From 255c81972792aac594749cd8807c9db0dc4e9350 Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Sun, 31 May 2015 15:40:41 +0100
Subject: [PATCH] optimise ES6 tail call transformer to only try TOC on
 functions that include a call to themselves

---
 .../transformers/es6/tail-call.js             | 27 +++++++++++++++----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/tail-call.js b/src/babel/transformation/transformers/es6/tail-call.js
index 78eb809380..cbe6ff95c2 100644
--- a/src/babel/transformation/transformers/es6/tail-call.js
+++ b/src/babel/transformation/transformers/es6/tail-call.js
@@ -9,18 +9,35 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
-export function Func/*tion*/(node, parent, scope, file) {
-  if (node.generator || node.async) return;
-  var tailCall = new TailCallTransformer(this, scope, file);
-  tailCall.run();
+export function CallExpression(node) {
+  var callee = this.get("callee");
+  if (!callee.isIdentifier()) return;
+
+  var binding = this.scope.getBinding(callee.node.name);
+  if (!binding) return;
+
+  if (!binding.path.isFunction()) return;
+  if (binding.identifier !== binding.path.node.id) return;
+
+  binding.path.setData("shouldTryTCO", true);
 }
 
+export var Func/*tion*/ = {
+  exit(node, parent, scope, file) {
+    if (node.generator || node.async) return;
+    if (!this.getData("shouldTryTCO")) return;
+
+    var tailCall = new TailCallTransformer(this, scope, file);
+    tailCall.run();
+  }
+};
+
 function returnBlock(expr) {
   return t.blockStatement([t.returnStatement(expr)]);
 }
 
 var visitor = {
-  enter(node, parent) {
+  BlockStatement(node, parent) {
     if (t.isTryStatement(parent)) {
       if (node === parent.block) {
         this.skip();