Made DeadAssignmentsElimination use ES6ScopeCreator.

Currently the hack is to move all the liveness analysis to exitScope. Also, all declarations are redeclared in the closest enclosing function scope during exitScope so that the function scope has the full picture to do the analysis.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=102382602

src/com/google/javascript/jscomp/DeadAssignmentsElimination.java

@@ -63,48 +63,57 @@ public DeadAssignmentsElimination(AbstractCompiler compiler) {
   public void process(Node externs, Node root) {
     Preconditions.checkNotNull(externs);
     Preconditions.checkNotNull(root);
-    NodeTraversal.traverse(compiler, root, this);
+    NodeTraversal.traverseEs6(compiler, root, this);
   }
 
   @Override
   public void enterScope(NodeTraversal t) {
-    Scope scope = t.getScope();
-    // Global scope _SHOULD_ work, however, liveness won't finish without
-    // -Xmx1024 in closure. We might have to look at coding conventions for
-    // exported variables as well.
-    if (scope.isGlobal()) {
-      return;
-    }
+  }
 
-    if (LiveVariablesAnalysis.MAX_VARIABLES_TO_ANALYZE <
-        t.getScope().getVarCount()) {
+  @Override
+  public void exitScope(NodeTraversal t) {
+    // Do nothing on global scope / global blocks
+    if (t.inGlobalHoistScope()) {
       return;
     }
 
-    // We are not going to do any dead assignment elimination in when there is
-    // at least one inner function because in most browsers, when there is a
-    // closure, ALL the variables are saved (escaped).
-    Node fnBlock = t.getScopeRoot().getLastChild();
-    if (NodeUtil.containsFunction(fnBlock)) {
-      return;
-    }
+    Scope scope = t.getScope();
+    // Elevate all variable declarations up till the enclosing function scope
+    // so the liveness analysis has all variables for the process.
+    if (!scope.isFunctionScope()) {
+      for (Var var : scope.getVarIterable()) {
+        Preconditions.checkArgument(
+            !var.isClass() && !var.isLet() && !var.isConst());
+        scope.getParent().declare(
+            var.getName(), var.getNameNode(), var.getInput());
+      }
+    } else {
+      if (LiveVariablesAnalysis.MAX_VARIABLES_TO_ANALYZE <
+          scope.getVarCount()) {
+        return;
+      }
 
-    // We don't do any dead assignment elimination if there are no assigns
-    // to eliminate. :)
-    if (!NodeUtil.has(fnBlock, matchRemovableAssigns,
-            Predicates.<Node>alwaysTrue())) {
-      return;
-    }
+      // We are not going to do any dead assignment elimination in when there is
+      // at least one inner function because in most browsers, when there is a
+      // closure, ALL the variables are saved (escaped).
+      Node fnBlock = t.getScopeRoot().getLastChild();
+      if (NodeUtil.containsFunction(fnBlock)) {
+        return;
+      }
 
-    // Computes liveness information first.
-    ControlFlowGraph<Node> cfg = t.getControlFlowGraph();
-    liveness = new LiveVariablesAnalysis(cfg, scope, compiler);
-    liveness.analyze();
-    tryRemoveDeadAssignments(t, cfg);
-  }
+      // We don't do any dead assignment elimination if there are no assigns
+      // to eliminate. :)
+      if (!NodeUtil.has(fnBlock, matchRemovableAssigns,
+              Predicates.<Node>alwaysTrue())) {
+        return;
+      }
 
-  @Override
-  public void exitScope(NodeTraversal t) {
+      // Computes liveness information first.
+      ControlFlowGraph<Node> cfg = t.getControlFlowGraph();
+      liveness = new LiveVariablesAnalysis(cfg, scope, compiler);
+      liveness.analyze();
+      tryRemoveDeadAssignments(t, cfg);
+    }
   }
 
   @Override

test/com/google/javascript/jscomp/DeadAssignmentsEliminationTest.java

@@ -33,7 +33,7 @@ public CompilerPass getProcessor(final Compiler compiler) {
     return new CompilerPass() {
       @Override
       public void process(Node externs, Node js) {
-        NodeTraversal.traverse(
+        NodeTraversal.traverseEs6(
             compiler, js, new DeadAssignmentsElimination(compiler));
       }
     };