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 CheckContext, CheckClassContext, 193 LoadContext # as the object providing the result 194 )) 195 196 def is_resultant_no_operation(self, instruction): 197 198 """ 199 Return whether 'instruction' merely stores its input where the input 200 originally came from. 201 """ 202 203 return ( 204 isinstance(instruction.input, LoadTemp) and isinstance(instruction, StoreTemp) and 205 instruction.input.attr == instruction.attr) or ( 206 isinstance(instruction.input, LoadResult) and isinstance(instruction, StoreResult) 207 ) 208 209 def is_input(self, instruction): 210 211 "Return whether 'instruction' provides an input." 212 213 return isinstance(instruction, current_value_instructions) 214 215 # Convenience tests on outputs. 216 217 def have_constant_target(self): 218 219 "Return whether the active instruction provides a constant target." 220 221 return self.is_constant_target(self.active) 222 223 def have_constant_source(self): 224 225 "Return whether the active instruction has a constant source." 226 227 return self.is_constant_input(self.active.source) 228 229 # Convenience tests on inputs. 230 231 def have_constant_input(self): 232 233 "Return whether the active instruction provides a constant input." 234 235 return self.is_constant_input(self.active_value) 236 237 have_known_target = have_constant_input 238 239 def have_simple_input(self): 240 241 "Return whether the active instruction provides a simple input." 242 243 return self.is_simple_input(self.active_value) 244 245 def have_input(self): 246 247 "Return whether the active instruction provides an input." 248 249 return self.is_input(self.active_value) 250 251 def have_self_input(self, unit): 252 253 """ 254 Return whether the active instruction is a reference to self in the 255 given 'unit'. 256 """ 257 258 return isinstance(unit, Function) and \ 259 unit.is_method() and isinstance(self.active_value, LoadName) and \ 260 self.active_value.attr.name == "self" 261 262 def have_temp_compatible_access(self): 263 264 """ 265 Indicate whether the active instruction can be used in place of access 266 to a temporary variable retaining the result of the last instruction. 267 """ 268 269 # LoadResult cannot be relied upon in general since the result register 270 # could be updated since first being referenced. 271 272 return isinstance(self.active_value, (LoadName, LoadTemp, LoadAddress, LoadConst)) or \ 273 isinstance(self.active_value, LoadResult) and self.active_value is self.active or \ 274 isinstance(self.active_value, LoadException) and self.active_value is self.active 275 276 def have_correct_self_for_target(self, context, unit): 277 278 "Return whether the 'context' is compatible with the given 'unit'." 279 280 if context is not None and self.have_self_input(unit): 281 282 parent = unit.parent 283 if parent is context or parent.has_subclass(context) or context.has_subclass(parent): 284 return 1 285 286 return 0 287 288 # Optimisation methods. See the supported_optimisations class attribute. 289 290 def optimise_constant_storage(self): 291 292 """ 293 Where the last operation stores a constant into a target which is also 294 constant, indicate that both operations should be optimised away. 295 """ 296 297 return self.should_optimise_constant_storage() and \ 298 self.have_constant_target() and \ 299 self.have_constant_source() 300 301 def optimise_constant_accessor(self): 302 303 """ 304 Where the object whose attribute is being accessed is constant, provide 305 information about its full name. 306 """ 307 308 if self.should_optimise_constant_accessor() and self.have_constant_input(): 309 value = self.active_value 310 311 # Get the details of the access. 312 313 if isinstance(value.attr, Const): 314 target_name = value.attr.value_type_name() 315 else: 316 target = value.attr.get_value() 317 318 if target is None: 319 return None # no clearly defined target 320 elif isinstance(target, Const): 321 return target.value_type_name() 322 elif isinstance(target, Instance): 323 return None # skip production of optimised code 324 else: 325 return target.full_name() 326 327 else: 328 return None 329 330 def optimise_known_target(self): 331 332 """ 333 Where the target of an invocation is known, provide information about it 334 and its context. If a class is being invoked and the conditions are 335 appropriate, get information about the specific initialiser. 336 """ 337 338 if self.should_optimise_known_target() and self.have_known_target(): 339 value = self.active_value 340 target = value.attr.get_value() 341 context = value.attr.get_context() 342 343 # Return target details only if this is clearly defined. 344 345 if target is not None: 346 return target, context 347 348 return None 349 350 def optimise_self_access(self, unit, attrname): 351 352 """ 353 Return whether code in the given 'unit' is able to access the given 354 'attrname' through the same position in all possible objects which might 355 be accessed. 356 """ 357 358 return self.should_optimise_self_access() and \ 359 self.have_self_input(unit) and not unit.is_relocated(attrname) 360 361 def optimise_temp_storage(self): 362 363 """ 364 Where the next operation would involve storing a value into temporary 365 storage at 'temp_position', record and remove any simple instruction 366 which produced the value to be stored such that instead of subsequently 367 accessing the temporary storage, that instruction is substituted. 368 369 If no optimisation can be achieved, a StoreTemp instruction is produced 370 and the appropriate LoadTemp instruction is returned. 371 372 Restriction: for use only in situations where the source of the 373 temporary data will not be disturbed between its first access and its 374 subsequent use. 375 """ 376 377 if self.should_optimise_temp_storage() and \ 378 self.have_temp_compatible_access(): 379 380 # Remove the active value contributor. 381 382 removed = self.remove_active_value() 383 384 # Extend the lifetime of any temporary storage location. 385 386 self.translation.ensure_temp(removed) 387 return removed 388 else: 389 return self.translation.get_temp() 390 391 def optimise_load_operations(self, instruction): 392 393 """ 394 Incorporate previous load operations into other operations. 395 """ 396 397 if self.should_optimise_load_operations() and \ 398 self.have_simple_input() and \ 399 self.is_simple_input_user(instruction): 400 401 self.remove_active_value() 402 instruction.input = self.active_value 403 404 def optimise_away_no_operations(self, instruction): 405 406 """ 407 Optimise away operations which just store their inputs in the place 408 the inputs originally came from. 409 """ 410 411 return self.should_optimise_away_no_operations() and \ 412 self.is_resultant_no_operation(instruction) 413 414 def optimise_unused_results(self): 415 416 "Discard results which will not be used." 417 418 if self.should_optimise_unused_results() and self.have_simple_input(): 419 self.remove_active_value() 420 421 # vim: tabstop=4 expandtab shiftwidth=4