1 /* Backward propagation of indirect loads through PHIs. 2 Copyright (C) 2007-2016 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 35 /* This pass propagates indirect loads through the PHI node for its 36 address to make the load source possibly non-addressable and to 37 allow for PHI optimization to trigger. 38 39 For example the pass changes 40 41 # addr_1 = PHI <&a, &b> 42 tmp_1 = *addr_1; 43 44 to 45 46 # tmp_1 = PHI <a, b> 47 48 but also handles more complex scenarios like 49 50 D.2077_2 = &this_1(D)->a1; 51 ... 52 53 # b_12 = PHI <&c(2), D.2077_2(3)> 54 D.2114_13 = *b_12; 55 ... 56 57 # b_15 = PHI <b_12(4), &b(5)> 58 D.2080_5 = &this_1(D)->a0; 59 ... 60 61 # b_18 = PHI <D.2080_5(6), &c(7)> 62 ... 63 64 # b_21 = PHI <b_15(8), b_18(9)> 65 D.2076_8 = *b_21; 66 67 where the addresses loaded are defined by PHIs itself. 68 The above happens for 69 70 std::max(std::min(a0, c), std::min(std::max(a1, c), b)) 71 72 where this pass transforms it to a form later PHI optimization 73 recognizes and transforms it to the simple 74 75 D.2109_10 = this_1(D)->a1; 76 D.2110_11 = c; 77 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>; 78 D.2115_14 = b; 79 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>; 80 D.2119_16 = this_1(D)->a0; 81 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>; 82 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>; 83 84 The pass does a dominator walk processing loads using a basic-block 85 local analysis and stores the result for use by transformations on 86 dominated basic-blocks. */ 87 88 89 /* Structure to keep track of the value of a dereferenced PHI result 90 and the virtual operand used for that dereference. */ 91 92 struct phiprop_d 93 { 94 tree value; 95 tree vuse; 96 }; 97 98 /* Verify if the value recorded for NAME in PHIVN is still valid at 99 the start of basic block BB. */ 100 101 static bool 102 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb) 103 { 104 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse; 105 gimple *use_stmt; 106 imm_use_iterator ui2; 107 bool ok = true; 108 109 /* The def stmts of the virtual uses need to be dominated by bb. */ 110 gcc_assert (vuse != NULL_TREE); 111 112 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse) 113 { 114 /* If BB does not dominate a VDEF, the value is invalid. */ 115 if ((gimple_vdef (use_stmt) != NULL_TREE 116 || gimple_code (use_stmt) == GIMPLE_PHI) 117 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb)) 118 { 119 ok = false; 120 BREAK_FROM_IMM_USE_STMT (ui2); 121 } 122 } 123 124 return ok; 125 } 126 127 /* Insert a new phi node for the dereference of PHI at basic_block 128 BB with the virtual operands from USE_STMT. */ 129 130 static tree 131 phiprop_insert_phi (basic_block bb, gphi *phi, gimple *use_stmt, 132 struct phiprop_d *phivn, size_t n) 133 { 134 tree res; 135 gphi *new_phi; 136 edge_iterator ei; 137 edge e; 138 139 gcc_assert (is_gimple_assign (use_stmt) 140 && gimple_assign_rhs_code (use_stmt) == MEM_REF); 141 142 /* Build a new PHI node to replace the definition of 143 the indirect reference lhs. */ 144 res = gimple_assign_lhs (use_stmt); 145 new_phi = create_phi_node (res, bb); 146 147 if (dump_file && (dump_flags & TDF_DETAILS)) 148 { 149 fprintf (dump_file, "Inserting PHI for result of load "); 150 print_gimple_stmt (dump_file, use_stmt, 0, 0); 151 } 152 153 /* Add PHI arguments for each edge inserting loads of the 154 addressable operands. */ 155 FOR_EACH_EDGE (e, ei, bb->preds) 156 { 157 tree old_arg, new_var; 158 gassign *tmp; 159 source_location locus; 160 161 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 162 locus = gimple_phi_arg_location_from_edge (phi, e); 163 while (TREE_CODE (old_arg) == SSA_NAME 164 && (SSA_NAME_VERSION (old_arg) >= n 165 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE)) 166 { 167 gimple *def_stmt = SSA_NAME_DEF_STMT (old_arg); 168 old_arg = gimple_assign_rhs1 (def_stmt); 169 locus = gimple_location (def_stmt); 170 } 171 172 if (TREE_CODE (old_arg) == SSA_NAME) 173 { 174 if (dump_file && (dump_flags & TDF_DETAILS)) 175 { 176 fprintf (dump_file, " for edge defining "); 177 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); 178 fprintf (dump_file, " reusing PHI result "); 179 print_generic_expr (dump_file, 180 phivn[SSA_NAME_VERSION (old_arg)].value, 0); 181 fprintf (dump_file, "\n"); 182 } 183 /* Reuse a formerly created dereference. */ 184 new_var = phivn[SSA_NAME_VERSION (old_arg)].value; 185 } 186 else 187 { 188 tree rhs = gimple_assign_rhs1 (use_stmt); 189 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); 190 new_var = make_ssa_name (TREE_TYPE (rhs)); 191 if (!is_gimple_min_invariant (old_arg)) 192 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 193 else 194 old_arg = unshare_expr (old_arg); 195 tmp = gimple_build_assign (new_var, 196 fold_build2 (MEM_REF, TREE_TYPE (rhs), 197 old_arg, 198 TREE_OPERAND (rhs, 1))); 199 gimple_set_location (tmp, locus); 200 201 gsi_insert_on_edge (e, tmp); 202 update_stmt (tmp); 203 204 if (dump_file && (dump_flags & TDF_DETAILS)) 205 { 206 fprintf (dump_file, " for edge defining "); 207 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); 208 fprintf (dump_file, " inserting load "); 209 print_gimple_stmt (dump_file, tmp, 0, 0); 210 } 211 } 212 213 add_phi_arg (new_phi, new_var, e, locus); 214 } 215 216 update_stmt (new_phi); 217 218 if (dump_file && (dump_flags & TDF_DETAILS)) 219 print_gimple_stmt (dump_file, new_phi, 0, 0); 220 221 return res; 222 } 223 224 /* Propagate between the phi node arguments of PHI in BB and phi result 225 users. For now this matches 226 # p_2 = PHI <&x, &y> 227 <Lx>:; 228 p_3 = p_2; 229 z_2 = *p_3; 230 and converts it to 231 # z_2 = PHI <x, y> 232 <Lx>:; 233 Returns true if a transformation was done and edge insertions 234 need to be committed. Global data PHIVN and N is used to track 235 past transformation results. We need to be especially careful here 236 with aliasing issues as we are moving memory reads. */ 237 238 static bool 239 propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn, 240 size_t n) 241 { 242 tree ptr = PHI_RESULT (phi); 243 gimple *use_stmt; 244 tree res = NULL_TREE; 245 gimple_stmt_iterator gsi; 246 imm_use_iterator ui; 247 use_operand_p arg_p, use; 248 ssa_op_iter i; 249 bool phi_inserted; 250 tree type = NULL_TREE; 251 252 if (!POINTER_TYPE_P (TREE_TYPE (ptr)) 253 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr)))) 254 return false; 255 256 /* Check if we can "cheaply" dereference all phi arguments. */ 257 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE) 258 { 259 tree arg = USE_FROM_PTR (arg_p); 260 /* Walk the ssa chain until we reach a ssa name we already 261 created a value for or we reach a definition of the form 262 ssa_name_n = &var; */ 263 while (TREE_CODE (arg) == SSA_NAME 264 && !SSA_NAME_IS_DEFAULT_DEF (arg) 265 && (SSA_NAME_VERSION (arg) >= n 266 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE)) 267 { 268 gimple *def_stmt = SSA_NAME_DEF_STMT (arg); 269 if (!gimple_assign_single_p (def_stmt)) 270 return false; 271 arg = gimple_assign_rhs1 (def_stmt); 272 } 273 if (TREE_CODE (arg) != ADDR_EXPR 274 && !(TREE_CODE (arg) == SSA_NAME 275 && SSA_NAME_VERSION (arg) < n 276 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE 277 && (!type 278 || types_compatible_p 279 (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value))) 280 && phivn_valid_p (phivn, arg, bb))) 281 return false; 282 if (!type 283 && TREE_CODE (arg) == SSA_NAME) 284 type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value); 285 } 286 287 /* Find a dereferencing use. First follow (single use) ssa 288 copy chains for ptr. */ 289 while (single_imm_use (ptr, &use, &use_stmt) 290 && gimple_assign_ssa_name_copy_p (use_stmt)) 291 ptr = gimple_assign_lhs (use_stmt); 292 293 /* Replace the first dereference of *ptr if there is one and if we 294 can move the loads to the place of the ptr phi node. */ 295 phi_inserted = false; 296 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) 297 { 298 gimple *def_stmt; 299 tree vuse; 300 301 /* Only replace loads in blocks that post-dominate the PHI node. That 302 makes sure we don't end up speculating loads. */ 303 if (!dominated_by_p (CDI_POST_DOMINATORS, 304 bb, gimple_bb (use_stmt))) 305 continue; 306 307 /* Check whether this is a load of *ptr. */ 308 if (!(is_gimple_assign (use_stmt) 309 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME 310 && gimple_assign_rhs_code (use_stmt) == MEM_REF 311 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr 312 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1)) 313 && (!type 314 || types_compatible_p 315 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type)) 316 /* We cannot replace a load that may throw or is volatile. */ 317 && !stmt_can_throw_internal (use_stmt))) 318 continue; 319 320 /* Check if we can move the loads. The def stmt of the virtual use 321 needs to be in a different basic block dominating bb. */ 322 vuse = gimple_vuse (use_stmt); 323 def_stmt = SSA_NAME_DEF_STMT (vuse); 324 if (!SSA_NAME_IS_DEFAULT_DEF (vuse) 325 && (gimple_bb (def_stmt) == bb 326 || !dominated_by_p (CDI_DOMINATORS, 327 bb, gimple_bb (def_stmt)))) 328 goto next; 329 330 /* Found a proper dereference. Insert a phi node if this 331 is the first load transformation. */ 332 if (!phi_inserted) 333 { 334 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); 335 type = TREE_TYPE (res); 336 337 /* Remember the value we created for *ptr. */ 338 phivn[SSA_NAME_VERSION (ptr)].value = res; 339 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse; 340 341 /* Remove old stmt. The phi is taken care of by DCE, if we 342 want to delete it here we also have to delete all intermediate 343 copies. */ 344 gsi = gsi_for_stmt (use_stmt); 345 gsi_remove (&gsi, true); 346 347 phi_inserted = true; 348 } 349 else 350 { 351 /* Further replacements are easy, just make a copy out of the 352 load. */ 353 gimple_assign_set_rhs1 (use_stmt, res); 354 update_stmt (use_stmt); 355 } 356 357 next:; 358 /* Continue searching for a proper dereference. */ 359 } 360 361 return phi_inserted; 362 } 363 364 /* Main entry for phiprop pass. */ 365 366 namespace { 367 368 const pass_data pass_data_phiprop = 369 { 370 GIMPLE_PASS, /* type */ 371 "phiprop", /* name */ 372 OPTGROUP_NONE, /* optinfo_flags */ 373 TV_TREE_PHIPROP, /* tv_id */ 374 ( PROP_cfg | PROP_ssa ), /* properties_required */ 375 0, /* properties_provided */ 376 0, /* properties_destroyed */ 377 0, /* todo_flags_start */ 378 TODO_update_ssa, /* todo_flags_finish */ 379 }; 380 381 class pass_phiprop : public gimple_opt_pass 382 { 383 public: 384 pass_phiprop (gcc::context *ctxt) 385 : gimple_opt_pass (pass_data_phiprop, ctxt) 386 {} 387 388 /* opt_pass methods: */ 389 virtual bool gate (function *) { return flag_tree_phiprop; } 390 virtual unsigned int execute (function *); 391 392 }; // class pass_phiprop 393 394 unsigned int 395 pass_phiprop::execute (function *fun) 396 { 397 vec<basic_block> bbs; 398 struct phiprop_d *phivn; 399 bool did_something = false; 400 basic_block bb; 401 gphi_iterator gsi; 402 unsigned i; 403 size_t n; 404 405 calculate_dominance_info (CDI_DOMINATORS); 406 calculate_dominance_info (CDI_POST_DOMINATORS); 407 408 n = num_ssa_names; 409 phivn = XCNEWVEC (struct phiprop_d, n); 410 411 /* Walk the dominator tree in preorder. */ 412 bbs = get_all_dominated_blocks (CDI_DOMINATORS, 413 single_succ (ENTRY_BLOCK_PTR_FOR_FN (fun))); 414 FOR_EACH_VEC_ELT (bbs, i, bb) 415 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 416 did_something |= propagate_with_phi (bb, gsi.phi (), phivn, n); 417 418 if (did_something) 419 gsi_commit_edge_inserts (); 420 421 bbs.release (); 422 free (phivn); 423 424 free_dominance_info (CDI_POST_DOMINATORS); 425 426 return 0; 427 } 428 429 } // anon namespace 430 431 gimple_opt_pass * 432 make_pass_phiprop (gcc::context *ctxt) 433 { 434 return new pass_phiprop (ctxt); 435 } 436