1 /* Backward propagation of indirect loads through PHIs. 2 Copyright (C) 2007-2018 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 "backend.h" 25 #include "tree.h" 26 #include "gimple.h" 27 #include "tree-pass.h" 28 #include "ssa.h" 29 #include "gimple-pretty-print.h" 30 #include "fold-const.h" 31 #include "tree-eh.h" 32 #include "gimplify.h" 33 #include "gimple-iterator.h" 34 #include "stor-layout.h" 35 #include "tree-ssa-loop.h" 36 37 /* This pass propagates indirect loads through the PHI node for its 38 address to make the load source possibly non-addressable and to 39 allow for PHI optimization to trigger. 40 41 For example the pass changes 42 43 # addr_1 = PHI <&a, &b> 44 tmp_1 = *addr_1; 45 46 to 47 48 # tmp_1 = PHI <a, b> 49 50 but also handles more complex scenarios like 51 52 D.2077_2 = &this_1(D)->a1; 53 ... 54 55 # b_12 = PHI <&c(2), D.2077_2(3)> 56 D.2114_13 = *b_12; 57 ... 58 59 # b_15 = PHI <b_12(4), &b(5)> 60 D.2080_5 = &this_1(D)->a0; 61 ... 62 63 # b_18 = PHI <D.2080_5(6), &c(7)> 64 ... 65 66 # b_21 = PHI <b_15(8), b_18(9)> 67 D.2076_8 = *b_21; 68 69 where the addresses loaded are defined by PHIs itself. 70 The above happens for 71 72 std::max(std::min(a0, c), std::min(std::max(a1, c), b)) 73 74 where this pass transforms it to a form later PHI optimization 75 recognizes and transforms it to the simple 76 77 D.2109_10 = this_1(D)->a1; 78 D.2110_11 = c; 79 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>; 80 D.2115_14 = b; 81 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>; 82 D.2119_16 = this_1(D)->a0; 83 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>; 84 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>; 85 86 The pass does a dominator walk processing loads using a basic-block 87 local analysis and stores the result for use by transformations on 88 dominated basic-blocks. */ 89 90 91 /* Structure to keep track of the value of a dereferenced PHI result 92 and the virtual operand used for that dereference. */ 93 94 struct phiprop_d 95 { 96 tree value; 97 tree vuse; 98 }; 99 100 /* Verify if the value recorded for NAME in PHIVN is still valid at 101 the start of basic block BB. */ 102 103 static bool 104 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb) 105 { 106 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse; 107 gimple *use_stmt; 108 imm_use_iterator ui2; 109 bool ok = true; 110 111 /* The def stmts of the virtual uses need to be dominated by bb. */ 112 gcc_assert (vuse != NULL_TREE); 113 114 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse) 115 { 116 /* If BB does not dominate a VDEF, the value is invalid. */ 117 if ((gimple_vdef (use_stmt) != NULL_TREE 118 || gimple_code (use_stmt) == GIMPLE_PHI) 119 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb)) 120 { 121 ok = false; 122 BREAK_FROM_IMM_USE_STMT (ui2); 123 } 124 } 125 126 return ok; 127 } 128 129 /* Insert a new phi node for the dereference of PHI at basic_block 130 BB with the virtual operands from USE_STMT. */ 131 132 static tree 133 phiprop_insert_phi (basic_block bb, gphi *phi, gimple *use_stmt, 134 struct phiprop_d *phivn, size_t n) 135 { 136 tree res; 137 gphi *new_phi = NULL; 138 edge_iterator ei; 139 edge e; 140 141 gcc_assert (is_gimple_assign (use_stmt) 142 && gimple_assign_rhs_code (use_stmt) == MEM_REF); 143 144 /* Build a new PHI node to replace the definition of 145 the indirect reference lhs. */ 146 res = gimple_assign_lhs (use_stmt); 147 if (TREE_CODE (res) == SSA_NAME) 148 new_phi = create_phi_node (res, bb); 149 150 if (dump_file && (dump_flags & TDF_DETAILS)) 151 { 152 fprintf (dump_file, "Inserting PHI for result of load "); 153 print_gimple_stmt (dump_file, use_stmt, 0); 154 } 155 156 /* Add PHI arguments for each edge inserting loads of the 157 addressable operands. */ 158 FOR_EACH_EDGE (e, ei, bb->preds) 159 { 160 tree old_arg, new_var; 161 gassign *tmp; 162 source_location locus; 163 164 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 165 locus = gimple_phi_arg_location_from_edge (phi, e); 166 while (TREE_CODE (old_arg) == SSA_NAME 167 && (SSA_NAME_VERSION (old_arg) >= n 168 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE)) 169 { 170 gimple *def_stmt = SSA_NAME_DEF_STMT (old_arg); 171 old_arg = gimple_assign_rhs1 (def_stmt); 172 locus = gimple_location (def_stmt); 173 } 174 175 if (TREE_CODE (old_arg) == SSA_NAME) 176 { 177 if (dump_file && (dump_flags & TDF_DETAILS)) 178 { 179 fprintf (dump_file, " for edge defining "); 180 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e)); 181 fprintf (dump_file, " reusing PHI result "); 182 print_generic_expr (dump_file, 183 phivn[SSA_NAME_VERSION (old_arg)].value); 184 fprintf (dump_file, "\n"); 185 } 186 /* Reuse a formerly created dereference. */ 187 new_var = phivn[SSA_NAME_VERSION (old_arg)].value; 188 } 189 else 190 { 191 tree rhs = gimple_assign_rhs1 (use_stmt); 192 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); 193 if (TREE_CODE (res) == SSA_NAME) 194 new_var = make_ssa_name (TREE_TYPE (rhs)); 195 else 196 new_var = unshare_expr (res); 197 if (!is_gimple_min_invariant (old_arg)) 198 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 199 else 200 old_arg = unshare_expr (old_arg); 201 tmp = gimple_build_assign (new_var, 202 fold_build2 (MEM_REF, TREE_TYPE (rhs), 203 old_arg, 204 TREE_OPERAND (rhs, 1))); 205 gimple_set_location (tmp, locus); 206 207 gsi_insert_on_edge (e, tmp); 208 update_stmt (tmp); 209 210 if (dump_file && (dump_flags & TDF_DETAILS)) 211 { 212 fprintf (dump_file, " for edge defining "); 213 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e)); 214 fprintf (dump_file, " inserting load "); 215 print_gimple_stmt (dump_file, tmp, 0); 216 } 217 } 218 219 if (new_phi) 220 add_phi_arg (new_phi, new_var, e, locus); 221 } 222 223 if (new_phi) 224 { 225 update_stmt (new_phi); 226 227 if (dump_file && (dump_flags & TDF_DETAILS)) 228 print_gimple_stmt (dump_file, new_phi, 0); 229 } 230 231 return res; 232 } 233 234 /* Verify if *idx is available at *DATA. */ 235 236 static bool 237 chk_uses (tree, tree *idx, void *data) 238 { 239 basic_block dom = (basic_block) data; 240 if (TREE_CODE (*idx) == SSA_NAME) 241 return (SSA_NAME_IS_DEFAULT_DEF (*idx) 242 || ! dominated_by_p (CDI_DOMINATORS, 243 gimple_bb (SSA_NAME_DEF_STMT (*idx)), dom)); 244 return true; 245 } 246 247 /* Propagate between the phi node arguments of PHI in BB and phi result 248 users. For now this matches 249 # p_2 = PHI <&x, &y> 250 <Lx>:; 251 p_3 = p_2; 252 z_2 = *p_3; 253 and converts it to 254 # z_2 = PHI <x, y> 255 <Lx>:; 256 Returns true if a transformation was done and edge insertions 257 need to be committed. Global data PHIVN and N is used to track 258 past transformation results. We need to be especially careful here 259 with aliasing issues as we are moving memory reads. */ 260 261 static bool 262 propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn, 263 size_t n) 264 { 265 tree ptr = PHI_RESULT (phi); 266 gimple *use_stmt; 267 tree res = NULL_TREE; 268 gimple_stmt_iterator gsi; 269 imm_use_iterator ui; 270 use_operand_p arg_p, use; 271 ssa_op_iter i; 272 bool phi_inserted; 273 bool changed; 274 tree type = NULL_TREE; 275 276 if (!POINTER_TYPE_P (TREE_TYPE (ptr)) 277 || (!is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))) 278 && TYPE_MODE (TREE_TYPE (TREE_TYPE (ptr))) == BLKmode)) 279 return false; 280 281 /* Check if we can "cheaply" dereference all phi arguments. */ 282 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE) 283 { 284 tree arg = USE_FROM_PTR (arg_p); 285 /* Walk the ssa chain until we reach a ssa name we already 286 created a value for or we reach a definition of the form 287 ssa_name_n = &var; */ 288 while (TREE_CODE (arg) == SSA_NAME 289 && !SSA_NAME_IS_DEFAULT_DEF (arg) 290 && (SSA_NAME_VERSION (arg) >= n 291 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE)) 292 { 293 gimple *def_stmt = SSA_NAME_DEF_STMT (arg); 294 if (!gimple_assign_single_p (def_stmt)) 295 return false; 296 arg = gimple_assign_rhs1 (def_stmt); 297 } 298 if (TREE_CODE (arg) != ADDR_EXPR 299 && !(TREE_CODE (arg) == SSA_NAME 300 && SSA_NAME_VERSION (arg) < n 301 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE 302 && (!type 303 || types_compatible_p 304 (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value))) 305 && phivn_valid_p (phivn, arg, bb))) 306 return false; 307 if (!type 308 && TREE_CODE (arg) == SSA_NAME) 309 type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value); 310 } 311 312 /* Find a dereferencing use. First follow (single use) ssa 313 copy chains for ptr. */ 314 while (single_imm_use (ptr, &use, &use_stmt) 315 && gimple_assign_ssa_name_copy_p (use_stmt)) 316 ptr = gimple_assign_lhs (use_stmt); 317 318 /* Replace the first dereference of *ptr if there is one and if we 319 can move the loads to the place of the ptr phi node. */ 320 phi_inserted = false; 321 changed = false; 322 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) 323 { 324 gimple *def_stmt; 325 tree vuse; 326 327 /* Only replace loads in blocks that post-dominate the PHI node. That 328 makes sure we don't end up speculating loads. */ 329 if (!dominated_by_p (CDI_POST_DOMINATORS, 330 bb, gimple_bb (use_stmt))) 331 continue; 332 333 /* Check whether this is a load of *ptr. */ 334 if (!(is_gimple_assign (use_stmt) 335 && gimple_assign_rhs_code (use_stmt) == MEM_REF 336 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr 337 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1)) 338 && (!type 339 || types_compatible_p 340 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type)) 341 /* We cannot replace a load that may throw or is volatile. 342 For volatiles the transform can change the number of 343 executions if the load is inside a loop but the address 344 computations outside (PR91812). We could relax this 345 if we guard against that appropriately. For loads that can 346 throw we could relax things if the moved loads all are 347 known to not throw. */ 348 && !stmt_can_throw_internal (use_stmt) 349 && !gimple_has_volatile_ops (use_stmt))) 350 continue; 351 352 /* Check if we can move the loads. The def stmt of the virtual use 353 needs to be in a different basic block dominating bb. When the 354 def is an edge-inserted one we know it dominates us. */ 355 vuse = gimple_vuse (use_stmt); 356 def_stmt = SSA_NAME_DEF_STMT (vuse); 357 if (!SSA_NAME_IS_DEFAULT_DEF (vuse) 358 && (gimple_bb (def_stmt) == bb 359 || (gimple_bb (def_stmt) 360 && !dominated_by_p (CDI_DOMINATORS, 361 bb, gimple_bb (def_stmt))))) 362 goto next; 363 364 /* Found a proper dereference with an aggregate copy. Just 365 insert aggregate copies on the edges instead. */ 366 if (!is_gimple_reg_type (TREE_TYPE (gimple_assign_lhs (use_stmt)))) 367 { 368 if (!gimple_vdef (use_stmt)) 369 goto next; 370 371 /* As we replicate the lhs on each incoming edge all 372 used SSA names have to be available there. */ 373 if (! for_each_index (gimple_assign_lhs_ptr (use_stmt), 374 chk_uses, 375 get_immediate_dominator (CDI_DOMINATORS, 376 gimple_bb (phi)))) 377 goto next; 378 379 gimple *vuse_stmt; 380 imm_use_iterator vui; 381 use_operand_p vuse_p; 382 /* In order to move the aggregate copies earlier, make sure 383 there are no statements that could read from memory 384 aliasing the lhs in between the start of bb and use_stmt. 385 As we require use_stmt to have a VDEF above, loads after 386 use_stmt will use a different virtual SSA_NAME. */ 387 FOR_EACH_IMM_USE_FAST (vuse_p, vui, vuse) 388 { 389 vuse_stmt = USE_STMT (vuse_p); 390 if (vuse_stmt == use_stmt) 391 continue; 392 if (!dominated_by_p (CDI_DOMINATORS, 393 gimple_bb (vuse_stmt), bb)) 394 continue; 395 if (ref_maybe_used_by_stmt_p (vuse_stmt, 396 gimple_assign_lhs (use_stmt))) 397 goto next; 398 } 399 400 phiprop_insert_phi (bb, phi, use_stmt, phivn, n); 401 402 /* Remove old stmt. The phi is taken care of by DCE. */ 403 gsi = gsi_for_stmt (use_stmt); 404 /* Unlinking the VDEF here is fine as we are sure that we process 405 stmts in execution order due to aggregate copies having VDEFs 406 and we emit loads on the edges in the very same order. 407 We get multiple copies (or intermediate register loads) handled 408 only by walking PHIs or immediate uses in a lucky order though, 409 so we could signal the caller to re-start iterating over PHIs 410 when we come here which would make it quadratic in the number 411 of PHIs. */ 412 unlink_stmt_vdef (use_stmt); 413 gsi_remove (&gsi, true); 414 415 changed = true; 416 } 417 418 /* Found a proper dereference. Insert a phi node if this 419 is the first load transformation. */ 420 else if (!phi_inserted) 421 { 422 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); 423 type = TREE_TYPE (res); 424 425 /* Remember the value we created for *ptr. */ 426 phivn[SSA_NAME_VERSION (ptr)].value = res; 427 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse; 428 429 /* Remove old stmt. The phi is taken care of by DCE, if we 430 want to delete it here we also have to delete all intermediate 431 copies. */ 432 gsi = gsi_for_stmt (use_stmt); 433 gsi_remove (&gsi, true); 434 435 phi_inserted = true; 436 changed = true; 437 } 438 else 439 { 440 /* Further replacements are easy, just make a copy out of the 441 load. */ 442 gimple_assign_set_rhs1 (use_stmt, res); 443 update_stmt (use_stmt); 444 changed = true; 445 } 446 447 next:; 448 /* Continue searching for a proper dereference. */ 449 } 450 451 return changed; 452 } 453 454 /* Main entry for phiprop pass. */ 455 456 namespace { 457 458 const pass_data pass_data_phiprop = 459 { 460 GIMPLE_PASS, /* type */ 461 "phiprop", /* name */ 462 OPTGROUP_NONE, /* optinfo_flags */ 463 TV_TREE_PHIPROP, /* tv_id */ 464 ( PROP_cfg | PROP_ssa ), /* properties_required */ 465 0, /* properties_provided */ 466 0, /* properties_destroyed */ 467 0, /* todo_flags_start */ 468 TODO_update_ssa, /* todo_flags_finish */ 469 }; 470 471 class pass_phiprop : public gimple_opt_pass 472 { 473 public: 474 pass_phiprop (gcc::context *ctxt) 475 : gimple_opt_pass (pass_data_phiprop, ctxt) 476 {} 477 478 /* opt_pass methods: */ 479 virtual bool gate (function *) { return flag_tree_phiprop; } 480 virtual unsigned int execute (function *); 481 482 }; // class pass_phiprop 483 484 unsigned int 485 pass_phiprop::execute (function *fun) 486 { 487 vec<basic_block> bbs; 488 struct phiprop_d *phivn; 489 bool did_something = false; 490 basic_block bb; 491 gphi_iterator gsi; 492 unsigned i; 493 size_t n; 494 495 calculate_dominance_info (CDI_DOMINATORS); 496 calculate_dominance_info (CDI_POST_DOMINATORS); 497 498 n = num_ssa_names; 499 phivn = XCNEWVEC (struct phiprop_d, n); 500 501 /* Walk the dominator tree in preorder. */ 502 bbs = get_all_dominated_blocks (CDI_DOMINATORS, 503 single_succ (ENTRY_BLOCK_PTR_FOR_FN (fun))); 504 FOR_EACH_VEC_ELT (bbs, i, bb) 505 { 506 /* Since we're going to move dereferences across predecessor 507 edges avoid blocks with abnormal predecessors. */ 508 if (bb_has_abnormal_pred (bb)) 509 continue; 510 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 511 did_something |= propagate_with_phi (bb, gsi.phi (), phivn, n); 512 } 513 514 if (did_something) 515 gsi_commit_edge_inserts (); 516 517 bbs.release (); 518 free (phivn); 519 520 free_dominance_info (CDI_POST_DOMINATORS); 521 522 return 0; 523 } 524 525 } // anon namespace 526 527 gimple_opt_pass * 528 make_pass_phiprop (gcc::context *ctxt) 529 { 530 return new pass_phiprop (ctxt); 531 } 532