[llvm] [SystemZ] Use getSignedConstant() where necessary (PR #117181)

[Nikita Popov via llvm-commits]

nikic wrote:

Thanks, I've adjusted the additional places you pointed out (apart from tryFoldLoadStoreIntoMemOperand, which works on APInt).

Most of these get away with not using getSignedConstant() because they work on i64, which is the one width where signedness is irrelevant because it matches the native width of APInt.

This doesn't apply to the SIMM8 etc ones -- presumably those just don't have test coverage with negative values.

https://github.com/llvm/llvm-project/pull/117181