As noticed in https://github.com/llvm/llvm-project/pull/140471, the
SystemZ target currently implements disassembly of PC-relative target
addresses differently from other back-ends. This patch brings SystemZ in
line with other targets.
Specifically, this patch changes the relevant MCInst instructions to
carry a PC-relative displacement instead of an absolute target address
in their immediate fields. When printing the instruction, this
displacement will either be shown as is (e.g. for llvm-mc), or else
translated into an absolute address at print time (e.g. for
llvm-objdump).
The existing llvm-mc based tests using PC-relative operands no longer
work and have to be rewritten, but printing displacements makes those
tests easier to maintain anyway.
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