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/*
* Copyright (C) 2022 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 "write_barrier_elimination.h"
#include "base/arena_allocator.h"
#include "base/scoped_arena_allocator.h"
#include "base/scoped_arena_containers.h"
#include "optimizing/nodes.h"
namespace art HIDDEN {
class WBEVisitor final : public HGraphVisitor {
public:
WBEVisitor(HGraph* graph, OptimizingCompilerStats* stats)
: HGraphVisitor(graph),
scoped_allocator_(graph->GetArenaStack()),
current_write_barriers_(scoped_allocator_.Adapter(kArenaAllocWBE)),
stats_(stats) {}
void VisitBasicBlock(HBasicBlock* block) override {
// We clear the map to perform this optimization only in the same block. Doing it across blocks
// would entail non-trivial merging of states.
current_write_barriers_.clear();
HGraphVisitor::VisitBasicBlock(block);
}
void VisitInstanceFieldSet(HInstanceFieldSet* instruction) override {
DCHECK(!instruction->GetSideEffects().Includes(SideEffects::CanTriggerGC()));
if (instruction->GetFieldType() != DataType::Type::kReference ||
instruction->GetValue()->IsNullConstant()) {
instruction->SetWriteBarrierKind(WriteBarrierKind::kDontEmit);
return;
}
MaybeRecordStat(stats_, MethodCompilationStat::kPossibleWriteBarrier);
HInstruction* obj = HuntForOriginalReference(instruction->InputAt(0));
auto it = current_write_barriers_.find(obj);
if (it != current_write_barriers_.end()) {
DCHECK(it->second->IsInstanceFieldSet());
DCHECK(it->second->AsInstanceFieldSet()->GetWriteBarrierKind() !=
WriteBarrierKind::kDontEmit);
DCHECK_EQ(it->second->GetBlock(), instruction->GetBlock());
it->second->AsInstanceFieldSet()->SetWriteBarrierKind(WriteBarrierKind::kEmitNoNullCheck);
instruction->SetWriteBarrierKind(WriteBarrierKind::kDontEmit);
MaybeRecordStat(stats_, MethodCompilationStat::kRemovedWriteBarrier);
} else {
const bool inserted = current_write_barriers_.insert({obj, instruction}).second;
DCHECK(inserted);
DCHECK(instruction->GetWriteBarrierKind() != WriteBarrierKind::kDontEmit);
}
}
void VisitStaticFieldSet(HStaticFieldSet* instruction) override {
DCHECK(!instruction->GetSideEffects().Includes(SideEffects::CanTriggerGC()));
if (instruction->GetFieldType() != DataType::Type::kReference ||
instruction->GetValue()->IsNullConstant()) {
instruction->SetWriteBarrierKind(WriteBarrierKind::kDontEmit);
return;
}
MaybeRecordStat(stats_, MethodCompilationStat::kPossibleWriteBarrier);
HInstruction* cls = HuntForOriginalReference(instruction->InputAt(0));
auto it = current_write_barriers_.find(cls);
if (it != current_write_barriers_.end()) {
DCHECK(it->second->IsStaticFieldSet());
DCHECK(it->second->AsStaticFieldSet()->GetWriteBarrierKind() != WriteBarrierKind::kDontEmit);
DCHECK_EQ(it->second->GetBlock(), instruction->GetBlock());
it->second->AsStaticFieldSet()->SetWriteBarrierKind(WriteBarrierKind::kEmitNoNullCheck);
instruction->SetWriteBarrierKind(WriteBarrierKind::kDontEmit);
MaybeRecordStat(stats_, MethodCompilationStat::kRemovedWriteBarrier);
} else {
const bool inserted = current_write_barriers_.insert({cls, instruction}).second;
DCHECK(inserted);
DCHECK(instruction->GetWriteBarrierKind() != WriteBarrierKind::kDontEmit);
}
}
void VisitArraySet(HArraySet* instruction) override {
if (instruction->GetSideEffects().Includes(SideEffects::CanTriggerGC())) {
ClearCurrentValues();
}
if (instruction->GetComponentType() != DataType::Type::kReference ||
instruction->GetValue()->IsNullConstant()) {
instruction->SetWriteBarrierKind(WriteBarrierKind::kDontEmit);
return;
}
HInstruction* arr = HuntForOriginalReference(instruction->InputAt(0));
MaybeRecordStat(stats_, MethodCompilationStat::kPossibleWriteBarrier);
auto it = current_write_barriers_.find(arr);
if (it != current_write_barriers_.end()) {
DCHECK(it->second->IsArraySet());
DCHECK(it->second->AsArraySet()->GetWriteBarrierKind() != WriteBarrierKind::kDontEmit);
DCHECK_EQ(it->second->GetBlock(), instruction->GetBlock());
// We never skip the null check in ArraySets so that value is already set.
DCHECK(it->second->AsArraySet()->GetWriteBarrierKind() == WriteBarrierKind::kEmitNoNullCheck);
instruction->SetWriteBarrierKind(WriteBarrierKind::kDontEmit);
MaybeRecordStat(stats_, MethodCompilationStat::kRemovedWriteBarrier);
} else {
const bool inserted = current_write_barriers_.insert({arr, instruction}).second;
DCHECK(inserted);
DCHECK(instruction->GetWriteBarrierKind() != WriteBarrierKind::kDontEmit);
}
}
void VisitInstruction(HInstruction* instruction) override {
if (instruction->GetSideEffects().Includes(SideEffects::CanTriggerGC())) {
ClearCurrentValues();
}
}
private:
void ClearCurrentValues() { current_write_barriers_.clear(); }
HInstruction* HuntForOriginalReference(HInstruction* ref) const {
// An original reference can be transformed by instructions like:
// i0 NewArray
// i1 HInstruction(i0) <-- NullCheck, BoundType, IntermediateAddress.
// i2 ArraySet(i1, index, value)
DCHECK(ref != nullptr);
while (ref->IsNullCheck() || ref->IsBoundType() || ref->IsIntermediateAddress()) {
ref = ref->InputAt(0);
}
return ref;
}
ScopedArenaAllocator scoped_allocator_;
// Stores a map of <Receiver, InstructionWhereTheWriteBarrierIs>.
// `InstructionWhereTheWriteBarrierIs` is used for DCHECKs only.
ScopedArenaHashMap<HInstruction*, HInstruction*> current_write_barriers_;
OptimizingCompilerStats* const stats_;
DISALLOW_COPY_AND_ASSIGN(WBEVisitor);
};
bool WriteBarrierElimination::Run() {
WBEVisitor wbe_visitor(graph_, stats_);
wbe_visitor.VisitReversePostOrder();
return true;
}
} // namespace art
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