1/* Tail call optimization on trees. 2 Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc. 3 4This file is part of GCC. 5 6GCC is free software; you can redistribute it and/or modify 7it under the terms of the GNU General Public License as published by 8the Free Software Foundation; either version 2, or (at your option) 9any later version. 10 11GCC is distributed in the hope that it will be useful, 12but WITHOUT ANY WARRANTY; without even the implied warranty of 13MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14GNU General Public License for more details. 15 16You should have received a copy of the GNU General Public License 17along with GCC; see the file COPYING. If not, write to 18the Free Software Foundation, 51 Franklin Street, Fifth Floor, 19Boston, MA 02110-1301, USA. */ 20 21#include "config.h" 22#include "system.h" 23#include "coretypes.h" 24#include "tm.h" 25#include "tree.h" 26#include "rtl.h" 27#include "tm_p.h" 28#include "hard-reg-set.h" 29#include "basic-block.h" 30#include "function.h" 31#include "tree-flow.h" 32#include "tree-dump.h" 33#include "diagnostic.h" 34#include "except.h" 35#include "tree-pass.h" 36#include "flags.h" 37#include "langhooks.h" 38 39/* The file implements the tail recursion elimination. It is also used to 40 analyze the tail calls in general, passing the results to the rtl level 41 where they are used for sibcall optimization. 42 43 In addition to the standard tail recursion elimination, we handle the most 44 trivial cases of making the call tail recursive by creating accumulators. 45 For example the following function 46 47 int sum (int n) 48 { 49 if (n > 0) 50 return n + sum (n - 1); 51 else 52 return 0; 53 } 54 55 is transformed into 56 57 int sum (int n) 58 { 59 int acc = 0; 60 61 while (n > 0) 62 acc += n--; 63 64 return acc; 65 } 66 67 To do this, we maintain two accumulators (a_acc and m_acc) that indicate 68 when we reach the return x statement, we should return a_acc + x * m_acc 69 instead. They are initially initialized to 0 and 1, respectively, 70 so the semantics of the function is obviously preserved. If we are 71 guaranteed that the value of the accumulator never change, we 72 omit the accumulator. 73 74 There are three cases how the function may exit. The first one is 75 handled in adjust_return_value, the other two in adjust_accumulator_values 76 (the second case is actually a special case of the third one and we 77 present it separately just for clarity): 78 79 1) Just return x, where x is not in any of the remaining special shapes. 80 We rewrite this to a gimple equivalent of return m_acc * x + a_acc. 81 82 2) return f (...), where f is the current function, is rewritten in a 83 classical tail-recursion elimination way, into assignment of arguments 84 and jump to the start of the function. Values of the accumulators 85 are unchanged. 86 87 3) return a + m * f(...), where a and m do not depend on call to f. 88 To preserve the semantics described before we want this to be rewritten 89 in such a way that we finally return 90 91 a_acc + (a + m * f(...)) * m_acc = (a_acc + a * m_acc) + (m * m_acc) * f(...). 92 93 I.e. we increase a_acc by a * m_acc, multiply m_acc by m and 94 eliminate the tail call to f. Special cases when the value is just 95 added or just multiplied are obtained by setting a = 0 or m = 1. 96 97 TODO -- it is possible to do similar tricks for other operations. */ 98 99/* A structure that describes the tailcall. */ 100 101struct tailcall 102{ 103 /* The block in that the call occur. */ 104 basic_block call_block; 105 106 /* The iterator pointing to the call statement. */ 107 block_stmt_iterator call_bsi; 108 109 /* True if it is a call to the current function. */ 110 bool tail_recursion; 111 112 /* The return value of the caller is mult * f + add, where f is the return 113 value of the call. */ 114 tree mult, add; 115 116 /* Next tailcall in the chain. */ 117 struct tailcall *next; 118}; 119 120/* The variables holding the value of multiplicative and additive 121 accumulator. */ 122static tree m_acc, a_acc; 123 124static bool suitable_for_tail_opt_p (void); 125static bool optimize_tail_call (struct tailcall *, bool); 126static void eliminate_tail_call (struct tailcall *); 127static void find_tail_calls (basic_block, struct tailcall **); 128 129/* Returns false when the function is not suitable for tail call optimization 130 from some reason (e.g. if it takes variable number of arguments). */ 131 132static bool 133suitable_for_tail_opt_p (void) 134{ 135 referenced_var_iterator rvi; 136 tree var; 137 138 if (current_function_stdarg) 139 return false; 140 141 /* No local variable nor structure field should be call-clobbered. We 142 ignore any kind of memory tag, as these are not real variables. */ 143 144 FOR_EACH_REFERENCED_VAR (var, rvi) 145 { 146 147 if (!is_global_var (var) 148 && (!MTAG_P (var) || TREE_CODE (var) == STRUCT_FIELD_TAG) 149 && is_call_clobbered (var)) 150 return false; 151 } 152 153 return true; 154} 155/* Returns false when the function is not suitable for tail call optimization 156 from some reason (e.g. if it takes variable number of arguments). 157 This test must pass in addition to suitable_for_tail_opt_p in order to make 158 tail call discovery happen. */ 159 160static bool 161suitable_for_tail_call_opt_p (void) 162{ 163 tree param; 164 165 /* alloca (until we have stack slot life analysis) inhibits 166 sibling call optimizations, but not tail recursion. */ 167 if (current_function_calls_alloca) 168 return false; 169 170 /* If we are using sjlj exceptions, we may need to add a call to 171 _Unwind_SjLj_Unregister at exit of the function. Which means 172 that we cannot do any sibcall transformations. */ 173 if (USING_SJLJ_EXCEPTIONS && current_function_has_exception_handlers ()) 174 return false; 175 176 /* Any function that calls setjmp might have longjmp called from 177 any called function. ??? We really should represent this 178 properly in the CFG so that this needn't be special cased. */ 179 if (current_function_calls_setjmp) 180 return false; 181 182 /* ??? It is OK if the argument of a function is taken in some cases, 183 but not in all cases. See PR15387 and PR19616. Revisit for 4.1. */ 184 for (param = DECL_ARGUMENTS (current_function_decl); 185 param; 186 param = TREE_CHAIN (param)) 187 if (TREE_ADDRESSABLE (param)) 188 return false; 189 190 return true; 191} 192 193/* Checks whether the expression EXPR in stmt AT is independent of the 194 statement pointed to by BSI (in a sense that we already know EXPR's value 195 at BSI). We use the fact that we are only called from the chain of 196 basic blocks that have only single successor. Returns the expression 197 containing the value of EXPR at BSI. */ 198 199static tree 200independent_of_stmt_p (tree expr, tree at, block_stmt_iterator bsi) 201{ 202 basic_block bb, call_bb, at_bb; 203 edge e; 204 edge_iterator ei; 205 206 if (is_gimple_min_invariant (expr)) 207 return expr; 208 209 if (TREE_CODE (expr) != SSA_NAME) 210 return NULL_TREE; 211 212 /* Mark the blocks in the chain leading to the end. */ 213 at_bb = bb_for_stmt (at); 214 call_bb = bb_for_stmt (bsi_stmt (bsi)); 215 for (bb = call_bb; bb != at_bb; bb = single_succ (bb)) 216 bb->aux = &bb->aux; 217 bb->aux = &bb->aux; 218 219 while (1) 220 { 221 at = SSA_NAME_DEF_STMT (expr); 222 bb = bb_for_stmt (at); 223 224 /* The default definition or defined before the chain. */ 225 if (!bb || !bb->aux) 226 break; 227 228 if (bb == call_bb) 229 { 230 for (; !bsi_end_p (bsi); bsi_next (&bsi)) 231 if (bsi_stmt (bsi) == at) 232 break; 233 234 if (!bsi_end_p (bsi)) 235 expr = NULL_TREE; 236 break; 237 } 238 239 if (TREE_CODE (at) != PHI_NODE) 240 { 241 expr = NULL_TREE; 242 break; 243 } 244 245 FOR_EACH_EDGE (e, ei, bb->preds) 246 if (e->src->aux) 247 break; 248 gcc_assert (e); 249 250 expr = PHI_ARG_DEF_FROM_EDGE (at, e); 251 if (TREE_CODE (expr) != SSA_NAME) 252 { 253 /* The value is a constant. */ 254 break; 255 } 256 } 257 258 /* Unmark the blocks. */ 259 for (bb = call_bb; bb != at_bb; bb = single_succ (bb)) 260 bb->aux = NULL; 261 bb->aux = NULL; 262 263 return expr; 264} 265 266/* Simulates the effect of an assignment of ASS in STMT on the return value 267 of the tail recursive CALL passed in ASS_VAR. M and A are the 268 multiplicative and the additive factor for the real return value. */ 269 270static bool 271process_assignment (tree ass, tree stmt, block_stmt_iterator call, tree *m, 272 tree *a, tree *ass_var) 273{ 274 tree op0, op1, non_ass_var; 275 tree dest = TREE_OPERAND (ass, 0); 276 tree src = TREE_OPERAND (ass, 1); 277 enum tree_code code = TREE_CODE (src); 278 tree src_var = src; 279 280 /* See if this is a simple copy operation of an SSA name to the function 281 result. In that case we may have a simple tail call. Ignore type 282 conversions that can never produce extra code between the function 283 call and the function return. */ 284 STRIP_NOPS (src_var); 285 if (TREE_CODE (src_var) == SSA_NAME) 286 { 287 if (src_var != *ass_var) 288 return false; 289 290 *ass_var = dest; 291 return true; 292 } 293 294 if (TREE_CODE_CLASS (code) != tcc_binary) 295 return false; 296 297 /* Accumulator optimizations will reverse the order of operations. 298 We can only do that for floating-point types if we're assuming 299 that addition and multiplication are associative. */ 300 if (!flag_unsafe_math_optimizations) 301 if (FLOAT_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl)))) 302 return false; 303 304 /* We only handle the code like 305 306 x = call (); 307 y = m * x; 308 z = y + a; 309 return z; 310 311 TODO -- Extend it for cases where the linear transformation of the output 312 is expressed in a more complicated way. */ 313 314 op0 = TREE_OPERAND (src, 0); 315 op1 = TREE_OPERAND (src, 1); 316 317 if (op0 == *ass_var 318 && (non_ass_var = independent_of_stmt_p (op1, stmt, call))) 319 ; 320 else if (op1 == *ass_var 321 && (non_ass_var = independent_of_stmt_p (op0, stmt, call))) 322 ; 323 else 324 return false; 325 326 switch (code) 327 { 328 case PLUS_EXPR: 329 /* There should be no previous addition. TODO -- it should be fairly 330 straightforward to lift this restriction -- just allow storing 331 more complicated expressions in *A, and gimplify it in 332 adjust_accumulator_values. */ 333 if (*a) 334 return false; 335 *a = non_ass_var; 336 *ass_var = dest; 337 return true; 338 339 case MULT_EXPR: 340 /* Similar remark applies here. Handling multiplication after addition 341 is just slightly more complicated -- we need to multiply both *A and 342 *M. */ 343 if (*a || *m) 344 return false; 345 *m = non_ass_var; 346 *ass_var = dest; 347 return true; 348 349 /* TODO -- Handle other codes (NEGATE_EXPR, MINUS_EXPR). */ 350 351 default: 352 return false; 353 } 354} 355 356/* Propagate VAR through phis on edge E. */ 357 358static tree 359propagate_through_phis (tree var, edge e) 360{ 361 basic_block dest = e->dest; 362 tree phi; 363 364 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi)) 365 if (PHI_ARG_DEF_FROM_EDGE (phi, e) == var) 366 return PHI_RESULT (phi); 367 368 return var; 369} 370 371/* Finds tailcalls falling into basic block BB. The list of found tailcalls is 372 added to the start of RET. */ 373 374static void 375find_tail_calls (basic_block bb, struct tailcall **ret) 376{ 377 tree ass_var, ret_var, stmt, func, param, args, call = NULL_TREE; 378 block_stmt_iterator bsi, absi; 379 bool tail_recursion; 380 struct tailcall *nw; 381 edge e; 382 tree m, a; 383 basic_block abb; 384 stmt_ann_t ann; 385 386 if (!single_succ_p (bb)) 387 return; 388 389 for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi)) 390 { 391 stmt = bsi_stmt (bsi); 392 393 /* Ignore labels. */ 394 if (TREE_CODE (stmt) == LABEL_EXPR) 395 continue; 396 397 /* Check for a call. */ 398 if (TREE_CODE (stmt) == MODIFY_EXPR) 399 { 400 ass_var = TREE_OPERAND (stmt, 0); 401 call = TREE_OPERAND (stmt, 1); 402 if (TREE_CODE (call) == WITH_SIZE_EXPR) 403 call = TREE_OPERAND (call, 0); 404 } 405 else 406 { 407 ass_var = NULL_TREE; 408 call = stmt; 409 } 410 411 if (TREE_CODE (call) == CALL_EXPR) 412 break; 413 414 /* If the statement has virtual or volatile operands, fail. */ 415 ann = stmt_ann (stmt); 416 if (!ZERO_SSA_OPERANDS (stmt, (SSA_OP_VUSE | SSA_OP_VIRTUAL_DEFS)) 417 || ann->has_volatile_ops) 418 return; 419 } 420 421 if (bsi_end_p (bsi)) 422 { 423 edge_iterator ei; 424 /* Recurse to the predecessors. */ 425 FOR_EACH_EDGE (e, ei, bb->preds) 426 find_tail_calls (e->src, ret); 427 428 return; 429 } 430 431 /* We found the call, check whether it is suitable. */ 432 tail_recursion = false; 433 func = get_callee_fndecl (call); 434 if (func == current_function_decl) 435 { 436 for (param = DECL_ARGUMENTS (func), args = TREE_OPERAND (call, 1); 437 param && args; 438 param = TREE_CHAIN (param), args = TREE_CHAIN (args)) 439 { 440 tree arg = TREE_VALUE (args); 441 if (param != arg) 442 { 443 /* Make sure there are no problems with copying. The parameter 444 have a copyable type and the two arguments must have reasonably 445 equivalent types. The latter requirement could be relaxed if 446 we emitted a suitable type conversion statement. */ 447 if (!is_gimple_reg_type (TREE_TYPE (param)) 448 || !lang_hooks.types_compatible_p (TREE_TYPE (param), 449 TREE_TYPE (arg))) 450 break; 451 452 /* The parameter should be a real operand, so that phi node 453 created for it at the start of the function has the meaning 454 of copying the value. This test implies is_gimple_reg_type 455 from the previous condition, however this one could be 456 relaxed by being more careful with copying the new value 457 of the parameter (emitting appropriate MODIFY_EXPR and 458 updating the virtual operands). */ 459 if (!is_gimple_reg (param)) 460 break; 461 } 462 } 463 if (!args && !param) 464 tail_recursion = true; 465 } 466 467 /* Now check the statements after the call. None of them has virtual 468 operands, so they may only depend on the call through its return 469 value. The return value should also be dependent on each of them, 470 since we are running after dce. */ 471 m = NULL_TREE; 472 a = NULL_TREE; 473 474 abb = bb; 475 absi = bsi; 476 while (1) 477 { 478 bsi_next (&absi); 479 480 while (bsi_end_p (absi)) 481 { 482 ass_var = propagate_through_phis (ass_var, single_succ_edge (abb)); 483 abb = single_succ (abb); 484 absi = bsi_start (abb); 485 } 486 487 stmt = bsi_stmt (absi); 488 489 if (TREE_CODE (stmt) == LABEL_EXPR) 490 continue; 491 492 if (TREE_CODE (stmt) == RETURN_EXPR) 493 break; 494 495 if (TREE_CODE (stmt) != MODIFY_EXPR) 496 return; 497 498 if (!process_assignment (stmt, stmt, bsi, &m, &a, &ass_var)) 499 return; 500 } 501 502 /* See if this is a tail call we can handle. */ 503 ret_var = TREE_OPERAND (stmt, 0); 504 if (ret_var 505 && TREE_CODE (ret_var) == MODIFY_EXPR) 506 { 507 tree ret_op = TREE_OPERAND (ret_var, 1); 508 STRIP_NOPS (ret_op); 509 if (!tail_recursion 510 && TREE_CODE (ret_op) != SSA_NAME) 511 return; 512 513 if (!process_assignment (ret_var, stmt, bsi, &m, &a, &ass_var)) 514 return; 515 ret_var = TREE_OPERAND (ret_var, 0); 516 } 517 518 /* We may proceed if there either is no return value, or the return value 519 is identical to the call's return. */ 520 if (ret_var 521 && (ret_var != ass_var)) 522 return; 523 524 /* If this is not a tail recursive call, we cannot handle addends or 525 multiplicands. */ 526 if (!tail_recursion && (m || a)) 527 return; 528 529 nw = XNEW (struct tailcall); 530 531 nw->call_block = bb; 532 nw->call_bsi = bsi; 533 534 nw->tail_recursion = tail_recursion; 535 536 nw->mult = m; 537 nw->add = a; 538 539 nw->next = *ret; 540 *ret = nw; 541} 542 543/* Adjust the accumulator values according to A and M after BSI, and update 544 the phi nodes on edge BACK. */ 545 546static void 547adjust_accumulator_values (block_stmt_iterator bsi, tree m, tree a, edge back) 548{ 549 tree stmt, var, phi, tmp; 550 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); 551 tree a_acc_arg = a_acc, m_acc_arg = m_acc; 552 553 if (a) 554 { 555 if (m_acc) 556 { 557 if (integer_onep (a)) 558 var = m_acc; 559 else 560 { 561 stmt = build2 (MODIFY_EXPR, ret_type, NULL_TREE, 562 build2 (MULT_EXPR, ret_type, m_acc, a)); 563 564 tmp = create_tmp_var (ret_type, "acc_tmp"); 565 add_referenced_var (tmp); 566 567 var = make_ssa_name (tmp, stmt); 568 TREE_OPERAND (stmt, 0) = var; 569 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT); 570 } 571 } 572 else 573 var = a; 574 575 stmt = build2 (MODIFY_EXPR, ret_type, NULL_TREE, 576 build2 (PLUS_EXPR, ret_type, a_acc, var)); 577 var = make_ssa_name (SSA_NAME_VAR (a_acc), stmt); 578 TREE_OPERAND (stmt, 0) = var; 579 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT); 580 a_acc_arg = var; 581 } 582 583 if (m) 584 { 585 stmt = build2 (MODIFY_EXPR, ret_type, NULL_TREE, 586 build2 (MULT_EXPR, ret_type, m_acc, m)); 587 var = make_ssa_name (SSA_NAME_VAR (m_acc), stmt); 588 TREE_OPERAND (stmt, 0) = var; 589 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT); 590 m_acc_arg = var; 591 } 592 593 if (a_acc) 594 { 595 for (phi = phi_nodes (back->dest); phi; phi = PHI_CHAIN (phi)) 596 if (PHI_RESULT (phi) == a_acc) 597 break; 598 599 add_phi_arg (phi, a_acc_arg, back); 600 } 601 602 if (m_acc) 603 { 604 for (phi = phi_nodes (back->dest); phi; phi = PHI_CHAIN (phi)) 605 if (PHI_RESULT (phi) == m_acc) 606 break; 607 608 add_phi_arg (phi, m_acc_arg, back); 609 } 610} 611 612/* Adjust value of the return at the end of BB according to M and A 613 accumulators. */ 614 615static void 616adjust_return_value (basic_block bb, tree m, tree a) 617{ 618 tree ret_stmt = last_stmt (bb), ret_var, var, stmt, tmp; 619 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); 620 block_stmt_iterator bsi = bsi_last (bb); 621 622 gcc_assert (TREE_CODE (ret_stmt) == RETURN_EXPR); 623 624 ret_var = TREE_OPERAND (ret_stmt, 0); 625 if (!ret_var) 626 return; 627 628 if (TREE_CODE (ret_var) == MODIFY_EXPR) 629 { 630 ret_var->common.ann = (tree_ann_t) stmt_ann (ret_stmt); 631 bsi_replace (&bsi, ret_var, true); 632 SSA_NAME_DEF_STMT (TREE_OPERAND (ret_var, 0)) = ret_var; 633 ret_var = TREE_OPERAND (ret_var, 0); 634 ret_stmt = build1 (RETURN_EXPR, TREE_TYPE (ret_stmt), ret_var); 635 bsi_insert_after (&bsi, ret_stmt, BSI_NEW_STMT); 636 } 637 638 if (m) 639 { 640 stmt = build2 (MODIFY_EXPR, ret_type, NULL_TREE, 641 build2 (MULT_EXPR, ret_type, m_acc, ret_var)); 642 643 tmp = create_tmp_var (ret_type, "acc_tmp"); 644 add_referenced_var (tmp); 645 646 var = make_ssa_name (tmp, stmt); 647 TREE_OPERAND (stmt, 0) = var; 648 bsi_insert_before (&bsi, stmt, BSI_SAME_STMT); 649 } 650 else 651 var = ret_var; 652 653 if (a) 654 { 655 stmt = build2 (MODIFY_EXPR, ret_type, NULL_TREE, 656 build2 (PLUS_EXPR, ret_type, a_acc, var)); 657 658 tmp = create_tmp_var (ret_type, "acc_tmp"); 659 add_referenced_var (tmp); 660 661 var = make_ssa_name (tmp, stmt); 662 TREE_OPERAND (stmt, 0) = var; 663 bsi_insert_before (&bsi, stmt, BSI_SAME_STMT); 664 } 665 666 TREE_OPERAND (ret_stmt, 0) = var; 667 update_stmt (ret_stmt); 668} 669 670/* Subtract COUNT and FREQUENCY from the basic block and it's 671 outgoing edge. */ 672static void 673decrease_profile (basic_block bb, gcov_type count, int frequency) 674{ 675 edge e; 676 bb->count -= count; 677 if (bb->count < 0) 678 bb->count = 0; 679 bb->frequency -= frequency; 680 if (bb->frequency < 0) 681 bb->frequency = 0; 682 if (!single_succ_p (bb)) 683 { 684 gcc_assert (!EDGE_COUNT (bb->succs)); 685 return; 686 } 687 e = single_succ_edge (bb); 688 e->count -= count; 689 if (e->count < 0) 690 e->count = 0; 691} 692 693/* Returns true if argument PARAM of the tail recursive call needs to be copied 694 when the call is eliminated. */ 695 696static bool 697arg_needs_copy_p (tree param) 698{ 699 tree def; 700 701 if (!is_gimple_reg (param) || !var_ann (param)) 702 return false; 703 704 /* Parameters that are only defined but never used need not be copied. */ 705 def = default_def (param); 706 if (!def) 707 return false; 708 709 return true; 710} 711 712/* Eliminates tail call described by T. TMP_VARS is a list of 713 temporary variables used to copy the function arguments. */ 714 715static void 716eliminate_tail_call (struct tailcall *t) 717{ 718 tree param, stmt, args, rslt, call; 719 basic_block bb, first; 720 edge e; 721 tree phi; 722 block_stmt_iterator bsi; 723 tree orig_stmt; 724 725 stmt = orig_stmt = bsi_stmt (t->call_bsi); 726 bb = t->call_block; 727 728 if (dump_file && (dump_flags & TDF_DETAILS)) 729 { 730 fprintf (dump_file, "Eliminated tail recursion in bb %d : ", 731 bb->index); 732 print_generic_stmt (dump_file, stmt, TDF_SLIM); 733 fprintf (dump_file, "\n"); 734 } 735 736 if (TREE_CODE (stmt) == MODIFY_EXPR) 737 stmt = TREE_OPERAND (stmt, 1); 738 739 first = single_succ (ENTRY_BLOCK_PTR); 740 741 /* Remove the code after call_bsi that will become unreachable. The 742 possibly unreachable code in other blocks is removed later in 743 cfg cleanup. */ 744 bsi = t->call_bsi; 745 bsi_next (&bsi); 746 while (!bsi_end_p (bsi)) 747 { 748 tree t = bsi_stmt (bsi); 749 /* Do not remove the return statement, so that redirect_edge_and_branch 750 sees how the block ends. */ 751 if (TREE_CODE (t) == RETURN_EXPR) 752 break; 753 754 bsi_remove (&bsi, true); 755 release_defs (t); 756 } 757 758 /* Number of executions of function has reduced by the tailcall. */ 759 e = single_succ_edge (t->call_block); 760 decrease_profile (EXIT_BLOCK_PTR, e->count, EDGE_FREQUENCY (e)); 761 decrease_profile (ENTRY_BLOCK_PTR, e->count, EDGE_FREQUENCY (e)); 762 if (e->dest != EXIT_BLOCK_PTR) 763 decrease_profile (e->dest, e->count, EDGE_FREQUENCY (e)); 764 765 /* Replace the call by a jump to the start of function. */ 766 e = redirect_edge_and_branch (single_succ_edge (t->call_block), first); 767 gcc_assert (e); 768 PENDING_STMT (e) = NULL_TREE; 769 770 /* Add phi node entries for arguments. The ordering of the phi nodes should 771 be the same as the ordering of the arguments. */ 772 for (param = DECL_ARGUMENTS (current_function_decl), 773 args = TREE_OPERAND (stmt, 1), 774 phi = phi_nodes (first); 775 param; 776 param = TREE_CHAIN (param), 777 args = TREE_CHAIN (args)) 778 { 779 if (!arg_needs_copy_p (param)) 780 continue; 781 gcc_assert (param == SSA_NAME_VAR (PHI_RESULT (phi))); 782 783 add_phi_arg (phi, TREE_VALUE (args), e); 784 phi = PHI_CHAIN (phi); 785 } 786 787 /* Update the values of accumulators. */ 788 adjust_accumulator_values (t->call_bsi, t->mult, t->add, e); 789 790 call = bsi_stmt (t->call_bsi); 791 if (TREE_CODE (call) == MODIFY_EXPR) 792 { 793 rslt = TREE_OPERAND (call, 0); 794 795 /* Result of the call will no longer be defined. So adjust the 796 SSA_NAME_DEF_STMT accordingly. */ 797 SSA_NAME_DEF_STMT (rslt) = build_empty_stmt (); 798 } 799 800 bsi_remove (&t->call_bsi, true); 801 release_defs (call); 802} 803 804/* Add phi nodes for the virtual operands defined in the function to the 805 header of the loop created by tail recursion elimination. 806 807 Originally, we used to add phi nodes only for call clobbered variables, 808 as the value of the non-call clobbered ones obviously cannot be used 809 or changed within the recursive call. However, the local variables 810 from multiple calls now share the same location, so the virtual ssa form 811 requires us to say that the location dies on further iterations of the loop, 812 which requires adding phi nodes. 813*/ 814static void 815add_virtual_phis (void) 816{ 817 referenced_var_iterator rvi; 818 tree var; 819 820 /* The problematic part is that there is no way how to know what 821 to put into phi nodes (there in fact does not have to be such 822 ssa name available). A solution would be to have an artificial 823 use/kill for all virtual operands in EXIT node. Unless we have 824 this, we cannot do much better than to rebuild the ssa form for 825 possibly affected virtual ssa names from scratch. */ 826 827 FOR_EACH_REFERENCED_VAR (var, rvi) 828 { 829 if (!is_gimple_reg (var) && default_def (var) != NULL_TREE) 830 mark_sym_for_renaming (var); 831 } 832 833 update_ssa (TODO_update_ssa_only_virtuals); 834} 835 836/* Optimizes the tailcall described by T. If OPT_TAILCALLS is true, also 837 mark the tailcalls for the sibcall optimization. */ 838 839static bool 840optimize_tail_call (struct tailcall *t, bool opt_tailcalls) 841{ 842 if (t->tail_recursion) 843 { 844 eliminate_tail_call (t); 845 return true; 846 } 847 848 if (opt_tailcalls) 849 { 850 tree stmt = bsi_stmt (t->call_bsi); 851 852 stmt = get_call_expr_in (stmt); 853 CALL_EXPR_TAILCALL (stmt) = 1; 854 if (dump_file && (dump_flags & TDF_DETAILS)) 855 { 856 fprintf (dump_file, "Found tail call "); 857 print_generic_expr (dump_file, stmt, dump_flags); 858 fprintf (dump_file, " in bb %i\n", t->call_block->index); 859 } 860 } 861 862 return false; 863} 864 865/* Optimizes tail calls in the function, turning the tail recursion 866 into iteration. */ 867 868static void 869tree_optimize_tail_calls_1 (bool opt_tailcalls) 870{ 871 edge e; 872 bool phis_constructed = false; 873 struct tailcall *tailcalls = NULL, *act, *next; 874 bool changed = false; 875 basic_block first = single_succ (ENTRY_BLOCK_PTR); 876 tree stmt, param, ret_type, tmp, phi; 877 edge_iterator ei; 878 879 if (!suitable_for_tail_opt_p ()) 880 return; 881 if (opt_tailcalls) 882 opt_tailcalls = suitable_for_tail_call_opt_p (); 883 884 FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds) 885 { 886 /* Only traverse the normal exits, i.e. those that end with return 887 statement. */ 888 stmt = last_stmt (e->src); 889 890 if (stmt 891 && TREE_CODE (stmt) == RETURN_EXPR) 892 find_tail_calls (e->src, &tailcalls); 893 } 894 895 /* Construct the phi nodes and accumulators if necessary. */ 896 a_acc = m_acc = NULL_TREE; 897 for (act = tailcalls; act; act = act->next) 898 { 899 if (!act->tail_recursion) 900 continue; 901 902 if (!phis_constructed) 903 { 904 /* Ensure that there is only one predecessor of the block. */ 905 if (!single_pred_p (first)) 906 first = split_edge (single_succ_edge (ENTRY_BLOCK_PTR)); 907 908 /* Copy the args if needed. */ 909 for (param = DECL_ARGUMENTS (current_function_decl); 910 param; 911 param = TREE_CHAIN (param)) 912 if (arg_needs_copy_p (param)) 913 { 914 tree name = default_def (param); 915 tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name)); 916 tree phi; 917 918 set_default_def (param, new_name); 919 phi = create_phi_node (name, first); 920 SSA_NAME_DEF_STMT (name) = phi; 921 add_phi_arg (phi, new_name, single_pred_edge (first)); 922 } 923 phis_constructed = true; 924 } 925 926 if (act->add && !a_acc) 927 { 928 ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); 929 930 tmp = create_tmp_var (ret_type, "add_acc"); 931 add_referenced_var (tmp); 932 933 phi = create_phi_node (tmp, first); 934 add_phi_arg (phi, 935 /* RET_TYPE can be a float when -ffast-maths is 936 enabled. */ 937 fold_convert (ret_type, integer_zero_node), 938 single_pred_edge (first)); 939 a_acc = PHI_RESULT (phi); 940 } 941 942 if (act->mult && !m_acc) 943 { 944 ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); 945 946 tmp = create_tmp_var (ret_type, "mult_acc"); 947 add_referenced_var (tmp); 948 949 phi = create_phi_node (tmp, first); 950 add_phi_arg (phi, 951 /* RET_TYPE can be a float when -ffast-maths is 952 enabled. */ 953 fold_convert (ret_type, integer_one_node), 954 single_pred_edge (first)); 955 m_acc = PHI_RESULT (phi); 956 } 957 } 958 959 960 if (phis_constructed) 961 { 962 /* Reverse the order of the phi nodes, so that it matches the order 963 of operands of the function, as assumed by eliminate_tail_call. */ 964 set_phi_nodes (first, phi_reverse (phi_nodes (first))); 965 } 966 967 for (; tailcalls; tailcalls = next) 968 { 969 next = tailcalls->next; 970 changed |= optimize_tail_call (tailcalls, opt_tailcalls); 971 free (tailcalls); 972 } 973 974 if (a_acc || m_acc) 975 { 976 /* Modify the remaining return statements. */ 977 FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds) 978 { 979 stmt = last_stmt (e->src); 980 981 if (stmt 982 && TREE_CODE (stmt) == RETURN_EXPR) 983 adjust_return_value (e->src, m_acc, a_acc); 984 } 985 } 986 987 if (changed) 988 { 989 free_dominance_info (CDI_DOMINATORS); 990 cleanup_tree_cfg (); 991 } 992 993 if (phis_constructed) 994 add_virtual_phis (); 995} 996 997static unsigned int 998execute_tail_recursion (void) 999{ 1000 tree_optimize_tail_calls_1 (false); 1001 return 0; 1002} 1003 1004static bool 1005gate_tail_calls (void) 1006{ 1007 return flag_optimize_sibling_calls != 0; 1008} 1009 1010static unsigned int 1011execute_tail_calls (void) 1012{ 1013 tree_optimize_tail_calls_1 (true); 1014 return 0; 1015} 1016 1017struct tree_opt_pass pass_tail_recursion = 1018{ 1019 "tailr", /* name */ 1020 gate_tail_calls, /* gate */ 1021 execute_tail_recursion, /* execute */ 1022 NULL, /* sub */ 1023 NULL, /* next */ 1024 0, /* static_pass_number */ 1025 0, /* tv_id */ 1026 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ 1027 0, /* properties_provided */ 1028 0, /* properties_destroyed */ 1029 0, /* todo_flags_start */ 1030 TODO_dump_func | TODO_verify_ssa, /* todo_flags_finish */ 1031 0 /* letter */ 1032}; 1033 1034struct tree_opt_pass pass_tail_calls = 1035{ 1036 "tailc", /* name */ 1037 gate_tail_calls, /* gate */ 1038 execute_tail_calls, /* execute */ 1039 NULL, /* sub */ 1040 NULL, /* next */ 1041 0, /* static_pass_number */ 1042 0, /* tv_id */ 1043 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ 1044 0, /* properties_provided */ 1045 0, /* properties_destroyed */ 1046 0, /* todo_flags_start */ 1047 TODO_dump_func | TODO_verify_ssa, /* todo_flags_finish */ 1048 0 /* letter */ 1049}; 1050