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 LoadCallable, 184 TestIdentity, TestIdentityAddress, CheckSelf, # as one of the operands 185 CheckException, CheckFrame, MakeObject, 186 LoadContext # as the object providing the result 187 )) 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)) 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 # Optimisation methods. See the supported_optimisations class attribute. 282 283 def optimise_constant_storage(self): 284 285 """ 286 Where the last operation stores a constant into a target which is also 287 constant, indicate that both operations should be optimised away. 288 """ 289 290 return self.should_optimise_constant_storage() and \ 291 self.have_constant_target() and \ 292 self.have_constant_source() 293 294 def optimise_constant_accessor(self): 295 296 """ 297 Where the object whose attribute is being accessed is constant, provide 298 information about its full name. 299 """ 300 301 if self.should_optimise_constant_accessor() and self.have_constant_input(): 302 value = self.active_value 303 304 # Get the details of the access. 305 306 if isinstance(value.attr, Const): 307 target_name = value.attr.value_type_name() 308 else: 309 target = value.attr.value 310 311 if isinstance(target, Const): 312 return target.value_type_name() 313 elif isinstance(target, Instance): 314 return None # skip production of optimised code 315 else: 316 return target.full_name() 317 318 else: 319 return None 320 321 def optimise_known_target(self): 322 323 """ 324 Where the target of an invocation is known, provide information about it 325 and its context. If a class is being invoked and the conditions are 326 appropriate, get information about the specific initialiser. 327 """ 328 329 if self.should_optimise_known_target() and self.have_known_target(): 330 value = self.active_value 331 target = value.attr.value 332 context = value.attr.context 333 334 return target, context 335 else: 336 return None 337 338 def optimise_self_access(self, unit, attrname): 339 340 """ 341 Return whether code in the given 'unit' is able to access the given 342 'attrname' through the same position in all possible objects which might 343 be accessed. 344 """ 345 346 return self.should_optimise_self_access() and \ 347 self.have_self_input(unit) and not unit.is_relocated(attrname) 348 349 def optimise_temp_storage(self): 350 351 """ 352 Where the next operation would involve storing a value into temporary 353 storage at 'temp_position', record and remove any simple instruction 354 which produced the value to be stored such that instead of subsequently 355 accessing the temporary storage, that instruction is substituted. 356 357 If no optimisation can be achieved, a StoreTemp instruction is produced 358 and the appropriate LoadTemp instruction is returned. 359 360 Restriction: for use only in situations where the source of the 361 temporary data will not be disturbed between its first access and its 362 subsequent use. 363 """ 364 365 if self.should_optimise_temp_storage() and \ 366 self.have_temp_compatible_access(): 367 368 # Remove the active value contributor. 369 370 removed = self.remove_active_value() 371 372 # Extend the lifetime of any temporary storage location. 373 374 self.translation.ensure_temp(removed) 375 return removed 376 else: 377 return self.translation.get_temp() 378 379 def optimise_load_operations(self, instruction): 380 381 """ 382 Incorporate previous load operations into other operations. 383 """ 384 385 if self.should_optimise_load_operations() and \ 386 self.have_simple_input() and \ 387 self.is_simple_input_user(instruction): 388 389 self.remove_active_value() 390 instruction.input = self.active_value 391 392 def optimise_away_no_operations(self, instruction): 393 394 """ 395 Optimise away operations which just store their inputs in the place 396 the inputs originally came from. 397 """ 398 399 return self.should_optimise_away_no_operations() and \ 400 self.is_resultant_no_operation(instruction) 401 402 def optimise_unused_results(self): 403 404 "Discard results which will not be used." 405 406 if self.should_optimise_unused_results() and self.have_simple_input(): 407 self.remove_active_value() 408 409 # vim: tabstop=4 expandtab shiftwidth=4