Implement loop variable assignment analysis.

src/compiler/graph-builder.h

Index: src/compiler/graph-builder.h
diff --git a/src/compiler/graph-builder.h b/src/compiler/graph-builder.h
index a2bbc307efef2fded7a05afb23e8b2f4a96a15e0..0fdd7692cc1a87a9b82a956384ab45b039308f7b 100644
--- a/src/compiler/graph-builder.h
+++ b/src/compiler/graph-builder.h
@@ -14,6 +14,9 @@
 
 namespace v8 {
 namespace internal {
+
+class BitVector;
+
 namespace compiler {
 
 class Node;
@@ -215,8 +218,8 @@ class StructuredGraphBuilder::Environment : public ZoneObject {
   }
 
   // Copies this environment at a loop header control-flow point.
-  Environment* CopyForLoop() {
-    PrepareForLoop();
+  Environment* CopyForLoop(BitVector* assigned) {
+    PrepareForLoop(assigned);
     return builder()->CopyEnvironment(this);
   }
 
@@ -230,7 +233,7 @@ class StructuredGraphBuilder::Environment : public ZoneObject {
   NodeVector* values() { return &values_; }
 
   // Prepare environment to be used as loop header.
-  void PrepareForLoop();
+  void PrepareForLoop(BitVector* assigned);
 
  private:
   StructuredGraphBuilder* builder_;