diff --git a/README.md b/README.md
index 2541e2f968e..aeea929dd5f 100644
--- a/README.md
+++ b/README.md
@@ -617,17 +617,17 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   the resultant code is shorter: `m(){return x}` becomes `m:()=>x`.
   This transform requires that the `ecma` compress option is set to `6` or greater.
 
-- `booleans` (default: `true`) -- various optimizations for boolean context, for example `!!a
-  ? b : c → a ? b : c`
+- `booleans` (default: `true`) -- various optimizations for boolean context,
+  for example `!!a ? b : c → a ? b : c`
 
-- `cascade` (default: `true`) -- small optimization for sequences, transform `x, x` into `x`
-  and `x = something(), x` into `x = something()`
+- `cascade` (default: `true`) -- small optimization for sequences, transform
+  `x, x` into `x` and `x = something(), x` into `x = something()`
 
-- `collapse_vars` (default: `true`) -- Collapse single-use non-constant variables - side
-  effects permitting.
+- `collapse_vars` (default: `true`) -- Collapse single-use non-constant variables,
+  side effects permitting.
 
-- `comparisons` (default: `true`) -- apply certain optimizations to binary nodes, for example:
-  `!(a <= b) → a > b` (only when `unsafe_comps`), attempts to negate binary
+- `comparisons` (default: `true`) -- apply certain optimizations to binary nodes,
+  e.g. `!(a <= b) → a > b` (only when `unsafe_comps`), attempts to negate binary
   nodes, e.g. `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc.
 
 - `computed_props` (default: `true`) -- Transforms constant computed properties
@@ -638,7 +638,7 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 
 - `dead_code` (default: `true`) -- remove unreachable code
 
-- `drop_console` (default: `false`) -- default `false`.  Pass `true` to discard calls to
+- `drop_console` (default: `false`) -- Pass `true` to discard calls to
   `console.*` functions. If you wish to drop a specific function call
   such as `console.info` and/or retain side effects from function arguments
   after dropping the function call then use `pure_funcs` instead.
@@ -650,14 +650,14 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 
 - `evaluate` (default: `true`) -- attempt to evaluate constant expressions
 
-- `expression` (default: `false`) -- default `false`.  Pass `true` to preserve completion values
+- `expression` (default: `false`) -- Pass `true` to preserve completion values
   from terminal statements without `return`, e.g. in bookmarklets.
 
 - `global_defs` (default: `{}`) -- see [conditional compilation](#conditional-compilation)
 
 - `hoist_funs` (default: `true`) -- hoist function declarations
 
-- `hoist_props` (default: `false`) -- hoist properties from constant object and
+- `hoist_props` (default: `true`) -- hoist properties from constant object and
   array literals into regular variables subject to a set of constraints. For example:
   `var o={p:1, q:2}; f(o.p, o.q);` is converted to `f(1, 2);`. Note: `hoist_props`
   works best with `mangle` enabled, the `compress` option `passes` set to `2` or higher,
@@ -676,19 +676,18 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   compressor from discarding class names.  See also: the `keep_classnames`
   [mangle option](#mangle).
 
-- `keep_fargs` (default: `true`) -- default `true`.  Prevents the
-  compressor from discarding unused function arguments.  You need this
-  for code which relies on `Function.length`.
+- `keep_fargs` (default: `true`) -- Prevents the compressor from discarding unused
+  function arguments.  You need this for code which relies on `Function.length`.
 
 - `keep_fnames` (default: `false`) -- Pass `true` to prevent the
   compressor from discarding function names.  Useful for code relying on
   `Function.prototype.name`. See also: the `keep_fnames` [mangle option](#mangle).
 
-- `keep_infinity` (default: `false`) -- default `false`. Pass `true` to prevent `Infinity` from
+- `keep_infinity` (default: `false`) -- Pass `true` to prevent `Infinity` from
   being compressed into `1/0`, which may cause performance issues on Chrome.
 
-- `loops` (default: `true`) -- optimizations for `do`, `while` and `for` loops when we can
-  statically determine the condition
+- `loops` (default: `true`) -- optimizations for `do`, `while` and `for` loops
+  when we can statically determine the condition.
 
 - `negate_iife` (default: `true`) -- negate "Immediately-Called Function Expressions"
   where the return value is discarded, to avoid the parens that the
@@ -719,11 +718,11 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   `foo` is certain to not throw, i.e. not `null` or `undefined`.
 
 - `reduce_funcs` (default: `true`) -- Allows single-use functions to be
-  inlined as function expressions when permissible allowing further 
-  optimization.  Enabled by default.  Option depends on `reduce_vars` 
-  being enabled.  Some code runs faster in the Chrome V8 engine if this 
+  inlined as function expressions when permissible allowing further
+  optimization.  Enabled by default.  Option depends on `reduce_vars`
+  being enabled.  Some code runs faster in the Chrome V8 engine if this
   option is disabled.  Does not negatively impact other major browsers.
-  
+
 - `reduce_vars` (default: `true`) -- Improve optimization on variables assigned with and
   used as constant values.
 
@@ -736,21 +735,22 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   occasions the default sequences limit leads to very slow compress times in which
   case a value of `20` or less is recommended.
 
-- `side_effects` (default: `true`) -- default `true`. Pass `false` to disable potentially dropping
+- `side_effects` (default: `true`) -- Pass `false` to disable potentially dropping
   functions marked as "pure".  A function call is marked as "pure" if a comment
   annotation `/*@__PURE__*/` or `/*#__PURE__*/` immediately precedes the call. For
   example: `/*@__PURE__*/foo();`
 
 - `switches` (default: `true`) -- de-duplicate and remove unreachable `switch` branches
 
-- `toplevel` (default: `false`) -- drop unreferenced functions (`"funcs"`) and/or variables (`"vars"`)
-  in the top level scope (`false` by default, `true` to drop both unreferenced
-  functions and variables)
+- `toplevel` (default: `false`) -- drop unreferenced functions (`"funcs"`) and/or
+  variables (`"vars"`) in the top level scope (`false` by default, `true` to drop
+  both unreferenced functions and variables)
 
-- `top_retain` (default: `null`) -- prevent specific toplevel functions and variables from `unused`
-  removal (can be array, comma-separated, RegExp or function. Implies `toplevel`)
+- `top_retain` (default: `null`) -- prevent specific toplevel functions and
+  variables from `unused` removal (can be array, comma-separated, RegExp or
+  function. Implies `toplevel`)
 
-- `typeofs` (default: `true`) -- default `true`.  Transforms `typeof foo == "undefined"` into
+- `typeofs` (default: `true`) -- Transforms `typeof foo == "undefined"` into
   `foo === void 0`.  Note: recommend to set this value to `false` for IE10 and
   earlier versions due to known issues.
 
@@ -788,31 +788,31 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 - `unsafe_regexp` (default: `false`) -- enable substitutions of variables with
   `RegExp` values the same way as if they are constants.
 
-- `unused` (default: `true`) -- drop unreferenced functions and variables (simple direct variable
-  assignments do not count as references unless set to `"keep_assign"`)
+- `unused` (default: `true`) -- drop unreferenced functions and variables (simple
+  direct variable assignments do not count as references unless set to `"keep_assign"`)
 
-- `warnings` (default: `false`) -- display warnings when dropping unreachable code or unused
-  declarations etc.
+- `warnings` (default: `false`) -- display warnings when dropping unreachable
+  code or unused declarations etc.
 
 ## Mangle options
 
-- `eval` (default `false`). Pass `true` to mangle names visible in scopes
+- `eval` (default `false`) -- Pass `true` to mangle names visible in scopes
   where `eval` or `with` are used.
 
-- `keep_classnames` (default `false`).  Pass `true` to not mangle class names.
+- `keep_classnames` (default `false`) -- Pass `true` to not mangle class names.
   See also: the `keep_classnames` [compress option](#compress-options).
 
-- `keep_fnames` (default `false`).  Pass `true` to not mangle function names.
+- `keep_fnames` (default `false`) -- Pass `true` to not mangle function names.
   Useful for code relying on `Function.prototype.name`. See also: the `keep_fnames`
   [compress option](#compress-options).
 
-- `reserved` (default `[]`). Pass an array of identifiers that should be
+- `reserved` (default `[]`) -- Pass an array of identifiers that should be
   excluded from mangling. Example: `["foo", "bar"]`.
 
-- `toplevel` (default `false`). Pass `true` to mangle names declared in the
+- `toplevel` (default `false`) -- Pass `true` to mangle names declared in the
   top level scope.
 
-- `safari10` (default `false`). Pass `true` to work around the Safari 10 loop
+- `safari10` (default `false`) -- Pass `true` to work around the Safari 10 loop
   iterator [bug](https://bugs.webkit.org/show_bug.cgi?id=171041)
   "Cannot declare a let variable twice".
 
diff --git a/bin/uglifyjs b/bin/uglifyjs
index e6d5c20b9c4..867df606fe6 100755
--- a/bin/uglifyjs
+++ b/bin/uglifyjs
@@ -49,6 +49,7 @@ program.option("--ie8", "Support non-standard Internet Explorer 8.");
 program.option("--keep-classnames", "Do not mangle/drop class names.");
 program.option("--keep-fnames", "Do not mangle/drop function names. Useful for code relying on Function.prototype.name.");
 program.option("--name-cache <file>", "File to hold mangled name mappings.");
+program.option("--no-rename", "Disable symbol expansion.");
 program.option("--self", "Build UglifyJS as a library (implies --wrap UglifyJS)");
 program.option("--source-map [options]", "Enable source map/specify source map options.", parse_source_map());
 program.option("--timings", "Display operations run time on STDERR.")
@@ -67,11 +68,13 @@ if (!program.output && program.sourceMap && program.sourceMap.url != "inline") {
     "compress",
     "ie8",
     "mangle",
+    "rename",
     "sourceMap",
     "toplevel",
     "wrap"
 ].forEach(function(name) {
     if (name in program) {
+        if (name == "rename" && program[name]) return;
         options[name] = program[name];
     }
 });
diff --git a/lib/compress.js b/lib/compress.js
index 48816ff7a93..b1f063f5e1a 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -63,7 +63,7 @@ function Compressor(options, false_by_default) {
         expression    : false,
         global_defs   : {},
         hoist_funs    : !false_by_default,
-        hoist_props   : false,
+        hoist_props   : !false_by_default,
         hoist_vars    : false,
         ie8           : false,
         if_return     : !false_by_default,
@@ -341,7 +341,7 @@ merge(Compressor.prototype, {
                             }
                         }
                     }
-                    mark_escaped(d, node, value, 0);
+                    mark_escaped(d, node.scope, node, value, 0);
                 }
                 if (node instanceof AST_SymbolCatch) {
                     node.definition().fixed = false;
@@ -627,7 +627,8 @@ merge(Compressor.prototype, {
                 || !immutable
                     && parent instanceof AST_Call
                     && parent.expression === node
-                    && (!(value instanceof AST_Function) || value.contains_this(parent))) {
+                    && (!(value instanceof AST_Function)
+                        || !(parent instanceof AST_New) && value.contains_this())) {
                 return true;
             } else if (parent instanceof AST_Array) {
                 return is_modified(parent, parent, level + 1);
@@ -639,10 +640,13 @@ merge(Compressor.prototype, {
             }
         }
 
-        function mark_escaped(d, node, value, level) {
+        function mark_escaped(d, scope, node, value, level) {
             var parent = tw.parent(level);
-            if (value instanceof AST_Constant || value instanceof AST_ClassExpression) return;
-            if (level > 0 && value instanceof AST_Function) return;
+            if (value) {
+                if (value.is_constant()) return;
+                if (value instanceof AST_ClassExpression) return;
+                if (level > 0 && value.is_constant_expression(scope)) return;
+            }
             if (parent instanceof AST_Assign && parent.operator == "=" && node === parent.right
                 || parent instanceof AST_Call && node !== parent.expression
                 || parent instanceof AST_Return && node === parent.value && node.scope !== d.scope
@@ -650,13 +654,13 @@ merge(Compressor.prototype, {
                 d.escaped = true;
                 return;
             } else if (parent instanceof AST_Array) {
-                mark_escaped(d, parent, parent, level + 1);
+                mark_escaped(d, scope, parent, parent, level + 1);
             } else if (parent instanceof AST_ObjectKeyVal && node === parent.value) {
                 var obj = tw.parent(level + 1);
-                mark_escaped(d, obj, obj, level + 2);
+                mark_escaped(d, scope, obj, obj, level + 2);
             } else if (parent instanceof AST_PropAccess && node === parent.expression) {
                 value = read_property(value, parent.property);
-                mark_escaped(d, parent, value, level + 1);
+                mark_escaped(d, scope, parent, value, level + 1);
                 if (value) return;
             }
             if (level == 0) d.direct_access = true;
@@ -845,6 +849,12 @@ merge(Compressor.prototype, {
         }
     }
 
+    function is_identifier_atom(node) {
+        return node instanceof AST_Infinity
+            || node instanceof AST_NaN
+            || node instanceof AST_Undefined;
+    }
+
     function tighten_body(statements, compressor) {
         var CHANGED, max_iter = 10;
         do {
@@ -911,7 +921,7 @@ merge(Compressor.prototype, {
                     && !(node instanceof AST_SymbolDeclaration)
                     && lhs.equivalent_to(node)) {
                     if (is_lhs(node, parent)) {
-                        if (candidate.multiple) replaced++;
+                        if (value_def) replaced++;
                         return node;
                     }
                     CHANGED = abort = true;
@@ -926,19 +936,24 @@ merge(Compressor.prototype, {
                         return make_node(AST_UnaryPrefix, candidate, candidate);
                     }
                     if (candidate instanceof AST_VarDef) {
-                        if (candidate.multiple) {
+                        if (value_def) {
                             abort = false;
                             return node;
                         }
                         var def = candidate.name.definition();
+                        var value = candidate.value;
                         if (def.references.length - def.replaced == 1 && !compressor.exposed(def)) {
                             def.replaced++;
-                            return maintain_this_binding(parent, node, candidate.value);
+                            if (funarg && is_identifier_atom(value)) {
+                                return value.transform(compressor);
+                            } else {
+                                return maintain_this_binding(parent, node, value);
+                            }
                         }
                         return make_node(AST_Assign, candidate, {
                             operator: "=",
                             left: make_node(AST_SymbolRef, candidate.name, candidate.name),
-                            right: candidate.value
+                            right: value
                         });
                     }
                     candidate.write_only = false;
@@ -1000,18 +1015,20 @@ merge(Compressor.prototype, {
                 extract_candidates(statements[stat_index]);
                 while (candidates.length > 0) {
                     var candidate = candidates.pop();
+                    var value_def = null;
                     var lhs = get_lhs(candidate);
                     if (!lhs || is_lhs_read_only(lhs) || lhs.has_side_effects(compressor)) continue;
                     // Locate symbols which may execute code outside of scanning range
                     var lvalues = get_lvalues(candidate);
                     if (lhs instanceof AST_SymbolRef) lvalues[lhs.name] = false;
-                    var replace_all = candidate.multiple;
+                    var replace_all = value_def;
                     if (!replace_all && lhs instanceof AST_SymbolRef) {
                         var def = lhs.definition();
                         replace_all = def.references.length - def.replaced == 1;
                     }
                     var side_effects = value_has_side_effects(candidate);
-                    var hit = candidate.name instanceof AST_SymbolFunarg;
+                    var funarg = candidate.name instanceof AST_SymbolFunarg;
+                    var hit = funarg;
                     var abort = false, replaced = 0, can_replace = !args || !hit;
                     if (!can_replace) {
                         for (var j = compressor.self().argnames.lastIndexOf(candidate.name) + 1; !abort && j < args.length; j++) {
@@ -1022,13 +1039,12 @@ merge(Compressor.prototype, {
                     for (var i = stat_index; !abort && i < statements.length; i++) {
                         statements[i].transform(scanner);
                     }
-                    if (candidate.multiple) {
+                    if (value_def) {
                         var def = candidate.name.definition();
                         if (abort && def.references.length - def.replaced > replaced) replaced = false;
                         else {
                             abort = false;
-                            hit = candidate.name instanceof AST_SymbolFunarg;
-                            var value_def = candidate.value.definition();
+                            hit = funarg;
                             for (var i = stat_index; !abort && i < statements.length; i++) {
                                 statements[i].transform(multi_replacer);
                             }
@@ -1131,13 +1147,13 @@ merge(Compressor.prototype, {
                 }
             }
 
-            function mangleable_var(expr) {
-                var value = expr.value;
-                if (!(value instanceof AST_SymbolRef)) return false;
-                if (value.name == "arguments") return false;
-                if (value.definition().undeclared) return false;
-                expr.multiple = true;
-                return true;
+            function mangleable_var(var_def) {
+                var value = var_def.value;
+                if (!(value instanceof AST_SymbolRef)) return;
+                if (value.name == "arguments") return;
+                var def = value.definition();
+                if (def.undeclared) return;
+                return value_def = def;
             }
 
             function get_lhs(expr) {
@@ -4062,9 +4078,7 @@ merge(Compressor.prototype, {
         if (self.operator == "delete"
             && !(e instanceof AST_SymbolRef
                 || e instanceof AST_PropAccess
-                || e instanceof AST_NaN
-                || e instanceof AST_Infinity
-                || e instanceof AST_Undefined)) {
+                || is_identifier_atom(e))) {
             if (e instanceof AST_Sequence) {
                 e = e.expressions.slice();
                 e.push(make_node(AST_True, self));
@@ -4972,6 +4986,17 @@ merge(Compressor.prototype, {
         if (compressor.option("properties")) {
             var key = prop.evaluate(compressor);
             if (key !== prop) {
+                if (typeof key == "string") {
+                    if (key == "undefined") {
+                        key = undefined;
+                    } else {
+                        var value = parseFloat(key);
+                        if (value.toString() == key) {
+                            key = value;
+                        }
+                    }
+                }
+                prop = self.property = best_of_expression(prop, make_node_from_constant(key, prop).transform(compressor));
                 var property = "" + key;
                 if (is_identifier_string(property)
                     && property.length <= prop.print_to_string().length + 1) {
@@ -4980,14 +5005,6 @@ merge(Compressor.prototype, {
                         property: property
                     }).optimize(compressor);
                 }
-                if (!(prop instanceof AST_Number)) {
-                    var value = parseFloat(property);
-                    if (value.toString() == property) {
-                        prop = self.property = make_node(AST_Number, prop, {
-                            value: value
-                        });
-                    }
-                }
             }
         }
         if (is_lhs(self, compressor.parent())) return self;
@@ -5044,8 +5061,7 @@ merge(Compressor.prototype, {
         return self;
     });
 
-    AST_Lambda.DEFMETHOD("contains_this", function(grandparent) {
-        if (grandparent instanceof AST_New) return false;
+    AST_Lambda.DEFMETHOD("contains_this", function() {
         var result;
         var self = this;
         self.walk(new TreeWalker(function(node) {
@@ -5071,7 +5087,8 @@ merge(Compressor.prototype, {
                     })) break;
                     var value = prop.value;
                     if ((value instanceof AST_Accessor || value instanceof AST_Function)
-                        && value.contains_this(compressor.parent())) break;
+                        && !(compressor.parent() instanceof AST_New)
+                        && value.contains_this()) break;
                     return make_node(AST_Sub, this, {
                         expression: make_node(AST_Array, expr, {
                             elements: props.map(function(prop) {
diff --git a/lib/minify.js b/lib/minify.js
index 2ac6afd642f..0fd6e1dc2c7 100644
--- a/lib/minify.js
+++ b/lib/minify.js
@@ -57,6 +57,7 @@ function minify(files, options) {
             nameCache: null,
             output: {},
             parse: {},
+            rename: undefined,
             sourceMap: false,
             timings: false,
             toplevel: false,
@@ -69,6 +70,9 @@ function minify(files, options) {
         if (options.keep_classnames === undefined) {
             options.keep_classnames = options.keep_fnames;
         }
+        if (options.rename === undefined) {
+            options.rename = options.compress && options.mangle;
+        }
         set_shorthand("ecma", options, [ "parse", "compress", "output" ]);
         set_shorthand("ie8", options, [ "compress", "mangle", "output" ]);
         set_shorthand("keep_classnames", options, [ "compress", "mangle" ]);
@@ -146,6 +150,11 @@ function minify(files, options) {
         if (options.wrap) {
             toplevel = toplevel.wrap_commonjs(options.wrap);
         }
+        if (timings) timings.rename = Date.now();
+        if (options.rename) {
+            toplevel.figure_out_scope(options.mangle);
+            toplevel.expand_names(options.mangle);
+        }
         if (timings) timings.compress = Date.now();
         if (options.compress) toplevel = new Compressor(options.compress).compress(toplevel);
         if (timings) timings.scope = Date.now();
@@ -206,7 +215,8 @@ function minify(files, options) {
         if (timings) {
             timings.end = Date.now();
             result.timings = {
-                parse: 1e-3 * (timings.compress - timings.parse),
+                parse: 1e-3 * (timings.rename - timings.parse),
+                rename: 1e-3 * (timings.compress - timings.rename),
                 compress: 1e-3 * (timings.scope - timings.compress),
                 scope: 1e-3 * (timings.mangle - timings.scope),
                 mangle: 1e-3 * (timings.properties - timings.mangle),
diff --git a/lib/scope.js b/lib/scope.js
index 224082024db..40ab844500e 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -43,7 +43,7 @@
 
 "use strict";
 
-function SymbolDef(scope, index, orig) {
+function SymbolDef(scope, orig) {
     this.name = orig.name;
     this.orig = [ orig ];
     this.eliminated = 0;
@@ -54,7 +54,6 @@ function SymbolDef(scope, index, orig) {
     this.export = false;
     this.mangled_name = null;
     this.undeclared = false;
-    this.index = index;
     this.id = SymbolDef.next_id++;
 };
 
@@ -346,7 +345,7 @@ AST_Toplevel.DEFMETHOD("def_global", function(node){
     if (globals.has(name)) {
         return globals.get(name);
     } else {
-        var g = new SymbolDef(this, globals.size(), node);
+        var g = new SymbolDef(this, node);
         g.undeclared = true;
         g.global = true;
         globals.set(name, g);
@@ -417,7 +416,7 @@ AST_Scope.DEFMETHOD("def_function", function(symbol){
 AST_Scope.DEFMETHOD("def_variable", function(symbol){
     var def;
     if (!this.variables.has(symbol.name)) {
-        def = new SymbolDef(this, this.variables.size(), symbol);
+        def = new SymbolDef(this, symbol);
         this.variables.set(symbol.name, def);
         def.global = !this.parent_scope;
     } else {
@@ -435,7 +434,7 @@ AST_Scope.DEFMETHOD("next_mangled", function(options){
 
         // https://github.com/mishoo/UglifyJS2/issues/242 -- do not
         // shadow a name reserved from mangling.
-        if (options.reserved.indexOf(m) >= 0) continue;
+        if (member(m, options.reserved)) continue;
 
         // we must ensure that the mangled name does not shadow a name
         // from some parent scope that is referenced in this or in
@@ -487,7 +486,7 @@ AST_Symbol.DEFMETHOD("global", function(){
     return this.definition().global;
 });
 
-AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options){
+AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options) {
     options = defaults(options, {
         eval        : false,
         ie8         : false,
@@ -497,15 +496,14 @@ AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options){
         toplevel    : false,
     });
     if (!Array.isArray(options.reserved)) options.reserved = [];
+    // Never mangle arguments
+    push_uniq(options.reserved, "arguments");
     return options;
 });
 
 AST_Toplevel.DEFMETHOD("mangle_names", function(options){
     options = this._default_mangler_options(options);
 
-    // Never mangle arguments
-    options.reserved.push('arguments');
-
     // We only need to mangle declaration nodes.  Special logic wired
     // into the code generator will display the mangled name if it's
     // present (and for AST_SymbolRef-s it'll use the mangled name of
@@ -514,11 +512,7 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
     var to_mangle = [];
 
     if (options.cache) {
-        this.globals.each(function(symbol){
-            if (options.reserved.indexOf(symbol.name) < 0) {
-                to_mangle.push(symbol);
-            }
-        });
+        this.globals.each(collect);
     }
 
     var tw = new TreeWalker(function(node, descend){
@@ -530,13 +524,7 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
             return true;        // don't descend again in TreeWalker
         }
         if (node instanceof AST_Scope) {
-            var p = tw.parent(), a = [];
-            node.variables.each(function(symbol){
-                if (options.reserved.indexOf(symbol.name) < 0) {
-                    a.push(symbol);
-                }
-            });
-            to_mangle.push.apply(to_mangle, a);
+            node.variables.each(collect);
             return;
         }
         if (node instanceof AST_Label) {
@@ -561,6 +549,74 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
     if (options.cache) {
         options.cache.cname = this.cname;
     }
+
+    function collect(symbol) {
+        if (!member(symbol.name, options.reserved)) {
+            to_mangle.push(symbol);
+        }
+    }
+});
+
+AST_Toplevel.DEFMETHOD("find_unique_prefix", function(options) {
+    var letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_";
+    var cache = options.cache && options.cache.props;
+    var prefixes = Object.create(null);
+    options.reserved.forEach(add_prefix);
+    this.globals.each(add_def);
+    this.walk(new TreeWalker(function(node) {
+        if (node instanceof AST_Scope) node.variables.each(add_def);
+        if (node instanceof AST_SymbolCatch) add_def(node.definition());
+    }));
+    var prefix, i = 0;
+    do {
+        prefix = create_name(i++);
+    } while (prefixes[prefix]);
+    return prefix;
+
+    function add_prefix(name) {
+        if (/[0-9]$/.test(name)) {
+            prefixes[name.replace(/[0-9]+$/, "")] = true;
+        }
+    }
+
+    function add_def(def) {
+        var name = def.name;
+        if (def.global && cache && cache.has(name)) name = cache.get(name);
+        else if (!def.unmangleable(options)) return;
+        add_prefix(name);
+    }
+
+    function create_name(num) {
+        var name = "";
+        do {
+            name += letters[num % letters.length];
+            num = Math.floor(num / letters.length);
+        } while (num);
+        return name;
+    }
+});
+
+AST_Toplevel.DEFMETHOD("expand_names", function(options) {
+    options = this._default_mangler_options(options);
+    var prefix = this.find_unique_prefix(options);
+    this.globals.each(rename);
+    this.walk(new TreeWalker(function(node) {
+        if (node instanceof AST_Scope) node.variables.each(rename);
+        if (node instanceof AST_SymbolCatch) rename(node.definition());
+    }));
+
+    function rename(def) {
+        if (def.global || def.unmangleable(options)) return;
+        if (member(def.name, options.reserved)) return;
+        var d = def.redefined();
+        def.name = d ? d.name : prefix + def.id;
+        def.orig.forEach(function(sym) {
+            sym.name = def.name;
+        });
+        def.references.forEach(function(sym) {
+            sym.name = def.name;
+        });
+    }
 });
 
 AST_Toplevel.DEFMETHOD("compute_char_frequency", function(options){
diff --git a/package.json b/package.json
index 385d866d7db..6599d355c23 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "homepage": "https://github.com/mishoo/UglifyJS2/tree/harmony",
   "author": "Mihai Bazon <mihai.bazon@gmail.com> (http://lisperator.net/)",
   "license": "BSD-2-Clause",
-  "version": "3.1.10",
+  "version": "3.2.0",
   "engines": {
     "node": ">=0.8.0"
   },
@@ -26,11 +26,11 @@
     "LICENSE"
   ],
   "dependencies": {
-    "commander": "~2.11.0",
+    "commander": "~2.12.1",
     "source-map": "~0.6.1"
   },
   "devDependencies": {
-    "acorn": "~5.1.1",
+    "acorn": "~5.2.1",
     "mocha": "~3.5.1",
     "semver": "~5.4.1"
   },
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 433ae9f2c2e..d44f5910aa4 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -3880,3 +3880,81 @@ issue_2436_14: {
     }
     expect_stdout: true
 }
+
+issue_2497: {
+    options = {
+        collapse_vars: true,
+        unused: true,
+    }
+    input: {
+        function sample() {
+            if (true) {
+                for (var i = 0; i < 1; ++i) {
+                    for (var k = 0; k < 1; ++k) {
+                        var value = 1;
+                        var x = value;
+                        value = x ? x + 1 : 0;
+                    }
+                }
+            } else {
+                for (var i = 0; i < 1; ++i) {
+                    for (var k = 0; k < 1; ++k) {
+                        var value = 1;
+                    }
+                }
+            }
+        }
+    }
+    expect: {
+        function sample() {
+            if (true)
+                for (i = 0; i < 1; ++i)
+                    for (k = 0; k < 1; ++k) {
+                        value = 1;
+                        value = value ? value + 1 : 0;
+                    }
+            else
+                for (var i = 0; i < 1; ++i)
+                    for (var k = 0; k < 1; ++k)
+                        var value=1;
+        }
+    }
+}
+
+issue_2506: {
+    options = {
+        collapse_vars: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        var c = 0;
+        function f0(bar) {
+            function f1(Infinity_2) {
+                function f13(NaN) {
+                    if (false <= NaN & this >> 1 >= 0) {
+                        c++;
+                    }
+                }
+                var b_2 = f13(NaN, c++);
+            }
+            var bar = f1(-3, -1);
+        }
+        f0(false);
+        console.log(c);
+    }
+    expect: {
+        var c = 0;
+        function f0(bar) {
+            (function(Infinity_2) {
+                (function(NaN) {
+                    if (false <= 0/0 & this >> 1 >= 0)
+                        c++;
+                })(0, c++);
+            })();
+        }
+        f0(false);
+        console.log(c);
+    }
+    expect_stdout: "1"
+}
diff --git a/test/compress/hoist_props.js b/test/compress/hoist_props.js
index e5f129a4722..94c8d986884 100644
--- a/test/compress/hoist_props.js
+++ b/test/compress/hoist_props.js
@@ -639,3 +639,136 @@ issue_2473_4: {
     }
     expect_stdout: "1 2"
 }
+
+issue_2508_1: {
+    options = {
+        collapse_vars: true,
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = {
+            a: [ 1 ],
+            f: function(x) {
+                console.log(x);
+            }
+        };
+        o.f(o.a);
+    }
+    expect: {
+        (function(x) {
+            console.log(x);
+        })([ 1 ]);
+    }
+    expect_stdout: true
+}
+
+issue_2508_2: {
+    options = {
+        collapse_vars: true,
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = {
+            a: { b: 2 },
+            f: function(x) {
+                console.log(x);
+            }
+        };
+        o.f(o.a);
+    }
+    expect: {
+        (function(x) {
+            console.log(x);
+        })({ b: 2 });
+    }
+    expect_stdout: true
+}
+
+issue_2508_3: {
+    options = {
+        collapse_vars: true,
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = {
+            a: [ o ],
+            f: function(x) {
+                console.log(x);
+            }
+        };
+        o.f(o.a);
+    }
+    expect: {
+        var o = {
+            a: [ o ],
+            f: function(x) {
+                console.log(x);
+            }
+        };
+        o.f(o.a);
+    }
+    expect_stdout: true
+}
+
+issue_2508_4: {
+    options = {
+        collapse_vars: true,
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = {
+            a: { b: o },
+            f: function(x) {
+                console.log(x);
+            }
+        };
+        o.f(o.a);
+    }
+    expect: {
+        var o = {
+            a: { b: o },
+            f: function(x) {
+                console.log(x);
+            }
+        };
+        o.f(o.a);
+    }
+    expect_stdout: true
+}
+
+issue_2508_5: {
+    options = {
+        collapse_vars: true,
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = {
+            f: function(x) {
+                console.log(x);
+            }
+        };
+        o.f(o.f);
+    }
+    expect: {
+        var o_f = function(x) {
+            console.log(x);
+        };
+        o_f(o_f);
+    }
+    expect_stdout: true
+}
diff --git a/test/compress/properties.js b/test/compress/properties.js
index e252d4956af..61d15e23de4 100644
--- a/test/compress/properties.js
+++ b/test/compress/properties.js
@@ -1305,3 +1305,29 @@ new_this: {
         }(42);
     }
 }
+
+issue_2513: {
+    options = {
+        evaluate: true,
+        properties: true,
+    }
+    input: {
+        !function(Infinity, NaN, undefined) {
+            console.log("a"[1/0], "b"["Infinity"]);
+            console.log("c"[0/0], "d"["NaN"]);
+            console.log("e"[void 0], "f"["undefined"]);
+        }(0, 0, 0);
+    }
+    expect: {
+        !function(Infinity, NaN, undefined) {
+            console.log("a"[1/0], "b"[1/0]);
+            console.log("c".NaN, "d".NaN);
+            console.log("e"[void 0], "f"[void 0]);
+        }(0, 0, 0);
+    }
+    expect_stdout: [
+        "undefined undefined",
+        "undefined undefined",
+        "undefined undefined",
+    ]
+}
diff --git a/test/compress/rename.js b/test/compress/rename.js
new file mode 100644
index 00000000000..defc6cf5653
--- /dev/null
+++ b/test/compress/rename.js
@@ -0,0 +1,536 @@
+mangle_catch: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: false,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var a="FAIL";try{throw 1}catch(o){a="PASS"}console.log(a);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_ie8: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: false,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var a="FAIL";try{throw 1}catch(args){a="PASS"}console.log(a);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_var: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: false,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            var a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var a="FAIL";try{throw 1}catch(o){var a="PASS"}console.log(a);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_var_ie8: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: false,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            var a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var a="FAIL";try{throw 1}catch(args){var a="PASS"}console.log(a);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_toplevel: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: true,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var o="FAIL";try{throw 1}catch(c){o="PASS"}console.log(o);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_ie8_toplevel: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: true,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var o="FAIL";try{throw 1}catch(c){o="PASS"}console.log(o);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_var_toplevel: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: true,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            var a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var o="FAIL";try{throw 1}catch(r){var o="PASS"}console.log(o);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_var_ie8_toplevel: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: true,
+    }
+    input: {
+        var a = "FAIL";
+        try {
+            throw 1;
+        } catch (args) {
+            var a = "PASS";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var o="FAIL";try{throw 1}catch(r){var o="PASS"}console.log(o);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_redef_1: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: false,
+    }
+    input: {
+        var a = "PASS";
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var a="PASS";try{throw"FAIL1"}catch(a){var a="FAIL2"}console.log(a);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_redef_1_ie8: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: false,
+    }
+    input: {
+        var a = "PASS";
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var a="PASS";try{throw"FAIL1"}catch(a){var a="FAIL2"}console.log(a);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_redef_1_toplevel: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: true,
+    }
+    input: {
+        var a = "PASS";
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var o="PASS";try{throw"FAIL1"}catch(o){var o="FAIL2"}console.log(o);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_redef_1_ie8_toplevel: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: true,
+    }
+    input: {
+        var a = "PASS";
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'var o="PASS";try{throw"FAIL1"}catch(o){var o="FAIL2"}console.log(o);'
+    expect_stdout: "PASS"
+}
+
+mangle_catch_redef_2: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: false,
+    }
+    input: {
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'try{throw"FAIL1"}catch(a){var a="FAIL2"}console.log(a);'
+    expect_stdout: "undefined"
+}
+
+mangle_catch_redef_2_ie8: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: false,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: false,
+    }
+    input: {
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'try{throw"FAIL1"}catch(a){var a="FAIL2"}console.log(a);'
+    expect_stdout: "undefined"
+}
+
+mangle_catch_redef_2_toplevel: {
+    rename = true
+    options = {
+        ie8: false,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: false,
+        toplevel: true,
+    }
+    input: {
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'try{throw"FAIL1"}catch(o){var o="FAIL2"}console.log(o);'
+    expect_stdout: "undefined"
+}
+
+mangle_catch_redef_2_ie8_toplevel: {
+    rename = true
+    options = {
+        ie8: true,
+        toplevel: true,
+    }
+    mangle = {
+        ie8: true,
+        toplevel: true,
+    }
+    input: {
+        try {
+            throw "FAIL1";
+        } catch (a) {
+            var a = "FAIL2";
+        }
+        console.log(a);
+    }
+    expect_exact: 'try{throw"FAIL1"}catch(o){var o="FAIL2"}console.log(o);'
+    expect_stdout: "undefined"
+}
+
+issue_2120_1: {
+    rename = true
+    mangle = {
+        ie8: false,
+    }
+    input: {
+        "aaaaaaaa";
+        var a = 1, b = "FAIL";
+        try {
+            throw 1;
+        } catch (c) {
+            try {
+                throw 0;
+            } catch (a) {
+                if (c) b = "PASS";
+            }
+        }
+        console.log(b);
+    }
+    expect: {
+        "aaaaaaaa";
+        var a = 1, b = "FAIL";
+        try {
+            throw 1;
+        } catch (t) {
+            try {
+                throw 0;
+            } catch (a) {
+                if (t) b = "PASS";
+            }
+        }
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_2120_2: {
+    rename = true
+    mangle = {
+        ie8: true,
+    }
+    input: {
+        "aaaaaaaa";
+        var a = 1, b = "FAIL";
+        try {
+            throw 1;
+        } catch (c) {
+            try {
+                throw 0;
+            } catch (a) {
+                if (c) b = "PASS";
+            }
+        }
+        console.log(b);
+    }
+    expect: {
+        "aaaaaaaa";
+        var a = 1, b = "FAIL";
+        try {
+            throw 1;
+        } catch (c) {
+            try {
+                throw 0;
+            } catch (a) {
+                if (c) b = "PASS";
+            }
+        }
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}
+function_iife_catch: {
+    rename = true
+    mangle = {
+        ie8: false,
+    }
+    input: {
+        function f(n) {
+            !function() {
+                try {
+                    throw 0;
+                } catch (n) {
+                    var a = 1;
+                    console.log(n, a);
+                }
+            }();
+        }
+        f();
+    }
+    expect_exact: "function f(o){!function(){try{throw 0}catch(c){var o=1;console.log(c,o)}}()}f();"
+    expect_stdout: "0 1"
+}
+
+function_iife_catch_ie8: {
+    rename = true
+    mangle = {
+        ie8: true,
+    }
+    input: {
+        function f(n) {
+            !function() {
+                try {
+                    throw 0;
+                } catch (n) {
+                    var a = 1;
+                    console.log(n, a);
+                }
+            }();
+        }
+        f();
+    }
+    expect_exact: "function f(o){!function(){try{throw 0}catch(o){var c=1;console.log(o,c)}}()}f();"
+    expect_stdout: "0 1"
+}
+
+function_catch_catch: {
+    rename = true
+    mangle = {
+        ie8: false,
+    }
+    input: {
+        var o = 0;
+        function f() {
+            try {
+                throw 1;
+            } catch (c) {
+                try {
+                    throw 2;
+                } catch (o) {
+                    var o = 3;
+                    console.log(o);
+                }
+            }
+            console.log(o);
+        }
+        f();
+    }
+    expect_exact: "var o=0;function f(){try{throw 1}catch(c){try{throw 2}catch(o){var o=3;console.log(o)}}console.log(o)}f();"
+    expect_stdout: [
+        "3",
+        "undefined",
+    ]
+}
+
+function_catch_catch_ie8: {
+    rename = true
+    mangle = {
+        ie8: true,
+    }
+    input: {
+        var o = 0;
+        function f() {
+            try {
+                throw 1;
+            } catch (c) {
+                try {
+                    throw 2;
+                } catch (o) {
+                    var o = 3;
+                    console.log(o);
+                }
+            }
+            console.log(o);
+        }
+        f();
+    }
+    expect_exact: "var o=0;function f(){try{throw 1}catch(c){try{throw 2}catch(o){var o=3;console.log(o)}}console.log(o)}f();"
+    expect_stdout: [
+        "3",
+        "undefined",
+    ]
+}
diff --git a/test/mocha/minify.js b/test/mocha/minify.js
index db41cd8b85e..05e319440d6 100644
--- a/test/mocha/minify.js
+++ b/test/mocha/minify.js
@@ -354,7 +354,8 @@ describe("minify", function() {
             Uglify.minify(ast, {
                 compress: {
                     sequences: false
-                }
+                },
+                mangle: false
             });
             assert.ok(stat.body);
             assert.strictEqual(stat.print_to_string(), "a=x()");
diff --git a/test/run-tests.js b/test/run-tests.js
index 0051c6c2f59..e95bbb83cd6 100755
--- a/test/run-tests.js
+++ b/test/run-tests.js
@@ -117,6 +117,10 @@ function run_compress_tests() {
                 test.mangle.properties.reserved = quoted_props;
                 U.reserve_quoted_keys(input, quoted_props);
             }
+            if (test.rename) {
+                input.figure_out_scope(test.mangle);
+                input.expand_names(test.mangle);
+            }
             var cmp = new U.Compressor(options, true);
             var output = cmp.compress(input);
             output.figure_out_scope(test.mangle);