1 /* Conditional constant propagation pass for the GNU compiler. 2 Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 3 Free Software Foundation, Inc. 4 Adapted from original RTL SSA-CCP by Daniel Berlin <dberlin@dberlin.org> 5 Adapted to GIMPLE trees by Diego Novillo <dnovillo@redhat.com> 6 7 This file is part of GCC. 8 9 GCC is free software; you can redistribute it and/or modify it 10 under the terms of the GNU General Public License as published by the 11 Free Software Foundation; either version 2, or (at your option) any 12 later version. 13 14 GCC is distributed in the hope that it will be useful, but WITHOUT 15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 17 for more details. 18 19 You should have received a copy of the GNU General Public License 20 along with GCC; see the file COPYING. If not, write to the Free 21 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 22 02110-1301, USA. */ 23 24 /* Conditional constant propagation (CCP) is based on the SSA 25 propagation engine (tree-ssa-propagate.c). Constant assignments of 26 the form VAR = CST are propagated from the assignments into uses of 27 VAR, which in turn may generate new constants. The simulation uses 28 a four level lattice to keep track of constant values associated 29 with SSA names. Given an SSA name V_i, it may take one of the 30 following values: 31 32 UNINITIALIZED -> This is the default starting value. V_i 33 has not been processed yet. 34 35 UNDEFINED -> V_i is a local variable whose definition 36 has not been processed yet. Therefore we 37 don't yet know if its value is a constant 38 or not. 39 40 CONSTANT -> V_i has been found to hold a constant 41 value C. 42 43 VARYING -> V_i cannot take a constant value, or if it 44 does, it is not possible to determine it 45 at compile time. 46 47 The core of SSA-CCP is in ccp_visit_stmt and ccp_visit_phi_node: 48 49 1- In ccp_visit_stmt, we are interested in assignments whose RHS 50 evaluates into a constant and conditional jumps whose predicate 51 evaluates into a boolean true or false. When an assignment of 52 the form V_i = CONST is found, V_i's lattice value is set to 53 CONSTANT and CONST is associated with it. This causes the 54 propagation engine to add all the SSA edges coming out the 55 assignment into the worklists, so that statements that use V_i 56 can be visited. 57 58 If the statement is a conditional with a constant predicate, we 59 mark the outgoing edges as executable or not executable 60 depending on the predicate's value. This is then used when 61 visiting PHI nodes to know when a PHI argument can be ignored. 62 63 64 2- In ccp_visit_phi_node, if all the PHI arguments evaluate to the 65 same constant C, then the LHS of the PHI is set to C. This 66 evaluation is known as the "meet operation". Since one of the 67 goals of this evaluation is to optimistically return constant 68 values as often as possible, it uses two main short cuts: 69 70 - If an argument is flowing in through a non-executable edge, it 71 is ignored. This is useful in cases like this: 72 73 if (PRED) 74 a_9 = 3; 75 else 76 a_10 = 100; 77 a_11 = PHI (a_9, a_10) 78 79 If PRED is known to always evaluate to false, then we can 80 assume that a_11 will always take its value from a_10, meaning 81 that instead of consider it VARYING (a_9 and a_10 have 82 different values), we can consider it CONSTANT 100. 83 84 - If an argument has an UNDEFINED value, then it does not affect 85 the outcome of the meet operation. If a variable V_i has an 86 UNDEFINED value, it means that either its defining statement 87 hasn't been visited yet or V_i has no defining statement, in 88 which case the original symbol 'V' is being used 89 uninitialized. Since 'V' is a local variable, the compiler 90 may assume any initial value for it. 91 92 93 After propagation, every variable V_i that ends up with a lattice 94 value of CONSTANT will have the associated constant value in the 95 array CONST_VAL[i].VALUE. That is fed into substitute_and_fold for 96 final substitution and folding. 97 98 99 Constant propagation in stores and loads (STORE-CCP) 100 ---------------------------------------------------- 101 102 While CCP has all the logic to propagate constants in GIMPLE 103 registers, it is missing the ability to associate constants with 104 stores and loads (i.e., pointer dereferences, structures and 105 global/aliased variables). We don't keep loads and stores in 106 SSA, but we do build a factored use-def web for them (in the 107 virtual operands). 108 109 For instance, consider the following code fragment: 110 111 struct A a; 112 const int B = 42; 113 114 void foo (int i) 115 { 116 if (i > 10) 117 a.a = 42; 118 else 119 { 120 a.b = 21; 121 a.a = a.b + 21; 122 } 123 124 if (a.a != B) 125 never_executed (); 126 } 127 128 We should be able to deduce that the predicate 'a.a != B' is always 129 false. To achieve this, we associate constant values to the SSA 130 names in the V_MAY_DEF and V_MUST_DEF operands for each store. 131 Additionally, since we also glob partial loads/stores with the base 132 symbol, we also keep track of the memory reference where the 133 constant value was stored (in the MEM_REF field of PROP_VALUE_T). 134 For instance, 135 136 # a_5 = V_MAY_DEF <a_4> 137 a.a = 2; 138 139 # VUSE <a_5> 140 x_3 = a.b; 141 142 In the example above, CCP will associate value '2' with 'a_5', but 143 it would be wrong to replace the load from 'a.b' with '2', because 144 '2' had been stored into a.a. 145 146 To support STORE-CCP, it is necessary to add a new value to the 147 constant propagation lattice. When evaluating a load for a memory 148 reference we can no longer assume a value of UNDEFINED if we 149 haven't seen a preceding store to the same memory location. 150 Consider, for instance global variables: 151 152 int A; 153 154 foo (int i) 155 { 156 if (i_3 > 10) 157 A_4 = 3; 158 # A_5 = PHI (A_4, A_2); 159 160 # VUSE <A_5> 161 A.0_6 = A; 162 163 return A.0_6; 164 } 165 166 The value of A_2 cannot be assumed to be UNDEFINED, as it may have 167 been defined outside of foo. If we were to assume it UNDEFINED, we 168 would erroneously optimize the above into 'return 3;'. Therefore, 169 when doing STORE-CCP, we introduce a fifth lattice value 170 (UNKNOWN_VAL), which overrides any other value when computing the 171 meet operation in PHI nodes. 172 173 Though STORE-CCP is not too expensive, it does have to do more work 174 than regular CCP, so it is only enabled at -O2. Both regular CCP 175 and STORE-CCP use the exact same algorithm. The only distinction 176 is that when doing STORE-CCP, the boolean variable DO_STORE_CCP is 177 set to true. This affects the evaluation of statements and PHI 178 nodes. 179 180 References: 181 182 Constant propagation with conditional branches, 183 Wegman and Zadeck, ACM TOPLAS 13(2):181-210. 184 185 Building an Optimizing Compiler, 186 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9. 187 188 Advanced Compiler Design and Implementation, 189 Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6 */ 190 191 #include "config.h" 192 #include "system.h" 193 #include "coretypes.h" 194 #include "tm.h" 195 #include "tree.h" 196 #include "flags.h" 197 #include "rtl.h" 198 #include "tm_p.h" 199 #include "ggc.h" 200 #include "basic-block.h" 201 #include "output.h" 202 #include "expr.h" 203 #include "function.h" 204 #include "diagnostic.h" 205 #include "timevar.h" 206 #include "tree-dump.h" 207 #include "tree-flow.h" 208 #include "tree-pass.h" 209 #include "tree-ssa-propagate.h" 210 #include "langhooks.h" 211 #include "target.h" 212 #include "toplev.h" 213 214 215 /* Possible lattice values. */ 216 typedef enum 217 { 218 UNINITIALIZED = 0, 219 UNDEFINED, 220 UNKNOWN_VAL, 221 CONSTANT, 222 VARYING 223 } ccp_lattice_t; 224 225 /* Array of propagated constant values. After propagation, 226 CONST_VAL[I].VALUE holds the constant value for SSA_NAME(I). If 227 the constant is held in an SSA name representing a memory store 228 (i.e., a V_MAY_DEF or V_MUST_DEF), CONST_VAL[I].MEM_REF will 229 contain the actual memory reference used to store (i.e., the LHS of 230 the assignment doing the store). */ 231 static prop_value_t *const_val; 232 233 /* True if we are also propagating constants in stores and loads. */ 234 static bool do_store_ccp; 235 236 /* Dump constant propagation value VAL to file OUTF prefixed by PREFIX. */ 237 238 static void 239 dump_lattice_value (FILE *outf, const char *prefix, prop_value_t val) 240 { 241 switch (val.lattice_val) 242 { 243 case UNINITIALIZED: 244 fprintf (outf, "%sUNINITIALIZED", prefix); 245 break; 246 case UNDEFINED: 247 fprintf (outf, "%sUNDEFINED", prefix); 248 break; 249 case VARYING: 250 fprintf (outf, "%sVARYING", prefix); 251 break; 252 case UNKNOWN_VAL: 253 fprintf (outf, "%sUNKNOWN_VAL", prefix); 254 break; 255 case CONSTANT: 256 fprintf (outf, "%sCONSTANT ", prefix); 257 print_generic_expr (outf, val.value, dump_flags); 258 break; 259 default: 260 gcc_unreachable (); 261 } 262 } 263 264 265 /* Print lattice value VAL to stderr. */ 266 267 void debug_lattice_value (prop_value_t val); 268 269 void 270 debug_lattice_value (prop_value_t val) 271 { 272 dump_lattice_value (stderr, "", val); 273 fprintf (stderr, "\n"); 274 } 275 276 277 /* The regular is_gimple_min_invariant does a shallow test of the object. 278 It assumes that full gimplification has happened, or will happen on the 279 object. For a value coming from DECL_INITIAL, this is not true, so we 280 have to be more strict ourselves. */ 281 282 static bool 283 ccp_decl_initial_min_invariant (tree t) 284 { 285 if (!is_gimple_min_invariant (t)) 286 return false; 287 if (TREE_CODE (t) == ADDR_EXPR) 288 { 289 /* Inline and unroll is_gimple_addressable. */ 290 while (1) 291 { 292 t = TREE_OPERAND (t, 0); 293 if (is_gimple_id (t)) 294 return true; 295 if (!handled_component_p (t)) 296 return false; 297 } 298 } 299 return true; 300 } 301 302 303 /* Compute a default value for variable VAR and store it in the 304 CONST_VAL array. The following rules are used to get default 305 values: 306 307 1- Global and static variables that are declared constant are 308 considered CONSTANT. 309 310 2- Any other value is considered UNDEFINED. This is useful when 311 considering PHI nodes. PHI arguments that are undefined do not 312 change the constant value of the PHI node, which allows for more 313 constants to be propagated. 314 315 3- If SSA_NAME_VALUE is set and it is a constant, its value is 316 used. 317 318 4- Variables defined by statements other than assignments and PHI 319 nodes are considered VARYING. 320 321 5- Variables that are not GIMPLE registers are considered 322 UNKNOWN_VAL, which is really a stronger version of UNDEFINED. 323 It's used to avoid the short circuit evaluation implied by 324 UNDEFINED in ccp_lattice_meet. */ 325 326 static prop_value_t 327 get_default_value (tree var) 328 { 329 tree sym = SSA_NAME_VAR (var); 330 prop_value_t val = { UNINITIALIZED, NULL_TREE, NULL_TREE }; 331 332 if (!do_store_ccp && !is_gimple_reg (var)) 333 { 334 /* Short circuit for regular CCP. We are not interested in any 335 non-register when DO_STORE_CCP is false. */ 336 val.lattice_val = VARYING; 337 } 338 else if (SSA_NAME_VALUE (var) 339 && is_gimple_min_invariant (SSA_NAME_VALUE (var))) 340 { 341 val.lattice_val = CONSTANT; 342 val.value = SSA_NAME_VALUE (var); 343 } 344 else if (TREE_STATIC (sym) 345 && TREE_READONLY (sym) 346 && !MTAG_P (sym) 347 && DECL_INITIAL (sym) 348 && ccp_decl_initial_min_invariant (DECL_INITIAL (sym))) 349 { 350 /* Globals and static variables declared 'const' take their 351 initial value. */ 352 val.lattice_val = CONSTANT; 353 val.value = DECL_INITIAL (sym); 354 val.mem_ref = sym; 355 } 356 else 357 { 358 tree stmt = SSA_NAME_DEF_STMT (var); 359 360 if (IS_EMPTY_STMT (stmt)) 361 { 362 /* Variables defined by an empty statement are those used 363 before being initialized. If VAR is a local variable, we 364 can assume initially that it is UNDEFINED. If we are 365 doing STORE-CCP, function arguments and non-register 366 variables are initially UNKNOWN_VAL, because we cannot 367 discard the value incoming from outside of this function 368 (see ccp_lattice_meet for details). */ 369 if (is_gimple_reg (sym) && TREE_CODE (sym) != PARM_DECL) 370 val.lattice_val = UNDEFINED; 371 else if (do_store_ccp) 372 val.lattice_val = UNKNOWN_VAL; 373 else 374 val.lattice_val = VARYING; 375 } 376 else if (TREE_CODE (stmt) == MODIFY_EXPR 377 || TREE_CODE (stmt) == PHI_NODE) 378 { 379 /* Any other variable defined by an assignment or a PHI node 380 is considered UNDEFINED (or UNKNOWN_VAL if VAR is not a 381 GIMPLE register). */ 382 val.lattice_val = is_gimple_reg (sym) ? UNDEFINED : UNKNOWN_VAL; 383 } 384 else 385 { 386 /* Otherwise, VAR will never take on a constant value. */ 387 val.lattice_val = VARYING; 388 } 389 } 390 391 return val; 392 } 393 394 395 /* Get the constant value associated with variable VAR. If 396 MAY_USE_DEFAULT_P is true, call get_default_value on variables that 397 have the lattice value UNINITIALIZED. */ 398 399 static prop_value_t * 400 get_value (tree var, bool may_use_default_p) 401 { 402 prop_value_t *val = &const_val[SSA_NAME_VERSION (var)]; 403 if (may_use_default_p && val->lattice_val == UNINITIALIZED) 404 *val = get_default_value (var); 405 406 return val; 407 } 408 409 410 /* Set the value for variable VAR to NEW_VAL. Return true if the new 411 value is different from VAR's previous value. */ 412 413 static bool 414 set_lattice_value (tree var, prop_value_t new_val) 415 { 416 prop_value_t *old_val = get_value (var, false); 417 418 /* Lattice transitions must always be monotonically increasing in 419 value. We allow two exceptions: 420 421 1- If *OLD_VAL and NEW_VAL are the same, return false to 422 inform the caller that this was a non-transition. 423 424 2- If we are doing store-ccp (i.e., DOING_STORE_CCP is true), 425 allow CONSTANT->UNKNOWN_VAL. The UNKNOWN_VAL state is a 426 special type of UNDEFINED state which prevents the short 427 circuit evaluation of PHI arguments (see ccp_visit_phi_node 428 and ccp_lattice_meet). */ 429 gcc_assert (old_val->lattice_val <= new_val.lattice_val 430 || (old_val->lattice_val == new_val.lattice_val 431 && old_val->value == new_val.value 432 && old_val->mem_ref == new_val.mem_ref) 433 || (do_store_ccp 434 && old_val->lattice_val == CONSTANT 435 && new_val.lattice_val == UNKNOWN_VAL)); 436 437 if (old_val->lattice_val != new_val.lattice_val) 438 { 439 if (dump_file && (dump_flags & TDF_DETAILS)) 440 { 441 dump_lattice_value (dump_file, "Lattice value changed to ", new_val); 442 fprintf (dump_file, ". %sdding SSA edges to worklist.\n", 443 new_val.lattice_val != UNDEFINED ? "A" : "Not a"); 444 } 445 446 *old_val = new_val; 447 448 /* Transitions UNINITIALIZED -> UNDEFINED are never interesting 449 for propagation purposes. In these cases return false to 450 avoid doing useless work. */ 451 return (new_val.lattice_val != UNDEFINED); 452 } 453 454 return false; 455 } 456 457 458 /* Return the likely CCP lattice value for STMT. 459 460 If STMT has no operands, then return CONSTANT. 461 462 Else if any operands of STMT are undefined, then return UNDEFINED. 463 464 Else if any operands of STMT are constants, then return CONSTANT. 465 466 Else return VARYING. */ 467 468 static ccp_lattice_t 469 likely_value (tree stmt) 470 { 471 bool found_constant; 472 stmt_ann_t ann; 473 tree use; 474 ssa_op_iter iter; 475 476 ann = stmt_ann (stmt); 477 478 /* If the statement has volatile operands, it won't fold to a 479 constant value. */ 480 if (ann->has_volatile_ops) 481 return VARYING; 482 483 /* If we are not doing store-ccp, statements with loads 484 and/or stores will never fold into a constant. */ 485 if (!do_store_ccp 486 && !ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS)) 487 return VARYING; 488 489 490 /* A CALL_EXPR is assumed to be varying. NOTE: This may be overly 491 conservative, in the presence of const and pure calls. */ 492 if (get_call_expr_in (stmt) != NULL_TREE) 493 return VARYING; 494 495 /* Anything other than assignments and conditional jumps are not 496 interesting for CCP. */ 497 if (TREE_CODE (stmt) != MODIFY_EXPR 498 && TREE_CODE (stmt) != COND_EXPR 499 && TREE_CODE (stmt) != SWITCH_EXPR) 500 return VARYING; 501 502 if (is_gimple_min_invariant (get_rhs (stmt))) 503 return CONSTANT; 504 505 found_constant = false; 506 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE|SSA_OP_VUSE) 507 { 508 prop_value_t *val = get_value (use, true); 509 510 if (val->lattice_val == VARYING) 511 return VARYING; 512 513 if (val->lattice_val == UNKNOWN_VAL) 514 { 515 /* UNKNOWN_VAL is invalid when not doing STORE-CCP. */ 516 gcc_assert (do_store_ccp); 517 return UNKNOWN_VAL; 518 } 519 520 if (val->lattice_val == CONSTANT) 521 found_constant = true; 522 } 523 524 if (found_constant 525 || ZERO_SSA_OPERANDS (stmt, SSA_OP_USE) 526 || ZERO_SSA_OPERANDS (stmt, SSA_OP_VUSE)) 527 return CONSTANT; 528 529 return UNDEFINED; 530 } 531 532 533 /* Initialize local data structures for CCP. */ 534 535 static void 536 ccp_initialize (void) 537 { 538 basic_block bb; 539 540 const_val = XNEWVEC (prop_value_t, num_ssa_names); 541 memset (const_val, 0, num_ssa_names * sizeof (*const_val)); 542 543 /* Initialize simulation flags for PHI nodes and statements. */ 544 FOR_EACH_BB (bb) 545 { 546 block_stmt_iterator i; 547 548 for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i)) 549 { 550 bool is_varying = false; 551 tree stmt = bsi_stmt (i); 552 553 if (likely_value (stmt) == VARYING) 554 555 { 556 tree def; 557 ssa_op_iter iter; 558 559 /* If the statement will not produce a constant, mark 560 all its outputs VARYING. */ 561 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS) 562 get_value (def, false)->lattice_val = VARYING; 563 564 /* Never mark conditional jumps with DONT_SIMULATE_AGAIN, 565 otherwise the propagator will never add the outgoing 566 control edges. */ 567 if (TREE_CODE (stmt) != COND_EXPR 568 && TREE_CODE (stmt) != SWITCH_EXPR) 569 is_varying = true; 570 } 571 572 DONT_SIMULATE_AGAIN (stmt) = is_varying; 573 } 574 } 575 576 /* Now process PHI nodes. */ 577 FOR_EACH_BB (bb) 578 { 579 tree phi; 580 581 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) 582 { 583 int i; 584 tree arg; 585 prop_value_t *val = get_value (PHI_RESULT (phi), false); 586 587 for (i = 0; i < PHI_NUM_ARGS (phi); i++) 588 { 589 arg = PHI_ARG_DEF (phi, i); 590 591 if (TREE_CODE (arg) == SSA_NAME 592 && get_value (arg, false)->lattice_val == VARYING) 593 { 594 val->lattice_val = VARYING; 595 break; 596 } 597 } 598 599 DONT_SIMULATE_AGAIN (phi) = (val->lattice_val == VARYING); 600 } 601 } 602 } 603 604 605 /* Do final substitution of propagated values, cleanup the flowgraph and 606 free allocated storage. */ 607 608 static void 609 ccp_finalize (void) 610 { 611 /* Perform substitutions based on the known constant values. */ 612 substitute_and_fold (const_val, false); 613 614 free (const_val); 615 } 616 617 618 /* Compute the meet operator between *VAL1 and *VAL2. Store the result 619 in VAL1. 620 621 any M UNDEFINED = any 622 any M UNKNOWN_VAL = UNKNOWN_VAL 623 any M VARYING = VARYING 624 Ci M Cj = Ci if (i == j) 625 Ci M Cj = VARYING if (i != j) 626 627 Lattice values UNKNOWN_VAL and UNDEFINED are similar but have 628 different semantics at PHI nodes. Both values imply that we don't 629 know whether the variable is constant or not. However, UNKNOWN_VAL 630 values override all others. For instance, suppose that A is a 631 global variable: 632 633 +------+ 634 | | 635 | / \ 636 | / \ 637 | | A_1 = 4 638 | \ / 639 | \ / 640 | A_3 = PHI (A_2, A_1) 641 | ... = A_3 642 | | 643 +----+ 644 645 If the edge into A_2 is not executable, the first visit to A_3 will 646 yield the constant 4. But the second visit to A_3 will be with A_2 647 in state UNKNOWN_VAL. We can no longer conclude that A_3 is 4 648 because A_2 may have been set in another function. If we had used 649 the lattice value UNDEFINED, we would have had wrongly concluded 650 that A_3 is 4. */ 651 652 653 static void 654 ccp_lattice_meet (prop_value_t *val1, prop_value_t *val2) 655 { 656 if (val1->lattice_val == UNDEFINED) 657 { 658 /* UNDEFINED M any = any */ 659 *val1 = *val2; 660 } 661 else if (val2->lattice_val == UNDEFINED) 662 { 663 /* any M UNDEFINED = any 664 Nothing to do. VAL1 already contains the value we want. */ 665 ; 666 } 667 else if (val1->lattice_val == UNKNOWN_VAL 668 || val2->lattice_val == UNKNOWN_VAL) 669 { 670 /* UNKNOWN_VAL values are invalid if we are not doing STORE-CCP. */ 671 gcc_assert (do_store_ccp); 672 673 /* any M UNKNOWN_VAL = UNKNOWN_VAL. */ 674 val1->lattice_val = UNKNOWN_VAL; 675 val1->value = NULL_TREE; 676 val1->mem_ref = NULL_TREE; 677 } 678 else if (val1->lattice_val == VARYING 679 || val2->lattice_val == VARYING) 680 { 681 /* any M VARYING = VARYING. */ 682 val1->lattice_val = VARYING; 683 val1->value = NULL_TREE; 684 val1->mem_ref = NULL_TREE; 685 } 686 else if (val1->lattice_val == CONSTANT 687 && val2->lattice_val == CONSTANT 688 && simple_cst_equal (val1->value, val2->value) == 1 689 && (!do_store_ccp 690 || (val1->mem_ref && val2->mem_ref 691 && operand_equal_p (val1->mem_ref, val2->mem_ref, 0)))) 692 { 693 /* Ci M Cj = Ci if (i == j) 694 Ci M Cj = VARYING if (i != j) 695 696 If these two values come from memory stores, make sure that 697 they come from the same memory reference. */ 698 val1->lattice_val = CONSTANT; 699 val1->value = val1->value; 700 val1->mem_ref = val1->mem_ref; 701 } 702 else 703 { 704 /* Any other combination is VARYING. */ 705 val1->lattice_val = VARYING; 706 val1->value = NULL_TREE; 707 val1->mem_ref = NULL_TREE; 708 } 709 } 710 711 712 /* Loop through the PHI_NODE's parameters for BLOCK and compare their 713 lattice values to determine PHI_NODE's lattice value. The value of a 714 PHI node is determined calling ccp_lattice_meet with all the arguments 715 of the PHI node that are incoming via executable edges. */ 716 717 static enum ssa_prop_result 718 ccp_visit_phi_node (tree phi) 719 { 720 int i; 721 prop_value_t *old_val, new_val; 722 723 if (dump_file && (dump_flags & TDF_DETAILS)) 724 { 725 fprintf (dump_file, "\nVisiting PHI node: "); 726 print_generic_expr (dump_file, phi, dump_flags); 727 } 728 729 old_val = get_value (PHI_RESULT (phi), false); 730 switch (old_val->lattice_val) 731 { 732 case VARYING: 733 return SSA_PROP_VARYING; 734 735 case CONSTANT: 736 new_val = *old_val; 737 break; 738 739 case UNKNOWN_VAL: 740 /* To avoid the default value of UNKNOWN_VAL overriding 741 that of its possible constant arguments, temporarily 742 set the PHI node's default lattice value to be 743 UNDEFINED. If the PHI node's old value was UNKNOWN_VAL and 744 the new value is UNDEFINED, then we prevent the invalid 745 transition by not calling set_lattice_value. */ 746 gcc_assert (do_store_ccp); 747 748 /* FALLTHRU */ 749 750 case UNDEFINED: 751 case UNINITIALIZED: 752 new_val.lattice_val = UNDEFINED; 753 new_val.value = NULL_TREE; 754 new_val.mem_ref = NULL_TREE; 755 break; 756 757 default: 758 gcc_unreachable (); 759 } 760 761 for (i = 0; i < PHI_NUM_ARGS (phi); i++) 762 { 763 /* Compute the meet operator over all the PHI arguments flowing 764 through executable edges. */ 765 edge e = PHI_ARG_EDGE (phi, i); 766 767 if (dump_file && (dump_flags & TDF_DETAILS)) 768 { 769 fprintf (dump_file, 770 "\n Argument #%d (%d -> %d %sexecutable)\n", 771 i, e->src->index, e->dest->index, 772 (e->flags & EDGE_EXECUTABLE) ? "" : "not "); 773 } 774 775 /* If the incoming edge is executable, Compute the meet operator for 776 the existing value of the PHI node and the current PHI argument. */ 777 if (e->flags & EDGE_EXECUTABLE) 778 { 779 tree arg = PHI_ARG_DEF (phi, i); 780 prop_value_t arg_val; 781 782 if (is_gimple_min_invariant (arg)) 783 { 784 arg_val.lattice_val = CONSTANT; 785 arg_val.value = arg; 786 arg_val.mem_ref = NULL_TREE; 787 } 788 else 789 arg_val = *(get_value (arg, true)); 790 791 ccp_lattice_meet (&new_val, &arg_val); 792 793 if (dump_file && (dump_flags & TDF_DETAILS)) 794 { 795 fprintf (dump_file, "\t"); 796 print_generic_expr (dump_file, arg, dump_flags); 797 dump_lattice_value (dump_file, "\tValue: ", arg_val); 798 fprintf (dump_file, "\n"); 799 } 800 801 if (new_val.lattice_val == VARYING) 802 break; 803 } 804 } 805 806 if (dump_file && (dump_flags & TDF_DETAILS)) 807 { 808 dump_lattice_value (dump_file, "\n PHI node value: ", new_val); 809 fprintf (dump_file, "\n\n"); 810 } 811 812 /* Check for an invalid change from UNKNOWN_VAL to UNDEFINED. */ 813 if (do_store_ccp 814 && old_val->lattice_val == UNKNOWN_VAL 815 && new_val.lattice_val == UNDEFINED) 816 return SSA_PROP_NOT_INTERESTING; 817 818 /* Otherwise, make the transition to the new value. */ 819 if (set_lattice_value (PHI_RESULT (phi), new_val)) 820 { 821 if (new_val.lattice_val == VARYING) 822 return SSA_PROP_VARYING; 823 else 824 return SSA_PROP_INTERESTING; 825 } 826 else 827 return SSA_PROP_NOT_INTERESTING; 828 } 829 830 831 /* CCP specific front-end to the non-destructive constant folding 832 routines. 833 834 Attempt to simplify the RHS of STMT knowing that one or more 835 operands are constants. 836 837 If simplification is possible, return the simplified RHS, 838 otherwise return the original RHS. */ 839 840 static tree 841 ccp_fold (tree stmt) 842 { 843 tree rhs = get_rhs (stmt); 844 enum tree_code code = TREE_CODE (rhs); 845 enum tree_code_class kind = TREE_CODE_CLASS (code); 846 tree retval = NULL_TREE; 847 848 if (TREE_CODE (rhs) == SSA_NAME) 849 { 850 /* If the RHS is an SSA_NAME, return its known constant value, 851 if any. */ 852 return get_value (rhs, true)->value; 853 } 854 else if (do_store_ccp && stmt_makes_single_load (stmt)) 855 { 856 /* If the RHS is a memory load, see if the VUSEs associated with 857 it are a valid constant for that memory load. */ 858 prop_value_t *val = get_value_loaded_by (stmt, const_val); 859 if (val && val->mem_ref) 860 { 861 if (operand_equal_p (val->mem_ref, rhs, 0)) 862 return val->value; 863 864 /* If RHS is extracting REALPART_EXPR or IMAGPART_EXPR of a 865 complex type with a known constant value, return it. */ 866 if ((TREE_CODE (rhs) == REALPART_EXPR 867 || TREE_CODE (rhs) == IMAGPART_EXPR) 868 && operand_equal_p (val->mem_ref, TREE_OPERAND (rhs, 0), 0)) 869 return fold_build1 (TREE_CODE (rhs), TREE_TYPE (rhs), val->value); 870 } 871 return NULL_TREE; 872 } 873 874 /* Unary operators. Note that we know the single operand must 875 be a constant. So this should almost always return a 876 simplified RHS. */ 877 if (kind == tcc_unary) 878 { 879 /* Handle unary operators which can appear in GIMPLE form. */ 880 tree op0 = TREE_OPERAND (rhs, 0); 881 882 /* Simplify the operand down to a constant. */ 883 if (TREE_CODE (op0) == SSA_NAME) 884 { 885 prop_value_t *val = get_value (op0, true); 886 if (val->lattice_val == CONSTANT) 887 op0 = get_value (op0, true)->value; 888 } 889 890 if ((code == NOP_EXPR || code == CONVERT_EXPR) 891 && tree_ssa_useless_type_conversion_1 (TREE_TYPE (rhs), 892 TREE_TYPE (op0))) 893 return op0; 894 return fold_unary (code, TREE_TYPE (rhs), op0); 895 } 896 897 /* Binary and comparison operators. We know one or both of the 898 operands are constants. */ 899 else if (kind == tcc_binary 900 || kind == tcc_comparison 901 || code == TRUTH_AND_EXPR 902 || code == TRUTH_OR_EXPR 903 || code == TRUTH_XOR_EXPR) 904 { 905 /* Handle binary and comparison operators that can appear in 906 GIMPLE form. */ 907 tree op0 = TREE_OPERAND (rhs, 0); 908 tree op1 = TREE_OPERAND (rhs, 1); 909 910 /* Simplify the operands down to constants when appropriate. */ 911 if (TREE_CODE (op0) == SSA_NAME) 912 { 913 prop_value_t *val = get_value (op0, true); 914 if (val->lattice_val == CONSTANT) 915 op0 = val->value; 916 } 917 918 if (TREE_CODE (op1) == SSA_NAME) 919 { 920 prop_value_t *val = get_value (op1, true); 921 if (val->lattice_val == CONSTANT) 922 op1 = val->value; 923 } 924 925 return fold_binary (code, TREE_TYPE (rhs), op0, op1); 926 } 927 928 /* We may be able to fold away calls to builtin functions if their 929 arguments are constants. */ 930 else if (code == CALL_EXPR 931 && TREE_CODE (TREE_OPERAND (rhs, 0)) == ADDR_EXPR 932 && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0)) 933 == FUNCTION_DECL) 934 && DECL_BUILT_IN (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0))) 935 { 936 if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_USE)) 937 { 938 tree *orig, var; 939 tree fndecl, arglist; 940 size_t i = 0; 941 ssa_op_iter iter; 942 use_operand_p var_p; 943 944 /* Preserve the original values of every operand. */ 945 orig = XNEWVEC (tree, NUM_SSA_OPERANDS (stmt, SSA_OP_USE)); 946 FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_USE) 947 orig[i++] = var; 948 949 /* Substitute operands with their values and try to fold. */ 950 replace_uses_in (stmt, NULL, const_val); 951 fndecl = get_callee_fndecl (rhs); 952 arglist = TREE_OPERAND (rhs, 1); 953 retval = fold_builtin (fndecl, arglist, false); 954 955 /* Restore operands to their original form. */ 956 i = 0; 957 FOR_EACH_SSA_USE_OPERAND (var_p, stmt, iter, SSA_OP_USE) 958 SET_USE (var_p, orig[i++]); 959 free (orig); 960 } 961 } 962 else 963 return rhs; 964 965 /* If we got a simplified form, see if we need to convert its type. */ 966 if (retval) 967 return fold_convert (TREE_TYPE (rhs), retval); 968 969 /* No simplification was possible. */ 970 return rhs; 971 } 972 973 974 /* Return the tree representing the element referenced by T if T is an 975 ARRAY_REF or COMPONENT_REF into constant aggregates. Return 976 NULL_TREE otherwise. */ 977 978 static tree 979 fold_const_aggregate_ref (tree t) 980 { 981 prop_value_t *value; 982 tree base, ctor, idx, field; 983 unsigned HOST_WIDE_INT cnt; 984 tree cfield, cval; 985 986 switch (TREE_CODE (t)) 987 { 988 case ARRAY_REF: 989 /* Get a CONSTRUCTOR. If BASE is a VAR_DECL, get its 990 DECL_INITIAL. If BASE is a nested reference into another 991 ARRAY_REF or COMPONENT_REF, make a recursive call to resolve 992 the inner reference. */ 993 base = TREE_OPERAND (t, 0); 994 switch (TREE_CODE (base)) 995 { 996 case VAR_DECL: 997 if (!TREE_READONLY (base) 998 || TREE_CODE (TREE_TYPE (base)) != ARRAY_TYPE 999 || !targetm.binds_local_p (base)) 1000 return NULL_TREE; 1001 1002 ctor = DECL_INITIAL (base); 1003 break; 1004 1005 case ARRAY_REF: 1006 case COMPONENT_REF: 1007 ctor = fold_const_aggregate_ref (base); 1008 break; 1009 1010 default: 1011 return NULL_TREE; 1012 } 1013 1014 if (ctor == NULL_TREE 1015 || (TREE_CODE (ctor) != CONSTRUCTOR 1016 && TREE_CODE (ctor) != STRING_CST) 1017 || !TREE_STATIC (ctor)) 1018 return NULL_TREE; 1019 1020 /* Get the index. If we have an SSA_NAME, try to resolve it 1021 with the current lattice value for the SSA_NAME. */ 1022 idx = TREE_OPERAND (t, 1); 1023 switch (TREE_CODE (idx)) 1024 { 1025 case SSA_NAME: 1026 if ((value = get_value (idx, true)) 1027 && value->lattice_val == CONSTANT 1028 && TREE_CODE (value->value) == INTEGER_CST) 1029 idx = value->value; 1030 else 1031 return NULL_TREE; 1032 break; 1033 1034 case INTEGER_CST: 1035 break; 1036 1037 default: 1038 return NULL_TREE; 1039 } 1040 1041 /* Fold read from constant string. */ 1042 if (TREE_CODE (ctor) == STRING_CST) 1043 { 1044 if ((TYPE_MODE (TREE_TYPE (t)) 1045 == TYPE_MODE (TREE_TYPE (TREE_TYPE (ctor)))) 1046 && (GET_MODE_CLASS (TYPE_MODE (TREE_TYPE (TREE_TYPE (ctor)))) 1047 == MODE_INT) 1048 && GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (TREE_TYPE (ctor)))) == 1 1049 && compare_tree_int (idx, TREE_STRING_LENGTH (ctor)) < 0) 1050 return build_int_cst (TREE_TYPE (t), (TREE_STRING_POINTER (ctor) 1051 [TREE_INT_CST_LOW (idx)])); 1052 return NULL_TREE; 1053 } 1054 1055 /* Whoo-hoo! I'll fold ya baby. Yeah! */ 1056 FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (ctor), cnt, cfield, cval) 1057 if (tree_int_cst_equal (cfield, idx)) 1058 return cval; 1059 break; 1060 1061 case COMPONENT_REF: 1062 /* Get a CONSTRUCTOR. If BASE is a VAR_DECL, get its 1063 DECL_INITIAL. If BASE is a nested reference into another 1064 ARRAY_REF or COMPONENT_REF, make a recursive call to resolve 1065 the inner reference. */ 1066 base = TREE_OPERAND (t, 0); 1067 switch (TREE_CODE (base)) 1068 { 1069 case VAR_DECL: 1070 if (!TREE_READONLY (base) 1071 || TREE_CODE (TREE_TYPE (base)) != RECORD_TYPE 1072 || !targetm.binds_local_p (base)) 1073 return NULL_TREE; 1074 1075 ctor = DECL_INITIAL (base); 1076 break; 1077 1078 case ARRAY_REF: 1079 case COMPONENT_REF: 1080 ctor = fold_const_aggregate_ref (base); 1081 break; 1082 1083 default: 1084 return NULL_TREE; 1085 } 1086 1087 if (ctor == NULL_TREE 1088 || TREE_CODE (ctor) != CONSTRUCTOR 1089 || !TREE_STATIC (ctor)) 1090 return NULL_TREE; 1091 1092 field = TREE_OPERAND (t, 1); 1093 1094 FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (ctor), cnt, cfield, cval) 1095 if (cfield == field 1096 /* FIXME: Handle bit-fields. */ 1097 && ! DECL_BIT_FIELD (cfield)) 1098 return cval; 1099 break; 1100 1101 case REALPART_EXPR: 1102 case IMAGPART_EXPR: 1103 { 1104 tree c = fold_const_aggregate_ref (TREE_OPERAND (t, 0)); 1105 if (c && TREE_CODE (c) == COMPLEX_CST) 1106 return fold_build1 (TREE_CODE (t), TREE_TYPE (t), c); 1107 break; 1108 } 1109 1110 default: 1111 break; 1112 } 1113 1114 return NULL_TREE; 1115 } 1116 1117 /* Evaluate statement STMT. */ 1118 1119 static prop_value_t 1120 evaluate_stmt (tree stmt) 1121 { 1122 prop_value_t val; 1123 tree simplified = NULL_TREE; 1124 ccp_lattice_t likelyvalue = likely_value (stmt); 1125 bool is_constant; 1126 1127 val.mem_ref = NULL_TREE; 1128 1129 fold_defer_overflow_warnings (); 1130 1131 /* If the statement is likely to have a CONSTANT result, then try 1132 to fold the statement to determine the constant value. */ 1133 if (likelyvalue == CONSTANT) 1134 simplified = ccp_fold (stmt); 1135 /* If the statement is likely to have a VARYING result, then do not 1136 bother folding the statement. */ 1137 if (likelyvalue == VARYING) 1138 simplified = get_rhs (stmt); 1139 /* If the statement is an ARRAY_REF or COMPONENT_REF into constant 1140 aggregates, extract the referenced constant. Otherwise the 1141 statement is likely to have an UNDEFINED value, and there will be 1142 nothing to do. Note that fold_const_aggregate_ref returns 1143 NULL_TREE if the first case does not match. */ 1144 else if (!simplified) 1145 simplified = fold_const_aggregate_ref (get_rhs (stmt)); 1146 1147 is_constant = simplified && is_gimple_min_invariant (simplified); 1148 1149 fold_undefer_overflow_warnings (is_constant, stmt, 0); 1150 1151 if (is_constant) 1152 { 1153 /* The statement produced a constant value. */ 1154 val.lattice_val = CONSTANT; 1155 val.value = simplified; 1156 } 1157 else 1158 { 1159 /* The statement produced a nonconstant value. If the statement 1160 had UNDEFINED operands, then the result of the statement 1161 should be UNDEFINED. Otherwise, the statement is VARYING. */ 1162 if (likelyvalue == UNDEFINED || likelyvalue == UNKNOWN_VAL) 1163 val.lattice_val = likelyvalue; 1164 else 1165 val.lattice_val = VARYING; 1166 1167 val.value = NULL_TREE; 1168 } 1169 1170 return val; 1171 } 1172 1173 1174 /* Visit the assignment statement STMT. Set the value of its LHS to the 1175 value computed by the RHS and store LHS in *OUTPUT_P. If STMT 1176 creates virtual definitions, set the value of each new name to that 1177 of the RHS (if we can derive a constant out of the RHS). */ 1178 1179 static enum ssa_prop_result 1180 visit_assignment (tree stmt, tree *output_p) 1181 { 1182 prop_value_t val; 1183 tree lhs, rhs; 1184 enum ssa_prop_result retval; 1185 1186 lhs = TREE_OPERAND (stmt, 0); 1187 rhs = TREE_OPERAND (stmt, 1); 1188 1189 if (TREE_CODE (rhs) == SSA_NAME) 1190 { 1191 /* For a simple copy operation, we copy the lattice values. */ 1192 prop_value_t *nval = get_value (rhs, true); 1193 val = *nval; 1194 } 1195 else if (do_store_ccp && stmt_makes_single_load (stmt)) 1196 { 1197 /* Same as above, but the RHS is not a gimple register and yet 1198 has a known VUSE. If STMT is loading from the same memory 1199 location that created the SSA_NAMEs for the virtual operands, 1200 we can propagate the value on the RHS. */ 1201 prop_value_t *nval = get_value_loaded_by (stmt, const_val); 1202 1203 if (nval && nval->mem_ref 1204 && operand_equal_p (nval->mem_ref, rhs, 0)) 1205 val = *nval; 1206 else 1207 val = evaluate_stmt (stmt); 1208 } 1209 else 1210 /* Evaluate the statement. */ 1211 val = evaluate_stmt (stmt); 1212 1213 /* If the original LHS was a VIEW_CONVERT_EXPR, modify the constant 1214 value to be a VIEW_CONVERT_EXPR of the old constant value. 1215 1216 ??? Also, if this was a definition of a bitfield, we need to widen 1217 the constant value into the type of the destination variable. This 1218 should not be necessary if GCC represented bitfields properly. */ 1219 { 1220 tree orig_lhs = TREE_OPERAND (stmt, 0); 1221 1222 if (TREE_CODE (orig_lhs) == VIEW_CONVERT_EXPR 1223 && val.lattice_val == CONSTANT) 1224 { 1225 tree w = fold_unary (VIEW_CONVERT_EXPR, 1226 TREE_TYPE (TREE_OPERAND (orig_lhs, 0)), 1227 val.value); 1228 1229 orig_lhs = TREE_OPERAND (orig_lhs, 0); 1230 if (w && is_gimple_min_invariant (w)) 1231 val.value = w; 1232 else 1233 { 1234 val.lattice_val = VARYING; 1235 val.value = NULL; 1236 } 1237 } 1238 1239 if (val.lattice_val == CONSTANT 1240 && TREE_CODE (orig_lhs) == COMPONENT_REF 1241 && DECL_BIT_FIELD (TREE_OPERAND (orig_lhs, 1))) 1242 { 1243 tree w = widen_bitfield (val.value, TREE_OPERAND (orig_lhs, 1), 1244 orig_lhs); 1245 1246 if (w && is_gimple_min_invariant (w)) 1247 val.value = w; 1248 else 1249 { 1250 val.lattice_val = VARYING; 1251 val.value = NULL_TREE; 1252 val.mem_ref = NULL_TREE; 1253 } 1254 } 1255 } 1256 1257 retval = SSA_PROP_NOT_INTERESTING; 1258 1259 /* Set the lattice value of the statement's output. */ 1260 if (TREE_CODE (lhs) == SSA_NAME) 1261 { 1262 /* If STMT is an assignment to an SSA_NAME, we only have one 1263 value to set. */ 1264 if (set_lattice_value (lhs, val)) 1265 { 1266 *output_p = lhs; 1267 if (val.lattice_val == VARYING) 1268 retval = SSA_PROP_VARYING; 1269 else 1270 retval = SSA_PROP_INTERESTING; 1271 } 1272 } 1273 else if (do_store_ccp && stmt_makes_single_store (stmt)) 1274 { 1275 /* Otherwise, set the names in V_MAY_DEF/V_MUST_DEF operands 1276 to the new constant value and mark the LHS as the memory 1277 reference associated with VAL. */ 1278 ssa_op_iter i; 1279 tree vdef; 1280 bool changed; 1281 1282 /* Stores cannot take on an UNDEFINED value. */ 1283 if (val.lattice_val == UNDEFINED) 1284 val.lattice_val = UNKNOWN_VAL; 1285 1286 /* Mark VAL as stored in the LHS of this assignment. */ 1287 val.mem_ref = lhs; 1288 1289 /* Set the value of every VDEF to VAL. */ 1290 changed = false; 1291 FOR_EACH_SSA_TREE_OPERAND (vdef, stmt, i, SSA_OP_VIRTUAL_DEFS) 1292 changed |= set_lattice_value (vdef, val); 1293 1294 /* Note that for propagation purposes, we are only interested in 1295 visiting statements that load the exact same memory reference 1296 stored here. Those statements will have the exact same list 1297 of virtual uses, so it is enough to set the output of this 1298 statement to be its first virtual definition. */ 1299 *output_p = first_vdef (stmt); 1300 if (changed) 1301 { 1302 if (val.lattice_val == VARYING) 1303 retval = SSA_PROP_VARYING; 1304 else 1305 retval = SSA_PROP_INTERESTING; 1306 } 1307 } 1308 1309 return retval; 1310 } 1311 1312 1313 /* Visit the conditional statement STMT. Return SSA_PROP_INTERESTING 1314 if it can determine which edge will be taken. Otherwise, return 1315 SSA_PROP_VARYING. */ 1316 1317 static enum ssa_prop_result 1318 visit_cond_stmt (tree stmt, edge *taken_edge_p) 1319 { 1320 prop_value_t val; 1321 basic_block block; 1322 1323 block = bb_for_stmt (stmt); 1324 val = evaluate_stmt (stmt); 1325 1326 /* Find which edge out of the conditional block will be taken and add it 1327 to the worklist. If no single edge can be determined statically, 1328 return SSA_PROP_VARYING to feed all the outgoing edges to the 1329 propagation engine. */ 1330 *taken_edge_p = val.value ? find_taken_edge (block, val.value) : 0; 1331 if (*taken_edge_p) 1332 return SSA_PROP_INTERESTING; 1333 else 1334 return SSA_PROP_VARYING; 1335 } 1336 1337 1338 /* Evaluate statement STMT. If the statement produces an output value and 1339 its evaluation changes the lattice value of its output, return 1340 SSA_PROP_INTERESTING and set *OUTPUT_P to the SSA_NAME holding the 1341 output value. 1342 1343 If STMT is a conditional branch and we can determine its truth 1344 value, set *TAKEN_EDGE_P accordingly. If STMT produces a varying 1345 value, return SSA_PROP_VARYING. */ 1346 1347 static enum ssa_prop_result 1348 ccp_visit_stmt (tree stmt, edge *taken_edge_p, tree *output_p) 1349 { 1350 tree def; 1351 ssa_op_iter iter; 1352 1353 if (dump_file && (dump_flags & TDF_DETAILS)) 1354 { 1355 fprintf (dump_file, "\nVisiting statement:\n"); 1356 print_generic_stmt (dump_file, stmt, dump_flags); 1357 fprintf (dump_file, "\n"); 1358 } 1359 1360 if (TREE_CODE (stmt) == MODIFY_EXPR) 1361 { 1362 /* If the statement is an assignment that produces a single 1363 output value, evaluate its RHS to see if the lattice value of 1364 its output has changed. */ 1365 return visit_assignment (stmt, output_p); 1366 } 1367 else if (TREE_CODE (stmt) == COND_EXPR || TREE_CODE (stmt) == SWITCH_EXPR) 1368 { 1369 /* If STMT is a conditional branch, see if we can determine 1370 which branch will be taken. */ 1371 return visit_cond_stmt (stmt, taken_edge_p); 1372 } 1373 1374 /* Any other kind of statement is not interesting for constant 1375 propagation and, therefore, not worth simulating. */ 1376 if (dump_file && (dump_flags & TDF_DETAILS)) 1377 fprintf (dump_file, "No interesting values produced. Marked VARYING.\n"); 1378 1379 /* Definitions made by statements other than assignments to 1380 SSA_NAMEs represent unknown modifications to their outputs. 1381 Mark them VARYING. */ 1382 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS) 1383 { 1384 prop_value_t v = { VARYING, NULL_TREE, NULL_TREE }; 1385 set_lattice_value (def, v); 1386 } 1387 1388 return SSA_PROP_VARYING; 1389 } 1390 1391 1392 /* Main entry point for SSA Conditional Constant Propagation. */ 1393 1394 static void 1395 execute_ssa_ccp (bool store_ccp) 1396 { 1397 do_store_ccp = store_ccp; 1398 ccp_initialize (); 1399 ssa_propagate (ccp_visit_stmt, ccp_visit_phi_node); 1400 ccp_finalize (); 1401 } 1402 1403 1404 static unsigned int 1405 do_ssa_ccp (void) 1406 { 1407 execute_ssa_ccp (false); 1408 return 0; 1409 } 1410 1411 1412 static bool 1413 gate_ccp (void) 1414 { 1415 return flag_tree_ccp != 0; 1416 } 1417 1418 1419 struct tree_opt_pass pass_ccp = 1420 { 1421 "ccp", /* name */ 1422 gate_ccp, /* gate */ 1423 do_ssa_ccp, /* execute */ 1424 NULL, /* sub */ 1425 NULL, /* next */ 1426 0, /* static_pass_number */ 1427 TV_TREE_CCP, /* tv_id */ 1428 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ 1429 0, /* properties_provided */ 1430 PROP_smt_usage, /* properties_destroyed */ 1431 0, /* todo_flags_start */ 1432 TODO_cleanup_cfg | TODO_dump_func | TODO_update_ssa 1433 | TODO_ggc_collect | TODO_verify_ssa 1434 | TODO_verify_stmts | TODO_update_smt_usage, /* todo_flags_finish */ 1435 0 /* letter */ 1436 }; 1437 1438 1439 static unsigned int 1440 do_ssa_store_ccp (void) 1441 { 1442 /* If STORE-CCP is not enabled, we just run regular CCP. */ 1443 execute_ssa_ccp (flag_tree_store_ccp != 0); 1444 return 0; 1445 } 1446 1447 static bool 1448 gate_store_ccp (void) 1449 { 1450 /* STORE-CCP is enabled only with -ftree-store-ccp, but when 1451 -fno-tree-store-ccp is specified, we should run regular CCP. 1452 That's why the pass is enabled with either flag. */ 1453 return flag_tree_store_ccp != 0 || flag_tree_ccp != 0; 1454 } 1455 1456 1457 struct tree_opt_pass pass_store_ccp = 1458 { 1459 "store_ccp", /* name */ 1460 gate_store_ccp, /* gate */ 1461 do_ssa_store_ccp, /* execute */ 1462 NULL, /* sub */ 1463 NULL, /* next */ 1464 0, /* static_pass_number */ 1465 TV_TREE_STORE_CCP, /* tv_id */ 1466 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ 1467 0, /* properties_provided */ 1468 PROP_smt_usage, /* properties_destroyed */ 1469 0, /* todo_flags_start */ 1470 TODO_dump_func | TODO_update_ssa 1471 | TODO_ggc_collect | TODO_verify_ssa 1472 | TODO_cleanup_cfg 1473 | TODO_verify_stmts | TODO_update_smt_usage, /* todo_flags_finish */ 1474 0 /* letter */ 1475 }; 1476 1477 /* Given a constant value VAL for bitfield FIELD, and a destination 1478 variable VAR, return VAL appropriately widened to fit into VAR. If 1479 FIELD is wider than HOST_WIDE_INT, NULL is returned. */ 1480 1481 tree 1482 widen_bitfield (tree val, tree field, tree var) 1483 { 1484 unsigned HOST_WIDE_INT var_size, field_size; 1485 tree wide_val; 1486 unsigned HOST_WIDE_INT mask; 1487 unsigned int i; 1488 1489 /* We can only do this if the size of the type and field and VAL are 1490 all constants representable in HOST_WIDE_INT. */ 1491 if (!host_integerp (TYPE_SIZE (TREE_TYPE (var)), 1) 1492 || !host_integerp (DECL_SIZE (field), 1) 1493 || !host_integerp (val, 0)) 1494 return NULL_TREE; 1495 1496 var_size = tree_low_cst (TYPE_SIZE (TREE_TYPE (var)), 1); 1497 field_size = tree_low_cst (DECL_SIZE (field), 1); 1498 1499 /* Give up if either the bitfield or the variable are too wide. */ 1500 if (field_size > HOST_BITS_PER_WIDE_INT || var_size > HOST_BITS_PER_WIDE_INT) 1501 return NULL_TREE; 1502 1503 gcc_assert (var_size >= field_size); 1504 1505 /* If the sign bit of the value is not set or the field's type is unsigned, 1506 just mask off the high order bits of the value. */ 1507 if (DECL_UNSIGNED (field) 1508 || !(tree_low_cst (val, 0) & (((HOST_WIDE_INT)1) << (field_size - 1)))) 1509 { 1510 /* Zero extension. Build a mask with the lower 'field_size' bits 1511 set and a BIT_AND_EXPR node to clear the high order bits of 1512 the value. */ 1513 for (i = 0, mask = 0; i < field_size; i++) 1514 mask |= ((HOST_WIDE_INT) 1) << i; 1515 1516 wide_val = fold_build2 (BIT_AND_EXPR, TREE_TYPE (var), val, 1517 build_int_cst (TREE_TYPE (var), mask)); 1518 } 1519 else 1520 { 1521 /* Sign extension. Create a mask with the upper 'field_size' 1522 bits set and a BIT_IOR_EXPR to set the high order bits of the 1523 value. */ 1524 for (i = 0, mask = 0; i < (var_size - field_size); i++) 1525 mask |= ((HOST_WIDE_INT) 1) << (var_size - i - 1); 1526 1527 wide_val = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (var), val, 1528 build_int_cst (TREE_TYPE (var), mask)); 1529 } 1530 1531 return wide_val; 1532 } 1533 1534 1535 /* A subroutine of fold_stmt_r. Attempts to fold *(A+O) to A[X]. 1536 BASE is an array type. OFFSET is a byte displacement. ORIG_TYPE 1537 is the desired result type. */ 1538 1539 static tree 1540 maybe_fold_offset_to_array_ref (tree base, tree offset, tree orig_type) 1541 { 1542 tree min_idx, idx, elt_offset = integer_zero_node; 1543 tree array_type, elt_type, elt_size; 1544 1545 /* If BASE is an ARRAY_REF, we can pick up another offset (this time 1546 measured in units of the size of elements type) from that ARRAY_REF). 1547 We can't do anything if either is variable. 1548 1549 The case we handle here is *(&A[N]+O). */ 1550 if (TREE_CODE (base) == ARRAY_REF) 1551 { 1552 tree low_bound = array_ref_low_bound (base); 1553 1554 elt_offset = TREE_OPERAND (base, 1); 1555 if (TREE_CODE (low_bound) != INTEGER_CST 1556 || TREE_CODE (elt_offset) != INTEGER_CST) 1557 return NULL_TREE; 1558 1559 elt_offset = int_const_binop (MINUS_EXPR, elt_offset, low_bound, 0); 1560 base = TREE_OPERAND (base, 0); 1561 } 1562 1563 /* Ignore stupid user tricks of indexing non-array variables. */ 1564 array_type = TREE_TYPE (base); 1565 if (TREE_CODE (array_type) != ARRAY_TYPE) 1566 return NULL_TREE; 1567 elt_type = TREE_TYPE (array_type); 1568 if (!lang_hooks.types_compatible_p (orig_type, elt_type)) 1569 return NULL_TREE; 1570 1571 /* If OFFSET and ELT_OFFSET are zero, we don't care about the size of the 1572 element type (so we can use the alignment if it's not constant). 1573 Otherwise, compute the offset as an index by using a division. If the 1574 division isn't exact, then don't do anything. */ 1575 elt_size = TYPE_SIZE_UNIT (elt_type); 1576 if (integer_zerop (offset)) 1577 { 1578 if (TREE_CODE (elt_size) != INTEGER_CST) 1579 elt_size = size_int (TYPE_ALIGN (elt_type)); 1580 1581 idx = integer_zero_node; 1582 } 1583 else 1584 { 1585 unsigned HOST_WIDE_INT lquo, lrem; 1586 HOST_WIDE_INT hquo, hrem; 1587 1588 if (TREE_CODE (elt_size) != INTEGER_CST 1589 || div_and_round_double (TRUNC_DIV_EXPR, 1, 1590 TREE_INT_CST_LOW (offset), 1591 TREE_INT_CST_HIGH (offset), 1592 TREE_INT_CST_LOW (elt_size), 1593 TREE_INT_CST_HIGH (elt_size), 1594 &lquo, &hquo, &lrem, &hrem) 1595 || lrem || hrem) 1596 return NULL_TREE; 1597 1598 idx = build_int_cst_wide (NULL_TREE, lquo, hquo); 1599 } 1600 1601 /* Assume the low bound is zero. If there is a domain type, get the 1602 low bound, if any, convert the index into that type, and add the 1603 low bound. */ 1604 min_idx = integer_zero_node; 1605 if (TYPE_DOMAIN (array_type)) 1606 { 1607 if (TYPE_MIN_VALUE (TYPE_DOMAIN (array_type))) 1608 min_idx = TYPE_MIN_VALUE (TYPE_DOMAIN (array_type)); 1609 else 1610 min_idx = fold_convert (TYPE_DOMAIN (array_type), min_idx); 1611 1612 if (TREE_CODE (min_idx) != INTEGER_CST) 1613 return NULL_TREE; 1614 1615 idx = fold_convert (TYPE_DOMAIN (array_type), idx); 1616 elt_offset = fold_convert (TYPE_DOMAIN (array_type), elt_offset); 1617 } 1618 1619 if (!integer_zerop (min_idx)) 1620 idx = int_const_binop (PLUS_EXPR, idx, min_idx, 0); 1621 if (!integer_zerop (elt_offset)) 1622 idx = int_const_binop (PLUS_EXPR, idx, elt_offset, 0); 1623 1624 return build4 (ARRAY_REF, orig_type, base, idx, min_idx, 1625 size_int (tree_low_cst (elt_size, 1) 1626 / (TYPE_ALIGN_UNIT (elt_type)))); 1627 } 1628 1629 1630 /* A subroutine of fold_stmt_r. Attempts to fold *(S+O) to S.X. 1631 BASE is a record type. OFFSET is a byte displacement. ORIG_TYPE 1632 is the desired result type. */ 1633 /* ??? This doesn't handle class inheritance. */ 1634 1635 static tree 1636 maybe_fold_offset_to_component_ref (tree record_type, tree base, tree offset, 1637 tree orig_type, bool base_is_ptr) 1638 { 1639 tree f, t, field_type, tail_array_field, field_offset; 1640 1641 if (TREE_CODE (record_type) != RECORD_TYPE 1642 && TREE_CODE (record_type) != UNION_TYPE 1643 && TREE_CODE (record_type) != QUAL_UNION_TYPE) 1644 return NULL_TREE; 1645 1646 /* Short-circuit silly cases. */ 1647 if (lang_hooks.types_compatible_p (record_type, orig_type)) 1648 return NULL_TREE; 1649 1650 tail_array_field = NULL_TREE; 1651 for (f = TYPE_FIELDS (record_type); f ; f = TREE_CHAIN (f)) 1652 { 1653 int cmp; 1654 1655 if (TREE_CODE (f) != FIELD_DECL) 1656 continue; 1657 if (DECL_BIT_FIELD (f)) 1658 continue; 1659 1660 field_offset = byte_position (f); 1661 if (TREE_CODE (field_offset) != INTEGER_CST) 1662 continue; 1663 1664 /* ??? Java creates "interesting" fields for representing base classes. 1665 They have no name, and have no context. With no context, we get into 1666 trouble with nonoverlapping_component_refs_p. Skip them. */ 1667 if (!DECL_FIELD_CONTEXT (f)) 1668 continue; 1669 1670 /* The previous array field isn't at the end. */ 1671 tail_array_field = NULL_TREE; 1672 1673 /* Check to see if this offset overlaps with the field. */ 1674 cmp = tree_int_cst_compare (field_offset, offset); 1675 if (cmp > 0) 1676 continue; 1677 1678 field_type = TREE_TYPE (f); 1679 1680 /* Here we exactly match the offset being checked. If the types match, 1681 then we can return that field. */ 1682 if (cmp == 0 1683 && lang_hooks.types_compatible_p (orig_type, field_type)) 1684 { 1685 if (base_is_ptr) 1686 base = build1 (INDIRECT_REF, record_type, base); 1687 t = build3 (COMPONENT_REF, field_type, base, f, NULL_TREE); 1688 return t; 1689 } 1690 1691 /* Don't care about offsets into the middle of scalars. */ 1692 if (!AGGREGATE_TYPE_P (field_type)) 1693 continue; 1694 1695 /* Check for array at the end of the struct. This is often 1696 used as for flexible array members. We should be able to 1697 turn this into an array access anyway. */ 1698 if (TREE_CODE (field_type) == ARRAY_TYPE) 1699 tail_array_field = f; 1700 1701 /* Check the end of the field against the offset. */ 1702 if (!DECL_SIZE_UNIT (f) 1703 || TREE_CODE (DECL_SIZE_UNIT (f)) != INTEGER_CST) 1704 continue; 1705 t = int_const_binop (MINUS_EXPR, offset, field_offset, 1); 1706 if (!tree_int_cst_lt (t, DECL_SIZE_UNIT (f))) 1707 continue; 1708 1709 /* If we matched, then set offset to the displacement into 1710 this field. */ 1711 offset = t; 1712 goto found; 1713 } 1714 1715 if (!tail_array_field) 1716 return NULL_TREE; 1717 1718 f = tail_array_field; 1719 field_type = TREE_TYPE (f); 1720 offset = int_const_binop (MINUS_EXPR, offset, byte_position (f), 1); 1721 1722 found: 1723 /* If we get here, we've got an aggregate field, and a possibly 1724 nonzero offset into them. Recurse and hope for a valid match. */ 1725 if (base_is_ptr) 1726 base = build1 (INDIRECT_REF, record_type, base); 1727 base = build3 (COMPONENT_REF, field_type, base, f, NULL_TREE); 1728 1729 t = maybe_fold_offset_to_array_ref (base, offset, orig_type); 1730 if (t) 1731 return t; 1732 return maybe_fold_offset_to_component_ref (field_type, base, offset, 1733 orig_type, false); 1734 } 1735 1736 1737 /* A subroutine of fold_stmt_r. Attempt to simplify *(BASE+OFFSET). 1738 Return the simplified expression, or NULL if nothing could be done. */ 1739 1740 static tree 1741 maybe_fold_stmt_indirect (tree expr, tree base, tree offset) 1742 { 1743 tree t; 1744 1745 /* We may well have constructed a double-nested PLUS_EXPR via multiple 1746 substitutions. Fold that down to one. Remove NON_LVALUE_EXPRs that 1747 are sometimes added. */ 1748 base = fold (base); 1749 STRIP_TYPE_NOPS (base); 1750 TREE_OPERAND (expr, 0) = base; 1751 1752 /* One possibility is that the address reduces to a string constant. */ 1753 t = fold_read_from_constant_string (expr); 1754 if (t) 1755 return t; 1756 1757 /* Add in any offset from a PLUS_EXPR. */ 1758 if (TREE_CODE (base) == PLUS_EXPR) 1759 { 1760 tree offset2; 1761 1762 offset2 = TREE_OPERAND (base, 1); 1763 if (TREE_CODE (offset2) != INTEGER_CST) 1764 return NULL_TREE; 1765 base = TREE_OPERAND (base, 0); 1766 1767 offset = int_const_binop (PLUS_EXPR, offset, offset2, 1); 1768 } 1769 1770 if (TREE_CODE (base) == ADDR_EXPR) 1771 { 1772 /* Strip the ADDR_EXPR. */ 1773 base = TREE_OPERAND (base, 0); 1774 1775 /* Fold away CONST_DECL to its value, if the type is scalar. */ 1776 if (TREE_CODE (base) == CONST_DECL 1777 && ccp_decl_initial_min_invariant (DECL_INITIAL (base))) 1778 return DECL_INITIAL (base); 1779 1780 /* Try folding *(&B+O) to B[X]. */ 1781 t = maybe_fold_offset_to_array_ref (base, offset, TREE_TYPE (expr)); 1782 if (t) 1783 return t; 1784 1785 /* Try folding *(&B+O) to B.X. */ 1786 t = maybe_fold_offset_to_component_ref (TREE_TYPE (base), base, offset, 1787 TREE_TYPE (expr), false); 1788 if (t) 1789 return t; 1790 1791 /* Fold *&B to B. We can only do this if EXPR is the same type 1792 as BASE. We can't do this if EXPR is the element type of an array 1793 and BASE is the array. */ 1794 if (integer_zerop (offset) 1795 && lang_hooks.types_compatible_p (TREE_TYPE (base), 1796 TREE_TYPE (expr))) 1797 return base; 1798 } 1799 else 1800 { 1801 /* We can get here for out-of-range string constant accesses, 1802 such as "_"[3]. Bail out of the entire substitution search 1803 and arrange for the entire statement to be replaced by a 1804 call to __builtin_trap. In all likelihood this will all be 1805 constant-folded away, but in the meantime we can't leave with 1806 something that get_expr_operands can't understand. */ 1807 1808 t = base; 1809 STRIP_NOPS (t); 1810 if (TREE_CODE (t) == ADDR_EXPR 1811 && TREE_CODE (TREE_OPERAND (t, 0)) == STRING_CST) 1812 { 1813 /* FIXME: Except that this causes problems elsewhere with dead 1814 code not being deleted, and we die in the rtl expanders 1815 because we failed to remove some ssa_name. In the meantime, 1816 just return zero. */ 1817 /* FIXME2: This condition should be signaled by 1818 fold_read_from_constant_string directly, rather than 1819 re-checking for it here. */ 1820 return integer_zero_node; 1821 } 1822 1823 /* Try folding *(B+O) to B->X. Still an improvement. */ 1824 if (POINTER_TYPE_P (TREE_TYPE (base))) 1825 { 1826 t = maybe_fold_offset_to_component_ref (TREE_TYPE (TREE_TYPE (base)), 1827 base, offset, 1828 TREE_TYPE (expr), true); 1829 if (t) 1830 return t; 1831 } 1832 } 1833 1834 /* Otherwise we had an offset that we could not simplify. */ 1835 return NULL_TREE; 1836 } 1837 1838 1839 /* A subroutine of fold_stmt_r. EXPR is a PLUS_EXPR. 1840 1841 A quaint feature extant in our address arithmetic is that there 1842 can be hidden type changes here. The type of the result need 1843 not be the same as the type of the input pointer. 1844 1845 What we're after here is an expression of the form 1846 (T *)(&array + const) 1847 where the cast doesn't actually exist, but is implicit in the 1848 type of the PLUS_EXPR. We'd like to turn this into 1849 &array[x] 1850 which may be able to propagate further. */ 1851 1852 static tree 1853 maybe_fold_stmt_addition (tree expr) 1854 { 1855 tree op0 = TREE_OPERAND (expr, 0); 1856 tree op1 = TREE_OPERAND (expr, 1); 1857 tree ptr_type = TREE_TYPE (expr); 1858 tree ptd_type; 1859 tree t; 1860 bool subtract = (TREE_CODE (expr) == MINUS_EXPR); 1861 1862 /* We're only interested in pointer arithmetic. */ 1863 if (!POINTER_TYPE_P (ptr_type)) 1864 return NULL_TREE; 1865 /* Canonicalize the integral operand to op1. */ 1866 if (INTEGRAL_TYPE_P (TREE_TYPE (op0))) 1867 { 1868 if (subtract) 1869 return NULL_TREE; 1870 t = op0, op0 = op1, op1 = t; 1871 } 1872 /* It had better be a constant. */ 1873 if (TREE_CODE (op1) != INTEGER_CST) 1874 return NULL_TREE; 1875 /* The first operand should be an ADDR_EXPR. */ 1876 if (TREE_CODE (op0) != ADDR_EXPR) 1877 return NULL_TREE; 1878 op0 = TREE_OPERAND (op0, 0); 1879 1880 /* If the first operand is an ARRAY_REF, expand it so that we can fold 1881 the offset into it. */ 1882 while (TREE_CODE (op0) == ARRAY_REF) 1883 { 1884 tree array_obj = TREE_OPERAND (op0, 0); 1885 tree array_idx = TREE_OPERAND (op0, 1); 1886 tree elt_type = TREE_TYPE (op0); 1887 tree elt_size = TYPE_SIZE_UNIT (elt_type); 1888 tree min_idx; 1889 1890 if (TREE_CODE (array_idx) != INTEGER_CST) 1891 break; 1892 if (TREE_CODE (elt_size) != INTEGER_CST) 1893 break; 1894 1895 /* Un-bias the index by the min index of the array type. */ 1896 min_idx = TYPE_DOMAIN (TREE_TYPE (array_obj)); 1897 if (min_idx) 1898 { 1899 min_idx = TYPE_MIN_VALUE (min_idx); 1900 if (min_idx) 1901 { 1902 if (TREE_CODE (min_idx) != INTEGER_CST) 1903 break; 1904 1905 array_idx = fold_convert (TREE_TYPE (min_idx), array_idx); 1906 if (!integer_zerop (min_idx)) 1907 array_idx = int_const_binop (MINUS_EXPR, array_idx, 1908 min_idx, 0); 1909 } 1910 } 1911 1912 /* Convert the index to a byte offset. */ 1913 array_idx = fold_convert (sizetype, array_idx); 1914 array_idx = int_const_binop (MULT_EXPR, array_idx, elt_size, 0); 1915 1916 /* Update the operands for the next round, or for folding. */ 1917 /* If we're manipulating unsigned types, then folding into negative 1918 values can produce incorrect results. Particularly if the type 1919 is smaller than the width of the pointer. */ 1920 if (subtract 1921 && TYPE_UNSIGNED (TREE_TYPE (op1)) 1922 && tree_int_cst_lt (array_idx, op1)) 1923 return NULL; 1924 op1 = int_const_binop (subtract ? MINUS_EXPR : PLUS_EXPR, 1925 array_idx, op1, 0); 1926 subtract = false; 1927 op0 = array_obj; 1928 } 1929 1930 /* If we weren't able to fold the subtraction into another array reference, 1931 canonicalize the integer for passing to the array and component ref 1932 simplification functions. */ 1933 if (subtract) 1934 { 1935 if (TYPE_UNSIGNED (TREE_TYPE (op1))) 1936 return NULL; 1937 op1 = fold_unary (NEGATE_EXPR, TREE_TYPE (op1), op1); 1938 /* ??? In theory fold should always produce another integer. */ 1939 if (op1 == NULL || TREE_CODE (op1) != INTEGER_CST) 1940 return NULL; 1941 } 1942 1943 ptd_type = TREE_TYPE (ptr_type); 1944 1945 /* At which point we can try some of the same things as for indirects. */ 1946 t = maybe_fold_offset_to_array_ref (op0, op1, ptd_type); 1947 if (!t) 1948 t = maybe_fold_offset_to_component_ref (TREE_TYPE (op0), op0, op1, 1949 ptd_type, false); 1950 if (t) 1951 t = build1 (ADDR_EXPR, ptr_type, t); 1952 1953 return t; 1954 } 1955 1956 /* For passing state through walk_tree into fold_stmt_r and its 1957 children. */ 1958 1959 struct fold_stmt_r_data 1960 { 1961 tree stmt; 1962 bool *changed_p; 1963 bool *inside_addr_expr_p; 1964 }; 1965 1966 /* Subroutine of fold_stmt called via walk_tree. We perform several 1967 simplifications of EXPR_P, mostly having to do with pointer arithmetic. */ 1968 1969 static tree 1970 fold_stmt_r (tree *expr_p, int *walk_subtrees, void *data) 1971 { 1972 struct fold_stmt_r_data *fold_stmt_r_data = (struct fold_stmt_r_data *) data; 1973 bool *inside_addr_expr_p = fold_stmt_r_data->inside_addr_expr_p; 1974 bool *changed_p = fold_stmt_r_data->changed_p; 1975 tree expr = *expr_p, t; 1976 1977 /* ??? It'd be nice if walk_tree had a pre-order option. */ 1978 switch (TREE_CODE (expr)) 1979 { 1980 case INDIRECT_REF: 1981 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); 1982 if (t) 1983 return t; 1984 *walk_subtrees = 0; 1985 1986 t = maybe_fold_stmt_indirect (expr, TREE_OPERAND (expr, 0), 1987 integer_zero_node); 1988 break; 1989 1990 /* ??? Could handle more ARRAY_REFs here, as a variant of INDIRECT_REF. 1991 We'd only want to bother decomposing an existing ARRAY_REF if 1992 the base array is found to have another offset contained within. 1993 Otherwise we'd be wasting time. */ 1994 case ARRAY_REF: 1995 /* If we are not processing expressions found within an 1996 ADDR_EXPR, then we can fold constant array references. */ 1997 if (!*inside_addr_expr_p) 1998 t = fold_read_from_constant_string (expr); 1999 else 2000 t = NULL; 2001 break; 2002 2003 case ADDR_EXPR: 2004 *inside_addr_expr_p = true; 2005 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); 2006 *inside_addr_expr_p = false; 2007 if (t) 2008 return t; 2009 *walk_subtrees = 0; 2010 2011 /* Set TREE_INVARIANT properly so that the value is properly 2012 considered constant, and so gets propagated as expected. */ 2013 if (*changed_p) 2014 recompute_tree_invariant_for_addr_expr (expr); 2015 return NULL_TREE; 2016 2017 case PLUS_EXPR: 2018 case MINUS_EXPR: 2019 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); 2020 if (t) 2021 return t; 2022 t = walk_tree (&TREE_OPERAND (expr, 1), fold_stmt_r, data, NULL); 2023 if (t) 2024 return t; 2025 *walk_subtrees = 0; 2026 2027 t = maybe_fold_stmt_addition (expr); 2028 break; 2029 2030 case COMPONENT_REF: 2031 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); 2032 if (t) 2033 return t; 2034 *walk_subtrees = 0; 2035 2036 /* Make sure the FIELD_DECL is actually a field in the type on the lhs. 2037 We've already checked that the records are compatible, so we should 2038 come up with a set of compatible fields. */ 2039 { 2040 tree expr_record = TREE_TYPE (TREE_OPERAND (expr, 0)); 2041 tree expr_field = TREE_OPERAND (expr, 1); 2042 2043 if (DECL_FIELD_CONTEXT (expr_field) != TYPE_MAIN_VARIANT (expr_record)) 2044 { 2045 expr_field = find_compatible_field (expr_record, expr_field); 2046 TREE_OPERAND (expr, 1) = expr_field; 2047 } 2048 } 2049 break; 2050 2051 case TARGET_MEM_REF: 2052 t = maybe_fold_tmr (expr); 2053 break; 2054 2055 case COND_EXPR: 2056 if (COMPARISON_CLASS_P (TREE_OPERAND (expr, 0))) 2057 { 2058 tree op0 = TREE_OPERAND (expr, 0); 2059 tree tem; 2060 bool set; 2061 2062 fold_defer_overflow_warnings (); 2063 tem = fold_binary (TREE_CODE (op0), TREE_TYPE (op0), 2064 TREE_OPERAND (op0, 0), 2065 TREE_OPERAND (op0, 1)); 2066 set = tem && is_gimple_condexpr (tem); 2067 fold_undefer_overflow_warnings (set, fold_stmt_r_data->stmt, 0); 2068 if (set) 2069 TREE_OPERAND (expr, 0) = tem; 2070 t = expr; 2071 break; 2072 } 2073 2074 default: 2075 return NULL_TREE; 2076 } 2077 2078 if (t) 2079 { 2080 *expr_p = t; 2081 *changed_p = true; 2082 } 2083 2084 return NULL_TREE; 2085 } 2086 2087 2088 /* Return the string length, maximum string length or maximum value of 2089 ARG in LENGTH. 2090 If ARG is an SSA name variable, follow its use-def chains. If LENGTH 2091 is not NULL and, for TYPE == 0, its value is not equal to the length 2092 we determine or if we are unable to determine the length or value, 2093 return false. VISITED is a bitmap of visited variables. 2094 TYPE is 0 if string length should be returned, 1 for maximum string 2095 length and 2 for maximum value ARG can have. */ 2096 2097 static bool 2098 get_maxval_strlen (tree arg, tree *length, bitmap visited, int type) 2099 { 2100 tree var, def_stmt, val; 2101 2102 if (TREE_CODE (arg) != SSA_NAME) 2103 { 2104 if (type == 2) 2105 { 2106 val = arg; 2107 if (TREE_CODE (val) != INTEGER_CST 2108 || tree_int_cst_sgn (val) < 0) 2109 return false; 2110 } 2111 else 2112 val = c_strlen (arg, 1); 2113 if (!val) 2114 return false; 2115 2116 if (*length) 2117 { 2118 if (type > 0) 2119 { 2120 if (TREE_CODE (*length) != INTEGER_CST 2121 || TREE_CODE (val) != INTEGER_CST) 2122 return false; 2123 2124 if (tree_int_cst_lt (*length, val)) 2125 *length = val; 2126 return true; 2127 } 2128 else if (simple_cst_equal (val, *length) != 1) 2129 return false; 2130 } 2131 2132 *length = val; 2133 return true; 2134 } 2135 2136 /* If we were already here, break the infinite cycle. */ 2137 if (bitmap_bit_p (visited, SSA_NAME_VERSION (arg))) 2138 return true; 2139 bitmap_set_bit (visited, SSA_NAME_VERSION (arg)); 2140 2141 var = arg; 2142 def_stmt = SSA_NAME_DEF_STMT (var); 2143 2144 switch (TREE_CODE (def_stmt)) 2145 { 2146 case MODIFY_EXPR: 2147 { 2148 tree rhs; 2149 2150 /* The RHS of the statement defining VAR must either have a 2151 constant length or come from another SSA_NAME with a constant 2152 length. */ 2153 rhs = TREE_OPERAND (def_stmt, 1); 2154 STRIP_NOPS (rhs); 2155 return get_maxval_strlen (rhs, length, visited, type); 2156 } 2157 2158 case PHI_NODE: 2159 { 2160 /* All the arguments of the PHI node must have the same constant 2161 length. */ 2162 int i; 2163 2164 for (i = 0; i < PHI_NUM_ARGS (def_stmt); i++) 2165 { 2166 tree arg = PHI_ARG_DEF (def_stmt, i); 2167 2168 /* If this PHI has itself as an argument, we cannot 2169 determine the string length of this argument. However, 2170 if we can find a constant string length for the other 2171 PHI args then we can still be sure that this is a 2172 constant string length. So be optimistic and just 2173 continue with the next argument. */ 2174 if (arg == PHI_RESULT (def_stmt)) 2175 continue; 2176 2177 if (!get_maxval_strlen (arg, length, visited, type)) 2178 return false; 2179 } 2180 2181 return true; 2182 } 2183 2184 default: 2185 break; 2186 } 2187 2188 2189 return false; 2190 } 2191 2192 2193 /* Fold builtin call FN in statement STMT. If it cannot be folded into a 2194 constant, return NULL_TREE. Otherwise, return its constant value. */ 2195 2196 static tree 2197 ccp_fold_builtin (tree stmt, tree fn) 2198 { 2199 tree result, val[3]; 2200 tree callee, arglist, a; 2201 int arg_mask, i, type; 2202 bitmap visited; 2203 bool ignore; 2204 2205 ignore = TREE_CODE (stmt) != MODIFY_EXPR; 2206 2207 /* First try the generic builtin folder. If that succeeds, return the 2208 result directly. */ 2209 callee = get_callee_fndecl (fn); 2210 arglist = TREE_OPERAND (fn, 1); 2211 result = fold_builtin (callee, arglist, ignore); 2212 if (result) 2213 { 2214 if (ignore) 2215 STRIP_NOPS (result); 2216 return result; 2217 } 2218 2219 /* Ignore MD builtins. */ 2220 if (DECL_BUILT_IN_CLASS (callee) == BUILT_IN_MD) 2221 return NULL_TREE; 2222 2223 /* If the builtin could not be folded, and it has no argument list, 2224 we're done. */ 2225 if (!arglist) 2226 return NULL_TREE; 2227 2228 /* Limit the work only for builtins we know how to simplify. */ 2229 switch (DECL_FUNCTION_CODE (callee)) 2230 { 2231 case BUILT_IN_STRLEN: 2232 case BUILT_IN_FPUTS: 2233 case BUILT_IN_FPUTS_UNLOCKED: 2234 arg_mask = 1; 2235 type = 0; 2236 break; 2237 case BUILT_IN_STRCPY: 2238 case BUILT_IN_STRNCPY: 2239 arg_mask = 2; 2240 type = 0; 2241 break; 2242 case BUILT_IN_MEMCPY_CHK: 2243 case BUILT_IN_MEMPCPY_CHK: 2244 case BUILT_IN_MEMMOVE_CHK: 2245 case BUILT_IN_MEMSET_CHK: 2246 case BUILT_IN_STRNCPY_CHK: 2247 arg_mask = 4; 2248 type = 2; 2249 break; 2250 case BUILT_IN_STRCPY_CHK: 2251 case BUILT_IN_STPCPY_CHK: 2252 arg_mask = 2; 2253 type = 1; 2254 break; 2255 case BUILT_IN_SNPRINTF_CHK: 2256 case BUILT_IN_VSNPRINTF_CHK: 2257 arg_mask = 2; 2258 type = 2; 2259 break; 2260 default: 2261 return NULL_TREE; 2262 } 2263 2264 /* Try to use the dataflow information gathered by the CCP process. */ 2265 visited = BITMAP_ALLOC (NULL); 2266 2267 memset (val, 0, sizeof (val)); 2268 for (i = 0, a = arglist; 2269 arg_mask; 2270 i++, arg_mask >>= 1, a = TREE_CHAIN (a)) 2271 if (arg_mask & 1) 2272 { 2273 bitmap_clear (visited); 2274 if (!get_maxval_strlen (TREE_VALUE (a), &val[i], visited, type)) 2275 val[i] = NULL_TREE; 2276 } 2277 2278 BITMAP_FREE (visited); 2279 2280 result = NULL_TREE; 2281 switch (DECL_FUNCTION_CODE (callee)) 2282 { 2283 case BUILT_IN_STRLEN: 2284 if (val[0]) 2285 { 2286 tree new = fold_convert (TREE_TYPE (fn), val[0]); 2287 2288 /* If the result is not a valid gimple value, or not a cast 2289 of a valid gimple value, then we can not use the result. */ 2290 if (is_gimple_val (new) 2291 || (is_gimple_cast (new) 2292 && is_gimple_val (TREE_OPERAND (new, 0)))) 2293 return new; 2294 } 2295 break; 2296 2297 case BUILT_IN_STRCPY: 2298 if (val[1] && is_gimple_val (val[1])) 2299 result = fold_builtin_strcpy (callee, arglist, val[1]); 2300 break; 2301 2302 case BUILT_IN_STRNCPY: 2303 if (val[1] && is_gimple_val (val[1])) 2304 result = fold_builtin_strncpy (callee, arglist, val[1]); 2305 break; 2306 2307 case BUILT_IN_FPUTS: 2308 result = fold_builtin_fputs (arglist, 2309 TREE_CODE (stmt) != MODIFY_EXPR, 0, 2310 val[0]); 2311 break; 2312 2313 case BUILT_IN_FPUTS_UNLOCKED: 2314 result = fold_builtin_fputs (arglist, 2315 TREE_CODE (stmt) != MODIFY_EXPR, 1, 2316 val[0]); 2317 break; 2318 2319 case BUILT_IN_MEMCPY_CHK: 2320 case BUILT_IN_MEMPCPY_CHK: 2321 case BUILT_IN_MEMMOVE_CHK: 2322 case BUILT_IN_MEMSET_CHK: 2323 if (val[2] && is_gimple_val (val[2])) 2324 result = fold_builtin_memory_chk (callee, arglist, val[2], ignore, 2325 DECL_FUNCTION_CODE (callee)); 2326 break; 2327 2328 case BUILT_IN_STRCPY_CHK: 2329 case BUILT_IN_STPCPY_CHK: 2330 if (val[1] && is_gimple_val (val[1])) 2331 result = fold_builtin_stxcpy_chk (callee, arglist, val[1], ignore, 2332 DECL_FUNCTION_CODE (callee)); 2333 break; 2334 2335 case BUILT_IN_STRNCPY_CHK: 2336 if (val[2] && is_gimple_val (val[2])) 2337 result = fold_builtin_strncpy_chk (arglist, val[2]); 2338 break; 2339 2340 case BUILT_IN_SNPRINTF_CHK: 2341 case BUILT_IN_VSNPRINTF_CHK: 2342 if (val[1] && is_gimple_val (val[1])) 2343 result = fold_builtin_snprintf_chk (arglist, val[1], 2344 DECL_FUNCTION_CODE (callee)); 2345 break; 2346 2347 default: 2348 gcc_unreachable (); 2349 } 2350 2351 if (result && ignore) 2352 result = fold_ignored_result (result); 2353 return result; 2354 } 2355 2356 2357 /* Fold the statement pointed to by STMT_P. In some cases, this function may 2358 replace the whole statement with a new one. Returns true iff folding 2359 makes any changes. */ 2360 2361 bool 2362 fold_stmt (tree *stmt_p) 2363 { 2364 tree rhs, result, stmt; 2365 struct fold_stmt_r_data fold_stmt_r_data; 2366 bool changed = false; 2367 bool inside_addr_expr = false; 2368 2369 stmt = *stmt_p; 2370 2371 fold_stmt_r_data.stmt = stmt; 2372 fold_stmt_r_data.changed_p = &changed; 2373 fold_stmt_r_data.inside_addr_expr_p = &inside_addr_expr; 2374 2375 /* If we replaced constants and the statement makes pointer dereferences, 2376 then we may need to fold instances of *&VAR into VAR, etc. */ 2377 if (walk_tree (stmt_p, fold_stmt_r, &fold_stmt_r_data, NULL)) 2378 { 2379 *stmt_p 2380 = build_function_call_expr (implicit_built_in_decls[BUILT_IN_TRAP], 2381 NULL); 2382 return true; 2383 } 2384 2385 rhs = get_rhs (stmt); 2386 if (!rhs) 2387 return changed; 2388 result = NULL_TREE; 2389 2390 if (TREE_CODE (rhs) == CALL_EXPR) 2391 { 2392 tree callee; 2393 2394 /* Check for builtins that CCP can handle using information not 2395 available in the generic fold routines. */ 2396 callee = get_callee_fndecl (rhs); 2397 if (callee && DECL_BUILT_IN (callee)) 2398 result = ccp_fold_builtin (stmt, rhs); 2399 else 2400 { 2401 /* Check for resolvable OBJ_TYPE_REF. The only sorts we can resolve 2402 here are when we've propagated the address of a decl into the 2403 object slot. */ 2404 /* ??? Should perhaps do this in fold proper. However, doing it 2405 there requires that we create a new CALL_EXPR, and that requires 2406 copying EH region info to the new node. Easier to just do it 2407 here where we can just smash the call operand. Also 2408 CALL_EXPR_RETURN_SLOT_OPT needs to be handled correctly and 2409 copied, fold_ternary does not have not information. */ 2410 callee = TREE_OPERAND (rhs, 0); 2411 if (TREE_CODE (callee) == OBJ_TYPE_REF 2412 && lang_hooks.fold_obj_type_ref 2413 && TREE_CODE (OBJ_TYPE_REF_OBJECT (callee)) == ADDR_EXPR 2414 && DECL_P (TREE_OPERAND 2415 (OBJ_TYPE_REF_OBJECT (callee), 0))) 2416 { 2417 tree t; 2418 2419 /* ??? Caution: Broken ADDR_EXPR semantics means that 2420 looking at the type of the operand of the addr_expr 2421 can yield an array type. See silly exception in 2422 check_pointer_types_r. */ 2423 2424 t = TREE_TYPE (TREE_TYPE (OBJ_TYPE_REF_OBJECT (callee))); 2425 t = lang_hooks.fold_obj_type_ref (callee, t); 2426 if (t) 2427 { 2428 TREE_OPERAND (rhs, 0) = t; 2429 changed = true; 2430 } 2431 } 2432 } 2433 } 2434 2435 /* If we couldn't fold the RHS, hand over to the generic fold routines. */ 2436 if (result == NULL_TREE) 2437 result = fold (rhs); 2438 2439 /* Strip away useless type conversions. Both the NON_LVALUE_EXPR that 2440 may have been added by fold, and "useless" type conversions that might 2441 now be apparent due to propagation. */ 2442 STRIP_USELESS_TYPE_CONVERSION (result); 2443 2444 if (result != rhs) 2445 changed |= set_rhs (stmt_p, result); 2446 2447 return changed; 2448 } 2449 2450 /* Perform the minimal folding on statement STMT. Only operations like 2451 *&x created by constant propagation are handled. The statement cannot 2452 be replaced with a new one. */ 2453 2454 bool 2455 fold_stmt_inplace (tree stmt) 2456 { 2457 tree old_stmt = stmt, rhs, new_rhs; 2458 struct fold_stmt_r_data fold_stmt_r_data; 2459 bool changed = false; 2460 bool inside_addr_expr = false; 2461 2462 fold_stmt_r_data.stmt = stmt; 2463 fold_stmt_r_data.changed_p = &changed; 2464 fold_stmt_r_data.inside_addr_expr_p = &inside_addr_expr; 2465 2466 walk_tree (&stmt, fold_stmt_r, &fold_stmt_r_data, NULL); 2467 gcc_assert (stmt == old_stmt); 2468 2469 rhs = get_rhs (stmt); 2470 if (!rhs || rhs == stmt) 2471 return changed; 2472 2473 new_rhs = fold (rhs); 2474 STRIP_USELESS_TYPE_CONVERSION (new_rhs); 2475 if (new_rhs == rhs) 2476 return changed; 2477 2478 changed |= set_rhs (&stmt, new_rhs); 2479 gcc_assert (stmt == old_stmt); 2480 2481 return changed; 2482 } 2483 2484 /* Convert EXPR into a GIMPLE value suitable for substitution on the 2485 RHS of an assignment. Insert the necessary statements before 2486 iterator *SI_P. */ 2487 2488 static tree 2489 convert_to_gimple_builtin (block_stmt_iterator *si_p, tree expr) 2490 { 2491 tree_stmt_iterator ti; 2492 tree stmt = bsi_stmt (*si_p); 2493 tree tmp, stmts = NULL; 2494 2495 push_gimplify_context (); 2496 tmp = get_initialized_tmp_var (expr, &stmts, NULL); 2497 pop_gimplify_context (NULL); 2498 2499 if (EXPR_HAS_LOCATION (stmt)) 2500 annotate_all_with_locus (&stmts, EXPR_LOCATION (stmt)); 2501 2502 /* The replacement can expose previously unreferenced variables. */ 2503 for (ti = tsi_start (stmts); !tsi_end_p (ti); tsi_next (&ti)) 2504 { 2505 tree new_stmt = tsi_stmt (ti); 2506 find_new_referenced_vars (tsi_stmt_ptr (ti)); 2507 bsi_insert_before (si_p, new_stmt, BSI_NEW_STMT); 2508 mark_new_vars_to_rename (bsi_stmt (*si_p)); 2509 bsi_next (si_p); 2510 } 2511 2512 return tmp; 2513 } 2514 2515 2516 /* A simple pass that attempts to fold all builtin functions. This pass 2517 is run after we've propagated as many constants as we can. */ 2518 2519 static unsigned int 2520 execute_fold_all_builtins (void) 2521 { 2522 bool cfg_changed = false; 2523 basic_block bb; 2524 FOR_EACH_BB (bb) 2525 { 2526 block_stmt_iterator i; 2527 for (i = bsi_start (bb); !bsi_end_p (i); ) 2528 { 2529 tree *stmtp = bsi_stmt_ptr (i); 2530 tree old_stmt = *stmtp; 2531 tree call = get_rhs (*stmtp); 2532 tree callee, result; 2533 enum built_in_function fcode; 2534 2535 if (!call || TREE_CODE (call) != CALL_EXPR) 2536 { 2537 bsi_next (&i); 2538 continue; 2539 } 2540 callee = get_callee_fndecl (call); 2541 if (!callee || DECL_BUILT_IN_CLASS (callee) != BUILT_IN_NORMAL) 2542 { 2543 bsi_next (&i); 2544 continue; 2545 } 2546 fcode = DECL_FUNCTION_CODE (callee); 2547 2548 result = ccp_fold_builtin (*stmtp, call); 2549 if (!result) 2550 switch (DECL_FUNCTION_CODE (callee)) 2551 { 2552 case BUILT_IN_CONSTANT_P: 2553 /* Resolve __builtin_constant_p. If it hasn't been 2554 folded to integer_one_node by now, it's fairly 2555 certain that the value simply isn't constant. */ 2556 result = integer_zero_node; 2557 break; 2558 2559 default: 2560 bsi_next (&i); 2561 continue; 2562 } 2563 2564 if (dump_file && (dump_flags & TDF_DETAILS)) 2565 { 2566 fprintf (dump_file, "Simplified\n "); 2567 print_generic_stmt (dump_file, *stmtp, dump_flags); 2568 } 2569 2570 if (!set_rhs (stmtp, result)) 2571 { 2572 result = convert_to_gimple_builtin (&i, result); 2573 if (result) 2574 { 2575 bool ok = set_rhs (stmtp, result); 2576 2577 gcc_assert (ok); 2578 } 2579 } 2580 mark_new_vars_to_rename (*stmtp); 2581 if (maybe_clean_or_replace_eh_stmt (old_stmt, *stmtp) 2582 && tree_purge_dead_eh_edges (bb)) 2583 cfg_changed = true; 2584 2585 if (dump_file && (dump_flags & TDF_DETAILS)) 2586 { 2587 fprintf (dump_file, "to\n "); 2588 print_generic_stmt (dump_file, *stmtp, dump_flags); 2589 fprintf (dump_file, "\n"); 2590 } 2591 2592 /* Retry the same statement if it changed into another 2593 builtin, there might be new opportunities now. */ 2594 call = get_rhs (*stmtp); 2595 if (!call || TREE_CODE (call) != CALL_EXPR) 2596 { 2597 bsi_next (&i); 2598 continue; 2599 } 2600 callee = get_callee_fndecl (call); 2601 if (!callee 2602 || DECL_BUILT_IN_CLASS (callee) != BUILT_IN_NORMAL 2603 || DECL_FUNCTION_CODE (callee) == fcode) 2604 bsi_next (&i); 2605 } 2606 } 2607 2608 /* Delete unreachable blocks. */ 2609 if (cfg_changed) 2610 cleanup_tree_cfg (); 2611 return 0; 2612 } 2613 2614 2615 struct tree_opt_pass pass_fold_builtins = 2616 { 2617 "fab", /* name */ 2618 NULL, /* gate */ 2619 execute_fold_all_builtins, /* execute */ 2620 NULL, /* sub */ 2621 NULL, /* next */ 2622 0, /* static_pass_number */ 2623 0, /* tv_id */ 2624 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ 2625 0, /* properties_provided */ 2626 0, /* properties_destroyed */ 2627 0, /* todo_flags_start */ 2628 TODO_dump_func 2629 | TODO_verify_ssa 2630 | TODO_update_ssa, /* todo_flags_finish */ 2631 0 /* letter */ 2632 }; 2633