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Diffstat (limited to 'compiler/optimizing/bounds_check_elimination.cc')
| -rw-r--r-- | compiler/optimizing/bounds_check_elimination.cc | 691 |
1 files changed, 691 insertions, 0 deletions
diff --git a/compiler/optimizing/bounds_check_elimination.cc b/compiler/optimizing/bounds_check_elimination.cc new file mode 100644 index 0000000000..91455bc7c4 --- /dev/null +++ b/compiler/optimizing/bounds_check_elimination.cc @@ -0,0 +1,691 @@ +/* + * Copyright (C) 2014 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 "bounds_check_elimination.h" +#include "nodes.h" +#include "utils/arena_containers.h" + +namespace art { + +class MonotonicValueRange; + +/** + * A value bound is represented as a pair of value and constant, + * e.g. array.length - 1. + */ +class ValueBound : public ValueObject { + public: + static ValueBound Create(HInstruction* instruction, int constant) { + if (instruction == nullptr) { + return ValueBound(nullptr, constant); + } + if (instruction->IsIntConstant()) { + return ValueBound(nullptr, instruction->AsIntConstant()->GetValue() + constant); + } + return ValueBound(instruction, constant); + } + + HInstruction* GetInstruction() const { return instruction_; } + int GetConstant() const { return constant_; } + + bool IsRelativeToArrayLength() const { + return instruction_ != nullptr && instruction_->IsArrayLength(); + } + + bool IsConstant() const { + return instruction_ == nullptr; + } + + static ValueBound Min() { return ValueBound(nullptr, INT_MIN); } + static ValueBound Max() { return ValueBound(nullptr, INT_MAX); } + + bool Equals(ValueBound bound) const { + return instruction_ == bound.instruction_ && constant_ == bound.constant_; + } + + // Returns if it's certain bound1 >= bound2. + bool GreaterThanOrEqual(ValueBound bound) const { + if (instruction_ == bound.instruction_) { + if (instruction_ == nullptr) { + // Pure constant. + return constant_ >= bound.constant_; + } + // There might be overflow/underflow. Be conservative for now. + return false; + } + // Not comparable. Just return false. + return false; + } + + // Returns if it's certain bound1 <= bound2. + bool LessThanOrEqual(ValueBound bound) const { + if (instruction_ == bound.instruction_) { + if (instruction_ == nullptr) { + // Pure constant. + return constant_ <= bound.constant_; + } + if (IsRelativeToArrayLength()) { + // Array length is guaranteed to be no less than 0. + // No overflow/underflow can happen if both constants are negative. + if (constant_ <= 0 && bound.constant_ <= 0) { + return constant_ <= bound.constant_; + } + // There might be overflow/underflow. Be conservative for now. + return false; + } + } + + // In case the array length is some constant, we can + // still compare. + if (IsConstant() && bound.IsRelativeToArrayLength()) { + HInstruction* array = bound.GetInstruction()->AsArrayLength()->InputAt(0); + if (array->IsNullCheck()) { + array = array->AsNullCheck()->InputAt(0); + } + if (array->IsNewArray()) { + HInstruction* len = array->InputAt(0); + if (len->IsIntConstant()) { + int len_const = len->AsIntConstant()->GetValue(); + return constant_ <= len_const + bound.GetConstant(); + } + } + } + + // Not comparable. Just return false. + return false; + } + + // Try to narrow lower bound. Returns the greatest of the two if possible. + // Pick one if they are not comparable. + static ValueBound NarrowLowerBound(ValueBound bound1, ValueBound bound2) { + if (bound1.instruction_ == bound2.instruction_) { + // Same instruction, compare the constant part. + return ValueBound(bound1.instruction_, + std::max(bound1.constant_, bound2.constant_)); + } + + // Not comparable. Just pick one. We may lose some info, but that's ok. + // Favor constant as lower bound. + return bound1.IsConstant() ? bound1 : bound2; + } + + // Try to narrow upper bound. Returns the lowest of the two if possible. + // Pick one if they are not comparable. + static ValueBound NarrowUpperBound(ValueBound bound1, ValueBound bound2) { + if (bound1.instruction_ == bound2.instruction_) { + // Same instruction, compare the constant part. + return ValueBound(bound1.instruction_, + std::min(bound1.constant_, bound2.constant_)); + } + + // Not comparable. Just pick one. We may lose some info, but that's ok. + // Favor array length as upper bound. + return bound1.IsRelativeToArrayLength() ? bound1 : bound2; + } + + // Add a constant to a ValueBound. If the constant part of the ValueBound + // overflows/underflows, then we can't accurately represent it. For correctness, + // just return Max/Min() depending on whether the returned ValueBound is used for + // lower/upper bound. + ValueBound Add(int c, bool for_lower_bound, bool* overflow_or_underflow) const { + *overflow_or_underflow = false; + if (c == 0) { + return *this; + } + + int new_constant; + if (c > 0) { + if (constant_ > INT_MAX - c) { + // Constant part overflows. + *overflow_or_underflow = true; + return for_lower_bound ? Min() : Max(); + } else { + new_constant = constant_ + c; + } + } else { + if (constant_ < INT_MIN - c) { + // Constant part underflows. + *overflow_or_underflow = true; + return for_lower_bound ? Min() : Max(); + } else { + new_constant = constant_ + c; + } + } + return ValueBound(instruction_, new_constant); + } + + private: + ValueBound(HInstruction* instruction, int constant) + : instruction_(instruction), constant_(constant) {} + + HInstruction* instruction_; + int constant_; +}; + +/** + * Represent a range of lower bound and upper bound, both being inclusive. + * Currently a ValueRange may be generated as a result of the following: + * comparisons related to array bounds, array bounds check, add/sub on top + * of an existing value range, or a loop phi corresponding to an + * incrementing/decrementing array index (MonotonicValueRange). + */ +class ValueRange : public ArenaObject<kArenaAllocMisc> { + public: + ValueRange(ArenaAllocator* allocator, ValueBound lower, ValueBound upper) + : allocator_(allocator), lower_(lower), upper_(upper) {} + + virtual ~ValueRange() {} + + virtual const MonotonicValueRange* AsMonotonicValueRange() const { return nullptr; } + bool IsMonotonicValueRange() const { + return AsMonotonicValueRange() != nullptr; + } + + ArenaAllocator* GetAllocator() const { return allocator_; } + ValueBound GetLower() const { return lower_; } + ValueBound GetUpper() const { return upper_; } + + // If it's certain that this value range fits in other_range. + virtual bool FitsIn(ValueRange* other_range) const { + if (other_range == nullptr) { + return true; + } + DCHECK(!other_range->IsMonotonicValueRange()); + return lower_.GreaterThanOrEqual(other_range->lower_) && + upper_.LessThanOrEqual(other_range->upper_); + } + + // Returns the intersection of this and range. + // If it's not possible to do intersection because some + // bounds are not comparable, it's ok to pick either bound. + virtual ValueRange* Narrow(ValueRange* range) { + if (range == nullptr) { + return this; + } + + if (range->IsMonotonicValueRange()) { + return this; + } + + return new (allocator_) ValueRange( + allocator_, + ValueBound::NarrowLowerBound(lower_, range->lower_), + ValueBound::NarrowUpperBound(upper_, range->upper_)); + } + + // Shift a range by a constant. If either bound can't be represented + // as (instruction+c) format due to possible overflow/underflow, + // return the full integer range. + ValueRange* Add(int constant) const { + bool overflow_or_underflow; + ValueBound lower = lower_.Add(constant, true, &overflow_or_underflow); + if (overflow_or_underflow) { + // We can't accurately represent the bounds anymore. + return FullIntRange(); + } + ValueBound upper = upper_.Add(constant, false, &overflow_or_underflow); + if (overflow_or_underflow) { + // We can't accurately represent the bounds anymore. + return FullIntRange(); + } + return new (allocator_) ValueRange(allocator_, lower, upper); + } + + // Return [INT_MIN, INT_MAX]. + ValueRange* FullIntRange() const { + return new (allocator_) ValueRange(allocator_, ValueBound::Min(), ValueBound::Max()); + } + + private: + ArenaAllocator* const allocator_; + const ValueBound lower_; // inclusive + const ValueBound upper_; // inclusive + + DISALLOW_COPY_AND_ASSIGN(ValueRange); +}; + +/** + * A monotonically incrementing/decrementing value range, e.g. + * the variable i in "for (int i=0; i<array.length; i++)". + * Special care needs to be taken to account for overflow/underflow + * of such value ranges. + */ +class MonotonicValueRange : public ValueRange { + public: + static MonotonicValueRange* Create(ArenaAllocator* allocator, + HInstruction* initial, int increment) { + DCHECK_NE(increment, 0); + // To be conservative, give it full range [INT_MIN, INT_MAX] in case it's + // used as a regular value range, due to possible overflow/underflow. + return new (allocator) MonotonicValueRange( + allocator, ValueBound::Min(), ValueBound::Max(), initial, increment); + } + + virtual ~MonotonicValueRange() {} + + const MonotonicValueRange* AsMonotonicValueRange() const OVERRIDE { return this; } + + // If it's certain that this value range fits in other_range. + bool FitsIn(ValueRange* other_range) const OVERRIDE { + if (other_range == nullptr) { + return true; + } + DCHECK(!other_range->IsMonotonicValueRange()); + return false; + } + + // Try to narrow this MonotonicValueRange given another range. + // Ideally it will return a normal ValueRange. But due to + // possible overflow/underflow, that may not be possible. + ValueRange* Narrow(ValueRange* range) OVERRIDE { + if (range == nullptr) { + return this; + } + DCHECK(!range->IsMonotonicValueRange()); + + if (increment_ > 0) { + // Monotonically increasing. + ValueBound lower = ValueBound::NarrowLowerBound( + ValueBound::Create(initial_, 0), range->GetLower()); + + // We currently conservatively assume max array length is INT_MAX. If we can + // make assumptions about the max array length, e.g. due to the max heap size, + // divided by the element size (such as 4 bytes for each integer array), we can + // lower this number and rule out some possible overflows. + int max_array_len = INT_MAX; + + int upper = INT_MAX; + if (range->GetUpper().IsConstant()) { + upper = range->GetUpper().GetConstant(); + } else if (range->GetUpper().IsRelativeToArrayLength()) { + int constant = range->GetUpper().GetConstant(); + if (constant <= 0) { + // Normal case. e.g. <= array.length - 1, <= array.length - 2, etc. + upper = max_array_len + constant; + } else { + // There might be overflow. Give up narrowing. + return this; + } + } else { + // There might be overflow. Give up narrowing. + return this; + } + + // If we can prove for the last number in sequence of initial_, + // initial_ + increment_, initial_ + 2 x increment_, ... + // that's <= upper, (last_num_in_sequence + increment_) doesn't trigger overflow, + // then this MonoticValueRange is narrowed to a normal value range. + + // Be conservative first, assume last number in the sequence hits upper. + int last_num_in_sequence = upper; + if (initial_->IsIntConstant()) { + int initial_constant = initial_->AsIntConstant()->GetValue(); + if (upper <= initial_constant) { + last_num_in_sequence = upper; + } else { + // Cast to int64_t for the substraction part to avoid int overflow. + last_num_in_sequence = initial_constant + + ((int64_t)upper - (int64_t)initial_constant) / increment_ * increment_; + } + } + if (last_num_in_sequence <= INT_MAX - increment_) { + // No overflow. The sequence will be stopped by the upper bound test as expected. + return new (GetAllocator()) ValueRange(GetAllocator(), lower, range->GetUpper()); + } + + // There might be overflow. Give up narrowing. + return this; + } else { + DCHECK_NE(increment_, 0); + // Monotonically decreasing. + ValueBound upper = ValueBound::NarrowUpperBound( + ValueBound::Create(initial_, 0), range->GetUpper()); + + // Need to take care of underflow. Try to prove underflow won't happen + // for common cases. Basically need to be able to prove for any value + // that's >= range->GetLower(), it won't be positive with value+increment. + if (range->GetLower().IsConstant()) { + int constant = range->GetLower().GetConstant(); + if (constant >= INT_MIN - increment_) { + return new (GetAllocator()) ValueRange(GetAllocator(), range->GetLower(), upper); + } + } + + // There might be underflow. Give up narrowing. + return this; + } + } + + private: + MonotonicValueRange(ArenaAllocator* allocator, ValueBound lower, + ValueBound upper, HInstruction* initial, int increment) + : ValueRange(allocator, lower, upper), + initial_(initial), + increment_(increment) {} + + HInstruction* const initial_; + const int increment_; + + DISALLOW_COPY_AND_ASSIGN(MonotonicValueRange); +}; + +class BCEVisitor : public HGraphVisitor { + public: + BCEVisitor(HGraph* graph) + : HGraphVisitor(graph), + maps_(graph->GetBlocks().Size()) {} + + private: + // Return the map of proven value ranges at the beginning of a basic block. + ArenaSafeMap<int, ValueRange*>* GetValueRangeMap(HBasicBlock* basic_block) { + int block_id = basic_block->GetBlockId(); + if (maps_.at(block_id) == nullptr) { + std::unique_ptr<ArenaSafeMap<int, ValueRange*>> map( + new ArenaSafeMap<int, ValueRange*>( + std::less<int>(), GetGraph()->GetArena()->Adapter())); + maps_.at(block_id) = std::move(map); + } + return maps_.at(block_id).get(); + } + + // Traverse up the dominator tree to look for value range info. + ValueRange* LookupValueRange(HInstruction* instruction, HBasicBlock* basic_block) { + while (basic_block != nullptr) { + ArenaSafeMap<int, ValueRange*>* map = GetValueRangeMap(basic_block); + if (map->find(instruction->GetId()) != map->end()) { + return map->Get(instruction->GetId()); + } + basic_block = basic_block->GetDominator(); + } + // Didn't find any. + return nullptr; + } + + // Try to detect useful value bound format from an instruction, e.g. + // a constant or array length related value. + ValueBound DetectValueBoundFromValue(HInstruction* instruction) { + if (instruction->IsIntConstant()) { + return ValueBound::Create(nullptr, instruction->AsIntConstant()->GetValue()); + } + + if (instruction->IsArrayLength()) { + return ValueBound::Create(instruction, 0); + } + // Try to detect (array.length + c) format. + if (instruction->IsAdd()) { + HAdd* add = instruction->AsAdd(); + HInstruction* left = add->GetLeft(); + HInstruction* right = add->GetRight(); + if (left->IsArrayLength() && right->IsIntConstant()) { + return ValueBound::Create(left, right->AsIntConstant()->GetValue()); + } + } + + // No useful bound detected. + return ValueBound::Max(); + } + + // Narrow the value range of 'instruction' at the end of 'basic_block' with 'range', + // and push the narrowed value range to 'successor'. + void ApplyRangeFromComparison(HInstruction* instruction, HBasicBlock* basic_block, + HBasicBlock* successor, ValueRange* range) { + ValueRange* existing_range = LookupValueRange(instruction, basic_block); + ValueRange* narrowed_range = (existing_range == nullptr) ? + range : existing_range->Narrow(range); + if (narrowed_range != nullptr) { + GetValueRangeMap(successor)->Overwrite(instruction->GetId(), narrowed_range); + } + } + + // Handle "if (left cmp_cond right)". + void HandleIf(HIf* instruction, HInstruction* left, HInstruction* right, IfCondition cond) { + HBasicBlock* block = instruction->GetBlock(); + + HBasicBlock* true_successor = instruction->IfTrueSuccessor(); + // There should be no critical edge at this point. + DCHECK_EQ(true_successor->GetPredecessors().Size(), 1u); + + HBasicBlock* false_successor = instruction->IfFalseSuccessor(); + // There should be no critical edge at this point. + DCHECK_EQ(false_successor->GetPredecessors().Size(), 1u); + + ValueBound bound = DetectValueBoundFromValue(right); + bool found = !bound.Equals(ValueBound::Max()); + + ValueBound lower = bound; + ValueBound upper = bound; + if (!found) { + // No constant or array.length+c bound found. + // For i<j, we can still use j's upper bound as i's upper bound. Same for lower. + ValueRange* range = LookupValueRange(right, block); + if (range != nullptr) { + lower = range->GetLower(); + upper = range->GetUpper(); + } else { + lower = ValueBound::Min(); + upper = ValueBound::Max(); + } + } + + bool overflow_or_underflow; + if (cond == kCondLT || cond == kCondLE) { + if (!upper.Equals(ValueBound::Max())) { + int compensation = (cond == kCondLT) ? -1 : 0; // upper bound is inclusive + ValueBound new_upper = upper.Add(compensation, false, &overflow_or_underflow); + // overflow_or_underflow is ignored here since we already use ValueBound::Min() + // for lower bound. + ValueRange* new_range = new (GetGraph()->GetArena()) + ValueRange(GetGraph()->GetArena(), ValueBound::Min(), new_upper); + ApplyRangeFromComparison(left, block, true_successor, new_range); + } + + // array.length as a lower bound isn't considered useful. + if (!lower.Equals(ValueBound::Min()) && !lower.IsRelativeToArrayLength()) { + int compensation = (cond == kCondLE) ? 1 : 0; // lower bound is inclusive + ValueBound new_lower = lower.Add(compensation, true, &overflow_or_underflow); + // overflow_or_underflow is ignored here since we already use ValueBound::Max() + // for upper bound. + ValueRange* new_range = new (GetGraph()->GetArena()) + ValueRange(GetGraph()->GetArena(), new_lower, ValueBound::Max()); + ApplyRangeFromComparison(left, block, false_successor, new_range); + } + } else if (cond == kCondGT || cond == kCondGE) { + // array.length as a lower bound isn't considered useful. + if (!lower.Equals(ValueBound::Min()) && !lower.IsRelativeToArrayLength()) { + int compensation = (cond == kCondGT) ? 1 : 0; // lower bound is inclusive + ValueBound new_lower = lower.Add(compensation, true, &overflow_or_underflow); + // overflow_or_underflow is ignored here since we already use ValueBound::Max() + // for upper bound. + ValueRange* new_range = new (GetGraph()->GetArena()) + ValueRange(GetGraph()->GetArena(), new_lower, ValueBound::Max()); + ApplyRangeFromComparison(left, block, true_successor, new_range); + } + + if (!upper.Equals(ValueBound::Max())) { + int compensation = (cond == kCondGE) ? -1 : 0; // upper bound is inclusive + ValueBound new_upper = upper.Add(compensation, false, &overflow_or_underflow); + // overflow_or_underflow is ignored here since we already use ValueBound::Min() + // for lower bound. + ValueRange* new_range = new (GetGraph()->GetArena()) + ValueRange(GetGraph()->GetArena(), ValueBound::Min(), new_upper); + ApplyRangeFromComparison(left, block, false_successor, new_range); + } + } + } + + void VisitBoundsCheck(HBoundsCheck* bounds_check) { + HBasicBlock* block = bounds_check->GetBlock(); + HInstruction* index = bounds_check->InputAt(0); + HInstruction* array_length = bounds_check->InputAt(1); + ValueRange* index_range = LookupValueRange(index, block); + + if (index_range != nullptr) { + ValueBound lower = ValueBound::Create(nullptr, 0); // constant 0 + ValueBound upper = ValueBound::Create(array_length, -1); // array_length - 1 + ValueRange* array_range = new (GetGraph()->GetArena()) + ValueRange(GetGraph()->GetArena(), lower, upper); + if (index_range->FitsIn(array_range)) { + ReplaceBoundsCheck(bounds_check, index); + return; + } + } + + if (index->IsIntConstant()) { + ValueRange* array_length_range = LookupValueRange(array_length, block); + int constant = index->AsIntConstant()->GetValue(); + if (array_length_range != nullptr && + array_length_range->GetLower().IsConstant()) { + if (constant < array_length_range->GetLower().GetConstant()) { + ReplaceBoundsCheck(bounds_check, index); + return; + } + } + + // Once we have an array access like 'array[5] = 1', we record array.length >= 6. + ValueBound lower = ValueBound::Create(nullptr, constant + 1); + ValueBound upper = ValueBound::Max(); + ValueRange* range = new (GetGraph()->GetArena()) + ValueRange(GetGraph()->GetArena(), lower, upper); + ValueRange* existing_range = LookupValueRange(array_length, block); + ValueRange* new_range = range; + if (existing_range != nullptr) { + new_range = range->Narrow(existing_range); + } + GetValueRangeMap(block)->Overwrite(array_length->GetId(), new_range); + } + } + + void ReplaceBoundsCheck(HInstruction* bounds_check, HInstruction* index) { + bounds_check->ReplaceWith(index); + bounds_check->GetBlock()->RemoveInstruction(bounds_check); + } + + void VisitPhi(HPhi* phi) { + if (phi->IsLoopHeaderPhi() && phi->GetType() == Primitive::kPrimInt) { + DCHECK(phi->InputCount() == 2); + HInstruction* instruction = phi->InputAt(1); + if (instruction->IsAdd()) { + HAdd* add = instruction->AsAdd(); + HInstruction* left = add->GetLeft(); + HInstruction* right = add->GetRight(); + if (left == phi && right->IsIntConstant()) { + HInstruction* initial_value = phi->InputAt(0); + ValueRange* range = nullptr; + if (right->AsIntConstant()->GetValue() == 0) { + // Add constant 0. It's really a fixed value. + range = new (GetGraph()->GetArena()) ValueRange( + GetGraph()->GetArena(), + ValueBound::Create(initial_value, 0), + ValueBound::Create(initial_value, 0)); + } else { + // Monotonically increasing/decreasing. + range = MonotonicValueRange::Create( + GetGraph()->GetArena(), + initial_value, + right->AsIntConstant()->GetValue()); + } + GetValueRangeMap(phi->GetBlock())->Overwrite(phi->GetId(), range); + } + } + } + } + + void VisitIf(HIf* instruction) { + if (instruction->InputAt(0)->IsCondition()) { + HCondition* cond = instruction->InputAt(0)->AsCondition(); + IfCondition cmp = cond->GetCondition(); + if (cmp == kCondGT || cmp == kCondGE || + cmp == kCondLT || cmp == kCondLE) { + HInstruction* left = cond->GetLeft(); + HInstruction* right = cond->GetRight(); + HandleIf(instruction, left, right, cmp); + } + } + } + + void VisitAdd(HAdd* add) { + HInstruction* right = add->GetRight(); + if (right->IsIntConstant()) { + ValueRange* left_range = LookupValueRange(add->GetLeft(), add->GetBlock()); + if (left_range == nullptr) { + return; + } + ValueRange* range = left_range->Add(right->AsIntConstant()->GetValue()); + if (range != nullptr) { + GetValueRangeMap(add->GetBlock())->Overwrite(add->GetId(), range); + } + } + } + + void VisitSub(HSub* sub) { + HInstruction* left = sub->GetLeft(); + HInstruction* right = sub->GetRight(); + if (right->IsIntConstant()) { + ValueRange* left_range = LookupValueRange(left, sub->GetBlock()); + if (left_range == nullptr) { + return; + } + ValueRange* range = left_range->Add(-right->AsIntConstant()->GetValue()); + if (range != nullptr) { + GetValueRangeMap(sub->GetBlock())->Overwrite(sub->GetId(), range); + return; + } + } + + // Here we are interested in the typical triangular case of nested loops, + // such as the inner loop 'for (int j=0; j<array.length-i; j++)' where i + // is the index for outer loop. In this case, we know j is bounded by array.length-1. + if (left->IsArrayLength()) { + HInstruction* array_length = left->AsArrayLength(); + ValueRange* right_range = LookupValueRange(right, sub->GetBlock()); + if (right_range != nullptr) { + ValueBound lower = right_range->GetLower(); + ValueBound upper = right_range->GetUpper(); + if (lower.IsConstant() && upper.IsRelativeToArrayLength()) { + HInstruction* upper_inst = upper.GetInstruction(); + if (upper_inst->IsArrayLength() && + upper_inst->AsArrayLength() == array_length) { + // (array.length - v) where v is in [c1, array.length + c2] + // gets [-c2, array.length - c1] as its value range. + ValueRange* range = new (GetGraph()->GetArena()) ValueRange( + GetGraph()->GetArena(), + ValueBound::Create(nullptr, - upper.GetConstant()), + ValueBound::Create(array_length, - lower.GetConstant())); + GetValueRangeMap(sub->GetBlock())->Overwrite(sub->GetId(), range); + } + } + } + } + } + + std::vector<std::unique_ptr<ArenaSafeMap<int, ValueRange*>>> maps_; + + DISALLOW_COPY_AND_ASSIGN(BCEVisitor); +}; + +void BoundsCheckElimination::Run() { + BCEVisitor visitor(graph_); + // Reverse post order guarantees a node's dominators are visited first. + // We want to visit in the dominator-based order since if a value is known to + // be bounded by a range at one instruction, it must be true that all uses of + // that value dominated by that instruction fits in that range. Range of that + // value can be narrowed further down in the dominator tree. + // + // TODO: only visit blocks that dominate some array accesses. + visitor.VisitReversePostOrder(); +} + +} // namespace art |