Missed optimization with multiple optional chaining calls on undefined #1400

This is a feature request

Version

5.18.0

Complete CLI command or minify() options used

{
  "module": true,
  "warnings": true,
  "ecma": 2021,
  "compress": {
    "passes": 4,
  },
  "mangle": {},
  "output": {},
  "parse": {},
  "rename": {},
}

terser input

const DEV_MODE = false;
const debugLog = DEV_MODE ? (v) => console.log(v) : undefined;

debugLog?.('one')
debugLog?.('two');
debugLog?.('three');

terser output

const o=void 0;o?.("one"),o?.("two"),o?.("three");

Expected result

This can be completely dead code eliminated. Interestingly, terser will dead code eliminate some similar programs.

If there's at most one call to debugLog, it will be compiled to zero.

If undefined is replaced with null, then terser will dead code up to two calls to debugLog.

If the syntax debugLog && debugLog('') is used instead, then any number of calls to debugLog will be compiled out.