;
 254 }
 255
 256 void
 257 evrp_dom_walker::after_dom_children (basic_block bb)
 258 {
 259   evrp_range_analyzer.leave (bb);
 260 }
 261
 262 /* Perform any cleanups after the main phase of EVRP has completed.  */
 263
 264 void
 265 evrp_dom_walker::cleanup (void)
 266 {
 267   if (dump_file)
 268     {
 269       fprintf (dump_file, "\nValue ranges after Early VRP:\n\n");
 270       evrp_range_analyzer.dump_all_value_ranges (dump_file);
 271       fprintf (dump_file, "\n");
 272     }
 273
 274   /* Remove stmts in reverse order to make debug stmt creation possible.  */
 275   while (! stmts_to_remove.is_empty ())
 276     {
 277       gimple *stmt = stmts_to_remove.pop ();
 278       if (dump_file && dump_flags & TDF_DETAILS)
 279         {
 280           fprintf (dump_file, "Removing dead stmt ");
 281           print_gimple_stmt (dump_file, stmt, 0);
 282           fprintf (dump_file, "\n");
 283         }
 284       gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
 285       if (gimple_code (stmt) == GIMPLE_PHI)
 286         remove_phi_node (&gsi, true);
 287       else
 288         {
 289           unlink_stmt_vdef (stmt);
 290           gsi_remove (&gsi, true);
 291           release_defs (stmt);
 292         }
 293     }
 294
 295   if (!bitmap_empty_p (need_eh_cleanup))
 296     gimple_purge_all_dead_eh_edges (need_eh_cleanup);
 297
 298   /* Fixup stmts that became noreturn calls.  This may require splitting
 299      blocks and thus isn't possible during the dominator walk.  Do this
 300      in reverse order so we don't inadvertedly remove a stmt we want to
 301      fixup by visiting a dominating now noreturn call first.  */
 302   while (!stmts_to_fixup.is_empty ())
 303     {
 304       gimple *stmt = stmts_to_fixup.pop ();
 305       fixup_noreturn_call (stmt);
 306     }
 307
 308   evrp_folder.vr_values->cleanup_edges_and_switches ();
 309 }
 310
 311 /* Main entry point for the early vrp pass which is a simplified non-iterative
 312    version of vrp where basic blocks are visited in dominance order.  Value
 313    ranges discovered in early vrp will also be used by ipa-vrp.  */
 314
 315 static unsigned int
 316 execute_early_vrp ()
 317 {
 318   /* Ideally this setup code would move into the ctor for the dominator
 319      walk.  However, this setup can change the number of blocks which
 320      invalidates the internal arrays that are set up by the dominator
 321      walker.  */
 322   loop_optimizer_init (LOOPS_NORMAL | LOOPS_HAVE_RECORDED_EXITS);
 323   rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa);
 324   scev_initialize ();
 325   calculate_dominance_info (CDI_DOMINATORS);
 326
 327   /* Walk stmts in dominance order and propagate VRP.  */
 328   evrp_dom_walker walker;
 329   walker.walk (ENTRY_BLOCK_PTR_FOR_FN (cfun));
 330   walker.cleanup ();
 331
 332   scev_finalize ();
 333   loop_optimizer_finalize ();
 334   return 0;
 335 }
 336
 337 namespace {
 338
 339 const pass_data pass_data_early_vrp =
 340 {
 341   GIMPLE_PASS, /* type */
 342   "evrp", /* name */
 343   OPTGROUP_NONE, /* optinfo_flags */
 344   TV_TREE_EARLY_VRP, /* tv_id */
 345   PROP_ssa, /* properties_required */
 346   0, /* properties_provided */
 347   0, /* properties_destroyed */
 348   0, /* todo_flags_start */
 349   ( TODO_cleanup_cfg | TODO_update_ssa | TODO_verify_all ),
 350 };
 351
 352 class pass_early_vrp : public gimple_opt_pass
 353 {
 354 public:
 355   pass_early_vrp (gcc::context *ctxt)
 356     : gimple_opt_pass (pass_data_early_vrp, ctxt)
 357     {}
 358
 359   /* opt_pass methods: */
 360   opt_pass * clone () { return new pass_early_vrp (m_ctxt); }
 361   virtual bool gate (function *)
 362     {
 363       return flag_tree_vrp != 0;
 364     }
 365   virtual unsigned int execute (function *)
 366     { return execute_early_vrp (); }
 367
 368 }; // class pass_vrp
 369 } // anon namespace
 370
 371 gimple_opt_pass *
 372 make_pass_early_vrp (gcc::context *ctxt)
 373 {
 374   return new pass_early_vrp (ctxt);
 375 }
 376