don't inline classes and functions when they're in different scopes in the utility.deadCodeElimination transformer

src/babel/transformation/transformers/minification/dead-code-elimination.js

@@ -33,6 +33,16 @@ export function ReferencedIdentifier(node, parent, scope) {
   }
   if (!replacement) return;
 
+  // ensure it's a "pure" type
+  if (!scope.isPure(replacement)) 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 (this.findParent((node) => node === replacement)) {
     return;
   }

test/core/fixtures/transformation/minification.dead-code-elimination/issue-1408/actual.js

@@ -1,4 +1,5 @@
 class A {
   constructor() { this.value = 12345; }
 }
+
 export default new A();

test/core/fixtures/transformation/minification.dead-code-elimination/issue-1408/expected.js

@@ -3,12 +3,9 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-
-var A = function A() {
+exports["default"] = new function A() {
   babelHelpers.classCallCheck(this, A);
   this.value = 12345;
-};
-
-exports["default"] = new A();
+}();
 module.exports = exports["default"];
 

test/core/fixtures/transformation/minification.dead-code-elimination/issue-1409/expected.js

@@ -1,6 +1,6 @@
 "use strict";
 
-var A = (function () {
+var a = new ((function () {
   function A() {
     babelHelpers.classCallCheck(this, A);
   }
@@ -12,6 +12,4 @@ var A = (function () {
     }
   }]);
   return A;
-})();
-
-var a = new A();
+})())();