diff --git a/README.md b/README.md
index 64a33c4e..931ae2e0 100644
--- a/README.md
+++ b/README.md
@@ -151,10 +151,10 @@ Additional options:
 - `--source-map "filename='<NAME>'"` to specify the name of the source map.
 
 - `--source-map "root='<URL>'"` to pass the URL where the original files can be found.
-  Otherwise UglifyJS assumes HTTP `X-SourceMap` is being used and will omit the
-  `//# sourceMappingURL=` directive.
 
 - `--source-map "url='<URL>'"` to specify the URL where the source map can be found.
+  Otherwise UglifyJS assumes HTTP `X-SourceMap` is being used and will omit the
+  `//# sourceMappingURL=` directive.
 
 For example:
 
@@ -201,11 +201,9 @@ Example:
 To enable the mangler you need to pass `--mangle` (`-m`).  The following
 (comma-separated) options are supported:
 
-- `toplevel` — mangle names declared in the top level scope (disabled by
-  default).
+- `toplevel` (default `false`) -- mangle names declared in the top level scope.
 
-- `eval` — mangle names visible in scopes where `eval` or `with` are used
-  (disabled by default).
+- `eval` (default `false`) -- mangle names visible in scopes where `eval` or `with` are used.
 
 When mangling is enabled but you want to prevent certain names from being
 mangled, you can declare those names with `--mangle reserved` — pass a
@@ -511,6 +509,9 @@ if (result.error) throw result.error;
 
 - `ie8` (default `false`) - set to `true` to support IE8.
 
+- `keep_fnames` (default: `false`) - pass `true` to prevent discarding or mangling
+  of function names.  Useful for code relying on `Function.prototype.name`.
+
 ## Minify options structure
 
 ```javascript
@@ -592,132 +593,93 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 ## Parse options
 
 - `bare_returns` (default `false`) -- support top level `return` statements
+
 - `ecma` (default: `8`) -- specify one of `5`, `6`, `7` or `8`. Note: this setting
   is not presently enforced except for ES8 optional trailing commas in function
   parameter lists and calls with `ecma` `8`.
+
 - `html5_comments` (default `true`)
+
 - `shebang` (default `true`) -- support `#!command` as the first line
 
 ## Compress options
 
-- `sequences` (default: true) -- join consecutive simple statements using the
-  comma operator.  May be set to a positive integer to specify the maximum number
-  of consecutive comma sequences that will be generated. If this option is set to
-  `true` then the default `sequences` limit is `200`. Set option to `false` or `0`
-  to disable. The smallest `sequences` length is `2`. A `sequences` value of `1`
-  is grandfathered to be equivalent to `true` and as such means `200`. On rare
-  occasions the default sequences limit leads to very slow compress times in which
-  case a value of `20` or less is recommended.
-
-- `properties` -- rewrite property access using the dot notation, for
-  example `foo["bar"] → foo.bar`
-
-- `dead_code` -- remove unreachable code
-
-- `drop_debugger` -- remove `debugger;` statements
-
-- `unsafe` (default: false) -- apply "unsafe" transformations (discussion below)
-
-- `unsafe_comps` (default: false) -- Reverse `<` and `<=` to `>` and `>=` to
-  allow improved compression. This might be unsafe when an at least one of two
-  operands is an object with computed values due the use of methods like `get`,
-  or `valueOf`. This could cause change in execution order after operands in the
-  comparison are switching. Compression only works if both `comparisons` and
-  `unsafe_comps` are both set to true.
-
-- `unsafe_Func` (default: false) -- compress and mangle `Function(args, code)`
-  when both `args` and `code` are string literals.
-
-- `unsafe_math` (default: false) -- optimize numerical expressions like
-  `2 * x * 3` into `6 * x`, which may give imprecise floating point results.
-
-- `unsafe_methods` (default: false) -- Converts `{ m: function(){} }` to
-  `{ m(){} }`. `ecma` must be set to `6` or greater to enable this transform.
-  If `unsafe_methods` is a RegExp then key/value pairs with keys matching the
-  RegExp will be converted to concise methods.
-  Note: if enabled there is a risk of getting a "`<method name>` is not a
-  constructor" TypeError should any code try to `new` the former function.
-
-- `unsafe_proto` (default: false) -- optimize expressions like
-  `Array.prototype.slice.call(a)` into `[].slice.call(a)`
-
-- `unsafe_regexp` (default: false) -- enable substitutions of variables with
-  `RegExp` values the same way as if they are constants.
-
-- `conditionals` -- apply optimizations for `if`-s and conditional
-  expressions
-
-- `comparisons` -- apply certain optimizations to binary nodes, for example:
-  `!(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.
-
-- `evaluate` -- attempt to evaluate constant expressions
-
 - `arrows` (default `true`) -- Converts `()=>{return x}` to `()=>x`. Class
   and object literal methods will also be converted to arrow expressions if
   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.
 
-- `unsafe_arrows` (default `false`) -- Convert ES5 style anonymous function
-  expressions to arrow functions if the function body does not reference `this`.
-  Note: it is not always safe to perform this conversion if code relies on the
-  the function having a `prototype`, which arrow functions lack.
-  This transform requires that the `ecma` compress option is set to `6` or greater.
-
-- `booleans` -- various optimizations for boolean context, for example `!!a
+- `booleans` (default: `true`) -- various optimizations for boolean context, for example `!!a
   ? b : c → a ? b : c`
 
-- `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.
-
-- `loops` -- optimizations for `do`, `while` and `for` loops when we can
-  statically determine the condition
-
-- `unused` -- drop unreferenced functions and variables (simple direct variable
-  assignments do not count as references unless set to `"keep_assign"`)
-
-- `toplevel` -- 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` -- prevent specific toplevel functions and variables from `unused`
-  removal (can be array, comma-separated, RegExp or function. Implies `toplevel`)
-
-- `hoist_funs` -- hoist function declarations
-
-- `hoist_vars` (default: false) -- hoist `var` declarations (this is `false`
-  by default because it seems to increase the size of the output in general)
-
-- `if_return` -- optimizations for if/return and if/continue
-
-- `inline` -- embed simple functions
-
-- `join_vars` -- join consecutive `var` statements
-
-- `cascade` -- small optimization for sequences, transform `x, x` into `x`
+- `cascade` (default: `true`) -- small optimization for sequences, transform `x, x` into `x`
   and `x = something(), x` into `x = something()`
 
-- `collapse_vars` -- Collapse single-use non-constant variables - side
+- `collapse_vars` (default: `true`) -- Collapse single-use non-constant variables - side
   effects permitting.
 
-- `reduce_vars` -- Improve optimization on variables assigned with and
-  used as constant values.
+- `comparisons` (default: `true`) -- apply certain optimizations to binary nodes, for example:
+  `!(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.
 
-- `warnings` -- display warnings when dropping unreachable code or unused
-  declarations etc.
+- `computed_props` -- default `true`. Transforms constant computed properties
+  into regular ones: `{["computed"]: 1}` is converted into `{computed: 1}`.
 
-- `negate_iife` -- negate "Immediately-Called Function Expressions"
+- `conditionals` (default: `true`) -- apply optimizations for `if`-s and conditional
+  expressions
+
+- `dead_code` (default: `true`) -- remove unreachable code
+
+- `drop_console` (default: `false`) -- 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.
+
+- `drop_debugger` (default: `true`) -- remove `debugger;` statements
+
+- `ecma` -- default `5`. Pass `6` or greater to enable `compress` options that
+  will transform ES5 code into smaller ES6+ equivalent forms.
+
+- `evaluate` (default: `true`) -- attempt to evaluate constant expressions
+
+- `expression` (default: `false`) -- 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_vars` (default: `false`) -- hoist `var` declarations (this is `false`
+  by default because it seems to increase the size of the output in general)
+
+- `if_return` (default: `true`) -- optimizations for if/return and if/continue
+
+- `inline` (default: `true`) -- embed simple functions
+
+- `join_vars` (default: `true`) -- join consecutive `var` statements
+
+- `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_infinity` (default: `false`) -- 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
+
+- `negate_iife` (default: `true`) -- negate "Immediately-Called Function Expressions"
   where the return value is discarded, to avoid the parens that the
   code generator would insert.
 
-- `pure_getters` -- the default is `false`.  If you pass `true` for
-  this, UglifyJS will assume that object property access
-  (e.g. `foo.bar` or `foo["bar"]`) doesn't have any side effects.
-  Specify `"strict"` to treat `foo.bar` as side-effect-free only when
-  `foo` is certain to not throw, i.e. not `null` or `undefined`.
+- `passes` (default: `1`) -- The maximum number of times to run compress.
+  In some cases more than one pass leads to further compressed code.  Keep in
+  mind more passes will take more time.
 
-- `pure_funcs` -- default `null`.  You can pass an array of names and
+- `properties` (default: `true`) -- rewrite property access using the dot notation, for
+  example `foo["bar"] → foo.bar`
+
+- `pure_funcs` (default: `null`) -- You can pass an array of names and
   UglifyJS will assume that those functions do not produce side
   effects.  DANGER: will not check if the name is redefined in scope.
   An example case here, for instance `var q = Math.floor(a/b)`.  If
@@ -728,54 +690,85 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   statement would get discarded.  The current implementation adds some
   overhead (compression will be slower).
 
-- `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.
+- `pure_getters` (default: `"strict"`) -- If you pass `true` for
+  this, UglifyJS will assume that object property access
+  (e.g. `foo.bar` or `foo["bar"]`) doesn't have any side effects.
+  Specify `"strict"` to treat `foo.bar` as side-effect-free only when
+  `foo` is certain to not throw, i.e. not `null` or `undefined`.
 
-- `expression` -- default `false`.  Pass `true` to preserve completion values
-  from terminal statements without `return`, e.g. in bookmarklets.
+- `reduce_vars` (default: `true`) -- Improve optimization on variables assigned with and
+  used as constant values.
 
-- `keep_fargs` -- default `true`.  Prevents the
-  compressor from discarding unused function arguments.  You need this
-  for code which relies on `Function.length`.
+- `sequences` (default: `true`) -- join consecutive simple statements using the
+  comma operator.  May be set to a positive integer to specify the maximum number
+  of consecutive comma sequences that will be generated. If this option is set to
+  `true` then the default `sequences` limit is `200`. Set option to `false` or `0`
+  to disable. The smallest `sequences` length is `2`. A `sequences` value of `1`
+  is grandfathered to be equivalent to `true` and as such means `200`. On rare
+  occasions the default sequences limit leads to very slow compress times in which
+  case a value of `20` or less is recommended.
 
-- `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).
-
-- `passes` -- default `1`. The maximum number of times to run compress.
-  In some cases more than one pass leads to further compressed code.  Keep in
-  mind more passes will take more time.
-
-- `keep_infinity` -- default `false`. Pass `true` to prevent `Infinity` from
-  being compressed into `1/0`, which may cause performance issues on Chrome.
-
-- `side_effects` -- default `true`. Pass `false` to disable potentially dropping
+- `side_effects` (default: `true`) -- 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();`
 
-- `ecma` -- default `5`. Pass `6` or greater to enable `compress` options that
-  will transform ES5 code into smaller ES6+ equivalent forms.
+- `switches` (default: `true`) -- de-duplicate and remove unreachable `switch` branches
 
-- `computed_props` -- default `true`. Transforms constant computed properties
-  into regular ones: `{["computed"]: 1}` is converted into `{computed: 1}`.
+- `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`)
+
+- `typeofs` (default: `true`) -- 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.
+
+- `unsafe_arrows` (default `false`) -- Convert ES5 style anonymous function
+  expressions to arrow functions if the function body does not reference `this`.
+  Note: it is not always safe to perform this conversion if code relies on the
+  the function having a `prototype`, which arrow functions lack.
+  This transform requires that the `ecma` compress option is set to `6` or greater.
+
+- `unsafe_comps` (default: `false`) -- Reverse `<` and `<=` to `>` and `>=` to
+  allow improved compression. This might be unsafe when an at least one of two
+  operands is an object with computed values due the use of methods like `get`,
+  or `valueOf`. This could cause change in execution order after operands in the
+  comparison are switching. Compression only works if both `comparisons` and
+  `unsafe_comps` are both set to true.
+
+- `unsafe` (default: `false`) -- apply "unsafe" transformations (discussion below)
+
+- `unsafe_Func` (default: `false`) -- compress and mangle `Function(args, code)`
+  when both `args` and `code` are string literals.
+
+- `unsafe_math` (default: `false`) -- optimize numerical expressions like
+  `2 * x * 3` into `6 * x`, which may give imprecise floating point results.
+
+- `unsafe_proto` (default: `false`) -- optimize expressions like
+  `Array.prototype.slice.call(a)` into `[].slice.call(a)`
+
+- `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"`)
+
+- `warnings` (default: `false`) -- display warnings when dropping unreachable code or unused
+  declarations etc.
 
 ## Mangle options
 
+- `keep_classnames` (default `false`).  Pass `true` to not mangle class names.
+
 - `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
   top level scope.
 
-- `keep_classnames` (default `false`).  Pass `true` to not mangle class 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).
-
 - `eval` (default `false`). Pass `true` to mangle names visible in scopes
   where `eval` or `with` are used.
 
@@ -807,16 +800,20 @@ UglifyJS.minify(code, { mangle: { toplevel: true } }).code;
 
 ### Mangle properties options
 
-- `reserved` (default: `[]`) -- Do not mangle property names listed in the
-  `reserved` array.
-- `regex` (default: `null`) -— Pass a RegExp literal to only mangle property
-  names matching the regular expression.
-- `keep_quoted` (default: `false`) -— Only mangle unquoted property names.
-- `debug` (default: `false`) -— Mangle names with the original name still present.
-  Pass an empty string `""` to enable, or a non-empty string to set the debug suffix.
 - `builtins` (default: `false`) -- Use `true` to allow the mangling of builtin
   DOM properties. Not recommended to override this setting.
 
+- `debug` (default: `false`) -— Mangle names with the original name still present.
+  Pass an empty string `""` to enable, or a non-empty string to set the debug suffix.
+
+- `keep_quoted` (default: `false`) -— Only mangle unquoted property names.
+
+- `regex` (default: `null`) -— Pass a RegExp literal to only mangle property
+  names matching the regular expression.
+
+- `reserved` (default: `[]`) -- Do not mangle property names listed in the
+  `reserved` array.
+
 ## Output options
 
 The code generator tries to output shortest code possible by default.  In
@@ -825,37 +822,50 @@ can pass additional arguments that control the code output:
 
 - `ascii_only` (default `false`) -- escape Unicode characters in strings and
   regexps (affects directives with non-ascii characters becoming invalid)
+
 - `beautify` (default `true`) -- whether to actually beautify the output.
   Passing `-b` will set this to true, but you might need to pass `-b` even
   when you want to generate minified code, in order to specify additional
   arguments, so you can use `-b beautify=false` to override it.
+
 - `bracketize` (default `false`) -- always insert brackets in `if`, `for`,
   `do`, `while` or `with` statements, even if their body is a single
   statement.
+
 - `comments` (default `false`) -- pass `true` or `"all"` to preserve all
   comments, `"some"` to preserve some comments, a regular expression string
   (e.g. `/^!/`) or a function.
+
 - `ecma` (default `5`) -- set output printing mode. Set `ecma` to `6` or
   greater to emit shorthand object properties - i.e.: `{a}` instead of `{a: a}`.
   The `ecma` option will only change the output in direct control of the
   beautifier. Non-compatible features in the abstract syntax tree will still
   be output as is. For example: an `ecma` setting of `5` will **not** convert
   ES6+ code to ES5.
-- `indent_level` (default 4)
-- `indent_start` (default 0) -- prefix all lines by that many spaces
+
+- `indent_level` (default `4`)
+
+- `indent_start` (default `0`) -- prefix all lines by that many spaces
+
 - `inline_script` (default `false`) -- escape the slash in occurrences of
   `</script` in strings
+
 - `keep_quoted_props` (default `false`) -- when turned on, prevents stripping
   quotes from property names in object literals.
+
 - `max_line_len` (default `false`) -- maximum line length (for uglified code)
+
 - `preamble` (default `null`) -- when passed it must be a string and
   it will be prepended to the output literally.  The source map will
   adjust for this text.  Can be used to insert a comment containing
   licensing information, for example.
+
 - `preserve_line` (default `false`) -- pass `true` to preserve lines, but it
   only works if `beautify` is set to `false`.
+
 - `quote_keys` (default `false`) -- pass `true` to quote all keys in literal
   objects
+
 - `quote_style` (default `0`) -- preferred quote style for strings (affects
   quoted property names and directives as well):
   - `0` -- prefers double quotes, switches to single quotes when there are
@@ -863,16 +873,20 @@ can pass additional arguments that control the code output:
   - `1` -- always use single quotes
   - `2` -- always use double quotes
   - `3` -- always use the original quotes
+
 - `semicolons` (default `true`) -- separate statements with semicolons.  If
   you pass `false` then whenever possible we will use a newline instead of a
   semicolon, leading to more readable output of uglified code (size before
   gzip could be smaller; size after gzip insignificantly larger).
+
 - `shebang` (default `true`) -- preserve shebang `#!` in preamble (bash scripts)
-- `width` (default 80) -- only takes effect when beautification is on, this
+
+- `width` (default `80`) -- only takes effect when beautification is on, this
   specifies an (orientative) line width that the beautifier will try to
   obey.  It refers to the width of the line text (excluding indentation).
   It doesn't work very well currently, but it does make the code generated
   by UglifyJS more readable.
+
 - `wrap_iife` (default `false`) -- pass `true` to wrap immediately invoked
   function expressions. See
   [#640](https://github.com/mishoo/UglifyJS2/issues/640) for more details.
diff --git a/lib/compress.js b/lib/compress.js
index 27d3c8eb..f0538434 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -303,6 +303,8 @@ merge(Compressor.prototype, {
             if (node instanceof AST_SymbolRef) d.references.push(node);
             d.fixed = false;
         });
+        var in_loop = null;
+        var loop_ids = Object.create(null);
         var tw = new TreeWalker(function(node, descend) {
             node._squeezed = false;
             node._optimized = false;
@@ -314,7 +316,7 @@ merge(Compressor.prototype, {
                     var d = node.definition();
                     d.references.push(node);
                     if (d.fixed === undefined || !safe_to_read(d)
-                        || is_modified(node, 0, is_immutable(node.fixed_value()))) {
+                        || is_modified(node, 0, is_immutable(node))) {
                         d.fixed = false;
                     } else {
                         var parent = tw.parent();
@@ -339,6 +341,7 @@ merge(Compressor.prototype, {
                                 d.fixed = function() {
                                     return node.value;
                                 };
+                                loop_ids[d.id] = in_loop;
                                 mark(d, false);
                                 descend();
                             } else {
@@ -398,6 +401,7 @@ merge(Compressor.prototype, {
                                     d.fixed = function() {
                                         return iife.args[i] || make_node(AST_Undefined, iife);
                                     };
+                                    loop_ids[d.id] = in_loop;
                                     mark(d, true);
                                 } else {
                                     d.fixed = false;
@@ -446,10 +450,13 @@ merge(Compressor.prototype, {
                     return true;
                 }
                 if (node instanceof AST_DWLoop) {
+                    var saved_loop = in_loop;
+                    in_loop = node;
                     push();
                     node.condition.walk(tw);
                     node.body.walk(tw);
                     pop();
+                    in_loop = saved_loop;
                     return true;
                 }
                 if (node instanceof AST_LabeledStatement) {
@@ -460,6 +467,8 @@ merge(Compressor.prototype, {
                 }
                 if (node instanceof AST_For) {
                     if (node.init) node.init.walk(tw);
+                    var saved_loop = in_loop;
+                    in_loop = node;
                     if (node.condition) {
                         push();
                         node.condition.walk(tw);
@@ -473,14 +482,18 @@ merge(Compressor.prototype, {
                         node.step.walk(tw);
                         pop();
                     }
+                    in_loop = saved_loop;
                     return true;
                 }
                 if (node instanceof AST_ForIn) {
                     node.init.walk(suppressor);
                     node.object.walk(tw);
+                    var saved_loop = in_loop;
+                    in_loop = node;
                     push();
                     node.body.walk(tw);
                     pop();
+                    in_loop = saved_loop;
                     return true;
                 }
                 if (node instanceof AST_Try) {
@@ -551,10 +564,23 @@ merge(Compressor.prototype, {
             }
             def.references = [];
             def.should_replace = undefined;
+            def.single_use = undefined;
         }
 
-        function is_immutable(value) {
-            return value && value.is_constant() || value instanceof AST_Lambda;
+        function is_immutable(node) {
+            var value = node.fixed_value();
+            if (!value) return false;
+            if (value.is_constant()) return true;
+            if (compressor.option("unused")) {
+                var d = node.definition();
+                if (d.single_use === undefined) {
+                    d.single_use = loop_ids[d.id] === in_loop
+                        && d.scope === node.scope
+                        && value.is_constant_expression();
+                }
+                if (d.references.length == 1 && d.single_use) return true;
+            }
+            return value instanceof AST_Lambda;
         }
 
         function is_modified(node, level, immutable) {
@@ -854,7 +880,7 @@ merge(Compressor.prototype, {
                         var sym;
                         if (node instanceof AST_Call
                             || node instanceof AST_Exit
-                            || node instanceof AST_PropAccess
+                            || node instanceof AST_PropAccess && node.has_side_effects(compressor)
                             || node instanceof AST_SymbolRef
                                && (lvalues[node.name]
                                    || side_effects && !references_in_scope(node.definition()))
@@ -2226,6 +2252,22 @@ merge(Compressor.prototype, {
         }
         def(AST_Node, return_false);
         def(AST_Constant, return_true);
+        def(AST_Function, function(){
+            var self = this;
+            var result = true;
+            self.walk(new TreeWalker(function(node) {
+                if (!result) return true;
+                if (node instanceof AST_SymbolRef) {
+                    var def = node.definition();
+                    if (self.enclosed.indexOf(def) >= 0
+                        && self.variables.get(def.name) !== def) {
+                        result = false;
+                        return true;
+                    }
+                }
+            }));
+            return result;
+        });
         def(AST_Unary, function(){
             return this.expression.is_constant_expression();
         });
@@ -4306,12 +4348,13 @@ merge(Compressor.prototype, {
                 d.fixed = fixed = make_node(AST_Function, fixed, fixed);
             }
             if (compressor.option("unused")
-                && is_func_expr(fixed)
                 && d.references.length == 1
-                && !(d.scope.uses_arguments && d.orig[0] instanceof AST_SymbolFunarg)
-                && !d.scope.uses_eval
-                && compressor.find_parent(AST_Scope) === fixed.parent_scope) {
-                return fixed.clone(true);
+                && (d.single_use || is_func_expr(fixed)
+                    && !(d.scope.uses_arguments && d.orig[0] instanceof AST_SymbolFunarg)
+                    && !d.scope.uses_eval
+                    && compressor.find_parent(AST_Scope) === fixed.parent_scope)) {
+                var value = fixed.optimize(compressor);
+                return value === fixed ? fixed.clone(true) : value;
             }
             if (compressor.option("evaluate") && fixed) {
                 if (d.should_replace === undefined) {
diff --git a/package.json b/package.json
index bd69d53e..b9eb72ad 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": "3.1.3",
+  "version": "3.1.4",
   "engines": {
     "node": ">=0.8.0"
   },
@@ -27,7 +27,7 @@
   ],
   "dependencies": {
     "commander": "~2.11.0",
-    "source-map": "~0.5.1"
+    "source-map": "~0.6.1"
   },
   "devDependencies": {
     "acorn": "~5.1.1",
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 6639d9ff..f11579d6 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -1268,22 +1268,21 @@ collapse_vars_short_circuited_conditions: {
 
 collapse_vars_regexp: {
     options = {
-        collapse_vars: true,
-        loops:         false,
-        sequences:     true,
-        dead_code:     true,
-        conditionals:  true,
-        comparisons:   true,
-        evaluate:      true,
         booleans:      true,
-        unused:        true,
-        hoist_funs:    true,
-        keep_fargs:    true,
+        cascade:       true,
+        collapse_vars: true,
+        comparisons:   true,
+        conditionals:  true,
+        dead_code:     true,
+        evaluate:      true,
         if_return:     true,
         join_vars:     true,
-        cascade:       true,
-        side_effects:  true,
+        hoist_funs:    true,
+        keep_fargs:    true,
+        loops:         false,
         reduce_vars:   true,
+        side_effects:  true,
+        unused:        true,
     }
     input: {
         function f1() {
@@ -1292,12 +1291,12 @@ collapse_vars_regexp: {
             return [rx, k];
         }
         function f2() {
-            var rx = /[abc123]+/;
+            var rx = /ab*/g;
             return function(s) {
                 return rx.exec(s);
             };
         }
-        (function(){
+        (function() {
             var result;
             var s = 'acdabcdeabbb';
             var rx = /ab*/g;
@@ -1305,22 +1304,35 @@ collapse_vars_regexp: {
                 console.log(result[0]);
             }
         })();
+        (function() {
+            var result;
+            var s = 'acdabcdeabbb';
+            var rx = f2();
+            while (result = rx(s)) {
+                console.log(result[0]);
+            }
+        })();
     }
     expect: {
         function f1() {
             return [/[A-Z]+/, 9];
         }
         function f2() {
-            var rx = /[abc123]+/;
+            var rx = /ab*/g;
             return function(s) {
                 return rx.exec(s);
             };
         }
-        (function(){
+        (function() {
             var result, rx = /ab*/g;
             while (result = rx.exec("acdabcdeabbb"))
                 console.log(result[0]);
         })();
+        (function() {
+            var result, rx = f2();
+            while (result = rx("acdabcdeabbb"))
+                console.log(result[0]);
+        })();
     }
     expect_stdout: true
 }
@@ -1933,9 +1945,9 @@ issue_1858: {
     }
     expect: {
         console.log(function(x) {
-            var a = {}, b = a.b = x;
+            var a = {}, b = a.b = 1;
             return a.b + b;
-        }(1));
+        }());
     }
     expect_stdout: "2"
 }
@@ -2795,3 +2807,70 @@ issue_2319_3: {
     }
     expect_stdout: "true"
 }
+
+prop_side_effects_1: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        pure_getters: "strict",
+        reduce_vars: true,
+        toplevel: true,
+        unsafe: true,
+        unused: true,
+    }
+    input: {
+        var C = 1;
+        console.log(C);
+        var obj = {
+            bar: function() {
+                return C + C;
+            }
+        };
+        console.log(obj.bar());
+    }
+    expect: {
+        console.log(1);
+        console.log({
+            bar: function() {
+                return 2;
+            }
+        }.bar());
+    }
+    expect_stdout: [
+        "1",
+        "2",
+    ]
+}
+
+prop_side_effects_2: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unsafe: true,
+        unused: true,
+    }
+    input: {
+        var C = 1;
+        console.log(C);
+        var obj = {
+            bar: function() {
+                return C + C;
+            }
+        };
+        console.log(obj.bar());
+    }
+    expect: {
+        console.log(1);
+        console.log(2);
+    }
+    expect_stdout: [
+        "1",
+        "2",
+    ]
+}
diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
index 763250fc..f849d69d 100644
--- a/test/compress/drop-unused.js
+++ b/test/compress/drop-unused.js
@@ -863,12 +863,12 @@ issue_1583: {
     expect: {
         function m(t) {
             (function(e) {
-                t = e();
-            })(function() {
-                return (function(a) {
-                    return a;
-                })(function(a) {});
-            });
+                t = function() {
+                    return (function(a) {
+                        return function(a) {};
+                    })();
+                }();
+            })();
         }
     }
 }
diff --git a/test/compress/evaluate.js b/test/compress/evaluate.js
index f015c601..29027768 100644
--- a/test/compress/evaluate.js
+++ b/test/compress/evaluate.js
@@ -1114,6 +1114,7 @@ issue_1964_1: {
     input: {
         function f() {
             var long_variable_name = /\s/;
+            console.log(long_variable_name.source);
             return "a b c".split(long_variable_name)[1];
         }
         console.log(f());
@@ -1121,11 +1122,15 @@ issue_1964_1: {
     expect: {
         function f() {
             var long_variable_name = /\s/;
+            console.log(long_variable_name.source);
             return "a b c".split(long_variable_name)[1];
         }
         console.log(f());
     }
-    expect_stdout: "b"
+    expect_stdout: [
+        "\\s",
+        "b",
+    ]
 }
 
 issue_1964_2: {
@@ -1138,17 +1143,22 @@ issue_1964_2: {
     input: {
         function f() {
             var long_variable_name = /\s/;
+            console.log(long_variable_name.source);
             return "a b c".split(long_variable_name)[1];
         }
         console.log(f());
     }
     expect: {
         function f() {
+            console.log(/\s/.source);
             return "a b c".split(/\s/)[1];
         }
         console.log(f());
     }
-    expect_stdout: "b"
+    expect_stdout: [
+        "\\s",
+        "b",
+    ]
 }
 
 array_slice_index: {
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index 994c0aee..0c758c0b 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -172,6 +172,7 @@ unsafe_evaluate: {
     options = {
         evaluate     : true,
         reduce_vars  : true,
+        side_effects : true,
         unsafe       : true,
         unused       : true
     }
@@ -1898,10 +1899,7 @@ redefine_farg_3: {
         console.log(f([]), g([]), h([]));
     }
     expect: {
-        console.log(function(a) {
-            var a;
-            return typeof a;
-        }([]), "number", "undefined");
+        console.log(typeof [], "number", "undefined");
     }
     expect_stdout: "object number undefined"
 }
@@ -2735,3 +2733,321 @@ for_in_prop: {
     }
     expect_stdout: "1"
 }
+
+obj_var_1: {
+    options = {
+        evaluate: true,
+        passes: 2,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var C = 1;
+        var obj = {
+            bar: function() {
+                return C + C;
+            }
+        };
+        console.log(obj.bar());
+    }
+    expect: {
+        console.log({
+            bar: function() {
+                return 2;
+            }
+        }.bar());
+    }
+    expect_stdout: "2"
+}
+
+obj_var_2: {
+    options = {
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unsafe: true,
+        unused: true,
+    }
+    input: {
+        var C = 1;
+        var obj = {
+            bar: function() {
+                return C + C;
+            }
+        };
+        console.log(obj.bar());
+    }
+    expect: {
+        console.log(2);
+    }
+    expect_stdout: "2"
+}
+
+obj_arg_1: {
+    options = {
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var C = 1;
+        function f(obj) {
+            return obj.bar();
+        }
+        console.log(f({
+            bar: function() {
+                return C + C;
+            }
+        }));
+    }
+    expect: {
+        console.log({
+            bar: function() {
+                return 2;
+            }
+        }.bar());
+    }
+    expect_stdout: "2"
+}
+
+obj_arg_2: {
+    options = {
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unsafe: true,
+        unused: true,
+    }
+    input: {
+        var C = 1;
+        function f(obj) {
+            return obj.bar();
+        }
+        console.log(f({
+            bar: function() {
+                return C + C;
+            }
+        }));
+    }
+    expect: {
+        console.log(2);
+    }
+    expect_stdout: "2"
+}
+
+func_arg_1: {
+    options = {
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = 42;
+        !function(a) {
+            console.log(a());
+        }(function() {
+            return a;
+        });
+    }
+    expect: {
+        console.log(42);
+    }
+    expect_stdout: "42"
+}
+
+func_arg_2: {
+    options = {
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = 42;
+        !function(a) {
+            console.log(a());
+        }(function(a) {
+            return a;
+        });
+    }
+    expect: {
+        console.log(void 0);
+    }
+    expect_stdout: "undefined"
+}
+
+regex_loop: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function f(x) {
+            for (var r, s = "acdabcdeabbb"; r = x().exec(s);)
+                console.log(r[0]);
+        }
+        var a = /ab*/g;
+        f(function() {
+            return a;
+        });
+    }
+    expect: {
+        var a = /ab*/g;
+        (function(x) {
+            for (var r, s = "acdabcdeabbb"; r = x().exec(s);)
+                console.log(r[0]);
+        })(function() {
+            return a;
+        });
+    }
+    expect_stdout: true
+}
+
+obj_for_1: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = { a: 1 };
+        for (var i = o.a--; i; i--)
+            console.log(i);
+    }
+    expect: {
+        // TODO make this work on harmony
+        var o = { a: 1 };
+        for (var i = o.a--; i; i--)
+            console.log(i);
+    }
+    expect_stdout: "1"
+}
+
+obj_for_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = { a: 1 };
+        for (var i; i = o.a--;)
+            console.log(i);
+    }
+    expect: {
+        var o = { a: 1 };
+        for (var i; i = o.a--;)
+            console.log(i);
+    }
+    expect_stdout: "1"
+}
+
+array_forin_1: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = [ 1, 2, 3 ];
+        for (var b in a)
+            console.log(b);
+    }
+    expect: {
+        // TODO make this work on harmony
+        var a = [ 1, 2, 3 ];
+        for (var b in a)
+            console.log(b);
+    }
+    expect_stdout: [
+        "0",
+        "1",
+        "2",
+    ]
+}
+
+array_forin_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = [];
+        for (var b in [ 1, 2, 3 ])
+            a.push(b);
+        console.log(a.length);
+    }
+    expect: {
+        var a = [];
+        for (var b in [ 1, 2, 3 ])
+            a.push(b);
+        console.log(a.length);
+    }
+    expect_stdout: "3"
+}
+
+array_forof_1: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = [ 1, 2, 3 ];
+        for (var b of a)
+            console.log(b);
+    }
+    expect: {
+        // TODO make this work on harmony
+        var a = [ 1, 2, 3 ];
+        for (var b of a)
+            console.log(b);
+    }
+    expect_stdout: [
+        "1",
+        "2",
+        "3",
+    ]
+    node_version: ">=0.12"
+}
+
+array_forof_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = [];
+        for (var b of [ 1, 2, 3 ])
+            a.push(b);
+        console.log(a.length);
+    }
+    expect: {
+        var a = [];
+        for (var b of [ 1, 2, 3 ])
+            a.push(b);
+        console.log(a.length);
+    }
+    expect_stdout: "3"
+    node_version: ">=0.12"
+}