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app_vue/node_modules/terser/lib/compress/reduce-vars.js

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+/***********************************************************************
+
+  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:
+
+    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>
+
+    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.
+
+ ***********************************************************************/
+
+import {
+    AST_Accessor,
+    AST_Array,
+    AST_Assign,
+    AST_Await,
+    AST_Binary,
+    AST_Block,
+    AST_Call,
+    AST_Case,
+    AST_Chain,
+    AST_Class,
+    AST_ClassStaticBlock,
+    AST_ClassExpression,
+    AST_Conditional,
+    AST_Default,
+    AST_Defun,
+    AST_Destructuring,
+    AST_Do,
+    AST_Exit,
+    AST_Expansion,
+    AST_For,
+    AST_ForIn,
+    AST_If,
+    AST_LabeledStatement,
+    AST_Lambda,
+    AST_New,
+    AST_Node,
+    AST_Number,
+    AST_ObjectKeyVal,
+    AST_PropAccess,
+    AST_Scope,
+    AST_Sequence,
+    AST_SimpleStatement,
+    AST_Symbol,
+    AST_SymbolCatch,
+    AST_SymbolConst,
+    AST_SymbolDeclaration,
+    AST_SymbolDefun,
+    AST_SymbolFunarg,
+    AST_SymbolLambda,
+    AST_SymbolRef,
+    AST_This,
+    AST_Toplevel,
+    AST_Try,
+    AST_Unary,
+    AST_UnaryPrefix,
+    AST_Undefined,
+    AST_VarDef,
+    AST_While,
+    AST_Yield,
+
+    walk,
+    walk_body,
+    walk_parent,
+} from "../ast.js";
+import { HOP, make_node, noop } from "../utils/index.js";
+
+import { lazy_op, is_modified, is_lhs } from "./inference.js";
+import { INLINED, clear_flag } from "./compressor-flags.js";
+import { read_property, has_break_or_continue, is_recursive_ref } from "./common.js";
+
+/**
+ * Define the method AST_Node#reduce_vars, which goes through the AST in
+ * execution order to perform basic flow analysis
+ */
+function def_reduce_vars(node, func) {
+    node.DEFMETHOD("reduce_vars", func);
+}
+
+def_reduce_vars(AST_Node, noop);
+
+/** Clear definition properties */
+function reset_def(compressor, def) {
+    def.assignments = 0;
+    def.chained = false;
+    def.direct_access = false;
+    def.escaped = 0;
+    def.recursive_refs = 0;
+    def.references = [];
+    def.single_use = undefined;
+    if (
+        def.scope.pinned()
+        || (def.orig[0] instanceof AST_SymbolFunarg && def.scope.uses_arguments)
+    ) {
+        def.fixed = false;
+    } else if (def.orig[0] instanceof AST_SymbolConst || !compressor.exposed(def)) {
+        def.fixed = def.init;
+    } else {
+        def.fixed = false;
+    }
+}
+
+function reset_variables(tw, compressor, node) {
+    node.variables.forEach(function(def) {
+        reset_def(compressor, def);
+        if (def.fixed === null) {
+            tw.defs_to_safe_ids.set(def.id, tw.safe_ids);
+            mark(tw, def, true);
+        } else if (def.fixed) {
+            tw.loop_ids.set(def.id, tw.in_loop);
+            mark(tw, def, true);
+        }
+    });
+}
+
+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 safe_to_read(tw, def) {
+    if (def.single_use == "m") return false;
+    if (tw.safe_ids[def.id]) {
+        if (def.fixed == null) {
+            var orig = def.orig[0];
+            if (orig instanceof AST_SymbolFunarg || orig.name == "arguments") return false;
+            def.fixed = make_node(AST_Undefined, orig);
+        }
+        return true;
+    }
+    return def.fixed instanceof AST_Defun;
+}
+
+function safe_to_assign(tw, def, scope, value) {
+    if (def.fixed === undefined) return true;
+    let def_safe_ids;
+    if (def.fixed === null
+        && (def_safe_ids = tw.defs_to_safe_ids.get(def.id))
+    ) {
+        def_safe_ids[def.id] = false;
+        tw.defs_to_safe_ids.delete(def.id);
+        return true;
+    }
+    if (!HOP(tw.safe_ids, def.id)) return false;
+    if (!safe_to_read(tw, def)) return false;
+    if (def.fixed === false) return false;
+    if (def.fixed != null && (!value || def.references.length > def.assignments)) return false;
+    if (def.fixed instanceof AST_Defun) {
+        return value instanceof AST_Node && def.fixed.parent_scope === scope;
+    }
+    return def.orig.every((sym) => {
+        return !(sym instanceof AST_SymbolConst
+            || sym instanceof AST_SymbolDefun
+            || sym instanceof AST_SymbolLambda);
+    });
+}
+
+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 suppress = node => walk(node, node => {
+    if (!(node instanceof AST_Symbol)) return;
+    var d = node.definition();
+    if (!d) return;
+    if (node instanceof AST_SymbolRef) d.references.push(node);
+    d.fixed = false;
+});
+
+def_reduce_vars(AST_Accessor, function(tw, descend, compressor) {
+    push(tw);
+    reset_variables(tw, compressor, this);
+    descend();
+    pop(tw);
+    return true;
+});
+
+def_reduce_vars(AST_Assign, function(tw, descend, compressor) {
+    var node = this;
+    if (node.left instanceof AST_Destructuring) {
+        suppress(node.left);
+        return;
+    }
+
+    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_ClassStaticBlock, function(tw, descend, compressor) {
+    reset_block_variables(compressor, this);
+});
+
+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) {
+    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);
+
+    var iife;
+    if (!this.name
+        && !this.uses_arguments
+        && !this.pinned()
+        && (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);
+
+    handle_defined_after_hoist(this);
+
+    return true;
+}
+
+/**
+ * It's possible for a hoisted function to use something that's not defined yet. Example:
+ *
+ * hoisted();
+ * var defined_after = true;
+ * function hoisted() {
+ *   // use defined_after
+ * }
+ *
+ * Or even indirectly:
+ *
+ * B();
+ * var defined_after = true;
+ * function A() {
+ *   // use defined_after
+ * }
+ * function B() {
+ *   A();
+ * }
+ *
+ * Access a variable before declaration will either throw a ReferenceError
+ * (if the variable is declared with `let` or `const`),
+ * or get an `undefined` (if the variable is declared with `var`).
+ *
+ * If the variable is inlined into the function, the behavior will change.
+ *
+ * This function is called on the parent to disallow inlining of such variables,
+ */
+function handle_defined_after_hoist(parent) {
+    const defuns = [];
+    walk(parent, node => {
+        if (node === parent) return;
+        if (node instanceof AST_Defun) {
+            defuns.push(node);
+            return true;
+        }
+        if (
+            node instanceof AST_Scope
+            || node instanceof AST_SimpleStatement
+        ) return true;
+    });
+
+    // `defun` id to array of `defun` it uses
+    const defun_dependencies_map = new Map();
+    // `defun` id to array of enclosing `def` that are used by the function
+    const dependencies_map = new Map();
+    // all symbol ids that will be tracked for read/write
+    const symbols_of_interest = new Set();
+    const defuns_of_interest = new Set();
+
+    for (const defun of defuns) {
+        const fname_def = defun.name.definition();
+        const enclosing_defs = [];
+
+        for (const def of defun.enclosed) {
+            if (
+                def.fixed === false
+                || def === fname_def
+                || def.scope.get_defun_scope() !== parent
+            ) {
+                continue;
+            }
+
+            symbols_of_interest.add(def.id);
+
+            // found a reference to another function
+            if (
+                def.assignments === 0
+                && def.orig.length === 1
+                && def.orig[0] instanceof AST_SymbolDefun
+            ) {
+                defuns_of_interest.add(def.id);
+                symbols_of_interest.add(def.id);
+
+                defuns_of_interest.add(fname_def.id);
+                symbols_of_interest.add(fname_def.id);
+
+                if (!defun_dependencies_map.has(fname_def.id)) {
+                    defun_dependencies_map.set(fname_def.id, []);
+                }
+                defun_dependencies_map.get(fname_def.id).push(def.id);
+
+                continue;
+            }
+
+            enclosing_defs.push(def);
+        }
+
+        if (enclosing_defs.length) {
+            dependencies_map.set(fname_def.id, enclosing_defs);
+            defuns_of_interest.add(fname_def.id);
+            symbols_of_interest.add(fname_def.id);
+        }
+    }
+
+    // No defuns use outside constants
+    if (!dependencies_map.size) {
+        return;
+    }
+
+    // Increment to count "symbols of interest" (defuns or defs) that we found.
+    // These are tracked in AST order so we can check which is after which.
+    let symbol_index = 1;
+    // Map a defun ID to its first read (a `symbol_index`)
+    const defun_first_read_map = new Map();
+    // Map a symbol ID to its last write (a `symbol_index`)
+    const symbol_last_write_map = new Map();
+
+    walk_parent(parent, (node, walk_info) => {
+        if (node instanceof AST_Symbol && node.thedef) {
+            const id = node.definition().id;
+
+            symbol_index++;
+
+            // Track last-writes to symbols
+            if (symbols_of_interest.has(id)) {
+                if (node instanceof AST_SymbolDeclaration || is_lhs(node, walk_info.parent())) {
+                    symbol_last_write_map.set(id, symbol_index);
+                }
+            }
+
+            // Track first-reads of defuns (refined later)
+            if (defuns_of_interest.has(id)) {
+                if (!defun_first_read_map.has(id) && !is_recursive_ref(walk_info, id)) {
+                    defun_first_read_map.set(id, symbol_index);
+                }
+            }
+        }
+    });
+
+    // Refine `defun_first_read_map` to be as high as possible
+    for (const [defun, defun_first_read] of defun_first_read_map) {
+        // Update all depdencies of `defun`
+        const queue = new Set(defun_dependencies_map.get(defun));
+        for (const enclosed_defun of queue) {
+            let enclosed_defun_first_read = defun_first_read_map.get(enclosed_defun);
+            if (enclosed_defun_first_read != null && enclosed_defun_first_read < defun_first_read) {
+                continue;
+            }
+
+            defun_first_read_map.set(enclosed_defun, defun_first_read);
+
+            for (const enclosed_enclosed_defun of defun_dependencies_map.get(enclosed_defun) || []) {
+                queue.add(enclosed_enclosed_defun);
+            }
+        }
+    }
+
+    // ensure write-then-read order, otherwise clear `fixed`
+    // This is safe because last-writes (found_symbol_writes) are assumed to be as late as possible, and first-reads (defun_first_read_map) are assumed to be as early as possible.
+    for (const [defun, defs] of dependencies_map) {
+        const defun_first_read = defun_first_read_map.get(defun);
+        if (defun_first_read === undefined) {
+            continue;
+        }
+
+        for (const def of defs) {
+            if (def.fixed === false) {
+                continue;
+            }
+
+            let def_last_write = symbol_last_write_map.get(def.id) || 0;
+
+            if (defun_first_read < def_last_write) {
+                def.fixed = false;
+            }
+        }
+    }
+}
+
+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
+            && is_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);
+    descend();
+    handle_defined_after_hoist(this);
+    return true;
+});
+
+def_reduce_vars(AST_Try, function(tw, descend, compressor) {
+    reset_block_variables(compressor, this);
+    push(tw);
+    this.body.walk(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;
+});