Help: A Question about AArch64 Register Class

I am modifying the new committed pass “aarch64-mi-peephole-opt”, but get unexpected errors.

My code:

const TargetRegisterClass *RC =

(RegSize == 32) ? &AArch64::GPR32spRegClass : &AArch64::GPR64spRegClass;

Register DstReg = MI.getOperand(0).getReg();

Register SrcReg = MI.getOperand(1).getReg();

Register TmpReg = MRI->createVirtualRegister(RC);

BuildMI(*MBB, MI, DL, TII->get(AArch64::SUBXri), TmpReg)




But when I tried to compile a simple function with

“llc a.ll -mtriple=aarch64 -verify-machineinstrs”, I got errors like

*** Bad machine code: Illegal virtual register for instruction ***

  • function: add_two_parts_imm_i64

  • basic block: %bb.0 (0x561f681b0410)

  • instruction: %3:gpr64common = SUBXri %0:gpr64, 2730, 12

  • operand 1: %0:gpr64

Expected a GPR64sp register, but got a GPR64 register

LLVM ERROR: Found 1 machine code errors.

But if I changed to Opcode from SUBXri to ANDXri, then the errors were eliminated.

What should I do to avoid the errors with Opcode SUBXri/ADDXri ?

Ben Shi

Hi Ben,

As the error message mentioned, the first operand of SUBXri needs to be GPR64sp register class. The ANDXri one is GPR64.

In order to align the register classes, you can use constrainRegClass with the SrcReg and it will constraint the register class to GPR64common which is common between GPR64sp and GPR64.

JinGu Kang