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

src/compiler/bytecode-graph-builder.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/bytecode-graph-builder.h"
 
 #include "src/compiler/bytecode-branch-analysis.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/operator-properties.h"
 #include "src/interpreter/bytecodes.h"
@@ skipping 1880 matching lines @@
   if (branch_analysis()->backward_branches_target(source_offset)) {
     // Add loop header and store a copy so we can connect merged back
     // edge inputs to the loop header.
     loop_header_environments_[source_offset] = environment()->CopyForLoop();
   }
 }
 
 
 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);
   }
   set_environment(nullptr);
 }
 
 
 void BytecodeGraphBuilder::BuildJump() {
   int source_offset = bytecode_iterator()->current_offset();
@@ skipping 190 matching lines @@
 
 void BytecodeGraphBuilder::UpdateControlDependencyToLeaveFunction(Node* exit) {
   if (environment()->IsMarkedAsUnreachable()) return;
   environment()->MarkAsUnreachable();
   exit_controls_.push_back(exit);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8