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