[llvm] [AArch64] treat `@llvm.ssub.sat` the same as `@llvm.aarch64.neon.sqsub` (PR #140454)

[David Green via llvm-commits]

davemgreen wrote:

This is still a draft, but probably deserves to be a proper review at this point.

https://github.com/llvm/llvm-project/pull/140454