/* * Copyright (C) 2015 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #ifndef ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_ #define ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_ #include "induction_var_analysis.h" namespace art { /** * This class implements range analysis on expressions within loops. It takes the results * of induction variable analysis in the constructor and provides a public API to obtain * a conservative lower and upper bound value on each instruction in the HIR. * * The range analysis is done with a combination of symbolic and partial integral evaluation * of expressions. The analysis avoids complications with wrap-around arithmetic on the integral * parts but all clients should be aware that wrap-around may occur on any of the symbolic parts. * For example, given a known range for [0,100] for i, the evaluation yields range [-100,100] * for expression -2*i+100, which is exact, and range [x,x+100] for expression i+x, which may * wrap-around anywhere in the range depending on the actual value of x. */ class InductionVarRange { public: /* * A value that can be represented as "a * instruction + b" for 32-bit constants, where * Value() denotes an unknown lower and upper bound. Although range analysis could yield * more complex values, the format is sufficiently powerful to represent useful cases * and feeds directly into optimizations like bounds check elimination. */ struct Value { Value() : instruction(nullptr), a_constant(0), b_constant(0), is_known(false) {} Value(HInstruction* i, int32_t a, int32_t b) : instruction(a != 0 ? i : nullptr), a_constant(a), b_constant(b), is_known(true) {} explicit Value(int32_t b) : Value(nullptr, 0, b) {} // Representation as: a_constant x instruction + b_constant. HInstruction* instruction; int32_t a_constant; int32_t b_constant; // If true, represented by prior fields. Otherwise unknown value. bool is_known; }; explicit InductionVarRange(HInductionVarAnalysis* induction); /** * Given a context denoted by the first instruction, returns a possibly conservative * lower and upper bound on the instruction's value in the output parameters min_val * and max_val, respectively. The need_finite_test flag denotes if an additional finite-test * is needed to protect the range evaluation inside its loop. Returns false on failure. */ bool GetInductionRange(HInstruction* context, HInstruction* instruction, /*out*/ Value* min_val, /*out*/ Value* max_val, /*out*/ bool* needs_finite_test); /** Refines the values with induction of next outer loop. Returns true on change. */ bool RefineOuter(/*in-out*/ Value* min_val, /*in-out*/ Value* max_val) const; /** * Returns true if range analysis is able to generate code for the lower and upper * bound expressions on the instruction in the given context. The need_finite_test * and need_taken test flags denote if an additional finite-test and/or taken-test * are needed to protect the range evaluation inside its loop. */ bool CanGenerateCode(HInstruction* context, HInstruction* instruction, /*out*/ bool* needs_finite_test, /*out*/ bool* needs_taken_test); /** * Generates the actual code in the HIR for the lower and upper bound expressions on the * instruction in the given context. Code for the lower and upper bound expression are * generated in given block and graph and are returned in the output parameters lower and * upper, respectively. For a loop invariant, lower is not set. * * For example, given expression x+i with range [0, 5] for i, calling this method * will generate the following sequence: * * block: * lower: add x, 0 * upper: add x, 5 * * Precondition: CanGenerateCode() returns true. */ void GenerateRangeCode(HInstruction* context, HInstruction* instruction, HGraph* graph, HBasicBlock* block, /*out*/ HInstruction** lower, /*out*/ HInstruction** upper); /** * Generates explicit taken-test for the loop in the given context. Code is generated in * given block and graph. The taken-test is returned in parameter test. * * Precondition: CanGenerateCode() returns true and needs_taken_test is set. */ void GenerateTakenTest(HInstruction* context, HGraph* graph, HBasicBlock* block, /*out*/ HInstruction** taken_test); private: /* * Enum used in IsConstant() request. */ enum ConstantRequest { kExact, kAtMost, kAtLeast }; /** * Returns true if exact or upper/lower bound on the given induction * information is known as a 64-bit constant, which is returned in value. */ bool IsConstant(HInductionVarAnalysis::InductionInfo* info, ConstantRequest request, /*out*/ int64_t *value) const; bool NeedsTripCount(HInductionVarAnalysis::InductionInfo* info) const; bool IsBodyTripCount(HInductionVarAnalysis::InductionInfo* trip) const; bool IsUnsafeTripCount(HInductionVarAnalysis::InductionInfo* trip) const; Value GetLinear(HInductionVarAnalysis::InductionInfo* info, HInductionVarAnalysis::InductionInfo* trip, bool in_body, bool is_min) const; Value GetFetch(HInstruction* instruction, HInductionVarAnalysis::InductionInfo* trip, bool in_body, bool is_min) const; Value GetVal(HInductionVarAnalysis::InductionInfo* info, HInductionVarAnalysis::InductionInfo* trip, bool in_body, bool is_min) const; Value GetMul(HInductionVarAnalysis::InductionInfo* info1, HInductionVarAnalysis::InductionInfo* info2, HInductionVarAnalysis::InductionInfo* trip, bool in_body, bool is_min) const; Value GetDiv(HInductionVarAnalysis::InductionInfo* info1, HInductionVarAnalysis::InductionInfo* info2, HInductionVarAnalysis::InductionInfo* trip, bool in_body, bool is_min) const; Value MulRangeAndConstant(Value v1, Value v2, Value c, bool is_min) const; Value DivRangeAndConstant(Value v1, Value v2, Value c, bool is_min) const; Value AddValue(Value v1, Value v2) const; Value SubValue(Value v1, Value v2) const; Value MulValue(Value v1, Value v2) const; Value DivValue(Value v1, Value v2) const; Value MergeVal(Value v1, Value v2, bool is_min) const; /** * Returns refined value using induction of next outer loop or the input value if no * further refinement is possible. */ Value RefineOuter(Value val, bool is_min) const; /** * Generates code for lower/upper/taken-test in the HIR. Returns true on success. * With values nullptr, the method can be used to determine if code generation * would be successful without generating actual code yet. */ bool GenerateCode(HInstruction* context, HInstruction* instruction, HGraph* graph, HBasicBlock* block, /*out*/ HInstruction** lower, /*out*/ HInstruction** upper, /*out*/ HInstruction** taken_test, /*out*/ bool* needs_finite_test, /*out*/ bool* needs_taken_test) const; bool GenerateCode(HInductionVarAnalysis::InductionInfo* info, HInductionVarAnalysis::InductionInfo* trip, HGraph* graph, HBasicBlock* block, /*out*/ HInstruction** result, bool in_body, bool is_min) const; /** Results of prior induction variable analysis. */ HInductionVarAnalysis *induction_analysis_; friend class HInductionVarAnalysis; friend class InductionVarRangeTest; DISALLOW_COPY_AND_ASSIGN(InductionVarRange); }; } // namespace art #endif // ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_