[llvm] [RISCV] Fold vector shift of sext/zext to widening multiply (PR #121563)

[Piotr Fusik via llvm-commits]

pfusik wrote:

I reverted restricting the transform to SpacemiT X60.
This is now same as approved by @lukel97, modulo the renamed function.

https://github.com/llvm/llvm-project/pull/121563