Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-threadedge.c @ 63:b7f97abdc517 gcc-4.6-20100522
update gcc from gcc-4.5.0 to gcc-4.6
| author | ryoma <e075725@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Mon, 24 May 2010 12:47:05 +0900 |
| parents | 77e2b8dfacca |
| children | f6334be47118 |
| 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 "tm_p.h" | |
| 28 #include "basic-block.h" | |
| 29 #include "cfgloop.h" | |
| 30 #include "output.h" | |
| 31 #include "expr.h" | |
| 32 #include "function.h" | |
| 33 #include "diagnostic.h" | |
| 34 #include "timevar.h" | |
| 35 #include "tree-dump.h" | |
| 36 #include "tree-flow.h" | |
| 37 #include "tree-pass.h" | |
| 38 #include "tree-ssa-propagate.h" | |
| 39 #include "langhooks.h" | |
| 40 #include "params.h" | |
| 41 | |
| 42 /* To avoid code explosion due to jump threading, we limit the | |
| 43 number of statements we are going to copy. This variable | |
| 44 holds the number of statements currently seen that we'll have | |
| 45 to copy as part of the jump threading process. */ | |
| 46 static int stmt_count; | |
| 47 | |
|
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48 /* Array to record value-handles per SSA_NAME. */ |
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49 VEC(tree,heap) *ssa_name_values; |
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50 |
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51 /* Set the value for the SSA name NAME to VALUE. */ |
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52 |
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53 void |
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54 set_ssa_name_value (tree name, tree value) |
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55 { |
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56 if (SSA_NAME_VERSION (name) >= VEC_length (tree, ssa_name_values)) |
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57 VEC_safe_grow_cleared (tree, heap, ssa_name_values, |
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58 SSA_NAME_VERSION (name) + 1); |
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59 VEC_replace (tree, ssa_name_values, SSA_NAME_VERSION (name), value); |
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60 } |
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61 |
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62 /* Initialize the per SSA_NAME value-handles array. Returns it. */ |
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63 void |
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64 threadedge_initialize_values (void) |
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65 { |
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66 gcc_assert (ssa_name_values == NULL); |
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67 ssa_name_values = VEC_alloc(tree, heap, num_ssa_names); |
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68 } |
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69 |
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70 /* Free the per SSA_NAME value-handle array. */ |
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71 void |
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72 threadedge_finalize_values (void) |
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73 { |
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74 VEC_free(tree, heap, ssa_name_values); |
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75 } |
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76 |
| 0 | 77 /* Return TRUE if we may be able to thread an incoming edge into |
| 78 BB to an outgoing edge from BB. Return FALSE otherwise. */ | |
| 79 | |
| 80 bool | |
| 81 potentially_threadable_block (basic_block bb) | |
| 82 { | |
| 83 gimple_stmt_iterator gsi; | |
| 84 | |
| 85 /* If BB has a single successor or a single predecessor, then | |
| 86 there is no threading opportunity. */ | |
| 87 if (single_succ_p (bb) || single_pred_p (bb)) | |
| 88 return false; | |
| 89 | |
| 90 /* If BB does not end with a conditional, switch or computed goto, | |
| 91 then there is no threading opportunity. */ | |
| 92 gsi = gsi_last_bb (bb); | |
| 93 if (gsi_end_p (gsi) | |
| 94 || ! gsi_stmt (gsi) | |
| 95 || (gimple_code (gsi_stmt (gsi)) != GIMPLE_COND | |
| 96 && gimple_code (gsi_stmt (gsi)) != GIMPLE_GOTO | |
| 97 && gimple_code (gsi_stmt (gsi)) != GIMPLE_SWITCH)) | |
| 98 return false; | |
| 99 | |
| 100 return true; | |
| 101 } | |
| 102 | |
| 103 /* Return the LHS of any ASSERT_EXPR where OP appears as the first | |
| 104 argument to the ASSERT_EXPR and in which the ASSERT_EXPR dominates | |
| 105 BB. If no such ASSERT_EXPR is found, return OP. */ | |
| 106 | |
| 107 static tree | |
| 108 lhs_of_dominating_assert (tree op, basic_block bb, gimple stmt) | |
| 109 { | |
| 110 imm_use_iterator imm_iter; | |
| 111 gimple use_stmt; | |
| 112 use_operand_p use_p; | |
| 113 | |
| 114 FOR_EACH_IMM_USE_FAST (use_p, imm_iter, op) | |
| 115 { | |
| 116 use_stmt = USE_STMT (use_p); | |
| 117 if (use_stmt != stmt | |
| 118 && gimple_assign_single_p (use_stmt) | |
| 119 && TREE_CODE (gimple_assign_rhs1 (use_stmt)) == ASSERT_EXPR | |
| 120 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == op | |
| 121 && dominated_by_p (CDI_DOMINATORS, bb, gimple_bb (use_stmt))) | |
| 122 { | |
| 123 return gimple_assign_lhs (use_stmt); | |
| 124 } | |
| 125 } | |
| 126 return op; | |
| 127 } | |
| 128 | |
| 129 /* We record temporary equivalences created by PHI nodes or | |
| 130 statements within the target block. Doing so allows us to | |
| 131 identify more jump threading opportunities, even in blocks | |
| 132 with side effects. | |
| 133 | |
| 134 We keep track of those temporary equivalences in a stack | |
| 135 structure so that we can unwind them when we're done processing | |
| 136 a particular edge. This routine handles unwinding the data | |
| 137 structures. */ | |
| 138 | |
| 139 static void | |
| 140 remove_temporary_equivalences (VEC(tree, heap) **stack) | |
| 141 { | |
| 142 while (VEC_length (tree, *stack) > 0) | |
| 143 { | |
| 144 tree prev_value, dest; | |
| 145 | |
| 146 dest = VEC_pop (tree, *stack); | |
| 147 | |
| 148 /* A NULL value indicates we should stop unwinding, otherwise | |
| 149 pop off the next entry as they're recorded in pairs. */ | |
| 150 if (dest == NULL) | |
| 151 break; | |
| 152 | |
| 153 prev_value = VEC_pop (tree, *stack); | |
|
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154 set_ssa_name_value (dest, prev_value); |
| 0 | 155 } |
| 156 } | |
| 157 | |
| 158 /* Record a temporary equivalence, saving enough information so that | |
| 159 we can restore the state of recorded equivalences when we're | |
| 160 done processing the current edge. */ | |
| 161 | |
| 162 static void | |
| 163 record_temporary_equivalence (tree x, tree y, VEC(tree, heap) **stack) | |
| 164 { | |
| 165 tree prev_x = SSA_NAME_VALUE (x); | |
| 166 | |
| 167 if (TREE_CODE (y) == SSA_NAME) | |
| 168 { | |
| 169 tree tmp = SSA_NAME_VALUE (y); | |
| 170 y = tmp ? tmp : y; | |
| 171 } | |
| 172 | |
|
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173 set_ssa_name_value (x, y); |
| 0 | 174 VEC_reserve (tree, heap, *stack, 2); |
| 175 VEC_quick_push (tree, *stack, prev_x); | |
| 176 VEC_quick_push (tree, *stack, x); | |
| 177 } | |
| 178 | |
| 179 /* Record temporary equivalences created by PHIs at the target of the | |
|
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180 edge E. Record unwind information for the equivalences onto STACK. |
| 0 | 181 |
| 182 If a PHI which prevents threading is encountered, then return FALSE | |
| 183 indicating we should not thread this edge, else return TRUE. */ | |
| 184 | |
| 185 static bool | |
| 186 record_temporary_equivalences_from_phis (edge e, VEC(tree, heap) **stack) | |
| 187 { | |
| 188 gimple_stmt_iterator gsi; | |
| 189 | |
| 190 /* Each PHI creates a temporary equivalence, record them. | |
| 191 These are context sensitive equivalences and will be removed | |
| 192 later. */ | |
| 193 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 194 { | |
| 195 gimple phi = gsi_stmt (gsi); | |
| 196 tree src = PHI_ARG_DEF_FROM_EDGE (phi, e); | |
| 197 tree dst = gimple_phi_result (phi); | |
| 198 | |
|
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199 /* If the desired argument is not the same as this PHI's result |
| 0 | 200 and it is set by a PHI in E->dest, then we can not thread |
| 201 through E->dest. */ | |
| 202 if (src != dst | |
| 203 && TREE_CODE (src) == SSA_NAME | |
| 204 && gimple_code (SSA_NAME_DEF_STMT (src)) == GIMPLE_PHI | |
| 205 && gimple_bb (SSA_NAME_DEF_STMT (src)) == e->dest) | |
| 206 return false; | |
| 207 | |
| 208 /* We consider any non-virtual PHI as a statement since it | |
| 209 count result in a constant assignment or copy operation. */ | |
| 210 if (is_gimple_reg (dst)) | |
| 211 stmt_count++; | |
| 212 | |
| 213 record_temporary_equivalence (dst, src, stack); | |
| 214 } | |
| 215 return true; | |
| 216 } | |
| 217 | |
| 218 /* Fold the RHS of an assignment statement and return it as a tree. | |
| 219 May return NULL_TREE if no simplification is possible. */ | |
| 220 | |
| 221 static tree | |
| 222 fold_assignment_stmt (gimple stmt) | |
| 223 { | |
| 224 enum tree_code subcode = gimple_assign_rhs_code (stmt); | |
| 225 | |
| 226 switch (get_gimple_rhs_class (subcode)) | |
| 227 { | |
| 228 case GIMPLE_SINGLE_RHS: | |
| 229 { | |
| 230 tree rhs = gimple_assign_rhs1 (stmt); | |
| 231 | |
| 232 if (TREE_CODE (rhs) == COND_EXPR) | |
| 233 { | |
| 234 /* Sadly, we have to handle conditional assignments specially | |
| 235 here, because fold expects all the operands of an expression | |
| 236 to be folded before the expression itself is folded, but we | |
| 237 can't just substitute the folded condition here. */ | |
| 238 tree cond = fold (COND_EXPR_COND (rhs)); | |
| 239 if (cond == boolean_true_node) | |
| 240 rhs = COND_EXPR_THEN (rhs); | |
| 241 else if (cond == boolean_false_node) | |
| 242 rhs = COND_EXPR_ELSE (rhs); | |
| 243 } | |
| 244 | |
| 245 return fold (rhs); | |
| 246 } | |
| 247 break; | |
| 248 case GIMPLE_UNARY_RHS: | |
| 249 { | |
| 250 tree lhs = gimple_assign_lhs (stmt); | |
| 251 tree op0 = gimple_assign_rhs1 (stmt); | |
| 252 return fold_unary (subcode, TREE_TYPE (lhs), op0); | |
| 253 } | |
| 254 break; | |
| 255 case GIMPLE_BINARY_RHS: | |
| 256 { | |
| 257 tree lhs = gimple_assign_lhs (stmt); | |
| 258 tree op0 = gimple_assign_rhs1 (stmt); | |
| 259 tree op1 = gimple_assign_rhs2 (stmt); | |
| 260 return fold_binary (subcode, TREE_TYPE (lhs), op0, op1); | |
| 261 } | |
| 262 break; | |
| 263 default: | |
| 264 gcc_unreachable (); | |
| 265 } | |
| 266 } | |
| 267 | |
| 268 /* Try to simplify each statement in E->dest, ultimately leading to | |
| 269 a simplification of the COND_EXPR at the end of E->dest. | |
| 270 | |
| 271 Record unwind information for temporary equivalences onto STACK. | |
| 272 | |
| 273 Use SIMPLIFY (a pointer to a callback function) to further simplify | |
|
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274 statements using pass specific information. |
| 0 | 275 |
| 276 We might consider marking just those statements which ultimately | |
| 277 feed the COND_EXPR. It's not clear if the overhead of bookkeeping | |
| 278 would be recovered by trying to simplify fewer statements. | |
| 279 | |
| 280 If we are able to simplify a statement into the form | |
| 281 SSA_NAME = (SSA_NAME | gimple invariant), then we can record | |
| 282 a context sensitive equivalence which may help us simplify | |
| 283 later statements in E->dest. */ | |
| 284 | |
| 285 static gimple | |
| 286 record_temporary_equivalences_from_stmts_at_dest (edge e, | |
| 287 VEC(tree, heap) **stack, | |
| 288 tree (*simplify) (gimple, | |
| 289 gimple)) | |
| 290 { | |
| 291 gimple stmt = NULL; | |
| 292 gimple_stmt_iterator gsi; | |
| 293 int max_stmt_count; | |
| 294 | |
| 295 max_stmt_count = PARAM_VALUE (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS); | |
| 296 | |
| 297 /* Walk through each statement in the block recording equivalences | |
| 298 we discover. Note any equivalences we discover are context | |
| 299 sensitive (ie, are dependent on traversing E) and must be unwound | |
| 300 when we're finished processing E. */ | |
| 301 for (gsi = gsi_start_bb (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 302 { | |
| 303 tree cached_lhs = NULL; | |
| 304 | |
| 305 stmt = gsi_stmt (gsi); | |
| 306 | |
| 307 /* Ignore empty statements and labels. */ | |
|
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308 if (gimple_code (stmt) == GIMPLE_NOP |
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309 || gimple_code (stmt) == GIMPLE_LABEL |
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310 || is_gimple_debug (stmt)) |
| 0 | 311 continue; |
| 312 | |
| 313 /* If the statement has volatile operands, then we assume we | |
| 314 can not thread through this block. This is overly | |
| 315 conservative in some ways. */ | |
| 316 if (gimple_code (stmt) == GIMPLE_ASM && gimple_asm_volatile_p (stmt)) | |
| 317 return NULL; | |
| 318 | |
| 319 /* If duplicating this block is going to cause too much code | |
| 320 expansion, then do not thread through this block. */ | |
| 321 stmt_count++; | |
| 322 if (stmt_count > max_stmt_count) | |
| 323 return NULL; | |
| 324 | |
| 325 /* If this is not a statement that sets an SSA_NAME to a new | |
| 326 value, then do not try to simplify this statement as it will | |
| 327 not simplify in any way that is helpful for jump threading. */ | |
| 328 if ((gimple_code (stmt) != GIMPLE_ASSIGN | |
| 329 || TREE_CODE (gimple_assign_lhs (stmt)) != SSA_NAME) | |
| 330 && (gimple_code (stmt) != GIMPLE_CALL | |
| 331 || gimple_call_lhs (stmt) == NULL_TREE | |
| 332 || TREE_CODE (gimple_call_lhs (stmt)) != SSA_NAME)) | |
| 333 continue; | |
| 334 | |
| 335 /* The result of __builtin_object_size depends on all the arguments | |
| 336 of a phi node. Temporarily using only one edge produces invalid | |
| 337 results. For example | |
| 338 | |
| 339 if (x < 6) | |
| 340 goto l; | |
| 341 else | |
| 342 goto l; | |
| 343 | |
| 344 l: | |
| 345 r = PHI <&w[2].a[1](2), &a.a[6](3)> | |
| 346 __builtin_object_size (r, 0) | |
| 347 | |
| 348 The result of __builtin_object_size is defined to be the maximum of | |
| 349 remaining bytes. If we use only one edge on the phi, the result will | |
| 350 change to be the remaining bytes for the corresponding phi argument. | |
| 351 | |
| 352 Similarly for __builtin_constant_p: | |
| 353 | |
| 354 r = PHI <1(2), 2(3)> | |
| 355 __builtin_constant_p (r) | |
| 356 | |
| 357 Both PHI arguments are constant, but x ? 1 : 2 is still not | |
| 358 constant. */ | |
| 359 | |
| 360 if (is_gimple_call (stmt)) | |
| 361 { | |
| 362 tree fndecl = gimple_call_fndecl (stmt); | |
| 363 if (fndecl | |
| 364 && (DECL_FUNCTION_CODE (fndecl) == BUILT_IN_OBJECT_SIZE | |
| 365 || DECL_FUNCTION_CODE (fndecl) == BUILT_IN_CONSTANT_P)) | |
| 366 continue; | |
| 367 } | |
| 368 | |
| 369 /* At this point we have a statement which assigns an RHS to an | |
| 370 SSA_VAR on the LHS. We want to try and simplify this statement | |
| 371 to expose more context sensitive equivalences which in turn may | |
|
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372 allow us to simplify the condition at the end of the loop. |
| 0 | 373 |
| 374 Handle simple copy operations as well as implied copies from | |
| 375 ASSERT_EXPRs. */ | |
| 376 if (gimple_assign_single_p (stmt) | |
| 377 && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME) | |
| 378 cached_lhs = gimple_assign_rhs1 (stmt); | |
| 379 else if (gimple_assign_single_p (stmt) | |
| 380 && TREE_CODE (gimple_assign_rhs1 (stmt)) == ASSERT_EXPR) | |
| 381 cached_lhs = TREE_OPERAND (gimple_assign_rhs1 (stmt), 0); | |
| 382 else | |
| 383 { | |
| 384 /* A statement that is not a trivial copy or ASSERT_EXPR. | |
| 385 We're going to temporarily copy propagate the operands | |
| 386 and see if that allows us to simplify this statement. */ | |
| 387 tree *copy; | |
| 388 ssa_op_iter iter; | |
| 389 use_operand_p use_p; | |
| 390 unsigned int num, i = 0; | |
| 391 | |
| 392 num = NUM_SSA_OPERANDS (stmt, (SSA_OP_USE | SSA_OP_VUSE)); | |
| 393 copy = XCNEWVEC (tree, num); | |
| 394 | |
| 395 /* Make a copy of the uses & vuses into USES_COPY, then cprop into | |
| 396 the operands. */ | |
| 397 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE | SSA_OP_VUSE) | |
| 398 { | |
| 399 tree tmp = NULL; | |
| 400 tree use = USE_FROM_PTR (use_p); | |
| 401 | |
| 402 copy[i++] = use; | |
| 403 if (TREE_CODE (use) == SSA_NAME) | |
| 404 tmp = SSA_NAME_VALUE (use); | |
| 405 if (tmp) | |
| 406 SET_USE (use_p, tmp); | |
| 407 } | |
| 408 | |
| 409 /* Try to fold/lookup the new expression. Inserting the | |
| 410 expression into the hash table is unlikely to help. */ | |
| 411 if (is_gimple_call (stmt)) | |
| 412 cached_lhs = fold_call_stmt (stmt, false); | |
| 413 else | |
| 414 cached_lhs = fold_assignment_stmt (stmt); | |
| 415 | |
| 416 if (!cached_lhs | |
| 417 || (TREE_CODE (cached_lhs) != SSA_NAME | |
| 418 && !is_gimple_min_invariant (cached_lhs))) | |
| 419 cached_lhs = (*simplify) (stmt, stmt); | |
|
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420 |
| 0 | 421 /* Restore the statement's original uses/defs. */ |
| 422 i = 0; | |
| 423 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE | SSA_OP_VUSE) | |
| 424 SET_USE (use_p, copy[i++]); | |
| 425 | |
| 426 free (copy); | |
| 427 } | |
| 428 | |
| 429 /* Record the context sensitive equivalence if we were able | |
| 430 to simplify this statement. */ | |
| 431 if (cached_lhs | |
| 432 && (TREE_CODE (cached_lhs) == SSA_NAME | |
| 433 || is_gimple_min_invariant (cached_lhs))) | |
| 434 record_temporary_equivalence (gimple_get_lhs (stmt), cached_lhs, stack); | |
| 435 } | |
| 436 return stmt; | |
| 437 } | |
| 438 | |
| 439 /* Simplify the control statement at the end of the block E->dest. | |
| 440 | |
| 441 To avoid allocating memory unnecessarily, a scratch GIMPLE_COND | |
| 442 is available to use/clobber in DUMMY_COND. | |
| 443 | |
| 444 Use SIMPLIFY (a pointer to a callback function) to further simplify | |
| 445 a condition using pass specific information. | |
| 446 | |
| 447 Return the simplified condition or NULL if simplification could | |
| 448 not be performed. */ | |
| 449 | |
| 450 static tree | |
| 451 simplify_control_stmt_condition (edge e, | |
| 452 gimple stmt, | |
| 453 gimple dummy_cond, | |
| 454 tree (*simplify) (gimple, gimple), | |
| 455 bool handle_dominating_asserts) | |
| 456 { | |
| 457 tree cond, cached_lhs; | |
| 458 enum gimple_code code = gimple_code (stmt); | |
| 459 | |
| 460 /* For comparisons, we have to update both operands, then try | |
| 461 to simplify the comparison. */ | |
| 462 if (code == GIMPLE_COND) | |
| 463 { | |
| 464 tree op0, op1; | |
| 465 enum tree_code cond_code; | |
| 466 | |
| 467 op0 = gimple_cond_lhs (stmt); | |
| 468 op1 = gimple_cond_rhs (stmt); | |
| 469 cond_code = gimple_cond_code (stmt); | |
| 470 | |
| 471 /* Get the current value of both operands. */ | |
| 472 if (TREE_CODE (op0) == SSA_NAME) | |
| 473 { | |
| 474 tree tmp = SSA_NAME_VALUE (op0); | |
| 475 if (tmp) | |
| 476 op0 = tmp; | |
| 477 } | |
| 478 | |
| 479 if (TREE_CODE (op1) == SSA_NAME) | |
| 480 { | |
| 481 tree tmp = SSA_NAME_VALUE (op1); | |
| 482 if (tmp) | |
| 483 op1 = tmp; | |
| 484 } | |
| 485 | |
| 486 if (handle_dominating_asserts) | |
| 487 { | |
| 488 /* Now see if the operand was consumed by an ASSERT_EXPR | |
| 489 which dominates E->src. If so, we want to replace the | |
| 490 operand with the LHS of the ASSERT_EXPR. */ | |
| 491 if (TREE_CODE (op0) == SSA_NAME) | |
| 492 op0 = lhs_of_dominating_assert (op0, e->src, stmt); | |
| 493 | |
| 494 if (TREE_CODE (op1) == SSA_NAME) | |
| 495 op1 = lhs_of_dominating_assert (op1, e->src, stmt); | |
| 496 } | |
| 497 | |
| 498 /* We may need to canonicalize the comparison. For | |
| 499 example, op0 might be a constant while op1 is an | |
| 500 SSA_NAME. Failure to canonicalize will cause us to | |
| 501 miss threading opportunities. */ | |
| 502 if (tree_swap_operands_p (op0, op1, false)) | |
| 503 { | |
| 504 tree tmp; | |
| 505 cond_code = swap_tree_comparison (cond_code); | |
| 506 tmp = op0; | |
| 507 op0 = op1; | |
| 508 op1 = tmp; | |
| 509 } | |
| 510 | |
| 511 /* Stuff the operator and operands into our dummy conditional | |
| 512 expression. */ | |
| 513 gimple_cond_set_code (dummy_cond, cond_code); | |
| 514 gimple_cond_set_lhs (dummy_cond, op0); | |
| 515 gimple_cond_set_rhs (dummy_cond, op1); | |
| 516 | |
| 517 /* We absolutely do not care about any type conversions | |
| 518 we only care about a zero/nonzero value. */ | |
| 519 fold_defer_overflow_warnings (); | |
| 520 | |
| 521 cached_lhs = fold_binary (cond_code, boolean_type_node, op0, op1); | |
| 522 if (cached_lhs) | |
| 523 while (CONVERT_EXPR_P (cached_lhs)) | |
| 524 cached_lhs = TREE_OPERAND (cached_lhs, 0); | |
| 525 | |
| 526 fold_undefer_overflow_warnings ((cached_lhs | |
| 527 && is_gimple_min_invariant (cached_lhs)), | |
| 528 stmt, WARN_STRICT_OVERFLOW_CONDITIONAL); | |
| 529 | |
| 530 /* If we have not simplified the condition down to an invariant, | |
| 531 then use the pass specific callback to simplify the condition. */ | |
| 532 if (!cached_lhs | |
| 533 || !is_gimple_min_invariant (cached_lhs)) | |
| 534 cached_lhs = (*simplify) (dummy_cond, stmt); | |
| 535 | |
| 536 return cached_lhs; | |
| 537 } | |
| 538 | |
| 539 if (code == GIMPLE_SWITCH) | |
| 540 cond = gimple_switch_index (stmt); | |
| 541 else if (code == GIMPLE_GOTO) | |
| 542 cond = gimple_goto_dest (stmt); | |
| 543 else | |
| 544 gcc_unreachable (); | |
| 545 | |
| 546 /* We can have conditionals which just test the state of a variable | |
| 547 rather than use a relational operator. These are simpler to handle. */ | |
| 548 if (TREE_CODE (cond) == SSA_NAME) | |
| 549 { | |
| 550 cached_lhs = cond; | |
| 551 | |
| 552 /* Get the variable's current value from the equivalence chains. | |
| 553 | |
| 554 It is possible to get loops in the SSA_NAME_VALUE chains | |
| 555 (consider threading the backedge of a loop where we have | |
| 556 a loop invariant SSA_NAME used in the condition. */ | |
| 557 if (cached_lhs | |
| 558 && TREE_CODE (cached_lhs) == SSA_NAME | |
| 559 && SSA_NAME_VALUE (cached_lhs)) | |
| 560 cached_lhs = SSA_NAME_VALUE (cached_lhs); | |
| 561 | |
| 562 /* If we're dominated by a suitable ASSERT_EXPR, then | |
| 563 update CACHED_LHS appropriately. */ | |
| 564 if (handle_dominating_asserts && TREE_CODE (cached_lhs) == SSA_NAME) | |
| 565 cached_lhs = lhs_of_dominating_assert (cached_lhs, e->src, stmt); | |
| 566 | |
| 567 /* If we haven't simplified to an invariant yet, then use the | |
| 568 pass specific callback to try and simplify it further. */ | |
| 569 if (cached_lhs && ! is_gimple_min_invariant (cached_lhs)) | |
| 570 cached_lhs = (*simplify) (stmt, stmt); | |
| 571 } | |
| 572 else | |
| 573 cached_lhs = NULL; | |
| 574 | |
| 575 return cached_lhs; | |
| 576 } | |
| 577 | |
| 578 /* We are exiting E->src, see if E->dest ends with a conditional | |
|
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579 jump which has a known value when reached via E. |
| 0 | 580 |
| 581 Special care is necessary if E is a back edge in the CFG as we | |
| 582 may have already recorded equivalences for E->dest into our | |
| 583 various tables, including the result of the conditional at | |
| 584 the end of E->dest. Threading opportunities are severely | |
| 585 limited in that case to avoid short-circuiting the loop | |
| 586 incorrectly. | |
| 587 | |
| 588 Note it is quite common for the first block inside a loop to | |
| 589 end with a conditional which is either always true or always | |
| 590 false when reached via the loop backedge. Thus we do not want | |
| 591 to blindly disable threading across a loop backedge. | |
|
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592 |
| 0 | 593 DUMMY_COND is a shared cond_expr used by condition simplification as scratch, |
| 594 to avoid allocating memory. | |
|
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595 |
| 0 | 596 HANDLE_DOMINATING_ASSERTS is true if we should try to replace operands of |
| 597 the simplified condition with left-hand sides of ASSERT_EXPRs they are | |
| 598 used in. | |
|
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599 |
| 0 | 600 STACK is used to undo temporary equivalences created during the walk of |
| 601 E->dest. | |
| 602 | |
| 603 SIMPLIFY is a pass-specific function used to simplify statements. */ | |
| 604 | |
| 605 void | |
| 606 thread_across_edge (gimple dummy_cond, | |
| 607 edge e, | |
| 608 bool handle_dominating_asserts, | |
| 609 VEC(tree, heap) **stack, | |
| 610 tree (*simplify) (gimple, gimple)) | |
| 611 { | |
| 612 gimple stmt; | |
| 613 | |
| 614 /* If E is a backedge, then we want to verify that the COND_EXPR, | |
| 615 SWITCH_EXPR or GOTO_EXPR at the end of e->dest is not affected | |
| 616 by any statements in e->dest. If it is affected, then it is not | |
| 617 safe to thread this edge. */ | |
| 618 if (e->flags & EDGE_DFS_BACK) | |
| 619 { | |
| 620 ssa_op_iter iter; | |
| 621 use_operand_p use_p; | |
| 622 gimple last = gsi_stmt (gsi_last_bb (e->dest)); | |
| 623 | |
| 624 FOR_EACH_SSA_USE_OPERAND (use_p, last, iter, SSA_OP_USE | SSA_OP_VUSE) | |
| 625 { | |
| 626 tree use = USE_FROM_PTR (use_p); | |
| 627 | |
| 628 if (TREE_CODE (use) == SSA_NAME | |
| 629 && gimple_code (SSA_NAME_DEF_STMT (use)) != GIMPLE_PHI | |
| 630 && gimple_bb (SSA_NAME_DEF_STMT (use)) == e->dest) | |
| 631 goto fail; | |
| 632 } | |
| 633 } | |
|
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diff
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|
634 |
| 0 | 635 stmt_count = 0; |
| 636 | |
| 637 /* PHIs create temporary equivalences. */ | |
| 638 if (!record_temporary_equivalences_from_phis (e, stack)) | |
| 639 goto fail; | |
| 640 | |
| 641 /* Now walk each statement recording any context sensitive | |
| 642 temporary equivalences we can detect. */ | |
| 643 stmt = record_temporary_equivalences_from_stmts_at_dest (e, stack, simplify); | |
| 644 if (!stmt) | |
| 645 goto fail; | |
| 646 | |
| 647 /* If we stopped at a COND_EXPR or SWITCH_EXPR, see if we know which arm | |
| 648 will be taken. */ | |
| 649 if (gimple_code (stmt) == GIMPLE_COND | |
| 650 || gimple_code (stmt) == GIMPLE_GOTO | |
| 651 || gimple_code (stmt) == GIMPLE_SWITCH) | |
| 652 { | |
| 653 tree cond; | |
| 654 | |
| 655 /* Extract and simplify the condition. */ | |
| 656 cond = simplify_control_stmt_condition (e, stmt, dummy_cond, simplify, handle_dominating_asserts); | |
| 657 | |
| 658 if (cond && is_gimple_min_invariant (cond)) | |
| 659 { | |
| 660 edge taken_edge = find_taken_edge (e->dest, cond); | |
| 661 basic_block dest = (taken_edge ? taken_edge->dest : NULL); | |
| 662 | |
| 663 if (dest == e->dest) | |
| 664 goto fail; | |
| 665 | |
| 666 remove_temporary_equivalences (stack); | |
| 667 register_jump_thread (e, taken_edge); | |
| 668 } | |
| 669 } | |
| 670 | |
| 671 fail: | |
| 672 remove_temporary_equivalences (stack); | |
| 673 } |