Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-tailcall.c @ 22:0eb6cac880f0
add cbc example of quicksort.
| author | kent <kent@cr.ie.u-ryukyu.ac.jp> |
|---|---|
| date | Tue, 13 Oct 2009 17:15:58 +0900 |
| parents | 58ad6c70ea60 |
| children | 3bfb6c00c1e0 |
| rev | line source |
|---|---|
| 0 | 1 /* Tail call optimization on trees. |
| 2 Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 | |
| 3 Free Software Foundation, Inc. | |
| 4 | |
| 5 This file is part of GCC. | |
| 6 | |
| 7 GCC is free software; you can redistribute it and/or modify | |
| 8 it under the terms of the GNU General Public License as published by | |
| 9 the Free Software Foundation; either version 3, or (at your option) | |
| 10 any later version. | |
| 11 | |
| 12 GCC is distributed in the hope that it will be useful, | |
| 13 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| 15 GNU General Public License for more details. | |
| 16 | |
| 17 You should have received a copy of the GNU General Public License | |
| 18 along with GCC; see the file COPYING3. If not see | |
| 19 <http://www.gnu.org/licenses/>. */ | |
| 20 | |
| 21 #include "config.h" | |
| 22 #include "system.h" | |
| 23 #include "coretypes.h" | |
| 24 #include "tm.h" | |
| 25 #include "tree.h" | |
| 26 #include "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 #include "dbgcnt.h" | |
| 39 | |
| 40 /* The file implements the tail recursion elimination. It is also used to | |
| 41 analyze the tail calls in general, passing the results to the rtl level | |
| 42 where they are used for sibcall optimization. | |
| 43 | |
| 44 In addition to the standard tail recursion elimination, we handle the most | |
| 45 trivial cases of making the call tail recursive by creating accumulators. | |
| 46 For example the following function | |
| 47 | |
| 48 int sum (int n) | |
| 49 { | |
| 50 if (n > 0) | |
| 51 return n + sum (n - 1); | |
| 52 else | |
| 53 return 0; | |
| 54 } | |
| 55 | |
| 56 is transformed into | |
| 57 | |
| 58 int sum (int n) | |
| 59 { | |
| 60 int acc = 0; | |
| 61 | |
| 62 while (n > 0) | |
| 63 acc += n--; | |
| 64 | |
| 65 return acc; | |
| 66 } | |
| 67 | |
| 68 To do this, we maintain two accumulators (a_acc and m_acc) that indicate | |
| 69 when we reach the return x statement, we should return a_acc + x * m_acc | |
| 70 instead. They are initially initialized to 0 and 1, respectively, | |
| 71 so the semantics of the function is obviously preserved. If we are | |
| 72 guaranteed that the value of the accumulator never change, we | |
| 73 omit the accumulator. | |
| 74 | |
| 75 There are three cases how the function may exit. The first one is | |
| 76 handled in adjust_return_value, the other two in adjust_accumulator_values | |
| 77 (the second case is actually a special case of the third one and we | |
| 78 present it separately just for clarity): | |
| 79 | |
| 80 1) Just return x, where x is not in any of the remaining special shapes. | |
| 81 We rewrite this to a gimple equivalent of return m_acc * x + a_acc. | |
| 82 | |
| 83 2) return f (...), where f is the current function, is rewritten in a | |
| 84 classical tail-recursion elimination way, into assignment of arguments | |
| 85 and jump to the start of the function. Values of the accumulators | |
| 86 are unchanged. | |
| 87 | |
| 88 3) return a + m * f(...), where a and m do not depend on call to f. | |
| 89 To preserve the semantics described before we want this to be rewritten | |
| 90 in such a way that we finally return | |
| 91 | |
| 92 a_acc + (a + m * f(...)) * m_acc = (a_acc + a * m_acc) + (m * m_acc) * f(...). | |
| 93 | |
| 94 I.e. we increase a_acc by a * m_acc, multiply m_acc by m and | |
| 95 eliminate the tail call to f. Special cases when the value is just | |
| 96 added or just multiplied are obtained by setting a = 0 or m = 1. | |
| 97 | |
| 98 TODO -- it is possible to do similar tricks for other operations. */ | |
| 99 | |
| 100 /* A structure that describes the tailcall. */ | |
| 101 | |
| 102 struct tailcall | |
| 103 { | |
| 104 /* The iterator pointing to the call statement. */ | |
| 105 gimple_stmt_iterator call_gsi; | |
| 106 | |
| 107 /* True if it is a call to the current function. */ | |
| 108 bool tail_recursion; | |
| 109 | |
| 110 /* The return value of the caller is mult * f + add, where f is the return | |
| 111 value of the call. */ | |
| 112 tree mult, add; | |
| 113 | |
| 114 /* Next tailcall in the chain. */ | |
| 115 struct tailcall *next; | |
| 116 }; | |
| 117 | |
| 118 /* The variables holding the value of multiplicative and additive | |
| 119 accumulator. */ | |
| 120 static tree m_acc, a_acc; | |
| 121 | |
| 122 static bool suitable_for_tail_opt_p (void); | |
| 123 static bool optimize_tail_call (struct tailcall *, bool); | |
| 124 static void eliminate_tail_call (struct tailcall *); | |
| 125 static void find_tail_calls (basic_block, struct tailcall **); | |
| 126 | |
| 127 /* Returns false when the function is not suitable for tail call optimization | |
| 128 from some reason (e.g. if it takes variable number of arguments). */ | |
| 129 | |
| 130 static bool | |
| 131 suitable_for_tail_opt_p (void) | |
| 132 { | |
| 133 referenced_var_iterator rvi; | |
| 134 tree var; | |
| 135 | |
| 136 if (cfun->stdarg) | |
| 137 return false; | |
| 138 | |
| 139 /* No local variable nor structure field should be call-used. We | |
| 140 ignore any kind of memory tag, as these are not real variables. */ | |
| 141 | |
| 142 FOR_EACH_REFERENCED_VAR (var, rvi) | |
| 143 { | |
| 144 if (!is_global_var (var) | |
| 145 && !MTAG_P (var) | |
| 146 && (gimple_aliases_computed_p (cfun)? is_call_used (var) | |
| 147 : TREE_ADDRESSABLE (var))) | |
| 148 return false; | |
| 149 } | |
| 150 | |
| 151 return true; | |
| 152 } | |
| 153 /* Returns false when the function is not suitable for tail call optimization | |
| 154 from some reason (e.g. if it takes variable number of arguments). | |
| 155 This test must pass in addition to suitable_for_tail_opt_p in order to make | |
| 156 tail call discovery happen. */ | |
| 157 | |
| 158 static bool | |
| 159 suitable_for_tail_call_opt_p (void) | |
| 160 { | |
| 161 tree param; | |
| 162 | |
| 163 /* alloca (until we have stack slot life analysis) inhibits | |
| 164 sibling call optimizations, but not tail recursion. */ | |
| 165 if (cfun->calls_alloca) | |
| 166 return false; | |
| 167 | |
| 168 /* If we are using sjlj exceptions, we may need to add a call to | |
| 169 _Unwind_SjLj_Unregister at exit of the function. Which means | |
| 170 that we cannot do any sibcall transformations. */ | |
| 171 if (USING_SJLJ_EXCEPTIONS && current_function_has_exception_handlers ()) | |
| 172 return false; | |
| 173 | |
| 174 /* Any function that calls setjmp might have longjmp called from | |
| 175 any called function. ??? We really should represent this | |
| 176 properly in the CFG so that this needn't be special cased. */ | |
| 177 if (cfun->calls_setjmp) | |
| 178 return false; | |
| 179 | |
| 180 /* ??? It is OK if the argument of a function is taken in some cases, | |
| 181 but not in all cases. See PR15387 and PR19616. Revisit for 4.1. */ | |
| 182 for (param = DECL_ARGUMENTS (current_function_decl); | |
| 183 param; | |
| 184 param = TREE_CHAIN (param)) | |
| 185 if (TREE_ADDRESSABLE (param)) | |
| 186 return false; | |
| 187 | |
| 188 return true; | |
| 189 } | |
| 190 | |
| 191 /* Checks whether the expression EXPR in stmt AT is independent of the | |
| 192 statement pointed to by GSI (in a sense that we already know EXPR's value | |
| 193 at GSI). We use the fact that we are only called from the chain of | |
| 194 basic blocks that have only single successor. Returns the expression | |
| 195 containing the value of EXPR at GSI. */ | |
| 196 | |
| 197 static tree | |
| 198 independent_of_stmt_p (tree expr, gimple at, gimple_stmt_iterator gsi) | |
| 199 { | |
| 200 basic_block bb, call_bb, at_bb; | |
| 201 edge e; | |
| 202 edge_iterator ei; | |
| 203 | |
| 204 if (is_gimple_min_invariant (expr)) | |
| 205 return expr; | |
| 206 | |
| 207 if (TREE_CODE (expr) != SSA_NAME) | |
| 208 return NULL_TREE; | |
| 209 | |
| 210 /* Mark the blocks in the chain leading to the end. */ | |
| 211 at_bb = gimple_bb (at); | |
| 212 call_bb = gimple_bb (gsi_stmt (gsi)); | |
| 213 for (bb = call_bb; bb != at_bb; bb = single_succ (bb)) | |
| 214 bb->aux = &bb->aux; | |
| 215 bb->aux = &bb->aux; | |
| 216 | |
| 217 while (1) | |
| 218 { | |
| 219 at = SSA_NAME_DEF_STMT (expr); | |
| 220 bb = gimple_bb (at); | |
| 221 | |
| 222 /* The default definition or defined before the chain. */ | |
| 223 if (!bb || !bb->aux) | |
| 224 break; | |
| 225 | |
| 226 if (bb == call_bb) | |
| 227 { | |
| 228 for (; !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 229 if (gsi_stmt (gsi) == at) | |
| 230 break; | |
| 231 | |
| 232 if (!gsi_end_p (gsi)) | |
| 233 expr = NULL_TREE; | |
| 234 break; | |
| 235 } | |
| 236 | |
| 237 if (gimple_code (at) != GIMPLE_PHI) | |
| 238 { | |
| 239 expr = NULL_TREE; | |
| 240 break; | |
| 241 } | |
| 242 | |
| 243 FOR_EACH_EDGE (e, ei, bb->preds) | |
| 244 if (e->src->aux) | |
| 245 break; | |
| 246 gcc_assert (e); | |
| 247 | |
| 248 expr = PHI_ARG_DEF_FROM_EDGE (at, e); | |
| 249 if (TREE_CODE (expr) != SSA_NAME) | |
| 250 { | |
| 251 /* The value is a constant. */ | |
| 252 break; | |
| 253 } | |
| 254 } | |
| 255 | |
| 256 /* Unmark the blocks. */ | |
| 257 for (bb = call_bb; bb != at_bb; bb = single_succ (bb)) | |
| 258 bb->aux = NULL; | |
| 259 bb->aux = NULL; | |
| 260 | |
| 261 return expr; | |
| 262 } | |
| 263 | |
| 264 /* Simulates the effect of an assignment STMT on the return value of the tail | |
| 265 recursive CALL passed in ASS_VAR. M and A are the multiplicative and the | |
| 266 additive factor for the real return value. */ | |
| 267 | |
| 268 static bool | |
| 269 process_assignment (gimple stmt, gimple_stmt_iterator call, tree *m, | |
| 270 tree *a, tree *ass_var) | |
| 271 { | |
| 272 tree op0, op1, non_ass_var; | |
| 273 tree dest = gimple_assign_lhs (stmt); | |
| 274 enum tree_code code = gimple_assign_rhs_code (stmt); | |
| 275 enum gimple_rhs_class rhs_class = get_gimple_rhs_class (code); | |
| 276 tree src_var = gimple_assign_rhs1 (stmt); | |
| 277 | |
| 278 /* See if this is a simple copy operation of an SSA name to the function | |
| 279 result. In that case we may have a simple tail call. Ignore type | |
| 280 conversions that can never produce extra code between the function | |
| 281 call and the function return. */ | |
| 282 if ((rhs_class == GIMPLE_SINGLE_RHS || gimple_assign_cast_p (stmt)) | |
| 283 && (TREE_CODE (src_var) == SSA_NAME)) | |
| 284 { | |
| 285 /* Reject a tailcall if the type conversion might need | |
| 286 additional code. */ | |
| 287 if (gimple_assign_cast_p (stmt) | |
| 288 && TYPE_MODE (TREE_TYPE (dest)) != TYPE_MODE (TREE_TYPE (src_var))) | |
| 289 return false; | |
| 290 | |
| 291 if (src_var != *ass_var) | |
| 292 return false; | |
| 293 | |
| 294 *ass_var = dest; | |
| 295 return true; | |
| 296 } | |
| 297 | |
| 298 if (rhs_class != GIMPLE_BINARY_RHS) | |
| 299 return false; | |
| 300 | |
| 301 /* Accumulator optimizations will reverse the order of operations. | |
| 302 We can only do that for floating-point types if we're assuming | |
| 303 that addition and multiplication are associative. */ | |
| 304 if (!flag_associative_math) | |
| 305 if (FLOAT_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl)))) | |
| 306 return false; | |
| 307 | |
| 308 /* We only handle the code like | |
| 309 | |
| 310 x = call (); | |
| 311 y = m * x; | |
| 312 z = y + a; | |
| 313 return z; | |
| 314 | |
| 315 TODO -- Extend it for cases where the linear transformation of the output | |
| 316 is expressed in a more complicated way. */ | |
| 317 | |
| 318 op0 = gimple_assign_rhs1 (stmt); | |
| 319 op1 = gimple_assign_rhs2 (stmt); | |
| 320 | |
| 321 if (op0 == *ass_var | |
| 322 && (non_ass_var = independent_of_stmt_p (op1, stmt, call))) | |
| 323 ; | |
| 324 else if (op1 == *ass_var | |
| 325 && (non_ass_var = independent_of_stmt_p (op0, stmt, call))) | |
| 326 ; | |
| 327 else | |
| 328 return false; | |
| 329 | |
| 330 switch (code) | |
| 331 { | |
| 332 case PLUS_EXPR: | |
| 333 /* There should be no previous addition. TODO -- it should be fairly | |
| 334 straightforward to lift this restriction -- just allow storing | |
| 335 more complicated expressions in *A, and gimplify it in | |
| 336 adjust_accumulator_values. */ | |
| 337 if (*a) | |
| 338 return false; | |
| 339 *a = non_ass_var; | |
| 340 *ass_var = dest; | |
| 341 return true; | |
| 342 | |
| 343 case MULT_EXPR: | |
| 344 /* Similar remark applies here. Handling multiplication after addition | |
| 345 is just slightly more complicated -- we need to multiply both *A and | |
| 346 *M. */ | |
| 347 if (*a || *m) | |
| 348 return false; | |
| 349 *m = non_ass_var; | |
| 350 *ass_var = dest; | |
| 351 return true; | |
| 352 | |
| 353 /* TODO -- Handle other codes (NEGATE_EXPR, MINUS_EXPR, | |
| 354 POINTER_PLUS_EXPR). */ | |
| 355 | |
| 356 default: | |
| 357 return false; | |
| 358 } | |
| 359 } | |
| 360 | |
| 361 /* Propagate VAR through phis on edge E. */ | |
| 362 | |
| 363 static tree | |
| 364 propagate_through_phis (tree var, edge e) | |
| 365 { | |
| 366 basic_block dest = e->dest; | |
| 367 gimple_stmt_iterator gsi; | |
| 368 | |
| 369 for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 370 { | |
| 371 gimple phi = gsi_stmt (gsi); | |
| 372 if (PHI_ARG_DEF_FROM_EDGE (phi, e) == var) | |
| 373 return PHI_RESULT (phi); | |
| 374 } | |
| 375 return var; | |
| 376 } | |
| 377 | |
| 378 /* Finds tailcalls falling into basic block BB. The list of found tailcalls is | |
| 379 added to the start of RET. */ | |
| 380 | |
| 381 static void | |
| 382 find_tail_calls (basic_block bb, struct tailcall **ret) | |
| 383 { | |
| 384 tree ass_var = NULL_TREE, ret_var, func, param; | |
| 385 gimple stmt, call = NULL; | |
| 386 gimple_stmt_iterator gsi, agsi; | |
| 387 bool tail_recursion; | |
| 388 struct tailcall *nw; | |
| 389 edge e; | |
| 390 tree m, a; | |
| 391 basic_block abb; | |
| 392 size_t idx; | |
| 393 | |
| 394 if (!single_succ_p (bb)) | |
| 395 return; | |
| 396 | |
| 397 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi)) | |
| 398 { | |
| 399 stmt = gsi_stmt (gsi); | |
| 400 | |
| 401 /* Ignore labels. */ | |
| 402 if (gimple_code (stmt) == GIMPLE_LABEL) | |
| 403 continue; | |
| 404 | |
| 405 /* Check for a call. */ | |
| 406 if (is_gimple_call (stmt)) | |
| 407 { | |
| 408 call = stmt; | |
| 409 ass_var = gimple_call_lhs (stmt); | |
| 410 break; | |
| 411 } | |
| 412 | |
| 413 /* If the statement has virtual or volatile operands, fail. */ | |
| 414 if (!ZERO_SSA_OPERANDS (stmt, (SSA_OP_VUSE | SSA_OP_VIRTUAL_DEFS)) | |
| 415 || gimple_has_volatile_ops (stmt) | |
| 416 || (!gimple_aliases_computed_p (cfun) | |
| 417 && gimple_references_memory_p (stmt))) | |
| 418 return; | |
| 419 } | |
| 420 | |
| 421 if (gsi_end_p (gsi)) | |
| 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 /* If the LHS of our call is not just a simple register, we can't | |
| 432 transform this into a tail or sibling call. This situation happens, | |
| 433 in (e.g.) "*p = foo()" where foo returns a struct. In this case | |
| 434 we won't have a temporary here, but we need to carry out the side | |
| 435 effect anyway, so tailcall is impossible. | |
| 436 | |
| 437 ??? In some situations (when the struct is returned in memory via | |
| 438 invisible argument) we could deal with this, e.g. by passing 'p' | |
| 439 itself as that argument to foo, but it's too early to do this here, | |
| 440 and expand_call() will not handle it anyway. If it ever can, then | |
| 441 we need to revisit this here, to allow that situation. */ | |
| 442 if (ass_var && !is_gimple_reg (ass_var)) | |
| 443 return; | |
| 444 | |
| 445 /* We found the call, check whether it is suitable. */ | |
| 446 tail_recursion = false; | |
| 447 func = gimple_call_fndecl (call); | |
| 448 if (func == current_function_decl) | |
| 449 { | |
| 450 tree arg; | |
| 451 for (param = DECL_ARGUMENTS (func), idx = 0; | |
| 452 param && idx < gimple_call_num_args (call); | |
| 453 param = TREE_CHAIN (param), idx ++) | |
| 454 { | |
| 455 arg = gimple_call_arg (call, idx); | |
| 456 if (param != arg) | |
| 457 { | |
| 458 /* Make sure there are no problems with copying. The parameter | |
| 459 have a copyable type and the two arguments must have reasonably | |
| 460 equivalent types. The latter requirement could be relaxed if | |
| 461 we emitted a suitable type conversion statement. */ | |
| 462 if (!is_gimple_reg_type (TREE_TYPE (param)) | |
| 463 || !useless_type_conversion_p (TREE_TYPE (param), | |
| 464 TREE_TYPE (arg))) | |
| 465 break; | |
| 466 | |
| 467 /* The parameter should be a real operand, so that phi node | |
| 468 created for it at the start of the function has the meaning | |
| 469 of copying the value. This test implies is_gimple_reg_type | |
| 470 from the previous condition, however this one could be | |
| 471 relaxed by being more careful with copying the new value | |
| 472 of the parameter (emitting appropriate GIMPLE_ASSIGN and | |
| 473 updating the virtual operands). */ | |
| 474 if (!is_gimple_reg (param)) | |
| 475 break; | |
| 476 } | |
| 477 } | |
| 478 if (idx == gimple_call_num_args (call) && !param) | |
| 479 tail_recursion = true; | |
| 480 } | |
| 481 | |
| 482 /* Now check the statements after the call. None of them has virtual | |
| 483 operands, so they may only depend on the call through its return | |
| 484 value. The return value should also be dependent on each of them, | |
| 485 since we are running after dce. */ | |
| 486 m = NULL_TREE; | |
| 487 a = NULL_TREE; | |
| 488 | |
| 489 abb = bb; | |
| 490 agsi = gsi; | |
| 491 while (1) | |
| 492 { | |
| 493 gsi_next (&agsi); | |
| 494 | |
| 495 while (gsi_end_p (agsi)) | |
| 496 { | |
| 497 ass_var = propagate_through_phis (ass_var, single_succ_edge (abb)); | |
| 498 abb = single_succ (abb); | |
| 499 agsi = gsi_start_bb (abb); | |
| 500 } | |
| 501 | |
| 502 stmt = gsi_stmt (agsi); | |
| 503 | |
| 504 if (gimple_code (stmt) == GIMPLE_LABEL) | |
| 505 continue; | |
| 506 | |
| 507 if (gimple_code (stmt) == GIMPLE_RETURN) | |
| 508 break; | |
| 509 | |
| 510 if (gimple_code (stmt) != GIMPLE_ASSIGN) | |
| 511 return; | |
| 512 | |
| 513 /* This is a gimple assign. */ | |
| 514 if (! process_assignment (stmt, gsi, &m, &a, &ass_var)) | |
| 515 return; | |
| 516 } | |
| 517 | |
| 518 /* See if this is a tail call we can handle. */ | |
| 519 ret_var = gimple_return_retval (stmt); | |
| 520 | |
| 521 /* We may proceed if there either is no return value, or the return value | |
| 522 is identical to the call's return. */ | |
| 523 if (ret_var | |
| 524 && (ret_var != ass_var)) | |
| 525 return; | |
| 526 | |
| 527 /* If this is not a tail recursive call, we cannot handle addends or | |
| 528 multiplicands. */ | |
| 529 if (!tail_recursion && (m || a)) | |
| 530 return; | |
| 531 | |
| 532 nw = XNEW (struct tailcall); | |
| 533 | |
| 534 nw->call_gsi = gsi; | |
| 535 | |
| 536 nw->tail_recursion = tail_recursion; | |
| 537 | |
| 538 nw->mult = m; | |
| 539 nw->add = a; | |
| 540 | |
| 541 nw->next = *ret; | |
| 542 *ret = nw; | |
| 543 } | |
| 544 | |
| 545 /* Helper to insert PHI_ARGH to the phi of VAR in the destination of edge E. */ | |
| 546 | |
| 547 static void | |
| 548 add_successor_phi_arg (edge e, tree var, tree phi_arg) | |
| 549 { | |
| 550 gimple_stmt_iterator gsi; | |
| 551 | |
| 552 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 553 if (PHI_RESULT (gsi_stmt (gsi)) == var) | |
| 554 break; | |
| 555 | |
| 556 gcc_assert (!gsi_end_p (gsi)); | |
| 557 add_phi_arg (gsi_stmt (gsi), phi_arg, e); | |
| 558 } | |
| 559 | |
| 560 /* Creates a GIMPLE statement which computes the operation specified by | |
| 561 CODE, OP0 and OP1 to a new variable with name LABEL and inserts the | |
| 562 statement in the position specified by GSI and UPDATE. Returns the | |
| 563 tree node of the statement's result. */ | |
| 564 | |
| 565 static tree | |
| 566 adjust_return_value_with_ops (enum tree_code code, const char *label, | |
| 567 tree op0, tree op1, gimple_stmt_iterator gsi, | |
| 568 enum gsi_iterator_update update) | |
| 569 { | |
| 570 | |
| 571 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); | |
| 572 tree tmp = create_tmp_var (ret_type, label); | |
| 573 gimple stmt = gimple_build_assign_with_ops (code, tmp, op0, op1); | |
| 574 tree result; | |
| 575 | |
|
19
58ad6c70ea60
update gcc from 4.4.0 to 4.4.1.
kent@firefly.cr.ie.u-ryukyu.ac.jp
parents:
0
diff
changeset
|
576 if (TREE_CODE (ret_type) == COMPLEX_TYPE |
|
58ad6c70ea60
update gcc from 4.4.0 to 4.4.1.
kent@firefly.cr.ie.u-ryukyu.ac.jp
parents:
0
diff
changeset
|
577 || TREE_CODE (ret_type) == VECTOR_TYPE) |
|
58ad6c70ea60
update gcc from 4.4.0 to 4.4.1.
kent@firefly.cr.ie.u-ryukyu.ac.jp
parents:
0
diff
changeset
|
578 DECL_GIMPLE_REG_P (tmp) = 1; |
| 0 | 579 add_referenced_var (tmp); |
| 580 result = make_ssa_name (tmp, stmt); | |
| 581 gimple_assign_set_lhs (stmt, result); | |
| 582 update_stmt (stmt); | |
| 583 gsi_insert_before (&gsi, stmt, update); | |
| 584 return result; | |
| 585 } | |
| 586 | |
| 587 /* Creates a new GIMPLE statement that adjusts the value of accumulator ACC by | |
| 588 the computation specified by CODE and OP1 and insert the statement | |
| 589 at the position specified by GSI as a new statement. Returns new SSA name | |
| 590 of updated accumulator. */ | |
| 591 | |
| 592 static tree | |
| 593 update_accumulator_with_ops (enum tree_code code, tree acc, tree op1, | |
| 594 gimple_stmt_iterator gsi) | |
| 595 { | |
| 596 gimple stmt = gimple_build_assign_with_ops (code, SSA_NAME_VAR (acc), acc, | |
| 597 op1); | |
| 598 tree var = make_ssa_name (SSA_NAME_VAR (acc), stmt); | |
| 599 gimple_assign_set_lhs (stmt, var); | |
| 600 update_stmt (stmt); | |
| 601 gsi_insert_after (&gsi, stmt, GSI_NEW_STMT); | |
| 602 return var; | |
| 603 } | |
| 604 | |
| 605 /* Adjust the accumulator values according to A and M after GSI, and update | |
| 606 the phi nodes on edge BACK. */ | |
| 607 | |
| 608 static void | |
| 609 adjust_accumulator_values (gimple_stmt_iterator gsi, tree m, tree a, edge back) | |
| 610 { | |
| 611 tree var, a_acc_arg = a_acc, m_acc_arg = m_acc; | |
| 612 | |
| 613 if (a) | |
| 614 { | |
| 615 if (m_acc) | |
| 616 { | |
| 617 if (integer_onep (a)) | |
| 618 var = m_acc; | |
| 619 else | |
| 620 var = adjust_return_value_with_ops (MULT_EXPR, "acc_tmp", m_acc, | |
| 621 a, gsi, GSI_NEW_STMT); | |
| 622 } | |
| 623 else | |
| 624 var = a; | |
| 625 | |
| 626 a_acc_arg = update_accumulator_with_ops (PLUS_EXPR, a_acc, var, gsi); | |
| 627 } | |
| 628 | |
| 629 if (m) | |
| 630 m_acc_arg = update_accumulator_with_ops (MULT_EXPR, m_acc, m, gsi); | |
| 631 | |
| 632 if (a_acc) | |
| 633 add_successor_phi_arg (back, a_acc, a_acc_arg); | |
| 634 | |
| 635 if (m_acc) | |
| 636 add_successor_phi_arg (back, m_acc, m_acc_arg); | |
| 637 } | |
| 638 | |
| 639 /* Adjust value of the return at the end of BB according to M and A | |
| 640 accumulators. */ | |
| 641 | |
| 642 static void | |
| 643 adjust_return_value (basic_block bb, tree m, tree a) | |
| 644 { | |
| 645 tree retval; | |
| 646 gimple ret_stmt = gimple_seq_last_stmt (bb_seq (bb)); | |
| 647 gimple_stmt_iterator gsi = gsi_last_bb (bb); | |
| 648 | |
| 649 gcc_assert (gimple_code (ret_stmt) == GIMPLE_RETURN); | |
| 650 | |
| 651 retval = gimple_return_retval (ret_stmt); | |
| 652 if (!retval || retval == error_mark_node) | |
| 653 return; | |
| 654 | |
| 655 if (m) | |
| 656 retval = adjust_return_value_with_ops (MULT_EXPR, "mul_tmp", m_acc, retval, | |
| 657 gsi, GSI_SAME_STMT); | |
| 658 if (a) | |
| 659 retval = adjust_return_value_with_ops (PLUS_EXPR, "acc_tmp", a_acc, retval, | |
| 660 gsi, GSI_SAME_STMT); | |
| 661 gimple_return_set_retval (ret_stmt, retval); | |
| 662 update_stmt (ret_stmt); | |
| 663 } | |
| 664 | |
| 665 /* Subtract COUNT and FREQUENCY from the basic block and it's | |
| 666 outgoing edge. */ | |
| 667 static void | |
| 668 decrease_profile (basic_block bb, gcov_type count, int frequency) | |
| 669 { | |
| 670 edge e; | |
| 671 bb->count -= count; | |
| 672 if (bb->count < 0) | |
| 673 bb->count = 0; | |
| 674 bb->frequency -= frequency; | |
| 675 if (bb->frequency < 0) | |
| 676 bb->frequency = 0; | |
| 677 if (!single_succ_p (bb)) | |
| 678 { | |
| 679 gcc_assert (!EDGE_COUNT (bb->succs)); | |
| 680 return; | |
| 681 } | |
| 682 e = single_succ_edge (bb); | |
| 683 e->count -= count; | |
| 684 if (e->count < 0) | |
| 685 e->count = 0; | |
| 686 } | |
| 687 | |
| 688 /* Returns true if argument PARAM of the tail recursive call needs to be copied | |
| 689 when the call is eliminated. */ | |
| 690 | |
| 691 static bool | |
| 692 arg_needs_copy_p (tree param) | |
| 693 { | |
| 694 tree def; | |
| 695 | |
| 696 if (!is_gimple_reg (param) || !var_ann (param)) | |
| 697 return false; | |
| 698 | |
| 699 /* Parameters that are only defined but never used need not be copied. */ | |
| 700 def = gimple_default_def (cfun, param); | |
| 701 if (!def) | |
| 702 return false; | |
| 703 | |
| 704 return true; | |
| 705 } | |
| 706 | |
| 707 /* Eliminates tail call described by T. TMP_VARS is a list of | |
| 708 temporary variables used to copy the function arguments. */ | |
| 709 | |
| 710 static void | |
| 711 eliminate_tail_call (struct tailcall *t) | |
| 712 { | |
| 713 tree param, rslt; | |
| 714 gimple stmt, call; | |
| 715 tree arg; | |
| 716 size_t idx; | |
| 717 basic_block bb, first; | |
| 718 edge e; | |
| 719 gimple phi; | |
| 720 gimple_stmt_iterator gsi; | |
| 721 gimple orig_stmt; | |
| 722 | |
| 723 stmt = orig_stmt = gsi_stmt (t->call_gsi); | |
| 724 bb = gsi_bb (t->call_gsi); | |
| 725 | |
| 726 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 727 { | |
| 728 fprintf (dump_file, "Eliminated tail recursion in bb %d : ", | |
| 729 bb->index); | |
| 730 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); | |
| 731 fprintf (dump_file, "\n"); | |
| 732 } | |
| 733 | |
| 734 gcc_assert (is_gimple_call (stmt)); | |
| 735 | |
| 736 first = single_succ (ENTRY_BLOCK_PTR); | |
| 737 | |
| 738 /* Remove the code after call_gsi that will become unreachable. The | |
| 739 possibly unreachable code in other blocks is removed later in | |
| 740 cfg cleanup. */ | |
| 741 gsi = t->call_gsi; | |
| 742 gsi_next (&gsi); | |
| 743 while (!gsi_end_p (gsi)) | |
| 744 { | |
| 745 gimple t = gsi_stmt (gsi); | |
| 746 /* Do not remove the return statement, so that redirect_edge_and_branch | |
| 747 sees how the block ends. */ | |
| 748 if (gimple_code (t) == GIMPLE_RETURN) | |
| 749 break; | |
| 750 | |
| 751 gsi_remove (&gsi, true); | |
| 752 release_defs (t); | |
| 753 } | |
| 754 | |
| 755 /* Number of executions of function has reduced by the tailcall. */ | |
| 756 e = single_succ_edge (gsi_bb (t->call_gsi)); | |
| 757 decrease_profile (EXIT_BLOCK_PTR, e->count, EDGE_FREQUENCY (e)); | |
| 758 decrease_profile (ENTRY_BLOCK_PTR, e->count, EDGE_FREQUENCY (e)); | |
| 759 if (e->dest != EXIT_BLOCK_PTR) | |
| 760 decrease_profile (e->dest, e->count, EDGE_FREQUENCY (e)); | |
| 761 | |
| 762 /* Replace the call by a jump to the start of function. */ | |
| 763 e = redirect_edge_and_branch (single_succ_edge (gsi_bb (t->call_gsi)), | |
| 764 first); | |
| 765 gcc_assert (e); | |
| 766 PENDING_STMT (e) = NULL; | |
| 767 | |
| 768 /* Add phi node entries for arguments. The ordering of the phi nodes should | |
| 769 be the same as the ordering of the arguments. */ | |
| 770 for (param = DECL_ARGUMENTS (current_function_decl), | |
| 771 idx = 0, gsi = gsi_start_phis (first); | |
| 772 param; | |
| 773 param = TREE_CHAIN (param), idx++) | |
| 774 { | |
| 775 if (!arg_needs_copy_p (param)) | |
| 776 continue; | |
| 777 | |
| 778 arg = gimple_call_arg (stmt, idx); | |
| 779 phi = gsi_stmt (gsi); | |
| 780 gcc_assert (param == SSA_NAME_VAR (PHI_RESULT (phi))); | |
| 781 | |
| 782 add_phi_arg (phi, arg, e); | |
| 783 gsi_next (&gsi); | |
| 784 } | |
| 785 | |
| 786 /* Update the values of accumulators. */ | |
| 787 adjust_accumulator_values (t->call_gsi, t->mult, t->add, e); | |
| 788 | |
| 789 call = gsi_stmt (t->call_gsi); | |
| 790 rslt = gimple_call_lhs (call); | |
| 791 if (rslt != NULL_TREE) | |
| 792 { | |
| 793 /* Result of the call will no longer be defined. So adjust the | |
| 794 SSA_NAME_DEF_STMT accordingly. */ | |
| 795 SSA_NAME_DEF_STMT (rslt) = gimple_build_nop (); | |
| 796 } | |
| 797 | |
| 798 gsi_remove (&t->call_gsi, true); | |
| 799 release_defs (call); | |
| 800 } | |
| 801 | |
| 802 /* Add phi nodes for the virtual operands defined in the function to the | |
| 803 header of the loop created by tail recursion elimination. | |
| 804 | |
| 805 Originally, we used to add phi nodes only for call clobbered variables, | |
| 806 as the value of the non-call clobbered ones obviously cannot be used | |
| 807 or changed within the recursive call. However, the local variables | |
| 808 from multiple calls now share the same location, so the virtual ssa form | |
| 809 requires us to say that the location dies on further iterations of the loop, | |
| 810 which requires adding phi nodes. | |
| 811 */ | |
| 812 static void | |
| 813 add_virtual_phis (void) | |
| 814 { | |
| 815 referenced_var_iterator rvi; | |
| 816 tree var; | |
| 817 | |
| 818 /* The problematic part is that there is no way how to know what | |
| 819 to put into phi nodes (there in fact does not have to be such | |
| 820 ssa name available). A solution would be to have an artificial | |
| 821 use/kill for all virtual operands in EXIT node. Unless we have | |
| 822 this, we cannot do much better than to rebuild the ssa form for | |
| 823 possibly affected virtual ssa names from scratch. */ | |
| 824 | |
| 825 FOR_EACH_REFERENCED_VAR (var, rvi) | |
| 826 { | |
| 827 if (!is_gimple_reg (var) && gimple_default_def (cfun, var) != NULL_TREE) | |
| 828 mark_sym_for_renaming (var); | |
| 829 } | |
| 830 } | |
| 831 | |
| 832 /* Optimizes the tailcall described by T. If OPT_TAILCALLS is true, also | |
| 833 mark the tailcalls for the sibcall optimization. */ | |
| 834 | |
| 835 static bool | |
| 836 optimize_tail_call (struct tailcall *t, bool opt_tailcalls) | |
| 837 { | |
| 838 if (t->tail_recursion) | |
| 839 { | |
| 840 eliminate_tail_call (t); | |
| 841 return true; | |
| 842 } | |
| 843 | |
| 844 if (opt_tailcalls) | |
| 845 { | |
| 846 gimple stmt = gsi_stmt (t->call_gsi); | |
| 847 | |
| 848 gimple_call_set_tail (stmt, true); | |
| 849 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 850 { | |
| 851 fprintf (dump_file, "Found tail call "); | |
| 852 print_gimple_stmt (dump_file, stmt, 0, dump_flags); | |
| 853 fprintf (dump_file, " in bb %i\n", (gsi_bb (t->call_gsi))->index); | |
| 854 } | |
| 855 } | |
| 856 | |
| 857 return false; | |
| 858 } | |
| 859 | |
| 860 /* Creates a tail-call accumulator of the same type as the return type of the | |
| 861 current function. LABEL is the name used to creating the temporary | |
| 862 variable for the accumulator. The accumulator will be inserted in the | |
| 863 phis of a basic block BB with single predecessor with an initial value | |
| 864 INIT converted to the current function return type. */ | |
| 865 | |
| 866 static tree | |
| 867 create_tailcall_accumulator (const char *label, basic_block bb, tree init) | |
| 868 { | |
| 869 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); | |
| 870 tree tmp = create_tmp_var (ret_type, label); | |
| 871 gimple phi; | |
| 872 | |
|
19
58ad6c70ea60
update gcc from 4.4.0 to 4.4.1.
kent@firefly.cr.ie.u-ryukyu.ac.jp
parents:
0
diff
changeset
|
873 if (TREE_CODE (ret_type) == COMPLEX_TYPE |
|
58ad6c70ea60
update gcc from 4.4.0 to 4.4.1.
kent@firefly.cr.ie.u-ryukyu.ac.jp
parents:
0
diff
changeset
|
874 || TREE_CODE (ret_type) == VECTOR_TYPE) |
|
58ad6c70ea60
update gcc from 4.4.0 to 4.4.1.
kent@firefly.cr.ie.u-ryukyu.ac.jp
parents:
0
diff
changeset
|
875 DECL_GIMPLE_REG_P (tmp) = 1; |
| 0 | 876 add_referenced_var (tmp); |
| 877 phi = create_phi_node (tmp, bb); | |
| 878 /* RET_TYPE can be a float when -ffast-maths is enabled. */ | |
| 879 add_phi_arg (phi, fold_convert (ret_type, init), single_pred_edge (bb)); | |
| 880 return PHI_RESULT (phi); | |
| 881 } | |
| 882 | |
| 883 /* Optimizes tail calls in the function, turning the tail recursion | |
| 884 into iteration. */ | |
| 885 | |
| 886 static unsigned int | |
| 887 tree_optimize_tail_calls_1 (bool opt_tailcalls) | |
| 888 { | |
| 889 edge e; | |
| 890 bool phis_constructed = false; | |
| 891 struct tailcall *tailcalls = NULL, *act, *next; | |
| 892 bool changed = false; | |
| 893 basic_block first = single_succ (ENTRY_BLOCK_PTR); | |
| 894 tree param; | |
| 895 gimple stmt; | |
| 896 edge_iterator ei; | |
| 897 | |
| 898 if (!suitable_for_tail_opt_p ()) | |
| 899 return 0; | |
| 900 if (opt_tailcalls) | |
| 901 opt_tailcalls = suitable_for_tail_call_opt_p (); | |
| 902 | |
| 903 FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds) | |
| 904 { | |
| 905 /* Only traverse the normal exits, i.e. those that end with return | |
| 906 statement. */ | |
| 907 stmt = last_stmt (e->src); | |
| 908 | |
| 909 if (stmt | |
| 910 && gimple_code (stmt) == GIMPLE_RETURN) | |
| 911 find_tail_calls (e->src, &tailcalls); | |
| 912 } | |
| 913 | |
| 914 /* Construct the phi nodes and accumulators if necessary. */ | |
| 915 a_acc = m_acc = NULL_TREE; | |
| 916 for (act = tailcalls; act; act = act->next) | |
| 917 { | |
| 918 if (!act->tail_recursion) | |
| 919 continue; | |
| 920 | |
| 921 if (!phis_constructed) | |
| 922 { | |
| 923 /* Ensure that there is only one predecessor of the block. */ | |
| 924 if (!single_pred_p (first)) | |
| 925 first = split_edge (single_succ_edge (ENTRY_BLOCK_PTR)); | |
| 926 | |
| 927 /* Copy the args if needed. */ | |
| 928 for (param = DECL_ARGUMENTS (current_function_decl); | |
| 929 param; | |
| 930 param = TREE_CHAIN (param)) | |
| 931 if (arg_needs_copy_p (param)) | |
| 932 { | |
| 933 tree name = gimple_default_def (cfun, param); | |
| 934 tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name)); | |
| 935 gimple phi; | |
| 936 | |
| 937 set_default_def (param, new_name); | |
| 938 phi = create_phi_node (name, first); | |
| 939 SSA_NAME_DEF_STMT (name) = phi; | |
| 940 add_phi_arg (phi, new_name, single_pred_edge (first)); | |
| 941 } | |
| 942 phis_constructed = true; | |
| 943 } | |
| 944 | |
| 945 if (act->add && !a_acc) | |
| 946 a_acc = create_tailcall_accumulator ("add_acc", first, | |
| 947 integer_zero_node); | |
| 948 | |
| 949 if (act->mult && !m_acc) | |
| 950 m_acc = create_tailcall_accumulator ("mult_acc", first, | |
| 951 integer_one_node); | |
| 952 } | |
| 953 | |
| 954 for (; tailcalls; tailcalls = next) | |
| 955 { | |
| 956 next = tailcalls->next; | |
| 957 changed |= optimize_tail_call (tailcalls, opt_tailcalls); | |
| 958 free (tailcalls); | |
| 959 } | |
| 960 | |
| 961 if (a_acc || m_acc) | |
| 962 { | |
| 963 /* Modify the remaining return statements. */ | |
| 964 FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds) | |
| 965 { | |
| 966 stmt = last_stmt (e->src); | |
| 967 | |
| 968 if (stmt | |
| 969 && gimple_code (stmt) == GIMPLE_RETURN) | |
| 970 adjust_return_value (e->src, m_acc, a_acc); | |
| 971 } | |
| 972 } | |
| 973 | |
| 974 if (changed) | |
| 975 free_dominance_info (CDI_DOMINATORS); | |
| 976 | |
| 977 if (phis_constructed) | |
| 978 add_virtual_phis (); | |
| 979 if (changed) | |
| 980 return TODO_cleanup_cfg | TODO_update_ssa_only_virtuals; | |
| 981 return 0; | |
| 982 } | |
| 983 | |
| 984 static unsigned int | |
| 985 execute_tail_recursion (void) | |
| 986 { | |
| 987 return tree_optimize_tail_calls_1 (false); | |
| 988 } | |
| 989 | |
| 990 static bool | |
| 991 gate_tail_calls (void) | |
| 992 { | |
| 993 return flag_optimize_sibling_calls != 0 && dbg_cnt (tail_call); | |
| 994 } | |
| 995 | |
| 996 static unsigned int | |
| 997 execute_tail_calls (void) | |
| 998 { | |
| 999 return tree_optimize_tail_calls_1 (true); | |
| 1000 } | |
| 1001 | |
| 1002 struct gimple_opt_pass pass_tail_recursion = | |
| 1003 { | |
| 1004 { | |
| 1005 GIMPLE_PASS, | |
| 1006 "tailr", /* name */ | |
| 1007 gate_tail_calls, /* gate */ | |
| 1008 execute_tail_recursion, /* execute */ | |
| 1009 NULL, /* sub */ | |
| 1010 NULL, /* next */ | |
| 1011 0, /* static_pass_number */ | |
| 1012 0, /* tv_id */ | |
| 1013 PROP_cfg | PROP_ssa, /* properties_required */ | |
| 1014 0, /* properties_provided */ | |
| 1015 0, /* properties_destroyed */ | |
| 1016 0, /* todo_flags_start */ | |
| 1017 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ | |
| 1018 } | |
| 1019 }; | |
| 1020 | |
| 1021 struct gimple_opt_pass pass_tail_calls = | |
| 1022 { | |
| 1023 { | |
| 1024 GIMPLE_PASS, | |
| 1025 "tailc", /* name */ | |
| 1026 gate_tail_calls, /* gate */ | |
| 1027 execute_tail_calls, /* execute */ | |
| 1028 NULL, /* sub */ | |
| 1029 NULL, /* next */ | |
| 1030 0, /* static_pass_number */ | |
| 1031 0, /* tv_id */ | |
| 1032 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ | |
| 1033 0, /* properties_provided */ | |
| 1034 0, /* properties_destroyed */ | |
| 1035 0, /* todo_flags_start */ | |
| 1036 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ | |
| 1037 } | |
| 1038 }; |