ART: ChildBlockIterator Implementation

- Added the API to be able to walk through a BasicBlock's children directly.
- When calling Reset(GrowableArray*), there is an assignment to the g_list_
    member. This is not possible with the g_list_ being const.

Change-Id: I25d06484fd93848d80ccf96a1324058370b2ee46
Signed-Off-By: Jean Christophe Beyler <jean.christophe.beyler@intel.com>
Signed-off-by: Razvan A Lupusoru <razvan.a.lupusoru@intel.com>
Signed-off-by: Yixin Shou <yixin.shou@intel.com>
Signed-off-by: Chao-ying Fu <chao-ying.fu@intel.com>
Signed-off-by: Udayan Banerji <udayan.banerji@intel.com>

2 files changed, 74 insertions, 0 deletions

diff --git a/compiler/dex/mir_graph.cc b/compiler/dex/mir_graph.cc
index 30d0bc3d0a..ca90a833cc 100644
--- a/compiler/dex/mir_graph.cc
+++ b/compiler/dex/mir_graph.cc
@@ -1257,4 +1257,55 @@ void MIRGraph::InitializeSSATransformation() {
   DoDFSPreOrderSSARename(GetEntryBlock());
 }
 
+ChildBlockIterator::ChildBlockIterator(BasicBlock* bb, MIRGraph* mir_graph)
+    : basic_block_(bb), mir_graph_(mir_graph), visited_fallthrough_(false),
+      visited_taken_(false), have_successors_(false) {
+  // Check if we actually do have successors.
+  if (basic_block_ != 0 && basic_block_->successor_block_list_type != kNotUsed) {
+    have_successors_ = true;
+    successor_iter_.Reset(basic_block_->successor_blocks);
+  }
+}
+
+BasicBlock* ChildBlockIterator::Next() {
+  // We check if we have a basic block. If we don't we cannot get next child.
+  if (basic_block_ == nullptr) {
+    return nullptr;
+  }
+
+  // If we haven't visited fallthrough, return that.
+  if (visited_fallthrough_ == false) {
+    visited_fallthrough_ = true;
+
+    BasicBlock* result = mir_graph_->GetBasicBlock(basic_block_->fall_through);
+    if (result != nullptr) {
+      return result;
+    }
+  }
+
+  // If we haven't visited taken, return that.
+  if (visited_taken_ == false) {
+    visited_taken_ = true;
+
+    BasicBlock* result = mir_graph_->GetBasicBlock(basic_block_->taken);
+    if (result != nullptr) {
+      return result;
+    }
+  }
+
+  // We visited both taken and fallthrough. Now check if we have successors we need to visit.
+  if (have_successors_ == true) {
+    // Get information about next successor block.
+    SuccessorBlockInfo* successor_block_info = successor_iter_.Next();
+
+    // If we don't have anymore successors, return nullptr.
+    if (successor_block_info != nullptr) {
+      return mir_graph_->GetBasicBlock(successor_block_info->block);
+    }
+  }
+
+  // We do not have anything.
+  return nullptr;
+}
+
 }  // namespace art
diff --git a/compiler/dex/mir_graph.h b/compiler/dex/mir_graph.h
index c728d84942..85a2d04306 100644
--- a/compiler/dex/mir_graph.h
+++ b/compiler/dex/mir_graph.h
@@ -341,6 +341,29 @@ struct SuccessorBlockInfo {
   int key;
 };
 
+/**
+ * @class ChildBlockIterator
+ * @brief Enable an easy iteration of the children.
+ */
+class ChildBlockIterator {
+ public:
+  /**
+   * @brief Constructs a child iterator.
+   * @param bb The basic whose children we need to iterate through.
+   * @param mir_graph The MIRGraph used to get the basic block during iteration.
+   */
+  ChildBlockIterator(BasicBlock* bb, MIRGraph* mir_graph);
+  BasicBlock* Next();
+
+ private:
+  BasicBlock* basic_block_;
+  MIRGraph* mir_graph_;
+  bool visited_fallthrough_;
+  bool visited_taken_;
+  bool have_successors_;
+  GrowableArray<SuccessorBlockInfo*>::Iterator successor_iter_;
+};
+
 /*
  * Whereas a SSA name describes a definition of a Dalvik vreg, the RegLocation describes
  * the type of an SSA name (and, can also be used by code generators to record where the