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