[Interpreter] Adds a placeholder merge node when visiting jumps.

src/compiler/bytecode-graph-builder.cc

Index: src/compiler/bytecode-graph-builder.cc
diff --git a/src/compiler/bytecode-graph-builder.cc b/src/compiler/bytecode-graph-builder.cc
index 843cd5f85808289c3b2b9a177757dff0d68a8edc..5f5949b6a39d5ebd6ab09a317d5aaf06f27ad8bd 100644
--- a/src/compiler/bytecode-graph-builder.cc
+++ b/src/compiler/bytecode-graph-builder.cc
@@ -1898,6 +1898,10 @@ void BytecodeGraphBuilder::BuildLoopHeaderForBackwardBranches(
 
 void BytecodeGraphBuilder::BuildJump(int source_offset, int target_offset) {
   DCHECK_NULL(merge_environments_[source_offset]);
+  // Append merge nodes to the environment. We may merge here with another
+  // environment. So add a place holder for merge nodes. We may add redundant
+  // but will be eliminated in a later pass.
+  NewMerge();

[Michael Starzinger, 2016/01/28 12:27:50]

This can be made nice when we forward propagate environments along the direction
of the data-flow. Can you leave TODO(mstarzinger) here in that regard?

[mythria, 2016/01/28 13:03:16]

Done.

   merge_environments_[source_offset] = environment();
   if (source_offset >= target_offset) {
     MergeEnvironmentsOfBackwardBranches(source_offset, target_offset);