Fix premature deoptimization if the loop body isn't entered.
Add a test between initial_ and end_ to see if the loop body is entered.
If the loop body isn't entered at all, we jump to the loop header. Loop header is
still executed and is going to test the condition again and loop body won't be
entered. This makes sure no deoptimization is triggered if the loop body isn't
even entered.
Bug: 21034044
Change-Id: I2b6de1f22fbc4568ca419f76382ebd87806d9694
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index cd91d2c..4baa05c 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -1510,6 +1510,81 @@
invoke->GetBlock()->RemoveInstruction(invoke);
}
+/*
+ * Loop will be transformed to:
+ * old_pre_header
+ * |
+ * if_block
+ * / \
+ * dummy_block deopt_block
+ * \ /
+ * new_pre_header
+ * |
+ * header
+ */
+void HGraph::TransformLoopHeaderForBCE(HBasicBlock* header) {
+ DCHECK(header->IsLoopHeader());
+ HBasicBlock* pre_header = header->GetDominator();
+
+ // Need this to avoid critical edge.
+ HBasicBlock* if_block = new (arena_) HBasicBlock(this, header->GetDexPc());
+ // Need this to avoid critical edge.
+ HBasicBlock* dummy_block = new (arena_) HBasicBlock(this, header->GetDexPc());
+ HBasicBlock* deopt_block = new (arena_) HBasicBlock(this, header->GetDexPc());
+ HBasicBlock* new_pre_header = new (arena_) HBasicBlock(this, header->GetDexPc());
+ AddBlock(if_block);
+ AddBlock(dummy_block);
+ AddBlock(deopt_block);
+ AddBlock(new_pre_header);
+
+ header->ReplacePredecessor(pre_header, new_pre_header);
+ pre_header->successors_.Reset();
+ pre_header->dominated_blocks_.Reset();
+
+ pre_header->AddSuccessor(if_block);
+ if_block->AddSuccessor(dummy_block); // True successor
+ if_block->AddSuccessor(deopt_block); // False successor
+ dummy_block->AddSuccessor(new_pre_header);
+ deopt_block->AddSuccessor(new_pre_header);
+
+ pre_header->dominated_blocks_.Add(if_block);
+ if_block->SetDominator(pre_header);
+ if_block->dominated_blocks_.Add(dummy_block);
+ dummy_block->SetDominator(if_block);
+ if_block->dominated_blocks_.Add(deopt_block);
+ deopt_block->SetDominator(if_block);
+ if_block->dominated_blocks_.Add(new_pre_header);
+ new_pre_header->SetDominator(if_block);
+ new_pre_header->dominated_blocks_.Add(header);
+ header->SetDominator(new_pre_header);
+
+ size_t index_of_header = 0;
+ while (reverse_post_order_.Get(index_of_header) != header) {
+ index_of_header++;
+ }
+ MakeRoomFor(&reverse_post_order_, 4, index_of_header - 1);
+ reverse_post_order_.Put(index_of_header++, if_block);
+ reverse_post_order_.Put(index_of_header++, dummy_block);
+ reverse_post_order_.Put(index_of_header++, deopt_block);
+ reverse_post_order_.Put(index_of_header++, new_pre_header);
+
+ HLoopInformation* info = pre_header->GetLoopInformation();
+ if (info != nullptr) {
+ if_block->SetLoopInformation(info);
+ dummy_block->SetLoopInformation(info);
+ deopt_block->SetLoopInformation(info);
+ new_pre_header->SetLoopInformation(info);
+ for (HLoopInformationOutwardIterator loop_it(*pre_header);
+ !loop_it.Done();
+ loop_it.Advance()) {
+ loop_it.Current()->Add(if_block);
+ loop_it.Current()->Add(dummy_block);
+ loop_it.Current()->Add(deopt_block);
+ loop_it.Current()->Add(new_pre_header);
+ }
+ }
+}
+
std::ostream& operator<<(std::ostream& os, const ReferenceTypeInfo& rhs) {
ScopedObjectAccess soa(Thread::Current());
os << "["