Improve simplifier slightly
It's possible thanks to the dead-code-elimination and other passes to
end up with a PredicatedInstanceFieldGet that either has a null or a
'never-null' target value. We can simplify this down to either the
default value or a normal ifield-get respectively.
Test: ./test.py --host
Change-Id: I92d9ff159a7b30294d29dbf4349d201dc654f0e1
diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index 23a432e..a6104ef 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -949,36 +949,12 @@
HPredicatedInstanceFieldGet* pred_get) {
HInstruction* target = pred_get->GetTarget();
HInstruction* default_val = pred_get->GetDefaultValue();
- // TODO Technically we could end up with a case where the target isn't a phi
- // (allowing us to eliminate the instruction and replace with either a
- // InstanceFieldGet or the default) but due to the ordering of compilation
- // passes this can't happen in ART.
- if (!target->IsPhi() || !default_val->IsPhi() || default_val->GetBlock() != target->GetBlock()) {
- // Already reduced the target or the phi selection will differ between the
- // target and default.
+ if (target->IsNullConstant()) {
+ pred_get->ReplaceWith(default_val);
+ pred_get->GetBlock()->RemoveInstruction(pred_get);
+ RecordSimplification();
return;
- }
- DCHECK_EQ(default_val->InputCount(), target->InputCount());
- // In the same block both phis only one non-null we can remove the phi from default_val.
- HInstruction* single_value = nullptr;
- auto inputs = target->GetInputs();
- for (auto [input, idx] : ZipCount(MakeIterationRange(inputs))) {
- if (input->CanBeNull()) {
- if (single_value == nullptr) {
- single_value = default_val->InputAt(idx);
- } else if (single_value != default_val->InputAt(idx) &&
- !single_value->Equals(default_val->InputAt(idx))) {
- // Multiple values are associated with potential nulls, can't combine.
- return;
- }
- }
- }
- if (single_value == nullptr) {
- // None of the inputs can be null so we can just remove the predicatedness
- // of this instruction.
- DCHECK(std::none_of(inputs.cbegin(), inputs.cend(), [](const HInstruction* input) {
- return input->CanBeNull();
- }));
+ } else if (!target->CanBeNull()) {
HInstruction* replace_with = new (GetGraph()->GetAllocator())
HInstanceFieldGet(pred_get->GetTarget(),
pred_get->GetFieldInfo().GetField(),
@@ -996,7 +972,32 @@
pred_get->ReplaceWith(replace_with);
pred_get->GetBlock()->RemoveInstruction(pred_get);
RecordSimplification();
- } else if (single_value->StrictlyDominates(pred_get)) {
+ return;
+ }
+ if (!target->IsPhi() || !default_val->IsPhi() || default_val->GetBlock() != target->GetBlock()) {
+ // The iget has already been reduced. We know the target or the phi
+ // selection will differ between the target and default.
+ return;
+ }
+ DCHECK_EQ(default_val->InputCount(), target->InputCount());
+ // In the same block both phis only one non-null we can remove the phi from default_val.
+ HInstruction* single_value = nullptr;
+ auto inputs = target->GetInputs();
+ for (auto [input, idx] : ZipCount(MakeIterationRange(inputs))) {
+ if (input->CanBeNull()) {
+ if (single_value == nullptr) {
+ single_value = default_val->InputAt(idx);
+ } else if (single_value != default_val->InputAt(idx) &&
+ !single_value->Equals(default_val->InputAt(idx))) {
+ // Multiple values are associated with potential nulls, can't combine.
+ return;
+ }
+ }
+ }
+ DCHECK(single_value != nullptr) << "All target values are non-null but the phi as a whole still"
+ << " can be null? This should not be possible." << std::endl
+ << pred_get->DumpWithArgs();
+ if (single_value->StrictlyDominates(pred_get)) {
// Combine all the maybe null values into one.
pred_get->ReplaceInput(single_value, 0);
RecordSimplification();