Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-threadedge.c @ 55:77e2b8dfacca gcc-4.4.5
update it from 4.4.3 to 4.5.0
| author | ryoma <e075725@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Fri, 12 Feb 2010 23:39:51 +0900 |
| parents | a06113de4d67 |
| children | b7f97abdc517 |
| rev | line source |
|---|---|
| 0 | 1 /* SSA Jump Threading |
| 2 Copyright (C) 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. | |
| 3 Contributed by Jeff Law <law@redhat.com> | |
| 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 "flags.h" | |
| 27 #include "rtl.h" | |
| 28 #include "tm_p.h" | |
| 29 #include "ggc.h" | |
| 30 #include "basic-block.h" | |
| 31 #include "cfgloop.h" | |
| 32 #include "output.h" | |
| 33 #include "expr.h" | |
| 34 #include "function.h" | |
| 35 #include "diagnostic.h" | |
| 36 #include "timevar.h" | |
| 37 #include "tree-dump.h" | |
| 38 #include "tree-flow.h" | |
| 39 #include "real.h" | |
| 40 #include "tree-pass.h" | |
| 41 #include "tree-ssa-propagate.h" | |
| 42 #include "langhooks.h" | |
| 43 #include "params.h" | |
| 44 | |
| 45 /* To avoid code explosion due to jump threading, we limit the | |
| 46 number of statements we are going to copy. This variable | |
| 47 holds the number of statements currently seen that we'll have | |
| 48 to copy as part of the jump threading process. */ | |
| 49 static int stmt_count; | |
| 50 | |
|
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51 /* Array to record value-handles per SSA_NAME. */ |
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52 VEC(tree,heap) *ssa_name_values; |
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53 |
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54 /* Set the value for the SSA name NAME to VALUE. */ |
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55 |
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56 void |
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57 set_ssa_name_value (tree name, tree value) |
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58 { |
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59 if (SSA_NAME_VERSION (name) >= VEC_length (tree, ssa_name_values)) |
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60 VEC_safe_grow_cleared (tree, heap, ssa_name_values, |
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61 SSA_NAME_VERSION (name) + 1); |
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62 VEC_replace (tree, ssa_name_values, SSA_NAME_VERSION (name), value); |
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63 } |
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64 |
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65 /* Initialize the per SSA_NAME value-handles array. Returns it. */ |
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66 void |
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67 threadedge_initialize_values (void) |
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68 { |
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69 gcc_assert (ssa_name_values == NULL); |
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70 ssa_name_values = VEC_alloc(tree, heap, num_ssa_names); |
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71 } |
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72 |
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73 /* Free the per SSA_NAME value-handle array. */ |
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74 void |
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75 threadedge_finalize_values (void) |
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76 { |
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77 VEC_free(tree, heap, ssa_name_values); |
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78 } |
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79 |
| 0 | 80 /* Return TRUE if we may be able to thread an incoming edge into |
| 81 BB to an outgoing edge from BB. Return FALSE otherwise. */ | |
| 82 | |
| 83 bool | |
| 84 potentially_threadable_block (basic_block bb) | |
| 85 { | |
| 86 gimple_stmt_iterator gsi; | |
| 87 | |
| 88 /* If BB has a single successor or a single predecessor, then | |
| 89 there is no threading opportunity. */ | |
| 90 if (single_succ_p (bb) || single_pred_p (bb)) | |
| 91 return false; | |
| 92 | |
| 93 /* If BB does not end with a conditional, switch or computed goto, | |
| 94 then there is no threading opportunity. */ | |
| 95 gsi = gsi_last_bb (bb); | |
| 96 if (gsi_end_p (gsi) | |
| 97 || ! gsi_stmt (gsi) | |
| 98 || (gimple_code (gsi_stmt (gsi)) != GIMPLE_COND | |
| 99 && gimple_code (gsi_stmt (gsi)) != GIMPLE_GOTO | |
| 100 && gimple_code (gsi_stmt (gsi)) != GIMPLE_SWITCH)) | |
| 101 return false; | |
| 102 | |
| 103 return true; | |
| 104 } | |
| 105 | |
| 106 /* Return the LHS of any ASSERT_EXPR where OP appears as the first | |
| 107 argument to the ASSERT_EXPR and in which the ASSERT_EXPR dominates | |
| 108 BB. If no such ASSERT_EXPR is found, return OP. */ | |
| 109 | |
| 110 static tree | |
| 111 lhs_of_dominating_assert (tree op, basic_block bb, gimple stmt) | |
| 112 { | |
| 113 imm_use_iterator imm_iter; | |
| 114 gimple use_stmt; | |
| 115 use_operand_p use_p; | |
| 116 | |
| 117 FOR_EACH_IMM_USE_FAST (use_p, imm_iter, op) | |
| 118 { | |
| 119 use_stmt = USE_STMT (use_p); | |
| 120 if (use_stmt != stmt | |
| 121 && gimple_assign_single_p (use_stmt) | |
| 122 && TREE_CODE (gimple_assign_rhs1 (use_stmt)) == ASSERT_EXPR | |
| 123 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == op | |
| 124 && dominated_by_p (CDI_DOMINATORS, bb, gimple_bb (use_stmt))) | |
| 125 { | |
| 126 return gimple_assign_lhs (use_stmt); | |
| 127 } | |
| 128 } | |
| 129 return op; | |
| 130 } | |
| 131 | |
| 132 /* We record temporary equivalences created by PHI nodes or | |
| 133 statements within the target block. Doing so allows us to | |
| 134 identify more jump threading opportunities, even in blocks | |
| 135 with side effects. | |
| 136 | |
| 137 We keep track of those temporary equivalences in a stack | |
| 138 structure so that we can unwind them when we're done processing | |
| 139 a particular edge. This routine handles unwinding the data | |
| 140 structures. */ | |
| 141 | |
| 142 static void | |
| 143 remove_temporary_equivalences (VEC(tree, heap) **stack) | |
| 144 { | |
| 145 while (VEC_length (tree, *stack) > 0) | |
| 146 { | |
| 147 tree prev_value, dest; | |
| 148 | |
| 149 dest = VEC_pop (tree, *stack); | |
| 150 | |
| 151 /* A NULL value indicates we should stop unwinding, otherwise | |
| 152 pop off the next entry as they're recorded in pairs. */ | |
| 153 if (dest == NULL) | |
| 154 break; | |
| 155 | |
| 156 prev_value = VEC_pop (tree, *stack); | |
|
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157 set_ssa_name_value (dest, prev_value); |
| 0 | 158 } |
| 159 } | |
| 160 | |
| 161 /* Record a temporary equivalence, saving enough information so that | |
| 162 we can restore the state of recorded equivalences when we're | |
| 163 done processing the current edge. */ | |
| 164 | |
| 165 static void | |
| 166 record_temporary_equivalence (tree x, tree y, VEC(tree, heap) **stack) | |
| 167 { | |
| 168 tree prev_x = SSA_NAME_VALUE (x); | |
| 169 | |
| 170 if (TREE_CODE (y) == SSA_NAME) | |
| 171 { | |
| 172 tree tmp = SSA_NAME_VALUE (y); | |
| 173 y = tmp ? tmp : y; | |
| 174 } | |
| 175 | |
|
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176 set_ssa_name_value (x, y); |
| 0 | 177 VEC_reserve (tree, heap, *stack, 2); |
| 178 VEC_quick_push (tree, *stack, prev_x); | |
| 179 VEC_quick_push (tree, *stack, x); | |
| 180 } | |
| 181 | |
| 182 /* Record temporary equivalences created by PHIs at the target of the | |
|
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183 edge E. Record unwind information for the equivalences onto STACK. |
| 0 | 184 |
| 185 If a PHI which prevents threading is encountered, then return FALSE | |
| 186 indicating we should not thread this edge, else return TRUE. */ | |
| 187 | |
| 188 static bool | |
| 189 record_temporary_equivalences_from_phis (edge e, VEC(tree, heap) **stack) | |
| 190 { | |
| 191 gimple_stmt_iterator gsi; | |
| 192 | |
| 193 /* Each PHI creates a temporary equivalence, record them. | |
| 194 These are context sensitive equivalences and will be removed | |
| 195 later. */ | |
| 196 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 197 { | |
| 198 gimple phi = gsi_stmt (gsi); | |
| 199 tree src = PHI_ARG_DEF_FROM_EDGE (phi, e); | |
| 200 tree dst = gimple_phi_result (phi); | |
| 201 | |
|
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202 /* If the desired argument is not the same as this PHI's result |
| 0 | 203 and it is set by a PHI in E->dest, then we can not thread |
| 204 through E->dest. */ | |
| 205 if (src != dst | |
| 206 && TREE_CODE (src) == SSA_NAME | |
| 207 && gimple_code (SSA_NAME_DEF_STMT (src)) == GIMPLE_PHI | |
| 208 && gimple_bb (SSA_NAME_DEF_STMT (src)) == e->dest) | |
| 209 return false; | |
| 210 | |
| 211 /* We consider any non-virtual PHI as a statement since it | |
| 212 count result in a constant assignment or copy operation. */ | |
| 213 if (is_gimple_reg (dst)) | |
| 214 stmt_count++; | |
| 215 | |
| 216 record_temporary_equivalence (dst, src, stack); | |
| 217 } | |
| 218 return true; | |
| 219 } | |
| 220 | |
| 221 /* Fold the RHS of an assignment statement and return it as a tree. | |
| 222 May return NULL_TREE if no simplification is possible. */ | |
| 223 | |
| 224 static tree | |
| 225 fold_assignment_stmt (gimple stmt) | |
| 226 { | |
| 227 enum tree_code subcode = gimple_assign_rhs_code (stmt); | |
| 228 | |
| 229 switch (get_gimple_rhs_class (subcode)) | |
| 230 { | |
| 231 case GIMPLE_SINGLE_RHS: | |
| 232 { | |
| 233 tree rhs = gimple_assign_rhs1 (stmt); | |
| 234 | |
| 235 if (TREE_CODE (rhs) == COND_EXPR) | |
| 236 { | |
| 237 /* Sadly, we have to handle conditional assignments specially | |
| 238 here, because fold expects all the operands of an expression | |
| 239 to be folded before the expression itself is folded, but we | |
| 240 can't just substitute the folded condition here. */ | |
| 241 tree cond = fold (COND_EXPR_COND (rhs)); | |
| 242 if (cond == boolean_true_node) | |
| 243 rhs = COND_EXPR_THEN (rhs); | |
| 244 else if (cond == boolean_false_node) | |
| 245 rhs = COND_EXPR_ELSE (rhs); | |
| 246 } | |
| 247 | |
| 248 return fold (rhs); | |
| 249 } | |
| 250 break; | |
| 251 case GIMPLE_UNARY_RHS: | |
| 252 { | |
| 253 tree lhs = gimple_assign_lhs (stmt); | |
| 254 tree op0 = gimple_assign_rhs1 (stmt); | |
| 255 return fold_unary (subcode, TREE_TYPE (lhs), op0); | |
| 256 } | |
| 257 break; | |
| 258 case GIMPLE_BINARY_RHS: | |
| 259 { | |
| 260 tree lhs = gimple_assign_lhs (stmt); | |
| 261 tree op0 = gimple_assign_rhs1 (stmt); | |
| 262 tree op1 = gimple_assign_rhs2 (stmt); | |
| 263 return fold_binary (subcode, TREE_TYPE (lhs), op0, op1); | |
| 264 } | |
| 265 break; | |
| 266 default: | |
| 267 gcc_unreachable (); | |
| 268 } | |
| 269 } | |
| 270 | |
| 271 /* Try to simplify each statement in E->dest, ultimately leading to | |
| 272 a simplification of the COND_EXPR at the end of E->dest. | |
| 273 | |
| 274 Record unwind information for temporary equivalences onto STACK. | |
| 275 | |
| 276 Use SIMPLIFY (a pointer to a callback function) to further simplify | |
|
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277 statements using pass specific information. |
| 0 | 278 |
| 279 We might consider marking just those statements which ultimately | |
| 280 feed the COND_EXPR. It's not clear if the overhead of bookkeeping | |
| 281 would be recovered by trying to simplify fewer statements. | |
| 282 | |
| 283 If we are able to simplify a statement into the form | |
| 284 SSA_NAME = (SSA_NAME | gimple invariant), then we can record | |
| 285 a context sensitive equivalence which may help us simplify | |
| 286 later statements in E->dest. */ | |
| 287 | |
| 288 static gimple | |
| 289 record_temporary_equivalences_from_stmts_at_dest (edge e, | |
| 290 VEC(tree, heap) **stack, | |
| 291 tree (*simplify) (gimple, | |
| 292 gimple)) | |
| 293 { | |
| 294 gimple stmt = NULL; | |
| 295 gimple_stmt_iterator gsi; | |
| 296 int max_stmt_count; | |
| 297 | |
| 298 max_stmt_count = PARAM_VALUE (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS); | |
| 299 | |
| 300 /* Walk through each statement in the block recording equivalences | |
| 301 we discover. Note any equivalences we discover are context | |
| 302 sensitive (ie, are dependent on traversing E) and must be unwound | |
| 303 when we're finished processing E. */ | |
| 304 for (gsi = gsi_start_bb (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 305 { | |
| 306 tree cached_lhs = NULL; | |
| 307 | |
| 308 stmt = gsi_stmt (gsi); | |
| 309 | |
| 310 /* Ignore empty statements and labels. */ | |
|
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311 if (gimple_code (stmt) == GIMPLE_NOP |
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312 || gimple_code (stmt) == GIMPLE_LABEL |
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313 || is_gimple_debug (stmt)) |
| 0 | 314 continue; |
| 315 | |
| 316 /* If the statement has volatile operands, then we assume we | |
| 317 can not thread through this block. This is overly | |
| 318 conservative in some ways. */ | |
| 319 if (gimple_code (stmt) == GIMPLE_ASM && gimple_asm_volatile_p (stmt)) | |
| 320 return NULL; | |
| 321 | |
| 322 /* If duplicating this block is going to cause too much code | |
| 323 expansion, then do not thread through this block. */ | |
| 324 stmt_count++; | |
| 325 if (stmt_count > max_stmt_count) | |
| 326 return NULL; | |
| 327 | |
| 328 /* If this is not a statement that sets an SSA_NAME to a new | |
| 329 value, then do not try to simplify this statement as it will | |
| 330 not simplify in any way that is helpful for jump threading. */ | |
| 331 if ((gimple_code (stmt) != GIMPLE_ASSIGN | |
| 332 || TREE_CODE (gimple_assign_lhs (stmt)) != SSA_NAME) | |
| 333 && (gimple_code (stmt) != GIMPLE_CALL | |
| 334 || gimple_call_lhs (stmt) == NULL_TREE | |
| 335 || TREE_CODE (gimple_call_lhs (stmt)) != SSA_NAME)) | |
| 336 continue; | |
| 337 | |
| 338 /* The result of __builtin_object_size depends on all the arguments | |
| 339 of a phi node. Temporarily using only one edge produces invalid | |
| 340 results. For example | |
| 341 | |
| 342 if (x < 6) | |
| 343 goto l; | |
| 344 else | |
| 345 goto l; | |
| 346 | |
| 347 l: | |
| 348 r = PHI <&w[2].a[1](2), &a.a[6](3)> | |
| 349 __builtin_object_size (r, 0) | |
| 350 | |
| 351 The result of __builtin_object_size is defined to be the maximum of | |
| 352 remaining bytes. If we use only one edge on the phi, the result will | |
| 353 change to be the remaining bytes for the corresponding phi argument. | |
| 354 | |
| 355 Similarly for __builtin_constant_p: | |
| 356 | |
| 357 r = PHI <1(2), 2(3)> | |
| 358 __builtin_constant_p (r) | |
| 359 | |
| 360 Both PHI arguments are constant, but x ? 1 : 2 is still not | |
| 361 constant. */ | |
| 362 | |
| 363 if (is_gimple_call (stmt)) | |
| 364 { | |
| 365 tree fndecl = gimple_call_fndecl (stmt); | |
| 366 if (fndecl | |
| 367 && (DECL_FUNCTION_CODE (fndecl) == BUILT_IN_OBJECT_SIZE | |
| 368 || DECL_FUNCTION_CODE (fndecl) == BUILT_IN_CONSTANT_P)) | |
| 369 continue; | |
| 370 } | |
| 371 | |
| 372 /* At this point we have a statement which assigns an RHS to an | |
| 373 SSA_VAR on the LHS. We want to try and simplify this statement | |
| 374 to expose more context sensitive equivalences which in turn may | |
|
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375 allow us to simplify the condition at the end of the loop. |
| 0 | 376 |
| 377 Handle simple copy operations as well as implied copies from | |
| 378 ASSERT_EXPRs. */ | |
| 379 if (gimple_assign_single_p (stmt) | |
| 380 && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME) | |
| 381 cached_lhs = gimple_assign_rhs1 (stmt); | |
| 382 else if (gimple_assign_single_p (stmt) | |
| 383 && TREE_CODE (gimple_assign_rhs1 (stmt)) == ASSERT_EXPR) | |
| 384 cached_lhs = TREE_OPERAND (gimple_assign_rhs1 (stmt), 0); | |
| 385 else | |
| 386 { | |
| 387 /* A statement that is not a trivial copy or ASSERT_EXPR. | |
| 388 We're going to temporarily copy propagate the operands | |
| 389 and see if that allows us to simplify this statement. */ | |
| 390 tree *copy; | |
| 391 ssa_op_iter iter; | |
| 392 use_operand_p use_p; | |
| 393 unsigned int num, i = 0; | |
| 394 | |
| 395 num = NUM_SSA_OPERANDS (stmt, (SSA_OP_USE | SSA_OP_VUSE)); | |
| 396 copy = XCNEWVEC (tree, num); | |
| 397 | |
| 398 /* Make a copy of the uses & vuses into USES_COPY, then cprop into | |
| 399 the operands. */ | |
| 400 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE | SSA_OP_VUSE) | |
| 401 { | |
| 402 tree tmp = NULL; | |
| 403 tree use = USE_FROM_PTR (use_p); | |
| 404 | |
| 405 copy[i++] = use; | |
| 406 if (TREE_CODE (use) == SSA_NAME) | |
| 407 tmp = SSA_NAME_VALUE (use); | |
| 408 if (tmp) | |
| 409 SET_USE (use_p, tmp); | |
| 410 } | |
| 411 | |
| 412 /* Try to fold/lookup the new expression. Inserting the | |
| 413 expression into the hash table is unlikely to help. */ | |
| 414 if (is_gimple_call (stmt)) | |
| 415 cached_lhs = fold_call_stmt (stmt, false); | |
| 416 else | |
| 417 cached_lhs = fold_assignment_stmt (stmt); | |
| 418 | |
| 419 if (!cached_lhs | |
| 420 || (TREE_CODE (cached_lhs) != SSA_NAME | |
| 421 && !is_gimple_min_invariant (cached_lhs))) | |
| 422 cached_lhs = (*simplify) (stmt, stmt); | |
|
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423 |
| 0 | 424 /* Restore the statement's original uses/defs. */ |
| 425 i = 0; | |
| 426 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE | SSA_OP_VUSE) | |
| 427 SET_USE (use_p, copy[i++]); | |
| 428 | |
| 429 free (copy); | |
| 430 } | |
| 431 | |
| 432 /* Record the context sensitive equivalence if we were able | |
| 433 to simplify this statement. */ | |
| 434 if (cached_lhs | |
| 435 && (TREE_CODE (cached_lhs) == SSA_NAME | |
| 436 || is_gimple_min_invariant (cached_lhs))) | |
| 437 record_temporary_equivalence (gimple_get_lhs (stmt), cached_lhs, stack); | |
| 438 } | |
| 439 return stmt; | |
| 440 } | |
| 441 | |
| 442 /* Simplify the control statement at the end of the block E->dest. | |
| 443 | |
| 444 To avoid allocating memory unnecessarily, a scratch GIMPLE_COND | |
| 445 is available to use/clobber in DUMMY_COND. | |
| 446 | |
| 447 Use SIMPLIFY (a pointer to a callback function) to further simplify | |
| 448 a condition using pass specific information. | |
| 449 | |
| 450 Return the simplified condition or NULL if simplification could | |
| 451 not be performed. */ | |
| 452 | |
| 453 static tree | |
| 454 simplify_control_stmt_condition (edge e, | |
| 455 gimple stmt, | |
| 456 gimple dummy_cond, | |
| 457 tree (*simplify) (gimple, gimple), | |
| 458 bool handle_dominating_asserts) | |
| 459 { | |
| 460 tree cond, cached_lhs; | |
| 461 enum gimple_code code = gimple_code (stmt); | |
| 462 | |
| 463 /* For comparisons, we have to update both operands, then try | |
| 464 to simplify the comparison. */ | |
| 465 if (code == GIMPLE_COND) | |
| 466 { | |
| 467 tree op0, op1; | |
| 468 enum tree_code cond_code; | |
| 469 | |
| 470 op0 = gimple_cond_lhs (stmt); | |
| 471 op1 = gimple_cond_rhs (stmt); | |
| 472 cond_code = gimple_cond_code (stmt); | |
| 473 | |
| 474 /* Get the current value of both operands. */ | |
| 475 if (TREE_CODE (op0) == SSA_NAME) | |
| 476 { | |
| 477 tree tmp = SSA_NAME_VALUE (op0); | |
| 478 if (tmp) | |
| 479 op0 = tmp; | |
| 480 } | |
| 481 | |
| 482 if (TREE_CODE (op1) == SSA_NAME) | |
| 483 { | |
| 484 tree tmp = SSA_NAME_VALUE (op1); | |
| 485 if (tmp) | |
| 486 op1 = tmp; | |
| 487 } | |
| 488 | |
| 489 if (handle_dominating_asserts) | |
| 490 { | |
| 491 /* Now see if the operand was consumed by an ASSERT_EXPR | |
| 492 which dominates E->src. If so, we want to replace the | |
| 493 operand with the LHS of the ASSERT_EXPR. */ | |
| 494 if (TREE_CODE (op0) == SSA_NAME) | |
| 495 op0 = lhs_of_dominating_assert (op0, e->src, stmt); | |
| 496 | |
| 497 if (TREE_CODE (op1) == SSA_NAME) | |
| 498 op1 = lhs_of_dominating_assert (op1, e->src, stmt); | |
| 499 } | |
| 500 | |
| 501 /* We may need to canonicalize the comparison. For | |
| 502 example, op0 might be a constant while op1 is an | |
| 503 SSA_NAME. Failure to canonicalize will cause us to | |
| 504 miss threading opportunities. */ | |
| 505 if (tree_swap_operands_p (op0, op1, false)) | |
| 506 { | |
| 507 tree tmp; | |
| 508 cond_code = swap_tree_comparison (cond_code); | |
| 509 tmp = op0; | |
| 510 op0 = op1; | |
| 511 op1 = tmp; | |
| 512 } | |
| 513 | |
| 514 /* Stuff the operator and operands into our dummy conditional | |
| 515 expression. */ | |
| 516 gimple_cond_set_code (dummy_cond, cond_code); | |
| 517 gimple_cond_set_lhs (dummy_cond, op0); | |
| 518 gimple_cond_set_rhs (dummy_cond, op1); | |
| 519 | |
| 520 /* We absolutely do not care about any type conversions | |
| 521 we only care about a zero/nonzero value. */ | |
| 522 fold_defer_overflow_warnings (); | |
| 523 | |
| 524 cached_lhs = fold_binary (cond_code, boolean_type_node, op0, op1); | |
| 525 if (cached_lhs) | |
| 526 while (CONVERT_EXPR_P (cached_lhs)) | |
| 527 cached_lhs = TREE_OPERAND (cached_lhs, 0); | |
| 528 | |
| 529 fold_undefer_overflow_warnings ((cached_lhs | |
| 530 && is_gimple_min_invariant (cached_lhs)), | |
| 531 stmt, WARN_STRICT_OVERFLOW_CONDITIONAL); | |
| 532 | |
| 533 /* If we have not simplified the condition down to an invariant, | |
| 534 then use the pass specific callback to simplify the condition. */ | |
| 535 if (!cached_lhs | |
| 536 || !is_gimple_min_invariant (cached_lhs)) | |
| 537 cached_lhs = (*simplify) (dummy_cond, stmt); | |
| 538 | |
| 539 return cached_lhs; | |
| 540 } | |
| 541 | |
| 542 if (code == GIMPLE_SWITCH) | |
| 543 cond = gimple_switch_index (stmt); | |
| 544 else if (code == GIMPLE_GOTO) | |
| 545 cond = gimple_goto_dest (stmt); | |
| 546 else | |
| 547 gcc_unreachable (); | |
| 548 | |
| 549 /* We can have conditionals which just test the state of a variable | |
| 550 rather than use a relational operator. These are simpler to handle. */ | |
| 551 if (TREE_CODE (cond) == SSA_NAME) | |
| 552 { | |
| 553 cached_lhs = cond; | |
| 554 | |
| 555 /* Get the variable's current value from the equivalence chains. | |
| 556 | |
| 557 It is possible to get loops in the SSA_NAME_VALUE chains | |
| 558 (consider threading the backedge of a loop where we have | |
| 559 a loop invariant SSA_NAME used in the condition. */ | |
| 560 if (cached_lhs | |
| 561 && TREE_CODE (cached_lhs) == SSA_NAME | |
| 562 && SSA_NAME_VALUE (cached_lhs)) | |
| 563 cached_lhs = SSA_NAME_VALUE (cached_lhs); | |
| 564 | |
| 565 /* If we're dominated by a suitable ASSERT_EXPR, then | |
| 566 update CACHED_LHS appropriately. */ | |
| 567 if (handle_dominating_asserts && TREE_CODE (cached_lhs) == SSA_NAME) | |
| 568 cached_lhs = lhs_of_dominating_assert (cached_lhs, e->src, stmt); | |
| 569 | |
| 570 /* If we haven't simplified to an invariant yet, then use the | |
| 571 pass specific callback to try and simplify it further. */ | |
| 572 if (cached_lhs && ! is_gimple_min_invariant (cached_lhs)) | |
| 573 cached_lhs = (*simplify) (stmt, stmt); | |
| 574 } | |
| 575 else | |
| 576 cached_lhs = NULL; | |
| 577 | |
| 578 return cached_lhs; | |
| 579 } | |
| 580 | |
| 581 /* We are exiting E->src, see if E->dest ends with a conditional | |
|
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582 jump which has a known value when reached via E. |
| 0 | 583 |
| 584 Special care is necessary if E is a back edge in the CFG as we | |
| 585 may have already recorded equivalences for E->dest into our | |
| 586 various tables, including the result of the conditional at | |
| 587 the end of E->dest. Threading opportunities are severely | |
| 588 limited in that case to avoid short-circuiting the loop | |
| 589 incorrectly. | |
| 590 | |
| 591 Note it is quite common for the first block inside a loop to | |
| 592 end with a conditional which is either always true or always | |
| 593 false when reached via the loop backedge. Thus we do not want | |
| 594 to blindly disable threading across a loop backedge. | |
|
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595 |
| 0 | 596 DUMMY_COND is a shared cond_expr used by condition simplification as scratch, |
| 597 to avoid allocating memory. | |
|
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598 |
| 0 | 599 HANDLE_DOMINATING_ASSERTS is true if we should try to replace operands of |
| 600 the simplified condition with left-hand sides of ASSERT_EXPRs they are | |
| 601 used in. | |
|
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602 |
| 0 | 603 STACK is used to undo temporary equivalences created during the walk of |
| 604 E->dest. | |
| 605 | |
| 606 SIMPLIFY is a pass-specific function used to simplify statements. */ | |
| 607 | |
| 608 void | |
| 609 thread_across_edge (gimple dummy_cond, | |
| 610 edge e, | |
| 611 bool handle_dominating_asserts, | |
| 612 VEC(tree, heap) **stack, | |
| 613 tree (*simplify) (gimple, gimple)) | |
| 614 { | |
| 615 gimple stmt; | |
| 616 | |
| 617 /* If E is a backedge, then we want to verify that the COND_EXPR, | |
| 618 SWITCH_EXPR or GOTO_EXPR at the end of e->dest is not affected | |
| 619 by any statements in e->dest. If it is affected, then it is not | |
| 620 safe to thread this edge. */ | |
| 621 if (e->flags & EDGE_DFS_BACK) | |
| 622 { | |
| 623 ssa_op_iter iter; | |
| 624 use_operand_p use_p; | |
| 625 gimple last = gsi_stmt (gsi_last_bb (e->dest)); | |
| 626 | |
| 627 FOR_EACH_SSA_USE_OPERAND (use_p, last, iter, SSA_OP_USE | SSA_OP_VUSE) | |
| 628 { | |
| 629 tree use = USE_FROM_PTR (use_p); | |
| 630 | |
| 631 if (TREE_CODE (use) == SSA_NAME | |
| 632 && gimple_code (SSA_NAME_DEF_STMT (use)) != GIMPLE_PHI | |
| 633 && gimple_bb (SSA_NAME_DEF_STMT (use)) == e->dest) | |
| 634 goto fail; | |
| 635 } | |
| 636 } | |
|
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|
637 |
| 0 | 638 stmt_count = 0; |
| 639 | |
| 640 /* PHIs create temporary equivalences. */ | |
| 641 if (!record_temporary_equivalences_from_phis (e, stack)) | |
| 642 goto fail; | |
| 643 | |
| 644 /* Now walk each statement recording any context sensitive | |
| 645 temporary equivalences we can detect. */ | |
| 646 stmt = record_temporary_equivalences_from_stmts_at_dest (e, stack, simplify); | |
| 647 if (!stmt) | |
| 648 goto fail; | |
| 649 | |
| 650 /* If we stopped at a COND_EXPR or SWITCH_EXPR, see if we know which arm | |
| 651 will be taken. */ | |
| 652 if (gimple_code (stmt) == GIMPLE_COND | |
| 653 || gimple_code (stmt) == GIMPLE_GOTO | |
| 654 || gimple_code (stmt) == GIMPLE_SWITCH) | |
| 655 { | |
| 656 tree cond; | |
| 657 | |
| 658 /* Extract and simplify the condition. */ | |
| 659 cond = simplify_control_stmt_condition (e, stmt, dummy_cond, simplify, handle_dominating_asserts); | |
| 660 | |
| 661 if (cond && is_gimple_min_invariant (cond)) | |
| 662 { | |
| 663 edge taken_edge = find_taken_edge (e->dest, cond); | |
| 664 basic_block dest = (taken_edge ? taken_edge->dest : NULL); | |
| 665 | |
| 666 if (dest == e->dest) | |
| 667 goto fail; | |
| 668 | |
| 669 remove_temporary_equivalences (stack); | |
| 670 register_jump_thread (e, taken_edge); | |
| 671 } | |
| 672 } | |
| 673 | |
| 674 fail: | |
| 675 remove_temporary_equivalences (stack); | |
| 676 } |