[llvm-dev] Aarch64: Build MachineInstruction for "ADR Xd, ."

[Max Muster via llvm-dev]

Hi,

In AArch64, the PC is not a general purpose register.
However, there are other methods to read the current value of the PC to a
register.

According to [1], you can read the PC value via the ADR instruction:
ADR Xd, .

Here, the dot (".") means "here". So a label at the current location.

The question is now, how to build an LLVM MachineInstruction with that?
Something like this:

Register PcReg = MRI.createVirtualRegister(&AArch64::GPR64RegClass);
BuildMI(bb, bb.instr_begin(),
  DebugLoc(), TII.get(AArch64::ADR))
   .addReg(PcReg)
   .addLabel(".");

However, I am struggling in adding a label  for the current location as the
second operand.

Best,
Max

[1]
https://developer.arm.com/architectures/learn-the-architecture/armv8-a-instruction-set-architecture/registers-in-aarch64-other-registers
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