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