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       if (fold_stmt (&gsi, follow_single_use_edges)
 179           || did_replace)
 180         {
 181           stmt = gsi_stmt (gsi);
 182           update_stmt (stmt);
 183           did_replace = true;
 184         }
 185       if (evrp_folder.simplify_stmt_using_ranges (&gsi))
 186         {
 187           stmt = gsi_stmt (gsi);
 188           update_stmt (stmt);
 189           did_replace = true;
 190         }
 191
 192       if (did_replace)
 193         {
 194           /* If we cleaned up EH information from the statement,
 195              remove EH edges.  */
 196           if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
 197             bitmap_set_bit (need_eh_cleanup, bb->index);
 198
 199           /* If we turned a not noreturn call into a noreturn one
 200              schedule it for fixup.  */
 201           if (!was_noreturn
 202               && is_gimple_call (stmt)
 203               && gimple_call_noreturn_p (stmt))
 204             stmts_to_fixup.safe_push (stmt);
 205
 206           if (gimple_assign_single_p (stmt))
 207             {
 208               tree rhs = gimple_assign_rhs1 (stmt);
 209               if (TREE_CODE (rhs) == ADDR_EXPR)
 210                 recompute_tree_invariant_for_addr_expr (rhs);
 211             }
 212         }
 213     }
 214
 215   /* Visit BB successor PHI nodes and replace PHI args.  */
 216   edge e;
 217   edge_iterator ei;
 218   FOR_EACH_EDGE (e, ei, bb->succs)
 219     {
 220       for (gphi_iterator gpi = gsi_start_phis (e->dest);
 221            !gsi_end_p (gpi); gsi_next (&gpi))
 222         {
 223           gphi *phi = gpi.phi ();
 224           use_operand_p use_p = PHI_ARG_DEF_PTR_FROM_EDGE (phi, e);
 225           tree arg = USE_FROM_PTR (use_p);
 226           if (TREE_CODE (arg) != SSA_NAME
 227               || virtual_operand_p (arg))
 228             continue;
 229           value_range *vr = evrp_range_analyzer.get_value_range (arg);
 230           tree val = value_range_constant_singleton (vr);
 231           if (val && may_propagate_copy (arg, val))
 232             propagate_value (use_p, val);
 233         }
 234     }
 235
 236   return taken_edge;
 237 }
 238
 239 void
 240 evrp_dom_walker::after_dom_children (basic_block bb)
 241 {
 242   evrp_range_analyzer.leave (bb);
 243 }
 244
 245 /* Perform any cleanups after the main phase of EVRP has completed.  */
 246
 247 void
 248 evrp_dom_walker::cleanup (void)
 249 {
 250   if (dump_file)
 251     {
 252       fprintf (dump_file, "\nValue ranges after Early VRP:\n\n");
 253       evrp_range_analyzer.dump_all_value_ranges (dump_file);
 254       fprintf (dump_file, "\n");
 255     }
 256
 257   /* Remove stmts in reverse order to make debug stmt creation possible.  */
 258   while (! stmts_to_remove.is_empty ())
 259     {
 260       gimple *stmt = stmts_to_remove.pop ();
 261       if (dump_file && dump_flags & TDF_DETAILS)
 262         {
 263           fprintf (dump_file, "Removing dead stmt ");
 264           print_gimple_stmt (dump_file, stmt, 0);
 265           fprintf (dump_file, "\n");
 266         }
 267       gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
 268       if (gimple_code (stmt) == GIMPLE_PHI)
 269         remove_phi_node (&gsi, true);
 270       else
 271         {
 272           unlink_stmt_vdef (stmt);
 273           gsi_remove (&gsi, true);
 274           release_defs (stmt);
 275         }
 276     }
 277
 278   if (!bitmap_empty_p (need_eh_cleanup))
 279     gimple_purge_all_dead_eh_edges (need_eh_cleanup);
 280
 281   /* Fixup stmts that became noreturn calls.  This may require splitting
 282      blocks and thus isn't possible during the dominator walk.  Do this
 283      in reverse order so we don't inadvertedly remove a stmt we want to
 284      fixup by visiting a dominating now noreturn call first.  */
 285   while (!stmts_to_fixup.is_empty ())
 286     {
 287       gimple *stmt = stmts_to_fixup.pop ();
 288       fixup_noreturn_call (stmt);
 289     }
 290
 291   evrp_folder.vr_values->cleanup_edges_and_switches ();
 292 }
 293
 294 /* Main entry point for the early vrp pass which is a simplified non-iterative
 295    version of vrp where basic blocks are visited in dominance order.  Value
 296    ranges discovered in early vrp will also be used by ipa-vrp.  */
 297
 298 static unsigned int
 299 execute_early_vrp ()
 300 {
 301   /* Ideally this setup code would move into the ctor for the dominator
 302      walk.  However, this setup can change the number of blocks which
 303      invalidates the internal arrays that are set up by the dominator
 304      walker.  */
 305   loop_optimizer_init (LOOPS_NORMAL | LOOPS_HAVE_RECORDED_EXITS);
 306   rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa);
 307   scev_initialize ();
 308   calculate_dominance_info (CDI_DOMINATORS);
 309
 310   /* Walk stmts in dominance order and propagate VRP.  */
 311   evrp_dom_walker walker;
 312   walker.walk (ENTRY_BLOCK_PTR_FOR_FN (cfun));
 313   walker.cleanup ();
 314
 315   scev_finalize ();
 316   loop_optimizer_finalize ();
 317   return 0;
 318 }
 319
 320 namespace {
 321
 322 const pass_data pass_data_early_vrp =
 323 {
 324   GIMPLE_PASS, /* type */
 325   "evrp", /* name */
 326   OPTGROUP_NONE, /* optinfo_flags */
 327   TV_TREE_EARLY_VRP, /* tv_id */
 328   PROP_ssa, /* properties_required */
 329   0, /* properties_provided */
 330   0, /* properties_destroyed */
 331   0, /* todo_flags_start */
 332   ( TODO_cleanup_cfg | TODO_update_ssa | TODO_verify_all ),
 333 };
 334
 335 class pass_early_vrp : public gimple_opt_pass
 336 {
 337 public:
 338   pass_early_vrp (gcc::context *ctxt)
 339     : gimple_opt_pass (pass_data_early_vrp, ctxt)
 340     {}
 341
 342   /* opt_pass methods: */
 343   opt_pass * clone () { return new pass_early_vrp (m_ctxt); }
 344   virtual bool gate (function *)
 345     {
 346       return flag_tree_vrp != 0;
 347     }
 348   virtual unsigned int execute (function *)
 349     { return execute_early_vrp (); }
 350
 351 }; // class pass_vrp
 352 } // anon namespace
 353
 354 gimple_opt_pass *
 355 make_pass_early_vrp (gcc::context *ctxt)
 356 {
 357   return new pass_early_vrp (ctxt);
 358 }
 359