[llvm] [LLVM][SVE][CodeGen] Fix incorrect isel for signed saturating instructions. (PR #88136)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

> This certainly sounds like one of those problems that is easy to get wrong. It sounds like the generation of the intrinsics in clang might need to change too?

Please can you elaborate?  We don't typically expose immediate forms to Clang unless that's the only instruction format available, which is not the case for sqadd/sqsub.  We leave it as a code generation optimisation to use them when appropriate.

https://github.com/llvm/llvm-project/pull/88136