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annotate gcc/tree-nrv.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 /* Language independent return value optimizations |
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2 Copyright (C) 2004, 2005, 2007, 2008, 2009 Free Software Foundation, Inc. |
| 0 | 3 |
| 4 This file is part of GCC. | |
| 5 | |
| 6 GCC is free software; you can redistribute it and/or modify | |
| 7 it under the terms of the GNU General Public License as published by | |
| 8 the Free Software Foundation; either version 3, or (at your option) | |
| 9 any later version. | |
| 10 | |
| 11 GCC is distributed in the hope that it will be useful, | |
| 12 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| 14 GNU General Public License for more details. | |
| 15 | |
| 16 You should have received a copy of the GNU General Public License | |
| 17 along with GCC; see the file COPYING3. If not see | |
| 18 <http://www.gnu.org/licenses/>. */ | |
| 19 | |
| 20 #include "config.h" | |
| 21 #include "system.h" | |
| 22 #include "coretypes.h" | |
| 23 #include "tm.h" | |
| 24 #include "tree.h" | |
| 25 #include "rtl.h" | |
| 26 #include "function.h" | |
| 27 #include "basic-block.h" | |
| 28 #include "expr.h" | |
| 29 #include "diagnostic.h" | |
| 30 #include "tree-flow.h" | |
| 31 #include "timevar.h" | |
| 32 #include "tree-dump.h" | |
| 33 #include "tree-pass.h" | |
| 34 #include "langhooks.h" | |
| 35 | |
| 36 /* This file implements return value optimizations for functions which | |
| 37 return aggregate types. | |
| 38 | |
| 39 Basically this pass searches the function for return statements which | |
| 40 return a local aggregate. When converted to RTL such statements will | |
| 41 generate a copy from the local aggregate to final return value destination | |
| 42 mandated by the target's ABI. | |
| 43 | |
| 44 That copy can often be avoided by directly constructing the return value | |
| 45 into the final destination mandated by the target's ABI. | |
| 46 | |
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47 This is basically a generic equivalent to the C++ front-end's |
| 0 | 48 Named Return Value optimization. */ |
| 49 | |
| 50 struct nrv_data | |
| 51 { | |
| 52 /* This is the temporary (a VAR_DECL) which appears in all of | |
| 53 this function's RETURN_EXPR statements. */ | |
| 54 tree var; | |
| 55 | |
| 56 /* This is the function's RESULT_DECL. We will replace all occurrences | |
| 57 of VAR with RESULT_DECL when we apply this optimization. */ | |
| 58 tree result; | |
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59 int modified; |
| 0 | 60 }; |
| 61 | |
| 62 static tree finalize_nrv_r (tree *, int *, void *); | |
| 63 | |
| 64 /* Callback for the tree walker. | |
| 65 | |
| 66 If TP refers to a RETURN_EXPR, then set the expression being returned | |
| 67 to nrv_data->result. | |
| 68 | |
| 69 If TP refers to nrv_data->var, then replace nrv_data->var with | |
| 70 nrv_data->result. | |
| 71 | |
| 72 If we reach a node where we know all the subtrees are uninteresting, | |
| 73 then set *WALK_SUBTREES to zero. */ | |
| 74 | |
| 75 static tree | |
| 76 finalize_nrv_r (tree *tp, int *walk_subtrees, void *data) | |
| 77 { | |
| 78 struct walk_stmt_info *wi = (struct walk_stmt_info *) data; | |
| 79 struct nrv_data *dp = (struct nrv_data *) wi->info; | |
| 80 | |
| 81 /* No need to walk into types. */ | |
| 82 if (TYPE_P (*tp)) | |
| 83 *walk_subtrees = 0; | |
| 84 | |
| 85 /* Otherwise replace all occurrences of VAR with RESULT. */ | |
| 86 else if (*tp == dp->var) | |
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87 { |
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88 *tp = dp->result; |
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89 dp->modified = 1; |
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90 } |
| 0 | 91 |
| 92 /* Keep iterating. */ | |
| 93 return NULL_TREE; | |
| 94 } | |
| 95 | |
| 96 /* Main entry point for return value optimizations. | |
| 97 | |
| 98 If this function always returns the same local variable, and that | |
| 99 local variable is an aggregate type, then replace the variable with | |
| 100 the function's DECL_RESULT. | |
| 101 | |
| 102 This is the equivalent of the C++ named return value optimization | |
| 103 applied to optimized trees in a language independent form. If we | |
| 104 ever encounter languages which prevent this kind of optimization, | |
| 105 then we could either have the languages register the optimization or | |
| 106 we could change the gating function to check the current language. */ | |
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107 |
| 0 | 108 static unsigned int |
| 109 tree_nrv (void) | |
| 110 { | |
| 111 tree result = DECL_RESULT (current_function_decl); | |
| 112 tree result_type = TREE_TYPE (result); | |
| 113 tree found = NULL; | |
| 114 basic_block bb; | |
| 115 gimple_stmt_iterator gsi; | |
| 116 struct nrv_data data; | |
| 117 | |
| 118 /* If this function does not return an aggregate type in memory, then | |
| 119 there is nothing to do. */ | |
| 120 if (!aggregate_value_p (result, current_function_decl)) | |
| 121 return 0; | |
| 122 | |
| 123 /* If a GIMPLE type is returned in memory, finalize_nrv_r might create | |
| 124 non-GIMPLE. */ | |
| 125 if (is_gimple_reg_type (result_type)) | |
| 126 return 0; | |
| 127 | |
| 128 /* If the front end already did something like this, don't do it here. */ | |
| 129 if (DECL_NAME (result)) | |
| 130 return 0; | |
| 131 | |
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132 /* If the result has its address taken then it might be modified |
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133 by means not detected in the following loop. Bail out in this |
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134 case. */ |
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135 if (TREE_ADDRESSABLE (result)) |
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136 return 0; |
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137 |
| 0 | 138 /* Look through each block for assignments to the RESULT_DECL. */ |
| 139 FOR_EACH_BB (bb) | |
| 140 { | |
| 141 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 142 { | |
| 143 gimple stmt = gsi_stmt (gsi); | |
| 144 tree ret_val; | |
| 145 | |
| 146 if (gimple_code (stmt) == GIMPLE_RETURN) | |
| 147 { | |
| 148 /* In a function with an aggregate return value, the | |
| 149 gimplifier has changed all non-empty RETURN_EXPRs to | |
| 150 return the RESULT_DECL. */ | |
| 151 ret_val = gimple_return_retval (stmt); | |
| 152 if (ret_val) | |
| 153 gcc_assert (ret_val == result); | |
| 154 } | |
| 155 else if (gimple_has_lhs (stmt) | |
| 156 && gimple_get_lhs (stmt) == result) | |
| 157 { | |
| 158 tree rhs; | |
| 159 | |
| 160 if (!gimple_assign_copy_p (stmt)) | |
| 161 return 0; | |
| 162 | |
| 163 rhs = gimple_assign_rhs1 (stmt); | |
| 164 | |
| 165 /* Now verify that this return statement uses the same value | |
| 166 as any previously encountered return statement. */ | |
| 167 if (found != NULL) | |
| 168 { | |
| 169 /* If we found a return statement using a different variable | |
| 170 than previous return statements, then we can not perform | |
| 171 NRV optimizations. */ | |
| 172 if (found != rhs) | |
| 173 return 0; | |
| 174 } | |
| 175 else | |
| 176 found = rhs; | |
| 177 | |
| 178 /* The returned value must be a local automatic variable of the | |
| 179 same type and alignment as the function's result. */ | |
| 180 if (TREE_CODE (found) != VAR_DECL | |
| 181 || TREE_THIS_VOLATILE (found) | |
| 182 || DECL_CONTEXT (found) != current_function_decl | |
| 183 || TREE_STATIC (found) | |
| 184 || TREE_ADDRESSABLE (found) | |
| 185 || DECL_ALIGN (found) > DECL_ALIGN (result) | |
| 186 || !useless_type_conversion_p (result_type, | |
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187 TREE_TYPE (found))) |
| 0 | 188 return 0; |
| 189 } | |
| 190 else if (gimple_has_lhs (stmt)) | |
| 191 { | |
| 192 tree addr = get_base_address (gimple_get_lhs (stmt)); | |
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193 /* If there's any MODIFY of component of RESULT, |
| 0 | 194 then bail out. */ |
| 195 if (addr && addr == result) | |
| 196 return 0; | |
| 197 } | |
| 198 } | |
| 199 } | |
| 200 | |
| 201 if (!found) | |
| 202 return 0; | |
| 203 | |
| 204 /* If dumping details, then note once and only the NRV replacement. */ | |
| 205 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 206 { | |
| 207 fprintf (dump_file, "NRV Replaced: "); | |
| 208 print_generic_expr (dump_file, found, dump_flags); | |
| 209 fprintf (dump_file, " with: "); | |
| 210 print_generic_expr (dump_file, result, dump_flags); | |
| 211 fprintf (dump_file, "\n"); | |
| 212 } | |
| 213 | |
| 214 /* At this point we know that all the return statements return the | |
| 215 same local which has suitable attributes for NRV. Copy debugging | |
| 216 information from FOUND to RESULT if it will be useful. But don't set | |
| 217 DECL_ABSTRACT_ORIGIN to point at another function. */ | |
| 218 if (!DECL_IGNORED_P (found) | |
| 219 && !(DECL_ABSTRACT_ORIGIN (found) | |
| 220 && DECL_CONTEXT (DECL_ABSTRACT_ORIGIN (found)) != current_function_decl)) | |
| 221 { | |
| 222 DECL_NAME (result) = DECL_NAME (found); | |
| 223 DECL_SOURCE_LOCATION (result) = DECL_SOURCE_LOCATION (found); | |
| 224 DECL_ABSTRACT_ORIGIN (result) = DECL_ABSTRACT_ORIGIN (found); | |
| 225 } | |
| 226 | |
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227 TREE_ADDRESSABLE (result) |= TREE_ADDRESSABLE (found); |
| 0 | 228 |
| 229 /* Now walk through the function changing all references to VAR to be | |
| 230 RESULT. */ | |
| 231 data.var = found; | |
| 232 data.result = result; | |
| 233 FOR_EACH_BB (bb) | |
| 234 { | |
| 235 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); ) | |
| 236 { | |
| 237 gimple stmt = gsi_stmt (gsi); | |
| 238 /* If this is a copy from VAR to RESULT, remove it. */ | |
| 239 if (gimple_assign_copy_p (stmt) | |
| 240 && gimple_assign_lhs (stmt) == result | |
| 241 && gimple_assign_rhs1 (stmt) == found) | |
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242 { |
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243 unlink_stmt_vdef (stmt); |
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244 gsi_remove (&gsi, true); |
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245 } |
| 0 | 246 else |
| 247 { | |
| 248 struct walk_stmt_info wi; | |
| 249 memset (&wi, 0, sizeof (wi)); | |
| 250 wi.info = &data; | |
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251 data.modified = 0; |
| 0 | 252 walk_gimple_op (stmt, finalize_nrv_r, &wi); |
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253 if (data.modified) |
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254 update_stmt (stmt); |
| 0 | 255 gsi_next (&gsi); |
| 256 } | |
| 257 } | |
| 258 } | |
| 259 | |
| 260 /* FOUND is no longer used. Ensure it gets removed. */ | |
| 261 var_ann (found)->used = 0; | |
| 262 return 0; | |
| 263 } | |
| 264 | |
| 265 static bool | |
| 266 gate_pass_return_slot (void) | |
| 267 { | |
| 268 return optimize > 0; | |
| 269 } | |
| 270 | |
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271 struct gimple_opt_pass pass_nrv = |
| 0 | 272 { |
| 273 { | |
| 274 GIMPLE_PASS, | |
| 275 "nrv", /* name */ | |
| 276 gate_pass_return_slot, /* gate */ | |
| 277 tree_nrv, /* execute */ | |
| 278 NULL, /* sub */ | |
| 279 NULL, /* next */ | |
| 280 0, /* static_pass_number */ | |
| 281 TV_TREE_NRV, /* tv_id */ | |
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282 PROP_ssa | PROP_cfg, /* properties_required */ |
| 0 | 283 0, /* properties_provided */ |
| 284 0, /* properties_destroyed */ | |
| 285 0, /* todo_flags_start */ | |
| 286 TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */ | |
| 287 } | |
| 288 }; | |
| 289 | |
| 290 /* Determine (pessimistically) whether DEST is available for NRV | |
| 291 optimization, where DEST is expected to be the LHS of a modify | |
| 292 expression where the RHS is a function returning an aggregate. | |
| 293 | |
| 294 We search for a base VAR_DECL and look to see if it is call clobbered. | |
| 295 Note that we could do better, for example, by | |
| 296 attempting to doing points-to analysis on INDIRECT_REFs. */ | |
| 297 | |
| 298 static bool | |
| 299 dest_safe_for_nrv_p (tree dest) | |
| 300 { | |
| 301 while (handled_component_p (dest)) | |
| 302 dest = TREE_OPERAND (dest, 0); | |
| 303 | |
| 304 if (! SSA_VAR_P (dest)) | |
| 305 return false; | |
| 306 | |
| 307 if (TREE_CODE (dest) == SSA_NAME) | |
| 308 dest = SSA_NAME_VAR (dest); | |
| 309 | |
| 310 if (is_call_used (dest)) | |
| 311 return false; | |
| 312 | |
| 313 return true; | |
| 314 } | |
| 315 | |
| 316 /* Walk through the function looking for GIMPLE_ASSIGNs with calls that | |
| 317 return in memory on the RHS. For each of these, determine whether it is | |
| 318 safe to pass the address of the LHS as the return slot, and mark the | |
| 319 call appropriately if so. | |
| 320 | |
| 321 The NRV shares the return slot with a local variable in the callee; this | |
| 322 optimization shares the return slot with the target of the call within | |
| 323 the caller. If the NRV is performed (which we can't know in general), | |
| 324 this optimization is safe if the address of the target has not | |
| 325 escaped prior to the call. If it has, modifications to the local | |
| 326 variable will produce visible changes elsewhere, as in PR c++/19317. */ | |
| 327 | |
| 328 static unsigned int | |
| 329 execute_return_slot_opt (void) | |
| 330 { | |
| 331 basic_block bb; | |
| 332 | |
| 333 FOR_EACH_BB (bb) | |
| 334 { | |
| 335 gimple_stmt_iterator gsi; | |
| 336 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 337 { | |
| 338 gimple stmt = gsi_stmt (gsi); | |
| 339 bool slot_opt_p; | |
| 340 | |
| 341 if (is_gimple_call (stmt) | |
| 342 && gimple_call_lhs (stmt) | |
| 343 && !gimple_call_return_slot_opt_p (stmt) | |
| 344 && aggregate_value_p (TREE_TYPE (gimple_call_lhs (stmt)), | |
| 345 gimple_call_fndecl (stmt)) | |
| 346 ) | |
| 347 { | |
| 348 /* Check if the location being assigned to is | |
| 349 call-clobbered. */ | |
| 350 slot_opt_p = dest_safe_for_nrv_p (gimple_call_lhs (stmt)); | |
| 351 gimple_call_set_return_slot_opt (stmt, slot_opt_p); | |
| 352 } | |
| 353 } | |
| 354 } | |
| 355 return 0; | |
| 356 } | |
| 357 | |
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358 struct gimple_opt_pass pass_return_slot = |
| 0 | 359 { |
| 360 { | |
| 361 GIMPLE_PASS, | |
| 362 "retslot", /* name */ | |
| 363 NULL, /* gate */ | |
| 364 execute_return_slot_opt, /* execute */ | |
| 365 NULL, /* sub */ | |
| 366 NULL, /* next */ | |
| 367 0, /* static_pass_number */ | |
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368 TV_NONE, /* tv_id */ |
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369 PROP_ssa, /* properties_required */ |
| 0 | 370 0, /* properties_provided */ |
| 371 0, /* properties_destroyed */ | |
| 372 0, /* todo_flags_start */ | |
| 373 0 /* todo_flags_finish */ | |
| 374 } | |
| 375 }; |