/*
* 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 or last value on each instruction in the HIR.
* The public API also provides a few general-purpose utility methods related to induction.
*
* 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. The parameter chase_hint defines an
* instruction at which chasing may stop. Returns false on failure.
*/
bool GetInductionRange(HInstruction* context,
HInstruction* instruction,
HInstruction* chase_hint,
/*out*/ Value* min_val,
/*out*/ Value* max_val,
/*out*/ bool* needs_finite_test);
/**
* 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 CanGenerateRange(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: CanGenerateRange() returns true.
*/
void GenerateRange(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. Returns generated taken-test.
*
* Precondition: CanGenerateRange() returns true and needs_taken_test is set.
*/
HInstruction* GenerateTakenTest(HInstruction* context, HGraph* graph, HBasicBlock* block);
/**
* Returns true if induction analysis is able to generate code for last value of
* the given instruction inside the closest enveloping loop.
*/
bool CanGenerateLastValue(HInstruction* instruction);
/**
* Generates last value of the given instruction in the closest enveloping loop.
* Code is generated in given block and graph. Returns generated last value.
*
* Precondition: CanGenerateLastValue() returns true.
*/
HInstruction* GenerateLastValue(HInstruction* instruction, HGraph* graph, HBasicBlock* block);
/**
* Updates all matching fetches with the given replacement in all induction information
* that is associated with the given instruction.
*/
void Replace(HInstruction* instruction, HInstruction* fetch, HInstruction* replacement);
/**
* Incrementally updates induction information for just the given loop.
*/
void ReVisit(HLoopInformation* loop) {
induction_analysis_->induction_.erase(loop);
for (HInstructionIterator it(loop->GetHeader()->GetPhis()); !it.Done(); it.Advance()) {
induction_analysis_->cycles_.erase(it.Current()->AsPhi());
}
induction_analysis_->VisitLoop(loop);
}
/**
* Lookup an interesting cycle associated with an entry phi.
*/
ArenaSet<HInstruction*>* LookupCycle(HPhi* phi) const {
return induction_analysis_->LookupCycle(phi);
}
/**
* Checks if the given phi instruction has been classified as anything by
* induction variable analysis. Returns false for anything that cannot be
* classified statically, such as reductions or other complex cycles.
*/
bool IsClassified(HPhi* phi) const {
HLoopInformation* lp = phi->GetBlock()->GetLoopInformation(); // closest enveloping loop
return (lp != nullptr) && (induction_analysis_->LookupInfo(lp, phi) != nullptr);
}
/**
* Checks if header logic of a loop terminates. If trip count is known sets 'trip_count' to its
* value.
*/
bool IsFinite(HLoopInformation* loop, /*out*/ int64_t* trip_count) const;
/**
* Checks if a trip count is known for the loop and sets 'trip_count' to its value in this case.
*/
bool HasKnownTripCount(HLoopInformation* loop, /*out*/ int64_t* trip_count) const;
/**
* Checks if the given instruction is a unit stride induction inside the closest enveloping
* loop of the context that is defined by the first parameter (e.g. pass an array reference
* as context and the index as instruction to make sure the stride is tested against the
* loop that envelops the reference the closest). Returns invariant offset on success.
*/
bool IsUnitStride(HInstruction* context,
HInstruction* instruction,
HGraph* graph,
/*out*/ HInstruction** offset) const;
/**
* Generates the trip count expression for the given loop. Code is generated in given block
* and graph. The expression is guarded by a taken test if needed. Returns the trip count
* expression on success or null otherwise.
*/
HInstruction* GenerateTripCount(HLoopInformation* loop, HGraph* graph, HBasicBlock* block);
private:
/*
* Enum used in IsConstant() request.
*/
enum ConstantRequest {
kExact,
kAtMost,
kAtLeast
};
/**
* Checks if header logic of a loop terminates. If trip count is known (constant) sets
* 'is_constant' to true and 'trip_count' to the trip count value.
*/
bool CheckForFiniteAndConstantProps(HLoopInformation* loop,
/*out*/ bool* is_constant,
/*out*/ int64_t* trip_count) const;
/**
* 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;
/** Returns whether induction information can be obtained. */
bool HasInductionInfo(HInstruction* context,
HInstruction* instruction,
/*out*/ HLoopInformation** loop,
/*out*/ HInductionVarAnalysis::InductionInfo** info,
/*out*/ HInductionVarAnalysis::InductionInfo** trip) const;
bool HasFetchInLoop(HInductionVarAnalysis::InductionInfo* info) const;
bool NeedsTripCount(HInductionVarAnalysis::InductionInfo* info,
/*out*/ int64_t* stride_value) const;
bool IsBodyTripCount(HInductionVarAnalysis::InductionInfo* trip) const;
bool IsUnsafeTripCount(HInductionVarAnalysis::InductionInfo* trip) const;
bool IsWellBehavedTripCount(HInductionVarAnalysis::InductionInfo* trip) const;
Value GetLinear(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
bool in_body,
bool is_min) const;
Value GetPolynomial(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
bool in_body,
bool is_min) const;
Value GetGeometric(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 GetRem(HInductionVarAnalysis::InductionInfo* info1,
HInductionVarAnalysis::InductionInfo* info2) const;
Value GetXor(HInductionVarAnalysis::InductionInfo* info1,
HInductionVarAnalysis::InductionInfo* info2) const;
Value MulRangeAndConstant(int64_t value,
HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
bool in_body,
bool is_min) const;
Value DivRangeAndConstant(int64_t value,
HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
bool in_body,
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;
/**
* Generates code for lower/upper/taken-test or last value 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 GenerateRangeOrLastValue(HInstruction* context,
HInstruction* instruction,
bool is_last_val,
HGraph* graph,
HBasicBlock* block,
/*out*/ HInstruction** lower,
/*out*/ HInstruction** upper,
/*out*/ HInstruction** taken_test,
/*out*/ int64_t* stride_value,
/*out*/ bool* needs_finite_test,
/*out*/ bool* needs_taken_test) const;
bool GenerateLastValuePolynomial(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
HGraph* graph,
HBasicBlock* block,
/*out*/HInstruction** result) const;
bool GenerateLastValueGeometric(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
HGraph* graph,
HBasicBlock* block,
/*out*/HInstruction** result) const;
bool GenerateLastValueWrapAround(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
HGraph* graph,
HBasicBlock* block,
/*out*/HInstruction** result) const;
bool GenerateLastValuePeriodic(HInductionVarAnalysis::InductionInfo* info,
HInductionVarAnalysis::InductionInfo* trip,
HGraph* graph,
HBasicBlock* block,
/*out*/HInstruction** result,
/*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;
void ReplaceInduction(HInductionVarAnalysis::InductionInfo* info,
HInstruction* fetch,
HInstruction* replacement);
/** Results of prior induction variable analysis. */
HInductionVarAnalysis* induction_analysis_;
/** Instruction at which chasing may stop. */
HInstruction* chase_hint_;
friend class HInductionVarAnalysis;
friend class InductionVarRangeTest;
DISALLOW_COPY_AND_ASSIGN(InductionVarRange);
};
} // namespace art
#endif // ART_COMPILER_OPTIMIZING_INDUCTION_VAR_RANGE_H_