Reproduction link or steps

https://repl.rolldown.rs/#eNptUEFqwzAQ/MqiSxIwfoBC+oWWnn0x9rqoyCsjrZIUo793ZVm40NxmtJqZnV3VpPSqDI34bDlkTEofvFGDUIsM4zTCDShae+2oo8FRYFi8m03APMAHfBR2PnsMzt6xAY/fOPAFbm+wdgS7yQahijVESZsM4diUQZVXlj0yTpKcLlu8GLVH+I6usi4qzT5iapR31o7uQa2sOpmvP+1eTEpPMy/OM/DPgrDC5/7tfWEjbSHBJDlwqvLTcYdipP9J9q6Glsgain07I/ft9iQNUzbB55YrV+ijrW4dqSQ17vn+PWNglX4BhDWVkQ==

What is expected?

The intermediate variable should not be removed since assigning dfd.promise relies on the fact that the promise initialization was run first. rollup does not erase the variable.

rollup repl:

https://rollupjs.org/repl/?version=4.53.2&shareable=eyJleGFtcGxlIjpudWxsLCJtb2R1bGVzIjpbeyJjb2RlIjoibGV0IGRmZCA9IG51bGw7XG5cbmNvbnN0IHByb21pc2UgPSBuZXcgUHJvbWlzZTxUPigocmVzb2x2ZSwgcmVqZWN0KSA9PiB7XG4gIGRmZCA9IHtcbiAgICBwcm9taXNlOiB1bmRlZmluZWQsXG4gICAgICByZXNvbHZlLFxuICAgICByZWplY3RcbiAgfTtcbn0pO1xuXG5kZmQucHJvbWlzZSA9IHByb21pc2U7IiwiaXNFbnRyeSI6dHJ1ZSwibmFtZSI6Im1haW4uanMifSx7ImNvZGUiOiJleHBvcnQgY29uc3QgcXV4ID0gJ1FVWCc7IiwiaXNFbnRyeSI6ZmFsc2UsIm5hbWUiOiJxdXguanMifV0sIm9wdGlvbnMiOnt9fQ==now

swc repl:

https://play.swc.rs/?version=1.15.2&code=H4sIAAAAAAAAA0WNQQqAIAAE775ijwXRA5J6Q3%2FIDQrTUKtD9Pe0jG6zC7OrGaBGhRZm01oKMVjjA1Znl8kz1TzQv6koHL3VOys4zhxCibbDKZAXEuFTG2xGcZwMVfX0n5tD8iNeUlxlvI0L9X%2BaSd4hvf81ngAAAA%3D%3D&config=H4sIAAAAAAAAA1WPSw7DIAwF9zkF8rrbdtE79BAWdSIifrKJVBTl7iUE0maH3xsz8jooBbNoeKq1PMsQkYX4nEsi2Sf8lARIOxTNJia49XaWvRrRCtVoOxpIyBOluiX3hoMNQajjLXPGmzH%2FC3VwkUnkCu4o%2BsnSVTc0JbjwXmrZDkk50qF%2FwA%2FqsvNjMPLqm4kXGrYvhlQioBQBAAA%3D

What is actually happening?

rolldown erases the intermediate variable causing a runtime exception (cannot assign to null)

System Info

System:
    OS: macOS 15.7.1
    CPU: (12) arm64 Apple M2 Pro
    Memory: 1.67 GB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.11.0 - /Users/jess7953/.nvm/versions/node/v24.11.0/bin/node
    npm: 11.6.1 - /Users/jess7953/.nvm/versions/node/v24.11.0/bin/npm
  npmPackages:
    rolldown: ^1.0.0-beta.50 => 1.0.0-beta.50

Any additional comments?

I know this is a contrived example and it's a bit dubious, but I think optimization should not change runtime behavior.