1 /* Backward propagation of indirect loads through PHIs. 2 Copyright (C) 2007, 2008 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 "ggc.h" 26 #include "tree.h" 27 #include "rtl.h" 28 #include "tm_p.h" 29 #include "basic-block.h" 30 #include "timevar.h" 31 #include "diagnostic.h" 32 #include "tree-flow.h" 33 #include "tree-pass.h" 34 #include "tree-dump.h" 35 #include "langhooks.h" 36 #include "flags.h" 37 38 /* This pass propagates indirect loads through the PHI node for its 39 address to make the load source possibly non-addressable and to 40 allow for PHI optimization to trigger. 41 42 For example the pass changes 43 44 # addr_1 = PHI <&a, &b> 45 tmp_1 = *addr_1; 46 47 to 48 49 # tmp_1 = PHI <a, b> 50 51 but also handles more complex scenarios like 52 53 D.2077_2 = &this_1(D)->a1; 54 ... 55 56 # b_12 = PHI <&c(2), D.2077_2(3)> 57 D.2114_13 = *b_12; 58 ... 59 60 # b_15 = PHI <b_12(4), &b(5)> 61 D.2080_5 = &this_1(D)->a0; 62 ... 63 64 # b_18 = PHI <D.2080_5(6), &c(7)> 65 ... 66 67 # b_21 = PHI <b_15(8), b_18(9)> 68 D.2076_8 = *b_21; 69 70 where the addresses loaded are defined by PHIs itself. 71 The above happens for 72 73 std::max(std::min(a0, c), std::min(std::max(a1, c), b)) 74 75 where this pass transforms it to a form later PHI optimization 76 recognizes and transforms it to the simple 77 78 D.2109_10 = this_1(D)->a1; 79 D.2110_11 = c; 80 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>; 81 D.2115_14 = b; 82 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>; 83 D.2119_16 = this_1(D)->a0; 84 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>; 85 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>; 86 87 The pass does a dominator walk processing loads using a basic-block 88 local analysis and stores the result for use by transformations on 89 dominated basic-blocks. */ 90 91 92 /* Structure to keep track of the value of a dereferenced PHI result 93 and the virtual operand used for that dereference. */ 94 95 struct phiprop_d 96 { 97 tree value; 98 tree vuse; 99 }; 100 101 /* Verify if the value recorded for NAME in PHIVN is still valid at 102 the start of basic block BB. */ 103 104 static bool 105 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb) 106 { 107 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse; 108 gimple use_stmt; 109 imm_use_iterator ui2; 110 bool ok = true; 111 112 /* The def stmts of the virtual uses need to be dominated by bb. */ 113 gcc_assert (vuse != NULL_TREE); 114 115 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse) 116 { 117 /* If BB does not dominate a VDEF, the value is invalid. */ 118 if ((gimple_vdef (use_stmt) != NULL_TREE 119 || gimple_code (use_stmt) == GIMPLE_PHI) 120 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb)) 121 { 122 ok = false; 123 BREAK_FROM_IMM_USE_STMT (ui2); 124 } 125 } 126 127 return ok; 128 } 129 130 /* Insert a new phi node for the dereference of PHI at basic_block 131 BB with the virtual operands from USE_STMT. */ 132 133 static tree 134 phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt, 135 struct phiprop_d *phivn, size_t n) 136 { 137 tree res; 138 gimple new_phi; 139 edge_iterator ei; 140 edge e; 141 142 gcc_assert (is_gimple_assign (use_stmt) 143 && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF); 144 145 /* Build a new PHI node to replace the definition of 146 the indirect reference lhs. */ 147 res = gimple_assign_lhs (use_stmt); 148 SSA_NAME_DEF_STMT (res) = 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, 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 gimple 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), 0); 181 fprintf (dump_file, " reusing PHI result "); 182 print_generic_expr (dump_file, 183 phivn[SSA_NAME_VERSION (old_arg)].value, 0); 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 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); 192 old_arg = TREE_OPERAND (old_arg, 0); 193 new_var = create_tmp_var (TREE_TYPE (old_arg), NULL); 194 tmp = gimple_build_assign (new_var, unshare_expr (old_arg)); 195 if (TREE_CODE (TREE_TYPE (old_arg)) == COMPLEX_TYPE 196 || TREE_CODE (TREE_TYPE (old_arg)) == VECTOR_TYPE) 197 DECL_GIMPLE_REG_P (new_var) = 1; 198 gcc_assert (is_gimple_reg (new_var)); 199 add_referenced_var (new_var); 200 new_var = make_ssa_name (new_var, tmp); 201 gimple_assign_set_lhs (tmp, new_var); 202 gimple_set_location (tmp, locus); 203 204 gsi_insert_on_edge (e, tmp); 205 update_stmt (tmp); 206 207 if (dump_file && (dump_flags & TDF_DETAILS)) 208 { 209 fprintf (dump_file, " for edge defining "); 210 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); 211 fprintf (dump_file, " inserting load "); 212 print_gimple_stmt (dump_file, tmp, 0, 0); 213 } 214 } 215 216 add_phi_arg (new_phi, new_var, e, locus); 217 } 218 219 update_stmt (new_phi); 220 221 if (dump_file && (dump_flags & TDF_DETAILS)) 222 print_gimple_stmt (dump_file, new_phi, 0, 0); 223 224 return res; 225 } 226 227 /* Propagate between the phi node arguments of PHI in BB and phi result 228 users. For now this matches 229 # p_2 = PHI <&x, &y> 230 <Lx>:; 231 p_3 = p_2; 232 z_2 = *p_3; 233 and converts it to 234 # z_2 = PHI <x, y> 235 <Lx>:; 236 Returns true if a transformation was done and edge insertions 237 need to be committed. Global data PHIVN and N is used to track 238 past transformation results. We need to be especially careful here 239 with aliasing issues as we are moving memory reads. */ 240 241 static bool 242 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn, 243 size_t n) 244 { 245 tree ptr = PHI_RESULT (phi); 246 gimple use_stmt; 247 tree res = NULL_TREE; 248 gimple_stmt_iterator gsi; 249 imm_use_iterator ui; 250 use_operand_p arg_p, use; 251 ssa_op_iter i; 252 bool phi_inserted; 253 254 if (!POINTER_TYPE_P (TREE_TYPE (ptr)) 255 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr)))) 256 return false; 257 258 /* Check if we can "cheaply" dereference all phi arguments. */ 259 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE) 260 { 261 tree arg = USE_FROM_PTR (arg_p); 262 /* Walk the ssa chain until we reach a ssa name we already 263 created a value for or we reach a definition of the form 264 ssa_name_n = &var; */ 265 while (TREE_CODE (arg) == SSA_NAME 266 && !SSA_NAME_IS_DEFAULT_DEF (arg) 267 && (SSA_NAME_VERSION (arg) >= n 268 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE)) 269 { 270 gimple def_stmt = SSA_NAME_DEF_STMT (arg); 271 if (!gimple_assign_single_p (def_stmt)) 272 return false; 273 arg = gimple_assign_rhs1 (def_stmt); 274 } 275 if ((TREE_CODE (arg) != ADDR_EXPR 276 /* Avoid to have to decay *&a to a[0] later. */ 277 || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg, 0)))) 278 && !(TREE_CODE (arg) == SSA_NAME 279 && SSA_NAME_VERSION (arg) < n 280 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE 281 && phivn_valid_p (phivn, arg, bb))) 282 return false; 283 } 284 285 /* Find a dereferencing use. First follow (single use) ssa 286 copy chains for ptr. */ 287 while (single_imm_use (ptr, &use, &use_stmt) 288 && gimple_assign_ssa_name_copy_p (use_stmt)) 289 ptr = gimple_assign_lhs (use_stmt); 290 291 /* Replace the first dereference of *ptr if there is one and if we 292 can move the loads to the place of the ptr phi node. */ 293 phi_inserted = false; 294 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) 295 { 296 gimple def_stmt; 297 tree vuse; 298 299 /* Check whether this is a load of *ptr. */ 300 if (!(is_gimple_assign (use_stmt) 301 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME 302 && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF 303 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr 304 /* We cannot replace a load that may throw or is volatile. */ 305 && !stmt_can_throw_internal (use_stmt))) 306 continue; 307 308 /* Check if we can move the loads. The def stmt of the virtual use 309 needs to be in a different basic block dominating bb. */ 310 vuse = gimple_vuse (use_stmt); 311 def_stmt = SSA_NAME_DEF_STMT (vuse); 312 if (!SSA_NAME_IS_DEFAULT_DEF (vuse) 313 && (gimple_bb (def_stmt) == bb 314 || !dominated_by_p (CDI_DOMINATORS, 315 bb, gimple_bb (def_stmt)))) 316 goto next; 317 318 /* Found a proper dereference. Insert a phi node if this 319 is the first load transformation. */ 320 if (!phi_inserted) 321 { 322 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); 323 324 /* Remember the value we created for *ptr. */ 325 phivn[SSA_NAME_VERSION (ptr)].value = res; 326 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse; 327 328 /* Remove old stmt. The phi is taken care of by DCE, if we 329 want to delete it here we also have to delete all intermediate 330 copies. */ 331 gsi = gsi_for_stmt (use_stmt); 332 gsi_remove (&gsi, false); 333 334 phi_inserted = true; 335 } 336 else 337 { 338 /* Further replacements are easy, just make a copy out of the 339 load. */ 340 gimple_assign_set_rhs1 (use_stmt, res); 341 update_stmt (use_stmt); 342 } 343 344 next:; 345 /* Continue searching for a proper dereference. */ 346 } 347 348 return phi_inserted; 349 } 350 351 /* Main entry for phiprop pass. */ 352 353 static unsigned int 354 tree_ssa_phiprop (void) 355 { 356 VEC(basic_block, heap) *bbs; 357 struct phiprop_d *phivn; 358 bool did_something = false; 359 basic_block bb; 360 gimple_stmt_iterator gsi; 361 unsigned i; 362 size_t n; 363 364 calculate_dominance_info (CDI_DOMINATORS); 365 366 n = num_ssa_names; 367 phivn = XCNEWVEC (struct phiprop_d, n); 368 369 /* Walk the dominator tree in preorder. */ 370 bbs = get_all_dominated_blocks (CDI_DOMINATORS, 371 single_succ (ENTRY_BLOCK_PTR)); 372 for (i = 0; VEC_iterate (basic_block, bbs, i, bb); ++i) 373 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 374 did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n); 375 376 if (did_something) 377 gsi_commit_edge_inserts (); 378 379 VEC_free (basic_block, heap, bbs); 380 free (phivn); 381 382 return 0; 383 } 384 385 static bool 386 gate_phiprop (void) 387 { 388 return flag_tree_phiprop; 389 } 390 391 struct gimple_opt_pass pass_phiprop = 392 { 393 { 394 GIMPLE_PASS, 395 "phiprop", /* name */ 396 gate_phiprop, /* gate */ 397 tree_ssa_phiprop, /* execute */ 398 NULL, /* sub */ 399 NULL, /* next */ 400 0, /* static_pass_number */ 401 TV_TREE_PHIPROP, /* tv_id */ 402 PROP_cfg | PROP_ssa, /* properties_required */ 403 0, /* properties_provided */ 404 0, /* properties_destroyed */ 405 0, /* todo_flags_start */ 406 TODO_dump_func 407 | TODO_ggc_collect 408 | TODO_update_ssa 409 | TODO_verify_ssa /* todo_flags_finish */ 410 } 411 }; 412