Revert "Revert "Deoptimization-based bce.""
This reverts commit 0ba627337274ccfb8c9cb9bf23fffb1e1b9d1430.
Change-Id: I1ca10d15bbb49897a0cf541ab160431ec180a006
diff --git a/compiler/optimizing/bounds_check_elimination.cc b/compiler/optimizing/bounds_check_elimination.cc
index 1d16794..01f7e91 100644
--- a/compiler/optimizing/bounds_check_elimination.cc
+++ b/compiler/optimizing/bounds_check_elimination.cc
@@ -443,9 +443,31 @@
class BCEVisitor : public HGraphVisitor {
public:
+ // The least number of bounds checks that should be eliminated by triggering
+ // the deoptimization technique.
+ static constexpr size_t kThresholdForAddingDeoptimize = 2;
+
+ // Very large constant index is considered as an anomaly. This is a threshold
+ // beyond which we don't bother to apply the deoptimization technique since
+ // it's likely some AIOOBE will be thrown.
+ static constexpr int32_t kMaxConstantForAddingDeoptimize = INT_MAX - 1024 * 1024;
+
explicit BCEVisitor(HGraph* graph)
: HGraphVisitor(graph),
- maps_(graph->GetBlocks().Size()) {}
+ maps_(graph->GetBlocks().Size()),
+ need_to_revisit_block_(false) {}
+
+ void VisitBasicBlock(HBasicBlock* block) OVERRIDE {
+ first_constant_index_bounds_check_map_.clear();
+ HGraphVisitor::VisitBasicBlock(block);
+ if (need_to_revisit_block_) {
+ AddComparesWithDeoptimization(block);
+ need_to_revisit_block_ = false;
+ first_constant_index_bounds_check_map_.clear();
+ GetValueRangeMap(block)->clear();
+ HGraphVisitor::VisitBasicBlock(block);
+ }
+ }
private:
// Return the map of proven value ranges at the beginning of a basic block.
@@ -701,9 +723,26 @@
}
}
+ if (first_constant_index_bounds_check_map_.find(array_length->GetId()) ==
+ first_constant_index_bounds_check_map_.end()) {
+ // Remember the first bounds check against array_length of a constant index.
+ // That bounds check instruction has an associated HEnvironment where we
+ // may add an HDeoptimize to eliminate bounds checks of constant indices
+ // against array_length.
+ first_constant_index_bounds_check_map_.Put(array_length->GetId(), bounds_check);
+ } else {
+ // We've seen it at least twice. It's beneficial to introduce a compare with
+ // deoptimization fallback to eliminate the bounds checks.
+ need_to_revisit_block_ = true;
+ }
+
// Once we have an array access like 'array[5] = 1', we record array.length >= 6.
// We currently don't do it for non-constant index since a valid array[i] can't prove
// a valid array[i-1] yet due to the lower bound side.
+ if (constant == INT_MAX) {
+ // INT_MAX as an index will definitely throw AIOOBE.
+ return;
+ }
ValueBound lower = ValueBound(nullptr, constant + 1);
ValueBound upper = ValueBound::Max();
ValueRange* range = new (GetGraph()->GetArena())
@@ -938,8 +977,90 @@
}
}
+ void VisitDeoptimize(HDeoptimize* deoptimize) {
+ // Right now it's only HLessThanOrEqual.
+ DCHECK(deoptimize->InputAt(0)->IsLessThanOrEqual());
+ HLessThanOrEqual* less_than_or_equal = deoptimize->InputAt(0)->AsLessThanOrEqual();
+ HInstruction* instruction = less_than_or_equal->InputAt(0);
+ if (instruction->IsArrayLength()) {
+ HInstruction* constant = less_than_or_equal->InputAt(1);
+ DCHECK(constant->IsIntConstant());
+ DCHECK(constant->AsIntConstant()->GetValue() <= kMaxConstantForAddingDeoptimize);
+ ValueBound lower = ValueBound(nullptr, constant->AsIntConstant()->GetValue() + 1);
+ ValueRange* range = new (GetGraph()->GetArena())
+ ValueRange(GetGraph()->GetArena(), lower, ValueBound::Max());
+ GetValueRangeMap(deoptimize->GetBlock())->Overwrite(instruction->GetId(), range);
+ }
+ }
+
+ void AddCompareWithDeoptimization(HInstruction* array_length,
+ HIntConstant* const_instr,
+ HBasicBlock* block) {
+ DCHECK(array_length->IsArrayLength());
+ ValueRange* range = LookupValueRange(array_length, block);
+ ValueBound lower_bound = range->GetLower();
+ DCHECK(lower_bound.IsConstant());
+ DCHECK(const_instr->GetValue() <= kMaxConstantForAddingDeoptimize);
+ DCHECK_EQ(lower_bound.GetConstant(), const_instr->GetValue() + 1);
+
+ // If array_length is less than lower_const, deoptimize.
+ HBoundsCheck* bounds_check = first_constant_index_bounds_check_map_.Get(
+ array_length->GetId())->AsBoundsCheck();
+ HCondition* cond = new (GetGraph()->GetArena()) HLessThanOrEqual(array_length, const_instr);
+ HDeoptimize* deoptimize = new (GetGraph()->GetArena())
+ HDeoptimize(cond, bounds_check->GetDexPc());
+ block->InsertInstructionBefore(cond, bounds_check);
+ block->InsertInstructionBefore(deoptimize, bounds_check);
+ deoptimize->SetEnvironment(bounds_check->GetEnvironment());
+ }
+
+ void AddComparesWithDeoptimization(HBasicBlock* block) {
+ for (ArenaSafeMap<int, HBoundsCheck*>::iterator it =
+ first_constant_index_bounds_check_map_.begin();
+ it != first_constant_index_bounds_check_map_.end();
+ ++it) {
+ HBoundsCheck* bounds_check = it->second;
+ HArrayLength* array_length = bounds_check->InputAt(1)->AsArrayLength();
+ HIntConstant* lower_bound_const_instr = nullptr;
+ int32_t lower_bound_const = INT_MIN;
+ size_t counter = 0;
+ // Count the constant indexing for which bounds checks haven't
+ // been removed yet.
+ for (HUseIterator<HInstruction*> it2(array_length->GetUses());
+ !it2.Done();
+ it2.Advance()) {
+ HInstruction* user = it2.Current()->GetUser();
+ if (user->GetBlock() == block &&
+ user->IsBoundsCheck() &&
+ user->AsBoundsCheck()->InputAt(0)->IsIntConstant()) {
+ DCHECK_EQ(array_length, user->AsBoundsCheck()->InputAt(1));
+ HIntConstant* const_instr = user->AsBoundsCheck()->InputAt(0)->AsIntConstant();
+ if (const_instr->GetValue() > lower_bound_const) {
+ lower_bound_const = const_instr->GetValue();
+ lower_bound_const_instr = const_instr;
+ }
+ counter++;
+ }
+ }
+ if (counter >= kThresholdForAddingDeoptimize &&
+ lower_bound_const_instr->GetValue() <= kMaxConstantForAddingDeoptimize) {
+ AddCompareWithDeoptimization(array_length, lower_bound_const_instr, block);
+ }
+ }
+ }
+
std::vector<std::unique_ptr<ArenaSafeMap<int, ValueRange*>>> maps_;
+ // Map an HArrayLength instruction's id to the first HBoundsCheck instruction in
+ // a block that checks a constant index against that HArrayLength.
+ SafeMap<int, HBoundsCheck*> first_constant_index_bounds_check_map_;
+
+ // For the block, there is at least one HArrayLength instruction for which there
+ // is more than one bounds check instruction with constant indexing. And it's
+ // beneficial to add a compare instruction that has deoptimization fallback and
+ // eliminate those bounds checks.
+ bool need_to_revisit_block_;
+
DISALLOW_COPY_AND_ASSIGN(BCEVisitor);
};