diff --git a/src/babel/transformation/transformers/minification/dead-code-elimination.js b/src/babel/transformation/transformers/minification/dead-code-elimination.js
index b99b1a5486..ec94d976b3 100644
--- a/src/babel/transformation/transformers/minification/dead-code-elimination.js
+++ b/src/babel/transformation/transformers/minification/dead-code-elimination.js
@@ -34,13 +34,13 @@ export function ReferencedIdentifier(node, parent, scope) {
   if (!replacement) return;
 
   // ensure it's a "pure" type
-  if (!scope.isPure(replacement)) return;
+  if (!scope.isPure(replacement, true)) return;
 
   if (t.isClass(replacement) || t.isFunction(replacement)) {
     // don't change this if it's in a different scope, this can be bad
     // for performance since it may be inside a loop or deeply nested in
     // hot code
-    if (!binding.path.scope.parent.is(scope)) return;
+    if (binding.path.scope.parent !== scope) return;
   }
 
   if (this.findParent((node) => node === replacement)) {
@@ -63,7 +63,7 @@ export function FunctionDeclaration(node, parent, scope) {
 export { FunctionDeclaration as ClassDeclaration };
 
 export function VariableDeclarator(node, parent, scope) {
-  if (!t.isIdentifier(node.id) || !scope.isPure(node.init)) return;
+  if (!t.isIdentifier(node.id) || !scope.isPure(node.init, true)) return;
   FunctionDeclaration.apply(this, arguments);
 }
 
diff --git a/src/babel/transformation/transformers/validation/undeclared-variable-check.js b/src/babel/transformation/transformers/validation/undeclared-variable-check.js
index f8d3b25a78..acb6ad1087 100644
--- a/src/babel/transformation/transformers/validation/undeclared-variable-check.js
+++ b/src/babel/transformation/transformers/validation/undeclared-variable-check.js
@@ -5,8 +5,7 @@ export var metadata = {
   optional: true
 };
 
-export function Identifier(node, parent, scope, file) {
-  if (!this.isReferenced()) return;
+export function ReferencedIdentifier(node, parent, scope, file) {
   if (scope.hasBinding(node.name)) return;
 
   // get the closest declaration to offer as a suggestion
diff --git a/src/babel/traversal/path/lib/hoister.js b/src/babel/traversal/path/lib/hoister.js
index 5964e6c088..9ee6ddd291 100644
--- a/src/babel/traversal/path/lib/hoister.js
+++ b/src/babel/traversal/path/lib/hoister.js
@@ -69,7 +69,7 @@ export default class PathHoister {
     if (scope.path.isFunction()) {
       if (this.hasOwnParamBindings(scope)) {
         // should ignore this scope since it's ourselves
-        if (this.scope.is(scope)) return;
+        if (this.scope === scope) return;
 
         // needs to be attached to the body
         return scope.path.get("body").get("body")[0];
diff --git a/src/babel/traversal/path/lib/virtual-types.js b/src/babel/traversal/path/lib/virtual-types.js
index 7f6ba09015..0698e92ec0 100644
--- a/src/babel/traversal/path/lib/virtual-types.js
+++ b/src/babel/traversal/path/lib/virtual-types.js
@@ -2,8 +2,8 @@ import * as t from "../../../types";
 
 export var ReferencedIdentifier = {
   types: ["Identifier", "JSXIdentifier"],
-  checkPath(path, opts) {
-    return t.isReferencedIdentifier(path.node, path.parent, opts);
+  checkPath({ node, parent }, opts) {
+    return (t.isIdentifier(node, opts) || t.isJSXIdentifier(node, opts)) && t.isReferenced(node, parent);
   }
 };
 
diff --git a/src/babel/traversal/scope/index.js b/src/babel/traversal/scope/index.js
index 15c2c8b64d..92fc9cc6c1 100644
--- a/src/babel/traversal/scope/index.js
+++ b/src/babel/traversal/scope/index.js
@@ -137,7 +137,7 @@ export default class Scope {
     if (cached && cached.parent === parent) {
       return cached;
     } else {
-      //path.setData("scope", this);
+      path.setData("scope", this);
     }
 
     this.parent = parent;
@@ -149,7 +149,7 @@ export default class Scope {
   }
 
   static globals = flatten([globals.builtin, globals.browser, globals.node].map(Object.keys));
-  static contextVariables = ["this", "arguments", "super"];
+  static contextVariables = ["this", "arguments", "super", "undefined"];
 
   /**
    * Description
@@ -546,12 +546,14 @@ export default class Scope {
    * Description
    */
 
-  isPure(node) {
+  isPure(node, constantsOnly) {
     if (t.isIdentifier(node)) {
       var bindingInfo = this.getBinding(node.name);
-      return bindingInfo && bindingInfo.constant;
+      return !!bindingInfo && (!constantsOnly || (constantsOnly && bindingInfo.constant));
     } else if (t.isClass(node)) {
       return !node.superClass;
+    } else if (t.isBinary(node)) {
+      return this.isPure(node.left, constantsOnly) && this.isPure(node.right, constantsOnly);
     } else {
       return t.isPure(node);
     }
diff --git a/src/babel/types/retrievers.js b/src/babel/types/retrievers.js
index d325aded1f..fd0c20e351 100644
--- a/src/babel/types/retrievers.js
+++ b/src/babel/types/retrievers.js
@@ -56,29 +56,3 @@ getBindingIdentifiers.keys = {
   ArrayPattern: ["elements"],
   ObjectPattern: ["properties"]
 };
-
-/**
- * Description
- */
-
-export function getLastStatements(node: Object): Array<Object> {
-  var nodes = [];
-
-  var add = function (node) {
-    nodes = nodes.concat(getLastStatements(node));
-  };
-
-  if (t.isIfStatement(node)) {
-    add(node.consequent);
-    add(node.alternate);
-  } else if (t.isFor(node) || t.isWhile(node)) {
-    add(node.body);
-  } else if (t.isProgram(node) || t.isBlockStatement(node)) {
-    add(node.body[node.body.length - 1]);
-  } else if (t.isLoop()) {
-  } else if (node) {
-    nodes.push(node);
-  }
-
-  return nodes;
-}
diff --git a/src/babel/types/validators.js b/src/babel/types/validators.js
index 9a066321f2..d393cf40a3 100644
--- a/src/babel/types/validators.js
+++ b/src/babel/types/validators.js
@@ -112,14 +112,6 @@ export function isReferenced(node: Object, parent: Object): boolean {
   return true;
 }
 
-/**
- * Check if the input `node` is an `Identifier` and `isReferenced`.
- */
-
-export function isReferencedIdentifier(node: Object, parent: Object, opts?: Object): boolean {
-  return (t.isIdentifier(node, opts) || t.isJSXIdentifier(node, opts)) && t.isReferenced(node, parent);
-}
-
 /**
  * Check if the input `name` is a valid identifier name
  * and isn't a reserved word.