[llvm] [RISCV] Use RISCVISD::SHL_ADD in transformAddShlImm [NFC] (PR #89832)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw approved this pull request.

LGTM.

> Doing so avoids negative interactions with other combines which don't know the shl_add is a single instruction.

Actually it works as expected. So this patch is not an NFC.


https://github.com/llvm/llvm-project/pull/89832