1 /* Backward propagation of indirect loads through PHIs. 2 Copyright (C) 2007, 2008, 2009, 2010 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 "timevar.h" 29 #include "tree-pretty-print.h" 30 #include "gimple-pretty-print.h" 31 #include "tree-flow.h" 32 #include "tree-pass.h" 33 #include "tree-dump.h" 34 #include "langhooks.h" 35 #include "flags.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, gimple phi, gimple use_stmt, 134 struct phiprop_d *phivn, size_t n) 135 { 136 tree res; 137 gimple new_phi; 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 SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb); 148 149 if (dump_file && (dump_flags & TDF_DETAILS)) 150 { 151 fprintf (dump_file, "Inserting PHI for result of load "); 152 print_gimple_stmt (dump_file, use_stmt, 0, 0); 153 } 154 155 /* Add PHI arguments for each edge inserting loads of the 156 addressable operands. */ 157 FOR_EACH_EDGE (e, ei, bb->preds) 158 { 159 tree old_arg, new_var; 160 gimple tmp; 161 source_location locus; 162 163 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 164 locus = gimple_phi_arg_location_from_edge (phi, e); 165 while (TREE_CODE (old_arg) == SSA_NAME 166 && (SSA_NAME_VERSION (old_arg) >= n 167 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE)) 168 { 169 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg); 170 old_arg = gimple_assign_rhs1 (def_stmt); 171 locus = gimple_location (def_stmt); 172 } 173 174 if (TREE_CODE (old_arg) == SSA_NAME) 175 { 176 if (dump_file && (dump_flags & TDF_DETAILS)) 177 { 178 fprintf (dump_file, " for edge defining "); 179 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); 180 fprintf (dump_file, " reusing PHI result "); 181 print_generic_expr (dump_file, 182 phivn[SSA_NAME_VERSION (old_arg)].value, 0); 183 fprintf (dump_file, "\n"); 184 } 185 /* Reuse a formerly created dereference. */ 186 new_var = phivn[SSA_NAME_VERSION (old_arg)].value; 187 } 188 else 189 { 190 tree rhs = gimple_assign_rhs1 (use_stmt); 191 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); 192 new_var = create_tmp_reg (TREE_TYPE (rhs), NULL); 193 if (!is_gimple_min_invariant (old_arg)) 194 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); 195 else 196 old_arg = unshare_expr (old_arg); 197 tmp = gimple_build_assign (new_var, 198 fold_build2 (MEM_REF, TREE_TYPE (rhs), 199 old_arg, 200 TREE_OPERAND (rhs, 1))); 201 gcc_assert (is_gimple_reg (new_var)); 202 add_referenced_var (new_var); 203 new_var = make_ssa_name (new_var, tmp); 204 gimple_assign_set_lhs (tmp, new_var); 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), 0); 214 fprintf (dump_file, " inserting load "); 215 print_gimple_stmt (dump_file, tmp, 0, 0); 216 } 217 } 218 219 add_phi_arg (new_phi, new_var, e, locus); 220 } 221 222 update_stmt (new_phi); 223 224 if (dump_file && (dump_flags & TDF_DETAILS)) 225 print_gimple_stmt (dump_file, new_phi, 0, 0); 226 227 return res; 228 } 229 230 /* Propagate between the phi node arguments of PHI in BB and phi result 231 users. For now this matches 232 # p_2 = PHI <&x, &y> 233 <Lx>:; 234 p_3 = p_2; 235 z_2 = *p_3; 236 and converts it to 237 # z_2 = PHI <x, y> 238 <Lx>:; 239 Returns true if a transformation was done and edge insertions 240 need to be committed. Global data PHIVN and N is used to track 241 past transformation results. We need to be especially careful here 242 with aliasing issues as we are moving memory reads. */ 243 244 static bool 245 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn, 246 size_t n) 247 { 248 tree ptr = PHI_RESULT (phi); 249 gimple use_stmt; 250 tree res = NULL_TREE; 251 gimple_stmt_iterator gsi; 252 imm_use_iterator ui; 253 use_operand_p arg_p, use; 254 ssa_op_iter i; 255 bool phi_inserted; 256 tree type = NULL_TREE; 257 bool one_invariant = false; 258 259 if (!POINTER_TYPE_P (TREE_TYPE (ptr)) 260 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr)))) 261 return false; 262 263 /* Check if we can "cheaply" dereference all phi arguments. */ 264 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE) 265 { 266 tree arg = USE_FROM_PTR (arg_p); 267 /* Walk the ssa chain until we reach a ssa name we already 268 created a value for or we reach a definition of the form 269 ssa_name_n = &var; */ 270 while (TREE_CODE (arg) == SSA_NAME 271 && !SSA_NAME_IS_DEFAULT_DEF (arg) 272 && (SSA_NAME_VERSION (arg) >= n 273 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE)) 274 { 275 gimple def_stmt = SSA_NAME_DEF_STMT (arg); 276 if (!gimple_assign_single_p (def_stmt)) 277 return false; 278 arg = gimple_assign_rhs1 (def_stmt); 279 } 280 if (TREE_CODE (arg) != ADDR_EXPR 281 && !(TREE_CODE (arg) == SSA_NAME 282 && SSA_NAME_VERSION (arg) < n 283 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE 284 && (!type 285 || types_compatible_p 286 (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value))) 287 && phivn_valid_p (phivn, arg, bb))) 288 return false; 289 if (!type 290 && TREE_CODE (arg) == SSA_NAME) 291 type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value); 292 if (TREE_CODE (arg) == ADDR_EXPR 293 && is_gimple_min_invariant (arg)) 294 one_invariant = true; 295 } 296 297 /* If we neither have an address of a decl nor can reuse a previously 298 inserted load, do not hoist anything. */ 299 if (!one_invariant 300 && !type) 301 return false; 302 303 /* Find a dereferencing use. First follow (single use) ssa 304 copy chains for ptr. */ 305 while (single_imm_use (ptr, &use, &use_stmt) 306 && gimple_assign_ssa_name_copy_p (use_stmt)) 307 ptr = gimple_assign_lhs (use_stmt); 308 309 /* Replace the first dereference of *ptr if there is one and if we 310 can move the loads to the place of the ptr phi node. */ 311 phi_inserted = false; 312 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) 313 { 314 gimple def_stmt; 315 tree vuse; 316 317 /* Only replace loads in blocks that post-dominate the PHI node. That 318 makes sure we don't end up speculating loads. */ 319 if (!dominated_by_p (CDI_POST_DOMINATORS, 320 bb, gimple_bb (use_stmt))) 321 continue; 322 323 /* Check whether this is a load of *ptr. */ 324 if (!(is_gimple_assign (use_stmt) 325 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME 326 && gimple_assign_rhs_code (use_stmt) == MEM_REF 327 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr 328 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1)) 329 && (!type 330 || types_compatible_p 331 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type)) 332 /* We cannot replace a load that may throw or is volatile. */ 333 && !stmt_can_throw_internal (use_stmt))) 334 continue; 335 336 /* Check if we can move the loads. The def stmt of the virtual use 337 needs to be in a different basic block dominating bb. */ 338 vuse = gimple_vuse (use_stmt); 339 def_stmt = SSA_NAME_DEF_STMT (vuse); 340 if (!SSA_NAME_IS_DEFAULT_DEF (vuse) 341 && (gimple_bb (def_stmt) == bb 342 || !dominated_by_p (CDI_DOMINATORS, 343 bb, gimple_bb (def_stmt)))) 344 goto next; 345 346 /* Found a proper dereference. Insert a phi node if this 347 is the first load transformation. */ 348 if (!phi_inserted) 349 { 350 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); 351 type = TREE_TYPE (res); 352 353 /* Remember the value we created for *ptr. */ 354 phivn[SSA_NAME_VERSION (ptr)].value = res; 355 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse; 356 357 /* Remove old stmt. The phi is taken care of by DCE, if we 358 want to delete it here we also have to delete all intermediate 359 copies. */ 360 gsi = gsi_for_stmt (use_stmt); 361 gsi_remove (&gsi, true); 362 363 phi_inserted = true; 364 } 365 else 366 { 367 /* Further replacements are easy, just make a copy out of the 368 load. */ 369 gimple_assign_set_rhs1 (use_stmt, res); 370 update_stmt (use_stmt); 371 } 372 373 next:; 374 /* Continue searching for a proper dereference. */ 375 } 376 377 return phi_inserted; 378 } 379 380 /* Main entry for phiprop pass. */ 381 382 static unsigned int 383 tree_ssa_phiprop (void) 384 { 385 VEC(basic_block, heap) *bbs; 386 struct phiprop_d *phivn; 387 bool did_something = false; 388 basic_block bb; 389 gimple_stmt_iterator gsi; 390 unsigned i; 391 size_t n; 392 393 calculate_dominance_info (CDI_DOMINATORS); 394 calculate_dominance_info (CDI_POST_DOMINATORS); 395 396 n = num_ssa_names; 397 phivn = XCNEWVEC (struct phiprop_d, n); 398 399 /* Walk the dominator tree in preorder. */ 400 bbs = get_all_dominated_blocks (CDI_DOMINATORS, 401 single_succ (ENTRY_BLOCK_PTR)); 402 FOR_EACH_VEC_ELT (basic_block, bbs, i, bb) 403 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 404 did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n); 405 406 if (did_something) 407 gsi_commit_edge_inserts (); 408 409 VEC_free (basic_block, heap, bbs); 410 free (phivn); 411 412 free_dominance_info (CDI_POST_DOMINATORS); 413 414 return 0; 415 } 416 417 static bool 418 gate_phiprop (void) 419 { 420 return flag_tree_phiprop; 421 } 422 423 struct gimple_opt_pass pass_phiprop = 424 { 425 { 426 GIMPLE_PASS, 427 "phiprop", /* name */ 428 gate_phiprop, /* gate */ 429 tree_ssa_phiprop, /* execute */ 430 NULL, /* sub */ 431 NULL, /* next */ 432 0, /* static_pass_number */ 433 TV_TREE_PHIPROP, /* tv_id */ 434 PROP_cfg | PROP_ssa, /* properties_required */ 435 0, /* properties_provided */ 436 0, /* properties_destroyed */ 437 0, /* todo_flags_start */ 438 TODO_ggc_collect 439 | TODO_update_ssa 440 | TODO_verify_ssa /* todo_flags_finish */ 441 } 442 }; 443