From 99b2e00d33c7190be0458357e7cc85e756ffddd0 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 01:38:51 +0100
Subject: [PATCH 01/18] add rest parameters optimization

---
 .../transformers/es6/parameters.rest.js       | 76 +++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index cda2b09175..2c2937bf2c 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -3,6 +3,64 @@ var t    = require("../../../types");
 
 exports.check = t.isRestElement;
 
+var memberExpressionVisitor = {
+  enter: function (node, parent, scope, state) {
+    var localDeclar = scope.getBindingIdentifier(state.name);
+    if (localDeclar !== state.outerDeclar) return;
+
+    if (t.isFunctionDeclaration(node) || t.isFunctionExpression(node)) {
+      state.isOptimizable = false;
+      this.skip();
+      return;
+    }
+
+    if (!t.isReferencedIdentifier(node, parent, { name: state.name })) return;
+
+    if (parent.type === 'MemberExpression') {
+      var prop = parent.property;
+      if (typeof prop.value === 'number' ||
+          prop.type === 'UnaryExpression' ||
+          prop.type === 'BinaryExpression') {
+        state.candidates.push({ node: node, parent: parent });
+        return;
+      }
+    }
+
+    state.isOptimizable = false;
+    this.stop();
+  }
+};
+
+function optimizeMemberExpression(node, parent, offset) {
+  var newExpr;
+
+  var prop = parent.property;
+  switch (prop.type) {
+  case 'Literal':
+    node.name = 'arguments';
+    prop.value += offset;
+    prop.raw = String(prop.value);
+    break;
+  case 'UnaryExpression': {
+    node.name = 'arguments';
+    newExpr = t.binaryExpression('+', prop, t.literal(offset));
+    parent.property = newExpr;
+    break;
+  }
+  case 'BinaryExpression': {
+    node.name = 'arguments';
+    newExpr = t.binaryExpression('+', prop, t.literal(offset));
+    parent.property = newExpr;
+    break;
+  }
+  default:
+    throw new Error('Unsupported property type');
+  }
+}
+
+function optimizeCandidates(candidates) {
+}
+
 var hasRest = function (node) {
   return t.isRestElement(node.params[node.params.length - 1]);
 };
@@ -17,6 +75,24 @@ exports.Function = function (node, parent, scope) {
   // otherwise `arguments` will be remapped in arrow functions
   argsId._ignoreAliasFunctions = true;
 
+  // check if rest is used only in member expressions
+  var restOuterDeclar = scope.getBindingIdentifier(rest.name);
+  var state = {
+    name: rest.name,
+    outerDeclar: restOuterDeclar,
+    isOptimizable: true,
+    candidates: []
+  };
+  scope.traverse(node, memberExpressionVisitor, state);
+
+  if (state.isOptimizable) {
+    for (var i = 0, count = state.candidates.length; i < count; ++i) {
+      var candidate = state.candidates[i];
+      optimizeMemberExpression(candidate.node, candidate.parent, node.params.length);
+    }
+    return;
+  }
+
   var start = t.literal(node.params.length);
   var key = scope.generateUidIdentifier("key");
   var len = scope.generateUidIdentifier("len");

From f2981b7e95c50296790b909818a45cfe5efd1562 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 03:02:48 +0100
Subject: [PATCH 02/18] replace direct node type checking with helper functions

---
 .../transformers/es6/parameters.rest.js       | 20 ++++++-------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 2c2937bf2c..12be9d2bd3 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -16,11 +16,11 @@ var memberExpressionVisitor = {
 
     if (!t.isReferencedIdentifier(node, parent, { name: state.name })) return;
 
-    if (parent.type === 'MemberExpression') {
+    if (t.isMemberExpression(parent)) {
       var prop = parent.property;
       if (typeof prop.value === 'number' ||
-          prop.type === 'UnaryExpression' ||
-          prop.type === 'BinaryExpression') {
+          t.isUnaryExpression(prop) ||
+          t.isBinaryExpression(prop)) {
         state.candidates.push({ node: node, parent: parent });
         return;
       }
@@ -35,26 +35,18 @@ function optimizeMemberExpression(node, parent, offset) {
   var newExpr;
 
   var prop = parent.property;
-  switch (prop.type) {
-  case 'Literal':
+  if (t.isLiteral(prop)) {
     node.name = 'arguments';
     prop.value += offset;
     prop.raw = String(prop.value);
-    break;
-  case 'UnaryExpression': {
+  } else if (t.isUnaryExpression(prop)) {
     node.name = 'arguments';
     newExpr = t.binaryExpression('+', prop, t.literal(offset));
     parent.property = newExpr;
-    break;
-  }
-  case 'BinaryExpression': {
+  } else if (t.isBinaryExpression(prop)) {
     node.name = 'arguments';
     newExpr = t.binaryExpression('+', prop, t.literal(offset));
     parent.property = newExpr;
-    break;
-  }
-  default:
-    throw new Error('Unsupported property type');
   }
 }
 

From 81ae6563588fa3f660a3d7d8d0f06d0001e063d9 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 03:05:57 +0100
Subject: [PATCH 03/18] remove unused function

---
 src/babel/transformation/transformers/es6/parameters.rest.js | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 12be9d2bd3..85b636d11b 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -50,9 +50,6 @@ function optimizeMemberExpression(node, parent, offset) {
   }
 }
 
-function optimizeCandidates(candidates) {
-}
-
 var hasRest = function (node) {
   return t.isRestElement(node.params[node.params.length - 1]);
 };

From 8ca854156a3764a6f46df42f74d274fb64281202 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 03:33:36 +0100
Subject: [PATCH 04/18] simplify and optimize local binding handling

---
 .../transformation/transformers/es6/parameters.rest.js    | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 85b636d11b..09e8fdd960 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -5,13 +5,13 @@ exports.check = t.isRestElement;
 
 var memberExpressionVisitor = {
   enter: function (node, parent, scope, state) {
-    var localDeclar = scope.getBindingIdentifier(state.name);
-    if (localDeclar !== state.outerDeclar) return;
+    if (t.isScope(node, parent) && !scope.bindingIdentifierEquals(state.name, state.outerDeclar)) {
+      return this.skip();
+    }
 
     if (t.isFunctionDeclaration(node) || t.isFunctionExpression(node)) {
       state.isOptimizable = false;
-      this.skip();
-      return;
+      return this.skip();
     }
 
     if (!t.isReferencedIdentifier(node, parent, { name: state.name })) return;

From e677c72d583d553c46f7ec1aeb52bbb1234c1d71 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 04:30:17 +0100
Subject: [PATCH 05/18] add patterns support

---
 .../transformers/es6/parameters.rest.js       | 27 ++++++++-----------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 09e8fdd960..7559619db5 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -64,6 +64,17 @@ exports.Function = function (node, parent, scope) {
   // otherwise `arguments` will be remapped in arrow functions
   argsId._ignoreAliasFunctions = true;
 
+  // support patterns
+  if (t.isPattern(rest)) {
+    var pattern = rest;
+    rest = scope.generateUidIdentifier("ref");
+    var declar = t.variableDeclaration("var", pattern.elements.map(function (elem, index) {
+      var accessExpr = t.memberExpression(rest, t.literal(index));
+      return t.variableDeclarator(elem, accessExpr);
+    }));
+    node.body.body.unshift(declar);
+  }
+
   // check if rest is used only in member expressions
   var restOuterDeclar = scope.getBindingIdentifier(rest.name);
   var state = {
@@ -107,22 +118,6 @@ exports.Function = function (node, parent, scope) {
     );
   }
 
-  // support patterns
-  if (t.isPattern(rest)) {
-    var pattern = rest;
-    rest = scope.generateUidIdentifier("ref");
-
-    // let the destructuring transformer handle this
-    var restDeclar = t.variableDeclaration("var", [
-      t.variableDeclarator(pattern, rest)
-    ]);
-
-    // retain evaluation position
-    restDeclar._blockHoist = node.params.length + 1;
-
-    node.body.body.unshift(restDeclar);
-  }
-
   scope.assignTypeGeneric(rest.name, "Array");
 
   var loop = util.template("rest", {

From 1265bc5a9282be3e807ce9794fe562488f1a3a4b Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 12:01:10 +0100
Subject: [PATCH 06/18] add better optimization when strictMode transformer is
 enabled

---
 .../transformers/es6/parameters.rest.js         | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 7559619db5..e76a1744ef 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -18,7 +18,8 @@ var memberExpressionVisitor = {
 
     if (t.isMemberExpression(parent)) {
       var prop = parent.property;
-      if (typeof prop.value === 'number' ||
+      if (state.strictMode ||
+          typeof prop.value === 'number' ||
           t.isUnaryExpression(prop) ||
           t.isBinaryExpression(prop)) {
         state.candidates.push({ node: node, parent: parent });
@@ -50,11 +51,17 @@ function optimizeMemberExpression(node, parent, offset) {
   }
 }
 
+function optimizeMemberExpressionStrict(node, parent, offset) {
+  var prop = parent.property;
+  node.name = 'arguments';
+  parent.property = t.binaryExpression('+', prop, t.literal(offset));
+}
+
 var hasRest = function (node) {
   return t.isRestElement(node.params[node.params.length - 1]);
 };
 
-exports.Function = function (node, parent, scope) {
+exports.Function = function (node, parent, scope, file) {
   if (!hasRest(node)) return;
 
   var rest = node.params.pop().argument;
@@ -81,14 +88,16 @@ exports.Function = function (node, parent, scope) {
     name: rest.name,
     outerDeclar: restOuterDeclar,
     isOptimizable: true,
-    candidates: []
+    candidates: [],
+    strictMode: file.transformers.useStrict.canRun()
   };
   scope.traverse(node, memberExpressionVisitor, state);
 
   if (state.isOptimizable) {
+    var optimize = state.strictMode ? optimizeMemberExpressionStrict : optimizeMemberExpression;
     for (var i = 0, count = state.candidates.length; i < count; ++i) {
       var candidate = state.candidates[i];
-      optimizeMemberExpression(candidate.node, candidate.parent, node.params.length);
+      optimize(candidate.node, candidate.parent, node.params.length);
     }
     return;
   }

From 8f540dfff328aa3ffe3ba36673dd4a52b6ef37a5 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 12:07:46 +0100
Subject: [PATCH 07/18] call non-strict mode optimizer before strict mode one
 to simplify literals

---
 src/babel/transformation/transformers/es6/parameters.rest.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index e76a1744ef..6f9cc0ecfc 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -52,6 +52,10 @@ function optimizeMemberExpression(node, parent, offset) {
 }
 
 function optimizeMemberExpressionStrict(node, parent, offset) {
+  // handle basic expressions specially (especially literals)
+  optimizeMemberExpression(node, parent, offset);
+  if (node.name === 'arguments') return;
+
   var prop = parent.property;
   node.name = 'arguments';
   parent.property = t.binaryExpression('+', prop, t.literal(offset));

From 662bddbacab8a46cddc7c9462b60b8f8bfc3dce2 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 12:14:53 +0100
Subject: [PATCH 08/18] simplify optimization code

---
 .../transformers/es6/parameters.rest.js       | 20 +++++++------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 6f9cc0ecfc..a179e0d7f2 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -32,10 +32,10 @@ var memberExpressionVisitor = {
   }
 };
 
-function optimizeMemberExpression(node, parent, offset) {
+function optimizeMemberExpression(node, parent, offset, strictMode) {
   var newExpr;
-
   var prop = parent.property;
+
   if (t.isLiteral(prop)) {
     node.name = 'arguments';
     prop.value += offset;
@@ -49,16 +49,11 @@ function optimizeMemberExpression(node, parent, offset) {
     newExpr = t.binaryExpression('+', prop, t.literal(offset));
     parent.property = newExpr;
   }
-}
 
-function optimizeMemberExpressionStrict(node, parent, offset) {
-  // handle basic expressions specially (especially literals)
-  optimizeMemberExpression(node, parent, offset);
-  if (node.name === 'arguments') return;
-
-  var prop = parent.property;
-  node.name = 'arguments';
-  parent.property = t.binaryExpression('+', prop, t.literal(offset));
+  if (strictMode && node.name !== 'arguments') {
+    node.name = 'arguments';
+    parent.property = t.binaryExpression('+', prop, t.literal(offset));
+  }
 }
 
 var hasRest = function (node) {
@@ -98,10 +93,9 @@ exports.Function = function (node, parent, scope, file) {
   scope.traverse(node, memberExpressionVisitor, state);
 
   if (state.isOptimizable) {
-    var optimize = state.strictMode ? optimizeMemberExpressionStrict : optimizeMemberExpression;
     for (var i = 0, count = state.candidates.length; i < count; ++i) {
       var candidate = state.candidates[i];
-      optimize(candidate.node, candidate.parent, node.params.length);
+      optimizeMemberExpression(candidate.node, candidate.parent, node.params.length, state.strictMode);
     }
     return;
   }

From c5913564f8c1a3591a5323c63a77925a3e5942af Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 12:16:41 +0100
Subject: [PATCH 09/18] replace quotes to conform to coding style

---
 .../transformers/es6/parameters.rest.js        | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index a179e0d7f2..a464e996dd 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -19,7 +19,7 @@ var memberExpressionVisitor = {
     if (t.isMemberExpression(parent)) {
       var prop = parent.property;
       if (state.strictMode ||
-          typeof prop.value === 'number' ||
+          typeof prop.value === "number" ||
           t.isUnaryExpression(prop) ||
           t.isBinaryExpression(prop)) {
         state.candidates.push({ node: node, parent: parent });
@@ -37,22 +37,22 @@ function optimizeMemberExpression(node, parent, offset, strictMode) {
   var prop = parent.property;
 
   if (t.isLiteral(prop)) {
-    node.name = 'arguments';
+    node.name = "arguments";
     prop.value += offset;
     prop.raw = String(prop.value);
   } else if (t.isUnaryExpression(prop)) {
-    node.name = 'arguments';
-    newExpr = t.binaryExpression('+', prop, t.literal(offset));
+    node.name = "arguments";
+    newExpr = t.binaryExpression("+", prop, t.literal(offset));
     parent.property = newExpr;
   } else if (t.isBinaryExpression(prop)) {
-    node.name = 'arguments';
-    newExpr = t.binaryExpression('+', prop, t.literal(offset));
+    node.name = "arguments";
+    newExpr = t.binaryExpression("+", prop, t.literal(offset));
     parent.property = newExpr;
   }
 
-  if (strictMode && node.name !== 'arguments') {
-    node.name = 'arguments';
-    parent.property = t.binaryExpression('+', prop, t.literal(offset));
+  if (strictMode && node.name !== "arguments") {
+    node.name = "arguments";
+    parent.property = t.binaryExpression("+", prop, t.literal(offset));
   }
 }
 

From e8741daee317346cc454140f93a463ebb0de08b5 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 14:13:15 +0100
Subject: [PATCH 10/18] use some ES6 to simplify code

---
 .../transformation/transformers/es6/parameters.rest.js     | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index a464e996dd..34e5e52c6f 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -4,7 +4,7 @@ var t    = require("../../../types");
 exports.check = t.isRestElement;
 
 var memberExpressionVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (t.isScope(node, parent) && !scope.bindingIdentifierEquals(state.name, state.outerDeclar)) {
       return this.skip();
     }
@@ -22,7 +22,7 @@ var memberExpressionVisitor = {
           typeof prop.value === "number" ||
           t.isUnaryExpression(prop) ||
           t.isBinaryExpression(prop)) {
-        state.candidates.push({ node: node, parent: parent });
+        state.candidates.push({ node, parent });
         return;
       }
     }
@@ -93,8 +93,7 @@ exports.Function = function (node, parent, scope, file) {
   scope.traverse(node, memberExpressionVisitor, state);
 
   if (state.isOptimizable) {
-    for (var i = 0, count = state.candidates.length; i < count; ++i) {
-      var candidate = state.candidates[i];
+    for (let candidate of state.candidates) {
       optimizeMemberExpression(candidate.node, candidate.parent, node.params.length, state.strictMode);
     }
     return;

From edb880f87c7f4a5d466c4648db70a53ea71bf101 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 14:26:28 +0100
Subject: [PATCH 11/18] add tests

---
 .../arrow-functions/actual.js                 |  3 ++-
 .../arrow-functions/expected.js               |  7 ++---
 .../es6-parameters.rest/deopt/actual.js       | 15 +++++++++++
 .../es6-parameters.rest/deopt/expected.js     | 26 +++++++++++++++++++
 .../es6-parameters.rest/multiple/actual.js    |  8 ++++--
 .../es6-parameters.rest/multiple/expected.js  | 13 +++++-----
 .../es6-parameters.rest/pattern/actual.js     |  1 -
 .../es6-parameters.rest/pattern/expected.js   |  9 +++----
 .../es6-parameters.rest/single/actual.js      |  6 +++--
 .../es6-parameters.rest/single/expected.js    | 11 ++++----
 10 files changed, 72 insertions(+), 27 deletions(-)
 create mode 100644 test/fixtures/transformation/es6-parameters.rest/deopt/actual.js
 create mode 100644 test/fixtures/transformation/es6-parameters.rest/deopt/expected.js

diff --git a/test/fixtures/transformation/es6-parameters.rest/arrow-functions/actual.js b/test/fixtures/transformation/es6-parameters.rest/arrow-functions/actual.js
index 4a130fad8d..854274b1e6 100644
--- a/test/fixtures/transformation/es6-parameters.rest/arrow-functions/actual.js
+++ b/test/fixtures/transformation/es6-parameters.rest/arrow-functions/actual.js
@@ -1,3 +1,4 @@
 var concat = (...arrs) => {
-
+    var x = arrs[0];
+    var y = arrs[1];
 };
diff --git a/test/fixtures/transformation/es6-parameters.rest/arrow-functions/expected.js b/test/fixtures/transformation/es6-parameters.rest/arrow-functions/expected.js
index 4b72d8d4cf..96e011a7fc 100644
--- a/test/fixtures/transformation/es6-parameters.rest/arrow-functions/expected.js
+++ b/test/fixtures/transformation/es6-parameters.rest/arrow-functions/expected.js
@@ -1,7 +1,8 @@
 "use strict";
 
+var _arguments = arguments;
 var concat = function () {
-  for (var _len = arguments.length, arrs = Array(_len), _key = 0; _key < _len; _key++) {
-    arrs[_key] = arguments[_key];
-  }
+    var x = _arguments[0];
+    var y = _arguments[1];
 };
+
diff --git a/test/fixtures/transformation/es6-parameters.rest/deopt/actual.js b/test/fixtures/transformation/es6-parameters.rest/deopt/actual.js
new file mode 100644
index 0000000000..be0fc35ff7
--- /dev/null
+++ b/test/fixtures/transformation/es6-parameters.rest/deopt/actual.js
@@ -0,0 +1,15 @@
+var x = function (foo, ...bar) {
+  console.log(bar);
+};
+
+var y = function (foo, ...bar) {
+  var x = function z(bar) {
+    bar[1] = 5;
+  };
+};
+
+var z = function (foo, ...bar) {
+    var x = function () {
+        bar[1] = 5;
+    };
+};
diff --git a/test/fixtures/transformation/es6-parameters.rest/deopt/expected.js b/test/fixtures/transformation/es6-parameters.rest/deopt/expected.js
new file mode 100644
index 0000000000..28492a1560
--- /dev/null
+++ b/test/fixtures/transformation/es6-parameters.rest/deopt/expected.js
@@ -0,0 +1,26 @@
+"use strict";
+
+var x = function x(foo) {
+  for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+    bar[_key - 1] = arguments[_key];
+  }
+
+  console.log(bar);
+};
+
+var y = function y(foo) {
+  var x = function z(bar) {
+    bar[1] = 5;
+  };
+};
+
+var z = function z(foo) {
+  for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+    bar[_key - 1] = arguments[_key];
+  }
+
+  var x = function x() {
+    bar[1] = 5;
+  };
+};
+
diff --git a/test/fixtures/transformation/es6-parameters.rest/multiple/actual.js b/test/fixtures/transformation/es6-parameters.rest/multiple/actual.js
index 49d78b919e..59f2c222f8 100644
--- a/test/fixtures/transformation/es6-parameters.rest/multiple/actual.js
+++ b/test/fixtures/transformation/es6-parameters.rest/multiple/actual.js
@@ -1,7 +1,11 @@
 var t = function (f, ...items) {
-
+    var x = f;
+    x = items[0];
+    x = items[1];
 };
 
 function t(f, ...items) {
-
+    var x = f;
+    x = items[0];
+    x = items[1];
 }
diff --git a/test/fixtures/transformation/es6-parameters.rest/multiple/expected.js b/test/fixtures/transformation/es6-parameters.rest/multiple/expected.js
index 470cd17396..18fc23f505 100644
--- a/test/fixtures/transformation/es6-parameters.rest/multiple/expected.js
+++ b/test/fixtures/transformation/es6-parameters.rest/multiple/expected.js
@@ -1,13 +1,14 @@
 "use strict";
 
 var t = function t(f) {
-  for (var _len = arguments.length, items = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
-    items[_key - 1] = arguments[_key];
-  }
+    var x = f;
+    x = arguments[1];
+    x = arguments[2];
 };
 
 function t(f) {
-  for (var _len = arguments.length, items = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
-    items[_key - 1] = arguments[_key];
-  }
+    var x = f;
+    x = arguments[1];
+    x = arguments[2];
 }
+
diff --git a/test/fixtures/transformation/es6-parameters.rest/pattern/actual.js b/test/fixtures/transformation/es6-parameters.rest/pattern/actual.js
index 020ad4f8f7..d26dae5716 100644
--- a/test/fixtures/transformation/es6-parameters.rest/pattern/actual.js
+++ b/test/fixtures/transformation/es6-parameters.rest/pattern/actual.js
@@ -1,3 +1,2 @@
 var foo = function (...[a, b]) {
-
 };
diff --git a/test/fixtures/transformation/es6-parameters.rest/pattern/expected.js b/test/fixtures/transformation/es6-parameters.rest/pattern/expected.js
index b3f2634c07..a52993a722 100644
--- a/test/fixtures/transformation/es6-parameters.rest/pattern/expected.js
+++ b/test/fixtures/transformation/es6-parameters.rest/pattern/expected.js
@@ -1,10 +1,7 @@
 "use strict";
 
 var foo = function foo() {
-  for (var _len = arguments.length, _ref = Array(_len), _key = 0; _key < _len; _key++) {
-    _ref[_key] = arguments[_key];
-  }
-
-  var a = _ref[0];
-  var b = _ref[1];
+  var a = arguments[0],
+      b = arguments[1];
 };
+
diff --git a/test/fixtures/transformation/es6-parameters.rest/single/actual.js b/test/fixtures/transformation/es6-parameters.rest/single/actual.js
index dc9fbe391a..8e81076ecc 100644
--- a/test/fixtures/transformation/es6-parameters.rest/single/actual.js
+++ b/test/fixtures/transformation/es6-parameters.rest/single/actual.js
@@ -1,7 +1,9 @@
 var t = function (...items) {
-
+    var x = items[0];
+    var y = items[1];
 }
 
 function t(...items) {
-
+    var x = items[0];
+    var y = items[1];
 }
diff --git a/test/fixtures/transformation/es6-parameters.rest/single/expected.js b/test/fixtures/transformation/es6-parameters.rest/single/expected.js
index 101e2f256c..add403243b 100644
--- a/test/fixtures/transformation/es6-parameters.rest/single/expected.js
+++ b/test/fixtures/transformation/es6-parameters.rest/single/expected.js
@@ -1,13 +1,12 @@
 "use strict";
 
 var t = function t() {
-  for (var _len = arguments.length, items = Array(_len), _key = 0; _key < _len; _key++) {
-    items[_key] = arguments[_key];
-  }
+    var x = arguments[0];
+    var y = arguments[1];
 };
 
 function t() {
-  for (var _len = arguments.length, items = Array(_len), _key = 0; _key < _len; _key++) {
-    items[_key] = arguments[_key];
-  }
+    var x = arguments[0];
+    var y = arguments[1];
 }
+

From c3f4091b6d1c443a53a6c9a6458569e42e7e1153 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 14:41:20 +0100
Subject: [PATCH 12/18] replace for-of with with for for performance reasons

---
 src/babel/transformation/transformers/es6/parameters.rest.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 34e5e52c6f..88ff4733dd 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -93,7 +93,8 @@ exports.Function = function (node, parent, scope, file) {
   scope.traverse(node, memberExpressionVisitor, state);
 
   if (state.isOptimizable) {
-    for (let candidate of state.candidates) {
+    for (let i = 0, count = state.candidates.length; i < count; ++i) {
+      let candidate = state.candidates[i];
       optimizeMemberExpression(candidate.node, candidate.parent, node.params.length, state.strictMode);
     }
     return;

From a808742c1909bf3db76cd251a121cd3582c5e0aa Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 15:24:45 +0100
Subject: [PATCH 13/18] remove strict-mode specific optimizations due to
 unsolvable ambiguities

---
 .../transformers/es6/parameters.rest.js       | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 88ff4733dd..0c72a42529 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -18,8 +18,7 @@ var memberExpressionVisitor = {
 
     if (t.isMemberExpression(parent)) {
       var prop = parent.property;
-      if (state.strictMode ||
-          typeof prop.value === "number" ||
+      if (typeof prop.value === "number" ||
           t.isUnaryExpression(prop) ||
           t.isBinaryExpression(prop)) {
         state.candidates.push({ node, parent });
@@ -32,7 +31,7 @@ var memberExpressionVisitor = {
   }
 };
 
-function optimizeMemberExpression(node, parent, offset, strictMode) {
+function optimizeMemberExpression(node, parent, offset) {
   var newExpr;
   var prop = parent.property;
 
@@ -40,19 +39,10 @@ function optimizeMemberExpression(node, parent, offset, strictMode) {
     node.name = "arguments";
     prop.value += offset;
     prop.raw = String(prop.value);
-  } else if (t.isUnaryExpression(prop)) {
+  } else {
     node.name = "arguments";
     newExpr = t.binaryExpression("+", prop, t.literal(offset));
     parent.property = newExpr;
-  } else if (t.isBinaryExpression(prop)) {
-    node.name = "arguments";
-    newExpr = t.binaryExpression("+", prop, t.literal(offset));
-    parent.property = newExpr;
-  }
-
-  if (strictMode && node.name !== "arguments") {
-    node.name = "arguments";
-    parent.property = t.binaryExpression("+", prop, t.literal(offset));
   }
 }
 
@@ -87,8 +77,7 @@ exports.Function = function (node, parent, scope, file) {
     name: rest.name,
     outerDeclar: restOuterDeclar,
     isOptimizable: true,
-    candidates: [],
-    strictMode: file.transformers.useStrict.canRun()
+    candidates: []
   };
   scope.traverse(node, memberExpressionVisitor, state);
 

From e6855b974b23367d24f703345fe01104fd61cd24 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 15:30:22 +0100
Subject: [PATCH 14/18] update tests

---
 .../es6-parameters.rest/deopt/actual.js       |  9 ++++
 .../es6-parameters.rest/deopt/expected.js     | 43 +++++++++++++------
 2 files changed, 39 insertions(+), 13 deletions(-)

diff --git a/test/fixtures/transformation/es6-parameters.rest/deopt/actual.js b/test/fixtures/transformation/es6-parameters.rest/deopt/actual.js
index be0fc35ff7..f7eab07df8 100644
--- a/test/fixtures/transformation/es6-parameters.rest/deopt/actual.js
+++ b/test/fixtures/transformation/es6-parameters.rest/deopt/actual.js
@@ -13,3 +13,12 @@ var z = function (foo, ...bar) {
         bar[1] = 5;
     };
 };
+
+var a = function (foo, ...bar) {
+    return bar.join(',');
+};
+
+var b = function (foo, ...bar) {
+    var join = "join";
+    return bar[join];
+};
diff --git a/test/fixtures/transformation/es6-parameters.rest/deopt/expected.js b/test/fixtures/transformation/es6-parameters.rest/deopt/expected.js
index 28492a1560..389762d336 100644
--- a/test/fixtures/transformation/es6-parameters.rest/deopt/expected.js
+++ b/test/fixtures/transformation/es6-parameters.rest/deopt/expected.js
@@ -1,26 +1,43 @@
 "use strict";
 
 var x = function x(foo) {
-  for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
-    bar[_key - 1] = arguments[_key];
-  }
+    for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+        bar[_key - 1] = arguments[_key];
+    }
 
-  console.log(bar);
+    console.log(bar);
 };
 
 var y = function y(foo) {
-  var x = function z(bar) {
-    bar[1] = 5;
-  };
+    var x = function z(bar) {
+        bar[1] = 5;
+    };
 };
 
 var z = function z(foo) {
-  for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
-    bar[_key - 1] = arguments[_key];
-  }
+    for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+        bar[_key - 1] = arguments[_key];
+    }
 
-  var x = function x() {
-    bar[1] = 5;
-  };
+    var x = function x() {
+        bar[1] = 5;
+    };
+};
+
+var a = function a(foo) {
+    for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+        bar[_key - 1] = arguments[_key];
+    }
+
+    return bar.join(",");
+};
+
+var b = function b(foo) {
+    for (var _len = arguments.length, bar = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+        bar[_key - 1] = arguments[_key];
+    }
+
+    var join = "join";
+    return bar[join];
 };
 

From 687b0f31809fd1a450739a3e564f72a7a88f1b67 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Wed, 25 Feb 2015 15:38:32 +0100
Subject: [PATCH 15/18] remove unused function argument

---
 src/babel/transformation/transformers/es6/parameters.rest.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 0c72a42529..5954904f26 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -50,7 +50,7 @@ var hasRest = function (node) {
   return t.isRestElement(node.params[node.params.length - 1]);
 };
 
-exports.Function = function (node, parent, scope, file) {
+exports.Function = function (node, parent, scope) {
   if (!hasRest(node)) return;
 
   var rest = node.params.pop().argument;

From 24ace3c8c2508bb375ee364e069758f6bbb214c8 Mon Sep 17 00:00:00 2001
From: Jamund Ferguson <jamund@gmail.com>
Date: Wed, 25 Feb 2015 13:51:26 -0800
Subject: [PATCH 16/18] feat(6to5/register) don't override uncaughtException
 handler

Maybe we could do this by default or even make it configurable?
---
 src/babel/api/register/node.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/babel/api/register/node.js b/src/babel/api/register/node.js
index b89c6544b9..ec603c1dcd 100644
--- a/src/babel/api/register/node.js
+++ b/src/babel/api/register/node.js
@@ -10,6 +10,7 @@ var util             = require("../../util");
 var fs               = require("fs");
 
 sourceMapSupport.install({
+  handleUncaughtExceptions: false,
   retrieveSourceMap(source) {
     var map = maps && maps[source];
     if (map) {

From 5d83638583f89b735824010e20c20418ce3c69a2 Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Thu, 26 Feb 2015 01:22:00 +0100
Subject: [PATCH 17/18] set literal MemberExpression as computed in rest array
 destructuring

---
 src/babel/transformation/transformers/es6/parameters.rest.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 5954904f26..2c0d73827d 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -65,7 +65,7 @@ exports.Function = function (node, parent, scope) {
     var pattern = rest;
     rest = scope.generateUidIdentifier("ref");
     var declar = t.variableDeclaration("var", pattern.elements.map(function (elem, index) {
-      var accessExpr = t.memberExpression(rest, t.literal(index));
+      var accessExpr = t.memberExpression(rest, t.literal(index), true);
       return t.variableDeclarator(elem, accessExpr);
     }));
     node.body.body.unshift(declar);

From b5f3c3f4ccdb70d846f92925e4cc31b67d078c4b Mon Sep 17 00:00:00 2001
From: Ondrej Kraus <neverberlerfellerer@gmail.com>
Date: Thu, 26 Feb 2015 02:05:26 +0100
Subject: [PATCH 18/18] stop traversal when it is clear that optimization is
 impossible

---
 src/babel/transformation/transformers/es6/parameters.rest.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 2c0d73827d..230f429a03 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/src/babel/transformation/transformers/es6/parameters.rest.js
@@ -11,7 +11,7 @@ var memberExpressionVisitor = {
 
     if (t.isFunctionDeclaration(node) || t.isFunctionExpression(node)) {
       state.isOptimizable = false;
-      return this.skip();
+      return this.stop();
     }
 
     if (!t.isReferencedIdentifier(node, parent, { name: state.name })) return;