FM / compress

/var/www/cobraambalaj/node_modules/terser/lib/compress/

/var/www/cobraambalaj/node_modules/terser/lib/compress

Name	Size	Mode	Actions
index.js	296263	0644	edit dl rm

Edit: /var/www/cobraambalaj/node_modules/terser/lib/compress/index.js (296263B)

/***********************************************************************

A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

-------------------------------- (C) ---------------------------------

Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

Distributed under the BSD license:

Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

* Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

* Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

***********************************************************************/

"use strict";

import {
    defaults,
    HOP,
    keep_name,
    make_node,
    makePredicate,
    map_add,
    MAP,
    member,
    noop,
    remove,
    return_false,
    return_null,
    return_this,
    return_true,
    string_template,
    regexp_source_fix,
    has_annotation
} from "../utils/index.js";
import { first_in_statement, } from "../utils/first_in_statement.js";
import {
    AST_Accessor,
    AST_Array,
    AST_Arrow,
    AST_Assign,
    AST_Await,
    AST_BigInt,
    AST_Binary,
    AST_Block,
    AST_BlockStatement,
    AST_Boolean,
    AST_Break,
    AST_Call,
    AST_Case,
    AST_Catch,
    AST_Chain,
    AST_Class,
    AST_ClassExpression,
    AST_ClassProperty,
    AST_ConciseMethod,
    AST_Conditional,
    AST_Const,
    AST_Constant,
    AST_Continue,
    AST_Debugger,
    AST_Default,
    AST_DefaultAssign,
    AST_DefClass,
    AST_Definitions,
    AST_Defun,
    AST_Destructuring,
    AST_Directive,
    AST_Do,
    AST_Dot,
    AST_DWLoop,
    AST_EmptyStatement,
    AST_Exit,
    AST_Expansion,
    AST_Export,
    AST_False,
    AST_Finally,
    AST_For,
    AST_ForIn,
    AST_Function,
    AST_Hole,
    AST_If,
    AST_Import,
    AST_Infinity,
    AST_IterationStatement,
    AST_Jump,
    AST_LabeledStatement,
    AST_Lambda,
    AST_Let,
    AST_LoopControl,
    AST_NaN,
    AST_New,
    AST_Node,
    AST_Null,
    AST_Number,
    AST_Object,
    AST_ObjectGetter,
    AST_ObjectKeyVal,
    AST_ObjectProperty,
    AST_ObjectSetter,
    AST_PrefixedTemplateString,
    AST_PropAccess,
    AST_RegExp,
    AST_Return,
    AST_Scope,
    AST_Sequence,
    AST_SimpleStatement,
    AST_Statement,
    AST_String,
    AST_Sub,
    AST_Switch,
    AST_SwitchBranch,
    AST_Symbol,
    AST_SymbolBlockDeclaration,
    AST_SymbolCatch,
    AST_SymbolClassProperty,
    AST_SymbolConst,
    AST_SymbolDeclaration,
    AST_SymbolDefun,
    AST_SymbolExport,
    AST_SymbolFunarg,
    AST_SymbolLambda,
    AST_SymbolLet,
    AST_SymbolMethod,
    AST_SymbolRef,
    AST_SymbolVar,
    AST_TemplateSegment,
    AST_TemplateString,
    AST_This,
    AST_Toplevel,
    AST_True,
    AST_Try,
    AST_Unary,
    AST_UnaryPostfix,
    AST_UnaryPrefix,
    AST_Undefined,
    AST_Var,
    AST_VarDef,
    AST_While,
    AST_With,
    AST_Yield,

TreeTransformer,
    TreeWalker,
    walk,
    walk_abort,
    walk_body,
    walk_parent,

_INLINE,
    _NOINLINE,
    _PURE
} from "../ast.js";
import { equivalent_to } from "../equivalent-to.js";
import {
    is_basic_identifier_string,
    JS_Parse_Error,
    parse,
    PRECEDENCE,
} from "../parse.js";
import { OutputStream } from "../output.js";
import {
    base54,
    SymbolDef,
} from "../scope.js";
import "../size.js";

const UNUSED    = 0b00000001;
const TRUTHY    = 0b00000010;
const FALSY     = 0b00000100;
const UNDEFINED = 0b00001000;
const INLINED   = 0b00010000;
// Nodes to which values are ever written. Used when keep_assign is part of the unused option string.
const WRITE_ONLY= 0b00100000;

// information specific to a single compression pass
const SQUEEZED  = 0b0000000100000000;
const OPTIMIZED = 0b0000001000000000;
const TOP       = 0b0000010000000000;

const CLEAR_BETWEEN_PASSES = SQUEEZED | OPTIMIZED | TOP;

/*@__INLINE__*/
const has_flag = (node, flag) => node.flags & flag;
/*@__INLINE__*/
const set_flag = (node, flag) => { node.flags |= flag; };
/*@__INLINE__*/
const clear_flag = (node, flag) => { node.flags &= ~flag; };

class Compressor extends TreeWalker {
    constructor(options, { false_by_default = false, mangle_options = false }) {
        super();
        if (options.defaults !== undefined && !options.defaults) false_by_default = true;
        this.options = defaults(options, {
            arguments     : false,
            arrows        : !false_by_default,
            booleans      : !false_by_default,
            booleans_as_integers : false,
            collapse_vars : !false_by_default,
            comparisons   : !false_by_default,
            computed_props: !false_by_default,
            conditionals  : !false_by_default,
            dead_code     : !false_by_default,
            defaults      : true,
            directives    : !false_by_default,
            drop_console  : false,
            drop_debugger : !false_by_default,
            ecma          : 5,
            evaluate      : !false_by_default,
            expression    : false,
            global_defs   : false,
            hoist_funs    : false,
            hoist_props   : !false_by_default,
            hoist_vars    : false,
            ie8           : false,
            if_return     : !false_by_default,
            inline        : !false_by_default,
            join_vars     : !false_by_default,
            keep_classnames: false,
            keep_fargs    : true,
            keep_fnames   : false,
            keep_infinity : false,
            loops         : !false_by_default,
            module        : false,
            negate_iife   : !false_by_default,
            passes        : 1,
            properties    : !false_by_default,
            pure_getters  : !false_by_default && "strict",
            pure_funcs    : null,
            reduce_funcs  : null,  // legacy
            reduce_vars   : !false_by_default,
            sequences     : !false_by_default,
            side_effects  : !false_by_default,
            switches      : !false_by_default,
            top_retain    : null,
            toplevel      : !!(options && options["top_retain"]),
            typeofs       : !false_by_default,
            unsafe        : false,
            unsafe_arrows : false,
            unsafe_comps  : false,
            unsafe_Function: false,
            unsafe_math   : false,
            unsafe_symbols: false,
            unsafe_methods: false,
            unsafe_proto  : false,
            unsafe_regexp : false,
            unsafe_undefined: false,
            unused        : !false_by_default,
            warnings      : false  // legacy
        }, true);
        var global_defs = this.options["global_defs"];
        if (typeof global_defs == "object") for (var key in global_defs) {
            if (key[0] === "@" && HOP(global_defs, key)) {
                global_defs[key.slice(1)] = parse(global_defs[key], {
                    expression: true
                });
            }
        }
        if (this.options["inline"] === true) this.options["inline"] = 3;
        var pure_funcs = this.options["pure_funcs"];
        if (typeof pure_funcs == "function") {
            this.pure_funcs = pure_funcs;
        } else {
            this.pure_funcs = pure_funcs ? function(node) {
                return !pure_funcs.includes(node.expression.print_to_string());
            } : return_true;
        }
        var top_retain = this.options["top_retain"];
        if (top_retain instanceof RegExp) {
            this.top_retain = function(def) {
                return top_retain.test(def.name);
            };
        } else if (typeof top_retain == "function") {
            this.top_retain = top_retain;
        } else if (top_retain) {
            if (typeof top_retain == "string") {
                top_retain = top_retain.split(/,/);
            }
            this.top_retain = function(def) {
                return top_retain.includes(def.name);
            };
        }
        if (this.options["module"]) {
            this.directives["use strict"] = true;
            this.options["toplevel"] = true;
        }
        var toplevel = this.options["toplevel"];
        this.toplevel = typeof toplevel == "string" ? {
            funcs: /funcs/.test(toplevel),
            vars: /vars/.test(toplevel)
        } : {
            funcs: toplevel,
            vars: toplevel
        };
        var sequences = this.options["sequences"];
        this.sequences_limit = sequences == 1 ? 800 : sequences | 0;
        this.evaluated_regexps = new Map();
        this._toplevel = undefined;
        this.mangle_options = mangle_options;
    }

option(key) {
        return this.options[key];
    }

exposed(def) {
        if (def.export) return true;
        if (def.global) for (var i = 0, len = def.orig.length; i < len; i++)
            if (!this.toplevel[def.orig[i] instanceof AST_SymbolDefun ? "funcs" : "vars"])
                return true;
        return false;
    }

in_boolean_context() {
        if (!this.option("booleans")) return false;
        var self = this.self();
        for (var i = 0, p; p = this.parent(i); i++) {
            if (p instanceof AST_SimpleStatement
                || p instanceof AST_Conditional && p.condition === self
                || p instanceof AST_DWLoop && p.condition === self
                || p instanceof AST_For && p.condition === self
                || p instanceof AST_If && p.condition === self
                || p instanceof AST_UnaryPrefix && p.operator == "!" && p.expression === self) {
                return true;
            }
            if (
                p instanceof AST_Binary
                    && (
                        p.operator == "&&"
                        || p.operator == "||"
                        || p.operator == "??"
                    )
                || p instanceof AST_Conditional
                || p.tail_node() === self
            ) {
                self = p;
            } else {
                return false;
            }
        }
    }

get_toplevel() {
        return this._toplevel;
    }

compress(toplevel) {
        toplevel = toplevel.resolve_defines(this);
        this._toplevel = toplevel;
        if (this.option("expression")) {
            this._toplevel.process_expression(true);
        }
        var passes = +this.options.passes || 1;
        var min_count = 1 / 0;
        var stopping = false;
        var mangle = { ie8: this.option("ie8") };
        for (var pass = 0; pass < passes; pass++) {
            this._toplevel.figure_out_scope(mangle);
            if (pass === 0 && this.option("drop_console")) {
                // must be run before reduce_vars and compress pass
                this._toplevel = this._toplevel.drop_console();
            }
            if (pass > 0 || this.option("reduce_vars")) {
                this._toplevel.reset_opt_flags(this);
            }
            this._toplevel = this._toplevel.transform(this);
            if (passes > 1) {
                let count = 0;
                walk(this._toplevel, () => { count++; });
                if (count < min_count) {
                    min_count = count;
                    stopping = false;
                } else if (stopping) {
                    break;
                } else {
                    stopping = true;
                }
            }
        }
        if (this.option("expression")) {
            this._toplevel.process_expression(false);
        }
        toplevel = this._toplevel;
        this._toplevel = undefined;
        return toplevel;
    }

before(node, descend) {
        if (has_flag(node, SQUEEZED)) return node;
        var was_scope = false;
        if (node instanceof AST_Scope) {
            node = node.hoist_properties(this);
            node = node.hoist_declarations(this);
            was_scope = true;
        }
        // Before https://github.com/mishoo/UglifyJS2/pull/1602 AST_Node.optimize()
        // would call AST_Node.transform() if a different instance of AST_Node is
        // produced after def_optimize().
        // This corrupts TreeWalker.stack, which cause AST look-ups to malfunction.
        // Migrate and defer all children's AST_Node.transform() to below, which
        // will now happen after this parent AST_Node has been properly substituted
        // thus gives a consistent AST snapshot.
        descend(node, this);
        // Existing code relies on how AST_Node.optimize() worked, and omitting the
        // following replacement call would result in degraded efficiency of both
        // output and performance.
        descend(node, this);
        var opt = node.optimize(this);
        if (was_scope && opt instanceof AST_Scope) {
            opt.drop_unused(this);
            descend(opt, this);
        }
        if (opt === node) set_flag(opt, SQUEEZED);
        return opt;
    }
}

function def_optimize(node, optimizer) {
    node.DEFMETHOD("optimize", function(compressor) {
        var self = this;
        if (has_flag(self, OPTIMIZED)) return self;
        if (compressor.has_directive("use asm")) return self;
        var opt = optimizer(self, compressor);
        set_flag(opt, OPTIMIZED);
        return opt;
    });
}

def_optimize(AST_Node, function(self) {
    return self;
});

AST_Toplevel.DEFMETHOD("drop_console", function() {
    return this.transform(new TreeTransformer(function(self) {
        if (self.TYPE == "Call") {
            var exp = self.expression;
            if (exp instanceof AST_PropAccess) {
                var name = exp.expression;
                while (name.expression) {
                    name = name.expression;
                }
                if (is_undeclared_ref(name) && name.name == "console") {
                    return make_node(AST_Undefined, self);
                }
            }
        }
    }));
});

AST_Node.DEFMETHOD("equivalent_to", function(node) {
    return equivalent_to(this, node);
});

AST_Scope.DEFMETHOD("process_expression", function(insert, compressor) {
    var self = this;
    var tt = new TreeTransformer(function(node) {
        if (insert && node instanceof AST_SimpleStatement) {
            return make_node(AST_Return, node, {
                value: node.body
            });
        }
        if (!insert && node instanceof AST_Return) {
            if (compressor) {
                var value = node.value && node.value.drop_side_effect_free(compressor, true);
                return value ? make_node(AST_SimpleStatement, node, {
                    body: value
                }) : make_node(AST_EmptyStatement, node);
            }
            return make_node(AST_SimpleStatement, node, {
                body: node.value || make_node(AST_UnaryPrefix, node, {
                    operator: "void",
                    expression: make_node(AST_Number, node, {
                        value: 0
                    })
                })
            });
        }
        if (node instanceof AST_Class || node instanceof AST_Lambda && node !== self) {
            return node;
        }
        if (node instanceof AST_Block) {
            var index = node.body.length - 1;
            if (index >= 0) {
                node.body[index] = node.body[index].transform(tt);
            }
        } else if (node instanceof AST_If) {
            node.body = node.body.transform(tt);
            if (node.alternative) {
                node.alternative = node.alternative.transform(tt);
            }
        } else if (node instanceof AST_With) {
            node.body = node.body.transform(tt);
        }
        return node;
    });
    self.transform(tt);
});

function read_property(obj, key) {
    key = get_value(key);
    if (key instanceof AST_Node) return;

var value;
    if (obj instanceof AST_Array) {
        var elements = obj.elements;
        if (key == "length") return make_node_from_constant(elements.length, obj);
        if (typeof key == "number" && key in elements) value = elements[key];
    } else if (obj instanceof AST_Object) {
        key = "" + key;
        var props = obj.properties;
        for (var i = props.length; --i >= 0;) {
            var prop = props[i];
            if (!(prop instanceof AST_ObjectKeyVal)) return;
            if (!value && props[i].key === key) value = props[i].value;
        }
    }

return value instanceof AST_SymbolRef && value.fixed_value() || value;
}

(function(def_reduce_vars) {
    def_reduce_vars(AST_Node, noop);

function reset_block_variables(compressor, node) {
        if (node.block_scope) node.block_scope.variables.forEach((def) => {
            reset_def(compressor, def);
        });
    }

function push(tw) {
        tw.safe_ids = Object.create(tw.safe_ids);
    }

function pop(tw) {
        tw.safe_ids = Object.getPrototypeOf(tw.safe_ids);
    }

function mark(tw, def, safe) {
        tw.safe_ids[def.id] = safe;
    }

function ref_once(tw, compressor, def) {
        return compressor.option("unused")
            && !def.scope.pinned()
            && def.references.length - def.recursive_refs == 1
            && tw.loop_ids.get(def.id) === tw.in_loop;
    }

function is_immutable(value) {
        if (!value) return false;
        return value.is_constant()
            || value instanceof AST_Lambda
            || value instanceof AST_This;
    }

// A definition "escapes" when its value can leave the point of use.
    // Example: `a = b || c`
    // In this example, "b" and "c" are escaping, because they're going into "a"
    //
    // def.escaped is != 0 when it escapes.
    //
    // When greater than 1, it means that N chained properties will be read off
    // of that def before an escape occurs. This is useful for evaluating
    // property accesses, where you need to know when to stop.
    function mark_escaped(tw, d, scope, node, value, level = 0, depth = 1) {
        var parent = tw.parent(level);
        if (value) {
            if (value.is_constant()) return;
            if (value instanceof AST_ClassExpression) return;
        }

if (
            parent instanceof AST_Assign && (parent.operator === "=" || parent.logical) && node === parent.right
            || parent instanceof AST_Call && (node !== parent.expression || parent instanceof AST_New)
            || parent instanceof AST_Exit && node === parent.value && node.scope !== d.scope
            || parent instanceof AST_VarDef && node === parent.value
            || parent instanceof AST_Yield && node === parent.value && node.scope !== d.scope
        ) {
            if (depth > 1 && !(value && value.is_constant_expression(scope))) depth = 1;
            if (!d.escaped || d.escaped > depth) d.escaped = depth;
            return;
        } else if (
            parent instanceof AST_Array
            || parent instanceof AST_Await
            || parent instanceof AST_Binary && lazy_op.has(parent.operator)
            || parent instanceof AST_Conditional && node !== parent.condition
            || parent instanceof AST_Expansion
            || parent instanceof AST_Sequence && node === parent.tail_node()
        ) {
            mark_escaped(tw, d, scope, parent, parent, level + 1, depth);
        } else if (parent instanceof AST_ObjectKeyVal && node === parent.value) {
            var obj = tw.parent(level + 1);

mark_escaped(tw, d, scope, obj, obj, level + 2, depth);
        } else if (parent instanceof AST_PropAccess && node === parent.expression) {
            value = read_property(value, parent.property);

mark_escaped(tw, d, scope, parent, value, level + 1, depth + 1);
            if (value) return;
        }

if (level > 0) return;
        if (parent instanceof AST_Sequence && node !== parent.tail_node()) return;
        if (parent instanceof AST_SimpleStatement) return;

d.direct_access = true;
    }

const finish_walk = () => {
            if (node.logical) {
                node.left.walk(tw);

push(tw);
                node.right.walk(tw);
                pop(tw);

return true;
            }
        };

var sym = node.left;
        if (!(sym instanceof AST_SymbolRef)) return finish_walk();

var def = sym.definition();
        var safe = safe_to_assign(tw, def, sym.scope, node.right);
        def.assignments++;
        if (!safe) return finish_walk();

var fixed = def.fixed;
        if (!fixed && node.operator != "=" && !node.logical) return finish_walk();

var eq = node.operator == "=";
        var value = eq ? node.right : node;
        if (is_modified(compressor, tw, node, value, 0)) return finish_walk();

def.references.push(sym);

if (!node.logical) {
            if (!eq) def.chained = true;

def.fixed = eq ? function() {
                return node.right;
            } : function() {
                return make_node(AST_Binary, node, {
                    operator: node.operator.slice(0, -1),
                    left: fixed instanceof AST_Node ? fixed : fixed(),
                    right: node.right
                });
            };
        }

if (node.logical) {
            mark(tw, def, false);
            push(tw);
            node.right.walk(tw);
            pop(tw);
            return true;
        }

mark(tw, def, false);
        node.right.walk(tw);
        mark(tw, def, true);

mark_escaped(tw, def, sym.scope, node, value, 0, 1);

return true;
    });
    def_reduce_vars(AST_Binary, function(tw) {
        if (!lazy_op.has(this.operator)) return;
        this.left.walk(tw);
        push(tw);
        this.right.walk(tw);
        pop(tw);
        return true;
    });
    def_reduce_vars(AST_Block, function(tw, descend, compressor) {
        reset_block_variables(compressor, this);
    });
    def_reduce_vars(AST_Case, function(tw) {
        push(tw);
        this.expression.walk(tw);
        pop(tw);
        push(tw);
        walk_body(this, tw);
        pop(tw);
        return true;
    });
    def_reduce_vars(AST_Class, function(tw, descend) {
        clear_flag(this, INLINED);
        push(tw);
        descend();
        pop(tw);
        return true;
    });
    def_reduce_vars(AST_Conditional, function(tw) {
        this.condition.walk(tw);
        push(tw);
        this.consequent.walk(tw);
        pop(tw);
        push(tw);
        this.alternative.walk(tw);
        pop(tw);
        return true;
    });

def_reduce_vars(AST_Chain, function(tw, descend) {
        // Chains' conditions apply left-to-right, cumulatively.
        // If we walk normally we don't go in that order because we would pop before pushing again
        // Solution: AST_PropAccess and AST_Call push when they are optional, and never pop.
        // Then we pop everything when they are done being walked.
        const safe_ids = tw.safe_ids;

descend();

// Unroll back to start
        tw.safe_ids = safe_ids;
        return true;
    });
    def_reduce_vars(AST_Call, function (tw) {
        // TODO this block should just be { return } but
        // for some reason the _walk function of AST_Call walks the callee last

this.expression.walk(tw);

if (this.optional) {
            // Never pop -- it's popped at AST_Chain above
            push(tw);
        }

for (const arg of this.args) arg.walk(tw);

return true;
    });
    def_reduce_vars(AST_PropAccess, function (tw) {
        if (!this.optional) return;

this.expression.walk(tw);

// Never pop -- it's popped at AST_Chain above
        push(tw);

if (this.property instanceof AST_Node) this.property.walk(tw);

return true;
    });
    def_reduce_vars(AST_Default, function(tw, descend) {
        push(tw);
        descend();
        pop(tw);
        return true;
    });
    function mark_lambda(tw, descend, compressor) {
        clear_flag(this, INLINED);
        push(tw);
        reset_variables(tw, compressor, this);
        if (this.uses_arguments) {
            descend();
            pop(tw);
            return;
        }
        var iife;
        if (!this.name
            && (iife = tw.parent()) instanceof AST_Call
            && iife.expression === this
            && !iife.args.some(arg => arg instanceof AST_Expansion)
            && this.argnames.every(arg_name => arg_name instanceof AST_Symbol)
        ) {
            // Virtually turn IIFE parameters into variable definitions:
            //   (function(a,b) {...})(c,d) => (function() {var a=c,b=d; ...})()
            // So existing transformation rules can work on them.
            this.argnames.forEach((arg, i) => {
                if (!arg.definition) return;
                var d = arg.definition();
                // Avoid setting fixed when there's more than one origin for a variable value
                if (d.orig.length > 1) return;
                if (d.fixed === undefined && (!this.uses_arguments || tw.has_directive("use strict"))) {
                    d.fixed = function() {
                        return iife.args[i] || make_node(AST_Undefined, iife);
                    };
                    tw.loop_ids.set(d.id, tw.in_loop);
                    mark(tw, d, true);
                } else {
                    d.fixed = false;
                }
            });
        }
        descend();
        pop(tw);
        return true;
    }

def_reduce_vars(AST_Lambda, mark_lambda);

def_reduce_vars(AST_Do, function(tw, descend, compressor) {
        reset_block_variables(compressor, this);
        const saved_loop = tw.in_loop;
        tw.in_loop = this;
        push(tw);
        this.body.walk(tw);
        if (has_break_or_continue(this)) {
            pop(tw);
            push(tw);
        }
        this.condition.walk(tw);
        pop(tw);
        tw.in_loop = saved_loop;
        return true;
    });
    def_reduce_vars(AST_For, function(tw, descend, compressor) {
        reset_block_variables(compressor, this);
        if (this.init) this.init.walk(tw);
        const saved_loop = tw.in_loop;
        tw.in_loop = this;
        push(tw);
        if (this.condition) this.condition.walk(tw);
        this.body.walk(tw);
        if (this.step) {
            if (has_break_or_continue(this)) {
                pop(tw);
                push(tw);
            }
            this.step.walk(tw);
        }
        pop(tw);
        tw.in_loop = saved_loop;
        return true;
    });
    def_reduce_vars(AST_ForIn, function(tw, descend, compressor) {
        reset_block_variables(compressor, this);
        suppress(this.init);
        this.object.walk(tw);
        const saved_loop = tw.in_loop;
        tw.in_loop = this;
        push(tw);
        this.body.walk(tw);
        pop(tw);
        tw.in_loop = saved_loop;
        return true;
    });

def_reduce_vars(AST_If, function(tw) {
        this.condition.walk(tw);
        push(tw);
        this.body.walk(tw);
        pop(tw);
        if (this.alternative) {
            push(tw);
            this.alternative.walk(tw);
            pop(tw);
        }
        return true;
    });
    def_reduce_vars(AST_LabeledStatement, function(tw) {
        push(tw);
        this.body.walk(tw);
        pop(tw);
        return true;
    });
    def_reduce_vars(AST_SymbolCatch, function() {
        this.definition().fixed = false;
    });

def_reduce_vars(AST_SymbolRef, function(tw, descend, compressor) {
        var d = this.definition();
        d.references.push(this);
        if (d.references.length == 1
            && !d.fixed
            && d.orig[0] instanceof AST_SymbolDefun) {
            tw.loop_ids.set(d.id, tw.in_loop);
        }
        var fixed_value;
        if (d.fixed === undefined || !safe_to_read(tw, d)) {
            d.fixed = false;
        } else if (d.fixed) {
            fixed_value = this.fixed_value();
            if (
                fixed_value instanceof AST_Lambda
                && recursive_ref(tw, d)
            ) {
                d.recursive_refs++;
            } else if (fixed_value
                && !compressor.exposed(d)
                && ref_once(tw, compressor, d)
            ) {
                d.single_use =
                    fixed_value instanceof AST_Lambda && !fixed_value.pinned()
                    || fixed_value instanceof AST_Class
                    || d.scope === this.scope && fixed_value.is_constant_expression();
            } else {
                d.single_use = false;
            }
            if (is_modified(compressor, tw, this, fixed_value, 0, is_immutable(fixed_value))) {
                if (d.single_use) {
                    d.single_use = "m";
                } else {
                    d.fixed = false;
                }
            }
        }
        mark_escaped(tw, d, this.scope, this, fixed_value, 0, 1);
    });
    def_reduce_vars(AST_Toplevel, function(tw, descend, compressor) {
        this.globals.forEach(function(def) {
            reset_def(compressor, def);
        });
        reset_variables(tw, compressor, this);
    });
    def_reduce_vars(AST_Try, function(tw, descend, compressor) {
        reset_block_variables(compressor, this);
        push(tw);
        walk_body(this, tw);
        pop(tw);
        if (this.bcatch) {
            push(tw);
            this.bcatch.walk(tw);
            pop(tw);
        }
        if (this.bfinally) this.bfinally.walk(tw);
        return true;
    });
    def_reduce_vars(AST_Unary, function(tw) {
        var node = this;
        if (node.operator !== "++" && node.operator !== "--") return;
        var exp = node.expression;
        if (!(exp instanceof AST_SymbolRef)) return;
        var def = exp.definition();
        var safe = safe_to_assign(tw, def, exp.scope, true);
        def.assignments++;
        if (!safe) return;
        var fixed = def.fixed;
        if (!fixed) return;
        def.references.push(exp);
        def.chained = true;
        def.fixed = function() {
            return make_node(AST_Binary, node, {
                operator: node.operator.slice(0, -1),
                left: make_node(AST_UnaryPrefix, node, {
                    operator: "+",
                    expression: fixed instanceof AST_Node ? fixed : fixed()
                }),
                right: make_node(AST_Number, node, {
                    value: 1
                })
            });
        };
        mark(tw, def, true);
        return true;
    });
    def_reduce_vars(AST_VarDef, function(tw, descend) {
        var node = this;
        if (node.name instanceof AST_Destructuring) {
            suppress(node.name);
            return;
        }
        var d = node.name.definition();
        if (node.value) {
            if (safe_to_assign(tw, d, node.name.scope, node.value)) {
                d.fixed = function() {
                    return node.value;
                };
                tw.loop_ids.set(d.id, tw.in_loop);
                mark(tw, d, false);
                descend();
                mark(tw, d, true);
                return true;
            } else {
                d.fixed = false;
            }
        }
    });
    def_reduce_vars(AST_While, function(tw, descend, compressor) {
        reset_block_variables(compressor, this);
        const saved_loop = tw.in_loop;
        tw.in_loop = this;
        push(tw);
        descend();
        pop(tw);
        tw.in_loop = saved_loop;
        return true;
    });
})(function(node, func) {
    node.DEFMETHOD("reduce_vars", func);
});

AST_Toplevel.DEFMETHOD("reset_opt_flags", function(compressor) {
    const self = this;
    const reduce_vars = compressor.option("reduce_vars");

AST_Symbol.DEFMETHOD("fixed_value", function() {
    var fixed = this.thedef.fixed;
    if (!fixed || fixed instanceof AST_Node) return fixed;
    return fixed();
});

AST_SymbolRef.DEFMETHOD("is_immutable", function() {
    var orig = this.definition().orig;
    return orig.length == 1 && orig[0] instanceof AST_SymbolLambda;
});

function is_func_expr(node) {
    return node instanceof AST_Arrow || node instanceof AST_Function;
}

function is_ref_of(ref, type) {
    if (!(ref instanceof AST_SymbolRef)) return false;
    var orig = ref.definition().orig;
    for (var i = orig.length; --i >= 0;) {
        if (orig[i] instanceof type) return true;
    }
}

function find_scope(tw) {
    for (let i = 0;;i++) {
        const p = tw.parent(i);
        if (p instanceof AST_Toplevel) return p;
        if (p instanceof AST_Lambda) return p;
        if (p.block_scope) return p.block_scope;
    }
}

function make_sequence(orig, expressions) {
    if (expressions.length == 1) return expressions[0];
    if (expressions.length == 0) throw new Error("trying to create a sequence with length zero!");
    return make_node(AST_Sequence, orig, {
        expressions: expressions.reduce(merge_sequence, [])
    });
}

// we shouldn't compress (1,func)(something) to
// func(something) because that changes the meaning of
// the func (becomes lexical instead of global).
function maintain_this_binding(parent, orig, val) {
    if (parent instanceof AST_UnaryPrefix && parent.operator == "delete"
        || parent instanceof AST_Call && parent.expression === orig
            && (val instanceof AST_PropAccess || val instanceof AST_SymbolRef && val.name == "eval")) {
        return make_sequence(orig, [ make_node(AST_Number, orig, { value: 0 }), val ]);
    }
    return val;
}

function merge_sequence(array, node) {
    if (node instanceof AST_Sequence) {
        array.push(...node.expressions);
    } else {
        array.push(node);
    }
    return array;
}

function as_statement_array(thing) {
    if (thing === null) return [];
    if (thing instanceof AST_BlockStatement) return thing.body;
    if (thing instanceof AST_EmptyStatement) return [];
    if (thing instanceof AST_Statement) return [ thing ];
    throw new Error("Can't convert thing to statement array");
}

function is_empty(thing) {
    if (thing === null) return true;
    if (thing instanceof AST_EmptyStatement) return true;
    if (thing instanceof AST_BlockStatement) return thing.body.length == 0;
    return false;
}

function can_be_evicted_from_block(node) {
    return !(
        node instanceof AST_DefClass ||
        node instanceof AST_Defun ||
        node instanceof AST_Let ||
        node instanceof AST_Const ||
        node instanceof AST_Export ||
        node instanceof AST_Import
    );
}

function loop_body(x) {
    if (x instanceof AST_IterationStatement) {
        return x.body instanceof AST_BlockStatement ? x.body : x;
    }
    return x;
}

function is_iife_call(node) {
    // Used to determine whether the node can benefit from negation.
    // Not the case with arrow functions (you need an extra set of parens).
    if (node.TYPE != "Call") return false;
    return node.expression instanceof AST_Function || is_iife_call(node.expression);
}

function is_undeclared_ref(node) {
    return node instanceof AST_SymbolRef && node.definition().undeclared;
}

var global_names = makePredicate("Array Boolean clearInterval clearTimeout console Date decodeURI decodeURIComponent encodeURI encodeURIComponent Error escape eval EvalError Function isFinite isNaN JSON Math Number parseFloat parseInt RangeError ReferenceError RegExp Object setInterval setTimeout String SyntaxError TypeError unescape URIError");
AST_SymbolRef.DEFMETHOD("is_declared", function(compressor) {
    return !this.definition().undeclared
        || compressor.option("unsafe") && global_names.has(this.name);
});

var identifier_atom = makePredicate("Infinity NaN undefined");
function is_identifier_atom(node) {
    return node instanceof AST_Infinity
        || node instanceof AST_NaN
        || node instanceof AST_Undefined;
}

// Tighten a bunch of statements together. Used whenever there is a block.
function tighten_body(statements, compressor) {
    var in_loop, in_try;
    var scope = compressor.find_parent(AST_Scope).get_defun_scope();
    find_loop_scope_try();
    var CHANGED, max_iter = 10;
    do {
        CHANGED = false;
        eliminate_spurious_blocks(statements);
        if (compressor.option("dead_code")) {
            eliminate_dead_code(statements, compressor);
        }
        if (compressor.option("if_return")) {
            handle_if_return(statements, compressor);
        }
        if (compressor.sequences_limit > 0) {
            sequencesize(statements, compressor);
            sequencesize_2(statements, compressor);
        }
        if (compressor.option("join_vars")) {
            join_consecutive_vars(statements);
        }
        if (compressor.option("collapse_vars")) {
            collapse(statements, compressor);
        }
    } while (CHANGED && max_iter-- > 0);

// Search from right to left for assignment-like expressions:
    // - `var a = x;`
    // - `a = x;`
    // - `++a`
    // For each candidate, scan from left to right for first usage, then try
    // to fold assignment into the site for compression.
    // Will not attempt to collapse assignments into or past code blocks
    // which are not sequentially executed, e.g. loops and conditionals.
    function collapse(statements, compressor) {
        if (scope.pinned()) return statements;
        var args;
        var candidates = [];
        var stat_index = statements.length;
        var scanner = new TreeTransformer(function(node) {
            if (abort) return node;
            // Skip nodes before `candidate` as quickly as possible
            if (!hit) {
                if (node !== hit_stack[hit_index]) return node;
                hit_index++;
                if (hit_index < hit_stack.length) return handle_custom_scan_order(node);
                hit = true;
                stop_after = find_stop(node, 0);
                if (stop_after === node) abort = true;
                return node;
            }
            // Stop immediately if these node types are encountered
            var parent = scanner.parent();
            if (node instanceof AST_Assign
                    && (node.logical || node.operator != "=" && lhs.equivalent_to(node.left))
                || node instanceof AST_Await
                || node instanceof AST_Call && lhs instanceof AST_PropAccess && lhs.equivalent_to(node.expression)
                || node instanceof AST_Debugger
                || node instanceof AST_Destructuring
                || node instanceof AST_Expansion
                   && node.expression instanceof AST_Symbol
                   && node.expression.definition().references.length > 1
                || node instanceof AST_IterationStatement && !(node instanceof AST_For)
                || node instanceof AST_LoopControl
                || node instanceof AST_Try
                || node instanceof AST_With
                || node instanceof AST_Yield
                || node instanceof AST_Export
                || node instanceof AST_Class
                || parent instanceof AST_For && node !== parent.init
                || !replace_all
                    && (
                        node instanceof AST_SymbolRef
                        && !node.is_declared(compressor)
                        && !pure_prop_access_globals.has(node))
                || node instanceof AST_SymbolRef
                    && parent instanceof AST_Call
                    && has_annotation(parent, _NOINLINE)
            ) {
                abort = true;
                return node;
            }
            // Stop only if candidate is found within conditional branches
            if (!stop_if_hit && (!lhs_local || !replace_all)
                && (parent instanceof AST_Binary && lazy_op.has(parent.operator) && parent.left !== node
                    || parent instanceof AST_Conditional && parent.condition !== node
                    || parent instanceof AST_If && parent.condition !== node)) {
                stop_if_hit = parent;
            }
            // Replace variable with assignment when found
            if (can_replace
                && !(node instanceof AST_SymbolDeclaration)
                && lhs.equivalent_to(node)
            ) {
                if (stop_if_hit) {
                    abort = true;
                    return node;
                }
                if (is_lhs(node, parent)) {
                    if (value_def) replaced++;
                    return node;
                } else {
                    replaced++;
                    if (value_def && candidate instanceof AST_VarDef) return node;
                }
                CHANGED = abort = true;
                if (candidate instanceof AST_UnaryPostfix) {
                    return make_node(AST_UnaryPrefix, candidate, candidate);
                }
                if (candidate instanceof AST_VarDef) {
                    var def = candidate.name.definition();
                    var value = candidate.value;
                    if (def.references.length - def.replaced == 1 && !compressor.exposed(def)) {
                        def.replaced++;
                        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: "=",
                        logical: false,
                        left: make_node(AST_SymbolRef, candidate.name, candidate.name),
                        right: value
                    });
                }
                clear_flag(candidate, WRITE_ONLY);
                return candidate;
            }
            // These node types have child nodes that execute sequentially,
            // but are otherwise not safe to scan into or beyond them.
            var sym;
            if (node instanceof AST_Call
                || node instanceof AST_Exit
                    && (side_effects || lhs instanceof AST_PropAccess || may_modify(lhs))
                || node instanceof AST_PropAccess
                    && (side_effects || node.expression.may_throw_on_access(compressor))
                || node instanceof AST_SymbolRef
                    && (lvalues.get(node.name) || side_effects && may_modify(node))
                || node instanceof AST_VarDef && node.value
                    && (lvalues.has(node.name.name) || side_effects && may_modify(node.name))
                || (sym = is_lhs(node.left, node))
                    && (sym instanceof AST_PropAccess || lvalues.has(sym.name))
                || may_throw
                    && (in_try ? node.has_side_effects(compressor) : side_effects_external(node))) {
                stop_after = node;
                if (node instanceof AST_Scope) abort = true;
            }
            return handle_custom_scan_order(node);
        }, function(node) {
            if (abort) return;
            if (stop_after === node) abort = true;
            if (stop_if_hit === node) stop_if_hit = null;
        });
        var multi_replacer = new TreeTransformer(function(node) {
            if (abort) return node;
            // Skip nodes before `candidate` as quickly as possible
            if (!hit) {
                if (node !== hit_stack[hit_index]) return node;
                hit_index++;
                if (hit_index < hit_stack.length) return;
                hit = true;
                return node;
            }
            // Replace variable when found
            if (node instanceof AST_SymbolRef
                && node.name == def.name) {
                if (!--replaced) abort = true;
                if (is_lhs(node, multi_replacer.parent())) return node;
                def.replaced++;
                value_def.replaced--;
                return candidate.value;
            }
            // Skip (non-executed) functions and (leading) default case in switch statements
            if (node instanceof AST_Default || node instanceof AST_Scope) return node;
        });
        while (--stat_index >= 0) {
            // Treat parameters as collapsible in IIFE, i.e.
            //   function(a, b){ ... }(x());
            // would be translated into equivalent assignments:
            //   var a = x(), b = undefined;
            if (stat_index == 0 && compressor.option("unused")) extract_args();
            // Find collapsible assignments
            var hit_stack = [];
            extract_candidates(statements[stat_index]);
            while (candidates.length > 0) {
                hit_stack = candidates.pop();
                var hit_index = 0;
                var candidate = hit_stack[hit_stack.length - 1];
                var value_def = null;
                var stop_after = null;
                var stop_if_hit = 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);
                var lhs_local = is_lhs_local(lhs);
                if (lhs instanceof AST_SymbolRef) lvalues.set(lhs.name, false);
                var side_effects = value_has_side_effects(candidate);
                var replace_all = replace_all_symbols();
                var may_throw = candidate.may_throw(compressor);
                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++) {
                        args[j].transform(scanner);
                    }
                    can_replace = true;
                }
                for (var i = stat_index; !abort && i < statements.length; i++) {
                    statements[i].transform(scanner);
                }
                if (value_def) {
                    var def = candidate.name.definition();
                    if (abort && def.references.length - def.replaced > replaced) replaced = false;
                    else {
                        abort = false;
                        hit_index = 0;
                        hit = funarg;
                        for (var i = stat_index; !abort && i < statements.length; i++) {
                            statements[i].transform(multi_replacer);
                        }
                        value_def.single_use = false;
                    }
                }
                if (replaced && !remove_candidate(candidate)) statements.splice(stat_index, 1);
            }
        }

function handle_custom_scan_order(node) {
            // Skip (non-executed) functions
            if (node instanceof AST_Scope) return node;

// Scan case expressions first in a switch statement
            if (node instanceof AST_Switch) {
                node.expression = node.expression.transform(scanner);
                for (var i = 0, len = node.body.length; !abort && i < len; i++) {
                    var branch = node.body[i];
                    if (branch instanceof AST_Case) {
                        if (!hit) {
                            if (branch !== hit_stack[hit_index]) continue;
                            hit_index++;
                        }
                        branch.expression = branch.expression.transform(scanner);
                        if (!replace_all) break;
                    }
                }
                abort = true;
                return node;
            }
        }

function redefined_within_scope(def, scope) {
            if (def.global) return false;
            let cur_scope = def.scope;
            while (cur_scope && cur_scope !== scope) {
                if (cur_scope.variables.has(def.name)) return true;
                cur_scope = cur_scope.parent_scope;
            }
            return false;
        }

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_rvalue(expr) {
            if (expr instanceof AST_Assign) {
                return expr.right;
            } else {
                return expr.value;
            }
        }

function is_lhs_local(lhs) {
            while (lhs instanceof AST_PropAccess) lhs = lhs.expression;
            return lhs instanceof AST_SymbolRef
                && lhs.definition().scope === scope
                && !(in_loop
                    && (lvalues.has(lhs.name)
                        || candidate instanceof AST_Unary
                        || (candidate instanceof AST_Assign
                            && !candidate.logical
                            && candidate.operator != "=")));
        }

function value_has_side_effects(expr) {
            if (expr instanceof AST_Unary) return unary_side_effects.has(expr.operator);
            return get_rvalue(expr).has_side_effects(compressor);
        }

function may_modify(sym) {
            if (!sym.definition) return true; // AST_Destructuring
            var def = sym.definition();
            if (def.orig.length == 1 && def.orig[0] instanceof AST_SymbolDefun) return false;
            if (def.scope.get_defun_scope() !== scope) return true;
            return !def.references.every((ref) => {
                var s = ref.scope.get_defun_scope();
                // "block" scope within AST_Catch
                if (s.TYPE == "Scope") s = s.parent_scope;
                return s === scope;
            });
        }

function side_effects_external(node, lhs) {
            if (node instanceof AST_Assign) return side_effects_external(node.left, true);
            if (node instanceof AST_Unary) return side_effects_external(node.expression, true);
            if (node instanceof AST_VarDef) return node.value && side_effects_external(node.value);
            if (lhs) {
                if (node instanceof AST_Dot) return side_effects_external(node.expression, true);
                if (node instanceof AST_Sub) return side_effects_external(node.expression, true);
                if (node instanceof AST_SymbolRef) return node.definition().scope !== scope;
            }
            return false;
        }
    }

function handle_if_return(statements, compressor) {
        var self = compressor.self();
        var multiple_if_returns = has_multiple_if_returns(statements);
        var in_lambda = self instanceof AST_Lambda;
        for (var i = statements.length; --i >= 0;) {
            var stat = statements[i];
            var j = next_index(i);
            var next = statements[j];

if (in_lambda && !next && stat instanceof AST_Return) {
                if (!stat.value) {
                    CHANGED = true;
                    statements.splice(i, 1);
                    continue;
                }
                if (stat.value instanceof AST_UnaryPrefix && stat.value.operator == "void") {
                    CHANGED = true;
                    statements[i] = make_node(AST_SimpleStatement, stat, {
                        body: stat.value.expression
                    });
                    continue;
                }
            }

if (stat instanceof AST_If) {
                var ab = aborts(stat.body);
                if (can_merge_flow(ab)) {
                    if (ab.label) {
                        remove(ab.label.thedef.references, ab);
                    }
                    CHANGED = true;
                    stat = stat.clone();
                    stat.condition = stat.condition.negate(compressor);
                    var body = as_statement_array_with_return(stat.body, ab);
                    stat.body = make_node(AST_BlockStatement, stat, {
                        body: as_statement_array(stat.alternative).concat(extract_functions())
                    });
                    stat.alternative = make_node(AST_BlockStatement, stat, {
                        body: body
                    });
                    statements[i] = stat.transform(compressor);
                    continue;
                }

if (stat instanceof AST_If && stat.body instanceof AST_Return) {
                var value = stat.body.value;
                //---
                // pretty silly case, but:
                // if (foo()) return; return; ==> foo(); return;
                if (!value && !stat.alternative
                    && (in_lambda && !next || next instanceof AST_Return && !next.value)) {
                    CHANGED = true;
                    statements[i] = make_node(AST_SimpleStatement, stat.condition, {
                        body: stat.condition
                    });
                    continue;
                }
                //---
                // if (foo()) return x; return y; ==> return foo() ? x : y;
                if (value && !stat.alternative && next instanceof AST_Return && next.value) {
                    CHANGED = true;
                    stat = stat.clone();
                    stat.alternative = next;
                    statements[i] = stat.transform(compressor);
                    statements.splice(j, 1);
                    continue;
                }
                //---
                // if (foo()) return x; [ return ; ] ==> return foo() ? x : undefined;
                if (value && !stat.alternative
                    && (!next && in_lambda && multiple_if_returns
                        || next instanceof AST_Return)) {
                    CHANGED = true;
                    stat = stat.clone();
                    stat.alternative = next || make_node(AST_Return, stat, {
                        value: null
                    });
                    statements[i] = stat.transform(compressor);
                    if (next) statements.splice(j, 1);
                    continue;
                }
                //---
                // if (a) return b; if (c) return d; e; ==> return a ? b : c ? d : void e;
                //
                // if sequences is not enabled, this can lead to an endless loop (issue #866).
                // however, with sequences on this helps producing slightly better output for
                // the example code.
                var prev = statements[prev_index(i)];
                if (compressor.option("sequences") && in_lambda && !stat.alternative
                    && prev instanceof AST_If && prev.body instanceof AST_Return
                    && next_index(j) == statements.length && next instanceof AST_SimpleStatement) {
                    CHANGED = true;
                    stat = stat.clone();
                    stat.alternative = make_node(AST_BlockStatement, next, {
                        body: [
                            next,
                            make_node(AST_Return, next, {
                                value: null
                            })
                        ]
                    });
                    statements[i] = stat.transform(compressor);
                    statements.splice(j, 1);
                    continue;
                }
            }
        }

function is_return_void(value) {
            return !value || value instanceof AST_UnaryPrefix && value.operator == "void";
        }

function can_merge_flow(ab) {
            if (!ab) return false;
            for (var j = i + 1, len = statements.length; j < len; j++) {
                var stat = statements[j];
                if (stat instanceof AST_Const || stat instanceof AST_Let) return false;
            }
            var lct = ab instanceof AST_LoopControl ? compressor.loopcontrol_target(ab) : null;
            return ab instanceof AST_Return && in_lambda && is_return_void(ab.value)
                || ab instanceof AST_Continue && self === loop_body(lct)
                || ab instanceof AST_Break && lct instanceof AST_BlockStatement && self === lct;
        }

function declarations_only(node) {
        return node.definitions.every((var_def) =>
            !var_def.value
        );
    }

function is_undefined(node, compressor) {
    return (
        has_flag(node, UNDEFINED)
        || node instanceof AST_Undefined
        || node instanceof AST_UnaryPrefix
            && node.operator == "void"
            && !node.expression.has_side_effects(compressor)
    );
}

// may_throw_on_access()
// returns true if this node may be null, undefined or contain `AST_Accessor`
(function(def_may_throw_on_access) {
    AST_Node.DEFMETHOD("may_throw_on_access", function(compressor) {
        return !compressor.option("pure_getters")
            || this._dot_throw(compressor);
    });

function is_strict(compressor) {
        return /strict/.test(compressor.option("pure_getters"));
    }

def_may_throw_on_access(AST_Node, is_strict);
    def_may_throw_on_access(AST_Null, return_true);
    def_may_throw_on_access(AST_Undefined, return_true);
    def_may_throw_on_access(AST_Constant, return_false);
    def_may_throw_on_access(AST_Array, return_false);
    def_may_throw_on_access(AST_Object, function(compressor) {
        if (!is_strict(compressor)) return false;
        for (var i = this.properties.length; --i >=0;)
            if (this.properties[i]._dot_throw(compressor)) return true;
        return false;
    });
    // Do not be as strict with classes as we are with objects.
    // Hopefully the community is not going to abuse static getters and setters.
    // https://github.com/terser/terser/issues/724#issuecomment-643655656
    def_may_throw_on_access(AST_Class, return_false);
    def_may_throw_on_access(AST_ObjectProperty, return_false);
    def_may_throw_on_access(AST_ObjectGetter, return_true);
    def_may_throw_on_access(AST_Expansion, function(compressor) {
        return this.expression._dot_throw(compressor);
    });
    def_may_throw_on_access(AST_Function, return_false);
    def_may_throw_on_access(AST_Arrow, return_false);
    def_may_throw_on_access(AST_UnaryPostfix, return_false);
    def_may_throw_on_access(AST_UnaryPrefix, function() {
        return this.operator == "void";
    });
    def_may_throw_on_access(AST_Binary, function(compressor) {
        return (this.operator == "&&" || this.operator == "||" || this.operator == "??")
            && (this.left._dot_throw(compressor) || this.right._dot_throw(compressor));
    });
    def_may_throw_on_access(AST_Assign, function(compressor) {
        if (this.logical) return true;

return this.operator == "="
            && this.right._dot_throw(compressor);
    });
    def_may_throw_on_access(AST_Conditional, function(compressor) {
        return this.consequent._dot_throw(compressor)
            || this.alternative._dot_throw(compressor);
    });
    def_may_throw_on_access(AST_Dot, function(compressor) {
        if (!is_strict(compressor)) return false;
        if (this.expression instanceof AST_Function && this.property == "prototype") return false;
        return true;
    });
    def_may_throw_on_access(AST_Chain, function(compressor) {
        return this.expression._dot_throw(compressor);
    });
    def_may_throw_on_access(AST_Sequence, function(compressor) {
        return this.tail_node()._dot_throw(compressor);
    });
    def_may_throw_on_access(AST_SymbolRef, function(compressor) {
        if (this.name === "arguments") return false;
        if (has_flag(this, UNDEFINED)) return true;
        if (!is_strict(compressor)) return false;
        if (is_undeclared_ref(this) && this.is_declared(compressor)) return false;
        if (this.is_immutable()) return false;
        var fixed = this.fixed_value();
        return !fixed || fixed._dot_throw(compressor);
    });
})(function(node, func) {
    node.DEFMETHOD("_dot_throw", func);
});

/* -----[ boolean/negation helpers ]----- */

// methods to determine whether an expression has a boolean result type
(function(def_is_boolean) {
    const unary_bool = makePredicate("! delete");
    const binary_bool = makePredicate("in instanceof == != === !== < <= >= >");
    def_is_boolean(AST_Node, return_false);
    def_is_boolean(AST_UnaryPrefix, function() {
        return unary_bool.has(this.operator);
    });
    def_is_boolean(AST_Binary, function() {
        return binary_bool.has(this.operator)
            || lazy_op.has(this.operator)
                && this.left.is_boolean()
                && this.right.is_boolean();
    });
    def_is_boolean(AST_Conditional, function() {
        return this.consequent.is_boolean() && this.alternative.is_boolean();
    });
    def_is_boolean(AST_Assign, function() {
        return this.operator == "=" && this.right.is_boolean();
    });
    def_is_boolean(AST_Sequence, function() {
        return this.tail_node().is_boolean();
    });
    def_is_boolean(AST_True, return_true);
    def_is_boolean(AST_False, return_true);
})(function(node, func) {
    node.DEFMETHOD("is_boolean", func);
});

// methods to determine if an expression has a numeric result type
(function(def_is_number) {
    def_is_number(AST_Node, return_false);
    def_is_number(AST_Number, return_true);
    var unary = makePredicate("+ - ~ ++ --");
    def_is_number(AST_Unary, function() {
        return unary.has(this.operator);
    });
    var binary = makePredicate("- * / % & | ^ << >> >>>");
    def_is_number(AST_Binary, function(compressor) {
        return binary.has(this.operator) || this.operator == "+"
            && this.left.is_number(compressor)
            && this.right.is_number(compressor);
    });
    def_is_number(AST_Assign, function(compressor) {
        return binary.has(this.operator.slice(0, -1))
            || this.operator == "=" && this.right.is_number(compressor);
    });
    def_is_number(AST_Sequence, function(compressor) {
        return this.tail_node().is_number(compressor);
    });
    def_is_number(AST_Conditional, function(compressor) {
        return this.consequent.is_number(compressor) && this.alternative.is_number(compressor);
    });
})(function(node, func) {
    node.DEFMETHOD("is_number", func);
});

// methods to determine if an expression has a string result type
(function(def_is_string) {
    def_is_string(AST_Node, return_false);
    def_is_string(AST_String, return_true);
    def_is_string(AST_TemplateString, return_true);
    def_is_string(AST_UnaryPrefix, function() {
        return this.operator == "typeof";
    });
    def_is_string(AST_Binary, function(compressor) {
        return this.operator == "+" &&
            (this.left.is_string(compressor) || this.right.is_string(compressor));
    });
    def_is_string(AST_Assign, function(compressor) {
        return (this.operator == "=" || this.operator == "+=") && this.right.is_string(compressor);
    });
    def_is_string(AST_Sequence, function(compressor) {
        return this.tail_node().is_string(compressor);
    });
    def_is_string(AST_Conditional, function(compressor) {
        return this.consequent.is_string(compressor) && this.alternative.is_string(compressor);
    });
})(function(node, func) {
    node.DEFMETHOD("is_string", func);
});

var lazy_op = makePredicate("&& || ??");
var unary_side_effects = makePredicate("delete ++ --");

function is_lhs(node, parent) {
    if (parent instanceof AST_Unary && unary_side_effects.has(parent.operator)) return parent.expression;
    if (parent instanceof AST_Assign && parent.left === node) return node;
}

AST_Toplevel.DEFMETHOD("resolve_defines", function(compressor) {
        if (!compressor.option("global_defs")) return this;
        this.figure_out_scope({ ie8: compressor.option("ie8") });
        return this.transform(new TreeTransformer(function(node) {
            var def = node._find_defs(compressor, "");
            if (!def) return;
            var level = 0, child = node, parent;
            while (parent = this.parent(level++)) {
                if (!(parent instanceof AST_PropAccess)) break;
                if (parent.expression !== child) break;
                child = parent;
            }
            if (is_lhs(child, parent)) {
                return;
            }
            return def;
        }));
    });
    def_find_defs(AST_Node, noop);
    def_find_defs(AST_Chain, function(compressor, suffix) {
        return this.expression._find_defs(compressor, suffix);
    });
    def_find_defs(AST_Dot, function(compressor, suffix) {
        return this.expression._find_defs(compressor, "." + this.property + suffix);
    });
    def_find_defs(AST_SymbolDeclaration, function() {
        if (!this.global()) return;
    });
    def_find_defs(AST_SymbolRef, function(compressor, suffix) {
        if (!this.global()) return;
        var defines = compressor.option("global_defs");
        var name = this.name + suffix;
        if (HOP(defines, name)) return to_node(defines[name], this);
    });
})(function(node, func) {
    node.DEFMETHOD("_find_defs", func);
});

function best_of_expression(ast1, ast2) {
    return ast1.size() > ast2.size() ? ast2 : ast1;
}

function best_of_statement(ast1, ast2) {
    return best_of_expression(
        make_node(AST_SimpleStatement, ast1, {
            body: ast1
        }),
        make_node(AST_SimpleStatement, ast2, {
            body: ast2
        })
    ).body;
}

function best_of(compressor, ast1, ast2) {
    return (first_in_statement(compressor) ? best_of_statement : best_of_expression)(ast1, ast2);
}

function convert_to_predicate(obj) {
    const out = new Map();
    for (var key of Object.keys(obj)) {
        out.set(key, makePredicate(obj[key]));
    }
    return out;
}

var object_fns = [
    "constructor",
    "toString",
    "valueOf",
];
var native_fns = convert_to_predicate({
    Array: [
        "indexOf",
        "join",
        "lastIndexOf",
        "slice",
    ].concat(object_fns),
    Boolean: object_fns,
    Function: object_fns,
    Number: [
        "toExponential",
        "toFixed",
        "toPrecision",
    ].concat(object_fns),
    Object: object_fns,
    RegExp: [
        "test",
    ].concat(object_fns),
    String: [
        "charAt",
        "charCodeAt",
        "concat",
        "indexOf",
        "italics",
        "lastIndexOf",
        "match",
        "replace",
        "search",
        "slice",
        "split",
        "substr",
        "substring",
        "toLowerCase",
        "toUpperCase",
        "trim",
    ].concat(object_fns),
});
var static_fns = convert_to_predicate({
    Array: [
        "isArray",
    ],
    Math: [
        "abs",
        "acos",
        "asin",
        "atan",
        "ceil",
        "cos",
        "exp",
        "floor",
        "log",
        "round",
        "sin",
        "sqrt",
        "tan",
        "atan2",
        "pow",
        "max",
        "min",
    ],
    Number: [
        "isFinite",
        "isNaN",
    ],
    Object: [
        "create",
        "getOwnPropertyDescriptor",
        "getOwnPropertyNames",
        "getPrototypeOf",
        "isExtensible",
        "isFrozen",
        "isSealed",
        "keys",
    ],
    String: [
        "fromCharCode",
    ],
});

// methods to evaluate a constant expression
(function(def_eval) {
    // If the node has been successfully reduced to a constant,
    // then its value is returned; otherwise the element itself
    // is returned.
    // They can be distinguished as constant value is never a
    // descendant of AST_Node.
    AST_Node.DEFMETHOD("evaluate", function(compressor) {
        if (!compressor.option("evaluate")) return this;
        var val = this._eval(compressor, 1);
        if (!val || val instanceof RegExp) return val;
        if (typeof val == "function" || typeof val == "object") return this;
        return val;
    });
    var unaryPrefix = makePredicate("! ~ - + void");
    AST_Node.DEFMETHOD("is_constant", function() {
        // Accomodate when compress option evaluate=false
        // as well as the common constant expressions !0 and -1
        if (this instanceof AST_Constant) {
            return !(this instanceof AST_RegExp);
        } else {
            return this instanceof AST_UnaryPrefix
                && this.expression instanceof AST_Constant
                && unaryPrefix.has(this.operator);
        }
    });
    def_eval(AST_Statement, function() {
        throw new Error(string_template("Cannot evaluate a statement [{file}:{line},{col}]", this.start));
    });
    def_eval(AST_Lambda, return_this);
    def_eval(AST_Class, return_this);
    def_eval(AST_Node, return_this);
    def_eval(AST_Constant, function() {
        return this.getValue();
    });
    def_eval(AST_BigInt, return_this);
    def_eval(AST_RegExp, function(compressor) {
        let evaluated = compressor.evaluated_regexps.get(this);
        if (evaluated === undefined) {
            try {
                evaluated = (0, eval)(this.print_to_string());
            } catch (e) {
                evaluated = null;
            }
            compressor.evaluated_regexps.set(this, evaluated);
        }
        return evaluated || this;
    });
    def_eval(AST_TemplateString, function() {
        if (this.segments.length !== 1) return this;
        return this.segments[0].value;
    });
    def_eval(AST_Function, function(compressor) {
        if (compressor.option("unsafe")) {
            var fn = function() {};
            fn.node = this;
            fn.toString = function() {
                return this.node.print_to_string();
            };
            return fn;
        }
        return this;
    });
    def_eval(AST_Array, function(compressor, depth) {
        if (compressor.option("unsafe")) {
            var elements = [];
            for (var i = 0, len = this.elements.length; i < len; i++) {
                var element = this.elements[i];
                var value = element._eval(compressor, depth);
                if (element === value) return this;
                elements.push(value);
            }
            return elements;
        }
        return this;
    });
    def_eval(AST_Object, function(compressor, depth) {
        if (compressor.option("unsafe")) {
            var val = {};
            for (var i = 0, len = this.properties.length; i < len; i++) {
                var prop = this.properties[i];
                if (prop instanceof AST_Expansion) return this;
                var key = prop.key;
                if (key instanceof AST_Symbol) {
                    key = key.name;
                } else if (key instanceof AST_Node) {
                    key = key._eval(compressor, depth);
                    if (key === prop.key) return this;
                }
                if (typeof Object.prototype[key] === "function") {
                    return this;
                }
                if (prop.value instanceof AST_Function) continue;
                val[key] = prop.value._eval(compressor, depth);
                if (val[key] === prop.value) return this;
            }
            return val;
        }
        return this;
    });
    var non_converting_unary = makePredicate("! typeof void");
    def_eval(AST_UnaryPrefix, function(compressor, depth) {
        var e = this.expression;
        // Function would be evaluated to an array and so typeof would
        // incorrectly return 'object'. Hence making is a special case.
        if (compressor.option("typeofs")
            && this.operator == "typeof"
            && (e instanceof AST_Lambda
                || e instanceof AST_SymbolRef
                    && e.fixed_value() instanceof AST_Lambda)) {
            return typeof function() {};
        }
        if (!non_converting_unary.has(this.operator)) depth++;
        e = e._eval(compressor, depth);
        if (e === this.expression) return this;
        switch (this.operator) {
          case "!": return !e;
          case "typeof":
            // typeof <RegExp> returns "object" or "function" on different platforms
            // so cannot evaluate reliably
            if (e instanceof RegExp) return this;
            return typeof e;
          case "void": return void e;
          case "~": return ~e;
          case "-": return -e;
          case "+": return +e;
        }
        return this;
    });
    var non_converting_binary = makePredicate("&& || ?? === !==");
    const identity_comparison = makePredicate("== != === !==");
    const has_identity = value =>
        typeof value === "object"
        || typeof value === "function"
        || typeof value === "symbol";

def_eval(AST_Binary, function(compressor, depth) {
        if (!non_converting_binary.has(this.operator)) depth++;

var left = this.left._eval(compressor, depth);
        if (left === this.left) return this;
        var right = this.right._eval(compressor, depth);
        if (right === this.right) return this;
        var result;

if (
            left != null
            && right != null
            && identity_comparison.has(this.operator)
            && has_identity(left)
            && has_identity(right)
            && typeof left === typeof right
        ) {
            // Do not compare by reference
            return this;
        }

switch (this.operator) {
          case "&&"  : result = left &&  right; break;
          case "||"  : result = left ||  right; break;
          case "??"  : result = left != null ? left : right; break;
          case "|"   : result = left |   right; break;
          case "&"   : result = left &   right; break;
          case "^"   : result = left ^   right; break;
          case "+"   : result = left +   right; break;
          case "*"   : result = left *   right; break;
          case "**"  : result = Math.pow(left, right); break;
          case "/"   : result = left /   right; break;
          case "%"   : result = left %   right; break;
          case "-"   : result = left -   right; break;
          case "<<"  : result = left <<  right; break;
          case ">>"  : result = left >>  right; break;
          case ">>>" : result = left >>> right; break;
          case "=="  : result = left ==  right; break;
          case "===" : result = left === right; break;
          case "!="  : result = left !=  right; break;
          case "!==" : result = left !== right; break;
          case "<"   : result = left <   right; break;
          case "<="  : result = left <=  right; break;
          case ">"   : result = left >   right; break;
          case ">="  : result = left >=  right; break;
          default:
              return this;
        }
        if (isNaN(result) && compressor.find_parent(AST_With)) {
            // leave original expression as is
            return this;
        }
        return result;
    });
    def_eval(AST_Conditional, function(compressor, depth) {
        var condition = this.condition._eval(compressor, depth);
        if (condition === this.condition) return this;
        var node = condition ? this.consequent : this.alternative;
        var value = node._eval(compressor, depth);
        return value === node ? this : value;
    });

// Set of AST_SymbolRef which are currently being evaluated.
    // Avoids infinite recursion of ._eval()
    const reentrant_ref_eval = new Set();
    def_eval(AST_SymbolRef, function(compressor, depth) {
        if (reentrant_ref_eval.has(this)) return this;

var fixed = this.fixed_value();
        if (!fixed) return this;

reentrant_ref_eval.add(this);
        const value = fixed._eval(compressor, depth);
        reentrant_ref_eval.delete(this);

if (value === fixed) return this;

if (value && typeof value == "object") {
            var escaped = this.definition().escaped;
            if (escaped && depth > escaped) return this;
        }
        return value;
    });
    var global_objs = { Array, Math, Number, Object, String };
    var static_values = convert_to_predicate({
        Math: [
            "E",
            "LN10",
            "LN2",
            "LOG2E",
            "LOG10E",
            "PI",
            "SQRT1_2",
            "SQRT2",
        ],
        Number: [
            "MAX_VALUE",
            "MIN_VALUE",
            "NaN",
            "NEGATIVE_INFINITY",
            "POSITIVE_INFINITY",
        ],
    });
    def_eval(AST_PropAccess, function(compressor, depth) {
        if (this.optional) {
            const obj = this.expression._eval(compressor, depth);
            if (obj == null) return undefined;
        }
        if (compressor.option("unsafe")) {
            var key = this.property;
            if (key instanceof AST_Node) {
                key = key._eval(compressor, depth);
                if (key === this.property) return this;
            }
            var exp = this.expression;
            var val;
            if (is_undeclared_ref(exp)) {

var aa;
                var first_arg = exp.name === "hasOwnProperty"
                    && key === "call"
                    && (aa = compressor.parent() && compressor.parent().args)
                    && (aa && aa[0]
                    && aa[0].evaluate(compressor));

first_arg = first_arg instanceof AST_Dot ? first_arg.expression : first_arg;

if (first_arg == null || first_arg.thedef && first_arg.thedef.undeclared) {
                    return this.clone();
                }
                var static_value = static_values.get(exp.name);
                if (!static_value || !static_value.has(key)) return this;
                val = global_objs[exp.name];
            } else {
                val = exp._eval(compressor, depth + 1);
                if (!val || val === exp || !HOP(val, key)) return this;
                if (typeof val == "function") switch (key) {
                  case "name":
                    return val.node.name ? val.node.name.name : "";
                  case "length":
                    return val.node.argnames.length;
                  default:
                    return this;
                }
            }
            return val[key];
        }
        return this;
    });
    def_eval(AST_Chain, function(compressor, depth) {
        const evaluated = this.expression._eval(compressor, depth);
        return evaluated === this.expression ? this : evaluated;
    });
    def_eval(AST_Call, function(compressor, depth) {
        var exp = this.expression;
        if (this.optional) {
            const callee = this.expression._eval(compressor, depth);
            if (callee == null) return undefined;
        }
        if (compressor.option("unsafe") && exp instanceof AST_PropAccess) {
            var key = exp.property;
            if (key instanceof AST_Node) {
                key = key._eval(compressor, depth);
                if (key === exp.property) return this;
            }
            var val;
            var e = exp.expression;
            if (is_undeclared_ref(e)) {
                var first_arg =
                    e.name === "hasOwnProperty" &&
                    key === "call" &&
                    (this.args[0] && this.args[0].evaluate(compressor));

first_arg = first_arg instanceof AST_Dot ? first_arg.expression : first_arg;

if ((first_arg == null || first_arg.thedef && first_arg.thedef.undeclared)) {
                    return this.clone();
                }
                var static_fn = static_fns.get(e.name);
                if (!static_fn || !static_fn.has(key)) return this;
                val = global_objs[e.name];
            } else {
                val = e._eval(compressor, depth + 1);
                if (val === e || !val) return this;
                var native_fn = native_fns.get(val.constructor.name);
                if (!native_fn || !native_fn.has(key)) return this;
            }
            var args = [];
            for (var i = 0, len = this.args.length; i < len; i++) {
                var arg = this.args[i];
                var value = arg._eval(compressor, depth);
                if (arg === value) return this;
                args.push(value);
            }
            try {
                return val[key].apply(val, args);
            } catch (ex) {
                // We don't really care
            }
        }
        return this;
    });
    def_eval(AST_New, return_this);
})(function(node, func) {
    node.DEFMETHOD("_eval", func);
});

// method to negate an expression
(function(def_negate) {
    function basic_negation(exp) {
        return make_node(AST_UnaryPrefix, exp, {
            operator: "!",
            expression: exp
        });
    }
    function best(orig, alt, first_in_statement) {
        var negated = basic_negation(orig);
        if (first_in_statement) {
            var stat = make_node(AST_SimpleStatement, alt, {
                body: alt
            });
            return best_of_expression(negated, stat) === stat ? alt : negated;
        }
        return best_of_expression(negated, alt);
    }
    def_negate(AST_Node, function() {
        return basic_negation(this);
    });
    def_negate(AST_Statement, function() {
        throw new Error("Cannot negate a statement");
    });
    def_negate(AST_Function, function() {
        return basic_negation(this);
    });
    def_negate(AST_Arrow, function() {
        return basic_negation(this);
    });
    def_negate(AST_UnaryPrefix, function() {
        if (this.operator == "!")
            return this.expression;
        return basic_negation(this);
    });
    def_negate(AST_Sequence, function(compressor) {
        var expressions = this.expressions.slice();
        expressions.push(expressions.pop().negate(compressor));
        return make_sequence(this, expressions);
    });
    def_negate(AST_Conditional, function(compressor, first_in_statement) {
        var self = this.clone();
        self.consequent = self.consequent.negate(compressor);
        self.alternative = self.alternative.negate(compressor);
        return best(this, self, first_in_statement);
    });
    def_negate(AST_Binary, function(compressor, first_in_statement) {
        var self = this.clone(), op = this.operator;
        if (compressor.option("unsafe_comps")) {
            switch (op) {
              case "<=" : self.operator = ">"  ; return self;
              case "<"  : self.operator = ">=" ; return self;
              case ">=" : self.operator = "<"  ; return self;
              case ">"  : self.operator = "<=" ; return self;
            }
        }
        switch (op) {
          case "==" : self.operator = "!="; return self;
          case "!=" : self.operator = "=="; return self;
          case "===": self.operator = "!=="; return self;
          case "!==": self.operator = "==="; return self;
          case "&&":
            self.operator = "||";
            self.left = self.left.negate(compressor, first_in_statement);
            self.right = self.right.negate(compressor);
            return best(this, self, first_in_statement);
          case "||":
            self.operator = "&&";
            self.left = self.left.negate(compressor, first_in_statement);
            self.right = self.right.negate(compressor);
            return best(this, self, first_in_statement);
          case "??":
            self.right = self.right.negate(compressor);
            return best(this, self, first_in_statement);
        }
        return basic_negation(this);
    });
})(function(node, func) {
    node.DEFMETHOD("negate", function(compressor, first_in_statement) {
        return func.call(this, compressor, first_in_statement);
    });
});

const pure_prop_access_globals = new Set([
    "Number",
    "String",
    "Array",
    "Object",
    "Function",
    "Promise",
]);
// determine if expression has side effects
(function(def_has_side_effects) {
    def_has_side_effects(AST_Node, return_true);

def_has_side_effects(AST_EmptyStatement, return_false);
    def_has_side_effects(AST_Constant, return_false);
    def_has_side_effects(AST_This, return_false);

function any(list, compressor) {
        for (var i = list.length; --i >= 0;)
            if (list[i].has_side_effects(compressor))
                return true;
        return false;
    }

def_has_side_effects(AST_Block, function(compressor) {
        return any(this.body, compressor);
    });
    def_has_side_effects(AST_Call, function(compressor) {
        if (
            !this.is_expr_pure(compressor)
            && (!this.expression.is_call_pure(compressor)
                || this.expression.has_side_effects(compressor))
        ) {
            return true;
        }
        return any(this.args, compressor);
    });
    def_has_side_effects(AST_Switch, function(compressor) {
        return this.expression.has_side_effects(compressor)
            || any(this.body, compressor);
    });
    def_has_side_effects(AST_Case, function(compressor) {
        return this.expression.has_side_effects(compressor)
            || any(this.body, compressor);
    });
    def_has_side_effects(AST_Try, function(compressor) {
        return any(this.body, compressor)
            || this.bcatch && this.bcatch.has_side_effects(compressor)
            || this.bfinally && this.bfinally.has_side_effects(compressor);
    });
    def_has_side_effects(AST_If, function(compressor) {
        return this.condition.has_side_effects(compressor)
            || this.body && this.body.has_side_effects(compressor)
            || this.alternative && this.alternative.has_side_effects(compressor);
    });
    def_has_side_effects(AST_LabeledStatement, function(compressor) {
        return this.body.has_side_effects(compressor);
    });
    def_has_side_effects(AST_SimpleStatement, function(compressor) {
        return this.body.has_side_effects(compressor);
    });
    def_has_side_effects(AST_Lambda, return_false);
    def_has_side_effects(AST_Class, function (compressor) {
        if (this.extends && this.extends.has_side_effects(compressor)) {
            return true;
        }
        return any(this.properties, compressor);
    });
    def_has_side_effects(AST_Binary, function(compressor) {
        return this.left.has_side_effects(compressor)
            || this.right.has_side_effects(compressor);
    });
    def_has_side_effects(AST_Assign, return_true);
    def_has_side_effects(AST_Conditional, function(compressor) {
        return this.condition.has_side_effects(compressor)
            || this.consequent.has_side_effects(compressor)
            || this.alternative.has_side_effects(compressor);
    });
    def_has_side_effects(AST_Unary, function(compressor) {
        return unary_side_effects.has(this.operator)
            || this.expression.has_side_effects(compressor);
    });
    def_has_side_effects(AST_SymbolRef, function(compressor) {
        return !this.is_declared(compressor) && !pure_prop_access_globals.has(this.name);
    });
    def_has_side_effects(AST_SymbolClassProperty, return_false);
    def_has_side_effects(AST_SymbolDeclaration, return_false);
    def_has_side_effects(AST_Object, function(compressor) {
        return any(this.properties, compressor);
    });
    def_has_side_effects(AST_ObjectProperty, function(compressor) {
        return (
            this.computed_key() && this.key.has_side_effects(compressor)
            || this.value && this.value.has_side_effects(compressor)
        );
    });
    def_has_side_effects(AST_ClassProperty, function(compressor) {
        return (
            this.computed_key() && this.key.has_side_effects(compressor)
            || this.static && this.value && this.value.has_side_effects(compressor)
        );
    });
    def_has_side_effects(AST_ConciseMethod, function(compressor) {
        return this.computed_key() && this.key.has_side_effects(compressor);
    });
    def_has_side_effects(AST_ObjectGetter, function(compressor) {
        return this.computed_key() && this.key.has_side_effects(compressor);
    });
    def_has_side_effects(AST_ObjectSetter, function(compressor) {
        return this.computed_key() && this.key.has_side_effects(compressor);
    });
    def_has_side_effects(AST_Array, function(compressor) {
        return any(this.elements, compressor);
    });
    def_has_side_effects(AST_Dot, function(compressor) {
        return !this.optional && this.expression.may_throw_on_access(compressor)
            || this.expression.has_side_effects(compressor);
    });
    def_has_side_effects(AST_Sub, function(compressor) {
        if (this.optional && is_nullish(this.expression)) {
            return false;
        }

return !this.optional && this.expression.may_throw_on_access(compressor)
            || this.expression.has_side_effects(compressor)
            || this.property.has_side_effects(compressor);
    });
    def_has_side_effects(AST_Chain, function (compressor) {
        return this.expression.has_side_effects(compressor);
    });
    def_has_side_effects(AST_Sequence, function(compressor) {
        return any(this.expressions, compressor);
    });
    def_has_side_effects(AST_Definitions, function(compressor) {
        return any(this.definitions, compressor);
    });
    def_has_side_effects(AST_VarDef, function() {
        return this.value;
    });
    def_has_side_effects(AST_TemplateSegment, return_false);
    def_has_side_effects(AST_TemplateString, function(compressor) {
        return any(this.segments, compressor);
    });
})(function(node, func) {
    node.DEFMETHOD("has_side_effects", func);
});

// determine if expression may throw
(function(def_may_throw) {
    def_may_throw(AST_Node, return_true);

def_may_throw(AST_Constant, return_false);
    def_may_throw(AST_EmptyStatement, return_false);
    def_may_throw(AST_Lambda, return_false);
    def_may_throw(AST_SymbolDeclaration, return_false);
    def_may_throw(AST_This, return_false);

function any(list, compressor) {
        for (var i = list.length; --i >= 0;)
            if (list[i].may_throw(compressor))
                return true;
        return false;
    }

def_may_throw(AST_Class, function(compressor) {
        if (this.extends && this.extends.may_throw(compressor)) return true;
        return any(this.properties, compressor);
    });

def_may_throw(AST_Array, function(compressor) {
        return any(this.elements, compressor);
    });
    def_may_throw(AST_Assign, function(compressor) {
        if (this.right.may_throw(compressor)) return true;
        if (!compressor.has_directive("use strict")
            && this.operator == "="
            && this.left instanceof AST_SymbolRef) {
            return false;
        }
        return this.left.may_throw(compressor);
    });
    def_may_throw(AST_Binary, function(compressor) {
        return this.left.may_throw(compressor)
            || this.right.may_throw(compressor);
    });
    def_may_throw(AST_Block, function(compressor) {
        return any(this.body, compressor);
    });
    def_may_throw(AST_Call, function(compressor) {
        if (this.optional && is_nullish(this.expression)) return false;
        if (any(this.args, compressor)) return true;
        if (this.is_expr_pure(compressor)) return false;
        if (this.expression.may_throw(compressor)) return true;
        return !(this.expression instanceof AST_Lambda)
            || any(this.expression.body, compressor);
    });
    def_may_throw(AST_Case, function(compressor) {
        return this.expression.may_throw(compressor)
            || any(this.body, compressor);
    });
    def_may_throw(AST_Conditional, function(compressor) {
        return this.condition.may_throw(compressor)
            || this.consequent.may_throw(compressor)
            || this.alternative.may_throw(compressor);
    });
    def_may_throw(AST_Definitions, function(compressor) {
        return any(this.definitions, compressor);
    });
    def_may_throw(AST_If, function(compressor) {
        return this.condition.may_throw(compressor)
            || this.body && this.body.may_throw(compressor)
            || this.alternative && this.alternative.may_throw(compressor);
    });
    def_may_throw(AST_LabeledStatement, function(compressor) {
        return this.body.may_throw(compressor);
    });
    def_may_throw(AST_Object, function(compressor) {
        return any(this.properties, compressor);
    });
    def_may_throw(AST_ObjectProperty, function(compressor) {
        // TODO key may throw too
        return this.value ? this.value.may_throw(compressor) : false;
    });
    def_may_throw(AST_ClassProperty, function(compressor) {
        return (
            this.computed_key() && this.key.may_throw(compressor)
            || this.static && this.value && this.value.may_throw(compressor)
        );
    });
    def_may_throw(AST_ConciseMethod, function(compressor) {
        return this.computed_key() && this.key.may_throw(compressor);
    });
    def_may_throw(AST_ObjectGetter, function(compressor) {
        return this.computed_key() && this.key.may_throw(compressor);
    });
    def_may_throw(AST_ObjectSetter, function(compressor) {
        return this.computed_key() && this.key.may_throw(compressor);
    });
    def_may_throw(AST_Return, function(compressor) {
        return this.value && this.value.may_throw(compressor);
    });
    def_may_throw(AST_Sequence, function(compressor) {
        return any(this.expressions, compressor);
    });
    def_may_throw(AST_SimpleStatement, function(compressor) {
        return this.body.may_throw(compressor);
    });
    def_may_throw(AST_Dot, function(compressor) {
        return !this.optional && this.expression.may_throw_on_access(compressor)
            || this.expression.may_throw(compressor);
    });
    def_may_throw(AST_Sub, function(compressor) {
        if (this.optional && is_nullish(this.expression)) return false;

return !this.optional && this.expression.may_throw_on_access(compressor)
            || this.expression.may_throw(compressor)
            || this.property.may_throw(compressor);
    });
    def_may_throw(AST_Chain, function(compressor) {
        return this.expression.may_throw(compressor);
    });
    def_may_throw(AST_Switch, function(compressor) {
        return this.expression.may_throw(compressor)
            || any(this.body, compressor);
    });
    def_may_throw(AST_SymbolRef, function(compressor) {
        return !this.is_declared(compressor) && !pure_prop_access_globals.has(this.name);
    });
    def_may_throw(AST_SymbolClassProperty, return_false);
    def_may_throw(AST_Try, function(compressor) {
        return this.bcatch ? this.bcatch.may_throw(compressor) : any(this.body, compressor)
            || this.bfinally && this.bfinally.may_throw(compressor);
    });
    def_may_throw(AST_Unary, function(compressor) {
        if (this.operator == "typeof" && this.expression instanceof AST_SymbolRef)
            return false;
        return this.expression.may_throw(compressor);
    });
    def_may_throw(AST_VarDef, function(compressor) {
        if (!this.value) return false;
        return this.value.may_throw(compressor);
    });
})(function(node, func) {
    node.DEFMETHOD("may_throw", func);
});

// determine if expression is constant
(function(def_is_constant_expression) {
    function all_refs_local(scope) {
        let result = true;
        walk(this, node => {
            if (node instanceof AST_SymbolRef) {
                if (has_flag(this, INLINED)) {
                    result = false;
                    return walk_abort;
                }
                var def = node.definition();
                if (
                    member(def, this.enclosed)
                    && !this.variables.has(def.name)
                ) {
                    if (scope) {
                        var scope_def = scope.find_variable(node);
                        if (def.undeclared ? !scope_def : scope_def === def) {
                            result = "f";
                            return true;
                        }
                    }
                    result = false;
                    return walk_abort;
                }
                return true;
            }
            if (node instanceof AST_This && this instanceof AST_Arrow) {
                // TODO check arguments too!
                result = false;
                return walk_abort;
            }
        });
        return result;
    }

def_is_constant_expression(AST_Node, return_false);
    def_is_constant_expression(AST_Constant, return_true);
    def_is_constant_expression(AST_Class, function(scope) {
        if (this.extends && !this.extends.is_constant_expression(scope)) {
            return false;
        }

for (const prop of this.properties) {
            if (prop.computed_key() && !prop.key.is_constant_expression(scope)) {
                return false;
            }
            if (prop.static && prop.value && !prop.value.is_constant_expression(scope)) {
                return false;
            }
        }

return all_refs_local.call(this, scope);
    });
    def_is_constant_expression(AST_Lambda, all_refs_local);
    def_is_constant_expression(AST_Unary, function() {
        return this.expression.is_constant_expression();
    });
    def_is_constant_expression(AST_Binary, function() {
        return this.left.is_constant_expression()
            && this.right.is_constant_expression();
    });
    def_is_constant_expression(AST_Array, function() {
        return this.elements.every((l) => l.is_constant_expression());
    });
    def_is_constant_expression(AST_Object, function() {
        return this.properties.every((l) => l.is_constant_expression());
    });
    def_is_constant_expression(AST_ObjectProperty, function() {
        return !!(!(this.key instanceof AST_Node) && this.value && this.value.is_constant_expression());
    });
})(function(node, func) {
    node.DEFMETHOD("is_constant_expression", func);
});

// tell me if a statement aborts
function aborts(thing) {
    return thing && thing.aborts();
}
(function(def_aborts) {
    def_aborts(AST_Statement, return_null);
    def_aborts(AST_Jump, return_this);
    function block_aborts() {
        for (var i = 0; i < this.body.length; i++) {
            if (aborts(this.body[i])) {
                return this.body[i];
            }
        }
        return null;
    }
    def_aborts(AST_Import, function() { return null; });
    def_aborts(AST_BlockStatement, block_aborts);
    def_aborts(AST_SwitchBranch, block_aborts);
    def_aborts(AST_If, function() {
        return this.alternative && aborts(this.body) && aborts(this.alternative) && this;
    });
})(function(node, func) {
    node.DEFMETHOD("aborts", func);
});

/* -----[ optimizers ]----- */

var directives = new Set(["use asm", "use strict"]);
def_optimize(AST_Directive, function(self, compressor) {
    if (compressor.option("directives")
        && (!directives.has(self.value) || compressor.has_directive(self.value) !== self)) {
        return make_node(AST_EmptyStatement, self);
    }
    return self;
});

def_optimize(AST_Debugger, function(self, compressor) {
    if (compressor.option("drop_debugger"))
        return make_node(AST_EmptyStatement, self);
    return self;
});

def_optimize(AST_LabeledStatement, function(self, compressor) {
    if (self.body instanceof AST_Break
        && compressor.loopcontrol_target(self.body) === self.body) {
        return make_node(AST_EmptyStatement, self);
    }
    return self.label.references.length == 0 ? self.body : self;
});

def_optimize(AST_Block, function(self, compressor) {
    tighten_body(self.body, compressor);
    return self;
});

function can_be_extracted_from_if_block(node) {
    return !(
        node instanceof AST_Const
        || node instanceof AST_Let
        || node instanceof AST_Class
    );
}

def_optimize(AST_BlockStatement, function(self, compressor) {
    tighten_body(self.body, compressor);
    switch (self.body.length) {
      case 1:
        if (!compressor.has_directive("use strict")
            && compressor.parent() instanceof AST_If
            && can_be_extracted_from_if_block(self.body[0])
            || can_be_evicted_from_block(self.body[0])) {
            return self.body[0];
        }
        break;
      case 0: return make_node(AST_EmptyStatement, self);
    }
    return self;
});

function opt_AST_Lambda(self, compressor) {
    tighten_body(self.body, compressor);
    if (compressor.option("side_effects")
        && self.body.length == 1
        && self.body[0] === compressor.has_directive("use strict")) {
        self.body.length = 0;
    }
    return self;
}
def_optimize(AST_Lambda, opt_AST_Lambda);

self.transform(tt);

AST_Scope.DEFMETHOD("hoist_declarations", function(compressor) {
    var self = this;
    if (compressor.has_directive("use asm")) return self;
    // Hoisting makes no sense in an arrow func
    if (!Array.isArray(self.body)) return self;

var hoist_funs = compressor.option("hoist_funs");
    var hoist_vars = compressor.option("hoist_vars");

if (hoist_funs || hoist_vars) {
        var dirs = [];
        var hoisted = [];
        var vars = new Map(), vars_found = 0, var_decl = 0;
        // let's count var_decl first, we seem to waste a lot of
        // space if we hoist `var` when there's only one.
        walk(self, node => {
            if (node instanceof AST_Scope && node !== self)
                return true;
            if (node instanceof AST_Var) {
                ++var_decl;
                return true;
            }
        });
        hoist_vars = hoist_vars && var_decl > 1;
        var tt = new TreeTransformer(
            function before(node) {
                if (node !== self) {
                    if (node instanceof AST_Directive) {
                        dirs.push(node);
                        return make_node(AST_EmptyStatement, node);
                    }
                    if (hoist_funs && node instanceof AST_Defun
                        && !(tt.parent() instanceof AST_Export)
                        && tt.parent() === self) {
                        hoisted.push(node);
                        return make_node(AST_EmptyStatement, node);
                    }
                    if (
                        hoist_vars
                        && node instanceof AST_Var
                        && !node.definitions.some(def => def.name instanceof AST_Destructuring)
                    ) {
                        node.definitions.forEach(function(def) {
                            vars.set(def.name.name, def);
                            ++vars_found;
                        });
                        var seq = node.to_assignments(compressor);
                        var p = tt.parent();
                        if (p instanceof AST_ForIn && p.init === node) {
                            if (seq == null) {
                                var def = node.definitions[0].name;
                                return make_node(AST_SymbolRef, def, def);
                            }
                            return seq;
                        }
                        if (p instanceof AST_For && p.init === node) {
                            return seq;
                        }
                        if (!seq) return make_node(AST_EmptyStatement, node);
                        return make_node(AST_SimpleStatement, node, {
                            body: seq
                        });
                    }
                    if (node instanceof AST_Scope)
                        return node; // to avoid descending in nested scopes
                }
            }
        );
        self = self.transform(tt);
        if (vars_found > 0) {
            // collect only vars which don't show up in self's arguments list
            var defs = [];
            const is_lambda = self instanceof AST_Lambda;
            const args_as_names = is_lambda ? self.args_as_names() : null;
            vars.forEach((def, name) => {
                if (is_lambda && args_as_names.some((x) => x.name === def.name.name)) {
                    vars.delete(name);
                } else {
                    def = def.clone();
                    def.value = null;
                    defs.push(def);
                    vars.set(name, def);
                }
            });
            if (defs.length > 0) {
                // try to merge in assignments
                for (var i = 0; i < self.body.length;) {
                    if (self.body[i] instanceof AST_SimpleStatement) {
                        var expr = self.body[i].body, sym, assign;
                        if (expr instanceof AST_Assign
                            && expr.operator == "="
                            && (sym = expr.left) instanceof AST_Symbol
                            && vars.has(sym.name)
                        ) {
                            var def = vars.get(sym.name);
                            if (def.value) break;
                            def.value = expr.right;
                            remove(defs, def);
                            defs.push(def);
                            self.body.splice(i, 1);
                            continue;
                        }
                        if (expr instanceof AST_Sequence
                            && (assign = expr.expressions[0]) instanceof AST_Assign
                            && assign.operator == "="
                            && (sym = assign.left) instanceof AST_Symbol
                            && vars.has(sym.name)
                        ) {
                            var def = vars.get(sym.name);
                            if (def.value) break;
                            def.value = assign.right;
                            remove(defs, def);
                            defs.push(def);
                            self.body[i].body = make_sequence(expr, expr.expressions.slice(1));
                            continue;
                        }
                    }
                    if (self.body[i] instanceof AST_EmptyStatement) {
                        self.body.splice(i, 1);
                        continue;
                    }
                    if (self.body[i] instanceof AST_BlockStatement) {
                        self.body.splice(i, 1, ...self.body[i].body);
                        continue;
                    }
                    break;
                }
                defs = make_node(AST_Var, self, {
                    definitions: defs
                });
                hoisted.push(defs);
            }
        }
        self.body = dirs.concat(hoisted, self.body);
    }
    return self;
});

AST_Scope.DEFMETHOD("hoist_properties", function(compressor) {
    var self = this;
    if (!compressor.option("hoist_props") || compressor.has_directive("use asm")) return self;
    var top_retain = self instanceof AST_Toplevel && compressor.top_retain || return_false;
    var defs_by_id = new Map();
    var hoister = new TreeTransformer(function(node, descend) {
        if (node instanceof AST_Definitions
            && hoister.parent() instanceof AST_Export) return node;
        if (node instanceof AST_VarDef) {
            const sym = node.name;
            let def;
            let value;
            if (sym.scope === self
                && (def = sym.definition()).escaped != 1
                && !def.assignments
                && !def.direct_access
                && !def.single_use
                && !compressor.exposed(def)
                && !top_retain(def)
                && (value = sym.fixed_value()) === node.value
                && value instanceof AST_Object
                && !value.properties.some(prop =>
                    prop instanceof AST_Expansion || prop.computed_key()
                )
            ) {
                descend(node, this);
                const defs = new Map();
                const assignments = [];
                value.properties.forEach(({ key, value }) => {
                    const scope = find_scope(hoister);
                    const symbol = self.create_symbol(sym.CTOR, {
                        source: sym,
                        scope,
                        conflict_scopes: new Set([
                            scope,
                            ...sym.definition().references.map(ref => ref.scope)
                        ]),
                        tentative_name: sym.name + "_" + key
                    });

defs.set(String(key), symbol.definition());

assignments.push(make_node(AST_VarDef, node, {
                        name: symbol,
                        value
                    }));
                });
                defs_by_id.set(def.id, defs);
                return MAP.splice(assignments);
            }
        } else if (node instanceof AST_PropAccess
            && node.expression instanceof AST_SymbolRef
        ) {
            const defs = defs_by_id.get(node.expression.definition().id);
            if (defs) {
                const def = defs.get(String(get_value(node.property)));
                const sym = make_node(AST_SymbolRef, node, {
                    name: def.name,
                    scope: node.expression.scope,
                    thedef: def
                });
                sym.reference({});
                return sym;
            }
        }
    });
    return self.transform(hoister);
});

// drop_side_effect_free()
// remove side-effect-free parts which only affects return value
(function(def_drop_side_effect_free) {
    // Drop side-effect-free elements from an array of expressions.
    // Returns an array of expressions with side-effects or null
    // if all elements were dropped. Note: original array may be
    // returned if nothing changed.
    function trim(nodes, compressor, first_in_statement) {
        var len = nodes.length;
        if (!len) return null;
        var ret = [], changed = false;
        for (var i = 0; i < len; i++) {
            var node = nodes[i].drop_side_effect_free(compressor, first_in_statement);
            changed |= node !== nodes[i];
            if (node) {
                ret.push(node);
                first_in_statement = false;
            }
        }
        return changed ? ret.length ? ret : null : nodes;
    }

def_drop_side_effect_free(AST_Node, return_this);
    def_drop_side_effect_free(AST_Constant, return_null);
    def_drop_side_effect_free(AST_This, return_null);
    def_drop_side_effect_free(AST_Call, function(compressor, first_in_statement) {
        if (this.optional && is_nullish(this.expression)) {
            return make_node(AST_Undefined, this);
        }

if (!this.is_expr_pure(compressor)) {
            if (this.expression.is_call_pure(compressor)) {
                var exprs = this.args.slice();
                exprs.unshift(this.expression.expression);
                exprs = trim(exprs, compressor, first_in_statement);
                return exprs && make_sequence(this, exprs);
            }
            if (is_func_expr(this.expression)
                && (!this.expression.name || !this.expression.name.definition().references.length)) {
                var node = this.clone();
                node.expression.process_expression(false, compressor);
                return node;
            }
            return this;
        }
        var args = trim(this.args, compressor, first_in_statement);
        return args && make_sequence(this, args);
    });
    def_drop_side_effect_free(AST_Accessor, return_null);
    def_drop_side_effect_free(AST_Function, return_null);
    def_drop_side_effect_free(AST_Arrow, return_null);
    def_drop_side_effect_free(AST_Class, function (compressor) {
        const with_effects = [];
        const trimmed_extends = this.extends && this.extends.drop_side_effect_free(compressor);
        if (trimmed_extends) with_effects.push(trimmed_extends);
        for (const prop of this.properties) {
            const trimmed_prop = prop.drop_side_effect_free(compressor);
            if (trimmed_prop) with_effects.push(trimmed_prop);
        }
        if (!with_effects.length) return null;
        return make_sequence(this, with_effects);
    });
    def_drop_side_effect_free(AST_Binary, function(compressor, first_in_statement) {
        var right = this.right.drop_side_effect_free(compressor);
        if (!right) return this.left.drop_side_effect_free(compressor, first_in_statement);
        if (lazy_op.has(this.operator)) {
            if (right === this.right) return this;
            var node = this.clone();
            node.right = right;
            return node;
        } else {
            var left = this.left.drop_side_effect_free(compressor, first_in_statement);
            if (!left) return this.right.drop_side_effect_free(compressor, first_in_statement);
            return make_sequence(this, [ left, right ]);
        }
    });
    def_drop_side_effect_free(AST_Assign, function(compressor) {
        if (this.logical) return this;

const value = this.static && this.value
            && this.value.drop_side_effect_free(compressor);

if (key && value) return make_sequence(this, [key, value]);
        return key || value || null;
    });
    def_drop_side_effect_free(AST_ConciseMethod, function () {
        return this.computed_key() ? this.key : null;
    });
    def_drop_side_effect_free(AST_ObjectGetter, function () {
        return this.computed_key() ? this.key : null;
    });
    def_drop_side_effect_free(AST_ObjectSetter, function () {
        return this.computed_key() ? this.key : null;
    });
    def_drop_side_effect_free(AST_Array, function(compressor, first_in_statement) {
        var values = trim(this.elements, compressor, first_in_statement);
        return values && make_sequence(this, values);
    });
    def_drop_side_effect_free(AST_Dot, function(compressor, first_in_statement) {
        if (this.optional) {
            return is_nullish(this.expression) ? make_node(AST_Undefined, this) : this;
        }
        if (this.expression.may_throw_on_access(compressor)) return this;

return this.expression.drop_side_effect_free(compressor, first_in_statement);
    });
    def_drop_side_effect_free(AST_Sub, function(compressor, first_in_statement) {
        if (this.optional) {
            return is_nullish(this.expression) ? make_node(AST_Undefined, this): this;
        }
        if (this.expression.may_throw_on_access(compressor)) return this;

def_optimize(AST_SimpleStatement, function(self, compressor) {
    if (compressor.option("side_effects")) {
        var body = self.body;
        var node = body.drop_side_effect_free(compressor, true);
        if (!node) {
            return make_node(AST_EmptyStatement, self);
        }
        if (node !== body) {
            return make_node(AST_SimpleStatement, self, { body: node });
        }
    }
    return self;
});

def_optimize(AST_While, function(self, compressor) {
    return compressor.option("loops") ? make_node(AST_For, self, self).optimize(compressor) : self;
});

def_optimize(AST_Do, function(self, compressor) {
    if (!compressor.option("loops")) return self;
    var cond = self.condition.tail_node().evaluate(compressor);
    if (!(cond instanceof AST_Node)) {
        if (cond) return make_node(AST_For, self, {
            body: make_node(AST_BlockStatement, self.body, {
                body: [
                    self.body,
                    make_node(AST_SimpleStatement, self.condition, {
                        body: self.condition
                    })
                ]
            })
        }).optimize(compressor);
        if (!has_break_or_continue(self, compressor.parent())) {
            return make_node(AST_BlockStatement, self.body, {
                body: [
                    self.body,
                    make_node(AST_SimpleStatement, self.condition, {
                        body: self.condition
                    })
                ]
            }).optimize(compressor);
        }
    }
    return self;
});

function is_break(node) {
        return node instanceof AST_Break
            && compressor.loopcontrol_target(node) === compressor.self();
    }

def_optimize(AST_For, function(self, compressor) {
    if (!compressor.option("loops")) return self;
    if (compressor.option("side_effects") && self.init) {
        self.init = self.init.drop_side_effect_free(compressor);
    }
    if (self.condition) {
        var cond = self.condition.evaluate(compressor);
        if (!(cond instanceof AST_Node)) {
            if (cond) self.condition = null;
            else if (!compressor.option("dead_code")) {
                var orig = self.condition;
                self.condition = make_node_from_constant(cond, self.condition);
                self.condition = best_of_expression(self.condition.transform(compressor), orig);
            }
        }
        if (compressor.option("dead_code")) {
            if (cond instanceof AST_Node) cond = self.condition.tail_node().evaluate(compressor);
            if (!cond) {
                var body = [];
                trim_unreachable_code(compressor, self.body, body);
                if (self.init instanceof AST_Statement) {
                    body.push(self.init);
                } else if (self.init) {
                    body.push(make_node(AST_SimpleStatement, self.init, {
                        body: self.init
                    }));
                }
                body.push(make_node(AST_SimpleStatement, self.condition, {
                    body: self.condition
                }));
                return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
            }
        }
    }
    return if_break_in_loop(self, compressor);
});

def_optimize(AST_If, function(self, compressor) {
    if (is_empty(self.alternative)) self.alternative = null;

if (!compressor.option("conditionals")) return self;
    // if condition can be statically determined, drop
    // one of the blocks.  note, statically determined implies
    // “has no side effects”; also it doesn't work for cases like
    // `x && true`, though it probably should.
    var cond = self.condition.evaluate(compressor);
    if (!compressor.option("dead_code") && !(cond instanceof AST_Node)) {
        var orig = self.condition;
        self.condition = make_node_from_constant(cond, orig);
        self.condition = best_of_expression(self.condition.transform(compressor), orig);
    }
    if (compressor.option("dead_code")) {
        if (cond instanceof AST_Node) cond = self.condition.tail_node().evaluate(compressor);
        if (!cond) {
            var body = [];
            trim_unreachable_code(compressor, self.body, body);
            body.push(make_node(AST_SimpleStatement, self.condition, {
                body: self.condition
            }));
            if (self.alternative) body.push(self.alternative);
            return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
        } else if (!(cond instanceof AST_Node)) {
            var body = [];
            body.push(make_node(AST_SimpleStatement, self.condition, {
                body: self.condition
            }));
            body.push(self.body);
            if (self.alternative) {
                trim_unreachable_code(compressor, self.alternative, body);
            }
            return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
        }
    }
    var negated = self.condition.negate(compressor);
    var self_condition_length = self.condition.size();
    var negated_length = negated.size();
    var negated_is_best = negated_length < self_condition_length;
    if (self.alternative && negated_is_best) {
        negated_is_best = false; // because we already do the switch here.
        // no need to swap values of self_condition_length and negated_length
        // here because they are only used in an equality comparison later on.
        self.condition = negated;
        var tmp = self.body;
        self.body = self.alternative || make_node(AST_EmptyStatement, self);
        self.alternative = tmp;
    }
    if (is_empty(self.body) && is_empty(self.alternative)) {
        return make_node(AST_SimpleStatement, self.condition, {
            body: self.condition.clone()
        }).optimize(compressor);
    }
    if (self.body instanceof AST_SimpleStatement
        && self.alternative instanceof AST_SimpleStatement) {
        return make_node(AST_SimpleStatement, self, {
            body: make_node(AST_Conditional, self, {
                condition   : self.condition,
                consequent  : self.body.body,
                alternative : self.alternative.body
            })
        }).optimize(compressor);
    }
    if (is_empty(self.alternative) && self.body instanceof AST_SimpleStatement) {
        if (self_condition_length === negated_length && !negated_is_best
            && self.condition instanceof AST_Binary && self.condition.operator == "||") {
            // although the code length of self.condition and negated are the same,
            // negated does not require additional surrounding parentheses.
            // see https://github.com/mishoo/UglifyJS2/issues/979
            negated_is_best = true;
        }
        if (negated_is_best) return make_node(AST_SimpleStatement, self, {
            body: make_node(AST_Binary, self, {
                operator : "||",
                left     : negated,
                right    : self.body.body
            })
        }).optimize(compressor);
        return make_node(AST_SimpleStatement, self, {
            body: make_node(AST_Binary, self, {
                operator : "&&",
                left     : self.condition,
                right    : self.body.body
            })
        }).optimize(compressor);
    }
    if (self.body instanceof AST_EmptyStatement
        && self.alternative instanceof AST_SimpleStatement) {
        return make_node(AST_SimpleStatement, self, {
            body: make_node(AST_Binary, self, {
                operator : "||",
                left     : self.condition,
                right    : self.alternative.body
            })
        }).optimize(compressor);
    }
    if (self.body instanceof AST_Exit
        && self.alternative instanceof AST_Exit
        && self.body.TYPE == self.alternative.TYPE) {
        return make_node(self.body.CTOR, self, {
            value: make_node(AST_Conditional, self, {
                condition   : self.condition,
                consequent  : self.body.value || make_node(AST_Undefined, self.body),
                alternative : self.alternative.value || make_node(AST_Undefined, self.alternative)
            }).transform(compressor)
        }).optimize(compressor);
    }
    if (self.body instanceof AST_If
        && !self.body.alternative
        && !self.alternative) {
        self = make_node(AST_If, self, {
            condition: make_node(AST_Binary, self.condition, {
                operator: "&&",
                left: self.condition,
                right: self.body.condition
            }),
            body: self.body.body,
            alternative: null
        });
    }
    if (aborts(self.body)) {
        if (self.alternative) {
            var alt = self.alternative;
            self.alternative = null;
            return make_node(AST_BlockStatement, self, {
                body: [ self, alt ]
            }).optimize(compressor);
        }
    }
    if (aborts(self.alternative)) {
        var body = self.body;
        self.body = self.alternative;
        self.condition = negated_is_best ? negated : self.condition.negate(compressor);
        self.alternative = null;
        return make_node(AST_BlockStatement, self, {
            body: [ self, body ]
        }).optimize(compressor);
    }
    return self;
});

def_optimize(AST_Switch, function(self, compressor) {
    if (!compressor.option("switches")) return self;
    var branch;
    var value = self.expression.evaluate(compressor);
    if (!(value instanceof AST_Node)) {
        var orig = self.expression;
        self.expression = make_node_from_constant(value, orig);
        self.expression = best_of_expression(self.expression.transform(compressor), orig);
    }
    if (!compressor.option("dead_code")) return self;
    if (value instanceof AST_Node) {
        value = self.expression.tail_node().evaluate(compressor);
    }
    var decl = [];
    var body = [];
    var default_branch;
    var exact_match;
    for (var i = 0, len = self.body.length; i < len && !exact_match; i++) {
        branch = self.body[i];
        if (branch instanceof AST_Default) {
            if (!default_branch) {
                default_branch = branch;
            } else {
                eliminate_branch(branch, body[body.length - 1]);
            }
        } else if (!(value instanceof AST_Node)) {
            var exp = branch.expression.evaluate(compressor);
            if (!(exp instanceof AST_Node) && exp !== value) {
                eliminate_branch(branch, body[body.length - 1]);
                continue;
            }
            if (exp instanceof AST_Node) exp = branch.expression.tail_node().evaluate(compressor);
            if (exp === value) {
                exact_match = branch;
                if (default_branch) {
                    var default_index = body.indexOf(default_branch);
                    body.splice(default_index, 1);
                    eliminate_branch(default_branch, body[default_index - 1]);
                    default_branch = null;
                }
            }
        }
        if (aborts(branch)) {
            var prev = body[body.length - 1];
            if (aborts(prev) && prev.body.length == branch.body.length
                && make_node(AST_BlockStatement, prev, prev).equivalent_to(make_node(AST_BlockStatement, branch, branch))) {
                prev.body = [];
            }
        }
        body.push(branch);
    }
    while (i < len) eliminate_branch(self.body[i++], body[body.length - 1]);
    if (body.length > 0) {
        body[0].body = decl.concat(body[0].body);
    }
    self.body = body;
    while (branch = body[body.length - 1]) {
        var stat = branch.body[branch.body.length - 1];
        if (stat instanceof AST_Break && compressor.loopcontrol_target(stat) === self)
            branch.body.pop();
        if (branch.body.length || branch instanceof AST_Case
            && (default_branch || branch.expression.has_side_effects(compressor))) break;
        if (body.pop() === default_branch) default_branch = null;
    }
    if (body.length == 0) {
        return make_node(AST_BlockStatement, self, {
            body: decl.concat(make_node(AST_SimpleStatement, self.expression, {
                body: self.expression
            }))
        }).optimize(compressor);
    }
    if (body.length == 1 && (body[0] === exact_match || body[0] === default_branch)) {
        var has_break = false;
        var tw = new TreeWalker(function(node) {
            if (has_break
                || node instanceof AST_Lambda
                || node instanceof AST_SimpleStatement) return true;
            if (node instanceof AST_Break && tw.loopcontrol_target(node) === self)
                has_break = true;
        });
        self.walk(tw);
        if (!has_break) {
            var statements = body[0].body.slice();
            var exp = body[0].expression;
            if (exp) statements.unshift(make_node(AST_SimpleStatement, exp, {
                body: exp
            }));
            statements.unshift(make_node(AST_SimpleStatement, self.expression, {
                body:self.expression
            }));
            return make_node(AST_BlockStatement, self, {
                body: statements
            }).optimize(compressor);
        }
    }
    return self;

def_optimize(AST_Try, function(self, compressor) {
    tighten_body(self.body, compressor);
    if (self.bcatch && self.bfinally && self.bfinally.body.every(is_empty)) self.bfinally = null;
    if (compressor.option("dead_code") && self.body.every(is_empty)) {
        var body = [];
        if (self.bcatch) {
            trim_unreachable_code(compressor, self.bcatch, body);
        }
        if (self.bfinally) body.push(...self.bfinally.body);
        return make_node(AST_BlockStatement, self, {
            body: body
        }).optimize(compressor);
    }
    return self;
});

AST_Definitions.DEFMETHOD("remove_initializers", function() {
    var decls = [];
    this.definitions.forEach(function(def) {
        if (def.name instanceof AST_SymbolDeclaration) {
            def.value = null;
            decls.push(def);
        } else {
            walk(def.name, node => {
                if (node instanceof AST_SymbolDeclaration) {
                    decls.push(make_node(AST_VarDef, def, {
                        name: node,
                        value: null
                    }));
                }
            });
        }
    });
    this.definitions = decls;
});

AST_Definitions.DEFMETHOD("to_assignments", function(compressor) {
    var reduce_vars = compressor.option("reduce_vars");
    var assignments = [];

for (const def of this.definitions) {
        if (def.value) {
            var name = make_node(AST_SymbolRef, def.name, def.name);
            assignments.push(make_node(AST_Assign, def, {
                operator : "=",
                logical: false,
                left     : name,
                right    : def.value
            }));
            if (reduce_vars) name.definition().fixed = false;
        } else if (def.value) {
            // Because it's a destructuring, do not turn into an assignment.
            var varDef = make_node(AST_VarDef, def, {
                name: def.name,
                value: def.value
            });
            var var_ = make_node(AST_Var, def, {
                definitions: [ varDef ]
            });
            assignments.push(var_);
        }
        const thedef = def.name.definition();
        thedef.eliminated++;
        thedef.replaced--;
    }

if (assignments.length == 0) return null;
    return make_sequence(this, assignments);
});

def_optimize(AST_Definitions, function(self) {
    if (self.definitions.length == 0)
        return make_node(AST_EmptyStatement, self);
    return self;
});

def_optimize(AST_VarDef, function(self) {
    if (
        self.name instanceof AST_SymbolLet
        && self.value != null
        && is_undefined(self.value)
    ) {
        self.value = null;
    }
    return self;
});

def_optimize(AST_Import, function(self) {
    return self;
});

// TODO this only works with AST_Defun, shouldn't it work for other ways of defining functions?
function retain_top_func(fn, compressor) {
    return compressor.top_retain
        && fn instanceof AST_Defun
        && has_flag(fn, TOP)
        && fn.name
        && compressor.top_retain(fn.name);
}

def_optimize(AST_Call, function(self, compressor) {
    var exp = self.expression;
    var fn = exp;
    inline_array_like_spread(self.args);
    var simple_args = self.args.every((arg) =>
        !(arg instanceof AST_Expansion)
    );

if (compressor.option("reduce_vars")
        && fn instanceof AST_SymbolRef
        && !has_annotation(self, _NOINLINE)
    ) {
        const fixed = fn.fixed_value();
        if (!retain_top_func(fixed, compressor)) {
            fn = fixed;
        }
    }

if (self.optional && is_nullish(fn)) {
        return make_node(AST_Undefined, self);
    }

var is_func = fn instanceof AST_Lambda;

if (is_func && fn.pinned()) return self;

if (compressor.option("unused")
        && simple_args
        && is_func
        && !fn.uses_arguments) {
        var pos = 0, last = 0;
        for (var i = 0, len = self.args.length; i < len; i++) {
            if (fn.argnames[i] instanceof AST_Expansion) {
                if (has_flag(fn.argnames[i].expression, UNUSED)) while (i < len) {
                    var node = self.args[i++].drop_side_effect_free(compressor);
                    if (node) {
                        self.args[pos++] = node;
                    }
                } else while (i < len) {
                    self.args[pos++] = self.args[i++];
                }
                last = pos;
                break;
            }
            var trim = i >= fn.argnames.length;
            if (trim || has_flag(fn.argnames[i], UNUSED)) {
                var node = self.args[i].drop_side_effect_free(compressor);
                if (node) {
                    self.args[pos++] = node;
                } else if (!trim) {
                    self.args[pos++] = make_node(AST_Number, self.args[i], {
                        value: 0
                    });
                    continue;
                }
            } else {
                self.args[pos++] = self.args[i];
            }
            last = pos;
        }
        self.args.length = last;
    }

if (compressor.option("unsafe")) {
        if (is_undeclared_ref(exp)) switch (exp.name) {
          case "Array":
            if (self.args.length != 1) {
                return make_node(AST_Array, self, {
                    elements: self.args
                }).optimize(compressor);
            } else if (self.args[0] instanceof AST_Number && self.args[0].value <= 11) {
                const elements = [];
                for (let i = 0; i < self.args[0].value; i++) elements.push(new AST_Hole);
                return new AST_Array({ elements });
            }
            break;
          case "Object":
            if (self.args.length == 0) {
                return make_node(AST_Object, self, {
                    properties: []
                });
            }
            break;
          case "String":
            if (self.args.length == 0) return make_node(AST_String, self, {
                value: ""
            });
            if (self.args.length <= 1) return make_node(AST_Binary, self, {
                left: self.args[0],
                operator: "+",
                right: make_node(AST_String, self, { value: "" })
            }).optimize(compressor);
            break;
          case "Number":
            if (self.args.length == 0) return make_node(AST_Number, self, {
                value: 0
            });
            if (self.args.length == 1 && compressor.option("unsafe_math")) {
                return make_node(AST_UnaryPrefix, self, {
                    expression: self.args[0],
                    operator: "+"
                }).optimize(compressor);
            }
            break;
          case "Symbol":
            if (self.args.length == 1 && self.args[0] instanceof AST_String && compressor.option("unsafe_symbols"))
                self.args.length = 0;
                break;
          case "Boolean":
            if (self.args.length == 0) return make_node(AST_False, self);
            if (self.args.length == 1) return make_node(AST_UnaryPrefix, self, {
                expression: make_node(AST_UnaryPrefix, self, {
                    expression: self.args[0],
                    operator: "!"
                }),
                operator: "!"
            }).optimize(compressor);
            break;
          case "RegExp":
            var params = [];
            if (self.args.length >= 1
                && self.args.length <= 2
                && self.args.every((arg) => {
                    var value = arg.evaluate(compressor);
                    params.push(value);
                    return arg !== value;
                })
            ) {
                let [ source, flags ] = params;
                source = regexp_source_fix(new RegExp(source).source);
                const rx = make_node(AST_RegExp, self, {
                    value: { source, flags }
                });
                if (rx._eval(compressor) !== rx) {
                    return rx;
                }
            }
            break;
        } else if (exp instanceof AST_Dot) switch(exp.property) {
          case "toString":
            if (self.args.length == 0 && !exp.expression.may_throw_on_access(compressor)) {
                return make_node(AST_Binary, self, {
                    left: make_node(AST_String, self, { value: "" }),
                    operator: "+",
                    right: exp.expression
                }).optimize(compressor);
            }
            break;
          case "join":
            if (exp.expression instanceof AST_Array) EXIT: {
                var separator;
                if (self.args.length > 0) {
                    separator = self.args[0].evaluate(compressor);
                    if (separator === self.args[0]) break EXIT; // not a constant
                }
                var elements = [];
                var consts = [];
                for (var i = 0, len = exp.expression.elements.length; i < len; i++) {
                    var el = exp.expression.elements[i];
                    if (el instanceof AST_Expansion) break EXIT;
                    var value = el.evaluate(compressor);
                    if (value !== el) {
                        consts.push(value);
                    } else {
                        if (consts.length > 0) {
                            elements.push(make_node(AST_String, self, {
                                value: consts.join(separator)
                            }));
                            consts.length = 0;
                        }
                        elements.push(el);
                    }
                }
                if (consts.length > 0) {
                    elements.push(make_node(AST_String, self, {
                        value: consts.join(separator)
                    }));
                }
                if (elements.length == 0) return make_node(AST_String, self, { value: "" });
                if (elements.length == 1) {
                    if (elements[0].is_string(compressor)) {
                        return elements[0];
                    }
                    return make_node(AST_Binary, elements[0], {
                        operator : "+",
                        left     : make_node(AST_String, self, { value: "" }),
                        right    : elements[0]
                    });
                }
                if (separator == "") {
                    var first;
                    if (elements[0].is_string(compressor)
                        || elements[1].is_string(compressor)) {
                        first = elements.shift();
                    } else {
                        first = make_node(AST_String, self, { value: "" });
                    }
                    return elements.reduce(function(prev, el) {
                        return make_node(AST_Binary, el, {
                            operator : "+",
                            left     : prev,
                            right    : el
                        });
                    }, first).optimize(compressor);
                }
                // need this awkward cloning to not affect original element
                // best_of will decide which one to get through.
                var node = self.clone();
                node.expression = node.expression.clone();
                node.expression.expression = node.expression.expression.clone();
                node.expression.expression.elements = elements;
                return best_of(compressor, self, node);
            }
            break;
          case "charAt":
            if (exp.expression.is_string(compressor)) {
                var arg = self.args[0];
                var index = arg ? arg.evaluate(compressor) : 0;
                if (index !== arg) {
                    return make_node(AST_Sub, exp, {
                        expression: exp.expression,
                        property: make_node_from_constant(index | 0, arg || exp)
                    }).optimize(compressor);
                }
            }
            break;
          case "apply":
            if (self.args.length == 2 && self.args[1] instanceof AST_Array) {
                var args = self.args[1].elements.slice();
                args.unshift(self.args[0]);
                return make_node(AST_Call, self, {
                    expression: make_node(AST_Dot, exp, {
                        expression: exp.expression,
                        optional: false,
                        property: "call"
                    }),
                    args: args
                }).optimize(compressor);
            }
            break;
          case "call":
            var func = exp.expression;
            if (func instanceof AST_SymbolRef) {
                func = func.fixed_value();
            }
            if (func instanceof AST_Lambda && !func.contains_this()) {
                return (self.args.length ? make_sequence(this, [
                    self.args[0],
                    make_node(AST_Call, self, {
                        expression: exp.expression,
                        args: self.args.slice(1)
                    })
                ]) : make_node(AST_Call, self, {
                    expression: exp.expression,
                    args: []
                })).optimize(compressor);
            }
            break;
        }
    }

if (compressor.option("unsafe_Function")
        && is_undeclared_ref(exp)
        && exp.name == "Function") {
        // new Function() => function(){}
        if (self.args.length == 0) return make_node(AST_Function, self, {
            argnames: [],
            body: []
        }).optimize(compressor);
        if (self.args.every((x) => x instanceof AST_String)) {
            // quite a corner-case, but we can handle it:
            //   https://github.com/mishoo/UglifyJS2/issues/203
            // if the code argument is a constant, then we can minify it.
            try {
                var code = "n(function(" + self.args.slice(0, -1).map(function(arg) {
                    return arg.value;
                }).join(",") + "){" + self.args[self.args.length - 1].value + "})";
                var ast = parse(code);
                var mangle = { ie8: compressor.option("ie8") };
                ast.figure_out_scope(mangle);
                var comp = new Compressor(compressor.options, {
                    mangle_options: compressor.mangle_options
                });
                ast = ast.transform(comp);
                ast.figure_out_scope(mangle);
                base54.reset();
                ast.compute_char_frequency(mangle);
                ast.mangle_names(mangle);
                var fun;
                walk(ast, node => {
                    if (is_func_expr(node)) {
                        fun = node;
                        return walk_abort;
                    }
                });
                var code = OutputStream();
                AST_BlockStatement.prototype._codegen.call(fun, fun, code);
                self.args = [
                    make_node(AST_String, self, {
                        value: fun.argnames.map(function(arg) {
                            return arg.print_to_string();
                        }).join(",")
                    }),
                    make_node(AST_String, self.args[self.args.length - 1], {
                        value: code.get().replace(/^{|}$/g, "")
                    })
                ];
                return self;
            } catch (ex) {
                if (!(ex instanceof JS_Parse_Error)) {
                    throw ex;
                }

// Otherwise, it crashes at runtime. Or maybe it's nonstandard syntax.
            }
        }
    }

// optimize identity function
        if (
            fn.argnames.length === 1
            && (fn.argnames[0] instanceof AST_SymbolFunarg)
            && self.args.length < 2
            && returned instanceof AST_SymbolRef
            && returned.name === fn.argnames[0].name
        ) {
            const replacement =
                (self.args[0] || make_node(AST_Undefined)).optimize(compressor);

let parent;
            if (
                replacement instanceof AST_PropAccess
                && (parent = compressor.parent()) instanceof AST_Call
                && parent.expression === self
            ) {
                // identity function was being used to remove `this`, like in
                //
                // id(bag.no_this)(...)
                //
                // Replace with a larger but more effish (0, bag.no_this) wrapper.

return make_sequence(self, [
                    make_node(AST_Number, self, { value: 0 }),
                    replacement
                ]);
            }
            // replace call with first argument or undefined if none passed
            return replacement;
        }
    }

if (can_inline) {
        var scope, in_loop, level = -1;
        let def;
        let returned_value;
        let nearest_scope;
        if (simple_args
            && !fn.uses_arguments
            && !(compressor.parent() instanceof AST_Class)
            && !(fn.name && fn instanceof AST_Function)
            && (returned_value = can_flatten_body(stat))
            && (exp === fn
                || has_annotation(self, _INLINE)
                || compressor.option("unused")
                    && (def = exp.definition()).references.length == 1
                    && !recursive_ref(compressor, def)
                    && fn.is_constant_expression(exp.scope))
            && !has_annotation(self, _PURE | _NOINLINE)
            && !fn.contains_this()
            && can_inject_symbols()
            && (nearest_scope = find_scope(compressor))
            && !scope_encloses_variables_in_this_scope(nearest_scope, fn)
            && !(function in_default_assign() {
                    // Due to the fact function parameters have their own scope
                    // which can't use `var something` in the function body within,
                    // we simply don't inline into DefaultAssign.
                    let i = 0;
                    let p;
                    while ((p = compressor.parent(i++))) {
                        if (p instanceof AST_DefaultAssign) return true;
                        if (p instanceof AST_Block) break;
                    }
                    return false;
                })()
            && !(scope instanceof AST_Class)
        ) {
            set_flag(fn, SQUEEZED);
            nearest_scope.add_child_scope(fn);
            return make_sequence(self, flatten_fn(returned_value)).optimize(compressor);
        }
    }

if (can_inline && has_annotation(self, _INLINE)) {
        set_flag(fn, SQUEEZED);
        fn = make_node(fn.CTOR === AST_Defun ? AST_Function : fn.CTOR, fn, fn);
        fn.figure_out_scope({}, {
            parent_scope: find_scope(compressor),
            toplevel: compressor.get_toplevel()
        });

return make_node(AST_Call, self, {
            expression: fn,
            args: self.args,
        }).optimize(compressor);
    }

const can_drop_this_call = is_regular_func && compressor.option("side_effects") && fn.body.every(is_empty);
    if (can_drop_this_call) {
        var args = self.args.concat(make_node(AST_Undefined, self));
        return make_sequence(self, args).optimize(compressor);
    }

if (compressor.option("negate_iife")
        && compressor.parent() instanceof AST_SimpleStatement
        && is_iife_call(self)) {
        return self.negate(compressor, true);
    }

var ev = self.evaluate(compressor);
    if (ev !== self) {
        ev = make_node_from_constant(ev, self).optimize(compressor);
        return best_of(compressor, ev, self);
    }

return self;

var safe_to_inject = !(scope instanceof AST_Toplevel) || compressor.toplevel.vars;
        var inline = compressor.option("inline");
        if (!can_inject_vars(block_scoped, inline >= 3 && safe_to_inject)) return false;
        if (!can_inject_args(block_scoped, inline >= 2 && safe_to_inject)) return false;
        return !in_loop || in_loop.length == 0 || !is_reachable(fn, in_loop);
    }

function append_var(decls, expressions, name, value) {
        var def = name.definition();

// Name already exists, only when a function argument had the same name
        const already_appended = scope.variables.has(name.name);
        if (!already_appended) {
            scope.variables.set(name.name, def);
            scope.enclosed.push(def);
            decls.push(make_node(AST_VarDef, name, {
                name: name,
                value: null
            }));
        }

var sym = make_node(AST_SymbolRef, name, name);
        def.references.push(sym);
        if (value) expressions.push(make_node(AST_Assign, self, {
            operator: "=",
            logical: false,
            left: sym,
            right: value.clone()
        }));
    }

def_optimize(AST_New, function(self, compressor) {
    if (
        compressor.option("unsafe") &&
        is_undeclared_ref(self.expression) &&
        ["Object", "RegExp", "Function", "Error", "Array"].includes(self.expression.name)
    ) return make_node(AST_Call, self, self).transform(compressor);
    return self;
});

def_optimize(AST_Sequence, function(self, compressor) {
    if (!compressor.option("side_effects")) return self;
    var expressions = [];
    filter_for_side_effects();
    var end = expressions.length - 1;
    trim_right_for_undefined();
    if (end == 0) {
        self = maintain_this_binding(compressor.parent(), compressor.self(), expressions[0]);
        if (!(self instanceof AST_Sequence)) self = self.optimize(compressor);
        return self;
    }
    self.expressions = expressions;
    return self;

AST_Unary.DEFMETHOD("lift_sequences", function(compressor) {
    if (compressor.option("sequences")) {
        if (this.expression instanceof AST_Sequence) {
            var x = this.expression.expressions.slice();
            var e = this.clone();
            e.expression = x.pop();
            x.push(e);
            return make_sequence(this, x).optimize(compressor);
        }
    }
    return this;
});

def_optimize(AST_UnaryPostfix, function(self, compressor) {
    return self.lift_sequences(compressor);
});

def_optimize(AST_UnaryPrefix, function(self, compressor) {
    var e = self.expression;
    if (self.operator == "delete"
        && !(e instanceof AST_SymbolRef
            || e instanceof AST_PropAccess
            || is_identifier_atom(e))) {
        if (e instanceof AST_Sequence) {
            const exprs = e.expressions.slice();
            exprs.push(make_node(AST_True, self));
            return make_sequence(self, exprs).optimize(compressor);
        }
        return make_sequence(self, [ e, make_node(AST_True, self) ]).optimize(compressor);
    }
    var seq = self.lift_sequences(compressor);
    if (seq !== self) {
        return seq;
    }
    if (compressor.option("side_effects") && self.operator == "void") {
        e = e.drop_side_effect_free(compressor);
        if (e) {
            self.expression = e;
            return self;
        } else {
            return make_node(AST_Undefined, self).optimize(compressor);
        }
    }
    if (compressor.in_boolean_context()) {
        switch (self.operator) {
          case "!":
            if (e instanceof AST_UnaryPrefix && e.operator == "!") {
                // !!foo ==> foo, if we're in boolean context
                return e.expression;
            }
            if (e instanceof AST_Binary) {
                self = best_of(compressor, self, e.negate(compressor, first_in_statement(compressor)));
            }
            break;
          case "typeof":
            // typeof always returns a non-empty string, thus it's
            // always true in booleans
            // And we don't need to check if it's undeclared, because in typeof, that's OK
            return (e instanceof AST_SymbolRef ? make_node(AST_True, self) : make_sequence(self, [
                e,
                make_node(AST_True, self)
            ])).optimize(compressor);
        }
    }
    if (self.operator == "-" && e instanceof AST_Infinity) {
        e = e.transform(compressor);
    }
    if (e instanceof AST_Binary
        && (self.operator == "+" || self.operator == "-")
        && (e.operator == "*" || e.operator == "/" || e.operator == "%")) {
        return make_node(AST_Binary, self, {
            operator: e.operator,
            left: make_node(AST_UnaryPrefix, e.left, {
                operator: self.operator,
                expression: e.left
            }),
            right: e.right
        });
    }
    // avoids infinite recursion of numerals
    if (self.operator != "-"
        || !(e instanceof AST_Number || e instanceof AST_Infinity || e instanceof AST_BigInt)) {
        var ev = self.evaluate(compressor);
        if (ev !== self) {
            ev = make_node_from_constant(ev, self).optimize(compressor);
            return best_of(compressor, ev, self);
        }
    }
    return self;
});

AST_Binary.DEFMETHOD("lift_sequences", function(compressor) {
    if (compressor.option("sequences")) {
        if (this.left instanceof AST_Sequence) {
            var x = this.left.expressions.slice();
            var e = this.clone();
            e.left = x.pop();
            x.push(e);
            return make_sequence(this, x).optimize(compressor);
        }
        if (this.right instanceof AST_Sequence && !this.left.has_side_effects(compressor)) {
            var assign = this.operator == "=" && this.left instanceof AST_SymbolRef;
            var x = this.right.expressions;
            var last = x.length - 1;
            for (var i = 0; i < last; i++) {
                if (!assign && x[i].has_side_effects(compressor)) break;
            }
            if (i == last) {
                x = x.slice();
                var e = this.clone();
                e.right = x.pop();
                x.push(e);
                return make_sequence(this, x).optimize(compressor);
            } else if (i > 0) {
                var e = this.clone();
                e.right = make_sequence(this.right, x.slice(i));
                x = x.slice(0, i);
                x.push(e);
                return make_sequence(this, x).optimize(compressor);
            }
        }
    }
    return this;
});

var commutativeOperators = makePredicate("== === != !== * & | ^");
function is_object(node) {
    return node instanceof AST_Array
        || node instanceof AST_Lambda
        || node instanceof AST_Object
        || node instanceof AST_Class;
}

def_optimize(AST_Binary, function(self, compressor) {
    function reversible() {
        return self.left.is_constant()
            || self.right.is_constant()
            || !self.left.has_side_effects(compressor)
                && !self.right.has_side_effects(compressor);
    }
    function reverse(op) {
        if (reversible()) {
            if (op) self.operator = op;
            var tmp = self.left;
            self.left = self.right;
            self.right = tmp;
        }
    }
    if (commutativeOperators.has(self.operator)) {
        if (self.right.is_constant()
            && !self.left.is_constant()) {
            // if right is a constant, whatever side effects the
            // left side might have could not influence the
            // result.  hence, force switch.

if (!(self.left instanceof AST_Binary
                  && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
                reverse();
            }
        }
    }
    self = self.lift_sequences(compressor);
    if (compressor.option("comparisons")) switch (self.operator) {
      case "===":
      case "!==":
        var is_strict_comparison = true;
        if ((self.left.is_string(compressor) && self.right.is_string(compressor)) ||
            (self.left.is_number(compressor) && self.right.is_number(compressor)) ||
            (self.left.is_boolean() && self.right.is_boolean()) ||
            self.left.equivalent_to(self.right)) {
            self.operator = self.operator.substr(0, 2);
        }
        // XXX: intentionally falling down to the next case
      case "==":
      case "!=":
        // void 0 == x => null == x
        if (!is_strict_comparison && is_undefined(self.left, compressor)) {
            self.left = make_node(AST_Null, self.left);
        } else if (compressor.option("typeofs")
            // "undefined" == typeof x => undefined === x
            && self.left instanceof AST_String
            && self.left.value == "undefined"
            && self.right instanceof AST_UnaryPrefix
            && self.right.operator == "typeof") {
            var expr = self.right.expression;
            if (expr instanceof AST_SymbolRef ? expr.is_declared(compressor)
                : !(expr instanceof AST_PropAccess && compressor.option("ie8"))) {
                self.right = expr;
                self.left = make_node(AST_Undefined, self.left).optimize(compressor);
                if (self.operator.length == 2) self.operator += "=";
            }
        } else if (self.left instanceof AST_SymbolRef
            // obj !== obj => false
            && self.right instanceof AST_SymbolRef
            && self.left.definition() === self.right.definition()
            && is_object(self.left.fixed_value())) {
            return make_node(self.operator[0] == "=" ? AST_True : AST_False, self);
        }
        break;
      case "&&":
      case "||":
        var lhs = self.left;
        if (lhs.operator == self.operator) {
            lhs = lhs.right;
        }
        if (lhs instanceof AST_Binary
            && lhs.operator == (self.operator == "&&" ? "!==" : "===")
            && self.right instanceof AST_Binary
            && lhs.operator == self.right.operator
            && (is_undefined(lhs.left, compressor) && self.right.left instanceof AST_Null
                || lhs.left instanceof AST_Null && is_undefined(self.right.left, compressor))
            && !lhs.right.has_side_effects(compressor)
            && lhs.right.equivalent_to(self.right.right)) {
            var combined = make_node(AST_Binary, self, {
                operator: lhs.operator.slice(0, -1),
                left: make_node(AST_Null, self),
                right: lhs.right
            });
            if (lhs !== self.left) {
                combined = make_node(AST_Binary, self, {
                    operator: self.operator,
                    left: self.left.left,
                    right: combined
                });
            }
            return combined;
        }
        break;
    }
    if (self.operator == "+" && compressor.in_boolean_context()) {
        var ll = self.left.evaluate(compressor);
        var rr = self.right.evaluate(compressor);
        if (ll && typeof ll == "string") {
            return make_sequence(self, [
                self.right,
                make_node(AST_True, self)
            ]).optimize(compressor);
        }
        if (rr && typeof rr == "string") {
            return make_sequence(self, [
                self.left,
                make_node(AST_True, self)
            ]).optimize(compressor);
        }
    }
    if (compressor.option("comparisons") && self.is_boolean()) {
        if (!(compressor.parent() instanceof AST_Binary)
            || compressor.parent() instanceof AST_Assign) {
            var negated = make_node(AST_UnaryPrefix, self, {
                operator: "!",
                expression: self.negate(compressor, first_in_statement(compressor))
            });
            self = best_of(compressor, self, negated);
        }
        if (compressor.option("unsafe_comps")) {
            switch (self.operator) {
              case "<": reverse(">"); break;
              case "<=": reverse(">="); break;
            }
        }
    }
    if (self.operator == "+") {
        if (self.right instanceof AST_String
            && self.right.getValue() == ""
            && self.left.is_string(compressor)) {
            return self.left;
        }
        if (self.left instanceof AST_String
            && self.left.getValue() == ""
            && self.right.is_string(compressor)) {
            return self.right;
        }
        if (self.left instanceof AST_Binary
            && self.left.operator == "+"
            && self.left.left instanceof AST_String
            && self.left.left.getValue() == ""
            && self.right.is_string(compressor)) {
            self.left = self.left.right;
            return self;
        }
    }
    if (compressor.option("evaluate")) {
        switch (self.operator) {
          case "&&":
            var ll = has_flag(self.left, TRUTHY)
                ? true
                : has_flag(self.left, FALSY)
                    ? false
                    : self.left.evaluate(compressor);
            if (!ll) {
                return maintain_this_binding(compressor.parent(), compressor.self(), self.left).optimize(compressor);
            } else if (!(ll instanceof AST_Node)) {
                return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
            }
            var rr = self.right.evaluate(compressor);
            if (!rr) {
                if (compressor.in_boolean_context()) {
                    return make_sequence(self, [
                        self.left,
                        make_node(AST_False, self)
                    ]).optimize(compressor);
                } else {
                    set_flag(self, FALSY);
                }
            } else if (!(rr instanceof AST_Node)) {
                var parent = compressor.parent();
                if (parent.operator == "&&" && parent.left === compressor.self() || compressor.in_boolean_context()) {
                    return self.left.optimize(compressor);
                }
            }
            // x || false && y ---> x ? y : false
            if (self.left.operator == "||") {
                var lr = self.left.right.evaluate(compressor);
                if (!lr) return make_node(AST_Conditional, self, {
                    condition: self.left.left,
                    consequent: self.right,
                    alternative: self.left.right
                }).optimize(compressor);
            }
            break;
          case "||":
            var ll = has_flag(self.left, TRUTHY)
              ? true
              : has_flag(self.left, FALSY)
                ? false
                : self.left.evaluate(compressor);
            if (!ll) {
                return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
            } else if (!(ll instanceof AST_Node)) {
                return maintain_this_binding(compressor.parent(), compressor.self(), self.left).optimize(compressor);
            }
            var rr = self.right.evaluate(compressor);
            if (!rr) {
                var parent = compressor.parent();
                if (parent.operator == "||" && parent.left === compressor.self() || compressor.in_boolean_context()) {
                    return self.left.optimize(compressor);
                }
            } else if (!(rr instanceof AST_Node)) {
                if (compressor.in_boolean_context()) {
                    return make_sequence(self, [
                        self.left,
                        make_node(AST_True, self)
                    ]).optimize(compressor);
                } else {
                    set_flag(self, TRUTHY);
                }
            }
            if (self.left.operator == "&&") {
                var lr = self.left.right.evaluate(compressor);
                if (lr && !(lr instanceof AST_Node)) return make_node(AST_Conditional, self, {
                    condition: self.left.left,
                    consequent: self.left.right,
                    alternative: self.right
                }).optimize(compressor);
            }
            break;
          case "??":
            if (is_nullish(self.left)) {
                return self.right;
            }

var ll = self.left.evaluate(compressor);
            if (!(ll instanceof AST_Node)) {
                // if we know the value for sure we can simply compute right away.
                return ll == null ? self.right : self.left;
            }

if (compressor.in_boolean_context()) {
                const rr = self.right.evaluate(compressor);
                if (!(rr instanceof AST_Node) && !rr) {
                    return self.left;
                }
            }
        }
        var associative = true;
        switch (self.operator) {
          case "+":
            // (x + "foo") + "bar" => x + "foobar"
            if (self.right instanceof AST_Constant
                && self.left instanceof AST_Binary
                && self.left.operator == "+"
                && self.left.is_string(compressor)) {
                var binary = make_node(AST_Binary, self, {
                    operator: "+",
                    left: self.left.right,
                    right: self.right,
                });
                var r = binary.optimize(compressor);
                if (binary !== r) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: self.left.left,
                        right: r
                    });
                }
            }
            // (x + "foo") + ("bar" + y) => (x + "foobar") + y
            if (self.left instanceof AST_Binary
                && self.left.operator == "+"
                && self.left.is_string(compressor)
                && self.right instanceof AST_Binary
                && self.right.operator == "+"
                && self.right.is_string(compressor)) {
                var binary = make_node(AST_Binary, self, {
                    operator: "+",
                    left: self.left.right,
                    right: self.right.left,
                });
                var m = binary.optimize(compressor);
                if (binary !== m) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: make_node(AST_Binary, self.left, {
                            operator: "+",
                            left: self.left.left,
                            right: m
                        }),
                        right: self.right.right
                    });
                }
            }
            // a + -b => a - b
            if (self.right instanceof AST_UnaryPrefix
                && self.right.operator == "-"
                && self.left.is_number(compressor)) {
                self = make_node(AST_Binary, self, {
                    operator: "-",
                    left: self.left,
                    right: self.right.expression
                });
                break;
            }
            // -a + b => b - a
            if (self.left instanceof AST_UnaryPrefix
                && self.left.operator == "-"
                && reversible()
                && self.right.is_number(compressor)) {
                self = make_node(AST_Binary, self, {
                    operator: "-",
                    left: self.right,
                    right: self.left.expression
                });
                break;
            }
            // `foo${bar}baz` + 1 => `foo${bar}baz1`
            if (self.left instanceof AST_TemplateString) {
                var l = self.left;
                var r = self.right.evaluate(compressor);
                if (r != self.right) {
                    l.segments[l.segments.length - 1].value += String(r);
                    return l;
                }
            }
            // 1 + `foo${bar}baz` => `1foo${bar}baz`
            if (self.right instanceof AST_TemplateString) {
                var r = self.right;
                var l = self.left.evaluate(compressor);
                if (l != self.left) {
                    r.segments[0].value = String(l) + r.segments[0].value;
                    return r;
                }
            }
            // `1${bar}2` + `foo${bar}baz` => `1${bar}2foo${bar}baz`
            if (self.left instanceof AST_TemplateString
                && self.right instanceof AST_TemplateString) {
                var l = self.left;
                var segments = l.segments;
                var r = self.right;
                segments[segments.length - 1].value += r.segments[0].value;
                for (var i = 1; i < r.segments.length; i++) {
                    segments.push(r.segments[i]);
                }
                return l;
            }
          case "*":
            associative = compressor.option("unsafe_math");
          case "&":
          case "|":
          case "^":
            // a + +b => +b + a
            if (self.left.is_number(compressor)
                && self.right.is_number(compressor)
                && reversible()
                && !(self.left instanceof AST_Binary
                    && self.left.operator != self.operator
                    && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
                var reversed = make_node(AST_Binary, self, {
                    operator: self.operator,
                    left: self.right,
                    right: self.left
                });
                if (self.right instanceof AST_Constant
                    && !(self.left instanceof AST_Constant)) {
                    self = best_of(compressor, reversed, self);
                } else {
                    self = best_of(compressor, self, reversed);
                }
            }
            if (associative && self.is_number(compressor)) {
                // a + (b + c) => (a + b) + c
                if (self.right instanceof AST_Binary
                    && self.right.operator == self.operator) {
                    self = make_node(AST_Binary, self, {
                        operator: self.operator,
                        left: make_node(AST_Binary, self.left, {
                            operator: self.operator,
                            left: self.left,
                            right: self.right.left,
                            start: self.left.start,
                            end: self.right.left.end
                        }),
                        right: self.right.right
                    });
                }
                // (n + 2) + 3 => 5 + n
                // (2 * n) * 3 => 6 + n
                if (self.right instanceof AST_Constant
                    && self.left instanceof AST_Binary
                    && self.left.operator == self.operator) {
                    if (self.left.left instanceof AST_Constant) {
                        self = make_node(AST_Binary, self, {
                            operator: self.operator,
                            left: make_node(AST_Binary, self.left, {
                                operator: self.operator,
                                left: self.left.left,
                                right: self.right,
                                start: self.left.left.start,
                                end: self.right.end
                            }),
                            right: self.left.right
                        });
                    } else if (self.left.right instanceof AST_Constant) {
                        self = make_node(AST_Binary, self, {
                            operator: self.operator,
                            left: make_node(AST_Binary, self.left, {
                                operator: self.operator,
                                left: self.left.right,
                                right: self.right,
                                start: self.left.right.start,
                                end: self.right.end
                            }),
                            right: self.left.left
                        });
                    }
                }
                // (a | 1) | (2 | d) => (3 | a) | b
                if (self.left instanceof AST_Binary
                    && self.left.operator == self.operator
                    && self.left.right instanceof AST_Constant
                    && self.right instanceof AST_Binary
                    && self.right.operator == self.operator
                    && self.right.left instanceof AST_Constant) {
                    self = make_node(AST_Binary, self, {
                        operator: self.operator,
                        left: make_node(AST_Binary, self.left, {
                            operator: self.operator,
                            left: make_node(AST_Binary, self.left.left, {
                                operator: self.operator,
                                left: self.left.right,
                                right: self.right.left,
                                start: self.left.right.start,
                                end: self.right.left.end
                            }),
                            right: self.left.left
                        }),
                        right: self.right.right
                    });
                }
            }
        }
    }
    // x && (y && z)  ==>  x && y && z
    // x || (y || z)  ==>  x || y || z
    // x + ("y" + z)  ==>  x + "y" + z
    // "x" + (y + "z")==>  "x" + y + "z"
    if (self.right instanceof AST_Binary
        && self.right.operator == self.operator
        && (lazy_op.has(self.operator)
            || (self.operator == "+"
                && (self.right.left.is_string(compressor)
                    || (self.left.is_string(compressor)
                        && self.right.right.is_string(compressor)))))
    ) {
        self.left = make_node(AST_Binary, self.left, {
            operator : self.operator,
            left     : self.left.transform(compressor),
            right    : self.right.left.transform(compressor)
        });
        self.right = self.right.right.transform(compressor);
        return self.transform(compressor);
    }
    var ev = self.evaluate(compressor);
    if (ev !== self) {
        ev = make_node_from_constant(ev, self).optimize(compressor);
        return best_of(compressor, ev, self);
    }
    return self;
});

def_optimize(AST_SymbolExport, function(self) {
    return self;
});

def_optimize(AST_SymbolRef, function(self, compressor) {
    if (
        !compressor.option("ie8")
        && is_undeclared_ref(self)
        && !compressor.find_parent(AST_With)
    ) {
        switch (self.name) {
          case "undefined":
            return make_node(AST_Undefined, self).optimize(compressor);
          case "NaN":
            return make_node(AST_NaN, self).optimize(compressor);
          case "Infinity":
            return make_node(AST_Infinity, self).optimize(compressor);
        }
    }

const parent = compressor.parent();
    if (compressor.option("reduce_vars") && is_lhs(self, parent) !== self) {
        const def = self.definition();
        const nearest_scope = find_scope(compressor);
        if (compressor.top_retain && def.global && compressor.top_retain(def)) {
            def.fixed = false;
            def.single_use = false;
            return self;
        }

let fixed = self.fixed_value();
        let single_use = def.single_use
            && !(parent instanceof AST_Call
                && (parent.is_expr_pure(compressor))
                    || has_annotation(parent, _NOINLINE))
            && !(parent instanceof AST_Export
                && fixed instanceof AST_Lambda
                && fixed.name);

if (single_use && (fixed instanceof AST_Lambda || fixed instanceof AST_Class)) {
            if (retain_top_func(fixed, compressor)) {
                single_use = false;
            } else if (def.scope !== self.scope
                && (def.escaped == 1
                    || has_flag(fixed, INLINED)
                    || within_array_or_object_literal(compressor))) {
                single_use = false;
            } else if (recursive_ref(compressor, def)) {
                single_use = false;
            } else if (def.scope !== self.scope || def.orig[0] instanceof AST_SymbolFunarg) {
                single_use = fixed.is_constant_expression(self.scope);
                if (single_use == "f") {
                    var scope = self.scope;
                    do {
                        if (scope instanceof AST_Defun || is_func_expr(scope)) {
                            set_flag(scope, INLINED);
                        }
                    } while (scope = scope.parent_scope);
                }
            }
        }
        if (single_use && fixed instanceof AST_Lambda) {
            single_use =
                def.scope === self.scope
                    && !scope_encloses_variables_in_this_scope(nearest_scope, fixed)
                || parent instanceof AST_Call
                    && parent.expression === self
                    && !scope_encloses_variables_in_this_scope(nearest_scope, fixed)
                    && !(fixed.name && fixed.name.definition().recursive_refs > 0);
        }
        if (single_use && fixed instanceof AST_Class) {
            const extends_inert = !fixed.extends
                || !fixed.extends.may_throw(compressor)
                    && !fixed.extends.has_side_effects(compressor);
            single_use = extends_inert
                && !fixed.properties.some(prop =>
                    prop.may_throw(compressor) || prop.has_side_effects(compressor)
                );
        }

if (single_use && fixed) {
            if (fixed instanceof AST_DefClass) {
                set_flag(fixed, SQUEEZED);
                fixed = make_node(AST_ClassExpression, fixed, fixed);
            }
            if (fixed instanceof AST_Defun) {
                set_flag(fixed, SQUEEZED);
                fixed = make_node(AST_Function, fixed, fixed);
            }
            if (def.recursive_refs > 0 && fixed.name instanceof AST_SymbolDefun) {
                const defun_def = fixed.name.definition();
                let lambda_def = fixed.variables.get(fixed.name.name);
                let name = lambda_def && lambda_def.orig[0];
                if (!(name instanceof AST_SymbolLambda)) {
                    name = make_node(AST_SymbolLambda, fixed.name, fixed.name);
                    name.scope = fixed;
                    fixed.name = name;
                    lambda_def = fixed.def_function(name);
                }
                walk(fixed, node => {
                    if (node instanceof AST_SymbolRef && node.definition() === defun_def) {
                        node.thedef = lambda_def;
                        lambda_def.references.push(node);
                    }
                });
            }
            if (
                (fixed instanceof AST_Lambda || fixed instanceof AST_Class)
                && fixed.parent_scope !== nearest_scope
            ) {
                fixed = fixed.clone(true, compressor.get_toplevel());

nearest_scope.add_child_scope(fixed);
            }
            return fixed.optimize(compressor);
        }

// multiple uses
        if (fixed) {
            let replace;

if (fixed instanceof AST_This) {
                if (!(def.orig[0] instanceof AST_SymbolFunarg)
                    && def.references.every((ref) =>
                        def.scope === ref.scope
                    )) {
                    replace = fixed;
                }
            } else {
                var ev = fixed.evaluate(compressor);
                if (
                    ev !== fixed
                    && (compressor.option("unsafe_regexp") || !(ev instanceof RegExp))
                ) {
                    replace = make_node_from_constant(ev, fixed);
                }
            }

if (replace) {
                const name_length = self.size(compressor);
                const replace_size = replace.size(compressor);

let overhead = 0;
                if (compressor.option("unused") && !compressor.exposed(def)) {
                    overhead =
                        (name_length + 2 + replace_size) /
                        (def.references.length - def.assignments);
                }

if (replace_size <= name_length + overhead) {
                    return replace;
                }
            }
        }
    }
    return self;
});

function is_atomic(lhs, self) {
    return lhs instanceof AST_SymbolRef || lhs.TYPE === self.TYPE;
}

def_optimize(AST_Undefined, function(self, compressor) {
    if (compressor.option("unsafe_undefined")) {
        var undef = find_variable(compressor, "undefined");
        if (undef) {
            var ref = make_node(AST_SymbolRef, self, {
                name   : "undefined",
                scope  : undef.scope,
                thedef : undef
            });
            set_flag(ref, UNDEFINED);
            return ref;
        }
    }
    var lhs = is_lhs(compressor.self(), compressor.parent());
    if (lhs && is_atomic(lhs, self)) return self;
    return make_node(AST_UnaryPrefix, self, {
        operator: "void",
        expression: make_node(AST_Number, self, {
            value: 0
        })
    });
});

def_optimize(AST_Infinity, function(self, compressor) {
    var lhs = is_lhs(compressor.self(), compressor.parent());
    if (lhs && is_atomic(lhs, self)) return self;
    if (
        compressor.option("keep_infinity")
        && !(lhs && !is_atomic(lhs, self))
        && !find_variable(compressor, "Infinity")
    ) {
        return self;
    }
    return make_node(AST_Binary, self, {
        operator: "/",
        left: make_node(AST_Number, self, {
            value: 1
        }),
        right: make_node(AST_Number, self, {
            value: 0
        })
    });
});

def_optimize(AST_NaN, function(self, compressor) {
    var lhs = is_lhs(compressor.self(), compressor.parent());
    if (lhs && !is_atomic(lhs, self)
        || find_variable(compressor, "NaN")) {
        return make_node(AST_Binary, self, {
            operator: "/",
            left: make_node(AST_Number, self, {
                value: 0
            }),
            right: make_node(AST_Number, self, {
                value: 0
            })
        });
    }
    return self;
});

function is_reachable(self, defs) {
    const find_ref = node => {
        if (node instanceof AST_SymbolRef && member(node.definition(), defs)) {
            return walk_abort;
        }
    };

return walk_parent(self, (node, info) => {
        if (node instanceof AST_Scope && node !== self) {
            var parent = info.parent();

if (parent instanceof AST_Call && parent.expression === node) return;

if (walk(node, find_ref)) return walk_abort;

return true;
        }
    });
}

const ASSIGN_OPS = makePredicate("+ - / * % >> << >>> | ^ &");
const ASSIGN_OPS_COMMUTATIVE = makePredicate("* | ^ &");
def_optimize(AST_Assign, function(self, compressor) {
    if (self.logical) {
        return self.lift_sequences(compressor);
    }

var def;
    if (compressor.option("dead_code")
        && self.left instanceof AST_SymbolRef
        && (def = self.left.definition()).scope === compressor.find_parent(AST_Lambda)) {
        var level = 0, node, parent = self;
        do {
            node = parent;
            parent = compressor.parent(level++);
            if (parent instanceof AST_Exit) {
                if (in_try(level, parent)) break;
                if (is_reachable(def.scope, [ def ])) break;
                if (self.operator == "=") return self.right;
                def.fixed = false;
                return make_node(AST_Binary, self, {
                    operator: self.operator.slice(0, -1),
                    left: self.left,
                    right: self.right
                }).optimize(compressor);
            }
        } while (parent instanceof AST_Binary && parent.right === node
            || parent instanceof AST_Sequence && parent.tail_node() === node);
    }
    self = self.lift_sequences(compressor);
    if (self.operator == "=" && self.left instanceof AST_SymbolRef && self.right instanceof AST_Binary) {
        // x = expr1 OP expr2
        if (self.right.left instanceof AST_SymbolRef
            && self.right.left.name == self.left.name
            && ASSIGN_OPS.has(self.right.operator)) {
            // x = x - 2  --->  x -= 2
            self.operator = self.right.operator + "=";
            self.right = self.right.right;
        } else if (self.right.right instanceof AST_SymbolRef
            && self.right.right.name == self.left.name
            && ASSIGN_OPS_COMMUTATIVE.has(self.right.operator)
            && !self.right.left.has_side_effects(compressor)) {
            // x = 2 & x  --->  x &= 2
            self.operator = self.right.operator + "=";
            self.right = self.right.left;
        }
    }
    return self;

def_optimize(AST_DefaultAssign, function(self, compressor) {
    if (!compressor.option("evaluate")) {
        return self;
    }
    var evaluateRight = self.right.evaluate(compressor);

// `[x = undefined] = foo` ---> `[x] = foo`
    if (evaluateRight === undefined) {
        self = self.left;
    } else if (evaluateRight !== self.right) {
        evaluateRight = make_node_from_constant(evaluateRight, self.right);
        self.right = best_of_expression(evaluateRight, self.right);
    }

return self;
});

function is_nullish(node) {
    let fixed;
    return (
        node instanceof AST_Null
        || is_undefined(node)
        || (
            node instanceof AST_SymbolRef
            && (fixed = node.definition().fixed) instanceof AST_Node
            && is_nullish(fixed)
        )
        // Recurse into those optional chains!
        || node instanceof AST_PropAccess && node.optional && is_nullish(node.expression)
        || node instanceof AST_Call && node.optional && is_nullish(node.expression)
        || node instanceof AST_Chain && is_nullish(node.expression)
    );
}

function is_nullish_check(check, check_subject, compressor) {
    if (check_subject.may_throw(compressor)) return false;

let nullish_side;

// foo == null
    if (
        check instanceof AST_Binary
        && check.operator === "=="
        // which side is nullish?
        && (
            (nullish_side = is_nullish(check.left) && check.left)
            || (nullish_side = is_nullish(check.right) && check.right)
        )
        // is the other side the same as the check_subject
        && (
            nullish_side === check.left
                ? check.right
                : check.left
        ).equivalent_to(check_subject)
    ) {
        return true;
    }

// foo === null || foo === undefined
    if (check instanceof AST_Binary && check.operator === "||") {
        let null_cmp;
        let undefined_cmp;

const find_comparison = cmp => {
            if (!(
                cmp instanceof AST_Binary
                && (cmp.operator === "===" || cmp.operator === "==")
            )) {
                return false;
            }

let found = 0;
            let defined_side;

if (cmp.left instanceof AST_Null) {
                found++;
                null_cmp = cmp;
                defined_side = cmp.right;
            }
            if (cmp.right instanceof AST_Null) {
                found++;
                null_cmp = cmp;
                defined_side = cmp.left;
            }
            if (is_undefined(cmp.left)) {
                found++;
                undefined_cmp = cmp;
                defined_side = cmp.right;
            }
            if (is_undefined(cmp.right)) {
                found++;
                undefined_cmp = cmp;
                defined_side = cmp.left;
            }

if (found !== 1) {
                return false;
            }

if (!defined_side.equivalent_to(check_subject)) {
                return false;
            }

return true;
        };

if (!find_comparison(check.left)) return false;
        if (!find_comparison(check.right)) return false;

if (null_cmp && undefined_cmp && null_cmp !== undefined_cmp) {
            return true;
        }
    }

return false;
}

def_optimize(AST_Conditional, function(self, compressor) {
    if (!compressor.option("conditionals")) return self;
    // This looks like lift_sequences(), should probably be under "sequences"
    if (self.condition instanceof AST_Sequence) {
        var expressions = self.condition.expressions.slice();
        self.condition = expressions.pop();
        expressions.push(self);
        return make_sequence(self, expressions);
    }
    var cond = self.condition.evaluate(compressor);
    if (cond !== self.condition) {
        if (cond) {
            return maintain_this_binding(compressor.parent(), compressor.self(), self.consequent);
        } else {
            return maintain_this_binding(compressor.parent(), compressor.self(), self.alternative);
        }
    }
    var negated = cond.negate(compressor, first_in_statement(compressor));
    if (best_of(compressor, cond, negated) === negated) {
        self = make_node(AST_Conditional, self, {
            condition: negated,
            consequent: self.alternative,
            alternative: self.consequent
        });
    }
    var condition = self.condition;
    var consequent = self.consequent;
    var alternative = self.alternative;
    // x?x:y --> x||y
    if (condition instanceof AST_SymbolRef
        && consequent instanceof AST_SymbolRef
        && condition.definition() === consequent.definition()) {
        return make_node(AST_Binary, self, {
            operator: "||",
            left: condition,
            right: alternative
        });
    }
    // if (foo) exp = something; else exp = something_else;
    //                   |
    //                   v
    // exp = foo ? something : something_else;
    if (
        consequent instanceof AST_Assign
        && alternative instanceof AST_Assign
        && consequent.operator === alternative.operator
        && consequent.logical === alternative.logical
        && consequent.left.equivalent_to(alternative.left)
        && (!self.condition.has_side_effects(compressor)
            || consequent.operator == "="
                && !consequent.left.has_side_effects(compressor))
    ) {
        return make_node(AST_Assign, self, {
            operator: consequent.operator,
            left: consequent.left,
            logical: consequent.logical,
            right: make_node(AST_Conditional, self, {
                condition: self.condition,
                consequent: consequent.right,
                alternative: alternative.right
            })
        });
    }
    // x ? y(a) : y(b) --> y(x ? a : b)
    var arg_index;
    if (consequent instanceof AST_Call
        && alternative.TYPE === consequent.TYPE
        && consequent.args.length > 0
        && consequent.args.length == alternative.args.length
        && consequent.expression.equivalent_to(alternative.expression)
        && !self.condition.has_side_effects(compressor)
        && !consequent.expression.has_side_effects(compressor)
        && typeof (arg_index = single_arg_diff()) == "number") {
        var node = consequent.clone();
        node.args[arg_index] = make_node(AST_Conditional, self, {
            condition: self.condition,
            consequent: consequent.args[arg_index],
            alternative: alternative.args[arg_index]
        });
        return node;
    }
    // a ? b : c ? b : d --> (a || c) ? b : d
    if (alternative instanceof AST_Conditional
        && consequent.equivalent_to(alternative.consequent)) {
        return make_node(AST_Conditional, self, {
            condition: make_node(AST_Binary, self, {
                operator: "||",
                left: condition,
                right: alternative.condition
            }),
            consequent: consequent,
            alternative: alternative.alternative
        }).optimize(compressor);
    }

// a == null ? b : a -> a ?? b
    if (
        compressor.option("ecma") >= 2020 &&
        is_nullish_check(condition, alternative, compressor)
    ) {
        return make_node(AST_Binary, self, {
            operator: "??",
            left: alternative,
            right: consequent
        }).optimize(compressor);
    }

// a ? b : (c, b) --> (a || c), b
    if (alternative instanceof AST_Sequence
        && consequent.equivalent_to(alternative.expressions[alternative.expressions.length - 1])) {
        return make_sequence(self, [
            make_node(AST_Binary, self, {
                operator: "||",
                left: condition,
                right: make_sequence(self, alternative.expressions.slice(0, -1))
            }),
            consequent
        ]).optimize(compressor);
    }
    // a ? b : (c && b) --> (a || c) && b
    if (alternative instanceof AST_Binary
        && alternative.operator == "&&"
        && consequent.equivalent_to(alternative.right)) {
        return make_node(AST_Binary, self, {
            operator: "&&",
            left: make_node(AST_Binary, self, {
                operator: "||",
                left: condition,
                right: alternative.left
            }),
            right: consequent
        }).optimize(compressor);
    }
    // x?y?z:a:a --> x&&y?z:a
    if (consequent instanceof AST_Conditional
        && consequent.alternative.equivalent_to(alternative)) {
        return make_node(AST_Conditional, self, {
            condition: make_node(AST_Binary, self, {
                left: self.condition,
                operator: "&&",
                right: consequent.condition
            }),
            consequent: consequent.consequent,
            alternative: alternative
        });
    }
    // x ? y : y --> x, y
    if (consequent.equivalent_to(alternative)) {
        return make_sequence(self, [
            self.condition,
            consequent
        ]).optimize(compressor);
    }
    // x ? y || z : z --> x && y || z
    if (consequent instanceof AST_Binary
        && consequent.operator == "||"
        && consequent.right.equivalent_to(alternative)) {
        return make_node(AST_Binary, self, {
            operator: "||",
            left: make_node(AST_Binary, self, {
                operator: "&&",
                left: self.condition,
                right: consequent.left
            }),
            right: alternative
        }).optimize(compressor);
    }
    var in_bool = compressor.in_boolean_context();
    if (is_true(self.consequent)) {
        if (is_false(self.alternative)) {
            // c ? true : false ---> !!c
            return booleanize(self.condition);
        }
        // c ? true : x ---> !!c || x
        return make_node(AST_Binary, self, {
            operator: "||",
            left: booleanize(self.condition),
            right: self.alternative
        });
    }
    if (is_false(self.consequent)) {
        if (is_true(self.alternative)) {
            // c ? false : true ---> !c
            return booleanize(self.condition.negate(compressor));
        }
        // c ? false : x ---> !c && x
        return make_node(AST_Binary, self, {
            operator: "&&",
            left: booleanize(self.condition.negate(compressor)),
            right: self.alternative
        });
    }
    if (is_true(self.alternative)) {
        // c ? x : true ---> !c || x
        return make_node(AST_Binary, self, {
            operator: "||",
            left: booleanize(self.condition.negate(compressor)),
            right: self.consequent
        });
    }
    if (is_false(self.alternative)) {
        // c ? x : false ---> !!c && x
        return make_node(AST_Binary, self, {
            operator: "&&",
            left: booleanize(self.condition),
            right: self.consequent
        });
    }

return self;

function booleanize(node) {
        if (node.is_boolean()) return node;
        // !!expression
        return make_node(AST_UnaryPrefix, node, {
            operator: "!",
            expression: node.negate(compressor)
        });
    }

// AST_True or !0
    function is_true(node) {
        return node instanceof AST_True
            || in_bool
                && node instanceof AST_Constant
                && node.getValue()
            || (node instanceof AST_UnaryPrefix
                && node.operator == "!"
                && node.expression instanceof AST_Constant
                && !node.expression.getValue());
    }
    // AST_False or !1
    function is_false(node) {
        return node instanceof AST_False
            || in_bool
                && node instanceof AST_Constant
                && !node.getValue()
            || (node instanceof AST_UnaryPrefix
                && node.operator == "!"
                && node.expression instanceof AST_Constant
                && node.expression.getValue());
    }

def_optimize(AST_Boolean, function(self, compressor) {
    if (compressor.in_boolean_context()) return make_node(AST_Number, self, {
        value: +self.value
    });
    var p = compressor.parent();
    if (compressor.option("booleans_as_integers")) {
        if (p instanceof AST_Binary && (p.operator == "===" || p.operator == "!==")) {
            p.operator = p.operator.replace(/=$/, "");
        }
        return make_node(AST_Number, self, {
            value: +self.value
        });
    }
    if (compressor.option("booleans")) {
        if (p instanceof AST_Binary && (p.operator == "=="
                                        || p.operator == "!=")) {
            return make_node(AST_Number, self, {
                value: +self.value
            });
        }
        return make_node(AST_UnaryPrefix, self, {
            operator: "!",
            expression: make_node(AST_Number, self, {
                value: 1 - self.value
            })
        });
    }
    return self;
});

function safe_to_flatten(value, compressor) {
    if (value instanceof AST_SymbolRef) {
        value = value.fixed_value();
    }
    if (!value) return false;
    if (!(value instanceof AST_Lambda || value instanceof AST_Class)) return true;
    if (!(value instanceof AST_Lambda && value.contains_this())) return true;
    return compressor.parent() instanceof AST_New;
}

AST_PropAccess.DEFMETHOD("flatten_object", function(key, compressor) {
    if (!compressor.option("properties")) return;
    var arrows = compressor.option("unsafe_arrows") && compressor.option("ecma") >= 2015;
    var expr = this.expression;
    if (expr instanceof AST_Object) {
        var props = expr.properties;
        for (var i = props.length; --i >= 0;) {
            var prop = props[i];
            if ("" + (prop instanceof AST_ConciseMethod ? prop.key.name : prop.key) == key) {
                if (!props.every((prop) => {
                    return prop instanceof AST_ObjectKeyVal
                        || arrows && prop instanceof AST_ConciseMethod && !prop.is_generator;
                })) break;
                if (!safe_to_flatten(prop.value, compressor)) break;
                return make_node(AST_Sub, this, {
                    expression: make_node(AST_Array, expr, {
                        elements: props.map(function(prop) {
                            var v = prop.value;
                            if (v instanceof AST_Accessor) v = make_node(AST_Function, v, v);
                            var k = prop.key;
                            if (k instanceof AST_Node && !(k instanceof AST_SymbolMethod)) {
                                return make_sequence(prop, [ k, v ]);
                            }
                            return v;
                        })
                    }),
                    property: make_node(AST_Number, this, {
                        value: i
                    })
                });
            }
        }
    }
});

def_optimize(AST_Sub, function(self, compressor) {
    var expr = self.expression;
    var prop = self.property;
    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_basic_identifier_string(property)
                && property.length <= prop.size() + 1) {
                return make_node(AST_Dot, self, {
                    expression: expr,
                    optional: self.optional,
                    property: property,
                    quote: prop.quote,
                }).optimize(compressor);
            }
        }
    }
    var fn;
    OPT_ARGUMENTS: if (compressor.option("arguments")
        && expr instanceof AST_SymbolRef
        && expr.name == "arguments"
        && expr.definition().orig.length == 1
        && (fn = expr.scope) instanceof AST_Lambda
        && fn.uses_arguments
        && !(fn instanceof AST_Arrow)
        && prop instanceof AST_Number) {
        var index = prop.getValue();
        var params = new Set();
        var argnames = fn.argnames;
        for (var n = 0; n < argnames.length; n++) {
            if (!(argnames[n] instanceof AST_SymbolFunarg)) {
                break OPT_ARGUMENTS; // destructuring parameter - bail
            }
            var param = argnames[n].name;
            if (params.has(param)) {
                break OPT_ARGUMENTS; // duplicate parameter - bail
            }
            params.add(param);
        }
        var argname = fn.argnames[index];
        if (argname && compressor.has_directive("use strict")) {
            var def = argname.definition();
            if (!compressor.option("reduce_vars") || def.assignments || def.orig.length > 1) {
                argname = null;
            }
        } else if (!argname && !compressor.option("keep_fargs") && index < fn.argnames.length + 5) {
            while (index >= fn.argnames.length) {
                argname = fn.create_symbol(AST_SymbolFunarg, {
                    source: fn,
                    scope: fn,
                    tentative_name: "argument_" + fn.argnames.length,
                });
                fn.argnames.push(argname);
            }
        }
        if (argname) {
            var sym = make_node(AST_SymbolRef, self, argname);
            sym.reference({});
            clear_flag(argname, UNUSED);
            return sym;
        }
    }
    if (is_lhs(self, compressor.parent())) return self;
    if (key !== prop) {
        var sub = self.flatten_object(property, compressor);
        if (sub) {
            expr = self.expression = sub.expression;
            prop = self.property = sub.property;
        }
    }
    if (compressor.option("properties") && compressor.option("side_effects")
        && prop instanceof AST_Number && expr instanceof AST_Array) {
        var index = prop.getValue();
        var elements = expr.elements;
        var retValue = elements[index];
        FLATTEN: if (safe_to_flatten(retValue, compressor)) {
            var flatten = true;
            var values = [];
            for (var i = elements.length; --i > index;) {
                var value = elements[i].drop_side_effect_free(compressor);
                if (value) {
                    values.unshift(value);
                    if (flatten && value.has_side_effects(compressor)) flatten = false;
                }
            }
            if (retValue instanceof AST_Expansion) break FLATTEN;
            retValue = retValue instanceof AST_Hole ? make_node(AST_Undefined, retValue) : retValue;
            if (!flatten) values.unshift(retValue);
            while (--i >= 0) {
                var value = elements[i];
                if (value instanceof AST_Expansion) break FLATTEN;
                value = value.drop_side_effect_free(compressor);
                if (value) values.unshift(value);
                else index--;
            }
            if (flatten) {
                values.push(retValue);
                return make_sequence(self, values).optimize(compressor);
            } else return make_node(AST_Sub, self, {
                expression: make_node(AST_Array, expr, {
                    elements: values
                }),
                property: make_node(AST_Number, prop, {
                    value: index
                })
            });
        }
    }
    var ev = self.evaluate(compressor);
    if (ev !== self) {
        ev = make_node_from_constant(ev, self).optimize(compressor);
        return best_of(compressor, ev, self);
    }
    if (self.optional && is_nullish(self.expression)) {
        return make_node(AST_Undefined, self);
    }
    return self;
});

def_optimize(AST_Chain, function (self, compressor) {
    self.expression = self.expression.optimize(compressor);
    return self;
});

AST_Lambda.DEFMETHOD("contains_this", function() {
    return walk(this, node => {
        if (node instanceof AST_This) return walk_abort;
        if (
            node !== this
            && node instanceof AST_Scope
            && !(node instanceof AST_Arrow)
        ) {
            return true;
        }
    });
});

def_optimize(AST_Dot, function(self, compressor) {
    const parent = compressor.parent();
    if (is_lhs(self, parent)) return self;
    if (compressor.option("unsafe_proto")
        && self.expression instanceof AST_Dot
        && self.expression.property == "prototype") {
        var exp = self.expression.expression;
        if (is_undeclared_ref(exp)) switch (exp.name) {
          case "Array":
            self.expression = make_node(AST_Array, self.expression, {
                elements: []
            });
            break;
          case "Function":
            self.expression = make_node(AST_Function, self.expression, {
                argnames: [],
                body: []
            });
            break;
          case "Number":
            self.expression = make_node(AST_Number, self.expression, {
                value: 0
            });
            break;
          case "Object":
            self.expression = make_node(AST_Object, self.expression, {
                properties: []
            });
            break;
          case "RegExp":
            self.expression = make_node(AST_RegExp, self.expression, {
                value: { source: "t", flags: "" }
            });
            break;
          case "String":
            self.expression = make_node(AST_String, self.expression, {
                value: ""
            });
            break;
        }
    }
    if (!(parent instanceof AST_Call) || !has_annotation(parent, _NOINLINE)) {
        const sub = self.flatten_object(self.property, compressor);
        if (sub) return sub.optimize(compressor);
    }
    let ev = self.evaluate(compressor);
    if (ev !== self) {
        ev = make_node_from_constant(ev, self).optimize(compressor);
        return best_of(compressor, ev, self);
    }
    if (self.optional && is_nullish(self.expression)) {
        return make_node(AST_Undefined, self);
    }
    return self;
});

function literals_in_boolean_context(self, compressor) {
    if (compressor.in_boolean_context()) {
        return best_of(compressor, self, make_sequence(self, [
            self,
            make_node(AST_True, self)
        ]).optimize(compressor));
    }
    return self;
}

def_optimize(AST_Array, function(self, compressor) {
    var optimized = literals_in_boolean_context(self, compressor);
    if (optimized !== self) {
        return optimized;
    }
    inline_array_like_spread(self.elements);
    return self;
});

def_optimize(AST_Object, function(self, compressor) {
    var optimized = literals_in_boolean_context(self, compressor);
    if (optimized !== self) {
        return optimized;
    }
    inline_object_prop_spread(self.properties);
    return self;
});

def_optimize(AST_RegExp, literals_in_boolean_context);

def_optimize(AST_Return, function(self, compressor) {
    if (self.value && is_undefined(self.value, compressor)) {
        self.value = null;
    }
    return self;
});

def_optimize(AST_Arrow, opt_AST_Lambda);

def_optimize(AST_Function, function(self, compressor) {
    self = opt_AST_Lambda(self, compressor);
    if (compressor.option("unsafe_arrows")
        && compressor.option("ecma") >= 2015
        && !self.name
        && !self.is_generator
        && !self.uses_arguments
        && !self.pinned()) {
        const uses_this = walk(self, node => {
            if (node instanceof AST_This) return walk_abort;
        });
        if (!uses_this) return make_node(AST_Arrow, self, self).optimize(compressor);
    }
    return self;
});

def_optimize(AST_Class, function(self) {
    // HACK to avoid compress failure.
    // AST_Class is not really an AST_Scope/AST_Block as it lacks a body.
    return self;
});

def_optimize(AST_Yield, function(self, compressor) {
    if (self.expression && !self.is_star && is_undefined(self.expression, compressor)) {
        self.expression = null;
    }
    return self;
});

def_optimize(AST_TemplateString, function(self, compressor) {
    if (
        !compressor.option("evaluate")
        || compressor.parent() instanceof AST_PrefixedTemplateString
    ) {
        return self;
    }

// `foo` => "foo"
    if (segments.length == 1) {
        return make_node(AST_String, self, segments[0]);
    }

if (
        segments.length === 3
        && segments[1] instanceof AST_Node
        && (
            segments[1].is_string(compressor)
            || segments[1].is_number(compressor)
            || is_nullish(segments[1])
            || compressor.option("unsafe")
        )
    ) {
        // `foo${bar}` => "foo" + bar
        if (segments[2].value === "") {
            return make_node(AST_Binary, self, {
                operator: "+",
                left: make_node(AST_String, self, {
                    value: segments[0].value,
                }),
                right: segments[1],
            });
        }
        // `${bar}baz` => bar + "baz"
        if (segments[0].value === "") {
            return make_node(AST_Binary, self, {
                operator: "+",
                left: segments[1],
                right: make_node(AST_String, self, {
                    value: segments[2].value,
                }),
            });
        }
    }
    return self;
});

def_optimize(AST_PrefixedTemplateString, function(self) {
    return self;
});

// ["p"]:1 ---> p:1
// [42]:1 ---> 42:1
function lift_key(self, compressor) {
    if (!compressor.option("computed_props")) return self;
    // save a comparison in the typical case
    if (!(self.key instanceof AST_Constant)) return self;
    // allow certain acceptable props as not all AST_Constants are true constants
    if (self.key instanceof AST_String || self.key instanceof AST_Number) {
        if (self.key.value === "__proto__") return self;
        if (self.key.value == "constructor"
            && compressor.parent() instanceof AST_Class) return self;
        if (self instanceof AST_ObjectKeyVal) {
            self.key = self.key.value;
        } else if (self instanceof AST_ClassProperty) {
            self.key = make_node(AST_SymbolClassProperty, self.key, {
                name: self.key.value
            });
        } else {
            self.key = make_node(AST_SymbolMethod, self.key, {
                name: self.key.value
            });
        }
    }
    return self;
}

def_optimize(AST_ObjectProperty, lift_key);

def_optimize(AST_ConciseMethod, function(self, compressor) {
    lift_key(self, compressor);
    // p(){return x;} ---> p:()=>x
    if (compressor.option("arrows")
        && compressor.parent() instanceof AST_Object
        && !self.is_generator
        && !self.value.uses_arguments
        && !self.value.pinned()
        && self.value.body.length == 1
        && self.value.body[0] instanceof AST_Return
        && self.value.body[0].value
        && !self.value.contains_this()) {
        var arrow = make_node(AST_Arrow, self.value, self.value);
        arrow.async = self.async;
        arrow.is_generator = self.is_generator;
        return make_node(AST_ObjectKeyVal, self, {
            key: self.key instanceof AST_SymbolMethod ? self.key.name : self.key,
            value: arrow,
            quote: self.quote,
        });
    }
    return self;
});

def_optimize(AST_ObjectKeyVal, function(self, compressor) {
    lift_key(self, compressor);
    // p:function(){} ---> p(){}
    // p:function*(){} ---> *p(){}
    // p:async function(){} ---> async p(){}
    // p:()=>{} ---> p(){}
    // p:async()=>{} ---> async p(){}
    var unsafe_methods = compressor.option("unsafe_methods");
    if (unsafe_methods
        && compressor.option("ecma") >= 2015
        && (!(unsafe_methods instanceof RegExp) || unsafe_methods.test(self.key + ""))) {
        var key = self.key;
        var value = self.value;
        var is_arrow_with_block = value instanceof AST_Arrow
            && Array.isArray(value.body)
            && !value.contains_this();
        if ((is_arrow_with_block || value instanceof AST_Function) && !value.name) {
            return make_node(AST_ConciseMethod, self, {
                async: value.async,
                is_generator: value.is_generator,
                key: key instanceof AST_Node ? key : make_node(AST_SymbolMethod, self, {
                    name: key,
                }),
                value: make_node(AST_Accessor, value, value),
                quote: self.quote,
            });
        }
    }
    return self;
});

def_optimize(AST_Destructuring, function(self, compressor) {
    if (compressor.option("pure_getters") == true
        && compressor.option("unused")
        && !self.is_array
        && Array.isArray(self.names)
        && !is_destructuring_export_decl(compressor)
        && !(self.names[self.names.length - 1] instanceof AST_Expansion)) {
        var keep = [];
        for (var i = 0; i < self.names.length; i++) {
            var elem = self.names[i];
            if (!(elem instanceof AST_ObjectKeyVal
                && typeof elem.key == "string"
                && elem.value instanceof AST_SymbolDeclaration
                && !should_retain(compressor, elem.value.definition()))) {
                keep.push(elem);
            }
        }
        if (keep.length != self.names.length) {
            self.names = keep;
        }
    }
    return self;

export {
    Compressor,
};

cmd: