1 /* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_ 18 #define ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_ 19 20 #include "induction_var_analysis.h" 21 22 namespace art { 23 24 /** 25 * This class implements range analysis on expressions within loops. It takes the results 26 * of induction variable analysis in the constructor and provides a public API to obtain 27 * a conservative lower and upper bound value or last value on each instruction in the HIR. 28 * The public API also provides a few general-purpose utility methods related to induction. 29 * 30 * The range analysis is done with a combination of symbolic and partial integral evaluation 31 * of expressions. The analysis avoids complications with wrap-around arithmetic on the integral 32 * parts but all clients should be aware that wrap-around may occur on any of the symbolic parts. 33 * For example, given a known range for [0,100] for i, the evaluation yields range [-100,100] 34 * for expression -2*i+100, which is exact, and range [x,x+100] for expression i+x, which may 35 * wrap-around anywhere in the range depending on the actual value of x. 36 */ 37 class InductionVarRange { 38 public: 39 /* 40 * A value that can be represented as "a * instruction + b" for 32-bit constants, where 41 * Value() denotes an unknown lower and upper bound. Although range analysis could yield 42 * more complex values, the format is sufficiently powerful to represent useful cases 43 * and feeds directly into optimizations like bounds check elimination. 44 */ 45 struct Value { 46 Value() : instruction(nullptr), a_constant(0), b_constant(0), is_known(false) {} 47 Value(HInstruction* i, int32_t a, int32_t b) 48 : instruction(a != 0 ? i : nullptr), a_constant(a), b_constant(b), is_known(true) {} 49 explicit Value(int32_t b) : Value(nullptr, 0, b) {} 50 // Representation as: a_constant x instruction + b_constant. 51 HInstruction* instruction; 52 int32_t a_constant; 53 int32_t b_constant; 54 // If true, represented by prior fields. Otherwise unknown value. 55 bool is_known; 56 }; 57 58 explicit InductionVarRange(HInductionVarAnalysis* induction); 59 60 /** 61 * Given a context denoted by the first instruction, returns a possibly conservative lower 62 * and upper bound on the instruction's value in the output parameters min_val and max_val, 63 * respectively. The need_finite_test flag denotes if an additional finite-test is needed 64 * to protect the range evaluation inside its loop. The parameter chase_hint defines an 65 * instruction at which chasing may stop. Returns false on failure. 66 */ 67 bool GetInductionRange(HInstruction* context, 68 HInstruction* instruction, 69 HInstruction* chase_hint, 70 /*out*/ Value* min_val, 71 /*out*/ Value* max_val, 72 /*out*/ bool* needs_finite_test); 73 74 /** 75 * Returns true if range analysis is able to generate code for the lower and upper 76 * bound expressions on the instruction in the given context. The need_finite_test 77 * and need_taken test flags denote if an additional finite-test and/or taken-test 78 * are needed to protect the range evaluation inside its loop. 79 */ 80 bool CanGenerateRange(HInstruction* context, 81 HInstruction* instruction, 82 /*out*/ bool* needs_finite_test, 83 /*out*/ bool* needs_taken_test); 84 85 /** 86 * Generates the actual code in the HIR for the lower and upper bound expressions on the 87 * instruction in the given context. Code for the lower and upper bound expression are 88 * generated in given block and graph and are returned in the output parameters lower and 89 * upper, respectively. For a loop invariant, lower is not set. 90 * 91 * For example, given expression x+i with range [0, 5] for i, calling this method 92 * will generate the following sequence: 93 * 94 * block: 95 * lower: add x, 0 96 * upper: add x, 5 97 * 98 * Precondition: CanGenerateRange() returns true. 99 */ 100 void GenerateRange(HInstruction* context, 101 HInstruction* instruction, 102 HGraph* graph, 103 HBasicBlock* block, 104 /*out*/ HInstruction** lower, 105 /*out*/ HInstruction** upper); 106 107 /** 108 * Generates explicit taken-test for the loop in the given context. Code is generated in 109 * given block and graph. Returns generated taken-test. 110 * 111 * Precondition: CanGenerateRange() returns true and needs_taken_test is set. 112 */ 113 HInstruction* GenerateTakenTest(HInstruction* context, HGraph* graph, HBasicBlock* block); 114 115 /** 116 * Returns true if induction analysis is able to generate code for last value of 117 * the given instruction inside the closest enveloping loop. 118 */ 119 bool CanGenerateLastValue(HInstruction* instruction); 120 121 /** 122 * Generates last value of the given instruction in the closest enveloping loop. 123 * Code is generated in given block and graph. Returns generated last value. 124 * 125 * Precondition: CanGenerateLastValue() returns true. 126 */ 127 HInstruction* GenerateLastValue(HInstruction* instruction, HGraph* graph, HBasicBlock* block); 128 129 /** 130 * Updates all matching fetches with the given replacement in all induction information 131 * that is associated with the given instruction. 132 */ 133 void Replace(HInstruction* instruction, HInstruction* fetch, HInstruction* replacement); 134 135 /** 136 * Incrementally updates induction information for just the given loop. 137 */ 138 void ReVisit(HLoopInformation* loop) { 139 induction_analysis_->induction_.erase(loop); 140 for (HInstructionIterator it(loop->GetHeader()->GetPhis()); !it.Done(); it.Advance()) { 141 induction_analysis_->cycles_.erase(it.Current()->AsPhi()); 142 } 143 induction_analysis_->VisitLoop(loop); 144 } 145 146 /** 147 * Lookup an interesting cycle associated with an entry phi. 148 */ 149 ArenaSet<HInstruction*>* LookupCycle(HPhi* phi) const { 150 return induction_analysis_->LookupCycle(phi); 151 } 152 153 /** 154 * Checks if the given phi instruction has been classified as anything by 155 * induction variable analysis. Returns false for anything that cannot be 156 * classified statically, such as reductions or other complex cycles. 157 */ 158 bool IsClassified(HPhi* phi) const { 159 HLoopInformation* lp = phi->GetBlock()->GetLoopInformation(); // closest enveloping loop 160 return (lp != nullptr) && (induction_analysis_->LookupInfo(lp, phi) != nullptr); 161 } 162 163 /** 164 * Checks if header logic of a loop terminates. Sets trip-count tc if known. 165 */ 166 bool IsFinite(HLoopInformation* loop, /*out*/ int64_t* tc) const; 167 168 /** 169 * Checks if the given instruction is a unit stride induction inside the closest enveloping 170 * loop of the context that is defined by the first parameter (e.g. pass an array reference 171 * as context and the index as instruction to make sure the stride is tested against the 172 * loop that envelops the reference the closest). Returns invariant offset on success. 173 */ 174 bool IsUnitStride(HInstruction* context, 175 HInstruction* instruction, 176 HGraph* graph, 177 /*out*/ HInstruction** offset) const; 178 179 /** 180 * Generates the trip count expression for the given loop. Code is generated in given block 181 * and graph. The expression is guarded by a taken test if needed. Returns the trip count 182 * expression on success or null otherwise. 183 */ 184 HInstruction* GenerateTripCount(HLoopInformation* loop, HGraph* graph, HBasicBlock* block); 185 186 private: 187 /* 188 * Enum used in IsConstant() request. 189 */ 190 enum ConstantRequest { 191 kExact, 192 kAtMost, 193 kAtLeast 194 }; 195 196 /** 197 * Returns true if exact or upper/lower bound on the given induction 198 * information is known as a 64-bit constant, which is returned in value. 199 */ 200 bool IsConstant(HInductionVarAnalysis::InductionInfo* info, 201 ConstantRequest request, 202 /*out*/ int64_t* value) const; 203 204 /** Returns whether induction information can be obtained. */ 205 bool HasInductionInfo(HInstruction* context, 206 HInstruction* instruction, 207 /*out*/ HLoopInformation** loop, 208 /*out*/ HInductionVarAnalysis::InductionInfo** info, 209 /*out*/ HInductionVarAnalysis::InductionInfo** trip) const; 210 211 bool HasFetchInLoop(HInductionVarAnalysis::InductionInfo* info) const; 212 bool NeedsTripCount(HInductionVarAnalysis::InductionInfo* info, 213 /*out*/ int64_t* stride_value) const; 214 bool IsBodyTripCount(HInductionVarAnalysis::InductionInfo* trip) const; 215 bool IsUnsafeTripCount(HInductionVarAnalysis::InductionInfo* trip) const; 216 bool IsWellBehavedTripCount(HInductionVarAnalysis::InductionInfo* trip) const; 217 218 Value GetLinear(HInductionVarAnalysis::InductionInfo* info, 219 HInductionVarAnalysis::InductionInfo* trip, 220 bool in_body, 221 bool is_min) const; 222 Value GetPolynomial(HInductionVarAnalysis::InductionInfo* info, 223 HInductionVarAnalysis::InductionInfo* trip, 224 bool in_body, 225 bool is_min) const; 226 Value GetGeometric(HInductionVarAnalysis::InductionInfo* info, 227 HInductionVarAnalysis::InductionInfo* trip, 228 bool in_body, 229 bool is_min) const; 230 Value GetFetch(HInstruction* instruction, 231 HInductionVarAnalysis::InductionInfo* trip, 232 bool in_body, 233 bool is_min) const; 234 Value GetVal(HInductionVarAnalysis::InductionInfo* info, 235 HInductionVarAnalysis::InductionInfo* trip, 236 bool in_body, 237 bool is_min) const; 238 Value GetMul(HInductionVarAnalysis::InductionInfo* info1, 239 HInductionVarAnalysis::InductionInfo* info2, 240 HInductionVarAnalysis::InductionInfo* trip, 241 bool in_body, 242 bool is_min) const; 243 Value GetDiv(HInductionVarAnalysis::InductionInfo* info1, 244 HInductionVarAnalysis::InductionInfo* info2, 245 HInductionVarAnalysis::InductionInfo* trip, 246 bool in_body, 247 bool is_min) const; 248 Value GetRem(HInductionVarAnalysis::InductionInfo* info1, 249 HInductionVarAnalysis::InductionInfo* info2) const; 250 Value GetXor(HInductionVarAnalysis::InductionInfo* info1, 251 HInductionVarAnalysis::InductionInfo* info2) const; 252 253 Value MulRangeAndConstant(int64_t value, 254 HInductionVarAnalysis::InductionInfo* info, 255 HInductionVarAnalysis::InductionInfo* trip, 256 bool in_body, 257 bool is_min) const; 258 Value DivRangeAndConstant(int64_t value, 259 HInductionVarAnalysis::InductionInfo* info, 260 HInductionVarAnalysis::InductionInfo* trip, 261 bool in_body, 262 bool is_min) const; 263 264 Value AddValue(Value v1, Value v2) const; 265 Value SubValue(Value v1, Value v2) const; 266 Value MulValue(Value v1, Value v2) const; 267 Value DivValue(Value v1, Value v2) const; 268 Value MergeVal(Value v1, Value v2, bool is_min) const; 269 270 /** 271 * Generates code for lower/upper/taken-test or last value in the HIR. Returns true on 272 * success. With values nullptr, the method can be used to determine if code generation 273 * would be successful without generating actual code yet. 274 */ 275 bool GenerateRangeOrLastValue(HInstruction* context, 276 HInstruction* instruction, 277 bool is_last_val, 278 HGraph* graph, 279 HBasicBlock* block, 280 /*out*/ HInstruction** lower, 281 /*out*/ HInstruction** upper, 282 /*out*/ HInstruction** taken_test, 283 /*out*/ int64_t* stride_value, 284 /*out*/ bool* needs_finite_test, 285 /*out*/ bool* needs_taken_test) const; 286 287 bool GenerateLastValuePolynomial(HInductionVarAnalysis::InductionInfo* info, 288 HInductionVarAnalysis::InductionInfo* trip, 289 HGraph* graph, 290 HBasicBlock* block, 291 /*out*/HInstruction** result) const; 292 293 bool GenerateLastValueGeometric(HInductionVarAnalysis::InductionInfo* info, 294 HInductionVarAnalysis::InductionInfo* trip, 295 HGraph* graph, 296 HBasicBlock* block, 297 /*out*/HInstruction** result) const; 298 299 bool GenerateLastValueWrapAround(HInductionVarAnalysis::InductionInfo* info, 300 HInductionVarAnalysis::InductionInfo* trip, 301 HGraph* graph, 302 HBasicBlock* block, 303 /*out*/HInstruction** result) const; 304 305 bool GenerateLastValuePeriodic(HInductionVarAnalysis::InductionInfo* info, 306 HInductionVarAnalysis::InductionInfo* trip, 307 HGraph* graph, 308 HBasicBlock* block, 309 /*out*/HInstruction** result, 310 /*out*/ bool* needs_taken_test) const; 311 312 bool GenerateCode(HInductionVarAnalysis::InductionInfo* info, 313 HInductionVarAnalysis::InductionInfo* trip, 314 HGraph* graph, 315 HBasicBlock* block, 316 /*out*/ HInstruction** result, 317 bool in_body, 318 bool is_min) const; 319 320 void ReplaceInduction(HInductionVarAnalysis::InductionInfo* info, 321 HInstruction* fetch, 322 HInstruction* replacement); 323 324 /** Results of prior induction variable analysis. */ 325 HInductionVarAnalysis* induction_analysis_; 326 327 /** Instruction at which chasing may stop. */ 328 HInstruction* chase_hint_; 329 330 friend class HInductionVarAnalysis; 331 friend class InductionVarRangeTest; 332 333 DISALLOW_COPY_AND_ASSIGN(InductionVarRange); 334 }; 335 336 } // namespace art 337 338 #endif // ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_ 339
