/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "load_store_analysis.h"
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namespace art {
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// A cap for the number of heap locations to prevent pathological time/space consumption.
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// The number of heap locations for most of the methods stays below this threshold.
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constexpr size_t kMaxNumberOfHeapLocations = 32;
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// Test if two integer ranges [l1,h1] and [l2,h2] overlap.
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// Note that the ranges are inclusive on both ends.
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// l1|------|h1
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// l2|------|h2
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static bool CanIntegerRangesOverlap(int64_t l1, int64_t h1, int64_t l2, int64_t h2) {
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return std::max(l1, l2) <= std::min(h1, h2);
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}
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static bool IsAddOrSub(const HInstruction* instruction) {
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return instruction->IsAdd() || instruction->IsSub();
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}
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static bool CanBinaryOpAndIndexAlias(const HBinaryOperation* idx1,
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const size_t vector_length1,
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const HInstruction* idx2,
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const size_t vector_length2) {
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if (!IsAddOrSub(idx1)) {
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// We currently only support Add and Sub operations.
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return true;
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}
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if (idx1->AsBinaryOperation()->GetLeastConstantLeft() != idx2) {
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// Cannot analyze [i+CONST1] and [j].
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return true;
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}
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if (!idx1->GetConstantRight()->IsIntConstant()) {
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return true;
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}
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// Since 'i' are the same in [i+CONST] and [i],
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// further compare [CONST] and [0].
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int64_t l1 = idx1->IsAdd() ?
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idx1->GetConstantRight()->AsIntConstant()->GetValue() :
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-idx1->GetConstantRight()->AsIntConstant()->GetValue();
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int64_t l2 = 0;
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int64_t h1 = l1 + (vector_length1 - 1);
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int64_t h2 = l2 + (vector_length2 - 1);
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return CanIntegerRangesOverlap(l1, h1, l2, h2);
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}
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static bool CanBinaryOpsAlias(const HBinaryOperation* idx1,
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const size_t vector_length1,
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const HBinaryOperation* idx2,
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const size_t vector_length2) {
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if (!IsAddOrSub(idx1) || !IsAddOrSub(idx2)) {
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// We currently only support Add and Sub operations.
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return true;
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}
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if (idx1->AsBinaryOperation()->GetLeastConstantLeft() !=
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idx2->AsBinaryOperation()->GetLeastConstantLeft()) {
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// Cannot analyze [i+CONST1] and [j+CONST2].
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return true;
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}
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if (!idx1->GetConstantRight()->IsIntConstant() ||
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!idx2->GetConstantRight()->IsIntConstant()) {
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return true;
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}
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// Since 'i' are the same in [i+CONST1] and [i+CONST2],
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// further compare [CONST1] and [CONST2].
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int64_t l1 = idx1->IsAdd() ?
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idx1->GetConstantRight()->AsIntConstant()->GetValue() :
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-idx1->GetConstantRight()->AsIntConstant()->GetValue();
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int64_t l2 = idx2->IsAdd() ?
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idx2->GetConstantRight()->AsIntConstant()->GetValue() :
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-idx2->GetConstantRight()->AsIntConstant()->GetValue();
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int64_t h1 = l1 + (vector_length1 - 1);
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int64_t h2 = l2 + (vector_length2 - 1);
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return CanIntegerRangesOverlap(l1, h1, l2, h2);
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}
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bool HeapLocationCollector::CanArrayElementsAlias(const HInstruction* idx1,
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const size_t vector_length1,
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const HInstruction* idx2,
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const size_t vector_length2) const {
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DCHECK(idx1 != nullptr);
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DCHECK(idx2 != nullptr);
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DCHECK_GE(vector_length1, HeapLocation::kScalar);
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DCHECK_GE(vector_length2, HeapLocation::kScalar);
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// [i] and [i].
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if (idx1 == idx2) {
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return true;
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}
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// [CONST1] and [CONST2].
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if (idx1->IsIntConstant() && idx2->IsIntConstant()) {
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int64_t l1 = idx1->AsIntConstant()->GetValue();
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int64_t l2 = idx2->AsIntConstant()->GetValue();
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// To avoid any overflow in following CONST+vector_length calculation,
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// use int64_t instead of int32_t.
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int64_t h1 = l1 + (vector_length1 - 1);
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int64_t h2 = l2 + (vector_length2 - 1);
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return CanIntegerRangesOverlap(l1, h1, l2, h2);
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}
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// [i+CONST] and [i].
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if (idx1->IsBinaryOperation() &&
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idx1->AsBinaryOperation()->GetConstantRight() != nullptr &&
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idx1->AsBinaryOperation()->GetLeastConstantLeft() == idx2) {
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return CanBinaryOpAndIndexAlias(idx1->AsBinaryOperation(),
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vector_length1,
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idx2,
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vector_length2);
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}
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// [i] and [i+CONST].
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if (idx2->IsBinaryOperation() &&
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idx2->AsBinaryOperation()->GetConstantRight() != nullptr &&
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idx2->AsBinaryOperation()->GetLeastConstantLeft() == idx1) {
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return CanBinaryOpAndIndexAlias(idx2->AsBinaryOperation(),
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vector_length2,
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idx1,
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vector_length1);
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}
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// [i+CONST1] and [i+CONST2].
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if (idx1->IsBinaryOperation() &&
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idx1->AsBinaryOperation()->GetConstantRight() != nullptr &&
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idx2->IsBinaryOperation() &&
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idx2->AsBinaryOperation()->GetConstantRight() != nullptr) {
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return CanBinaryOpsAlias(idx1->AsBinaryOperation(),
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vector_length1,
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idx2->AsBinaryOperation(),
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vector_length2);
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}
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// By default, MAY alias.
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return true;
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}
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bool LoadStoreAnalysis::Run() {
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for (HBasicBlock* block : graph_->GetReversePostOrder()) {
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heap_location_collector_.VisitBasicBlock(block);
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}
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if (heap_location_collector_.GetNumberOfHeapLocations() > kMaxNumberOfHeapLocations) {
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// Bail out if there are too many heap locations to deal with.
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heap_location_collector_.CleanUp();
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return false;
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}
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if (!heap_location_collector_.HasHeapStores()) {
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// Without heap stores, this pass would act mostly as GVN on heap accesses.
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heap_location_collector_.CleanUp();
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return false;
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}
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if (heap_location_collector_.HasVolatile() || heap_location_collector_.HasMonitorOps()) {
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// Don't do load/store elimination if the method has volatile field accesses or
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// monitor operations, for now.
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// TODO: do it right.
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heap_location_collector_.CleanUp();
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return false;
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}
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heap_location_collector_.BuildAliasingMatrix();
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return true;
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}
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} // namespace art
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