1 files changed, 107 insertions, 0 deletions
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 8f37236ede..9cfa89b7d0 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -460,6 +460,113 @@ GraphAnalysisResult HGraph::AnalyzeLoops() const {
   return kAnalysisSuccess;
 }
 
+static bool InSameLoop(HLoopInformation* first_loop, HLoopInformation* second_loop) {
+  return first_loop == second_loop;
+}
+
+static bool IsLoop(HLoopInformation* info) {
+  return info != nullptr;
+}
+
+static bool IsInnerLoop(HLoopInformation* outer, HLoopInformation* inner) {
+  return (inner != outer)
+      && (inner != nullptr)
+      && (outer != nullptr)
+      && inner->IsIn(*outer);
+}
+
+// Helper method to update work list for linear order.
+static void AddToListForLinearization(ArenaVector<HBasicBlock*>* worklist, HBasicBlock* block) {
+  HLoopInformation* block_loop = block->GetLoopInformation();
+  auto insert_pos = worklist->rbegin();  // insert_pos.base() will be the actual position.
+  for (auto end = worklist->rend(); insert_pos != end; ++insert_pos) {
+    HBasicBlock* current = *insert_pos;
+    HLoopInformation* current_loop = current->GetLoopInformation();
+    if (InSameLoop(block_loop, current_loop)
+        || !IsLoop(current_loop)
+        || IsInnerLoop(current_loop, block_loop)) {
+      // The block can be processed immediately.
+      break;
+    }
+  }
+  worklist->insert(insert_pos.base(), block);
+}
+
+// Helper method to validate linear order.
+static bool IsLinearOrderWellFormed(const HGraph& graph) {
+  for (HBasicBlock* header : graph.GetBlocks()) {
+    if (header == nullptr || !header->IsLoopHeader()) {
+      continue;
+    }
+    HLoopInformation* loop = header->GetLoopInformation();
+    size_t num_blocks = loop->GetBlocks().NumSetBits();
+    size_t found_blocks = 0u;
+    for (HLinearOrderIterator it(graph); !it.Done(); it.Advance()) {
+      HBasicBlock* current = it.Current();
+      if (loop->Contains(*current)) {
+        found_blocks++;
+        if (found_blocks == 1u && current != header) {
+          // First block is not the header.
+          return false;
+        } else if (found_blocks == num_blocks && !loop->IsBackEdge(*current)) {
+          // Last block is not a back edge.
+          return false;
+        }
+      } else if (found_blocks != 0u && found_blocks != num_blocks) {
+        // Blocks are not adjacent.
+        return false;
+      }
+    }
+    DCHECK_EQ(found_blocks, num_blocks);
+  }
+  return true;
+}
+
+void HGraph::Linearize() {
+  // Create a reverse post ordering with the following properties:
+  // - Blocks in a loop are consecutive,
+  // - Back-edge is the last block before loop exits.
+
+  // (1): Record the number of forward predecessors for each block. This is to
+  //      ensure the resulting order is reverse post order. We could use the
+  //      current reverse post order in the graph, but it would require making
+  //      order queries to a GrowableArray, which is not the best data structure
+  //      for it.
+  ArenaVector<uint32_t> forward_predecessors(blocks_.size(),
+                                             arena_->Adapter(kArenaAllocSsaLiveness));
+  for (HReversePostOrderIterator it(*this); !it.Done(); it.Advance()) {
+    HBasicBlock* block = it.Current();
+    size_t number_of_forward_predecessors = block->GetPredecessors().size();
+    if (block->IsLoopHeader()) {
+      number_of_forward_predecessors -= block->GetLoopInformation()->NumberOfBackEdges();
+    }
+    forward_predecessors[block->GetBlockId()] = number_of_forward_predecessors;
+  }
+
+  // (2): Following a worklist approach, first start with the entry block, and
+  //      iterate over the successors. When all non-back edge predecessors of a
+  //      successor block are visited, the successor block is added in the worklist
+  //      following an order that satisfies the requirements to build our linear graph.
+  linear_order_.reserve(GetReversePostOrder().size());
+  ArenaVector<HBasicBlock*> worklist(arena_->Adapter(kArenaAllocSsaLiveness));
+  worklist.push_back(GetEntryBlock());
+  do {
+    HBasicBlock* current = worklist.back();
+    worklist.pop_back();
+    linear_order_.push_back(current);
+    for (HBasicBlock* successor : current->GetSuccessors()) {
+      int block_id = successor->GetBlockId();
+      size_t number_of_remaining_predecessors = forward_predecessors[block_id];
+      if (number_of_remaining_predecessors == 1) {
+        AddToListForLinearization(&worklist, successor);
+      }
+      forward_predecessors[block_id] = number_of_remaining_predecessors - 1;
+    }
+  } while (!worklist.empty());
+
+  DCHECK(HasIrreducibleLoops() || IsLinearOrderWellFormed(*this));
+}
+
 void HLoopInformation::Dump(std::ostream& os) {
   os << "header: " << header_->GetBlockId() << std::endl;
   os << "pre header: " << GetPreHeader()->GetBlockId() << std::endl;