临时所写，可能有bug

// 变量传播
function varibalePropagation(ast) {
    var update = false;
    traverse(ast, {
        VariableDeclaration(path) {
            try {
                const {
                    declarations
                } = path.node;
                if (declarations.length !== 1) return;
                const {
                    id,
                    init
                } = declarations[0];
                if (!(te.isIdentifier(id) && te.isIdentifier(init))) return;
                const targetBinding = path.scope.getBinding(init.name);
                if (!targetBinding) return;
                const binding = path.scope.getBinding(id.name);
                if (!binding) return;
                if (!binding.references || binding.references.length === 0) return;  // 其实这里可以remove path
                const referencePaths = binding.referencePaths;
                referencePaths.forEach((refPath) => {
                    // 跳过更新表达式，如 a++、a--
                    if (te.isUpdateExpression(refPath.parentPath.node)) return;
                    // 跳过赋值表达式的左侧，如 a = 1、a += 1
                    if (refPath.parentPath.isAssignmentExpression() && refPath.parentPath.node.left === refPath.node) return;
                    // 跳过 delete 操作数，如 delete a
                    if (refPath.parentPath.isUnaryExpression({
                            operator: 'delete'
                        }) && refPath.parentPath.node.argument === refPath.node) return;
                    // 防止自引用（几乎不会发生，保留也无妨）
                    if (refPath.node === init) return;
                    refPath.replaceWith(te.identifier(init.name));
                    console.log(`Variable propagation: ${id.name} -> ${init.name}`);
                    update = true;
                });
            } catch (error) {
                console.log(`Error in variable propagation: ${error.message}`);
            }
        }
    });
    if (update) {
        try {
            const code = generator(ast).code;
            ast = parser.parse(code);
        } catch (e) {
            console.error('varibalePropagation 重新解析错误:', e.message);
        }
    }
    return {
        ast: ast,
        update_: update
    };
}

// 函数越狱
function replaceParams(exprNode, paramNames, argNodes) {
    const newExpr = te.cloneNode(exprNode);
    var can_replace = true;
    function replaceNode(node) {
        if (!te.isNode(node)) return node;
        if (te.isIdentifier(node)) {
            const index = paramNames.indexOf(node.name);
            if (index > -1) {
                return te.cloneNode(argNodes[index]);
            } else {
                can_replace = false;
            }
        } else if (te.isThisExpression(node)) {
            can_replace = false;
        }
        for (const key in node) {
            if (node[key] && typeof node[key] === 'object') {
                if (Array.isArray(node[key])) {
                    node[key] = node[key].map(item => replaceNode(item));
                } else {
                    node[key] = replaceNode(node[key]);
                }
            }
        }
        return node;
    }
    if (!can_replace) return exprNode;
    return replaceNode(newExpr);
}
function functionConfinement(ast) {
    var update = false;
    traverse(ast, {
        FunctionDeclaration(path) {
            const {
                id,
                params,
                body
            } = path.node;
            const blockBody = body.body;
            if (blockBody.length !== 1) return;
            const firstStatement = blockBody[0];
            if (!te.isReturnStatement(firstStatement)) return;
            const returnExpr = firstStatement.argument;
            if (generator(returnExpr).code.length > 50) return;  // 如果很长的话，可能有复杂表达式，这里粗略跳过
            const funcName = id.name;
            const paramNames = params.map(param => param.name);
            const binding = path.parentPath.scope.getBinding(funcName);
            if (!binding || !binding.referencePaths.length) {
                if (!binding.referencePaths.length) {
                    path.remove();
                    update = true;
                }
                return;
            }
            try {
                binding.referencePaths.forEach(ref => {
                    const refParentPath = ref.parentPath;
                    if (!te.isCallExpression(refParentPath.node)) return;
                    const args = refParentPath.node.arguments;
                    if (!args) return;
                    const nCode = generator(refParentPath.node).code;
                    const newExpr = replaceParams(returnExpr, paramNames, args);
                    if (newExpr === returnExpr) return;
                    refParentPath.replaceWith(newExpr);
                    console.log(`Function confinement: ${nCode} -> ${generator(newExpr).code}`);
                    update = true;
                });
            } catch (error) {
                console.error(`Function confinement error: ${error.message}`);
            }
            path.scope.crawl();
        }
    });
    if (update) {
        try {
            const code = generator(ast).code;
            ast = parser.parse(code);
        } catch (e) {
            console.error('functionConfinement 重新解析错误:', e.message);
        }
    }
    return {
        ast: ast,
        update_: update
    };
}

示例：
原代码：

! function(e, t) {
    function n(e, t, n, o, r) {
        return m$5(e - -127, r);
    }
    const o = A$5();
    function r(e, t, n, o, r) {
        return m$5(e - -51, r);
    }
    function a(e, t, n, o, r) {
        return m$5(e - -421, n);
    }
    function i(e, t, n, o, r) {
        return m$5(r - 544, o);
    }
    for (;;) try {
        if (573587 === -parseInt((l = 607, s = "6]qe", m$5(l - -25, s))) / 1 * (parseInt(n(233, 0, 0, 0, "#upy")) / 2) + -parseInt(r(490, 0, 0, 0, "DgCf")) / 3 + -parseInt(a(157, 0, "29Uu")) / 4 * (-parseInt(r(324, 0, 0, 0, "g]^N")) / 5) + parseInt(i(0, 0, 0, "*S7N", 1294)) / 6 + -parseInt(a(235, 0, "AmNL")) / 7 + -parseInt(a(-54, 0, "AmNL")) / 8 * (-parseInt(i(0, 0, 0, "Q4Q]", 1288)) / 9) + -parseInt(i(0, 0, 0, "!zsp", 1330)) / 10 * (-parseInt(n(212, 0, 0, 0, "5QdF")) / 11)) {
            break;
        }
        o.push(o.shift());
    } catch (s) {
        o.push(o.shift());
    }
    var l;
    var s;
}();
var a = 'a',
    b = 10;
function c(a, b) {
    var d = b++;
    var e = a;
    console.log(e);
    return a + b + d;
}

运行后：

!function (e, t) {
  function n(e, t, n, o, r) {
    return m$5(e - -127, r);
  }
  const o = A$5();
  function r(e, t, n, o, r) {
    return m$5(e - -51, r);
  }
  function a(e, t, n, o, r) {
    return m$5(e - -421, n);
  }
  function i(e, t, n, o, r) {
    return m$5(r - 544, o);
  }
  for (;;) try {
    if (573587 === -parseInt((l = 607, s = "6]qe", m$5(l - -25, s))) / 1 * (parseInt(m$5(233 - -127, "#upy")) / 2) + -parseInt(m$5(490 - -51, "DgCf")) / 3 + -parseInt(m$5(157 - -421, "29Uu")) / 4 * (-parseInt(m$5(324 - -51, "g]^N")) / 5) + parseInt(m$5(1294 - 544, "*S7N")) / 6 + -parseInt(m$5(235 - -421, "AmNL")) / 7 + -parseInt(m$5(-54 - -421, "AmNL")) / 8 * (-parseInt(m$5(1288 - 544, "Q4Q]")) / 9) + -parseInt(m$5(1330 - 544, "!zsp")) / 10 * (-parseInt(m$5(212 - -127, "5QdF")) / 11)) {
      break;
    }
    o.push(o.shift());
  } catch (s) {
    o.push(o.shift());
  }
  var l;
  var s;
}();
var a = 'a',
  b = 10;
function c(a, b) {
  var d = b++;
  var e = a;
  console.log(a);
  return a + b + d;
}