Recompute dominator tree after DCE.
bug:22031382
Change-Id: Ifebe169897b76872015e3ce0ed7d0a9662f80cef
diff --git a/compiler/optimizing/boolean_simplifier.cc b/compiler/optimizing/boolean_simplifier.cc
index 8100a29..daf7d67 100644
--- a/compiler/optimizing/boolean_simplifier.cc
+++ b/compiler/optimizing/boolean_simplifier.cc
@@ -141,6 +141,12 @@
block->MergeWith(false_block);
block->MergeWith(merge_block);
+ // No need to update any dominance information, as we are simplifying
+ // a simple diamond shape, where the join block is merged with the
+ // entry block. Any following blocks would have had the join block
+ // as a dominator, and `MergeWith` handles changing that to the
+ // entry block.
+
// Remove the original condition if it is now unused.
if (!if_condition->HasUses()) {
if_condition->GetBlock()->RemoveInstructionOrPhi(if_condition);
diff --git a/compiler/optimizing/dead_code_elimination.cc b/compiler/optimizing/dead_code_elimination.cc
index fdfe518..5de629d 100644
--- a/compiler/optimizing/dead_code_elimination.cc
+++ b/compiler/optimizing/dead_code_elimination.cc
@@ -68,6 +68,7 @@
ArenaBitVector affected_loops(allocator, graph_->GetBlocks().Size(), false);
MarkReachableBlocks(graph_->GetEntryBlock(), &live_blocks);
+ bool removed_one_or_more_blocks = false;
// Remove all dead blocks. Iterate in post order because removal needs the
// block's chain of dominators and nested loops need to be updated from the
@@ -84,9 +85,17 @@
MaybeRecordDeadBlock(block);
MarkLoopHeadersContaining(*block, &affected_loops);
block->DisconnectAndDelete();
+ removed_one_or_more_blocks = true;
}
}
+ // If we removed at least one block, we need to recompute the full
+ // dominator tree.
+ if (removed_one_or_more_blocks) {
+ graph_->ClearDominanceInformation();
+ graph_->ComputeDominanceInformation();
+ }
+
// Connect successive blocks created by dead branches. Order does not matter.
for (HReversePostOrderIterator it(*graph_); !it.Done();) {
HBasicBlock* block = it.Current();
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 01eb2d7..3891a15 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -117,9 +117,24 @@
// dominators and the reverse post order.
SimplifyCFG();
- // (5) Compute the immediate dominator of each block. We visit
- // the successors of a block only when all its forward branches
- // have been processed.
+ // (5) Compute the dominance information and the reverse post order.
+ ComputeDominanceInformation();
+}
+
+void HGraph::ClearDominanceInformation() {
+ for (HReversePostOrderIterator it(*this); !it.Done(); it.Advance()) {
+ it.Current()->ClearDominanceInformation();
+ }
+ reverse_post_order_.Reset();
+}
+
+void HBasicBlock::ClearDominanceInformation() {
+ dominated_blocks_.Reset();
+ dominator_ = nullptr;
+}
+
+void HGraph::ComputeDominanceInformation() {
+ DCHECK(reverse_post_order_.IsEmpty());
GrowableArray<size_t> visits(arena_, blocks_.Size());
visits.SetSize(blocks_.Size());
reverse_post_order_.Add(entry_block_);
@@ -1133,8 +1148,7 @@
}
predecessors_.Reset();
- // Disconnect the block from its successors and update their dominators
- // and phis.
+ // Disconnect the block from its successors and update their phis.
for (size_t i = 0, e = successors_.Size(); i < e; ++i) {
HBasicBlock* successor = successors_.Get(i);
// Delete this block from the list of predecessors.
@@ -1145,19 +1159,6 @@
// dominator of `successor` which violates the order DCHECKed at the top.
DCHECK(!successor->predecessors_.IsEmpty());
- // Recompute the successor's dominator.
- HBasicBlock* old_dominator = successor->GetDominator();
- HBasicBlock* new_dominator = successor->predecessors_.Get(0);
- for (size_t j = 1, f = successor->predecessors_.Size(); j < f; ++j) {
- new_dominator = graph_->FindCommonDominator(
- new_dominator, successor->predecessors_.Get(j));
- }
- if (old_dominator != new_dominator) {
- successor->SetDominator(new_dominator);
- old_dominator->RemoveDominatedBlock(successor);
- new_dominator->AddDominatedBlock(successor);
- }
-
// Remove this block's entries in the successor's phis.
if (successor->predecessors_.Size() == 1u) {
// The successor has just one predecessor left. Replace phis with the only
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 26eee1c..581645f 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -183,6 +183,9 @@
return true;
}
+ void ComputeDominanceInformation();
+ void ClearDominanceInformation();
+
void BuildDominatorTree();
void TransformToSsa();
void SimplifyCFG();
@@ -590,11 +593,10 @@
LOG(FATAL) << "Unreachable";
UNREACHABLE();
}
+ void ClearDominanceInformation();
int NumberOfBackEdges() const {
- return loop_information_ == nullptr
- ? 0
- : loop_information_->NumberOfBackEdges();
+ return IsLoopHeader() ? loop_information_->NumberOfBackEdges() : 0;
}
HInstruction* GetFirstInstruction() const { return instructions_.first_instruction_; }