minify.compress may cause memory overflow?

[noyobo]

Describe the bug

Today I encountered a problem. I suddenly found that swc compression code was very slow. After investigation, I found that it was caused by the following code.

When minify.compress is enabled, swc will merge "a" + "b" into "ab", but if a is a variable, it will be repeated many times, which will cause it to be very slow. And after exceeding a certain threshold, memory overflows.

For example, in my example, the variable is in the current scope and does not need to be merged. It seems that this compression cooperation operation can be skipped?

// build.js
import {transformSync} from "@swc/core";

function genCode(len) {
  return `
    export function add(a) {
      return ${'a + "hello swc, minify" + '.repeat(len)} 'c'
    }
  `;
}

function minifyLen(len, fn) {
  try {
    const start = Date.now();
    const code = fn(len);
    transformSync(code, {
      jsc: {
        parser: {
          syntax: "ecmascript",
        },
        transform: {},
        minify: {
          mangle: true,
          compress: true,
        },
      },
      minify: true,
    });
    console.log(fn.name, len, 'cost:', Date.now() - start, 'ms');
  } catch (e) {
    console.log(fn.name, len, 'error:', e);
  }
}

minifyLen(100, genCode)
minifyLen(1000, genCode)
minifyLen(2000, genCode)
minifyLen(3000, genCode)

case1: ${'a + "hello swc, minify" + '.repeat(len)} 'c'

genCode 100 cost: 113 ms
genCode 1000 cost: 222 ms
genCode 2000 cost: 1019 ms
[1]    57128 segmentation fault  node ./build.js

case2: ${'"a" + "hello swc, minify" + '.repeat(len)} 'c'

genCode2 100 cost: 94 ms
genCode2 1000 cost: 6 ms
genCode2 2000 cost: 18 ms
[1]    57423 segmentation fault  node ./build2.js

case3: ${'a + b + '.repeat(len)} c;

genCode3 100 cost: 10 ms
genCode3 1000 cost: 148 ms
genCode3 2000 cost: 638 ms
[1]    57461 segmentation fault  node ./build3.js

Input code

Config

Playground link (or link to the minimal reproduction)

https://github.com/noyobo/swc-issues/tree/swc-minify

SWC Info output

    Operating System:
        Platform: darwin
        Arch: x64
        Machine Type: x86_64
        Version: Darwin Kernel Version 23.1.0: Mon Oct  9 21:27:27 PDT 2023; root:xnu-10002.41.9~6/RELEASE_X86_64
        CPU: (12 cores)
            Models: Intel(R) Core(TM) i7-8750H CPU @ 2.20GHz

    Binaries:
        Node: 20.12.0
        npm: 10.5.0
        Yarn: 1.22.22
        pnpm: 9.4.0

    Relevant Packages:
        @swc/core: 1.11.10
        @swc/helpers: N/A
        @swc/types: N/A


    SWC Config:
        output: N/A
        .swcrc path: N/A

    Next.js info:
        output: N/A

Expected behavior

Compress code fast

Actual behavior

No response

Version

1.11.10

Additional context

No response

[kdy1]

I didn't think about such input while implementing, so I'm sure there's a time complexity bug in string concat logic.