1/* Loop unswitching. 2 Copyright (C) 2004-2015 Free Software Foundation, Inc. 3 4This file is part of GCC. 5 6GCC is free software; you can redistribute it and/or modify it 7under the terms of the GNU General Public License as published by the 8Free Software Foundation; either version 3, or (at your option) any 9later version. 10 11GCC is distributed in the hope that it will be useful, but WITHOUT 12ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14for more details. 15 16You should have received a copy of the GNU General Public License 17along 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 "tm.h" 24#include "hash-set.h" 25#include "machmode.h" 26#include "vec.h" 27#include "double-int.h" 28#include "input.h" 29#include "alias.h" 30#include "symtab.h" 31#include "wide-int.h" 32#include "inchash.h" 33#include "tree.h" 34#include "fold-const.h" 35#include "tm_p.h" 36#include "predict.h" 37#include "hard-reg-set.h" 38#include "input.h" 39#include "function.h" 40#include "dominance.h" 41#include "cfg.h" 42#include "basic-block.h" 43#include "tree-ssa-alias.h" 44#include "internal-fn.h" 45#include "gimple-expr.h" 46#include "is-a.h" 47#include "gimple.h" 48#include "gimplify.h" 49#include "gimple-ssa.h" 50#include "tree-cfg.h" 51#include "tree-phinodes.h" 52#include "ssa-iterators.h" 53#include "tree-ssa-loop-niter.h" 54#include "tree-ssa-loop.h" 55#include "tree-into-ssa.h" 56#include "cfgloop.h" 57#include "params.h" 58#include "tree-pass.h" 59#include "tree-inline.h" 60 61/* This file implements the loop unswitching, i.e. transformation of loops like 62 63 while (A) 64 { 65 if (inv) 66 B; 67 68 X; 69 70 if (!inv) 71 C; 72 } 73 74 where inv is the loop invariant, into 75 76 if (inv) 77 { 78 while (A) 79 { 80 B; 81 X; 82 } 83 } 84 else 85 { 86 while (A) 87 { 88 X; 89 C; 90 } 91 } 92 93 Inv is considered invariant iff the values it compares are both invariant; 94 tree-ssa-loop-im.c ensures that all the suitable conditions are in this 95 shape. */ 96 97static struct loop *tree_unswitch_loop (struct loop *, basic_block, tree); 98static bool tree_unswitch_single_loop (struct loop *, int); 99static tree tree_may_unswitch_on (basic_block, struct loop *); 100 101/* Main entry point. Perform loop unswitching on all suitable loops. */ 102 103unsigned int 104tree_ssa_unswitch_loops (void) 105{ 106 struct loop *loop; 107 bool changed = false; 108 HOST_WIDE_INT iterations; 109 110 /* Go through inner loops (only original ones). */ 111 FOR_EACH_LOOP (loop, LI_ONLY_INNERMOST) 112 { 113 if (dump_file && (dump_flags & TDF_DETAILS)) 114 fprintf (dump_file, ";; Considering loop %d\n", loop->num); 115 116 /* Do not unswitch in cold regions. */ 117 if (optimize_loop_for_size_p (loop)) 118 { 119 if (dump_file && (dump_flags & TDF_DETAILS)) 120 fprintf (dump_file, ";; Not unswitching cold loops\n"); 121 continue; 122 } 123 124 /* The loop should not be too large, to limit code growth. */ 125 if (tree_num_loop_insns (loop, &eni_size_weights) 126 > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS)) 127 { 128 if (dump_file && (dump_flags & TDF_DETAILS)) 129 fprintf (dump_file, ";; Not unswitching, loop too big\n"); 130 continue; 131 } 132 133 /* If the loop is not expected to iterate, there is no need 134 for unswitching. */ 135 iterations = estimated_loop_iterations_int (loop); 136 if (iterations >= 0 && iterations <= 1) 137 { 138 if (dump_file && (dump_flags & TDF_DETAILS)) 139 fprintf (dump_file, ";; Not unswitching, loop is not expected to iterate\n"); 140 continue; 141 } 142 143 changed |= tree_unswitch_single_loop (loop, 0); 144 } 145 146 if (changed) 147 return TODO_cleanup_cfg; 148 return 0; 149} 150 151/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its 152 basic blocks (for what it means see comments below). */ 153 154static tree 155tree_may_unswitch_on (basic_block bb, struct loop *loop) 156{ 157 gimple last, def; 158 gcond *stmt; 159 tree cond, use; 160 basic_block def_bb; 161 ssa_op_iter iter; 162 163 /* BB must end in a simple conditional jump. */ 164 last = last_stmt (bb); 165 if (!last || gimple_code (last) != GIMPLE_COND) 166 return NULL_TREE; 167 stmt = as_a <gcond *> (last); 168 169 /* To keep the things simple, we do not directly remove the conditions, 170 but just replace tests with 0 != 0 resp. 1 != 0. Prevent the infinite 171 loop where we would unswitch again on such a condition. */ 172 if (gimple_cond_true_p (stmt) || gimple_cond_false_p (stmt)) 173 return NULL_TREE; 174 175 /* Condition must be invariant. */ 176 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) 177 { 178 def = SSA_NAME_DEF_STMT (use); 179 def_bb = gimple_bb (def); 180 if (def_bb 181 && flow_bb_inside_loop_p (loop, def_bb)) 182 return NULL_TREE; 183 } 184 185 cond = build2 (gimple_cond_code (stmt), boolean_type_node, 186 gimple_cond_lhs (stmt), gimple_cond_rhs (stmt)); 187 188 return cond; 189} 190 191/* Simplifies COND using checks in front of the entry of the LOOP. Just very 192 simplish (sufficient to prevent us from duplicating loop in unswitching 193 unnecessarily). */ 194 195static tree 196simplify_using_entry_checks (struct loop *loop, tree cond) 197{ 198 edge e = loop_preheader_edge (loop); 199 gimple stmt; 200 201 while (1) 202 { 203 stmt = last_stmt (e->src); 204 if (stmt 205 && gimple_code (stmt) == GIMPLE_COND 206 && gimple_cond_code (stmt) == TREE_CODE (cond) 207 && operand_equal_p (gimple_cond_lhs (stmt), 208 TREE_OPERAND (cond, 0), 0) 209 && operand_equal_p (gimple_cond_rhs (stmt), 210 TREE_OPERAND (cond, 1), 0)) 211 return (e->flags & EDGE_TRUE_VALUE 212 ? boolean_true_node 213 : boolean_false_node); 214 215 if (!single_pred_p (e->src)) 216 return cond; 217 218 e = single_pred_edge (e->src); 219 if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun)) 220 return cond; 221 } 222} 223 224/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow 225 it to grow too much, it is too easy to create example on that the code would 226 grow exponentially. */ 227 228static bool 229tree_unswitch_single_loop (struct loop *loop, int num) 230{ 231 basic_block *bbs; 232 struct loop *nloop; 233 unsigned i, found; 234 tree cond = NULL_TREE; 235 gimple stmt; 236 bool changed = false; 237 238 i = 0; 239 bbs = get_loop_body (loop); 240 found = loop->num_nodes; 241 242 while (1) 243 { 244 /* Find a bb to unswitch on. */ 245 for (; i < loop->num_nodes; i++) 246 if ((cond = tree_may_unswitch_on (bbs[i], loop))) 247 break; 248 249 if (i == loop->num_nodes) 250 { 251 if (dump_file 252 && num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL) 253 && (dump_flags & TDF_DETAILS)) 254 fprintf (dump_file, ";; Not unswitching anymore, hit max level\n"); 255 256 if (found == loop->num_nodes) 257 { 258 free (bbs); 259 return changed; 260 } 261 break; 262 } 263 264 cond = simplify_using_entry_checks (loop, cond); 265 stmt = last_stmt (bbs[i]); 266 if (integer_nonzerop (cond)) 267 { 268 /* Remove false path. */ 269 gimple_cond_set_condition_from_tree (as_a <gcond *> (stmt), 270 boolean_true_node); 271 changed = true; 272 } 273 else if (integer_zerop (cond)) 274 { 275 /* Remove true path. */ 276 gimple_cond_set_condition_from_tree (as_a <gcond *> (stmt), 277 boolean_false_node); 278 changed = true; 279 } 280 /* Do not unswitch too much. */ 281 else if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL)) 282 { 283 i++; 284 continue; 285 } 286 /* In nested tree_unswitch_single_loop first optimize all conditions 287 using entry checks, then discover still reachable blocks in the 288 loop and find the condition only among those still reachable bbs. */ 289 else if (num != 0) 290 { 291 if (found == loop->num_nodes) 292 found = i; 293 i++; 294 continue; 295 } 296 else 297 { 298 found = i; 299 break; 300 } 301 302 update_stmt (stmt); 303 i++; 304 } 305 306 if (num != 0) 307 { 308 basic_block *tos, *worklist; 309 310 /* When called recursively, first do a quick discovery 311 of reachable bbs after the above changes and only 312 consider conditions in still reachable bbs. */ 313 tos = worklist = XNEWVEC (basic_block, loop->num_nodes); 314 315 for (i = 0; i < loop->num_nodes; i++) 316 bbs[i]->flags &= ~BB_REACHABLE; 317 318 /* Start with marking header. */ 319 *tos++ = bbs[0]; 320 bbs[0]->flags |= BB_REACHABLE; 321 322 /* Iterate: find everything reachable from what we've already seen 323 within the same innermost loop. Don't look through false edges 324 if condition is always true or true edges if condition is 325 always false. */ 326 while (tos != worklist) 327 { 328 basic_block b = *--tos; 329 edge e; 330 edge_iterator ei; 331 int flags = 0; 332 333 if (EDGE_COUNT (b->succs) == 2) 334 { 335 gimple stmt = last_stmt (b); 336 if (stmt 337 && gimple_code (stmt) == GIMPLE_COND) 338 { 339 gcond *cond_stmt = as_a <gcond *> (stmt); 340 if (gimple_cond_true_p (cond_stmt)) 341 flags = EDGE_FALSE_VALUE; 342 else if (gimple_cond_false_p (cond_stmt)) 343 flags = EDGE_TRUE_VALUE; 344 } 345 } 346 347 FOR_EACH_EDGE (e, ei, b->succs) 348 { 349 basic_block dest = e->dest; 350 351 if (dest->loop_father == loop 352 && !(dest->flags & BB_REACHABLE) 353 && !(e->flags & flags)) 354 { 355 *tos++ = dest; 356 dest->flags |= BB_REACHABLE; 357 } 358 } 359 } 360 361 free (worklist); 362 363 /* Find a bb to unswitch on. */ 364 for (; found < loop->num_nodes; found++) 365 if ((bbs[found]->flags & BB_REACHABLE) 366 && (cond = tree_may_unswitch_on (bbs[found], loop))) 367 break; 368 369 if (found == loop->num_nodes) 370 { 371 free (bbs); 372 return changed; 373 } 374 } 375 376 if (dump_file && (dump_flags & TDF_DETAILS)) 377 fprintf (dump_file, ";; Unswitching loop\n"); 378 379 initialize_original_copy_tables (); 380 /* Unswitch the loop on this condition. */ 381 nloop = tree_unswitch_loop (loop, bbs[found], cond); 382 if (!nloop) 383 { 384 free_original_copy_tables (); 385 free (bbs); 386 return changed; 387 } 388 389 /* Update the SSA form after unswitching. */ 390 update_ssa (TODO_update_ssa); 391 free_original_copy_tables (); 392 393 /* Invoke itself on modified loops. */ 394 tree_unswitch_single_loop (nloop, num + 1); 395 tree_unswitch_single_loop (loop, num + 1); 396 free (bbs); 397 return true; 398} 399 400/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support 401 unswitching of innermost loops. COND is the condition determining which 402 loop is entered -- the new loop is entered if COND is true. Returns NULL 403 if impossible, new loop otherwise. */ 404 405static struct loop * 406tree_unswitch_loop (struct loop *loop, 407 basic_block unswitch_on, tree cond) 408{ 409 unsigned prob_true; 410 edge edge_true, edge_false; 411 412 /* Some sanity checking. */ 413 gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on)); 414 gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2); 415 gcc_assert (loop->inner == NULL); 416 417 extract_true_false_edges_from_block (unswitch_on, &edge_true, &edge_false); 418 prob_true = edge_true->probability; 419 return loop_version (loop, unshare_expr (cond), 420 NULL, prob_true, prob_true, 421 REG_BR_PROB_BASE - prob_true, false); 422} 423 424/* Loop unswitching pass. */ 425 426namespace { 427 428const pass_data pass_data_tree_unswitch = 429{ 430 GIMPLE_PASS, /* type */ 431 "unswitch", /* name */ 432 OPTGROUP_LOOP, /* optinfo_flags */ 433 TV_TREE_LOOP_UNSWITCH, /* tv_id */ 434 PROP_cfg, /* properties_required */ 435 0, /* properties_provided */ 436 0, /* properties_destroyed */ 437 0, /* todo_flags_start */ 438 0, /* todo_flags_finish */ 439}; 440 441class pass_tree_unswitch : public gimple_opt_pass 442{ 443public: 444 pass_tree_unswitch (gcc::context *ctxt) 445 : gimple_opt_pass (pass_data_tree_unswitch, ctxt) 446 {} 447 448 /* opt_pass methods: */ 449 virtual bool gate (function *) { return flag_unswitch_loops != 0; } 450 virtual unsigned int execute (function *); 451 452}; // class pass_tree_unswitch 453 454unsigned int 455pass_tree_unswitch::execute (function *fun) 456{ 457 if (number_of_loops (fun) <= 1) 458 return 0; 459 460 return tree_ssa_unswitch_loops (); 461} 462 463} // anon namespace 464 465gimple_opt_pass * 466make_pass_tree_unswitch (gcc::context *ctxt) 467{ 468 return new pass_tree_unswitch (ctxt); 469} 470 471 472