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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 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_
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