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/*
* 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 bound on the instruction's value.
*/
Value GetMinInduction(HInstruction* context, HInstruction* instruction);
/**
* Given a context denoted by the first instruction, returns a,
* possibly conservative, upper bound on the instruction's value.
*/
Value GetMaxInduction(HInstruction* context, HInstruction* instruction);
private:
//
// Private helper methods.
//
HInductionVarAnalysis::InductionInfo* GetTripCount(HLoopInformation* loop, HInstruction* context);
static Value GetFetch(HInstruction* instruction,
HInductionVarAnalysis::InductionInfo* trip,
bool is_min);
static Value GetMin(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip);
static Value GetMax(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip);
static Value GetMul(HInductionVarAnalysis::InductionInfo* info1,
HInductionVarAnalysis::InductionInfo* info2,
HInductionVarAnalysis::InductionInfo* trip,
bool is_min);
static Value GetDiv(HInductionVarAnalysis::InductionInfo* info1,
HInductionVarAnalysis::InductionInfo* info2,
HInductionVarAnalysis::InductionInfo* trip,
bool is_min);
static Value AddValue(Value v1, Value v2);
static Value SubValue(Value v1, Value v2);
static Value MulValue(Value v1, Value v2);
static Value DivValue(Value v1, Value v2);
static Value MinValue(Value v1, Value v2);
static Value MaxValue(Value v1, Value v2);
/** 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_
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