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

[Ulrich Weigand via llvm-commits]

uweigand wrote:

Not sure what exactly the rule is, but if we're now supposed to use `getSignedConstant` in all cases where the constant is signed (possibly negative), then I see the following additional places that might need to be changed:

In SystemZSelectionDAGInfo.cpp - emitMemMemReg
In SystemZISelDAGToDAG.cpp - tryFoldLoadStoreIntoMemOperand
In SystemZISelLowering.cpp - lowerVectorSETCC, lowerGlobalAddress, lowerRETURNADDR, getCSAddressAndShifts
In SystemZOperands.td - SIMM8, SIMM16, NEGSIMM16, SIMM32, NEGSIMM32


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