/*
* 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.
*/
#include "load_store_elimination.h"
#include "escape.h"
#include "side_effects_analysis.h"
#include <iostream>
namespace art {
class ReferenceInfo;
// A cap for the number of heap locations to prevent pathological time/space consumption.
// The number of heap locations for most of the methods stays below this threshold.
constexpr size_t kMaxNumberOfHeapLocations = 32;
// A ReferenceInfo contains additional info about a reference such as
// whether it's a singleton, returned, etc.
class ReferenceInfo : public ArenaObject<kArenaAllocMisc> {
public:
ReferenceInfo(HInstruction* reference, size_t pos)
: reference_(reference),
position_(pos),
is_singleton_(true),
is_singleton_and_not_returned_(true),
is_singleton_and_not_deopt_visible_(true),
has_index_aliasing_(false) {
CalculateEscape(reference_,
nullptr,
&is_singleton_,
&is_singleton_and_not_returned_,
&is_singleton_and_not_deopt_visible_);
}
HInstruction* GetReference() const {
return reference_;
}
size_t GetPosition() const {
return position_;
}
// Returns true if reference_ is the only name that can refer to its value during
// the lifetime of the method. So it's guaranteed to not have any alias in
// the method (including its callees).
bool IsSingleton() const {
return is_singleton_;
}
// Returns true if reference_ is a singleton and not returned to the caller or
// used as an environment local of an HDeoptimize instruction.
// The allocation and stores into reference_ may be eliminated for such cases.
bool IsSingletonAndRemovable() const {
return is_singleton_and_not_returned_ && is_singleton_and_not_deopt_visible_;
}
// Returns true if reference_ is a singleton and returned to the caller or
// used as an environment local of an HDeoptimize instruction.
bool IsSingletonAndNonRemovable() const {
return is_singleton_ &&
(!is_singleton_and_not_returned_ || !is_singleton_and_not_deopt_visible_);
}
bool HasIndexAliasing() {
return has_index_aliasing_;
}
void SetHasIndexAliasing(bool has_index_aliasing) {
// Only allow setting to true.
DCHECK(has_index_aliasing);
has_index_aliasing_ = has_index_aliasing;
}
private:
HInstruction* const reference_;
const size_t position_; // position in HeapLocationCollector's ref_info_array_.
// Can only be referred to by a single name in the method.
bool is_singleton_;
// Is singleton and not returned to caller.
bool is_singleton_and_not_returned_;
// Is singleton and not used as an environment local of HDeoptimize.
bool is_singleton_and_not_deopt_visible_;
// Some heap locations with reference_ have array index aliasing,
// e.g. arr[i] and arr[j] may be the same location.
bool has_index_aliasing_;
DISALLOW_COPY_AND_ASSIGN(ReferenceInfo);
};
// A heap location is a reference-offset/index pair that a value can be loaded from
// or stored to.
class HeapLocation : public ArenaObject<kArenaAllocMisc> {
public:
static constexpr size_t kInvalidFieldOffset = -1;
// TODO: more fine-grained array types.
static constexpr int16_t kDeclaringClassDefIndexForArrays = -1;
HeapLocation(ReferenceInfo* ref_info,
size_t offset,
HInstruction* index,
int16_t declaring_class_def_index)
: ref_info_(ref_info),
offset_(offset),
index_(index),
declaring_class_def_index_(declaring_class_def_index),
value_killed_by_loop_side_effects_(true) {
DCHECK(ref_info != nullptr);
DCHECK((offset == kInvalidFieldOffset && index != nullptr) ||
(offset != kInvalidFieldOffset && index == nullptr));
if (ref_info->IsSingleton() && !IsArrayElement()) {
// Assume this location's value cannot be killed by loop side effects
// until proven otherwise.
value_killed_by_loop_side_effects_ = false;
}
}
ReferenceInfo* GetReferenceInfo() const { return ref_info_; }
size_t GetOffset() const { return offset_; }
HInstruction* GetIndex() const { return index_; }
// Returns the definition of declaring class' dex index.
// It's kDeclaringClassDefIndexForArrays for an array element.
int16_t GetDeclaringClassDefIndex() const {
return declaring_class_def_index_;
}
bool IsArrayElement() const {
return index_ != nullptr;
}
bool IsValueKilledByLoopSideEffects() const {
return value_killed_by_loop_side_effects_;
}
void SetValueKilledByLoopSideEffects(bool val) {
value_killed_by_loop_side_effects_ = val;
}
private:
ReferenceInfo* const ref_info_; // reference for instance/static field or array access.
const size_t offset_; // offset of static/instance field.
HInstruction* const index_; // index of an array element.
const int16_t declaring_class_def_index_; // declaring class's def's dex index.
bool value_killed_by_loop_side_effects_; // value of this location may be killed by loop
// side effects because this location is stored
// into inside a loop. This gives
// better info on whether a singleton's location
// value may be killed by loop side effects.
DISALLOW_COPY_AND_ASSIGN(HeapLocation);
};
static HInstruction* HuntForOriginalReference(HInstruction* ref) {
DCHECK(ref != nullptr);
while (ref->IsNullCheck() || ref->IsBoundType()) {
ref = ref->InputAt(0);
}
return ref;
}
// A HeapLocationCollector collects all relevant heap locations and keeps
// an aliasing matrix for all locations.
class HeapLocationCollector : public HGraphVisitor {
public:
static constexpr size_t kHeapLocationNotFound = -1;
// Start with a single uint32_t word. That's enough bits for pair-wise
// aliasing matrix of 8 heap locations.
static constexpr uint32_t kInitialAliasingMatrixBitVectorSize = 32;
explicit HeapLocationCollector(HGraph* graph)
: HGraphVisitor(graph),
ref_info_array_(graph->GetArena()->Adapter(kArenaAllocLSE)),
heap_locations_(graph->GetArena()->Adapter(kArenaAllocLSE)),
aliasing_matrix_(graph->GetArena(),
kInitialAliasingMatrixBitVectorSize,
true,
kArenaAllocLSE),
has_heap_stores_(false),
has_volatile_(false),
has_monitor_operations_(false) {}
size_t GetNumberOfHeapLocations() const {
return heap_locations_.size();
}
HeapLocation* GetHeapLocation(size_t index) const {
return heap_locations_[index];
}
ReferenceInfo* FindReferenceInfoOf(HInstruction* ref) const {
for (size_t i = 0; i < ref_info_array_.size(); i++) {
ReferenceInfo* ref_info = ref_info_array_[i];
if (ref_info->GetReference() == ref) {
DCHECK_EQ(i, ref_info->GetPosition());
return ref_info;
}
}
return nullptr;
}
bool HasHeapStores() const {
return has_heap_stores_;
}
bool HasVolatile() const {
return has_volatile_;
}
bool HasMonitorOps() const {
return has_monitor_operations_;
}
// Find and return the heap location index in heap_locations_.
size_t FindHeapLocationIndex(ReferenceInfo* ref_info,
size_t offset,
HInstruction* index,
int16_t declaring_class_def_index) const {
for (size_t i = 0; i < heap_locations_.size(); i++) {
HeapLocation* loc = heap_locations_[i];
if (loc->GetReferenceInfo() == ref_info &&
loc->GetOffset() == offset &&
loc->GetIndex() == index &&
loc->GetDeclaringClassDefIndex() == declaring_class_def_index) {
return i;
}
}
return kHeapLocationNotFound;
}
// Returns true if heap_locations_[index1] and heap_locations_[index2] may alias.
bool MayAlias(size_t index1, size_t index2) const {
if (index1 < index2) {
return aliasing_matrix_.IsBitSet(AliasingMatrixPosition(index1, index2));
} else if (index1 > index2) {
return aliasing_matrix_.IsBitSet(AliasingMatrixPosition(index2, index1));
} else {
DCHECK(false) << "index1 and index2 are expected to be different";
return true;
}
}
void BuildAliasingMatrix() {
const size_t number_of_locations = heap_locations_.size();
if (number_of_locations == 0) {
return;
}
size_t pos = 0;
// Compute aliasing info between every pair of different heap locations.
// Save the result in a matrix represented as a BitVector.
for (size_t i = 0; i < number_of_locations - 1; i++) {
for (size_t j = i + 1; j < number_of_locations; j++) {
if (ComputeMayAlias(i, j)) {
aliasing_matrix_.SetBit(CheckedAliasingMatrixPosition(i, j, pos));
}
pos++;
}
}
}
private:
// An allocation cannot alias with a name which already exists at the point
// of the allocation, such as a parameter or a load happening before the allocation.
bool MayAliasWithPreexistenceChecking(ReferenceInfo* ref_info1, ReferenceInfo* ref_info2) const {
if (ref_info1->GetReference()->IsNewInstance() || ref_info1->GetReference()->IsNewArray()) {
// Any reference that can alias with the allocation must appear after it in the block/in
// the block's successors. In reverse post order, those instructions will be visited after
// the allocation.
return ref_info2->GetPosition() >= ref_info1->GetPosition();
}
return true;
}
bool CanReferencesAlias(ReferenceInfo* ref_info1, ReferenceInfo* ref_info2) const {
if (ref_info1 == ref_info2) {
return true;
} else if (ref_info1->IsSingleton()) {
return false;
} else if (ref_info2->IsSingleton()) {
return false;
} else if (!MayAliasWithPreexistenceChecking(ref_info1, ref_info2) ||
!MayAliasWithPreexistenceChecking(ref_info2, ref_info1)) {
return false;
}
return true;
}
// `index1` and `index2` are indices in the array of collected heap locations.
// Returns the position in the bit vector that tracks whether the two heap
// locations may alias.
size_t AliasingMatrixPosition(size_t index1, size_t index2) const {
DCHECK(index2 > index1);
const size_t number_of_locations = heap_locations_.size();
// It's (num_of_locations - 1) + ... + (num_of_locations - index1) + (index2 - index1 - 1).
return (number_of_locations * index1 - (1 + index1) * index1 / 2 + (index2 - index1 - 1));
}
// An additional position is passed in to make sure the calculated position is correct.
size_t CheckedAliasingMatrixPosition(size_t index1, size_t index2, size_t position) {
size_t calculated_position = AliasingMatrixPosition(index1, index2);
DCHECK_EQ(calculated_position, position);
return calculated_position;
}
// Compute if two locations may alias to each other.
bool ComputeMayAlias(size_t index1, size_t index2) const {
HeapLocation* loc1 = heap_locations_[index1];
HeapLocation* loc2 = heap_locations_[index2];
if (loc1->GetOffset() != loc2->GetOffset()) {
// Either two different instance fields, or one is an instance
// field and the other is an array element.
return false;
}
if (loc1->GetDeclaringClassDefIndex() != loc2->GetDeclaringClassDefIndex()) {
// Different types.
return false;
}
if (!CanReferencesAlias(loc1->GetReferenceInfo(), loc2->GetReferenceInfo())) {
return false;
}
if (loc1->IsArrayElement() && loc2->IsArrayElement()) {
HInstruction* array_index1 = loc1->GetIndex();
HInstruction* array_index2 = loc2->GetIndex();
DCHECK(array_index1 != nullptr);
DCHECK(array_index2 != nullptr);
if (array_index1->IsIntConstant() &&
array_index2->IsIntConstant() &&
array_index1->AsIntConstant()->GetValue() != array_index2->AsIntConstant()->GetValue()) {
// Different constant indices do not alias.
return false;
}
ReferenceInfo* ref_info = loc1->GetReferenceInfo();
ref_info->SetHasIndexAliasing(true);
}
return true;
}
ReferenceInfo* GetOrCreateReferenceInfo(HInstruction* instruction) {
ReferenceInfo* ref_info = FindReferenceInfoOf(instruction);
if (ref_info == nullptr) {
size_t pos = ref_info_array_.size();
ref_info = new (GetGraph()->GetArena()) ReferenceInfo(instruction, pos);
ref_info_array_.push_back(ref_info);
}
return ref_info;
}
void CreateReferenceInfoForReferenceType(HInstruction* instruction) {
if (instruction->GetType() != Primitive::kPrimNot) {
return;
}
DCHECK(FindReferenceInfoOf(instruction) == nullptr);
GetOrCreateReferenceInfo(instruction);
}
HeapLocation* GetOrCreateHeapLocation(HInstruction* ref,
size_t offset,
HInstruction* index,
int16_t declaring_class_def_index) {
HInstruction* original_ref = HuntForOriginalReference(ref);
ReferenceInfo* ref_info = GetOrCreateReferenceInfo(original_ref);
size_t heap_location_idx = FindHeapLocationIndex(
ref_info, offset, index, declaring_class_def_index);
if (heap_location_idx == kHeapLocationNotFound) {
HeapLocation* heap_loc = new (GetGraph()->GetArena())
HeapLocation(ref_info, offset, index, declaring_class_def_index);
heap_locations_.push_back(heap_loc);
return heap_loc;
}
return heap_locations_[heap_location_idx];
}
HeapLocation* VisitFieldAccess(HInstruction* ref, const FieldInfo& field_info) {
if (field_info.IsVolatile()) {
has_volatile_ = true;
}
const uint16_t declaring_class_def_index = field_info.GetDeclaringClassDefIndex();
const size_t offset = field_info.GetFieldOffset().SizeValue();
return GetOrCreateHeapLocation(ref, offset, nullptr, declaring_class_def_index);
}
void VisitArrayAccess(HInstruction* array, HInstruction* index) {
GetOrCreateHeapLocation(array, HeapLocation::kInvalidFieldOffset,
index, HeapLocation::kDeclaringClassDefIndexForArrays);
}
void VisitInstanceFieldGet(HInstanceFieldGet* instruction) OVERRIDE {
VisitFieldAccess(instruction->InputAt(0), instruction->GetFieldInfo());
CreateReferenceInfoForReferenceType(instruction);
}
void VisitInstanceFieldSet(HInstanceFieldSet* instruction) OVERRIDE {
HeapLocation* location = VisitFieldAccess(instruction->InputAt(0), instruction->GetFieldInfo());
has_heap_stores_ = true;
if (location->GetReferenceInfo()->IsSingleton()) {
// A singleton's location value may be killed by loop side effects if it's
// defined before that loop, and it's stored into inside that loop.
HLoopInformation* loop_info = instruction->GetBlock()->GetLoopInformation();
if (loop_info != nullptr) {
HInstruction* ref = location->GetReferenceInfo()->GetReference();
DCHECK(ref->IsNewInstance());
if (loop_info->IsDefinedOutOfTheLoop(ref)) {
// ref's location value may be killed by this loop's side effects.
location->SetValueKilledByLoopSideEffects(true);
} else {
// ref is defined inside this loop so this loop's side effects cannot
// kill its location value at the loop header since ref/its location doesn't
// exist yet at the loop header.
}
}
} else {
// For non-singletons, value_killed_by_loop_side_effects_ is inited to
// true.
DCHECK_EQ(location->IsValueKilledByLoopSideEffects(), true);
}
}
void VisitStaticFieldGet(HStaticFieldGet* instruction) OVERRIDE {
VisitFieldAccess(instruction->InputAt(0), instruction->GetFieldInfo());
CreateReferenceInfoForReferenceType(instruction);
}
void VisitStaticFieldSet(HStaticFieldSet* instruction) OVERRIDE {
VisitFieldAccess(instruction->InputAt(0), instruction->GetFieldInfo());
has_heap_stores_ = true;
}
// We intentionally don't collect HUnresolvedInstanceField/HUnresolvedStaticField accesses
// since we cannot accurately track the fields.
void VisitArrayGet(HArrayGet* instruction) OVERRIDE {
VisitArrayAccess(instruction->InputAt(0), instruction->InputAt(1));
CreateReferenceInfoForReferenceType(instruction);
}
void VisitArraySet(HArraySet* instruction) OVERRIDE {
VisitArrayAccess(instruction->InputAt(0), instruction->InputAt(1));
has_heap_stores_ = true;
}
void VisitNewInstance(HNewInstance* new_instance) OVERRIDE {
// Any references appearing in the ref_info_array_ so far cannot alias with new_instance.
CreateReferenceInfoForReferenceType(new_instance);
}
void VisitInvokeStaticOrDirect(HInvokeStaticOrDirect* instruction) OVERRIDE {
CreateReferenceInfoForReferenceType(instruction);
}
void VisitInvokeVirtual(HInvokeVirtual* instruction) OVERRIDE {
CreateReferenceInfoForReferenceType(instruction);
}
void VisitInvokeInterface(HInvokeInterface* instruction) OVERRIDE {
CreateReferenceInfoForReferenceType(instruction);
}
void VisitParameterValue(HParameterValue* instruction) OVERRIDE {
CreateReferenceInfoForReferenceType(instruction);
}
void VisitSelect(HSelect* instruction) OVERRIDE {
CreateReferenceInfoForReferenceType(instruction);
}
void VisitMonitorOperation(HMonitorOperation* monitor ATTRIBUTE_UNUSED) OVERRIDE {
has_monitor_operations_ = true;
}
ArenaVector<ReferenceInfo*> ref_info_array_; // All references used for heap accesses.
ArenaVector<HeapLocation*> heap_locations_; // All heap locations.
ArenaBitVector aliasing_matrix_; // aliasing info between each pair of locations.
bool has_heap_stores_; // If there is no heap stores, LSE acts as GVN with better
// alias analysis and won't be as effective.
bool has_volatile_; // If there are volatile field accesses.
bool has_monitor_operations_; // If there are monitor operations.
DISALLOW_COPY_AND_ASSIGN(HeapLocationCollector);
};
// An unknown heap value. Loads with such a value in the heap location cannot be eliminated.
// A heap location can be set to kUnknownHeapValue when:
// - initially set a value.
// - killed due to aliasing, merging, invocation, or loop side effects.
static HInstruction* const kUnknownHeapValue =
reinterpret_cast<HInstruction*>(static_cast<uintptr_t>(-1));
// Default heap value after an allocation.
// A heap location can be set to that value right after an allocation.
static HInstruction* const kDefaultHeapValue =
reinterpret_cast<HInstruction*>(static_cast<uintptr_t>(-2));
class LSEVisitor : public HGraphVisitor {
public:
LSEVisitor(HGraph* graph,
const HeapLocationCollector& heap_locations_collector,
const SideEffectsAnalysis& side_effects)
: HGraphVisitor(graph),
heap_location_collector_(heap_locations_collector),
side_effects_(side_effects),
heap_values_for_(graph->GetBlocks().size(),
ArenaVector<HInstruction*>(heap_locations_collector.
GetNumberOfHeapLocations(),
kUnknownHeapValue,
graph->GetArena()->Adapter(kArenaAllocLSE)),
graph->GetArena()->Adapter(kArenaAllocLSE)),
removed_loads_(graph->GetArena()->Adapter(kArenaAllocLSE)),
substitute_instructions_for_loads_(graph->GetArena()->Adapter(kArenaAllocLSE)),
possibly_removed_stores_(graph->GetArena()->Adapter(kArenaAllocLSE)),
singleton_new_instances_(graph->GetArena()->Adapter(kArenaAllocLSE)),
singleton_new_arrays_(graph->GetArena()->Adapter(kArenaAllocLSE)) {
}
void VisitBasicBlock(HBasicBlock* block) OVERRIDE {
// Populate the heap_values array for this block.
// TODO: try to reuse the heap_values array from one predecessor if possible.
if (block->IsLoopHeader()) {
HandleLoopSideEffects(block);
} else {
MergePredecessorValues(block);
}
HGraphVisitor::VisitBasicBlock(block);
}
// Remove recorded instructions that should be eliminated.
void RemoveInstructions() {
size_t size = removed_loads_.size();
DCHECK_EQ(size, substitute_instructions_for_loads_.size());
for (size_t i = 0; i < size; i++) {
HInstruction* load = removed_loads_[i];
DCHECK(load != nullptr);
DCHECK(load->IsInstanceFieldGet() ||
load->IsStaticFieldGet() ||
load->IsArrayGet());
HInstruction* substitute = substitute_instructions_for_loads_[i];
DCHECK(substitute != nullptr);
// Keep tracing substitute till one that's not removed.
HInstruction* sub_sub = FindSubstitute(substitute);
while (sub_sub != substitute) {
substitute = sub_sub;
sub_sub = FindSubstitute(substitute);
}
load->ReplaceWith(substitute);
load->GetBlock()->RemoveInstruction(load);
}
// At this point, stores in possibly_removed_stores_ can be safely removed.
for (HInstruction* store : possibly_removed_stores_) {
DCHECK(store->IsInstanceFieldSet() || store->IsStaticFieldSet() || store->IsArraySet());
store->GetBlock()->RemoveInstruction(store);
}
// Eliminate allocations that are not used.
for (HInstruction* new_instance : singleton_new_instances_) {
if (!new_instance->HasNonEnvironmentUses()) {
new_instance->RemoveEnvironmentUsers();
new_instance->GetBlock()->RemoveInstruction(new_instance);
}
}
for (HInstruction* new_array : singleton_new_arrays_) {
if (!new_array->HasNonEnvironmentUses()) {
new_array->RemoveEnvironmentUsers();
new_array->GetBlock()->RemoveInstruction(new_array);
}
}
}
private:
// If heap_values[index] is an instance field store, need to keep the store.
// This is necessary if a heap value is killed due to merging, or loop side
// effects (which is essentially merging also), since a load later from the
// location won't be eliminated.
void KeepIfIsStore(HInstruction* heap_value) {
if (heap_value == kDefaultHeapValue ||
heap_value == kUnknownHeapValue ||
!(heap_value->IsInstanceFieldSet() || heap_value->IsArraySet())) {
return;
}
auto idx = std::find(possibly_removed_stores_.begin(),
possibly_removed_stores_.end(), heap_value);
if (idx != possibly_removed_stores_.end()) {
// Make sure the store is kept.
possibly_removed_stores_.erase(idx);
}
}
void HandleLoopSideEffects(HBasicBlock* block) {
DCHECK(block->IsLoopHeader());
int block_id = block->GetBlockId();
ArenaVector<HInstruction*>& heap_values = heap_values_for_[block_id];
// Don't eliminate loads in irreducible loops. This is safe for singletons, because
// they are always used by the non-eliminated loop-phi.
if (block->GetLoopInformation()->IsIrreducible()) {
if (kIsDebugBuild) {
for (size_t i = 0; i < heap_values.size(); i++) {
DCHECK_EQ(heap_values[i], kUnknownHeapValue);
}
}
return;
}
HBasicBlock* pre_header = block->GetLoopInformation()->GetPreHeader();
ArenaVector<HInstruction*>& pre_header_heap_values =
heap_values_for_[pre_header->GetBlockId()];
// Inherit the values from pre-header.
for (size_t i = 0; i < heap_values.size(); i++) {
heap_values[i] = pre_header_heap_values[i];
}
// We do a single pass in reverse post order. For loops, use the side effects as a hint
// to see if the heap values should be killed.
if (side_effects_.GetLoopEffects(block).DoesAnyWrite()) {
for (size_t i = 0; i < heap_values.size(); i++) {
HeapLocation* location = heap_location_collector_.GetHeapLocation(i);
ReferenceInfo* ref_info = location->GetReferenceInfo();
if (ref_info->IsSingletonAndRemovable() &&
!location->IsValueKilledByLoopSideEffects()) {
// A removable singleton's field that's not stored into inside a loop is
// invariant throughout the loop. Nothing to do.
DCHECK(ref_info->IsSingletonAndRemovable());
} else {
// heap value is killed by loop side effects (stored into directly, or
// due to aliasing). Or the heap value may be needed after method return
// or deoptimization.
KeepIfIsStore(pre_header_heap_values[i]);
heap_values[i] = kUnknownHeapValue;
}
}
}
}
void MergePredecessorValues(HBasicBlock* block) {
const ArenaVector<HBasicBlock*>& predecessors = block->GetPredecessors();
if (predecessors.size() == 0) {
return;
}
ArenaVector<HInstruction*>& heap_values = heap_values_for_[block->GetBlockId()];
for (size_t i = 0; i < heap_values.size(); i++) {
HInstruction* merged_value = nullptr;
// Whether merged_value is a result that's merged from all predecessors.
bool from_all_predecessors = true;
ReferenceInfo* ref_info = heap_location_collector_.GetHeapLocation(i)->GetReferenceInfo();
HInstruction* singleton_ref = nullptr;
if (ref_info->IsSingleton()) {
// We do more analysis of liveness when merging heap values for such
// cases since stores into such references may potentially be eliminated.
singleton_ref = ref_info->GetReference();
}
for (HBasicBlock* predecessor : predecessors) {
HInstruction* pred_value = heap_values_for_[predecessor->GetBlockId()][i];
if ((singleton_ref != nullptr) &&
!singleton_ref->GetBlock()->Dominates(predecessor)) {
// singleton_ref is not live in this predecessor. Skip this predecessor since
// it does not really have the location.
DCHECK_EQ(pred_value, kUnknownHeapValue);
from_all_predecessors = false;
continue;
}
if (merged_value == nullptr) {
// First seen heap value.
merged_value = pred_value;
} else if (pred_value != merged_value) {
// There are conflicting values.
merged_value = kUnknownHeapValue;
break;
}
}
if (merged_value == kUnknownHeapValue || ref_info->IsSingletonAndNonRemovable()) {
// There are conflicting heap values from different predecessors,
// or the heap value may be needed after method return or deoptimization.
// Keep the last store in each predecessor since future loads cannot be eliminated.
for (HBasicBlock* predecessor : predecessors) {
ArenaVector<HInstruction*>& pred_values = heap_values_for_[predecessor->GetBlockId()];
KeepIfIsStore(pred_values[i]);
}
}
if ((merged_value == nullptr) || !from_all_predecessors) {
DCHECK(singleton_ref != nullptr);
DCHECK((singleton_ref->GetBlock() == block) ||
!singleton_ref->GetBlock()->Dominates(block));
// singleton_ref is not defined before block or defined only in some of its
// predecessors, so block doesn't really have the location at its entry.
heap_values[i] = kUnknownHeapValue;
} else {
heap_values[i] = merged_value;
}
}
}
// `instruction` is being removed. Try to see if the null check on it
// can be removed. This can happen if the same value is set in two branches
// but not in dominators. Such as:
// int[] a = foo();
// if () {
// a[0] = 2;
// } else {
// a[0] = 2;
// }
// // a[0] can now be replaced with constant 2, and the null check on it can be removed.
void TryRemovingNullCheck(HInstruction* instruction) {
HInstruction* prev = instruction->GetPrevious();
if ((prev != nullptr) && prev->IsNullCheck() && (prev == instruction->InputAt(0))) {
// Previous instruction is a null check for this instruction. Remove the null check.
prev->ReplaceWith(prev->InputAt(0));
prev->GetBlock()->RemoveInstruction(prev);
}
}
HInstruction* GetDefaultValue(Primitive::Type type) {
switch (type) {
case Primitive::kPrimNot:
return GetGraph()->GetNullConstant();
case Primitive::kPrimBoolean:
case Primitive::kPrimByte:
case Primitive::kPrimChar:
case Primitive::kPrimShort:
case Primitive::kPrimInt:
return GetGraph()->GetIntConstant(0);
case Primitive::kPrimLong:
return GetGraph()->GetLongConstant(0);
case Primitive::kPrimFloat:
return GetGraph()->GetFloatConstant(0);
case Primitive::kPrimDouble:
return GetGraph()->GetDoubleConstant(0);
default:
UNREACHABLE();
}
}
void VisitGetLocation(HInstruction* instruction,
HInstruction* ref,
size_t offset,
HInstruction* index,
int16_t declaring_class_def_index) {
HInstruction* original_ref = HuntForOriginalReference(ref);
ReferenceInfo* ref_info = heap_location_collector_.FindReferenceInfoOf(original_ref);
size_t idx = heap_location_collector_.FindHeapLocationIndex(
ref_info, offset, index, declaring_class_def_index);
DCHECK_NE(idx, HeapLocationCollector::kHeapLocationNotFound);
ArenaVector<HInstruction*>& heap_values =
heap_values_for_[instruction->GetBlock()->GetBlockId()];
HInstruction* heap_value = heap_values[idx];
if (heap_value == kDefaultHeapValue) {
HInstruction* constant = GetDefaultValue(instruction->GetType());
removed_loads_.push_back(instruction);
substitute_instructions_for_loads_.push_back(constant);
heap_values[idx] = constant;
return;
}
if (heap_value != kUnknownHeapValue) {
if (heap_value->IsInstanceFieldSet() || heap_value->IsArraySet()) {
HInstruction* store = heap_value;
// This load must be from a singleton since it's from the same
// field/element that a "removed" store puts the value. That store
// must be to a singleton's field/element.
DCHECK(ref_info->IsSingleton());
// Get the real heap value of the store.
heap_value = heap_value->IsInstanceFieldSet() ? store->InputAt(1) : store->InputAt(2);
}
}
if (heap_value == kUnknownHeapValue) {
// Load isn't eliminated. Put the load as the value into the HeapLocation.
// This acts like GVN but with better aliasing analysis.
heap_values[idx] = instruction;
} else {
if (Primitive::PrimitiveKind(heap_value->GetType())
!= Primitive::PrimitiveKind(instruction->GetType())) {
// The only situation where the same heap location has different type is when
// we do an array get on an instruction that originates from the null constant
// (the null could be behind a field access, an array access, a null check or
// a bound type).
// In order to stay properly typed on primitive types, we do not eliminate
// the array gets.
if (kIsDebugBuild) {
DCHECK(heap_value->IsArrayGet()) << heap_value->DebugName();
DCHECK(instruction->IsArrayGet()) << instruction->DebugName();
}
return;
}
removed_loads_.push_back(instruction);
substitute_instructions_for_loads_.push_back(heap_value);
TryRemovingNullCheck(instruction);
}
}
bool Equal(HInstruction* heap_value, HInstruction* value) {
if (heap_value == value) {
return true;
}
if (heap_value == kDefaultHeapValue && GetDefaultValue(value->GetType()) == value) {
return true;
}
return false;
}
void VisitSetLocation(HInstruction* instruction,
HInstruction* ref,
size_t offset,
HInstruction* index,
int16_t declaring_class_def_index,
HInstruction* value) {
HInstruction* original_ref = HuntForOriginalReference(ref);
ReferenceInfo* ref_info = heap_location_collector_.FindReferenceInfoOf(original_ref);
size_t idx = heap_location_collector_.FindHeapLocationIndex(
ref_info, offset, index, declaring_class_def_index);
DCHECK_NE(idx, HeapLocationCollector::kHeapLocationNotFound);
ArenaVector<HInstruction*>& heap_values =
heap_values_for_[instruction->GetBlock()->GetBlockId()];
HInstruction* heap_value = heap_values[idx];
bool same_value = false;
bool possibly_redundant = false;
if (Equal(heap_value, value)) {
// Store into the heap location with the same value.
same_value = true;
} else if (index != nullptr && ref_info->HasIndexAliasing()) {
// For array element, don't eliminate stores if the index can be aliased.
} else if (ref_info->IsSingleton()) {
// Store into a field of a singleton. The value cannot be killed due to
// aliasing/invocation. It can be redundant since future loads can
// directly get the value set by this instruction. The value can still be killed due to
// merging or loop side effects. Stores whose values are killed due to merging/loop side
// effects later will be removed from possibly_removed_stores_ when that is detected.
// Stores whose values may be needed after method return or deoptimization
// are also removed from possibly_removed_stores_ when that is detected.
possibly_redundant = true;
HNewInstance* new_instance = ref_info->GetReference()->AsNewInstance();
if (new_instance != nullptr && new_instance->IsFinalizable()) {
// Finalizable objects escape globally. Need to keep the store.
possibly_redundant = false;
} else {
HLoopInformation* loop_info = instruction->GetBlock()->GetLoopInformation();
if (loop_info != nullptr) {
// instruction is a store in the loop so the loop must does write.
DCHECK(side_effects_.GetLoopEffects(loop_info->GetHeader()).DoesAnyWrite());
if (loop_info->IsDefinedOutOfTheLoop(original_ref)) {
DCHECK(original_ref->GetBlock()->Dominates(loop_info->GetPreHeader()));
// Keep the store since its value may be needed at the loop header.
possibly_redundant = false;
} else {
// The singleton is created inside the loop. Value stored to it isn't needed at
// the loop header. This is true for outer loops also.
}
}
}
}
if (same_value || possibly_redundant) {
possibly_removed_stores_.push_back(instruction);
}
if (!same_value) {
if (possibly_redundant) {
DCHECK(instruction->IsInstanceFieldSet() || instruction->IsArraySet());
// Put the store as the heap value. If the value is loaded from heap
// by a load later, this store isn't really redundant.
heap_values[idx] = instruction;
} else {
heap_values[idx] = value;
}
}
// This store may kill values in other heap locations due to aliasing.
for (size_t i = 0; i < heap_values.size(); i++) {
if (i == idx) {
continue;
}
if (heap_values[i] == value) {
// Same value should be kept even if aliasing happens.
continue;
}
if (heap_values[i] == kUnknownHeapValue) {
// Value is already unknown, no need for aliasing check.
continue;
}
if (heap_location_collector_.MayAlias(i, idx)) {
// Kill heap locations that may alias.
heap_values[i] = kUnknownHeapValue;
}
}
}
void VisitInstanceFieldGet(HInstanceFieldGet* instruction) OVERRIDE {
HInstruction* obj = instruction->InputAt(0);
size_t offset = instruction->GetFieldInfo().GetFieldOffset().SizeValue();
int16_t declaring_class_def_index = instruction->GetFieldInfo().GetDeclaringClassDefIndex();
VisitGetLocation(instruction, obj, offset, nullptr, declaring_class_def_index);
}
void VisitInstanceFieldSet(HInstanceFieldSet* instruction) OVERRIDE {
HInstruction* obj = instruction->InputAt(0);
size_t offset = instruction->GetFieldInfo().GetFieldOffset().SizeValue();
int16_t declaring_class_def_index = instruction->GetFieldInfo().GetDeclaringClassDefIndex();
HInstruction* value = instruction->InputAt(1);
VisitSetLocation(instruction, obj, offset, nullptr, declaring_class_def_index, value);
}
void VisitStaticFieldGet(HStaticFieldGet* instruction) OVERRIDE {
HInstruction* cls = instruction->InputAt(0);
size_t offset = instruction->GetFieldInfo().GetFieldOffset().SizeValue();
int16_t declaring_class_def_index = instruction->GetFieldInfo().GetDeclaringClassDefIndex();
VisitGetLocation(instruction, cls, offset, nullptr, declaring_class_def_index);
}
void VisitStaticFieldSet(HStaticFieldSet* instruction) OVERRIDE {
HInstruction* cls = instruction->InputAt(0);
size_t offset = instruction->GetFieldInfo().GetFieldOffset().SizeValue();
int16_t declaring_class_def_index = instruction->GetFieldInfo().GetDeclaringClassDefIndex();
HInstruction* value = instruction->InputAt(1);
VisitSetLocation(instruction, cls, offset, nullptr, declaring_class_def_index, value);
}
void VisitArrayGet(HArrayGet* instruction) OVERRIDE {
HInstruction* array = instruction->InputAt(0);
HInstruction* index = instruction->InputAt(1);
VisitGetLocation(instruction,
array,
HeapLocation::kInvalidFieldOffset,
index,
HeapLocation::kDeclaringClassDefIndexForArrays);
}
void VisitArraySet(HArraySet* instruction) OVERRIDE {
HInstruction* array = instruction->InputAt(0);
HInstruction* index = instruction->InputAt(1);
HInstruction* value = instruction->InputAt(2);
VisitSetLocation(instruction,
array,
HeapLocation::kInvalidFieldOffset,
index,
HeapLocation::kDeclaringClassDefIndexForArrays,
value);
}
void VisitDeoptimize(HDeoptimize* instruction) {
const ArenaVector<HInstruction*>& heap_values =
heap_values_for_[instruction->GetBlock()->GetBlockId()];
for (HInstruction* heap_value : heap_values) {
// Filter out fake instructions before checking instruction kind below.
if (heap_value == kUnknownHeapValue || heap_value == kDefaultHeapValue) {
continue;
}
// A store is kept as the heap value for possibly removed stores.
if (heap_value->IsInstanceFieldSet() || heap_value->IsArraySet()) {
// Check whether the reference for a store is used by an environment local of
// HDeoptimize.
HInstruction* reference = heap_value->InputAt(0);
DCHECK(heap_location_collector_.FindReferenceInfoOf(reference)->IsSingleton());
for (const HUseListNode<HEnvironment*>& use : reference->GetEnvUses()) {
HEnvironment* user = use.GetUser();
if (user->GetHolder() == instruction) {
// The singleton for the store is visible at this deoptimization
// point. Need to keep the store so that the heap value is
// seen by the interpreter.
KeepIfIsStore(heap_value);
}
}
}
}
}
void HandleInvoke(HInstruction* invoke) {
ArenaVector<HInstruction*>& heap_values =
heap_values_for_[invoke->GetBlock()->GetBlockId()];
for (size_t i = 0; i < heap_values.size(); i++) {
ReferenceInfo* ref_info = heap_location_collector_.GetHeapLocation(i)->GetReferenceInfo();
if (ref_info->IsSingleton()) {
// Singleton references cannot be seen by the callee.
} else {
heap_values[i] = kUnknownHeapValue;
}
}
}
void VisitInvokeStaticOrDirect(HInvokeStaticOrDirect* invoke) OVERRIDE {
HandleInvoke(invoke);
}
void VisitInvokeVirtual(HInvokeVirtual* invoke) OVERRIDE {
HandleInvoke(invoke);
}
void VisitInvokeInterface(HInvokeInterface* invoke) OVERRIDE {
HandleInvoke(invoke);
}
void VisitInvokeUnresolved(HInvokeUnresolved* invoke) OVERRIDE {
HandleInvoke(invoke);
}
void VisitInvokePolymorphic(HInvokePolymorphic* invoke) OVERRIDE {
HandleInvoke(invoke);
}
void VisitClinitCheck(HClinitCheck* clinit) OVERRIDE {
HandleInvoke(clinit);
}
void VisitUnresolvedInstanceFieldGet(HUnresolvedInstanceFieldGet* instruction) OVERRIDE {
// Conservatively treat it as an invocation.
HandleInvoke(instruction);
}
void VisitUnresolvedInstanceFieldSet(HUnresolvedInstanceFieldSet* instruction) OVERRIDE {
// Conservatively treat it as an invocation.
HandleInvoke(instruction);
}
void VisitUnresolvedStaticFieldGet(HUnresolvedStaticFieldGet* instruction) OVERRIDE {
// Conservatively treat it as an invocation.
HandleInvoke(instruction);
}
void VisitUnresolvedStaticFieldSet(HUnresolvedStaticFieldSet* instruction) OVERRIDE {
// Conservatively treat it as an invocation.
HandleInvoke(instruction);
}
void VisitNewInstance(HNewInstance* new_instance) OVERRIDE {
ReferenceInfo* ref_info = heap_location_collector_.FindReferenceInfoOf(new_instance);
if (ref_info == nullptr) {
// new_instance isn't used for field accesses. No need to process it.
return;
}
if (ref_info->IsSingletonAndRemovable() &&
!new_instance->IsFinalizable() &&
!new_instance->NeedsChecks()) {
singleton_new_instances_.push_back(new_instance);
}
ArenaVector<HInstruction*>& heap_values =
heap_values_for_[new_instance->GetBlock()->GetBlockId()];
for (size_t i = 0; i < heap_values.size(); i++) {
HInstruction* ref =
heap_location_collector_.GetHeapLocation(i)->GetReferenceInfo()->GetReference();
size_t offset = heap_location_collector_.GetHeapLocation(i)->GetOffset();
if (ref == new_instance && offset >= mirror::kObjectHeaderSize) {
// Instance fields except the header fields are set to default heap values.
heap_values[i] = kDefaultHeapValue;
}
}
}
void VisitNewArray(HNewArray* new_array) OVERRIDE {
ReferenceInfo* ref_info = heap_location_collector_.FindReferenceInfoOf(new_array);
if (ref_info == nullptr) {
// new_array isn't used for array accesses. No need to process it.
return;
}
if (ref_info->IsSingletonAndRemovable()) {
singleton_new_arrays_.push_back(new_array);
}
ArenaVector<HInstruction*>& heap_values =
heap_values_for_[new_array->GetBlock()->GetBlockId()];
for (size_t i = 0; i < heap_values.size(); i++) {
HeapLocation* location = heap_location_collector_.GetHeapLocation(i);
HInstruction* ref = location->GetReferenceInfo()->GetReference();
if (ref == new_array && location->GetIndex() != nullptr) {
// Array elements are set to default heap values.
heap_values[i] = kDefaultHeapValue;
}
}
}
// Find an instruction's substitute if it should be removed.
// Return the same instruction if it should not be removed.
HInstruction* FindSubstitute(HInstruction* instruction) {
size_t size = removed_loads_.size();
for (size_t i = 0; i < size; i++) {
if (removed_loads_[i] == instruction) {
return substitute_instructions_for_loads_[i];
}
}
return instruction;
}
const HeapLocationCollector& heap_location_collector_;
const SideEffectsAnalysis& side_effects_;
// One array of heap values for each block.
ArenaVector<ArenaVector<HInstruction*>> heap_values_for_;
// We record the instructions that should be eliminated but may be
// used by heap locations. They'll be removed in the end.
ArenaVector<HInstruction*> removed_loads_;
ArenaVector<HInstruction*> substitute_instructions_for_loads_;
// Stores in this list may be removed from the list later when it's
// found that the store cannot be eliminated.
ArenaVector<HInstruction*> possibly_removed_stores_;
ArenaVector<HInstruction*> singleton_new_instances_;
ArenaVector<HInstruction*> singleton_new_arrays_;
DISALLOW_COPY_AND_ASSIGN(LSEVisitor);
};
void LoadStoreElimination::Run() {
if (graph_->IsDebuggable() || graph_->HasTryCatch()) {
// Debugger may set heap values or trigger deoptimization of callers.
// Try/catch support not implemented yet.
// Skip this optimization.
return;
}
HeapLocationCollector heap_location_collector(graph_);
for (HBasicBlock* block : graph_->GetReversePostOrder()) {
heap_location_collector.VisitBasicBlock(block);
}
if (heap_location_collector.GetNumberOfHeapLocations() > kMaxNumberOfHeapLocations) {
// Bail out if there are too many heap locations to deal with.
return;
}
if (!heap_location_collector.HasHeapStores()) {
// Without heap stores, this pass would act mostly as GVN on heap accesses.
return;
}
if (heap_location_collector.HasVolatile() || heap_location_collector.HasMonitorOps()) {
// Don't do load/store elimination if the method has volatile field accesses or
// monitor operations, for now.
// TODO: do it right.
return;
}
heap_location_collector.BuildAliasingMatrix();
LSEVisitor lse_visitor(graph_, heap_location_collector, side_effects_);
for (HBasicBlock* block : graph_->GetReversePostOrder()) {
lse_visitor.VisitBasicBlock(block);
}
lse_visitor.RemoveInstructions();
}
} // namespace art