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 header logic of a loop terminates. Sets trip-count tc if known. 155 */ 156 bool IsFinite(HLoopInformation* loop, /*out*/ int64_t* tc) const; 157 158 /** 159 * Checks if the given instruction is a unit stride induction inside the closest enveloping 160 * loop of the context that is defined by the first parameter (e.g. pass an array reference 161 * as context and the index as instruction to make sure the stride is tested against the 162 * loop that envelops the reference the closest). Returns invariant offset on success. 163 */ 164 bool IsUnitStride(HInstruction* context, 165 HInstruction* instruction, 166 HGraph* graph, 167 /*out*/ HInstruction** offset) const; 168 169 /** 170 * Generates the trip count expression for the given loop. Code is generated in given block 171 * and graph. The expression is guarded by a taken test if needed. Returns the trip count 172 * expression on success or null otherwise. 173 */ 174 HInstruction* GenerateTripCount(HLoopInformation* loop, HGraph* graph, HBasicBlock* block); 175 176 private: 177 /* 178 * Enum used in IsConstant() request. 179 */ 180 enum ConstantRequest { 181 kExact, 182 kAtMost, 183 kAtLeast 184 }; 185 186 /** 187 * Returns true if exact or upper/lower bound on the given induction 188 * information is known as a 64-bit constant, which is returned in value. 189 */ 190 bool IsConstant(HInductionVarAnalysis::InductionInfo* info, 191 ConstantRequest request, 192 /*out*/ int64_t* value) const; 193 194 /** Returns whether induction information can be obtained. */ 195 bool HasInductionInfo(HInstruction* context, 196 HInstruction* instruction, 197 /*out*/ HLoopInformation** loop, 198 /*out*/ HInductionVarAnalysis::InductionInfo** info, 199 /*out*/ HInductionVarAnalysis::InductionInfo** trip) const; 200 201 bool HasFetchInLoop(HInductionVarAnalysis::InductionInfo* info) const; 202 bool NeedsTripCount(HInductionVarAnalysis::InductionInfo* info, 203 /*out*/ int64_t* stride_value) const; 204 bool IsBodyTripCount(HInductionVarAnalysis::InductionInfo* trip) const; 205 bool IsUnsafeTripCount(HInductionVarAnalysis::InductionInfo* trip) const; 206 bool IsWellBehavedTripCount(HInductionVarAnalysis::InductionInfo* trip) const; 207 208 Value GetLinear(HInductionVarAnalysis::InductionInfo* info, 209 HInductionVarAnalysis::InductionInfo* trip, 210 bool in_body, 211 bool is_min) const; 212 Value GetPolynomial(HInductionVarAnalysis::InductionInfo* info, 213 HInductionVarAnalysis::InductionInfo* trip, 214 bool in_body, 215 bool is_min) const; 216 Value GetGeometric(HInductionVarAnalysis::InductionInfo* info, 217 HInductionVarAnalysis::InductionInfo* trip, 218 bool in_body, 219 bool is_min) const; 220 Value GetFetch(HInstruction* instruction, 221 HInductionVarAnalysis::InductionInfo* trip, 222 bool in_body, 223 bool is_min) const; 224 Value GetVal(HInductionVarAnalysis::InductionInfo* info, 225 HInductionVarAnalysis::InductionInfo* trip, 226 bool in_body, 227 bool is_min) const; 228 Value GetMul(HInductionVarAnalysis::InductionInfo* info1, 229 HInductionVarAnalysis::InductionInfo* info2, 230 HInductionVarAnalysis::InductionInfo* trip, 231 bool in_body, 232 bool is_min) const; 233 Value GetDiv(HInductionVarAnalysis::InductionInfo* info1, 234 HInductionVarAnalysis::InductionInfo* info2, 235 HInductionVarAnalysis::InductionInfo* trip, 236 bool in_body, 237 bool is_min) const; 238 Value GetRem(HInductionVarAnalysis::InductionInfo* info1, 239 HInductionVarAnalysis::InductionInfo* info2) const; 240 Value GetXor(HInductionVarAnalysis::InductionInfo* info1, 241 HInductionVarAnalysis::InductionInfo* info2) const; 242 243 Value MulRangeAndConstant(int64_t value, 244 HInductionVarAnalysis::InductionInfo* info, 245 HInductionVarAnalysis::InductionInfo* trip, 246 bool in_body, 247 bool is_min) const; 248 Value DivRangeAndConstant(int64_t value, 249 HInductionVarAnalysis::InductionInfo* info, 250 HInductionVarAnalysis::InductionInfo* trip, 251 bool in_body, 252 bool is_min) const; 253 254 Value AddValue(Value v1, Value v2) const; 255 Value SubValue(Value v1, Value v2) const; 256 Value MulValue(Value v1, Value v2) const; 257 Value DivValue(Value v1, Value v2) const; 258 Value MergeVal(Value v1, Value v2, bool is_min) const; 259 260 /** 261 * Generates code for lower/upper/taken-test or last value in the HIR. Returns true on 262 * success. With values nullptr, the method can be used to determine if code generation 263 * would be successful without generating actual code yet. 264 */ 265 bool GenerateRangeOrLastValue(HInstruction* context, 266 HInstruction* instruction, 267 bool is_last_val, 268 HGraph* graph, 269 HBasicBlock* block, 270 /*out*/ HInstruction** lower, 271 /*out*/ HInstruction** upper, 272 /*out*/ HInstruction** taken_test, 273 /*out*/ int64_t* stride_value, 274 /*out*/ bool* needs_finite_test, 275 /*out*/ bool* needs_taken_test) const; 276 277 bool GenerateLastValuePolynomial(HInductionVarAnalysis::InductionInfo* info, 278 HInductionVarAnalysis::InductionInfo* trip, 279 HGraph* graph, 280 HBasicBlock* block, 281 /*out*/HInstruction** result) const; 282 283 bool GenerateLastValueGeometric(HInductionVarAnalysis::InductionInfo* info, 284 HInductionVarAnalysis::InductionInfo* trip, 285 HGraph* graph, 286 HBasicBlock* block, 287 /*out*/HInstruction** result) const; 288 289 bool GenerateLastValueWrapAround(HInductionVarAnalysis::InductionInfo* info, 290 HInductionVarAnalysis::InductionInfo* trip, 291 HGraph* graph, 292 HBasicBlock* block, 293 /*out*/HInstruction** result) const; 294 295 bool GenerateLastValuePeriodic(HInductionVarAnalysis::InductionInfo* info, 296 HInductionVarAnalysis::InductionInfo* trip, 297 HGraph* graph, 298 HBasicBlock* block, 299 /*out*/HInstruction** result, 300 /*out*/ bool* needs_taken_test) const; 301 302 bool GenerateCode(HInductionVarAnalysis::InductionInfo* info, 303 HInductionVarAnalysis::InductionInfo* trip, 304 HGraph* graph, 305 HBasicBlock* block, 306 /*out*/ HInstruction** result, 307 bool in_body, 308 bool is_min) const; 309 310 void ReplaceInduction(HInductionVarAnalysis::InductionInfo* info, 311 HInstruction* fetch, 312 HInstruction* replacement); 313 314 /** Results of prior induction variable analysis. */ 315 HInductionVarAnalysis* induction_analysis_; 316 317 /** Instruction at which chasing may stop. */ 318 HInstruction* chase_hint_; 319 320 friend class HInductionVarAnalysis; 321 friend class InductionVarRangeTest; 322 323 DISALLOW_COPY_AND_ASSIGN(InductionVarRange); 324 }; 325 326 } // namespace art 327 328 #endif // ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_ 329
