Propagate reaching definitions to the instuctions of a block.

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 339cfa140e834d8d43fd60c0d6e8e755a72e90d0..9fc4af0dba022827ed1b822ba18954f4837f653b 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -78,14 +78,16 @@ VariableProxy::VariableProxy(Handle<String> name,
     var_(NULL),
     is_this_(is_this),
     inside_with_(inside_with),
-    is_trivial_(false) {
+    is_trivial_(false),
+    reaching_definitions_(NULL) {
   // names must be canonicalized for fast equality checks
   ASSERT(name->IsSymbol());
 }
 
 
 VariableProxy::VariableProxy(bool is_this)
-  : is_this_(is_this) {
+  : is_this_(is_this),
+    reaching_definitions_(NULL) {
 }