1 /* Backward propagation of indirect loads through PHIs. 2 Copyright (C) 2007-2013 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 "tm.h" 25 #include "tree.h" 26 #include "tm_p.h" 27 #include "basic-block.h" 28 #include "gimple-pretty-print.h" 29 #include "tree-flow.h" 30 #include "tree-pass.h" 31 #include "langhooks.h" 32 #include "flags.h" 33 34 /* This pass propagates indirect loads through the PHI node for its 35 address to make the load source possibly non-addressable and to 36 allow for PHI optimization to trigger. 37 38 For example the pass changes 39 40 # addr_1 = PHI <&a, &b> 41 tmp_1 = *addr_1; 42 43 to 44 45 # tmp_1 = PHI <a, b> 46 47 but also handles more complex scenarios like 48 49 D.2077_2 = &this_1(D)->a1; 50 ... 51 52 # b_12 = PHI <&c(2), D.2077_2(3)> 53 D.2114_13 = *b_12; 54 ... 55 56 # b_15 = PHI <b_12(4), &b(5)> 57 D.2080_5 = &this_1(D)->a0; 58 ... 59 60 # b_18 = PHI <D.2080_5(6), &c(7)> 61 ... 62 63 # b_21 = PHI <b_15(8), b_18(9)> 64 D.2076_8 = *b_21; 65 66 where the addresses loaded are defined by PHIs itself. 67 The above happens for 68 69 std::max(std::min(a0, c), std::min(std::max(a1, c), b)) 70 71 where this pass transforms it to a form later PHI optimization 72 recognizes and transforms it to the simple 73 74 D.2109_10 = this_1(D)->a1; 75 D.2110_11 = c; 76 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>; 77 D.2115_14 = b; 78 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>; 79 D.2119_16 = this_1(D)->a0; 80 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>; 81 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>; 82 83 The pass does a dominator walk processing loads using a basic-block 84 local analysis and stores the result for use by transformations on 85 dominated basic-blocks. */ 86 87 88 /* Structure to keep track of the value of a dereferenced PHI result 89 and the virtual operand used for that dereference. */ 90 91 struct phiprop_d 92 { 93 tree value; 94 tree vuse; 95 }; 96 97 /* Verify if the value recorded for NAME in PHIVN is still valid at 98 the start of basic block BB. */ 99 100 static bool 101 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb) 102 { 103 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse; 104 gimple use_stmt; 105 imm_use_iterator ui2; 106 bool ok = true; 107 108 /* The def stmts of the virtual uses need to be dominated by bb. */ 109 gcc_assert (vuse != NULL_TREE); 110 111 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse) 112 { 113 /* If BB does not dominate a VDEF, the value is invalid. */ 114 if ((gimple_vdef (use_stmt) != NULL_TREE 115 || gimple_code (use_stmt) == GIMPLE_PHI) 116 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb)) 117 { 118 ok = false; 119 BREAK_FROM_IMM_USE_STMT (ui2); 120 } 121 } 122 123 return ok; 124 } 125 126 /* Insert a new phi node for the dereference of PHI at basic_block 127 BB with the virtual operands from USE_STMT. */ 128 129 static tree 130 phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt, 131 struct phiprop_d *phivn, size_t n) 132 { 133 tree res; 134 gimple new_phi; 135 edge_iterator ei; 136 edge e; 137 138 gcc_assert (is_gimple_assign (use_stmt) 139 && gimple_assign_rhs_code (use_stmt) == MEM_REF); 140 141 /* Build a new PHI node to replace the definition of 142 the indirect reference lhs. */ 143 res = gimple_assign_lhs (use_stmt); 144 new_phi = create_phi_node (res, bb); 145 146 if (dump_file && (dump_flags & TDF_DETAILS)) 147 { 148 fprintf (dump_file, "Inserting PHI for result of load "); 149 print_gimple_stmt (dump_file, use_stmt, 0, 0); 150 } 151 152 /* Add PHI arguments for each edge inserting loads of the 153 addressable operands. */ 154 FOR_EACH_EDGE (e, ei, bb->preds) 155 { 156 tree old_arg, new_var; 157 gimple tmp; 158 source_location locus; 159 160 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 161 locus = gimple_phi_arg_location_from_edge (phi, e); 162 while (TREE_CODE (old_arg) == SSA_NAME 163 && (SSA_NAME_VERSION (old_arg) >= n 164 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE)) 165 { 166 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg); 167 old_arg = gimple_assign_rhs1 (def_stmt); 168 locus = gimple_location (def_stmt); 169 } 170 171 if (TREE_CODE (old_arg) == SSA_NAME) 172 { 173 if (dump_file && (dump_flags & TDF_DETAILS)) 174 { 175 fprintf (dump_file, " for edge defining "); 176 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); 177 fprintf (dump_file, " reusing PHI result "); 178 print_generic_expr (dump_file, 179 phivn[SSA_NAME_VERSION (old_arg)].value, 0); 180 fprintf (dump_file, "\n"); 181 } 182 /* Reuse a formerly created dereference. */ 183 new_var = phivn[SSA_NAME_VERSION (old_arg)].value; 184 } 185 else 186 { 187 tree rhs = gimple_assign_rhs1 (use_stmt); 188 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); 189 new_var = make_ssa_name (TREE_TYPE (rhs), NULL); 190 if (!is_gimple_min_invariant (old_arg)) 191 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 192 else 193 old_arg = unshare_expr (old_arg); 194 tmp = gimple_build_assign (new_var, 195 fold_build2 (MEM_REF, TREE_TYPE (rhs), 196 old_arg, 197 TREE_OPERAND (rhs, 1))); 198 gimple_set_location (tmp, locus); 199 200 gsi_insert_on_edge (e, tmp); 201 update_stmt (tmp); 202 203 if (dump_file && (dump_flags & TDF_DETAILS)) 204 { 205 fprintf (dump_file, " for edge defining "); 206 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); 207 fprintf (dump_file, " inserting load "); 208 print_gimple_stmt (dump_file, tmp, 0, 0); 209 } 210 } 211 212 add_phi_arg (new_phi, new_var, e, locus); 213 } 214 215 update_stmt (new_phi); 216 217 if (dump_file && (dump_flags & TDF_DETAILS)) 218 print_gimple_stmt (dump_file, new_phi, 0, 0); 219 220 return res; 221 } 222 223 /* Propagate between the phi node arguments of PHI in BB and phi result 224 users. For now this matches 225 # p_2 = PHI <&x, &y> 226 <Lx>:; 227 p_3 = p_2; 228 z_2 = *p_3; 229 and converts it to 230 # z_2 = PHI <x, y> 231 <Lx>:; 232 Returns true if a transformation was done and edge insertions 233 need to be committed. Global data PHIVN and N is used to track 234 past transformation results. We need to be especially careful here 235 with aliasing issues as we are moving memory reads. */ 236 237 static bool 238 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn, 239 size_t n) 240 { 241 tree ptr = PHI_RESULT (phi); 242 gimple use_stmt; 243 tree res = NULL_TREE; 244 gimple_stmt_iterator gsi; 245 imm_use_iterator ui; 246 use_operand_p arg_p, use; 247 ssa_op_iter i; 248 bool phi_inserted; 249 tree type = NULL_TREE; 250 bool one_invariant = false; 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 if (TREE_CODE (arg) == ADDR_EXPR 286 && is_gimple_min_invariant (arg)) 287 one_invariant = true; 288 } 289 290 /* If we neither have an address of a decl nor can reuse a previously 291 inserted load, do not hoist anything. */ 292 if (!one_invariant 293 && !type) 294 return false; 295 296 /* Find a dereferencing use. First follow (single use) ssa 297 copy chains for ptr. */ 298 while (single_imm_use (ptr, &use, &use_stmt) 299 && gimple_assign_ssa_name_copy_p (use_stmt)) 300 ptr = gimple_assign_lhs (use_stmt); 301 302 /* Replace the first dereference of *ptr if there is one and if we 303 can move the loads to the place of the ptr phi node. */ 304 phi_inserted = false; 305 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) 306 { 307 gimple def_stmt; 308 tree vuse; 309 310 /* Only replace loads in blocks that post-dominate the PHI node. That 311 makes sure we don't end up speculating loads. */ 312 if (!dominated_by_p (CDI_POST_DOMINATORS, 313 bb, gimple_bb (use_stmt))) 314 continue; 315 316 /* Check whether this is a load of *ptr. */ 317 if (!(is_gimple_assign (use_stmt) 318 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME 319 && gimple_assign_rhs_code (use_stmt) == MEM_REF 320 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr 321 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1)) 322 && (!type 323 || types_compatible_p 324 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type)) 325 /* We cannot replace a load that may throw or is volatile. */ 326 && !stmt_can_throw_internal (use_stmt))) 327 continue; 328 329 /* Check if we can move the loads. The def stmt of the virtual use 330 needs to be in a different basic block dominating bb. */ 331 vuse = gimple_vuse (use_stmt); 332 def_stmt = SSA_NAME_DEF_STMT (vuse); 333 if (!SSA_NAME_IS_DEFAULT_DEF (vuse) 334 && (gimple_bb (def_stmt) == bb 335 || !dominated_by_p (CDI_DOMINATORS, 336 bb, gimple_bb (def_stmt)))) 337 goto next; 338 339 /* Found a proper dereference. Insert a phi node if this 340 is the first load transformation. */ 341 if (!phi_inserted) 342 { 343 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); 344 type = TREE_TYPE (res); 345 346 /* Remember the value we created for *ptr. */ 347 phivn[SSA_NAME_VERSION (ptr)].value = res; 348 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse; 349 350 /* Remove old stmt. The phi is taken care of by DCE, if we 351 want to delete it here we also have to delete all intermediate 352 copies. */ 353 gsi = gsi_for_stmt (use_stmt); 354 gsi_remove (&gsi, true); 355 356 phi_inserted = true; 357 } 358 else 359 { 360 /* Further replacements are easy, just make a copy out of the 361 load. */ 362 gimple_assign_set_rhs1 (use_stmt, res); 363 update_stmt (use_stmt); 364 } 365 366 next:; 367 /* Continue searching for a proper dereference. */ 368 } 369 370 return phi_inserted; 371 } 372 373 /* Main entry for phiprop pass. */ 374 375 static unsigned int 376 tree_ssa_phiprop (void) 377 { 378 vec<basic_block> bbs; 379 struct phiprop_d *phivn; 380 bool did_something = false; 381 basic_block bb; 382 gimple_stmt_iterator gsi; 383 unsigned i; 384 size_t n; 385 386 calculate_dominance_info (CDI_DOMINATORS); 387 calculate_dominance_info (CDI_POST_DOMINATORS); 388 389 n = num_ssa_names; 390 phivn = XCNEWVEC (struct phiprop_d, n); 391 392 /* Walk the dominator tree in preorder. */ 393 bbs = get_all_dominated_blocks (CDI_DOMINATORS, 394 single_succ (ENTRY_BLOCK_PTR)); 395 FOR_EACH_VEC_ELT (bbs, i, bb) 396 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 397 did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n); 398 399 if (did_something) 400 gsi_commit_edge_inserts (); 401 402 bbs.release (); 403 free (phivn); 404 405 free_dominance_info (CDI_POST_DOMINATORS); 406 407 return 0; 408 } 409 410 static bool 411 gate_phiprop (void) 412 { 413 return flag_tree_phiprop; 414 } 415 416 struct gimple_opt_pass pass_phiprop = 417 { 418 { 419 GIMPLE_PASS, 420 "phiprop", /* name */ 421 OPTGROUP_NONE, /* optinfo_flags */ 422 gate_phiprop, /* gate */ 423 tree_ssa_phiprop, /* execute */ 424 NULL, /* sub */ 425 NULL, /* next */ 426 0, /* static_pass_number */ 427 TV_TREE_PHIPROP, /* tv_id */ 428 PROP_cfg | PROP_ssa, /* properties_required */ 429 0, /* properties_provided */ 430 0, /* properties_destroyed */ 431 0, /* todo_flags_start */ 432 TODO_ggc_collect 433 | TODO_update_ssa 434 | TODO_verify_ssa /* todo_flags_finish */ 435 } 436 }; 437