1 #!/usr/bin/env python 2 3 """ 4 Optimise code produced by the AST translator. 5 6 Copyright (C) 2007, 2008, 2009 Paul Boddie <paul@boddie.org.uk> 7 8 This program is free software; you can redistribute it and/or modify it under 9 the terms of the GNU General Public License as published by the Free Software 10 Foundation; either version 3 of the License, or (at your option) any later 11 version. 12 13 This program is distributed in the hope that it will be useful, but WITHOUT 14 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 15 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more 16 details. 17 18 You should have received a copy of the GNU General Public License along with 19 this program. If not, see <http://www.gnu.org/licenses/>. 20 """ 21 22 from micropython.common import * 23 from micropython.data import * 24 from micropython.rsvp import * 25 26 class Optimiser: 27 28 "A code optimiser." 29 30 supported_optimisations = [ 31 # Code generation optimisations: 32 "constant_storage", "constant_accessor", "known_target", "self_access", 33 "temp_storage", "load_operations", "no_operations", "unused_results", 34 "unused_handlers", 35 # Inspection optimisations: 36 "unused_objects" 37 ] 38 39 def __init__(self, translation, optimisations=None): 40 41 """ 42 Provide for the given 'translation' an optimiser for the desired 43 'optimisations'. See the 'supported_optimisations' attribute of this 44 class for permitted values. 45 """ 46 47 self.translation = translation 48 self.optimisations = set(optimisations or []) 49 50 # The current "active" instruction. 51 # As a rule, this will become the last instruction, but some 52 # control-flow operations will flush the "active" instruction. 53 54 self.active = None 55 56 # The instruction providing the active value. 57 58 self.active_value = None 59 60 def reset(self): 61 62 "Reset the optimiser, clearing the active instructions." 63 64 self.clear_active_value() 65 self.clear_active() 66 67 def set_new(self, op): 68 69 "Set the latest 'op' as the active instruction." 70 71 self.set_active(op) 72 self.set_active_value(op) 73 74 def set_active_value(self, op): 75 76 "Set the value-providing active instruction." 77 78 if isinstance(op, current_value_instructions): 79 self.active_value = op 80 81 def clear_active_value(self): 82 83 "Clear the value-providing active instruction." 84 85 self.active_value = None 86 87 def remove_active_value(self): 88 89 """ 90 Remove the value-providing active instruction from the generated code, 91 if appropriate, but keep a record of the active instruction itself. 92 """ 93 94 if self.active_value is self.active: 95 removed = self.active 96 self.translation.remove_op() 97 return removed 98 else: 99 return None 100 101 def set_source(self, expr): 102 103 "Set the source of the active instruction to 'expr'." 104 105 if self.active is not None: 106 self.active.source = expr 107 108 def set_active(self, op): 109 110 "Set the active instruction." 111 112 self.active = op 113 114 def clear_active(self): 115 116 "Clear the active instruction." 117 118 self.active = None 119 120 # Optimisation tests. 121 122 def should_optimise_constant_storage(self): 123 return "constant_storage" in self.optimisations 124 125 def should_optimise_constant_accessor(self): 126 return "constant_accessor" in self.optimisations 127 128 def should_optimise_known_target(self): 129 return "known_target" in self.optimisations 130 131 def should_optimise_self_access(self): 132 return "self_access" in self.optimisations 133 134 def should_optimise_temp_storage(self): 135 return "temp_storage" in self.optimisations 136 137 def should_optimise_load_operations(self): 138 return "load_operations" in self.optimisations 139 140 def should_optimise_away_no_operations(self): 141 return "no_operations" in self.optimisations 142 143 def should_optimise_unused_results(self): 144 return "unused_results" in self.optimisations 145 146 def should_optimise_unused_handlers(self): 147 return "unused_handlers" in self.optimisations 148 149 # Simple tests. 150 151 def is_constant_input(self, instruction): 152 153 "Return whether 'instruction' provides a constant input." 154 155 return isinstance(instruction, LoadAddress) and instruction.attr.assignments == 1 and \ 156 isinstance(instruction.attr.get_value(), Constant) or \ 157 isinstance(instruction, (LoadConst, LoadClass, LoadFunction)) 158 159 def is_constant_target(self, instruction): 160 161 "Return whether 'instruction' provides a constant target." 162 163 # NOTE: Removed StoreName, since this would then demand population of 164 # NOTE: locals/frames. 165 166 return isinstance(instruction, (StoreAddress, StoreAddressContext)) and \ 167 instruction.attr.assignments == 1 168 169 def is_simple_input(self, instruction): 170 171 """ 172 Return whether 'instruction' provides a simple input (typically a load 173 instruction). A simple input is something which would be represented by 174 a load operation from a CPU register or special memory location. 175 """ 176 177 return isinstance(instruction, (LoadConst, LoadClass, LoadFunction, LoadName, LoadTemp, LoadResult, LoadException, LoadAddress)) 178 179 def is_simple_input_user(self, instruction): 180 181 """ 182 Return whether 'instruction' can use simple input from the current 183 value. Such instructions would, in a low-level implementation, be able 184 to have the simple input registers as operands. 185 """ 186 187 return isinstance(instruction, simple_input_user_instructions) 188 189 def is_resultant_no_operation(self, instruction): 190 191 """ 192 Return whether 'instruction' merely stores its input where the input 193 originally came from. 194 """ 195 196 return ( 197 isinstance(instruction.input, LoadTemp) and isinstance(instruction, StoreTemp) and 198 instruction.input.attr == instruction.attr) or ( 199 isinstance(instruction.input, LoadResult) and isinstance(instruction, StoreResult) 200 ) 201 202 def is_input(self, instruction): 203 204 "Return whether 'instruction' provides an input." 205 206 return isinstance(instruction, current_value_instructions) 207 208 # Convenience tests on outputs. 209 210 def have_constant_target(self): 211 212 "Return whether the active instruction provides a constant target." 213 214 return self.is_constant_target(self.active) 215 216 def have_constant_source(self): 217 218 "Return whether the active instruction has a constant source." 219 220 return self.is_constant_input(self.active.source) 221 222 # Convenience tests on inputs. 223 224 def have_constant_input(self): 225 226 "Return whether the active instruction provides a constant input." 227 228 return self.is_constant_input(self.active_value) 229 230 have_known_target = have_constant_input 231 232 def have_simple_input(self): 233 234 "Return whether the active instruction provides a simple input." 235 236 return self.is_simple_input(self.active_value) 237 238 def have_input(self): 239 240 "Return whether the active instruction provides an input." 241 242 return self.is_input(self.active_value) 243 244 def have_self_input(self, unit): 245 246 """ 247 Return whether the active instruction is a reference to self in the 248 given 'unit'. 249 """ 250 251 return isinstance(unit, Function) and \ 252 unit.is_method() and isinstance(self.active_value, LoadName) and \ 253 self.active_value.attr.name == "self" 254 255 def have_temp_compatible_access(self): 256 257 """ 258 Indicate whether the active instruction can be used in place of access 259 to a temporary variable retaining the result of the last instruction. 260 """ 261 262 # LoadResult cannot be relied upon in general since the result register 263 # could be updated since first being referenced. 264 265 return isinstance(self.active_value, (LoadName, LoadTemp, LoadAddress, LoadConst, LoadClass, LoadFunction)) or \ 266 isinstance(self.active_value, LoadResult) and self.active_value is self.active or \ 267 isinstance(self.active_value, LoadException) and self.active_value is self.active 268 269 def have_correct_self_for_target(self, context, unit): 270 271 "Return whether the 'context' is compatible with the given 'unit'." 272 273 if context is not None and self.have_self_input(unit): 274 275 parent = unit.parent 276 if parent is context or parent.has_subclass(context) or context.has_subclass(parent): 277 return 1 278 279 return 0 280 281 def have_empty_handler(self, instruction): 282 283 """ 284 Return whether the active instruction defined a handler for exceptions 285 which is then discarded by the given 'instruction'. 286 """ 287 288 return isinstance(self.translation.last_op(), PushHandler) and isinstance(instruction, PopHandler) 289 290 # Optimisation methods. See the supported_optimisations class attribute. 291 292 def optimise_constant_storage(self): 293 294 """ 295 Where the last operation stores a constant into a target which is also 296 constant, indicate that both operations should be optimised away. 297 """ 298 299 return self.should_optimise_constant_storage() and \ 300 self.have_constant_target() and \ 301 self.have_constant_source() 302 303 def optimise_constant_accessor(self): 304 305 """ 306 Where the object whose attribute is being accessed is constant, provide 307 information about its full name. 308 """ 309 310 if self.should_optimise_constant_accessor() and self.have_constant_input(): 311 value = self.active_value 312 313 # Get the details of the access. 314 315 if isinstance(value.attr, Const): 316 target_name = value.attr.value_type_name() 317 else: 318 target = value.attr.get_value() 319 320 if target is None: 321 return None # no clearly defined target 322 elif isinstance(target, Const): 323 return target.value_type_name() 324 elif isinstance(target, Instance): 325 return None # skip production of optimised code 326 else: 327 return target.full_name() 328 329 else: 330 return None 331 332 def optimise_known_target(self): 333 334 """ 335 Where the target of an invocation is known, provide information about it 336 and its context. If a class is being invoked and the conditions are 337 appropriate, get information about the specific initialiser. 338 """ 339 340 if self.should_optimise_known_target() and self.have_known_target(): 341 value = self.active_value 342 target = value.attr.get_value() 343 context = value.attr.get_context() 344 345 # Return target details only if this is clearly defined. 346 347 if target is not None: 348 return target, context 349 350 return None 351 352 def optimise_self_access(self, unit, attrname): 353 354 """ 355 Return whether code in the given 'unit' is able to access the given 356 'attrname' through the same position in all possible objects which might 357 be accessed. 358 """ 359 360 return self.should_optimise_self_access() and \ 361 self.have_self_input(unit) and not unit.is_relocated(attrname) 362 363 def optimise_temp_storage(self): 364 365 """ 366 Where the next operation would involve storing a value into temporary 367 storage at 'temp_position', record and remove any simple instruction 368 which produced the value to be stored such that instead of subsequently 369 accessing the temporary storage, that instruction is substituted. 370 371 If no optimisation can be achieved, a StoreTemp instruction is produced 372 and the appropriate LoadTemp instruction is returned. 373 374 Restriction: for use only in situations where the source of the 375 temporary data will not be disturbed between its first access and its 376 subsequent use. 377 """ 378 379 if self.should_optimise_temp_storage() and \ 380 self.have_temp_compatible_access(): 381 382 # Remove the active value contributor. 383 384 removed = self.remove_active_value() 385 386 # Extend the lifetime of any temporary storage location. 387 388 self.translation.ensure_temp(removed) 389 return removed 390 else: 391 return self.translation.get_temp() 392 393 def optimise_load_operations(self, instruction): 394 395 """ 396 Incorporate previous load operations into other operations. 397 """ 398 399 if self.should_optimise_load_operations() and \ 400 self.have_simple_input() and \ 401 self.is_simple_input_user(instruction): 402 403 self.remove_active_value() 404 instruction.input = self.active_value 405 406 def optimise_away_no_operations(self, instruction): 407 408 """ 409 Optimise away operations which just store their inputs in the place 410 the inputs originally came from. 411 """ 412 413 return self.should_optimise_away_no_operations() and \ 414 self.is_resultant_no_operation(instruction) 415 416 def optimise_unused_results(self): 417 418 "Discard results which will not be used." 419 420 if self.should_optimise_unused_results() and self.have_simple_input(): 421 self.remove_active_value() 422 423 def optimise_unused_handlers(self, instruction): 424 425 "Discard handlers which will not be used." 426 427 if self.should_optimise_unused_handlers() and self.have_empty_handler(instruction): 428 self.translation.remove_op() 429 return 1 430 else: 431 return 0 432 433 # vim: tabstop=4 expandtab shiftwidth=4