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 # NOTE: Removed StoreName, since this would then demand population of 159 # NOTE: locals/frames. 160 161 return isinstance(instruction, StoreAddress) and \ 162 instruction.attr.assignments == 1 163 164 def is_simple_input(self, instruction): 165 166 """ 167 Return whether 'instruction' provides a simple input (typically a load 168 instruction). A simple input is something which would be represented by 169 a load operation from a CPU register or special memory location. 170 """ 171 172 return isinstance(instruction, (LoadConst, LoadName, LoadTemp, LoadResult, LoadException, LoadAddress)) 173 174 def is_simple_input_user(self, instruction): 175 176 """ 177 Return whether 'instruction' can use simple input from the current 178 value. Such instructions would, in a low-level implementation, be able 179 to have the simple input registers as operands. 180 """ 181 182 return isinstance(instruction, ( 183 StoreTemp, StoreFrame, StoreResult, StoreException, # as the value being stored 184 LoadAddressContext, LoadAddressContextCond, # as the object being referenced 185 LoadAttr, LoadAttrIndex, LoadAttrIndexContext, # as the object being referenced 186 LoadAttrIndexContextCond, # as the object being referenced 187 StoreAttr, StoreAttrIndex, StoreCallable, # as the object being referenced 188 StoreFrameIndex, # as the object being referenced 189 LoadCallable, 190 TestIdentity, TestIdentityAddress, CheckSelf, # as one of the operands 191 CheckException, CheckFrame, MakeObject, 192 LoadContext # as the object providing the result 193 )) 194 195 def is_resultant_no_operation(self, instruction): 196 197 """ 198 Return whether 'instruction' merely stores its input where the input 199 originally came from. 200 """ 201 202 return ( 203 isinstance(instruction.input, LoadTemp) and isinstance(instruction, StoreTemp) and 204 instruction.input.attr == instruction.attr) or ( 205 isinstance(instruction.input, LoadResult) and isinstance(instruction, StoreResult) 206 ) 207 208 def is_input(self, instruction): 209 210 "Return whether 'instruction' provides an input." 211 212 return isinstance(instruction, current_value_instructions) 213 214 # Convenience tests on outputs. 215 216 def have_constant_target(self): 217 218 "Return whether the active instruction provides a constant target." 219 220 return self.is_constant_target(self.active) 221 222 def have_constant_source(self): 223 224 "Return whether the active instruction has a constant source." 225 226 return self.is_constant_input(self.active.source) 227 228 # Convenience tests on inputs. 229 230 def have_constant_input(self): 231 232 "Return whether the active instruction provides a constant input." 233 234 return self.is_constant_input(self.active_value) 235 236 have_known_target = have_constant_input 237 238 def have_simple_input(self): 239 240 "Return whether the active instruction provides a simple input." 241 242 return self.is_simple_input(self.active_value) 243 244 def have_input(self): 245 246 "Return whether the active instruction provides an input." 247 248 return self.is_input(self.active_value) 249 250 def have_self_input(self, unit): 251 252 """ 253 Return whether the active instruction is a reference to self in the 254 given 'unit'. 255 """ 256 257 return isinstance(unit, Function) and \ 258 unit.is_method() and isinstance(self.active_value, LoadName) and \ 259 self.active_value.attr.name == "self" 260 261 def have_temp_compatible_access(self): 262 263 """ 264 Indicate whether the active instruction can be used in place of access 265 to a temporary variable retaining the result of the last instruction. 266 """ 267 268 # LoadResult cannot be relied upon in general since the result register 269 # could be updated since first being referenced. 270 271 return isinstance(self.active_value, (LoadName, LoadTemp, LoadAddress, LoadConst)) or \ 272 isinstance(self.active_value, LoadResult) and self.active_value is self.active or \ 273 isinstance(self.active_value, LoadException) and self.active_value is self.active 274 275 def have_correct_self_for_target(self, context, unit): 276 277 "Return whether the 'context' is compatible with the given 'unit'." 278 279 if context is not None and self.have_self_input(unit): 280 281 parent = unit.parent 282 if parent is context or parent.has_subclass(context) or context.has_subclass(parent): 283 return 1 284 285 return 0 286 287 # Optimisation methods. See the supported_optimisations class attribute. 288 289 def optimise_constant_storage(self): 290 291 """ 292 Where the last operation stores a constant into a target which is also 293 constant, indicate that both operations should be optimised away. 294 """ 295 296 return self.should_optimise_constant_storage() and \ 297 self.have_constant_target() and \ 298 self.have_constant_source() 299 300 def optimise_constant_accessor(self): 301 302 """ 303 Where the object whose attribute is being accessed is constant, provide 304 information about its full name. 305 """ 306 307 if self.should_optimise_constant_accessor() and self.have_constant_input(): 308 value = self.active_value 309 310 # Get the details of the access. 311 312 if isinstance(value.attr, Const): 313 target_name = value.attr.value_type_name() 314 else: 315 target = value.attr.get_value() 316 317 if target is None: 318 return None # no clearly defined target 319 elif isinstance(target, Const): 320 return target.value_type_name() 321 elif isinstance(target, Instance): 322 return None # skip production of optimised code 323 else: 324 return target.full_name() 325 326 else: 327 return None 328 329 def optimise_known_target(self): 330 331 """ 332 Where the target of an invocation is known, provide information about it 333 and its context. If a class is being invoked and the conditions are 334 appropriate, get information about the specific initialiser. 335 """ 336 337 if self.should_optimise_known_target() and self.have_known_target(): 338 value = self.active_value 339 target = value.attr.get_value() 340 context = value.attr.get_context() 341 342 # Return target details only if this is clearly defined. 343 344 if target is not None: 345 return target, context 346 347 return None 348 349 def optimise_self_access(self, unit, attrname): 350 351 """ 352 Return whether code in the given 'unit' is able to access the given 353 'attrname' through the same position in all possible objects which might 354 be accessed. 355 """ 356 357 return self.should_optimise_self_access() and \ 358 self.have_self_input(unit) and not unit.is_relocated(attrname) 359 360 def optimise_temp_storage(self): 361 362 """ 363 Where the next operation would involve storing a value into temporary 364 storage at 'temp_position', record and remove any simple instruction 365 which produced the value to be stored such that instead of subsequently 366 accessing the temporary storage, that instruction is substituted. 367 368 If no optimisation can be achieved, a StoreTemp instruction is produced 369 and the appropriate LoadTemp instruction is returned. 370 371 Restriction: for use only in situations where the source of the 372 temporary data will not be disturbed between its first access and its 373 subsequent use. 374 """ 375 376 if self.should_optimise_temp_storage() and \ 377 self.have_temp_compatible_access(): 378 379 # Remove the active value contributor. 380 381 removed = self.remove_active_value() 382 383 # Extend the lifetime of any temporary storage location. 384 385 self.translation.ensure_temp(removed) 386 return removed 387 else: 388 return self.translation.get_temp() 389 390 def optimise_load_operations(self, instruction): 391 392 """ 393 Incorporate previous load operations into other operations. 394 """ 395 396 if self.should_optimise_load_operations() and \ 397 self.have_simple_input() and \ 398 self.is_simple_input_user(instruction): 399 400 self.remove_active_value() 401 instruction.input = self.active_value 402 403 def optimise_away_no_operations(self, instruction): 404 405 """ 406 Optimise away operations which just store their inputs in the place 407 the inputs originally came from. 408 """ 409 410 return self.should_optimise_away_no_operations() and \ 411 self.is_resultant_no_operation(instruction) 412 413 def optimise_unused_results(self): 414 415 "Discard results which will not be used." 416 417 if self.should_optimise_unused_results() and self.have_simple_input(): 418 self.remove_active_value() 419 420 # vim: tabstop=4 expandtab shiftwidth=4